A Holistic Approach to the Environmental Certification of Green Airports

Abstract

Airports around the world are more and more environmentally concerned, increasing their efforts in reducing aviation impacts by applying environmental management, certification systems, or other types of ecological rating systems to their infrastructures and operation. Especially relevant are the airports’ efforts to manage and reduce their CO₂ emissions through Airport Carbon Accreditation, the efforts made by Eurocontrol to encourage collaborative environmental management, or the increasing numbers of airports worldwide that get their terminals certified according to several world-recognized Green Building Rating Standards (GBRS). However, although these standards are state-of-the-art sustainability valuation programs, none of them fully cover all the environmental impacts of aeronautical activity at an airport. This paper presents the results of an exploratory research where the use of a GBRS into a more holistic certification scheme for airports is discussed and areas of challenge are highlighted. The paper seeks to shed some light on the value of holistic approaches from the perspective of maximizing environmental management efficiency and effectiveness, the integration of actions of individual airport partners to potentially encourage greater coordination of efforts, the challenges of dealing with both construction and operational impacts within one scheme, and the accountability difficulties.

1. Introduction

The interest of industry in ecological certification systems that give an indication of the companies’ commitment to the environment has grown in the recent years [1,2,3,4,5,6]. Similarly, the concerns of the aviation industry have recently been increasing. Today, for example, almost all air traffic control centers and airports have implemented environmental management systems that conform to UNE-EN ISO 14001.

Airports are committed to reduce carbon emissions from their operations, with the ultimate goal of becoming carbon neutral. As of February 2019, 262 airports were accredited by Airports Council International’s (ACI) Airport Carbon Accreditation. That involves more than 43% of global air passenger traffic in over 70 countries across the world. Airport Carbon Accreditation [7] was developed by Airports Council International (ACI) Europe in 2009, and today it is the only global carbon management standard for airports. The objective of the initiative is to reduce carbon emissions and achieve best practice in carbon management from operations fully within the control of the airports, with the ultimate target of becoming carbon neutral. In addition, there is a long-term commitment for 100% carbon neutral airports in Europe by 2030.

Eurocontrol promotes the process of Collaborative Environmental Management (CEM) [8] to formalize collaboration among the core operational stakeholders at airports and minimize the environmental impact of their combined operations. This is facilitated by setting out generic, high level requirements and recommended practices necessary and by establishing CEM working arrangements in a pragmatic protocol to suit local needs and capabilities.

Recently, increasing numbers of airports worldwide are investing efforts to get their terminals, and certain other buildings and infrastructures, certified according to several world-recognized building rating standards. These standards are state-of-the-art valuation programs for sustainable construction and recognize the most advanced techniques for mitigating certain environmental impacts such as water and energy consumption, land use, contaminants, waste management, and other areas not yet effectively covered by aeronautical standards.

However, at present, all these standards and initiatives do not individually fully cover all the impacts caused as a result of the aeronautical activity at an airport, or they are lacking focus in certain areas that, although they are specific to aviation, have a significant environmental impact.

This paper explores how different airport environmental programs and approaches, considered together, could lead to a more holistic and comprehensive framework to minimize aviation environmental impacts at and around airports. Such a framework should aim to account for all airport-related activities and impacts, including airport landside and airside development and operation, as well as impacts derived from air navigation and aircraft operation. It should aim also to account for the whole aviation lifecycle at and around the airport, considering infrastructure development as well as operation and decommissioning. Finally, it should also aim to cooperatively integrate and maximize the efforts and resources of the different stakeholders, specifically airport managers, air navigation services providers, and third companies providing services and running industrial activities within the airport environment, such as handling agents, as well as the own users and passengers.

To achieve this holistic approach the paper acknowledges the limits and overlaps of the three main airport environmental frameworks nowadays: ACI’s Carbon Accreditation Scheme, Eurocontrol CEM, and Green Building Rating Standards (GBRS). Starting from ACI’s Carbon Accreditation Scheme and the efforts made by Eurocontrol to encourage collaborative environmental management, the paper put an emphasis on the possible extension of GBRS systems as a complementary basis for a more holistic airport environmental certification. Applying different layers of benchmarking, the paper addresses, based on an operational model of the airport, the environmental concerns of the airport stakeholders and aviation authorities, and compares them with state-of-the-art rating models to identify gaps and needs for an extension of these models. Finally, by benchmarking the best practices in the airport community, researchers develop a rating system to fill the gaps in current GRBS for an airport environment.

2. Methodology

The research methodology applied different benchmark layers to the analysis of the environmental impacts of airport activities. Data and information for the benchmarks were mined from Corporate Sustainability Reports and from research reports and publications. Figure 1 summarizes the methodological approach followed in this research.

• Research started with the development of a functional airport model that provided the base for the identification of the main environmental impacts associated with airports. This functional airport model is detailed in Section 3.
• The next step consisted of a benchmark to identify the key areas of concern regarding the environmental impacts of airports and to address the environmental concerns of the airport stakeholders and aviation authorities. The outcome of this benchmark is presented in Section 4.
• In addition, state-of-the-art environmental certification systems and rating models were comparatively analyzed, outlining their strengths and limitations and quantifying their application in the airport domain. In particular, Section 5 compares the main environmental initiatives at airports nowadays, including ACI’s Airport Carbon Accreditation, Eurocontrol CEM, and main GBRS models. As the emphasis in this paper is on GBRS extension, Section 6 describes in more detail the GBRS model that is currently the most used in airports. These models were contrasted with the airport impacts to identify gaps and needs for extension to complement ACI and Eurocontrol initiatives.
• A final benchmark was performed to identify the best practices applied by the industry to minimize negative airport impacts.
• Based on the previous results, we identified the elements that should complement the current GBRS certification standards, in particular, the LEED (Leadership in Energy and Environmental Design) system, to make them fully applicable and effective within a holistic approach to airport industry environmental certification.
• Results of the exploratory research on a new credit system was outlined, including a description of categories and certification criterion, a brief summary of each of the credits, the requirements to obtain them, and the scores with which they are valued, with examples of airports that implement initiatives rating positively in the credit system. The organization of the credits, the number of them that are needed to obtain an environmental certification, and how it could be implemented was also defined.
• The last step in the methodology is the validation of the proposed rating system. Validation and usability testing were accomplished with the help of Aena’s experts. Aena is the biggest airport operator in the world, with more than 65 airports in two continents and serving more than 280 million passengers. The model proposed was validated through an iterative process following a twofold approach. Aena’s experts were divided into groups who assessed iteratively the models to detect inconsistencies and discrepancies. In total 12 experts participated in the validation exercise organized in four groups.

Additionally, representativeness of the categories, criteria’s, and credits were independently contrasted with the available literature and evidences of best practices already applied by the airport community. When no evidence of best practices was found to sustain the criteria and credits proposed or the expert’s appreciation, the proposal was modified. Additionally, consistency checks have been applied to verify that all variables were clearly defined and have unique meanings, so that all relevant variables have been included and that all the states are exhaustive and exclusive.

To keep the length of the paper reasonable, not all certification criterion and credits are described in detail. Section 7 provides a short summary of the proposed certification model, while Section 8 discusses in more detail the criterion and credits specific to the airports and how they differ from the LEEDs system. For each of them, Section 8 explain what the credit signifies and evaluates, what its relevance is, and how it is interpreted, as well as what practices will be awarded certification credits. This section pays attention to the novel contribution airport and aviation could make in terms of the evolution of environmental rating systems.

3. Functional Airport Model for Environmental Impact Analysis

One of the aims of this research is to determine to what extent current environmental rating systems could be upgraded to fit the particularities of airport infrastructures. For this, it is necessary to develop a functional model of the airport that facilitates the consideration of its infrastructures and derives its environmental impacts.

It must bear in mind that the airport behaves as a set of very different spaces and that each of these spaces will need to be evaluated. The airport includes terminal buildings for commercial activities and passenger treatment (cafeterias, restaurants, shops, rest areas, checking facilities, security controls, etc.). It also includes buildings and facilities where the air traffic is managed or basic aeronautical activities are carried out. These buildings can be considered as being similar to offices, in which a pleasant work environment should be created. Finally, there are the hangars, the tracks, and all the structures dedicated to aircraft operation or maintenance. These infrastructures will differ most from the existing certifying models for buildings. Figure 2 represents the general structure of an airport, defining the various functions performed within it.

Airport operations involve a range of functions that affect the environment, including operation of aircraft; operation of airport and passenger vehicles and airport ground service equipment (GSE); cleaning and maintenance of aircraft, GSE, and motor vehicles; de-icing and anti-icing of aircraft and airfields; fuelling and fuel storage of aircraft and vehicles; airport facility operations and maintenance; and construction. The environmental impacts of these activities may intensify if an airport is undergoing expansion. These functions are listed in

Table 1. Functional elements of the airport impacting the environment.

Airport Areas	Functional Element
Airport infrastructure and ground traffic	1. Airport access: Road connections and public transport to the airport. 2. Parking. 3. Passenger terminals. 4. Control tower (air navigation). 5. Aeronautical office buildings. 6. Aircraft/airport vehicles maintenance facilities. 7. Hangars. 8. Runways and taxiways.
De-icing protection for aircraft and runways and runoff water	9. De-icing equipment for aircraft. 10. Tanks with antifreeze liquid (glycol). 11. Aircraft parking area with drainage pipes. 12. De-icing equipment for the tracks. 13. Tanks with antifreeze liquid (acetates and formates).
Aircraft refueling	14. Equipment for refueling aircraft. 15. Tanks for fuel storage.
Maintenance equipment and public services:	16. Fuel for the maintenance team. 17. Urban waste. 18. Hazardous waste. 19. Services for buildings (water and heating).
Aircraft movement	20. Aircraft maintenance test. 21. Aircraft takeoff, landing, and rolling.

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4. Key Areas of Concern Regarding the Environmental Impacts of Airports

The “greening” of airport terminals is underway. The design and retrofit of terminals have benefited from improvements in green building technologies during recent decades. However, airport environmental sustainability implies more than building certification, it will ultimately need to encompass the entire airfield complexity and its connections to the metropolitan region.

The European Aviation Environmental Report [9] identifies the main aviation environmental impacts as being noise, air quality, and climate change. The environmental survey undertaken by ACI in 2018 specifically addressed the status of environmental impacts at European airports. The Order Code RL33949 by the EU (European Union) Congress in 2007 [10] also identified the main impacts of airport operations, maintenance, and expansion as: (1) noise issues; (2) water quality issues including effects of de-icing and anti-icing activities, as well as from fuel storage; and (3) air quality issues and emission of toxic air pollutants.

Aviation noise negatively affects the quality of life, health, and value of the properties of those who live near the airport. Although the percentage of people affected by aeronautical noise has been significantly reduced during the last 35 years, it continues to be a major problem because air traffic is continuously growing and becoming more concentrated in many airports.

Airport operations can result in the discharge of pollutants into nearby waters due to de-icing and anti-icing of aircraft and airports, storage of fuel and refuelling, cleaning and maintenance of aircraft and vehicles, and construction. The management of de-icing and anti-icing chemical products represents the biggest challenge for water quality since the airport is ultimately responsible for the management of the resulting wastewater. Because airports need to store fuel onsite to refuel aircraft and airport ground service equipment, most airports are required to develop a Spill Prevention, Control, and Countermeasure (SPCC) plan to prevent environmental damage resulting from oil spills. Airport emissions affecting local air quality come from the aircraft, motor vehicles (e.g., cars and buses for airport operations, and passenger, employee, and rental agency vehicles), ground service equipment (e.g., aircraft tugs, baggage and belt loaders, generators, lawn mowers, snow plows, loaders, tractors, air-conditioning units, and cargo moving equipment), and stationary sources (e.g., boilers, space heaters, emergency generators, incinerators, fire training facilities, aircraft engine testing facilities, painting operations, and solvent degreasers). Airport operations may produce volatile organic compounds (VOCs), carbon monoxide (CO), particulate matter (PM), lead, sulphur oxides (SOx), and nitrogen oxides (NOx), known collectively as “criteria” pollutants. They also may produce a complex array of toxic or hazardous air pollutants (HAPs).

Biodiversity impacts refer to impacts on plants and animals. These include a reduction in the type and extent of habitats, bird strikes, and roadkill.

Figure 3 summarises the main environmental impacts of airports per functional element of the airport.

5. Comparative Benchmark of Main Environmental Certification, Standards, and Rating Systems

As stated previously, ACI’ Airport Carbon Accreditation programme provides airport operators a detailed, multi-step path to carbon neutrality. Its aim is to enable airports to implement best practices in carbon management, with the ultimate objective of becoming carbon neutral. The program has four progressively stringent levels of accreditation:

• Mapping;
• Reduction;
• Optimisation; and
• Neutrality.

One key element addressed by the program is the accountability for those sources of emissions that are under the control of the airport but also for those that are not under its direct control. The principle behind this is the definition of the airport “operational boundary” and the emissions sources within that boundary as defined by the Greenhouse Gas (CHG) Protocol.

Airport Carbon Accreditation is based on existing international standards in the reporting and accounting of GHG emissions, including the GHG Protocol and ISO 14064. It requires airports to measure their GHG (CO₂) emissions in accordance with the GHG Protocol and to get their emissions inventory assured in accordance with ISO 14064 by an independent third party. As such, the programme is consistent, compatible, and compliant with national and international management and reporting of carbon emissions. This helps to ensure that it remains relevant as the carbon management certification standard for the airport industry.

Direct emissions come from sources that are owned or controlled by the reporting entity. Indirect emissions are a consequence of the activities of the reporting entity but occur at sources owned or controlled by another entity. The GHG Protocol further categorizes these direct and indirect emissions into three broad scopes:

• Scope 1: All direct GHG emissions.
• Scope 2: Indirect GHG emissions from consumption of purchased electricity, heat, or steam.
• Scope 3: Other indirect emissions, such as:

  ○

  The extraction, production, and transport of purchased materials and fuels.

  ○

  Transport-related activities in vehicles not owned or controlled by the reporting entity.

  ○

  Outsourced activities.

  ○

  Waste disposal, etc.

Within this framework, airports should identify the relevant emissions sources and determine where they have control over emissions (scope 1, 2, and airport staff business travel) and where they can guide or influence emissions from activities of other stakeholders (scope 3).

To reduce their carbon emissions, airport operators need to consider the full extent of the emissions sources under their direct control, with investment in, for example, energy efficient lighting, heating, switching to hybrid or electric ground vehicles, onsite renewables, energy management tools, and employee behavioural change. At the two highest levels of the programme, operators must engage with other stakeholders on the airport site, with initiatives such as Airport Collaborative Decision Making (A-CDM), to support lowering airline-associated carbon emissions through Continuous Descent Operations and Time-Based Separation, and offering cleaner transport solutions to passengers travelling to and from the airport.

Carbon accreditation is very much focussed towards greenhouse gas emission sources, for example: Stationary combustion sources, e.g., generators; mobile sources, e.g., vehicles; emissions from the purchase of electricity; refrigerants, e.g., air conditioning units and drinking machines; and others such as fire extinguishers and compressed gases. Impacts other than greenhouse gases (biodiversity, noise, land use, or air quality) are not contemplated. For example, site waste and wastewater management are only included from the point-of-view of greenhouse gasses generated by its treatment, but other environmental effects such as soil spoil, etc., are not considered. Additionally, since carbon accreditation is mainly considering operational impacts, no attention is devoted to infrastructure and building construction.

The Eurocontrol CEM specification is an effective way to enlarge the scope of the environmental impacts considered, because it is primarily targeted at the three core operational stakeholders at airports: Airport operators, aircraft operators, and ANSPs (air navigation service providers). CEM is not a certification system but a specification that formalises collaboration amongst the core operational stakeholders at and around airports. The objective is to minimise the environmental impact of their combined operations, by setting out generic, high level requirements and recommended practices necessary to either establish CEM working arrangements, or flexibly adapt existing ones in a pragmatic protocol to suit local needs and capabilities.

Accountability for sources of impacts under the responsibility of different stakeholders is considered through common awareness and understanding of the interdependencies and constraints facing each other’s business. This, in turn, can facilitate the development of shared environmental solutions on which they can then collaborate in joint planning and implementation. CEM may thus be used to facilitate enhanced relationships, for example, ANSPs assisting airports with capacity and airports and ANSPs assisting airlines with fuel savings, thus contributing to high performing airport operations.

CEM explicitly includes the following topics under the collaboration agreement:

• Noise;
• Local air quality (LAQ);
• Greenhouse gas emissions;
• NOX emissions
• Particulate matter (PM) including ultra-fine particles (UFPs);
• Black carbon;
• Fuel burn;
• CO2 emissions;
• Risks to ATM (Air Traffic Management) operations and structures arising from climate change such as sea level changes and severe weather events;
• Implementation of Continuous Descent Operations (CDO) [11];
• The review and coordination of the introduction of new concepts of operations to improve environmental performance;
• Identification of interdependencies between impacts and between their potential solutions;
• Identification of trade-offs that would have to be made by each stakeholder when delivering solutions (in terms of issues such as capacity, operational flexibility, cost, and customer service standards);
• Modifications to airport and CNS/ATM (Communications, Navigation and Surveillance/ Air Traffic Management) infrastructure;
• Interaction with external stakeholders;
• Communication;
• Identification of applicable local, national, and European legislation;
• Alignment with state or local plans, such as air quality plans or climate action plans; and
• Any other environmental issue that impact on the airport.

The following ones might/may be part of the agreement:

• Waste management and refuse management in general;
• Wildlife hazard management;
• Conservation of biodiversity;
• Areas of Special Scientific Interest or their equivalent;
• Renewable energy possibilities such as wind turbines, biomass, solar panels, etc.;
• Land use in the vicinity of the airport; and
• Third-party risk.

CEM tackles a broad variety of airport impacts, except contraction of buildings and infrastructure, although it is not a certification system.

To address the environmental impacts of airport infrastructures development most airport around the world are applying different GBRSs. The main focus of rating systems is environmental sustainability. However, there is no consensus regarding the secondary priorities. Illankoon et al. [12] found that the focus of most GBRSs is environmental and social sustainability, while economic sustainability is lacking attention. A study by Awadh [13] came to a similar conclusion and affirmed that the main GBRSs are focused on the environmental sustainability while they pay less attention to social sustainability.

In [14], the authors identify major research efforts conducted in 15 main GBRSs and propose future GBRS research. Among this set of 15 GBRSs, the essential evaluation criteria were identified as: Energy, indoor environment, site, land, outdoor environment, and innovation. Despite the large number of methods analysed, all of them corresponded to private initiatives and no governmental methods were revised. Recently, in [15], the authors performed a critical comparison of some environmental building rating systems (LEED, BREEAM—Building Research Establishment’s Environmental Assessment Method, CASBEE—Comprehensive Assessment System for Built Environment Efficiency, and Green Star). In [16], private and governmental systems were also compared.

Our research concentrates on those studies that cover environmental criteria: Project management, energy efficiency, water and resource saving, waste management, site-planning, and outdoor and indoor environmental quality. In [17], the authors compared the main standards in China (Evaluation Standard for Green Building (ESGB)), the UK (Code for Sustainable Homes (CSH)), and the US (LEED), with consideration of the energy-saving, water-saving, material-saving quality, site selection, and the outdoor and indoor environmental quality. They found that there was a large overlap in the criteria of the indoor environmental quality among these methods. The Building Environmental Assessment Method (BEAM) was found [18] to allocate the highest importance to “site planning and design”. In [19], the authors compared project management in LEED, GG—Green Globes, and GM—Green Manufacturing, confirming that all three of them allocate around 20% of the credits to items related to project management because of its impact on reducing costs and eliminating barriers. Passive design to improve energy efficiency was evaluated by Chen et al. [11] in five GBRSs: BREEAM, LEED, CASBEE, BEAM, and ASGB (Assessment Standard for Green Buildings). Wu et al. [20] compared waste management at five selected GBRSs (i.e., LEED, BREEAM, GG, ASGB, and Green Building Index (GBI)) finding common principles, namely reduce, reuse, and recycle, although with different emphasis for each method.

Based on these analyses, we identify the four main environmental assessment methods that, to a certain extent, have been applied in the airport environment and compare how they apply environmental criteria. The selected methods are:

• BREEAM, which was developed in the U.K. in 1990,
• LEED, which was developed in the U.S.A in 1998,
• GBTool (Green Building Assessment Tool), which was developed by National Resource Canada and combined 14 countries in 1998, and
• CASBEE, which was developed in Japan in 2003.

Energy is the principal evaluation criterion for assessing and certifying green buildings and had the highest consideration among the majority of existing GBRSs. The category of energy looks at the reduction of energy use, peak load energy, energy monitoring and reporting, energy efficient appliances, equipment and systems, and the use of renewable energy. Dynamic energy simulation plays an important role in GBRS and it is currently applied for airport terminal LEED or BREAM building certification. Nowadays energy consumption is focused on terminal buildings since terminal buildings are the part of the airport that consumes the most energy. The most important measures can be listed as lighting, HVAC (Heat, Ventilation and Air conditioning) system design, power appliances, and the type of energy sources to be used. Typical tools used for energy simulation are Design Builder, Energy Plus, and Transient Systems Simulation Program (TRNSYS).

At the research level there is currently a gap in the literature for energy modelling designs for airports [21]. A number of qualities, complexities, and common characteristics of airport terminal buildings make them exceptional buildings and create issues for energy simulation: Architectural features such as large glazed facades with high ceilings/open plan spaces, a wide range of functional space, 24 h operations, acoustics, security and safety, occupancy, building age and redevelopment, etc. Ortega and Manana performed a recent review on energy research and simulations at airports [22], paying particular attention to the status of energy simulation in the airport domain. Among the most advance methods, they signaled:

• Analytical and simulation models for the floor cooling system;
• Computational fluid dynamics (CFD) simulations of the thermal effect of the wind environment around a large airport;
• HVAC modeling and thermal simulation of the terminal building;
• Indoors thermal conditions using computational fluid dynamics methodologies (CFD);
• Small-scale fluid dynamics modeling to optimize the design of air distribution in a large airport; and
• Simulation by CFD of the potential of natural ventilation and air modulation by mechanical fans under typical meteorological conditions.

Additionally, non-destructive methods are essential for energy assessment at the airports. Non-destructive technologies are used for energy assessment at airport buildings. One of the most important measures to conservation and energy efficiency at airports is associated with conducting an energy audit of the facilities. With this audit, the way an airport consumes energy is analyzed, and it becomes easier to propose measures to improve energy performance. Other methods include thermal infrared (IR) inspections of the building envelopes and HVAC installations, an assessment of indoor environmental quality (IEQ) through long term monitoring, and spot measurements of indoor thermal and visual conditions, as well as personnel and passenger questionnaires.

Finally, while the impacts of interventions on energy performance and comfort can be quantified in advance using simulation software, conservation aspects are less tangible. Proposal in [23,24] might be worth consideration for this airport problem.

Under the site criterion, site-related items are evaluated, such as site location, site planning, site design, site assessment, the available off-site services, and site regeneration and development. This criterion pays more attention to the sustainability during the implementation of green construction projects.

The indoor environment criterion covers a wide range of indicators relating to the indoor environment such as the sound environment, thermal comfort, lighting and illumination, healthy ventilation delivery, air quality, hygiene, occupant well-being facilities, and visual and acoustic comfort.

The land and outdoor environments are concerned with the use of land, remediation of contaminated land, ecological enhancement, long-term impact on biodiversity, habitat creation and restoration, improved outdoor thermal comfort, accessible community facilities, active urban environments, private outdoor space, and public transport.

The evaluation criterion of materials mainly assesses buildings in terms of material sourcing, the efficient use of materials, the use of recycled and certified materials, and the environmental impact of materials. The water criterion mainly looks at water quality, water saving performance, water cycling, the use of water efficient appliances, and alternative water sources. In some of the methods, the criterion of water was included under a higher level of criterion termed as “resources”.

The literature reflects the degree of implementation of these methods [25]. BREEAM, LEED, and CASBEE have been utilized since the late 2000s, while Green Star is still in its earlier stages. However, their application in the airport domain has not been studied to date, and the data to sustain such a study are spread among different sources and are difficult to compile.

The final line of research considered is the development of particular GBRSs that are tailored to certain purposes: Store buildings in China (2015) [26], residential units in Jordan [27], planning [28], etc. However, to date, no specific adaptation of these methods has been performed for airports.

BREAM and LEED are the two systems that are most applied in airport buildings. Around 270 buildings related to an airport are certified as LEED or in the process of being certified. On the other hand, although BREAM has become one of the world’s most comprehensive methods of assessing the sustainability of buildings and complexes, its application within the airport domain is incipient. Only 13 out of more than 16,000 projects listed on the official BREAM web page correspond to airport buildings or infrastructure. Particularly relevant is the certification of the Heathrow T2B airport terminal, the London Southend Airport (Phase 3), Finnair’s COOL Nordic Cargo Hub (2018), Gothenburg Landvetter Airport (under construction), Oslo Airport Terminal 2 (2017), and Heathrow South Cargo Center.

As appreciated from the previous discussion, comparison of the methods is complicated due to a lack of seamless correspondence among impact categories, rate of points, credits, or score of each method. The comparative assessment requires that the criteria of each environmental assessment method are classified into common categories, allowing for a reference framework. Based on all these previous studies, a benchmark of categories and criteria for the methods most used at airports is presented in

Table 2. Benchmark of environmental rating systems.

CATEGORIES	CRITERIA			METHODS
		ACI	CEM	CASBEE	LEED	BREAM	GBTool
Indoor Environment/Health and Comfort Management	Thermal Comfort	✓		✓	✓	✓	✓
	Lighting			✓	✓	✓	✓
	Air Quality		✓	✓	✓	✓	✓
	Low-Emitting Materials			✓	++	✓	✓
	Noise and Acoustic		✓	✓	NA	✓	✓
	HVAC System			✓	✓	++	✓
	Ventilation System	✓	✓	✓	✓	++	✓
Quality of Service	Service Ability			+	NA	-	✓
	Durability and Reliability		✓	+	NA	-	✓
	Flexibility and Adaptability		✓	+	NA	-	✓
Outdoor Environment on Site/Environmental Loading/Sustainable Sites/Site Ecology and Pollution and Land Use	Preservation and Creation of Biotope		✓	-	✓	✓	++
	Townscape and Landscape		✓	++	-	-	-
	Local Characteristics and Outdoor Amenity			++	-	-	-
	Site Selection			✓	+	✓	✓
Energy and Atmosphere	Building Thermal Load	✓	✓	✓	✓	✓	✓
	Natural Energy Utilization	✓	✓	✓	✓	✓	✓
	Efficiency in the Building Service System	✓	✓	✓	✓	✓	✓
	Efficient Operation	✓	✓	+	NA	NA	NA
	Simulation on Energy Consumption and CO2 Emissions	✓	✓	✓	+	+	+
	Commissioning Prerequisite	✓	✓	NA	NA	+	+
Resources and Materials/Resource Consumption	Water Resources and Conservation			++	++	++	++
	Rainwater and a Grey Water Reuse System			+	✓	✓	✓
	Water Consumption			+	✓	✓	✓
	Materials of Low Environmental Load			✓	✓	✓	✓
	Reuse of Existing Building Structure			++	++	++	++
	Volume of Recyclable Materials			++	++	++	++
Off-site Environment/Location and Transportation	Air Pollution		✓	✓	✓	✓	✓
	NOx Emission		✓	+	NA	+	+
	Noise		✓	✓	✓	✓	✓
	Vibration			✓	✓	✓	✓
	Wind Damage and Sunlight			✓	✓	✓	✓
	Obstruction			✓	✓	✓	✓
	Light Pollution	✓		✓	✓	✓	✓
	Heat Island Effect	✓		✓	✓	NA	NA
	Load on Local Infrastructure			✓	✓	✓	✓
	Location and Transportation			✓	✓	✓	✓

++ important criteria, + assessed in detail, NA—not applicable for this method, ✓ criteria considered, - few criteria.

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The benchmark of main environmental certification, standards, and rating systems shed some light on the following key topics:

• The value of a holistic approach from the perspective of maximizing environmental management efficiency and effectiveness.

As stated in the previous discussion, each of the main airport environmental initiatives can be considered best in class from different environmental perspectives. However, none of them in isolation deals effectively with all aviation impacts in and around airports.

ACI’s Airport Carbon Accreditation program enable airports to implement best practices in carbon management, with the ultimate objective of becoming carbon neutral. CEM fully accounts for ANSPs activities, thus contributing to high-performing airport operations. GBRS focus on buddings and infrastructures construction, development, and further operation, which is particularly relevant given the expansion of infrastructure at most airports. However, they still need some upgrade to contemplate particular infrastructure and facilities at airports other than normal buildings.

A holistic approach coordinating the three of them might maximize environmental management efficiency and effectiveness. Additionally, a holistic overview can be used to inform the actions of individual airport partners and potentially encourage greater coordination of efforts.

2.

How construction and operational impacts can be dealt with within one scheme.

Airport Carbon Accreditation and CEM aim to, fundamentally, reduce environmental impacts derived from airport operation, but they pay minor attention to the impacts derived from airport development and expansion activities. By this focus into operation, they unintentionally have created a disconnection between airport operation and airport construction impacts.

On the other hand, GBRS systems have found an effective approach to deal with such a dichotomy, because they cover the environmental impact derived from the whole lifecycle of a building or facility, including its design, construction, operation, maintenance, and decommissioning. In its current status GBRS are already been used by airports to certify their terminals and main buildings. GBRS can be easily adapted to some aeronautical buildings exclusive from airports. However, more significant efforts would be required to extend these rating systems to all airport infrastructures such as runways, taxiways, aprons, de-icing zones, aircraft parking, etc.

3.

The balance between the need for coordination and the requirement for accountability, as environmental impacts come from sources that sometimes are not owned or controlled directly by the airport entity.

Airports are complex sociotechnical systems, operated by a large number of different private and public entities, which interact and contribute to the final aim of a safe and efficient air transport operation. Organizational issues might be a problem for the implementation of a global certification system in such a complex environment. However, at the same time, airports are highly regulated environments, with a common ground of international technical, operational, managerial, and economic standards defined by ICAO (International Civil Aviation Organization). In particular, ICAO have set “Standards and Recommended Practices for Certification of Aerodromes and Operators Obligations” that are mandatory for the United States. As part of this set of processes and minimum requirements for airports certification, the principle of Airport Operator responsibility stands out [29,30,31]. This principle states that the Airport Operator is responsible and accountable for any aeronautical activity that take place in the airport.

To cope with this responsibility, the Airport Operator should, among other things, establishes management systems and procedures to assure that services and activities provided by third parties, contractors, or any private /public entity that operates at the airport, respond up to the same airport’s level of quality and safety. In particular, “the aerodrome operator shall oblige all users of the aerodrome, including fixed-base operators, ground handling agencies and other organizations that perform activities independently at the aerodrome in relation to flight or aircraft handling, to cooperate and comply with the requirements laid down by the aerodrome operator with regard to safety at the aerodrome and monitor such cooperation and compliance”.

Additionally, airports are obliged to implement EMS covering all the airport’s activities, products, and services that can interact with the environment in either a beneficial or a negative way (e.g., consumption of materials, discharges, spills, etc.) [32].

Airport carbon certification addresses accountability for those sources of emissions by defining the airport “operational boundary” and the emissions sources within that boundary according to the CHG Protocol.

Accountability for sources of impacts under the responsibility of different stakeholders is considered CEM through common awareness and understanding of the interdependencies and collaboration in joint planning and implementation.

Additionally, accountability and transparency are corner stones in GBRS. In particular, to deal with the large supply chain that might be involved in the construction and operation of complex infrastructures, GBRS contemplate the extension of accountability through a third-party certification process.

These three different approaches are not exclusive but complementary, which will greatly facilitate environmental efficiency in such a complex context as an airport. All these elements provide the framework that will allow defining and implementing an environmental certification that applies to all airport activities and integrates all companies that operate in the airport environment.

5.1. LEED Performance Credit System

LEED is an ecology-oriented building certification program to ensure that buildings are environmentally compatible, provide a healthy work environment, and are profitable [33]. This system was devised by the USGBC (U.S. Green Building Council) in the United States. Since started in 1998, LEED standards have been applied to more than 119,000 projects in the United States and 150 countries and territories worldwide, covering more than 13.8 billion square feet of building space, participating in the suite of rating systems, and 1.85 million feet of space is certified per day around the world [34].

This certification is voluntary, and it consists of a set of rules and strategies for sustainability in all types of buildings. LEED has special rating systems that apply to all kinds of structures, including schools and retail and healthcare facilities. Rating systems are available for new constructions and major renovations, as well as for existing buildings.

Over the 20 years since its inception, the U.S. Green Building Council’s LEED green building rating system has become the most popular way to certify that a building has taken certain steps to improve its environmental impact. The latest version, LEED v4, concentrates its efforts on improving performance across six key areas of environmental and human health where points can be earned:

• Sustainable Sites,
• Water Efficiency,
• Energy and Atmosphere,
• Materials and Resources,
• Indoor Environmental Quality, and
• Location and Transportation.

The last one, Location and Transportation, was added to all rating systems, placing more emphasis and attention on reducing the main contributor to global warming, transportation. The Location and Transportation category includes strategies to reduce costs, pollution, and resource depletion related to daily commutes.

Additionally, the system has evolved to include 21 rating-system adaptations, which can be divided across five broad categories:

• Building Design and Construction (BD + C),
• Interior Design and Construction (ID + C),
• Operations and Maintenance (O + M),
• Neighborhood Development (ND), and
• Homes.

Despite its high level of application in terminals and other airport buildings, no adaptation has been performed yet to this environment, thus being one of the motivations of this research.

Each category in an LEED rating system consists of prerequisites and credits. Prerequisites are required elements or green building strategies that must be included in any LEED-certified project. Credits are optional elements or strategies that projects can elect to pursue to obtain points toward LEED certification.

The rating system aims to allocate points “based on the potential environmental impacts and human benefits of each credit.” These are weighed using the previous six environmental impact categories. LEED rating systems generally have 100 base points distributed across the six credit categories. Four additional points may be received for Regional Priority Credits, and six additional points for Innovation in Design. Projects can qualify for four levels of certification:

• Certified: 40–49 points.
• Silver: 50–59 points.
• Gold: 60–79 points.
• Platinum: 80 points and above.

5.2. Application of an LEED Certification System at Airports

Several airports have adopted the LEED program and created airport-specific sustainability guidelines and metrics for their particular programs. However, the initiative is almost restricted to the area of the United States. A total of 51 projects were registered with the Airport Council International North America in 2014, including San Francisco International Airport, Chicago O’Hare International Airport, the Port Authority of New York and New Jersey, Los Angeles Airports, and Columbus International Airport. San Diego International Airport became, in 2014, the first in the world to be awarded LEED Platinum—the highest environmental certification possible—for its new energy-efficient green terminal. However, LEED is often associated with building structures and has not been applied to the entire airport but only to a few of its buildings. A listing of LEED-certified airport projects can be consulted in [35]. Around 270 buildings related to an airport are LEED certified or in the process of being certified. Figure 4 provides detail about the level of certification of this set of airport facilities. It can be observed that 29% of the airport buildings are just registered and, therefore, are in the first steps of the certification process. A total of 14% are certified at the lowest level. A total of 31% have been granted a Silver certification, 23 a Gold certification, and only a 3% have achieved Platinum certification. Figure 5 shows the points distribution achieved by the airport buildings certified. It summarizes how many airports that have achieved a certain value of points in its certification. It can be seen that only one airport achieved a maximum rating of 86 points, and the minimum number of points was 21. Most of the airports achieved a rating between 30 and 46 or between 50 and 65.

Figure 6 shows the distribution of certified airport buildings according to the building activity. As can be seen, most of the buildings certified are dedicated to offices and services in general. There is an incipient number of industrial and manufacturing facilities, as well as military bases and public buildings. The total certified buildings constitute a surface of more than 74,000 square feet, distributed as indicated in Figure 7.

According to these data, the LEED certification, although widespread in other type of buildings [36,37], has not yet significantly permeated aeronautical facilities. This low level of certification may be due to the fact that airports are particular cases of buildings that require a specific certification. At an airport, we can encounter passenger terminals that resemble commercial buildings with shops, rest areas, parking, etc. There are office buildings or other areas comparable to industrial buildings (hangars for maintenance, cargo warehouses, buildings for the power supply, etc.). The airport also has specific facilities such as the control tower, runways and taxiways, areas dedicated to telecommunications and radio navigation aids, parking stands at the platform, etc.

The complexity and wide variety of airport facilities require a much more detailed and tailor-made model for their environmental certification. In addition to developing this certification, this paper tries to extend it to all the elements managed by the airport decision makers, including systems and procedures for air navigation and for airline operation, airport layout, airport infrastructure, handling companies and facilities, etc.

6. Gap Analysis and Benchmark of Best Practices

The comparison of the categories and criterion detailed in Section 5 with the airport impacts detailed in Section 4 allows us to identify the gaps that prevent the effective application of current GBRS rating systems to airport environmental sustainability. These gaps are identified in Figure 8. New categories and certification criterion are proposed to extend the LEED system to the airport environments and cover the gaps. As can be seen, the criteria are divided into three different colors:

• Yellow: Criteria marked in yellow are specific to the new green airport certification method, i.e., they do not exist in current LEED standards.
• Orange: Criteria marked in orange are partially covered by LEED standards, although the practices and solutions applicable at the airport differ from those applied at other buildings and, therefore, the evaluation criteria are specific to the new green airport certification method.
• Green: Criteria marked in green do not present a significant difference to the categories and criteria already included in LEED.

It must be noted that yellow and orange criteria differ greatly in the new aviation system compared to the original LEED model. More specifically, the green airport includes two categories (Noise, and Pollution and Emissions) that can be considered as the main drivers of environmental impact from airports and that current certification systems (not just LEED) do not adequately address. These two categories could be added to any certification system in order to award a green building designation to an airport. Despite noise and pollution differing substantially (18 out of 39), they are not the only ones, with 10 additional criteria presenting significant differences.

It is to be noticed that one of the goals that guided the development of GBRS is reversing a building’s contribution to global climate change. For example, 35 of the 100 total points in LEED v4 are distributed to reward climate change mitigation strategies. This consideration is also primary for a BGRS adapted to the airport environment.

This approach addressed a structure’s planning, design, construction, operations, and end-of-life, as well as considering energy, water, indoor environmental quality, materials selection, and location. Green airport buildings and infrastructures reduce landfill waste, enable alternative transportation use, and encourage retention and creation of vegetated land areas and roofs. It rewards thoughtful decisions about building location, with credits that encourage compact development and connection with transit and amenities. When a building consumes less water, the energy otherwise required to withdraw, treat, and pump that water from the source to the building are avoided. Additionally, less transport of materials to and from the building cuts associated fuel consumption. Other ways that acknowledges mitigation of contribution to global climate change are, for example, GHG emissions reduction from building operations energy use, from transportation energy use, from the embodied energy of materials and water use, from a cleaner energy supply, or global warming potential reduction from non-energy related drivers.

The rating system that is proposed is described in Section 7. This section lists the credits that conform to the Green Airport environmental certification, together with the points of each credit and each of the environmental categories.

The benchmark of the best practices applied at airports all over the world allows us to define in detail how the credit system will be implemented and provide practical examples on how to obtain the credits awarded by the system. These details are provided in Section 8. For the sake of ensuring the paper does not exceed a reasonable length, only those credits presenting significant differences to the LEED system are described in detail. Credits already included in LEED that were not significantly modified or upgraded are not included in Section 8. The LEED manual is referred to in order to obtain more information on these credits.

7. Outline of the Green Airport Certification System

The rating system proposed in this paper, which we call “Green Airport”, is directed at those companies whose business is the management of airports and/or the provision of air navigation services, and may be obtained for the following cases:

• The airport and air navigation operation.
• The entire airport.
• Certain buildings or facilities inside the airport.
• The air navigation system at the airport.

As for the LEED model, the scoring system proposed in this paper is based on obtaining a certain amount of credits and points earned by the degree of compliance with certain environmental concepts. The credits are divided into two separate parts:

• Airport (ARP), and
• Air Navigation (NAV).

In turn, the “Green Airport” certification is divided into “environmental categories” of credits that are aimed at different environmental aspects upon which aviation has a negative impact, these are:

• Noise (N): 20 points.
• Pollution and emissions (PM): 30 points.
• Energy (E): 10 points.
• Materials and wastes (MW): 10 points.
• Water (W): 10 points.
• Land use (L): 10 points.
• Biodiversity and landscape (BL): 10 points.

An additional category takes into account aspects related to research, development, and innovation: Category III—Innovation, Research, Integration, and Information with four extra points. An airport can get a maximum of 100 points upon consideration of all the environmental categories, distributed between the airport mode (70 points) and the air navigation mode (30), and four extra points in Category III (Innovation, Research, Integration, and Information). The 30 points of NAV correspond only to the categories of noise (15 points) and emissions (15 points). The 70 points of ARP are spread among the different environmental categories of credits. If, for example, an airport only wants to certify its air navigation system, it would score about 30 points plus four extra points from Section III. If, however, the airport only wants to certify one of its buildings or facilities, it would score about 70 points plus four extra points from Category III. The Green Airport certification provides a wide range of services, although it is preferably designed to integrate all aviation facilities and the management of air traffic operations at the airport. A summary of the points allocation structure is presented in Figure 9.

There are four different levels of certification. Therefore, the companies may progressively improve their environmental responsibilities and obtain access to the next grade in the certification.

• Certified: 50–64 points.
• Silver: 65–79 points.
• Gold: 80–94 points.
• Platinum: more than 95 points.

First, the airport must meet the mandatory prerequisites for each of the credits. Mandatory requirements are mandatory only to airports.

The proposed credit system takes into account that air navigation activities are an important source of environmental impacts at the airport. So, a significant amount of credits is related with navigation activities and its impacts. While the proposed certification is preferably designed to integrate all aviation facilities and the management of air traffic operations at the airport, it also recognizes that air navigation services should be offered more flexibility since they are linked to safety. Therefore, provisions are included for the case airport and navigation activities certification need different timelines and speeds, and the system contemplates the possibility of an airport or ANSP access one partial certification as shown in

Table 3. Credits score in the case that only a one-part certification is intended.

AIRPORTS	NAVIGATION
Certified: 35–44 points. Silver: 45–54 points. Gold: 55–64 points. Platinum: more than 65 points.	Certified: 15–19 points. Silver: 20–24 points. Gold: 25–29 points. Platinum: more than 30 points.

.

Finally, the four extra points in Category III were scored the same way as other credits and are an aid to progress to higher levels of certification.

Certification Credit Description

This section lists the credits that conform to the Green Airport environmental certification, together with the points of each credit and each of the environmental categories (Please see

Table 4. Credits in the environmental category “Noise” (N).

NOISE (N): 20 POINTS.
AIRPORTS (ARP)	NAVIGATION (NAV)
N1: Noise evaluation and management. (Mandatory) N2: Acoustic isolation plan. (Mandatory + 2 points) N3: Acoustic efficiency. (2 points) N4: Engine testing restrictions. (1 point)	N5: Track keeping. (4 points) N6: Noise preferential routes. (4 points) N7: Runway use prioritization. (2 points) N8: Night flight restrictions. (5 points)

,

Table 5. Credits in the environmental category “Pollution and Emissions” (PE).

POLLUTION and EMISSIONS (PE): 30 POINTS
AIRPORTS (ARP)	NAVIGATION (NAV)
PE1: Airport’s emissions control. (Mandatory + 2 points) PE2: Ecological cars. (4 points) PE3: Biofuels use. (2 points) PE4: Indoor air quality. (Mandatory + 5 points) PE5: APUs and GPUs use limitations. (2 points)	PE6: Continuous descent approach. (4 points) PE7: Continuous ascend departures. (3 points) PE8: Tailored arrivals. (3 points) PE9: Restrictions on the use of engine ground. (4 points) PE10: On route operation optimization. (1 point)

,

Table 6. Credits in the environmental category “Energy” (E).

ENERGY (E): 10 POINTS AIRPORTS (ARP)
E1: Energy consumption management. (Mandatory + 4 points) E2: Use of renewable energy. (2 points) E3: Air conditioning equipment control. (Mandatory + 2 points) E4: Indoor lighting. (Mandatory + 2 points)

,

Table 7. Credits in the environmental category “Materials and Waste” (MW).

MATERIALS and WASTE (MW): 10 POINTS AIRPORTS (ARP)
MW1: Hazardous waste treatment. (Mandatory) MW2: Waste recycling. (Mandatory + 1 point) MW3: Infrastructure lifecycle impact. (Mandatory + 4 points) MW4: Choice of building materials. (5 points)

,

Table 8. Credits in the environmental category “Water Resources” (W).

WATER RESOURCES (W): 10 POINTS. AIRPORTS (ARP)
W1: Control of water consumption. (Mandatory) W2: Reducing of water consumption outdoor. (Mandatory + 3 points) W3: Reduction of water consumption indoors. (Mandatory + 2 points) W4: Reduction of water consumption in handling. (2 points) W5: Management of runoff. (2 points) W6: Wastewater Treatment. (Mandatory + 1 point)

,

Table 9. Credits in the environmental category “Land Use” (L).

LAND USE (L): 10 POINTS. AIRPORTS (ARP)
L1: Site selection. (Mandatory + 3 points) L2: Connections with public transport. (Mandatory + 2 points) L3: Connections with private transport. (2 points) L4: Soil protection. (Mandatory + 3 points)

,

Table 10. Credits in the environmental category “Biodiversity and Landscape” (BL).

BIODIVERSITY and LANSCAPE (BL): 10 POINTS. AIRPORTS (ARP)
BL1: Landscape protection. (Mandatory + 4 points) BL2: Reducing light pollution. (Mandatory + 1 point) BL3: Reduced heat island effect. (1 point) BL4: Protection of biodiversity. (Mandatory + 4 points)

and

Table 11. Credits in the environmental category “Innovation, Research, Integration, and Information” (III).

INNOVATION, RESEARCH, INTEGRATION, and INFORMATION (III): + 4 EXTRA POINTS AIPORTS (ARP)
I1: Innovation. (1 extra point) I2: Research. (1 extra point) I3: Integrated management. (1 extra point) I4: Information. (1 extra point)

).

The Green Airport model, and its credit structure, are built upon management models currently applied by airports or air navigation providers for:

• Noise pollution reduction;
• Decrease in emissions;
• Air pollution cutback;
• Energy saving;
• Better use of materials;
• Waste treatment;
• Reduction in consumption and better treatment of water resources;
• Improved soil management;
• Control of biodiversity impact; or
• R&D in clean technologies and methods.

8. Description of the Most Relevant Criteria and Credits

As an example, and to illustrate the certification system, the following section outlines the most relevant credits. For each of the credits, we analyse its meaning, its relevance, and how it is interpreted. To keep the length of the paper reasonable, only those credits presenting significant differences to the LEED system are described in detail. The LEED manual is referred to in order to obtain more information on these credits.

8.1. Noise Category

The noise generated by transport infrastructure is one of the most important disruptive agents originated by the aeronautical sector. Noise can cause health problems that are both physical (discomfort, ear and hearing problems, etc.) and psychological (fatigue, irritability, headaches, etc.). Therefore, the environmental certification emphasises this section of credits and values the use of noise assessment methods, actions in terms of sound insulation, territorial control, etc.

8.1.1. Noise Assessment and Management

Meaning: This credit evaluates the existence of a Plan for the Assessment and Management of Noise which should include a Strategic Noise Map and the corresponding Action Plan for noise mitigation [38,39]. These documents will be used to determine the evolution of the areas affected by the acoustic contamination, and to evaluate the actions taken or planned to minimize potential increases in the exposure [40].

Relevance: Obtaining these credits entails compliance with the regulations at national and European levels. It will also result in an improvement in the treatment of noise pollution, unless the affected areas expand, or their conditions worsen. The role of noise planning will be to control future noise by measures such as land management, systems engineering in air traffic management, noise insulation measures, and the reduction of fight noise at its source. In Spain, for example, Aena has developed and published Strategic Maps for airports with more than 50,000 movements per year (according to Directive 2002/49/EC of the European Parliament and of the Council [41,42]).

Interpretation: In addition to regulation compliance, the elaboration of Strategic Noise Maps will be mandatory. These maps should be reviewed and, if necessary, amended every five years. A Plan for the Assessment and Management of Noise shall contain all the information relating to noise generated by airport activities and the measures taken to mitigate them. The noise levels Ld (day), Le (evening), and Ln (night), referred to a 12 h day, a 4 h evening and an 8 h night must be calculated. These indices are expressed in dBA and are defined in the European Directive already mentioned, the Lden index:

$$L_{den}=101g\frac{1}{24}(12\ast {10}^{\frac{L_{day}}{10}}+4\ast {10}^{\frac{L_{evening}+5}{10}}+8\ast {10}^{\frac{L_{nigth}+10}{10}}.$$

(1)

Maximum noise limits to which a population may be exposed to in the areas surrounding the airport are defined in national legislation. In the case of Spain, these limits appear in the Royal Decree 1367/2007 and are specified in the

Table 12. Noise limit values for new airport infrastructures.

Type of Acoustic Areas	Maximum Noise Limits
	Ld	Le	Ln	LAMAX
Health, educational and cultural land uses	55	55	45	80
Residential land uses	60	60	50	85
Tertiary land use	65	65	55	88
Recreational land use	68	68	58	90
Industrial land use	70	70	60	90

below.

8.1.2. Sound Insulation Programs

Meaning: This credit evaluates the steps taken to acoustically isolate those dwellings or buildings dedicated to education, health, or activities of a cultural nature, which are exposed to levels above the desirable noise level and that could cause a harmful effect on health. Exposed populations must be evaluated by estimating the number of residents in the area bounded by the various stripes of Lden and Lnight defined in the Strategic Noise Maps [43,44].

Relevance: Acoustic Insulation Plans minimize the nuisance caused by noise from aircraft and airport operations. Its objective is, therefore, to reduce the number of people affected by the noise generated in the operations of take-off, landing, taxiing, engine tests, etc. A good example of an initiative to meet the costs of sound insulation of buildings and homes affected, is the tax adopted by Strasbourg Airport in France. In this airport, a tax on airlines is applied: TnsA (Taxe sur les Nuisances Sonores Aériennes). This money is reinvested in soundproofing homes in populations affected by noise. The administrative body of the airport offered full support to potential beneficiaries, providing assistance in the preparation of the grant application, informing them of the progress of the same, and assisting in the organization of work soundproofing to ensure quality.

Interpretation: There are many dimensions by which to judge the efficacy of insulation schemes. Schemes can be defined by their geographical extent, noise thresholds for inclusion, levels of funding available, sound insulation level (windows, lofts, air conditioning, etc), dB reductions achieved, etc. All would need to be considered in any effective evaluation system for insulation provision [45].

8.1.3. Acoustic Efficiency

Meaning: The acoustic efficiency of the airports is evaluated as the relationship between the problems the noise generates to the population and the connectivity this population obtains from the airport. The Lden and Lnight noise indicators, already defined in previous sections, will be used to relate them to the number of movements (in hundreds) of aircraft per year.

Relevance: This parameter assesses the social benefit generated by the airport, against the acoustic impact generated on the surrounding populations. Within the certification, a minimum social benefit margin will be established to encourage airport managers to take actions and measures aimed at reducing noise pollution affecting the towns near their facilities. This type of indicator is being used in many European airports in response to Directive 2002/49/EC.

Interpretation: Up to two points can be obtained if the values in

Table 13. Required acoustic efficiency.

Residential Land	Acoustic Efficiencies
	Ld	Le
50–55dBA	---	3.5
55–60 dBA	9.5	0.75
60–65 dBA	3.5	0.50
65–70dBA	1.00	---
>dBA	0.50	---

are achieved. The exposed population will be calculated using the Strategic Noise Maps and will be determined for the different bands of Lden and Ln (of 5 dBA of margin each).

8.1.4. Restrictions on Engine Tests

Meaning: The values that govern the realization of the tests of engines in the airport. For this purpose, engine tests at certain times will be prohibited or restricted to certain areas of the airport.

Relevance: These measures will result in a lesser acoustic impact on the populations surrounding the airport. Nearly all airports already apply measures that limit outdoor engine testing at certain airport locations. Some of them, as the Madrid–Barajas airport, have taken these initiatives further, prohibiting engine tests outside those facilities designed for that purpose.

Interpretation: A point can be obtained in this section of credits if engine tests are prohibited during the night (23:00–06:00). Furthermore, the tests are limited to idling during the day for specific facilities for this purpose and measures have been taken to mitigate the noise generated by engine tests.

8.1.5. Track Keeping

Meaning: The objective of this credit section is to improve the accuracy of the departure and approach trajectories. The noise that affects populations near airports depends on the number of aircraft that fly over them. Therefore, if the trajectories are adjusted to the maximum, the number of overflights of these populations can be reduced or even avoided.

Relevance: Best management and information of the trajectories on the part of the provider of the air navigation service, together with an adequate execution by the pilot and the technological improvements in the navigation systems of the aircraft, allow for increasingly greater adjustments to be made to the defined trajectories. This will result in a decrease in the overflights of the populated areas and better control of the acoustic impact generated by air traffic.

Big airports, such as Madrid–Barajas, Valencia, Palma de Mallorca, or Barcelona, have Noise Monitoring Systems for the control of noise pollution in the area surrounding the airport. The data obtained from the measurements of a series of microphones installed in strategic areas around the airport are analyzed, associating the measurements with the corresponding flights. In this way, monitoring and control of the areas affected by the noise are achieved, enabling the trajectories of the aircraft to be improved so as to avoid or minimize the inconvenience to the populations.

Interpretation: Credits will depend on compliance with the following parameters:

• Install Noise Monitoring Systems (1 point).
• Adjustment of at least 70% of the trajectories to lower the acoustic impact (2 points).
• Distribution of the noise by means of a beam of trajectories (1 point).

8.1.6. Noise Preferential Routes

Meaning: It consists of the publication in the Airport AIP (Aeronautical Information Publication) of NPR—Noise Preferential Routes, which are less harmful in terms of noise pollution of adjacent urban areas.

Relevance: NPRs are designed to avoid populated areas and reduce the problem of noise pollution. However, although the acoustic impact on the populations is reduced, the total amount of noise emitted can be increased. On the other hand, fuel consumption and greenhouse gas emissions usually increase due to the need to fly longer routes to avoid flying over populated areas. This increase does not have to be significant and a balance between noise, fuel consumption, and emissions must be evaluated before deciding whether to fly using an NPR. ICAO Doc 9829 identifies four principal elements for the application of the Balanced Approach to Aircraft Noise Management around airports: Reduction of noise at source, land-use planning and management, noise abatement procedures, and operational restrictions. Examples of this initiative are the implementation of the curved approach trajectories south of the city of Stockholm or at the airport of Arlanda (Sweden).

Interpretation: Up to four points may be granted upon compliance with the following initiatives:

• Study and publication of the NPRs (1 point).
• Tracking of the NPR routes by at least 20% of the annual aircraft. If the tracking of the NPR routes is met for at least 30% of the aircraft, one more point may be obtained (Up to 2 points).
• Establishment of operational restrictions for non-NPR routes that fly over populated areas in order to limit their use by certain types of aircraft that marginally comply with Chapter 3 of Annex 16 of the ICAO (International Civil Aviation Organization) that classifies aircraft acoustically (1 point).

8.1.7. Runway-Use Prioritization

Meaning: Give priority to the use of airport runways that involve a decrease in the populated areas affected by noise and/or suggest specific approach methods for certain tracks.

Relevance: Although the reduction of noise pollution is ensured, the reduction of emissions depends on the design and conditions of each particular airport, which may positively or negatively affect fuel consumption and emissions. Examples of these procedures can be found at Madrid–Barajas runway 18 R.

Interpretation: One point will be awarded to those airports that publish recommendations on the use of any of their runways in their AIP with the purpose of reducing noise pollution generated by air traffic. The other point may be obtained if restrictions are applied to some types of aircraft.

8.1.8. Restriction of Night Flights

Meaning: It consists of applying restrictions in a certain time slot (between 11 o’clock at night and 6 o’clock in the morning) to the type of aircraft that can operate at the airport. These measures should not affect the air traffic service offered by the airport.

Relevance: This simple measure would reduce the exposure to nocturnal noise of the inhabited areas close to the airport facilities, with hardly any cost for the airport management company. An example of this measure is Bristol Airport in England, which has implemented a noise quota system that limits operations at night (23:00–07:00) for the noisiest aircraft. The fee consists of an account related to the acoustic classification of aircraft and that is seasonal, 1260 “points” in the summer period and 900 for the winter season. Each time an aircraft performs an operation at night, the equivalent points are deducted. Once all the points are used up, the aircraft will not be able to fly during this seasonal period at night.

Interpretation: Up to five points can be obtained using the following measures:

• Development of a Noise Quota System for the night period that assesses the noise impact (EPNdB) of aircraft (2 points).
• Limitation of night flights for those aircraft that do not correctly comply with Chapter 3 of Annex 16 (1 point) [46].
• Limitation of the use of the reverse in the landing of aircraft only to those locations that require it for safety reasons (2 points).

8.2. Pollution and Emissions Category

According to Eurostat, transportation, in general, is one of the sectors which has the greatest impact on the atmosphere, accounting for 23% of the total greenhouse gas emissions associated with energy consumption. This category takes into account emissions from the large number of activities carried out at airports. The main sources of emission of polluting gases within the airport facilities are:

• Aircraft: Engines start-up, rolling, LTO (Landing and Take-Off) cycle, APU (Air Power unit) units, etc.
• Handling: GPU (Ground Power unit), air conditioning, conveyor belts, forklifts, vehicles, support machinery, etc.
• Infrastructures/buildings: Generating sets, heating systems, maintenance/construction, etc.
• Road traffic access to the airport: Private vehicles, buses, heavy machinery, etc.

The main atmospheric pollutants produced by the aeronautical industry are nitrogen oxides (NOx), sulfur oxides (SOx), carbon monoxide (CO), particulate matter (PM), volatile organic compounds (VOCs), carbon dioxide (CO₂), and greenhouse gases (NO₂, CO₂, CH₄).

8.2.1. Biofuels Use

Meaning: The role played by airports in providing airlines with refueling services use biofuels and incentivizing them for their use will be valued, offering them economic advantages when paying airport taxes. Variations in the composition of kerosene to achieve significant environmental improvements are already very limited, which will mean that the growing demand for air traffic will inevitably lead to an increase in emissions from the aviation sector. It is expected that by 2050, 30% of the fuel consumed by the aviation sector will be biofuels.

Relevance: The use of alternative fuels will offer airlines significant economic and environmental benefits. For example, biofuel emissions do not require obtaining ETS (Emission Trading System) emission rights. It is estimated that the incorporation of biofuels into aviation would make it possible to avoid at least 250,000 tons of CO₂ by 2016, 3% of the CO₂ emissions from air transport planned for that year.

Interpretation: Two points can be obtained in this category. The first can be obtained by promoting the use of biofuels in airports, with those airlines that use biofuels for at least 5% of their operations at the airport benefiting from more favorable airport rates. The second point may be awarded to the airport if it includes any type of biofuel in its handling or refueling services.

8.2.2. APU- and GPU-Use Limitations

Meaning: In this section, the use of fixed sources of power and air conditioning on the use of APUs and GPUs will be evaluated.

Relevance: Limitation in the use of APUs and GPUs will mean a palpable reduction in the emissions generated by the airport and its operations. It is estimated that emissions could be reduced by up to 35 tons per year. At Heathrow Airport, maximum operating times of the APUs used in arrivals and departures have been established, and these were complied with by up to 85% in 2010 and, at present, by more than 90%.

Interpretation: In this section of credits, a total of two points can be achieved:

• One more point will be obtained by using the FEGPs (Fixed Electrical Ground Power) and the PCAs (Pre-Conditioned Air) for only up to 50% of the operating times of the APUs and the GPUs.
• Another point will be granted if the use of APUs is restricted to daytime hours.

8.2.3. Continuous Descent (CDA or Continuous Descend Approach)

Meaning: It consists of an approach maneuver with a continuous descent, without horizontal stretches, and at low engine speed. The aircraft descends from an optimal position, with the minimum thrust, and in a constant trajectory, thus avoiding the different flight levels used in the conventional approach.

Relevance: In addition to achieving a significant reduction in noise pollution in areas close to the airport, the continuous descent system allows a reduction of around 25% in the CO₂ emissions and an equivalent saving in the fuel consumption. It is estimated that for large airplanes, you can save around 200 kg of fuel per descent and a reduction of approximately 640 kg in the CO₂ emissions. In addition, the CDA can move the concentration of noise by a distance of up to about 10 km from the airport.

Interpretation: Up to four points can be obtained in this section:

• One point for publishing at least one CDA approach.
• One point for applying the continuous descent in at least 50% of the annual operations during night period (23:00–06:00), and two points if applied to all the annual operations at night.
• One point if the CDA is applied in at least 25% of the daytime annual operations (06:00–23:00).

8.2.4. Continuous Ascend Departures (CCD or Continuous Climb Departure)

Meaning: It consists of the continuous ascent up to the optimum level of flight, avoiding intermediate steps that increase fuel consumption and greenhouse gas emissions.

Relevance: The reduction in fuel consumption is certainly significant, with a reduction by up to 5% of the fuel consumed in a CCD with respect to an ascent with an intermediate level (up to 200 kg of fuel), or by 6% with respect to an ascent conventional with two intermediate levels (about 250 kg of fuel). Copenhagen is an example of an airport that applies this procedure. They have been able to avoid up to 32,000 tons of CO₂ emissions per year, the equivalent of saving 10,000 tons of fuel.

Interpretation: Up to three points can be obtained if the following measures are met:

• One point for CCDs in at least 50% of the annual operations at night, and two points if applied to all the annual operations at night.
• One point for applying CCDs in at least 25% of the airport’s annual daytime operations.

8.2.5. Restrictions on the Use of the Engine on the Ground

Meaning: It implies taxiing with a single engine or with one of the engines turned off and optimizing taxiing and ground movements. Optimum taxiing means adjusting the duration, the taxiing route, the power, the number of engines in operation, the delays in the parking, and instances where the engine is turned off in the case of delays.

Relevance: A reduction in noise is achieved, as well as fuel savings and reduced emissions, thanks to the use of fewer engines. It is estimated that, depending on the type of aircraft and operation, a reduction of between 20%–40% in the CO₂ emissions and between 10%–30% of the NOx emissions emitted during the taxiing phases can be achieved. One example is the French airport of Charles de Gaulle.

Interpretation: Four points can be obtained by:

• A reduction of the waiting times for at least 25% of the annual operations. One point more if the times are reduced by half, that is, at least 50% (up to 2 points).
• At least 10% of annual operations run without an engine, while, of course, always respecting the safety criteria (1 point).
• At least 5% of annual operations run without two engines, while also always assessing the safety of air traffic first (1 point).

8.3. Materials and Waste Category

The materials used in the construction of the airports do not differ in characteristics from those used for the construction of other types of buildings, there are only differences in the type of constructions developed. On the other hand, waste must be treated in a special way because there are dangerous residues derived from the exercise of aviation activities, as well as residues described as “of strange jurisdiction” because they are the international waste that arrives on airplanes. In addition, urban waste similar to that of any other commercial activity will be generated and must also be managed and treated carefully. Most of the waste generated in airports is classed as urban or non-hazardous (49%), followed by urban waste susceptible to recycling (48%) and, finally, hazardous waste (3%).

8.3.1. Hazardous Waste Treatment

Meaning: The correct treatment of hazardous waste generated in the airport environment, as well as waste from international flights, is mandatory and must be done in accordance with the law or the regulations in force.

Table 14. Hazardous residuals at airports.

	AIRCRAFT SYSTEMS		AIRCRAFT MAINTENANCE
Liquids	Gasoline, kerosene, hydraulic fluids, brake fluids, antifreeze fluids, etc.	Solvents and cleaners	Toluene, engine cleaners and carburettors, methyl ethyl ketones, etc.
Freons, etc.	Nitrogen, oxygen, halons gases	Lubricants	Dry lubricants/spray, oils, etc.
Other	Alcohols, methanol, glycol, batteries, degreasers, disinfectants	Paints and foundations	Strippers, primers, varnishes, lacquers, enamels, epoxies, etc.
		Adhesives	Fiberglass resins, rubber adhesives for joints, etc.
		Other	Elements welding, oxidants, hydrochloric acid

summarises the most common hazardous residues found at the airports. In addition to hazardous waste, there are the previously mentioned residues of strange jurisdiction from international flights. For example, food remains, containers, cleaning waste, sewage liquids, etc. In this case, the waste must be properly treated by the airport staff, by being incinerated in a controlled manner in facilities established for exactly that purpose.

Relevance: The treatment of hazardous waste for health and the environment is defined by the law, for which compliance will be mandatory. On the other hand, there are dangerous residues that can be treated in such a way that they are valued, thus acting positively toward the environment. This type of measure will be evaluated with a point in the next section of credits (recycling of waste).

An example of dangerous elements being converted to something of value is that of the catering companies of Heathrow Airport, which convert kitchen oil into biofuel. At this airport, where meals are prepared for more than 150,000 people, 100% of the oil used in the airport kitchen is being recycled in some way. A total of 85% of the oil is recycled as biodiesel and is incorporated into the national fuel supply network. Currently, attempts are being made to integrate part of that biofuel within the airport itself for the future.

Interpretation: The airports will be obliged to have areas properly qualified for waste management in general, with specific areas for hazardous wastes. The regulations must be followed regarding the identification and labelling of the products, as well as their storage and subsequent treatment, either at the airport’s own facilities or by qualified third-party companies recognized by the administration for waste management.

8.3.2. Infrastructure Lifecycle Impact

Meaning: To reduce waste due to the construction or demolition of airport infrastructures that end up in landfills and waste incineration facilities and that constitute the most significant environmental impact in terms of materials. The environmental cost of maintaining the infrastructures built will also be evaluated.

Relevance: The integration of all the processes of development and projection of an aeronautical infrastructure, as well as the study of the complete life cycle of it, supposes a reduction in the use of materials and a lower generation of waste due to the processes of construction/demolition. Heathrow Airport in England is a good example of environmental performance. In the construction of Terminal 5, an environmental management plan was introduced from the first moment of the project’s development. In this way, the necessary materials and waste due to the construction of the terminal were planned with greater efficiency.

Interpretation: The development and implementation of a construction/maintenance/demolition management plan is established as a mandatory requirement for all newly constructed airports. In addition, it will be positively assessed not to generate more than 10 kg of waste per square meter built (1 point). Likewise, the reduction in the use of materials and in the generation of waste throughout the life cycle of the airport facility must be demonstrated. This can be carried out in various ways such as:

• Reuse through the renovation of abandoned or deteriorated buildings or infrastructures (1 point).
• The integrated evaluation of the entire life cycle of the infrastructure (this measure can aid up to a 10% reduction in the impact on the environment) (up to 2 points).

8.4. Water Resources Category

The management of water consumption, together with the consumption of energy seen in the previous sections, accounts for most of the consumption of natural resources at airports. Airports consume a large amount of water for the usual processes of commercial and business buildings, but also consume a large part of that amount in handling and maintenance services. Likewise, runoff water must be properly managed so that it does not pose a risk to the environment or the health of people. This water is the result of the high number of paved areas in the airport infrastructures, which can also be contaminated by the different types of hazardous substances used in the maintenance of facilities and aircraft.

8.4.1. Reducing of Water Consumption Outdoor

Meaning: The savings in water consumption used for the handling and maintenance services of aircraft will be evaluated. The reuse of water that is not suitable for consumption or that is non-potable will be encouraged to achieve more significant saving of water resources.

Relevance: A good initiative in this regard is the campaign initiated by the airline Air France, which could be useful for other companies as well as for those companies that facilitate the handling services. This airline is using new cleaning methods for the exterior of aircraft that use one-hundredth of the amount of water necessary using traditional methods. The technique consists of applying the cleaning products with cloths, which requires a much smaller amount of water, going from 10,000 L needed for cleaning, for example, a Boeing 777, to an amount of about 100 L per plane. The products used are 96% biodegradable, neither toxic nor flammable and allow the cleaning staff to work without special protective equipment.

Interpretation: In this section of credits, it is possible to obtain up to two points that will be valued by the certifying staff for the achievement of objectives such as:

• Reuse of rainwater and grey water (waters that have already been used but have undergone a treatment that enables them for new uses) for maintenance activities in which non-potable water can be used.
• For winter campaigns, where mixtures of glycol and water are used to defrost aircraft, reuse the water used and use recycled water as much as possible.
• Application of measures aimed at reducing water consumption used for aircraft cleaning operations, catering services, and other on-board services.

8.4.2. Management of Runoff

Meaning: It is concerned with the treatment of runoff waters to avoid their contamination or percolation in groundwater, and which will be evaluated. In addition, its treatment will be encouraged for the purpose of reuse in airport activities.

Relevance: In airport facilities, where most of the land is paved, rainwater or maintenance services can flow along the surface, dragging contaminants in its path. For this reason, it is necessary to channel it to be able to deal with it later. At Barcelona Airport, for example, the low slope and high water levels make it difficult to drain the airport surface, favoring the accumulation of surface water. These pose a problem for safety and, therefore, water catchment channels have been installed in the flight field and they are driven to three pumping stations. To maintain the ecological and chemical quality of these runoff waters, different control mechanisms have been followed:

• Installation of hydrocarbon separators and closing gates in the airport channels for the containment of accidental spills of hydrocarbons.
• Periodic analytical control of the ecological and chemical status of the surface and groundwater of the airport grounds.
• A piezometric control network of groundwater.
• Periodic visual inspection of the waters of the channels.

Interpretation: Up to two points can be obtained in the management of runoff waters that will depend on their treatment and reuse.

• Channelling of the superficial waters that run through the airport to avoid its discharge into the environment without prior control of its quality.
• Management and treatment within airport facilities or through accredited companies of runoff waters to eliminate polluting substances that they may contain.
• Control of the percolation of the superficial waters in the land to obtain the maintenance of the quality of the groundwater.

8.5. Land Use Category

Territories occupied by the areas dedicated to air transport have peculiarities that the lands occupied by other means of transport do not have. For example, limitations on the use of the soil of the aeronautical easements or obstacle-limiting surfaces that protect the air navigation operations. In some cases, no building is allowed to be carried out in these areas, in others, it is the height of the building elements above the ground that is limited.

8.5.1. Site Selection

Meaning: In addition to environmental factors and social factors, compliance with the needs of the aeronautical industry must be ensured. This will mean taking into account aviation safety, the possibility or need for expansion of infrastructures, the areas necessary for obstacle limitation areas, airspace, the compatibility of the adjoining land with the development of air traffic activity, the noise pollution generated by aircraft, etc.

Relevance: An example of compensatory measures adopted by an airport for the restoration of the ecological impact on the territory is the one developed in the Expansion Project of the Madrid Airport System. From the airport of Barajas and from Aena, compensatory measures were adopted, such as acquisitions of farms, reforestation, and recovery actions on the banks of the streams on the Jarama and Henares river basins.

Interpretation: It will be mandatory to carry out a management plan for land use, from the very beginning of the projection of the aeronautical infrastructures that will be built. The plan must present the planning, design, and management measures of the infrastructures that will be developed or renewed, taking into account factors such as noise (also assessed in the corresponding section), the areas that could be affected by the risk of accidents, the land uses of the adjacent areas, the obstacle-limiting zones, the ecosystems that would be disturbed, etc. In addition, three extra points may be obtained according to the compensatory measures adopted.

8.5.2. Soil Protection

Meaning: The recovery of soils contaminated by aeronautical activity and the adoption of initiatives to reduce the impact on them will be evaluated.

Relevance: The problems derived from the chemical disturbances that all industry assumes in the soil, as well as erosion problems, will be solved. Chemical contaminants such as heavy metals, asphalt particles, and other toxic agents produce disturbances to the environment, altering the quality of the soil. In addition, these pollutants tend to be concentrated in the vicinity of the infrastructures that generate them, but sometimes their effect can spread and affect other areas further away from the emission sources.

In the airport of Leipzig–Halle, which serves two German cities, several measures have been developed to protect the soils. For example, the small quantities of kerosene discharged during the refueling of aircraft are treated with a binding agent and collected by the airport fire department using special instrumentation. After collection, the kerosene is appropriately treated as a hazardous waste.

Interpretation: In the case of newly constructed airports or the extension of airport facilities, a report evaluating the quality of the soil prior to the construction processes must be presented, with measures to minimize erosive effects, as well as proposing initiatives dedicated to its subsequent restoration in the case of damage. In addition, three more points can be obtained by measures to improve the quality of the soil and control its contamination, for example:

• Control of hazardous waste that is prone to percolation in the soils of the airport environment and contaminates them.
• Develop a campaign to control soil contamination and decontamination of those affected areas.
• Special control of winter campaigns to develop means aimed at the use of less harmful and less polluting antifreeze.

Although water treatment and control has already been dealt with in another section of credits, pollution of groundwater and aquifers can also be considered in this section. This is because the contamination of this type of water is linked to the soil, therefore, a control on the soil quality of the airport land will be a determinant of the quality of groundwater.

8.6. Biodiversity and Landscape Category

According to the Convention on Biological Diversity (CBD), biodiversity is understood as: “The variability among living organisms of all kinds, including, among others, the terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species and ecosystems”. In this section, we will deal with biodiversity and those aspects of it that also affect ecosystems, such as the modification of the landscape or the influence of the airport facilities on the environment (island of heat, light pollution, etc.).

8.6.1. Reducing Light Pollution

Meaning: Light pollution is defined as the light that illuminates outside of those areas that are meant to be illuminated. The objective of the management of light pollution will be to improve the environmental conditions for the development of wildlife, as well as the quality of life of the populations that surround the airport. In this case, the correct and safe operation of air traffic must be prioritized as an essential requirement. It will be mandatory, therefore, to respect and monitor the aeronautical regulations that define the luminous indications necessary for air navigation.

Relevance: These credits are intended to assess the improvement in the conditions of light emissions due to external lighting elements that can be found in areas such as road accesses, parking areas, passenger terminals, hangars and buildings dedicated to maintenance, aircraft parking areas, etc. An example of reducing light pollution is the parking area for employees at Schiphol Airport in Amsterdam. There, LED lighting (Light-Emitting Diode) has been installed, replacing the previous one of conventional high-pressure sodium lamps. Besides producing less light pollution, they need less maintenance and save energy, with an estimated saving of 137,000 kWh per year.

Interpretation: The renewal of at least 75% of the lights used in outdoor spaces not governed by aeronautical regulations will be mandatory for obtaining the certification. Illumination tolerance limits per airport zone are indicated in

Table 15. Illumination zone tolerance limits.

Illumination Zone		Tolerance Limits *
LZ0	Without ambient lighting. Areas where the natural environment could be seriously affected by the presence of lighting.	0%
LZ1	Low ambient lighting. Areas where lighting could affect flora, fauna, or the ecosystem.	0%
LZ2	Moderate environmental lighting. Areas of human activity where users are adapted and need moderate lighting.	1.5%
LZ3	Moderate–high ambient lighting. Areas of human activity where users are adapted and need moderate–high lighting.	3%
LZ	High ambient lighting. Areas of human activity where users are adapted and need high lighting.	6%

* Luminous emission horizontal to the focus, referred to as a percentage of the total lumens of emission of the luminaire.

. The evaluation of this will follow the international model prepared by the IDA (International Dark-Sky Association) called Model Lighting Ordinance (MLO), which establishes tolerance limits of luminous emission horizontal to the focus.

8.6.2. Protection of Biodiversity

Meaning: The objective will be to minimize the possible interference to ecosystems and their organisms present in the airport environment, as well as their protection and conservation. Additionally, within this section of credits, the necessary control of birds in the areas of operations of the airport will be included as they can pose a serious problem for safety. In addition, the impacts of birds on aircraft represent a high economic cost, estimated at more than 500 million US dollars per year.

Relevance: Owing to the implementation of measures that benefit the biological sustainability, better management of ecosystems in the areas of operations of the airport will be achieved. This will not mean that there will be zero impact on the flora and fauna populations or on their ecosystem since any anthropogenic activity will affect them. However, it seeks to minimize this impact and try to lessen, with measures in this regard, the negative impact on the environment.

Likewise, it will try to reduce the impact of bird control on avian fauna and the ecosystem in general. Therefore, the adoption of measures that are less damaging to the environment in terms of bird control for the maintenance of aviation safety will be evaluated.

Table 16. Bird control measurements.

Bird Control Measurements	Examples
Optical and visual	Lights, lasers, pyrotechnics, lures, hot air balloons, comets, reflective tapes, predator models, mirrors, etc.
Sound systems	Speakers, subsonic and ultrasonic generators, microwaves, high-intensity sounds, etc.
Physical/chemical	Chemical repellents, gas cannons, radiation, etc.
Natural	Falconry, dogs

summarises the measures that are currently used to carry out this control.

The German airport in Frankfurt has implemented a plan for the conservation of biodiversity which includes measures such as:

• The repopulation and conservation of an alluvial forest (in Hoenaue), reforestation (in Hofgut Schönau), and the renewal of wooded areas (in Mörfelden).
• The resettlement of wildlife species threatened by aeronautical activities (e.g., sand lizards and flying deer).
• The registration and monitoring of species diversity through surveillance systems such as that which is used for bees.

Interpretation: The protection of biodiversity will be one of the compulsory credits in this section and, in addition, one of the most valued. It will be mandatory, therefore, to carry out an impact assessment report on fauna and flora prior to any infrastructure construction project. In addition, an extra point may be obtained depending on the quantity and quality of the mitigation measures adopted. For example, the realization of wildlife battles prior to the execution of the project, information and education of airport personnel in relation to the wildlife control service, and collaboration with entities related to the protection of wildlife biodiversity, etc., will be evaluated. The impact of the measures adopted for the control of avian fauna will also be assessed, whether or not a point is awarded.

9. Conclusions

Concern for the environment has increased sharply over the last decade within the aviation industry. Today, an important number of airports worldwide have implemented UNE-EN ISO 14001 environmental management systems, and have invested efforts to get their terminals certified according to several world-recognized rating standards.

This paper studied how existing rating systems could evolve to address properly all the needs and environmental impacts from airport operations. The research has been based on a combination of airport functional analysis and different layers of benchmarking to assess the environmental impacts of the airport activities, compare them with state-of-the-art rating models, and identify gaps and needs for extension. By benchmarking the best practices in the airport community, we have developed and validated a rating system to fill these gaps.

The functional model of the airport identified five airport areas and 21 functional elements as main sources of environmental impacts, including construction and operation of airport infrastructures and ground traffic; de-icing protection for aircraft and runways and runoff water; aircraft refueling; maintenance of equipment; public services; and aircraft operations.

A benchmark of airport stakeholder reports allowed us to rank the principal airport environmental impacts of airport operations, maintenance, and expansion as (1) noise issues, (2) water quality issues including effects of de-icing and anti-icing activities, as well as from fuel storage, and (3) air quality issues and emission of toxic air pollutants.

Impacts produced by each of these 21 functional elements in the airport functional model have been classified either as air pollution, biodiversity impacts, climate change, landscape, noise, water pollution, and water use and waste.

In parallel the most extended state-of-the-art Green Building Rating Systems (GBRSs) were comparatively analyzed. We identified the four main environmental assessment methods that, to a certain extent, have been applied in the airport environment and compared how they apply environmental criteria. Energy (reduction of energy use, peak load energy, energy monitoring and reporting, energy efficient appliances, equipment and systems, and the use of renewable energy), was identified as the principal evaluation criterion for assessing and certifying green buildings with the highest consideration among the majority of existing GBRSs. It is followed by site criterion, indoor environment, land and outdoor environments, materials, and finally water, although this last one is sometimes included under a higher level of criterion termed as “resources”. BREAM and LEED have been found to be the two systems most applied in airport buildings. Around 270 buildings related to an airport are certified as LEED certified and 13 as BREAM.

When contrasting current rating systems with airport environmental impacts gaps and needs for expansion were identified. It was found that relevant environmental airport impacts are not currently covered by those systems, in particular those related with Noise and Pollution and Emissions.

Noise accounts for specific aviation criteria such as noise evaluation and management, acoustic isolation plan, acoustic efficiency, engine testing restrictions, routes use restrictions, runway-use prioritization, and night flight restrictions. Pollution and emissions accounts for airports emissions control, ecological cars, biofuels use, indoor quality, APU- and GPU-use limitations, a continuous descent approach, continuous ascend departures, tailored arrivals, restrictions on the use of engine ground, and on route operation optimization.

These two categories of impacts can be considered as the main drivers of environmental impact from airports and current certification systems do not adequately address these issues. Another 10 additional criteria were observed as presenting significant differences between existing GBRSs and what must be required at an airport. These criteria belong to the categories of materials and resources, water efficiency, sustainable sites, and locations and transportation.

Finally, we performed a benchmark of best practices currently applied by the industry to minimize negative airport impacts, which has allowed us to identify the key elements that should complement the current certification standards.

With all this information, the new Green Airport credit was defined, including a description of categories and certification criterion: A brief summary of each of the credits; the requirements to obtain them; and the scores with which they are valued, with examples of airports that implement initiatives rating positively in the credit system. The organization of the credits, the number of them that are needed to obtain an environmental certification, and how the Green Airport certification could be implemented was also defined.

The model proposed was validated through an iterative process following a twofold approach, with the help of Aena’s experts who were divided into groups assessing iteratively the models to detect inconsistencies and discrepancies. Representativeness of the categories, criteria, and credits were independently contrasted with the available literature and evidence of best practices already applied by the airport community. Consistency checks were also applied to verify that all variables were clearly defined and have unique meanings, so that all relevant variables have been included and that all the states are exhaustive and exclusive.

The final outcome of this research is the development of an “Green Airport” environmental certification rating system that applies to all aviation infrastructure at the airport, including airport buildings and installations, as well as air navigation systems and facilities. This certification model is based on the concept of Leadership in Energy and Environmental Design (LEED), but the categories and criteria defined could be added to any certification system in order to award a green building designation to an airport.