A limitation of the studies that examined IAQ in green buildings is that none attempted to explore whether the effects of improved IAQ can be attributed to the higher number of credits awarded for IAQ in green buildings。 The studies implicitly assumed that this was the case。 Another major limitation is that the main evidence for improvements in IAQ arises from subjective evaluations。 In most cases, no measurements were performed in parallel to subjective evaluations to document whether the pollutant levels and expo- sures in the investigated green buildings were truly different from conventional buildings。 It was also not documented whether thermal conditions were different, temperatures and relative hu- midity being an important modifier of the perception of quality of indoor air [31]; [32]。

Perceptions of indoor air quality can also be attributed in part to other factors, not just pollutant levels or actual exposures。 For example, it is well documented that the occupants of green build- ings are proud of being able to work in their buildings [46], many of which are iconic buildings and owned by successful businesses。 The overall high satisfaction of working in these buildings may propa- gate on satisfaction with IAQ。 This postulation is supported by studies that show that occupants of green buildings are apparently more tolerant to less optimal indoor environmental quality [23]。

Many studies reporting measurements in green buildings did not adequately control their findings for several potential con- founding factors, and did not perform satisfactory statistical ana- lyses of the measurements。 Further, in many studies, responses from different cohorts of people working in different buildings were compared。 The studies attempting to match the green buildings and the conventional buildings to control for confound- ing factors are sparse (e。g。, [62]。

In conclusion, the majority of available measurements in green buildings do show that IAQ, as perceived by building occupants, is improved。 The studies do not make sufficient connection, however, between these results and the physical and chemical measure- ments of actual exposure levels, and between these results and the credits awarded by the certification schemes for managing  IAQ。

1。5。 How can green practices compromise the IAQ of a green building?

A variety of green practices can be applied in green building projects to achieve a certification level as high as possible [78]。 Some of these practices award credits for solutions related with reducing resource use, environmental impacts, or CO2 emissions, such as maintaining minimum code ventilation requirements, us- ing recycled materials, or promoting low-carbon commuting。 However, some green practices can also compromise IAQ in green buildings。 Further, the cross-category interaction is not accounted for in certification schemes, whereby positive credits obtained in one category can negatively influence indoor air  quality。

One example of green practices having potentially negative consequences for IAQ is the use of waste-based materials, recycled materials, or reused materials。 For instance, application of fly ash as an additive to building materials can increase the exposure of building occupants to a suite of heavy metals that may have toxic properties (e。g。, [49]。 Materials that are recycled or reused can re- emit pollutants that were adsorbed on their surfaces, used in the recycling process, or accumulated in previous applications; potentially toxic materials can also be reused and reapplied in buildings (e。g。, [65]。

Another example are actions to keep outdoor air supply at minimum rates and reduce the need for cooling and air- conditioning, and supplement them with other less energy demanding solutions。 These actions comprise the use of air puri- fication     methods     and     flushing     or     enhanced   ventilation,