of indoor air environments。

1。3。 Do green building certification schemes address  IAQ?

Since the birth of green building certification schemes, IAQ has been included as one of their default elements。 Currently, IAQ is included, in some way, in all schemes presently in use。 However, we lack systematic information on how many of the credits addressing IAQ are actually exploited during the certification process and, if all are awarded, whether this would significantly improve  IAQ。

The categories that include IAQ in various schemes are differ- ently termed。 For example, in BREEAM, IAQ is included in the category for health and well-being, in LEED and Green Star in the category called indoor environmental quality, while in DGNB in the category describing socio-cultural and functional quality。 In addi- tion to credits for IAQ, categories that include IAQ also provide credits for other aspects related to IEQ, such as for daylight, artificial light, acoustic and thermal  environment。

The contribution of credits for IAQ in green building schemes is on average 7。5%, and spans from about 3% to 11%, based on a recent evaluation of 55 green building schemes in 30 countries [86]。 The relatively small percentage of credits for IAQ may be considered as inadequate incentive to pursue these credits, or even as inadequate representation of the importance of IAQ。 On the other hand, green certification schemes include many components, and any single component (with the exception of perhaps energy performance) may not receive a large percentage of credit。

It is useful to examine how IAQ is addressed in the certification schemes and which aspects are awarded。 Credits are received for measures related to source control (mainly attained through se- lection of low emitting building materials and products, but also by use of green cleaning products and policies, and low emitting equipment), for ventilation (mainly by specifying minimum ventilation requirements or referring to relevant standards or codes prescribing ventilation, and also specifying requirements such as minimum filtration levels, location of main air intakes, and main exhaust outlets), and for conducting indoor air quality measure- ments (either before or during occupancy, or during both periods)。 Among the 55 certification schemes reviewed by Ref。 [86]; 100% of them award credits for ventilation, 77% award credits for source control and 66% for conducting IAQ measurements。

Credits are also received if levels of specific pollutants are tar- geted。 The most frequently addressed pollutants are volatile organic compounds (VOCs), formaldehyde, and carbon dioxide (CO2)。 These three pollutants are included in at least 65% of the schemes reviewed by Ref。 [86]。 In addition, requirements are defined for levels of asbestos, microbes, ETS, carbon monoxide (CO), total VOCs (TVOC), sulphur oxides (SOx), nitrogen oxides (NOx), radon, particles, ammonia, ozone and semi-volatile organic com- pounds (SVOCs) but the requirements for these pollutants are present less frequently in the schemes than for the three pollutants mentioned above, and none are mandatory。

In addition to direct credits for IAQ, credits in other categories can indirectly affect IAQ。 For example, site selection can influence outdoor air quality。 Thus, the building envelope quality and tight- ness, as well as type of ventilation, can affect the migration of pollutants between indoors and outdoors, and energy-efficient systems can improve or impair IAQ depending on outdoor air quality。 Credits for these criteria generally do not add to the total credit for measures for promoting IAQ。

Many certification schemes allow “trading” of credits across different categories and, with few exceptions (e。g。, DGNB), it is the total number of credits awarded that determines the level of building certification, not the credits received in each category。 Consequently, in some schemes, the highest certification level  can