1. Introduction
In 2002, the European Commission issued a Directive [
1] aiming to reduce the energy consumption in buildings, bearing in mind that buildings are responsible for 20%–30% of energy consumptions in the European Union. This Directive intends to specify minimum energetic performance requirements for new buildings, as well as for existing buildings having an area larger than 1000 m
2, and aims to put into practice an energy consumption labelling scheme for buildings. The member states of the European Union adopted this Directive which came into force in 2006.
Since the early 1990s, Portugal has had national legislation issuing orientations for building construction and operation (mainly regarding insulation of walls, location to maximize solar exposition, as well as performance requirements for air conditioning systems) [
2,
3], intending to decrease energy consumption in buildings.
Therefore, Portugal adopted the 2002 European Directive by issuing law decrees in 2006 [
4,
5,
6], which considers not only the energy saving aspects, but also additional specific measures aiming to protect indoor air quality (IAQ) in accordance to the approach proposed by the EN standard 15251 [
7]. Although the reduction of energy consumption in buildings can result in lower ventilation rates and, thus, in lower IAQ, it should be noted that the European Directive of 2002 did not have any imposition, on member states, regarding IAQ. Portugal is one of the few member states of the European Union to issue air quality standards for buildings that are presented in
Table 1.
Nowadays, the Portuguese government is trying to enforce this new legislation and issued specific regulations regarding the auditing and evaluation scheme of IAQ. Therefore, it will be necessary to define compliance acceptance levels regarding the prescribed indoor air limits. The use of comfort or environmental indexes could be of considerable help in order to ameliorate the evaluation of IAQ, as reviewed by de Gennaro et al. [
8] and Tham [
9].
It should be noted that the European Directive of 2002 considers the labelling of buildings in terms of energy consumption. Likewise, the Portuguese regulations to be issued could prescribe the use of a similar labelling system for buildings regarding IAQ.
In fact, several efforts have been made to formulate a global measure of indoor air pollution [
10,
11]. Such a metric is distinct from a measure of several individual indoor pollutants and should be associated with symptoms of those exposed to indoor air pollution. More than that, it must satisfy three basic requirements as pointed out by Moschandreas and Sofoglu [
12]:
- (i)
it must be understood easily by all involved in assessing the environment, comprising the consumer, the potential polluter, the evaluator, and the regulator;
- (ii)
it must associate well with measurements of impact caused by the contamination ranked by the metric;
- (iii)
it must enable those concerned to manage the environment efficiently.
Environmental quality indices do not constitute a new tool of inquiry and have been developed and used for ambient air [
13,
14] and water quality [
15,
16]. Some indices have been proposed such as the Indoor Air Pollution Index (IAPI) [
17], the Indoor Discomfort Index (IDI) [
10], and the Indoor Environmental Index (IEI) [
10].
3. Results and Discussion
A previous European project [
18] constituted an exhaustive study of auditing the IAQ in 56 European office buildings. During this study, physical and chemical measurements were made in the space of those office buildings, resulting in a systematic evaluation of the indoor concentrations of pollutants such as carbon dioxide (CO
2), carbon monoxide (CO), total volatile organic compounds (TVOCs), particulate matter (PM
10), as well as the thermal parameters operative temperature and relative humidity. The main characteristics of the selected buildings are presented in
Table 2.
For these office buildings, the determination of the most significant indoor air pollutants (CO, CO
2, particulate matter, and total volatile organic compounds) was performed. The reported average concentrations found in buildings per country are presented in
Table 3. Moreover, the air temperature and relative humidity were measured and the average values per country are presented in
Table 4.
The average indoor level for CO2 ranges from 516 to 778 ppm, with a mean level of 673 ± 60 ppm, and no evidence of geographic differences were found along the north–south or east–west axes or between maritime and more continental settings. The average indoor CO level was below 1 ppm. The particulate matter values were log-normally distributed, with a geometric mean of 66 µg/m3, a large geometric standard deviation of 2.7 and a median at 62 µg/m3. In general, the particulate concentration remained below 120 μg/m3, except for several buildings in Greece (GR) and Switzerland (CH). The average TVOCs per building were log-normally distributed. The average TVOC per building in the investigated rooms ranged from 118 to 528 μg/m3, with a median of 162, a geometric mean of 172, and a geometric standard deviation of 2.1. The mean air temperatures measured in the buildings per country were, in general, in the upper limit of the recommended values given in the thermal comfort standard ISO/CEN 7730 for the winter (20–24 °C).
The Nordic countries (Denmark (DK), Finland (SF), and Norway (N)) had a relative indoor humidity below 30%, which is not uncommon in these countries, whereas the highest relative indoor humidity values were found in France (FR) and Germany (D).
In this project, the perceived air qualities in the investigated buildings were also evaluated by trained panels, expressed in decipol [
18]. The mean perceived air quality for all 56 European audited buildings was about 6 decipol, which corresponds to roughly 50% dissatisfied visitors.
Using this data, the air quality indexes pIAPI, IDI, and IEI were calculated for the “average” building per country, using the previously described Equations (1)–(3), and the obtained values are presented in
Table 5.
The newly proposed index for the Portuguese situation results in the following: IAPI = 3.559; IDI = 4.250; IEI = 3.094. It should be noted that the calculated IEI index closely compares with the IEI index in
Table 5 for Greece (GR), which (among the referred countries) has more similarities with Portugal in terms of office construction, climate, and cultural habits. This is a good indication about this index, although it still requires further validation from actual measurements that are to be done, in future, in Portuguese office buildings.
As a preliminary study, this methodology was applied to a set of measurements performed on university office buildings located in downtown Lisbon [
19] presented in
Table 6.
Considering these measurements, the air pollution indexes were calculated as before, and are presented in
Table 7.
It can be easily observed that the calculated individual indexes (for each university building) somewhat differ from the average value calculated as IEI = 3.094, as referred previously. Although the average indexes in this case are only based on 6 observations, IEI = 3.092 is in clear accordance with the postulated mean index for Portugal of IEI = 3.094. Nevertheless, further measurements are still needed for this task, considering that the available data is somewhat limited.