http://dx。doi。org/10。1016/j。buildenv。2016。11。010 0360-1323/© 2016  Elsevier  Ltd。  All  rights reserved。

building standard [87], even if not termed green building。 However, it is unclear whether such programs are any more effective than green building programs in promoting healthy IAQ。 Despite the prevalence of green building certification programs and several common features, no internationally consistent criteria exist for green buildings。 Also, relatively little systematic research has been conducted to determine whether and how elements of green building programs improve IAQ (e。g。, [62,79]。

In conclusion, green buildings are implemented by various programs and criteria around the world。 They typically emphasize efficient use of energy and resources and, to lesser extent, healthy indoor air quality。

1。2。 What is indoor air  quality?

Similar to green buildings, “indoor air quality” has no universal or standard definition。 In general, IAQ is related to pollutants (e。g。, biological, chemical, and physical) within indoor environments that can affect the health of occupants。 IAQ is considered a subset of indoor environmental quality (IEQ); the latter includes factors such as lighting, ergonomics, acoustics, and temperature in addition to pollutants。

Indoor air quality definitions can vary depending on perspec- tives of the human user, the indoor air of the space, and the sources contributing to the indoor air pollution [12]。 A definition provided by the US Environmental Protection Agency [28] is as follows: “Indoor Air Quality (IAQ) refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants。”

However, in the US as in many other countries, no federal law specifically regulates IAQ [77], even though people typically spend more than 90% of their time indoors, pollutant levels are typically several times to several hundred times higher indoors than out- doors, and consequently indoor air typically accounts for over 90% of human exposure to pollutants [64]。 Some agencies do offer guidelines, such as World Health Organization [90], for the pro- tection of public health from common chemicals in indoor air。 For example, the [90] indoor air quality guideline for formaldehyde (30-min average concentration) is 100 mg/m3 (0。08 ppm)。

While air quality regulations in the US [29], European Union [30], Australia [9] and other countries regulate “ambient air,” the term has been interpreted as “outdoor air,” or air external to buildings, excluding indoor air。 While outdoor air quality can affect the indoors, and indoor air contains pollutants from both outdoor and indoor origin, indoor air quality is concerned with the air within buildings and other indoor spaces, regardless of the sources of pollutants。

Indoor air quality is difficult to measure and assess for many reasons; among them: (1) The lack of consistent metrics, standards, and consensus on what constitutes favorable IAQ; (2) The persity and complexity of pollutants found indoors that can affect human health and well-being, even at exceptionally low levels; (3) The inadequate understanding of links between pollutant levels in- doors, exposures to those pollutants (both inpidually and in mixtures), and their effects (both acute and chronic); (4) The range of health effects related to indoor pollutant exposures, and that the same pollutant exposure can affect different humans in different ways; (5) The question of whether the pollutants being measured are the ones that really matter; and (6) The lack of requirements to measure and monitor IAQ, leading to a lack of awareness of po- tential problems and remedies。

In conclusion, attention to IAQ is often voluntary from a regu- latory perspective, though important from a health and well-being perspective。 While some agencies offer guidance, no consistent metrics or regulations exist for determining and assuring the health