Environmental Benefits of Hydrogen-Powered Buses: A Case Study of Coke Oven Gas

Abstract

This study conducted a Life Cycle Assessment (LCA) of alternative (electric and hydrogen) and conventional diesel buses in a large metropolitan area. The primary focus was on hydrogen derived from coke oven gas, a byproduct of the coking process, which is a crucial step in the steel production value chain. The functional unit was 1,000,000 km traveled over 15 years. LCA analysis using SimaPro v9.3 revealed significant environmental differences between the bus types. Hydrogen buses outperformed electric buses in all 11 environmental impact categories and in 5 of 11 categories compared to conventional diesel buses. The most substantial improvements for hydrogen buses were observed in ozone depletion (8.6% of diesel buses) and global warming (29.9% of diesel buses). As a bridge to a future dominated by green hydrogen, employing grey hydrogen from coke oven gas in buses provides a practical way to decrease environmental harm in regions abundant with this resource. This interim solution can significantly contribute to climate policy goals.

1. Introduction

1.1. Reasoning behind the Research

In 2022, global greenhouse gas (GHG) emissions from transport reached 7.5 billion Mg CO_2eq, of which about 70% was generated by road transport. The largest emitters, in the transport sector, are the economies of the US, China, and the EU. In 2022, transport emissions in the US were approximately 1558 million Mg of CO₂; in China, 966 million Mg of CO₂; and in the European Union (EU), approximately 785 million Mg of CO₂ [1]. The EU is among the world’s leading major economies when it comes to tackling GHG emissions. As part of its policy to reduce the fluxes of these pollutants, the EU has set a target to reduce transport emissions by 60% by 2050 compared to 1990 levels [2,3]. The EU’s plan for a green transition “Fit for 55” provides interim targets to reduce CO₂ emissions from cars by 55% and light trucks by 50% by 2030. The introduction of alternative fuels and alternative propulsion systems is an important strategy that was included in the EU Transport White Paper. According to the EU, greater use of alternative fuels should improve the quality of the environment and human health and reduce the dependence of European transport on hydrocarbon fuels, that is, oil imports [4]. Currently, LPG (liquefied petroleum gas), natural gas in the form of CNG (compressed natural gas) and LNG (liquefied natural gas), electricity, synthetic and paraffinic fuels, biofuels, and hydrogen are used mainly in global transport as substitutes for conventional fuels. The proliferation of electric vehicles, the most popular alternative vehicles, in the world’s three largest economies, China, Europe, and the United States, is evolving unevenly. In 2015, the share of electric vehicles in new registrations in the three markets was less than 1%. In 2021, the European market increased to 19%. In a similar vein, the Chinese market experienced a 15% increase. In contrast, electric vehicles are not as popular in the United States; the share in the transport sector in 2021 is only 4%. However, the number of units sold (0.7 million in 2021) and the percentage share of the US market do not approach the level of the Chinese or European market [5]. Alternative electric vehicles have certain limitations, mainly due to their limited use in trucks and long-distance transport. Particular hopes in terms of solving these problems lie in the use of hydrogen. Hydrogen vehicles can demonstrate an advantage in long-distance heavy transport applications, where the longest possible range per charge is crucial. The International Energy Agency (IEA), as part of its Advanced Fuel Cell Technology Cooperation Program (AFC TCP), conducts an annual global data report. At the end of 2022, a fuel cell vehicle fleet surpassed the 70,000 unit mark being refueled by a network of more than 1000 hydrogen refueling stations, of which 700 are located in Asia, mainly in China, South Korea, and Japan. This number includes passenger cars; buses; light commercial vehicles; and medium and heavy trucks. The largest number of FCEVs is located in South Korea, followed by the United States, China, and Japan. In Europe, the leaders are Germany, the Netherlands, and France. The global number of fuel cell buses (FCB) is estimated at 6460 at the end of 2022. Most FCBs are in China, with 84% of the population spanning 5410 buses. The other countries with more than 100 FCBs are the Republic of Korea with 281, the United States with 211, and Japan with 124. The United Kingdom (98 FCBs), Germany (68), India (58), and the Netherlands (54) are other countries with more than 50 FCBs. The list continues with France (33), Austria (25), Switzerland and Italy (20 each), Canada, Norway, and Latvia (10 each), Spain (9), Luxemburg (5), Denmark and Belgium (4 each), Portugal and Sweden (2 each), and Brazil and Costa Rica (1 each). At the continental level, at least 9 out of 10 FCBs are in Asia.

Currently, hydrogen is produced mainly from fossil fuels. At the end of 2021, almost 47% of the global hydrogen production originated from natural gas, 27% from coal, 22% from oil (as a by-product), and only around 4% came from electrolysis. With a global average renewable share in electricity of about 33% in 2021, only about 1% of global hydrogen production is produced with renewable energy. One of the alternative processes for obtaining hydrogen from COG can be its recovery from COG, which is a byproduct generated in the coking process and is a key step in steel production. The hydrogen content in COG ranges from 55% to 60% [3]. The technology of producing H2 from COG (H2COG) enables compensation for the negative impact of the coking process on the environment through the simultaneous separation of a “clean” energy carrier, which is H2COG, which can be a substitute for conventional fuels in the transport sector. The coke industry belongs to the group of key branches of the heavy industry. This is due to industrialization and economic development, as well as the growing demand for steel products around the world. The progressing environmental requirements and the increase in market competitiveness force the use of by-products (i.e., COG) of attractive economic or energy value. This extends the industrial chain, which is extremely important for the global improvement in the quality of the environment and sustainable development. Coke production, and thus COG, is mainly concentrated in Asian countries; In 2020, it was 688.5 Mt, of which over 68% is attributable to China. Other countries such as India (6%), Japan (4%), Russia (4%), South Korea. (3%), the USA (2%), Ukraine (2%), Germany (1%), and Poland (1%) have a much smaller share in the global coke production. On the other hand, the largest coke exporters in 2020 were Poland (5.4 million Mg), China (3.5 million Mg), and Colombia (3.4 million Mg)—these countries represented nearly 50% of the volume of global trade in this commodity [4,5]. In 2020, coke production in China reached nearly 471.27 Mt [6], with the generation of nearly 200 billion Nm³ of COG. Europe, with coke production of 30 million Mg in the same year, generated around 12 billion Nm³ of COG. The United States, as the next major world economy, produced 5.5 billion Nm³ of COG with 13.77 million Mg of coke production. About 50% of COG is used for the technological process of producing coke, while the other half constitutes an excess that can be used for other purposes. This means that it is only in China, which simultaneously leads in the implementation of hydrogen buses, that it is, theoretically, possible to produce an additional 50 billion Nm³ (ca. 4.5 million Mg) of hydrogen without increasing the use of fossil fuels for this purpose. Therefore, ways to use COG are being searched, which will be a strategic means of compensating for the resource shortage and reducing carbon dioxide emissions, with the simultaneous sustainable development of the coking industry. In this context, COG is an attractive source of hydrogen in the interim until the share of hydrogen from renewable sources increases significantly. H2COG could significantly contribute to the transformation of the transport sector, for both heavy and long distance and for air and environmental protection, allowing one to use the full potential contained in the by-products of the coal coking process. This seems particularly important for countries and regions where coking plants are located, such as China, India, Japan, the United States, and some European countries such as Germany, France, and Poland.

This study aims to evaluate the environmental impact of using H2COG as an alternative fuel in public transportation. By analyzing the life cycle of H2COG production, we seek to provide valuable data for policymakers and public transport companies developing low-emission climate strategies. The results can also inform future research on H2COG’s suitability for electric motorization technologies. We have assessed the environmental burdens associated with replacing traditional fuels with H2COG in urban transport, filling a gap in public transport hydrogen studies. Our analysis draws on data from a coking plant in southern Poland, including mass and energy flows, balances, and relevant reports. By identifying key environmental factors and exploring opportunities for cleaner coke production, this study contributes to understanding the potential benefits of H2COG as a more sustainable fuel option. Currently, there is a lack of detailed environmental analysis in the scientific literature on the transformation of the conventional bus fleet to vehicles equipped with H2COG fuel cell electric vehicles (FCEVs). We believe that the results of our environmental modeling analysis can be applied to agglomerations with similar economic and industrial characteristics, where coking plants are in operation as a source of COG for hydrogen production. The key findings of this work may provide an answer to the question of whether hydrogen from coal pyrolysis can be an environmentally friendly alternative to power urban vehicles. Additionally, our LCA analysis is relevant to the environmental competitiveness and availability of hydrogen from coke oven gas relative to that of natural gas, which is the substrate currently most popular for hydrogen production. Furthermore, we believe that this LCA study is important because coal is on the EU CRM list and is crucial to the steel industry. It is essential to remember that without steel, even the smallest pro-environmental or alternative technologies for a low-carbon transformation of the EU or the rest of the world would be impossible. Therefore, it is vital to fully exploit and explore the potential of coal coking and the possibilities of feeding other sectors of the economy with products derived from it.

1.2. World Trends in Bus Environmental Research

In the transport and automotive sectors, recent years have seen the development of methods related to the assessment of sustainability aspects and an increased interest in environmental issues. For this purpose, the Life Cycle Analysis (LCA) method is widely used, which illustrates the complex interactions that occur between a product or technology and the environment, where the main categories of environmental impact consider the effects on human health, the use of natural resources, and the impact on the quality of the ecosystem [7,8]. LCA is recognized as one of the best environmental management tools for comparing the impacts of different alternative systems, products, or processes [9]. LCA considers the environmental aspects of the entire life cycle of a product, from raw material sourcing through production, use, post-processing, and final disposal. For this reason, in the automotive industry, an LCA analysis from cradle to grave/end of life is often performed under the name well-to-wheel (WTW) [10]. It is divided into two stages: (i) the well-to-pump/well-to-tank (WTP/WTT) phase, which includes emissions associated with fuel production, transportation to the distribution site, and vehicle refueling, and (ii) the tank-to-wheels (TTW) phase, which illustrates emissions resulting from the conversion of fuel energy within the vehicle. In the vehicle life cycle, which is linked in part to the fuel life cycle at the WTW boundary, the following stages can be distinguished: (i) material production, (ii) vehicle assembly, (iii) vehicle distribution, (iv) vehicle maintenance, and (v) vehicle disposal or decommissioning [11,12].

The currently available literature on the LCA of buses, or public transport in general, is very extensive and focuses on different assumptions on the limits of the system under consideration, different methods of impact assessment, and above all, on different fuels and alternative propulsion systems. The importance of assumptions, methods for assessing the potential environmental impact, and the validity of data in the LCA analysis of buses is addressed in their work [13]. They checked whether an old LCA study remains valid after a certain period of time. For this purpose, they performed an LCA of a bus stop in Barcelona that was performed about 20 years ago. The original study used SimaPro software; data came from IVAM LCA, BUWAL 250, IDEMAT 96, and PRe4 databases; and the CML 1992 impact assessment methodology was used. The new study used Thinkstep GaBi6 software (Service Package 29 and ecoinvnet v3.1), GaBi6 Professional + extension databases, and the CML 2001 methodology. The authors’ evaluation included an analysis of the key drivers of variance, models, and databases. The overall results obtained in both studies were quite similar or at least comparable. The main reasons for the discrepancies were found to be updating assessment methodologies and characterization factors; improving databases; and changes in technology and improving environmental policies. It was proven that after 15–20 years, LCA results cannot be considered reliable. However, the results can be used as an indication of the expected order of magnitude of impacts and the relative importance of processes at different stages of the life cycle. Jwa et al. [14] conducted a Life Cycle Assessment of an electric bus equipped with a lithium-ion battery and a diesel bus. To investigate the environmental impact of alternative vehicles, an analysis was performed using GREET 2016. The study confirmed the claim that electric buses still face the problem of range of driving. Furthermore, it was indicated that the energy consumption and direct emissions of an electric bus are environmentally preferable to those of a diesel bus. Harris et al. [15] developed a novel framework to help decision makers assess the uncertainty associated with the life cycle impacts of alternative bus technologies. A technology impact prediction methodology was applied by combining it with a life cycle model. The evaluation of trade-offs of alternative powertrain technologies and operational scenarios was considered. Eleven scenarios were evaluated that looked at combinations of battery technology, tank access paths, charging infrastructure, and ancillary requirements. Electric buses equipped with a lithium-tief battery were proven to be the most effective scenario for reducing greenhouse gas emissions at the additional cost of the new technology to the operator. Chang et al. [16] analyzed a specific route in Tainan City for the measurement of carbon footprint (CF). They measured the environmental benefits of alternative buses. Carbon footprint was presented in turn: for LNG—63.14 g CO_2e/passenger km (pkm); for diesel—54.6 g CO_2e/pkm; for liquid gas—47.4 g CO_2e/pkm; for plug-in electrician—37.82 g CO_2e/pkm; and for a fuel cell bus—29.17 g CO_2e/pkm. The use of hydrogen fuel cell buses was found to potentially reduce CO₂ emissions in Tainan City by 1,244,081 Mg for the model route assumed in the study. The avoided CO₂ emissions, from the potential conversion of buses to hydrogen fuel cells, has been compared with planting 22.78 million trees. Gabriel et al. [17] conducted an LCA of substitution of diesel buses for electric and CNG buses. They analyzed the environmental impact in terms of global warming or stratospheric ozone depletion. The electric bus charging infrastructure was also considered. It was found that switching from diesel buses to electric or CNG buses would result in a 54–55% and 37–41% decrease, respectively, in overall harm to human health and ecosystems, an 88% and 80% decrease in resource depletion, and a 48% or 60% decrease in lifetime costs, respectively. The authors proved that among CNG buses and electric buses, CNG buses are a cheaper option, while electric buses cause less damage to the ecosystem, human health, and resource depletion. Iannuzzi et al. [18] made the first comparison of energy and LCA between internal combustion engine buses and some alternative and variant technologies, focusing on buses powered by compressed hydrogen. The LCA analysis covered the extraction of the feedstock up to its consumption as fuel. Hydrogen production from renewable sources, green hydrogen, and non-renewable sources, grey hydrogen, was considered. They have shown that buses fueled by renewable hydrogen meet one of the main sustainability criteria for EU biofuels. In turn, Pederzolli et al. [19] conducted an LCA environmental assessment of a hydrogen-powered bus system obtained in three ways: water electrolysis, chlor-alkali electrolysis, and steam methane reforming. They included the operation of the fuel charging system in their study. The authors concluded that hydrogen-powered buses, compared to diesel-powered buses, have the potential to reduce emissions during the use phase if renewable resources are used. Additionally, it was found that the impacts associated with vehicle production, including the battery pack and the fuel cell stack, dominate the environmental load. When it comes to hydrogen buses, it is impossible to ignore the multitude of technologies for obtaining this fuel, which WTW or complete life cycle (CLC) LCAs should consider. Rinawati et al. [20] reveal a systematic review of the literature on technical aspects and methodological choices in LCA studies of hydrogen use in road transport. The authors reviewed more than 70 scientific articles published between 2000 and 2021, which found more than 350 case studies on hydrogen use in the automotive sector. On the basis of these studies, the hydrogen production process analyzed globally was divided into four categories: thermochemical, electrochemical, thermoelectrochemical, and biochemical. In Rinawati’s research, analysis, and discussion of hydrogen, no mention was made of hydrogen derived from coke oven gas. Their work did not include any studies focused specifically on this source of hydrogen

2. Materials and Methods

2.1. Life Cycle Assessment

This LCA has been conducted in accordance with the principles of ISO 14040:2006 [21] and ISO 14044:2006 [22]. According to the standards mentioned, the LCA analysis was divided into three main phases. In phase 1, the purpose and scope of the study, the boundary of the analysis system, and the functional unit were defined. Phase 2 of the study included an analysis of input and output data sets (Life Cycle Inventory, LCI) and a discussion of the basic assumptions made for the analysis. Phase 3, the Life Cycle Impact Assessment (LCIA), allowed the assignment of appropriate values for environmental impact categories.

2.1.1. Goal and Scope: System Boundary and Functional Unit

The purpose of this LCA was to evaluate the potential environmental impact of using hydrogen obtained from coke oven gas by pyrolysis of indigenous raw material in the Silesia region and then fueling public transport buses with such fuel. The scope of the analysis, presented in Figure 1, was divided into two parts:

• The first part of the analysis consists of two steps: (a) an analysis concerning the energy carrier (diesel, electricity, and hydrogen), hereinafter referred to as well-to-tank (WTT), and (b) an analysis concerning the fuel usage, tank-to-wheel (TTW); hence, the first part of the analysis (the sum of steps a and b) will hereinafter be referred to as well-to-wheel (WTW);
• The second part includes a vehicle bus cradle-to-gate analysis.

This will be followed by a Fuel Bus Life Cycle Study + Vehicle Bus Life Cycle Study (FBLC + VBLC), as assumed in the LCA analysis. The analysis took into account the vehicle lifespan as reported by the manufacturers, the materials required for the replacement of batteries and energy carriers, and the emissions resulting from vehicle operation (fuel combustion, energy consumption, wear and tear of brake pads and discs, tire wear, use of cooling agents, replacement of oils and lubricants, etc.). The authors excluded end-of-life activities (EoL) from the scope of the analysis. The technology of battery production and disposal, including the creation of energy storage, recycling, or disposal of the battery, is developing rapidly and may be different at the time of purchase or decommissioning of the vehicle. However, due to the multitude of possibilities as to the direction of battery use, as well as the lack of standardization and developed technology, the highly efficient recycling industry led the authors to abandon the EoL stage of the bus. The study also did not include the construction of infrastructure and the operation and maintenance of vehicle charging stations due to the difficulty in estimating the corresponding values. This is due to the dynamic development of vehicles and alternative infrastructure and its technological solutions or the multiplicity of charging station options.

The limits of the LCA analysis system adopted for the study are shown in Figure 1. Data for the inventory phase in terms of fuel production processes, WTT (diesel and electricity—Polish energy mix) were taken from one of the world’s leading life cycle inventory (LCI) databases—ecoinvent v3.7.1. The exception is the WTT of hydrogen from coke oven gas, which was modeled by the authors of this paper, for coke oven gas purified by standard methods currently used in the coking industry. The masses of materials necessary for the construction of the bus from the cradle to the gate stage were taken from the available literature, while their indices for LCI were also taken from the ecoinvent database. The emissions from the TTW phase were derived from technical studies and scientific publications on buses. LCA analysis was performed using SimaPro 9.3 software using the Ecoinvent database. The functional unit in the study was also assumed. According to ISO standards, the definition of a functional unit (FU) is based on the quantified performance of a product system, with the intention of finding a reference unit for LCA [21,22]. An FU is defined as a measurement of the performance of a process or system necessary to satisfy a function expressed by an FU. The function of our system is to transport people, by alternative buses, from one point to another under certain traffic conditions of the agglomeration located close to the industrial area with the coke plant. In the opinion of the authors, public transport vehicles operate on a fixed route regardless of the bus filling up. Vehicles perform assumed functions until failure or end of life (e.g., drive battery depletion), as declared by the manufacturer or resulting from other factors. Therefore, the FU chosen for this study is the life expectancy of the buses considered. According to the assumptions made in this analysis, FU equal to 1,057,757 km was assumed, which results from the average activity of the bus at the level of 70,505 km during the year, over the period of 15 years of the assumed life of the bus (indication from the manufacturer), gives more than a million kilometers. We then related this value to 100 km, which is easier to perceive and interpret for interested decision makers and passengers of public transport.

2.1.2. Life Cycle Inventory—Analysis of Inputs and Outputs. Assumptions Made for the Analysis. Case Study—Silesia Region in Southern Poland in Europe

For the purpose of this study, the Silesian Region (SR), in southern Poland, was selected. It is the largest mining region in the European Union and the center of the location of national coking plants, that is, potential sources of H2COG. The powertrain structure in public transport in the SR consists mainly of diesel engines (1400) and about 300 alternative vehicles. This distribution is due to several factors. The SR has an area of more than 2500 km², with 41 municipalities (including cities) in the SR; the average route length for a selected bus line is 25 km; SR vehicles travel approximately 100 million km per year; diesel vehicles travel more distances in a single fuel tank than alternative vehicles [24]. Additionally, there is a higher prevalence of diesel fuel and fuel stations compared to alternative fuels and the often prohibitive price of purchasing and possibly repairing an alternative vehicle and its infrastructure. However, when it comes to retrofitting the bus fleet, electric buses are considered in scientific reports to be the main alternative to conventional diesel. Therefore, for the analyses presented in this study, three bus models with different power units were configured:

• Conventional buses fully fueled with diesel fuel (Diesel bus, DB), as the ones with the largest share in the structure of SR, are subject to possible replacement due to environmental restrictions;
• Electric vehicle bus (EVB) as the most environmentally beneficial in the literature;
• Fuel cell electric vehicle bus (FCEVB) powered by hydrogen from coke oven gas as an alternative to DB vehicles.

Following the sequence of steps during the LCA analysis assumed in Section 2.1.1, the authors of this article made several assumptions during the WTT phase of the LCI. Inventory data for diesel fuel (for DB) and electricity (for EVB) were taken from Ecoinvent databases. On the other hand, information concerning hydrogen from coke oven gas (for FCEVB) was obtained from own simulations assuming, among others, the composition of the coal mixture, the technological configuration of the preparation of coal charge and its coking, the energy needs of these processes, and finally, the determination of the yield and composition of the crude coke oven gas. Methane was released during the mining of coking coal. Part of it was released into the atmosphere (40%) together with the ventilation air, while the remaining part was released in the form of mine gas (60%) and used for energy purposes by the heat and power plants belonging to the mine. The energy and heat yield indicators are given in

Table 1. Indicators of the development of mine gas in the mining thermal power plant.

Parameter	Unit	Value
The amount of mine gas that flared in the CHP * plant converted to methane	mln. m3(NTP)/year	67,520,000
Technological blowdown (residual gas from the CHP plant)	mln. m3(NTP)/year	92,691,900
Average methane content in the mine gas	% vol.	56.66
Average calorific value of methane in mine gas	MJ/m3	35.810
Amount of electricity produced from the gas of the gas of the mine	MWh/year	183,026
Amount of heat produced from the mine gas (including cooling)	GJ/year	451,310
Compressed air production	thousand m3/rok	32,899

* CHP—combined heat and power; NTP—normal temperature and pressure.

.

The coking process was carried out in the chambers of a coking battery with a useful chamber volume of approximately 30 m³ (approximately 70% of the coke is produced in this type of battery). The batteries were heated exclusively by the plant’s own coke-oven gas. After the coking process is completed, the basic product, coke, is pushed out of the chamber, cooled, and then sorted and dispatched to customers. The by-product, raw coke oven gas, is sent for further processing. The balance of the coking process products and the stream and composition of the crude coke oven gas are determined, presented in

Table 2. Balance of the products of the coking process [kg/kg coal as received state].

Stream	Yield [kg]
Coke	0.743
Dry gas	0.117
Steam	0.093
Benzol	0.011
Tar	0.036

and

Table 3. Composition of crude coke oven gas [25].

Component	% m	% v
H2	6.0	41.7
CO	4.6	2.3
CH4	22.6	19.7
CO2	3.1	1.0
C2H6	5.6	2.6
H2S	1.4	0.6
NH3	2.3	1.9
H2O	36.2	28.0
Benzol	4.3	0.8
Tar	14.0	1.5

, respectively. The composition of crude coke oven gas has been adopted from previous work of authors [25].

The raw coke oven gas was cooled and then pumped into hydrogen sulfide, ammonia, and benzol treatment plants. The gas thus purified was divided into two streams, one of which is used for the needs of the coking plant (mainly for heating the coking battery, 50%), while the other was intended for hydrogen production. The hydrogen production system includes a coke oven gas reforming system with cooling (convection/quench coolers); oxygen generation system (cryogenic air separation); CO conversion and COS hydrolysis system; desulphurization and CO₂ removal system; and H₂ separation system using PSA technology (85%) and auxiliary systems. The selected substrates and products of the coking process combined with the production of hydrogen from excess gas, which is most relevant for this analysis, are shown in

Table 4. Parameters of the most important process streams of the installation for the production of hydrogen from the gas from the coke oven.

Input			Output			LHV MJ/kg	Allocation Coefficient $\raisebox{1ex}{${\mathit{m}}_{\mathit{i}}·{\mathit{L}\mathit{H}\mathit{V}}_{\mathit{i}}$}\!\left/ \!\raisebox{-1ex}{$\sum _{\mathit{i}}{\mathit{m}}_{\mathit{i}}·{\mathit{L}\mathit{H}\mathit{V}}_{\mathit{i}}$}\right.$
Coal	132.48	kg	Hydrogen	1	kg	120	0.04
Oxygen	3.24	kg	CO2 from PSA	8.34	kg	-	-
Steam	3.61	kg	CO2 in the flue gas	3.9	kg	-	-
Water	4.03	kg	Coke	96	kg	28.6	0.9
Electricity	5.79	kWh	Tar	3.65	kg	38.7	0.05
Heat	13.71	MJ	Benzene	1.22	kg	32.8	0.01

. Because the coking process is aimed at coke production, and the resulting tar, benzol, and hydrogen are additional products, an allocation procedure was applied, taking as a criterion the energy stream contained in the individual products.

During the inventory of LCI data for the TtW stage, certain complexes concerning both direct emissions, referred to as exhaust (emissions from the pipe) and non-exhaust emissions (resulting, e.g., from abrasion of brake discs, tires, and road surface). It was assumed that the DB vehicle participates in both types of emissions, while EVB and FCEVB emit only non-exhaust emissions. Furthermore, it was assumed that no distinction would be made in the case of non-exhaust emissions resulting from the difference in power units and consequently in the mass of vehicles and the difference in the operation of brakes, for example. Data for this stage were obtained on the basis of assumptions and calculations presented in the EMEP/EEA guidebook [26] and COPERT 4 software.

For the inventory stage of vehicle bus production (cradle to the gate), the authors made the following assumptions. The three bus models configured for analysis are standard-size buses, belonging to the M3 category, compliant with Directive 2007/46/EC [27]. For the standard size, the bus was assumed to have a mass of approximately 11–20 t depending on the model (propulsion type) and a length of about 12 m.

Table 5. Materials list for configurable bus models with different power units [17,28].

Material [kg]	Notes	DB	EVB	FCEVB
Stell	Average	5366	3766	5971
	High-Strength	0	0	2895
	Stainless	429	429	317
Iron	Cast	966	100
Aluminium	Average wrought	966	1500	1185
	Average cast	0	0	789
Copper		80	80	856
Zinc		80	80	40
Magnesium		80	80	52
Powder Metals		80	80	184
Glass		537	537	407
Rubber		644	644	895
Fluids and lubricants		429	429	856
Fibre Glass		0	0	0
Plastics	High-density polyethylene	0	0	0
	Polyethylene terephthalate	0	0	0
	Polyprolylene	0	0	0
	Average	644	644	1580
Composites	Glass Fibre Composite Plastic	0	0	0
	CF For general use	0	0	816
	CF For High Pressure	0	0	816
Lead	Average	0	0	157
Nickel	Avearge	0	0	77
Titanium		0	0	0
Lithium battery		0	3000	0
Other		429	429	1315
Total		10,301	11,798	19,200

presents a summary of the materials used in the construction of each of the three bus models assumed in the study. The balance of construction materials for the inventory in the LCI stage was taken from [28] and from [17]. Material handling processes and vehicle parts are also included. Depending on the type of propulsion, Table 5, buses differ in the amount of materials used, i.e., steel or cast iron. The design of the FCEVB is significantly heavier than that of the DB or EVB and is primarily intended to ensure the safety and comfort of the hydrogen-powered vehicle. Hydrogen has a very low density. This means that for a given mass of gas, a large volume of storage tanks are needed, which are placed on the roof of the vehicle to avoid limiting the space for passengers. In addition, a negative phenomenon associated with the use of materials in a hydrogen environment is called hydrogen embrittlement (hydrogen corrosion). The use of stainless steel solves this problem while increasing the weight of the hydrogen vehicle compared to its conventional counterparts. Metals are also the basic building materials of fuel cells that convert chemical energy into electricity. The powertrain of an FCEV is a system of power generation components that includes a fuel cell array, a hydrogen tank, a battery, a power control unit, and a balance of plant (BoP) system. The data and assumptions used to model the production of the various components that make up FCEV are based on the work of [29,30] and were modified and scaled to meet the objectives of this study. The Miotti inventory was adapted to the technical characteristics of the FCEVB and then supplemented with information from the Evangelisti evaluation. The FC consists of (i’) a membrane that divides the cell into two parts, separating the reduction and oxidation reactions, allowing only protons to pass through, thus forcing electrons to pass through the outer circuit; (ii’) a gas diffusion layer (GDL) that allows direct and uniform access of the fuel (oxidant) to the catalyst layer; (iii’) the catalyst, which helps the electrochemical reaction to occur, generating high reaction rates; (iv’) the membrane electrode assembly (MEA) is a combination of a catalyzed membrane and two gas diffusion layers; (v’) the bipolar plates (BPP) perform various functions in fuel cells, such as facilitating water and heat management, separating different cells in a stack, and conducting electrical current from the cell; and (vi’) end plates, along with compression bands, are responsible for keeping individual cells aligned. The material data for the FC system of the FCEVB bus, together with the structure of the FC components, are presented in

Table 6. Fuel cell system bill of materials for FCEVB vehicle.

FCEVB Vehicle Bus with FC, 70 kW	Unit	Value
Production of tetrafluoroethylen	kg	0.55
Production of Sulfuric Acids	kg	0.03
Tetrafluoroethylen Production	kg	0.06
Fleece production	kg	0.59
Carbon fibre-reinforced plastic inj moulted glo	kg	1.19
Production of tetrafluoroethylen	kg	0.10
Carbon Black Prod	kg	0.29
Production of tetrafluoroethylen	kg	0.09
Organic Solvent Production	kg	0.02
Textile production, cotton, dying	kg	1.19
Extrusion, Plastic Film	kg	1.46
Selective coating of cooper sheet, sputering	kg	5.39
Thermoforming with calendering	kg	4.48
Polysulphide Production Sealing	kg	3.30
Injection moulding	kg	3.30
Platinum Group Metal Extr and Refinery	kg	0.01
Treatment of automobile catalyst	kg	0.00
Carbon Black Prod	kg	0.01
Production of tetrafluoroethylen	kg	0.00
Organic Solvent Production	kg	0.12
Selective coating of cooper sheet, sputering	kg	5.39
Steel Cromium Hot-Rolled	kg	17.15
Titanium dioxide production chloride	kg	1.72
Graphite production	kg	1.72
Phenolic resin production	kg	0.24
Deep draving, steel 650 kn press autom	kg	15.83
Selective coating of cooper sheet, sputering	kg	13.20
Glass fibre production	kg	Value
Epoxy resin prod liq	kg	0.55
Copper production primary	kg	0.03
Steel prod chromium hot-roled	kg	0.06
Polypropylen ranulate	kg	0.59
Injection moulding	kg	1.19
Metal working/average for cooper prod manu	kg	0.10
thermoforming with calendering	kg	3.96

. The bus models analyzed were configured using averaged material data available from various sources in the literature and the technical specifications of the bus manufacturers most numerous in the SR fleet. They should be treated as an example scenario, although very close to the specifications of real units. Furthermore,

Table 7. Summary of exhaust and non-exhaust emissions and factors adopted for the LCI stage for DB, EVB, and FCEVB vehicles.

Parameter	Unit	DB	EVB	FCEVB
exhaust:			0	0
CO2	g/kg of fuel	3140	0	0
CH4	g/kg of fuel	0.2	0	0
N2O	g/kg of fuel	0.1	0	0
NMVOC	g/kg of fuel	8	0	0
CO	g/kg of fuel	36	0	0
NO2	g/kg of fuel	42	0	0
Particulates, Diesel Soot	g/kg of fuel	0.94	0	0
Ammonia	g/kg of fuel	0.013	0	0
Indeno(1,2,3-cd)pyrene	µg/kg fuel	7.9	0	0
bezno(k)fluoranathene	µg/kg fuel	34.4	0	0
bezno(b)fluoranathene	µg/kg fuel	30.8	0	0
benzo(a)pyrene	µg/kg fuel	5.1	0	0
Lead	µg/kg fuel	52	0	0
non-exhaust:
PM2.5 tire wear	mg/km	14.84	14.84	14.84
PM2.5 brake	mg/km	21.44	21.44	21.44
PM2.5 road	mg/km	20.52	20.52	20.52
PM10 tire wear	mg/km	21.2	21.2	21.2
PM10 brake	mg/km	53.6	53.6	53.6
PM10 road	mg/km	38	38	38
average vehicle speed (urban)	km/h	17	17	17
average combustion/energy consumption (urban)	kg fuel oil a, kWh b, kg H2 c/100 km	37 a	110 b	9 c

presents the values of the emission factors resulting from vehicle operation and the quantities and types of maintenance operations necessary for the proper functioning of buses, as recommended by manufacturers.

To select the materials and processes from the ecoinvent database in SimaPro necessary to model the processes and vehicles, certain assumptions had to be made that applied to all components of the configured bus models. For materials, activities that represent global processes were selected, while for processes, activities specific to the geographical region of Europe were selected. This gives some reflection of the reality of the automotive market, where some components and parts are manufactured anywhere in the world (e.g., China) and the main bus factory is located in Europe. Furthermore, the LCA analysis assumes a cutoff system model, which assumes that the waste, by-products, and recyclable materials from the selected activities are free of burdens that may have different environmental impacts.

2.1.3. Life Cycle Impact Assessment (LCIA) Method

The CML method was used to perform a multidimensional life cycle impact assessment (LCIA). The CML method [31], by Centrum voor Milieukunde of the University of Leiden, recommended by the FC-Hy Guide [32], is one of the methods used in the impact assessment phase to identify the environmental links of all inputs and outputs included in the LCA model and to estimate the magnitude of the impact of the entire life cycle of technology on the environment and human health. The task of the CML method is to quantitatively represent all direct material and energy exchange relationships between the environment and the product system. It is a middle-point method and ensures, according to FC-Hy, scientific soundness, a low level of uncertainty, and is in line with European environmental policy objectives. This method is intended to guarantee the comparability of LCA studies on a technological level. In the CML baseline method, the following recommended indicators were used for the system considered in this study. Global Warming Potential (GHG) [33]; Acidification Potential (AP) [34]; Abiotic Depletion Potential in MJ and kg Sb eq(ADP) [35]; Eutrophication (EP) [36] and optional indicators: Ozone Layer Depletion (ODP) [37]; Human Toxicity Potential (HTP) [38]; Freshwater Aquatic EcoToxicity Potential (FAETP) [39]; Marine Aquatic EcoToxicity Potential (MAETP) [40]; Terrestial EcoToxicity Potential (TETP) [41]; and Photochemical Oxidation Potential (POCP) [42].

3. Results and Discussion

The consideration of the potential environmental impact of the hydrogen bus LCA and its competing vehicles in the SR fleet was divided into several stages in terms of the life cycle assumed in the study for both the vehicle and the fuel. As a result, multiple metrics were obtained in the 11 impact categories of the CML method, as well as WSI metrics for the environmental assessment of WF. The authors decided that to make the results obtained easier to perceive and more easy to visualize, the impact values should be presented as percentage points in the CML midpoint category, for an impact of 100%.

3.1. Well-to-Tank (WTT) Phase

The WTT phase is the first part of the LCIA analysis, described in Section 2.1.1, of the potential environmental impacts of fuel production for buses: DB, EVB, and FCEVB. As the FU of the analysis for this step, 1 MJ of energy contained in the energy carrier was assumed. The results of the WTT analysis are presented in Figure 2. A clear trend can be observed in which significant impacts are shown in most categories of DB fuel. This fuel has a 100% share in 8 of the 11 LCIA impact categories, that is: ADP in MJ and kg Sb eq; GWP100a; ODP; HTP; TETP; POCP; and in AP. DB fuel contributes the lowest share to the MAETP category, 64.26%. The EVB fuel in the 2020 energy mix (EVB fuel 2020) has the highest 100% impact in three impact categories, including FAETP and EP. The lowest environmental impact, EVB 2020 fuel, is shown in the ODP category, with 0.63%. The production of FCEVB fuel, in the WTT stage, shows the lowest environmental impacts compared to its competitors. In each of the 11 impact categories, at the midpoints, FCEVB fuel does not exceed 20%. Overall, at this stage of the analysis, WTT, it can be concluded that hydrogen vehicle fuel from coke oven gas is environmentally preferable to conventional DB fuel and also to the alternative fuel EVB 2020 fuel.

3.2. Tank-to-Wheel (TTW) Phase

The results of the TTW analysis are presented in Figure 3. To compare the use of energy factors in the selected buses, it was assumed that the functional unit (Section 2.1.1) is FU 100 km of distance covered from the perspective of the assumed 15 years of operation of the vehicle under the conditions of SR. Analysis of the results of the TTW phase shows that the environmental load generated in the fuel use stage for the modeled buses is most numerous for diesel vehicles (DB). In this phase of the study, there are exhaust emissions and nonexhaust emissions (brakes, tire heat, and pavement abrasion). DB, during operation, will share in the pollution of both types. As shown by the results of the TTW analysis, the so-called zero-emission vehicles, electric as well as hydrogen, actually emit pollutants, but only in the nonexhaust title. The environmental burden generated during the TtW phase for EVB and FCEVB is only in the category of HTP impact. Compared to diesel-powered vehicles, which show a contribution in 8 of the 11 impact categories, zero-emission vehicles are clearly environmentally preferable. Factors such as PM10 and PM2.5, soot from diesel combustion, elements Cu and Pb, and PAHs were assumed for the consideration of TTW.

3.3. Production of Vehicle Buses: From the Cradle to the Gate

The results of the second part of the analysis, assumed in Section 2.1.1, are presented in Figure 4. The production of one DB, EVB, and FCEVB bus was selected as the functional unit for this stage of the LCA analysis. The materials needed to produce each bus model are listed in Table 5 and Table 6. The first is the material balance of the bodies, motors, and batteries of DB, EVB, and FCEVB. Table 6 is a listing of the materials that make up the FCEVB—FC cell. In the 11 LCIA impact categories of the cradle-to-gate vehicle bus stage, it is the conventional DB vehicle that presents the least environmental risk, contributing approximately 20% to impacts, in all categories. The electric bus, which is the lightest, contains significant amounts of aluminum in its construction and also a large lithium-ion drive battery, which ultimately contributes to an adverse, 100%, impact in the ADP category. Other environmental impacts on the EVB vehicle are on the order of 26–66%. LCIA results from the FCEVB vehicle production stage indicate its dominant 100% impact in 10 categories of potential LCIA impacts. According to the authors, this has to do with the incomparably higher mass of the FCEVB vehicle, compared to the others in the study, due to the complexity of the design and the quality of the materials used.

3.4. Fuel Bus Life Cycle + Vehicle Bus Life Cycle (FBLC + VBLC)

The results of the Fuel Bus Life Cycle + Vehicle Bus Life Cycle analysis (FBLC + VBLC) are presented separately for the DB, EVB, and FCEVB buses in Figure 5, Figure 6 and Figure 7, respectively. This phase includes the previously assumed and analyzed phases of energy carrier production, WTT; vehicle energy factor with and without emissions, TTW; and bus production, cradle-to-gate vehicle bus. The values were converted to the FU previously assumed in the study (Section 2.1.1). In addition, at this stage of the LCA analysis, the authors structured, in terms of potential environmental impacts, the midpoints, for energy factor production; vehicle production; non-exhaust emissions; and vehicle operation activities, i.e., oil changes; battery changes; and FC cell replacement. Figure 5 presents the LCA analysis for a DB diesel bus. From the results presented, it is clear that the predominant environmental impact is observed in most of the impact categories of the fuel combustion stage. The categories of ADP fossil fuels, GWP100a; ODP; POCP; AP and EP, are those where fuel combustion has the greatest, approximately 100%, potential environmental impact over the life cycle and operation of the bus. Required in-service operations, such as tire, battery, oil changes, and nonfuel emissions, contribute a marginal contribution to the structure of all impact categories considered in this study. In terms of HTP impacts, non-fuel-dependent, non-exhaust emissions that cannot be eliminated during vehicle operation have the primary 98% impact in this category. The vehicle production phase has a potential LCIA environmental impact, ranging from 31.5 to 70.8% for the four impact categories, TETP; MAETP; FAETP; and ADP.

Figure 6 presents the graphical results of the FBLC + VBLC analysis of the EVB bus. The dominant contributors to 10 of the 11 LCIA impact categories are factors due to the presence versus subsequent replacement of the propulsion battery (Li-on battery) and the 2020 national energy mix. These factors contribute mixed shares to environmental impact structures ranging from 83.9:11.8% (2020 mix: battery replacement) for EP to 41.0:47.0% (2020 mix: battery replacement) for the TETP category. Electric bus production contributes to the LCIA from 3.2% for the GWP100a category to 20.8% for the ADP category. Non-combustion emissions resulting from the operation of an electric vehicle over an assumed 15-year life cycle have a major impact, 87.3%, in the HTP category.

Figure 7, presents the results of the FBLC + VBLC analysis of a hydrogen bus powered by hydrogen from the coke oven gas, FCEVB. The results clearly show that the dominant factors with potential environmental impact are fuel production and bus manufacturing steps. Only in the fossil fuel categories EP and ADP, the hydrogen recovery step from coke oven gas has a share ranging from 78.9 to 85.8%, respectively. Non-combustion emissions, as in previous vehicle types, occupy the largest share in the HTP structure, 92.7%. The Li-On battery, which acts as a storage for excess energy produced in the hydrogen bus, contributes 34.2% to the overall ADP structure. It would seem that the mass balance presented in Table 5 and Table 6 with respect to FC construction materials, as well as subsequent replacements in the life cycle of the spent cell, would contribute significant values to the influence category structures. However, as indicated by the results presented graphically in Figure 7, cell replacement contributes significantly only to the ODP category, with a value of 29.5%.

3.5. Comparison of the Life Cycle of FBLC + VBLC for DB, EVB, and FCEVB

Figure 8 presents a comparison of the results of the FBLC + VBLC analyses for buses with different power units assumed in the study. The results, for the midpoints of the CML method, clearly indicate which vehicle exhibits the least and the greatest potential environmental damage. The values presented are expressed for the FU assumed in Section 2.1.1. The zero-emission EVB bus, during the 15-year life cycle assumed in the study, shows the most numerous environmental impacts, 100%, in 6 of the 11 potential harm categories, that is: ADP; HTP; FAETP; MAETP; and TETP and EP category. The lowest share, which the EVB vehicle shows for the ODP category, is 12.8%. The DB bus, although it is a conventional vehicle and has both exhaust and nonexhaust emissions, contributes less potential environmental damage than a zero-emission vehicle such as the EVB. DB contributes 100% to the structure of the five damage categories, the most important from the perspective of global warming issues being GWP100. DB makes the lowest contribution to the ADP category, 2.3%. The FCEVB vehicle, which is powered by grey hydrogen derived from coke oven gas, appears to be the most favorable environmental solution for urban use. FCEVB shows the highest share value in the HTP category, 94.1%, and in the ADP fossil fuel category with a share of 70.0%. The other categories of damage to FCEVB may seem marginal from the perspective of comparisons with DB or EVB. The hydrogen bus contributes between 8.7 and 50.1% to ODP and EP impacts, respectively.

Only the current national energy mix (2020) has been considered in the WTT, TTW, and FBLC + VBLC analyses. However, the authors are aware that the transformation of the energy production mix in a low-carbon direction is of particular importance for the EVB bus considered in this analysis. In designing Poland’s energy mix for the purpose of this analysis, the authors were guided by the document “The Future Energy Mix of Poland: Determinants, Tools, and Projections” [43], which presents the current energy mix and projections and requirements for its structure according to the guidelines of the European Commission’s EU Reference Scenario and the National Energy and Climate Plan (NERP) for 2021–2030. Therefore, Figure 9 presents the WTT phase analysis of EVB fuel for future national energy production structures compared to the current state. Figure 10 presents the results of the life cycle study FBLC + VBLC for DB, EVB, and FCEVB not only for diesel, electricity (2020), and hydrogen from coke oven gas but also for the 2030 and 2040 energy mix to supply EVB. The structure of the Polish power sector is presented in

Table 8. Current and projected structures (%) of domestic energy production for 2030 and 2040 [43].

Energy Carrier	2020 (Current)	2030	2040
	EU REF	EU REF	EU REF
Crude oil	0	0	0
Coal	65	65	35
Natural Gas	8	15	20
Nuclear	0	0	19
Biomass, biogas, and waste	5	8	10
Hydropower	2	1	1
Geothermal	0	0	0
Wind power	14	11	15
Solar energy	2	0	0
Tidal power	0	0	0
Other	3
Total	100	100	100

. The year 2030 can be called a transition year, with the biggest differences visible in 2020 and 2040. When comparing 2020 and 2040, the main changes will consist of a decrease in coal energy production, from 65% to 35%, and an increase in energy production from gaseous fuels, from 8% to 20%. Nuclear energy is also expected to appear in the future mix, from 0% at the moment to as much as 19% in 2040. Other changes in the structure of the energy mix are less dynamic. The total losses in the energy distribution were estimated to be 5%.

In Figure 9, there is a clear decrease in share in the nine impact categories, according to the transformation of the energy mix of 2020 to the most sustainable, 2040. Interestingly, the transition from the current mix to 2040 causes an increase in the share in % points for the midpoints in the ADP and ODP categories; this may have to do with the mining of radioactive earth for nuclear power. However, significantly with regard to the authors’ opinion, the FCEVB vehicle continues to show the least potential environmental harm. Compared to Figure 8, it can be seen that the FCEVB hydrogen vehicle exhibits significantly lower shares in t10 of the 11 categories of potential environmental impacts, according to CML. In both the GWP100 and HTP categories, which are important in terms of combating global warming, as well as human health in congested urban areas, the superiority of the FCEVB vehicle over zero-emission EVB takes on particular significance.

3.6. Substitution of DB Vehicles by FCEVB: A Case Study

As mentioned in Section 2.1.2, the SR structure shows a fleet share of 1400 conventional DB vehicles and approximately 300 alternative vehicles, which are expected to be joined by hydrogen FCEVB vehicles in the near future. Since, in the decision makers’ assumptions and in the literature on the topic, it is the conventional vehicles (DB) that are supposed to be replaced by zero-emission ones, in order to analyze the changes in environmental impacts caused by the transformation of the SR bus fleet, the authors prepared a hypothetical scenario of DB substitution by FCEVB vehicles; in the authors’ opinion, the substitution of EVB vehicles does not make sense. For this part of the simulation, the guidelines [31] were followed and only the five recommended most relevant environmental impact categories were presented: GWP100; AP; ADP (in MJ and kg Sb eq); and EP. A base case scenario was assumed to simulate the current situation where there are 1400 DB vehicles, 300 EVBs, and not a single FCEVB in the SR fleet. This was followed by a 10% replacement of DB vehicles with FCEVB vehicles over the base case, to a 90% share of the 1400-unit fleet. The zero-emission EVB vehicles remained at a constant 300 units throughout the simulation. The results of the assumed simulation are presented in Figure 11. When planning an LCA analysis of a technology based on a non-renewable resource, oil (diesel) or coal (hydrogen from gas), it is necessary to consider the protection of nature and biodiversity in terms of acidification and eutrophication. In this context, the AP and EP impact categories are most relevant. The key pollutants in the AP impact category are SO_X, NH₃, and NO_X, which are the main sources of forest and soil damage. In the CML method used in this study, the characterization parameter for acidification impacts is the potential calculated for air emissions according to the RAINS 10 model, which describes the accumulation of acidifying substances. In general, the substitution of conventional buses for hydrogen buses results in a reduction in emissions to the environment for all the factors considered, with the greatest difference observed in the categories of global warming and acidification. Substituting 90% of conventional buses with hydrogen buses powered by coke oven gas results in approximately half the greenhouse gas emissions (from 2.32 × 10⁹ kg CO_{2_eq} to 1.07 × 10⁹ kg CO_{2_eq}) and acidifying factors (from 1.54 × 10⁷ kg SO_{2_eq} to 6.89 × 10⁷ kg SO_{2_eq}). The negative effects of bus substitution include increased mineral resource depletion, which is mainly related to its increased consumption at the bus manufacturing stage.

4. Conclusions

This study analyzes the environmental impacts of three different types of urban buses: diesel (DB), electric (EVB), and fuel cell electric (FCEVB) buses. The analysis considers various environmental harm categories, including global warming potential, ozone depletion potential, acidification, eutrophication, and human toxicity.

Key findings are summarized below:

• The analysis of the WTT phase demonstrates that hydrogen fuel from coke oven gas is considered environmentally preferable to both conventional diesel fuel and electricity for alternative electric vehicle fuel. Hydrogen produced from coke oven gas has the lowest environmental impact among all fuels analyzed at the WTT stage. It does not exceed 20% in any LCIA category, while diesel fuel has the highest impact in most LCIA categories, contributing 100% in 8 of 11 categories;
• The analysis of the TTW phase for the modeled buses demonstrates that diesel vehicles (DB) generate the most significant environmental load during fuel use. This is due to their exhaust and non-exhaust emissions. Zero-emission vehicles (EVB and FCEVB) also emit pollutants, but only in the form of non-exhaust emissions. While they have a lower overall environmental impact compared to diesel vehicles, they still contribute to HTP (human toxicity) impacts. Key factors considered in the TTW analysis include PM10, PM2.5, soot, Cu, Pb, and PAHs. Based on these factors, zero-emission vehicles are clearly more environmentally preferable than diesel-powered vehicles;
• The analysis of the cradle-to-gate stage, examining the environmental impacts of producing each bus model showed that the DB bus had the lowest overall environmental impact. This was primarily due to its lower weight and simpler design compared to the EVB and FCEVB. The EVB, while lighter than the FCEVB, had significant environmental impacts due to the aluminum used in its construction and the large lithium-ion battery. The FCEVB had the highest environmental impact in almost all categories, primarily attributed to its heavier weight and complex design;
• Life Cycle Assessment (LCA) analysis of a DB diesel bus demonstrates that the predominant environmental impact occurs during the fuel combustion stage for most impact categories. Specifically, categories such as ADP fossil fuels, GWP100a, ODP, POCP, AP, and EP show a nearly 100% contribution from fuel combustion to the total environmental impact throughout the bus’s life cycle and operation. In-service operations like tire, battery, oil changes, and non-fuel emissions have a negligible impact on these impact categories
• Life Cycle Assessment (LCA), conducted on an electric bus, reveals that the dominant contributors to environmental impact are factors related to the lithium-ion battery and the national energy mix. These factors contribute to varying shares of environmental impact, ranging from 83.9% for EP to 41.0% for TETP. The production of the electric bus contributes to LCIA from 3.2% to 20.8%. Non-combustion emissions from the operation of the electric bus over its 15-year life cycle have a significant impact, accounting for 87.3% of the HTP category;
• LCA analysis of a hydrogen bus powered by hydrogen from coke oven gas reveals that fuel production and bus manufacturing are the primary contributors to environmental impact. The recovery of hydrogen from coke oven gas accounts for a significant portion of emissions in fossil fuel categories. Non-combustion emissions constitute the largest share of the overall environmental impact. The Li-On battery, used for energy storage, contributes substantially to the ADP structure;
• Fuel cell electric vehicles (FCEVB H2) perform best in most of the analyzed harm categories. This means that they are the most environmentally friendly of the three types of buses compared. They achieve particularly favorable results in terms of depletion of fossil resources (fuels) and global warming;
• Electric vehicles (EVB) also have a relatively low environmental impact, especially in the category of fossil resource depletion. However, their environmental impact largely depends on the source of the electricity used to power them. If the electricity comes from renewable sources, the environmental impact of EVBs is even lower;
• Diesel buses (DB) have the highest environmental impact in most of the analyzed categories. They have a particularly adverse impact on global warming, ozone layer depletion, and air pollution;
• The results suggest that replacing diesel buses with hydrogen buses can be a beneficial strategy for reducing greenhouse gas emissions and improving air quality. However, the trade-off in terms of increased mineral resource consumption should be carefully considered.