A State of the art review was prepared of facts and problems related to indoor air quality from three points of view (the human, the indoor air of the space and the sources contributing to indoor air pollution) to address the question:
Why is indoor air quality (still) an issue?
This state of the art report was published in the journal Building and Environment 44 (2009) 1980–1989 and can be downloaded here.
The state of the art review was prepared to identify the current state of knowledge on indoor air quality (IAQ). It was decided to consider indoor air quality from three points of view:
- The human well-being as the receiver and perceiver (health and comfort)
- The indoor air of the space as the carrier
- The sources as emitters and contributors to indoor air pollution.
These are three distinct but inter-related aspects of IAQ. A source (or sources) emits pollutants into the indoor air of a space, directly or indirectly. Those pollutants can react with each other or with pollutants from other sources (including outdoor sources), creating new compounds (indoor air chemistry). Also, pollutants can react with surface materials in the building.
A person entering or occupying the indoor space is exposed to those pollutants present in the air of the space, which possibly creates a response (immediate or after some time), probably influenced by previous and “future” exposures in the same or other spaces. It can therefore be very difficult to relate a particular response to a pollutant or source. Experiments using laboratory controlled exposures to specific pollutants focused on particular responses have been performed, but even then, people’s response can vary widely and it can be difficult to relate the results to the multi-pollutant exposures and other environmental stressors that occur in buildings over time.
Currently, standards and guidelines that are in use mainly address the indoor air and to a lesser extent the sources: WHO air quality guidelines, ASHRAE, CEN and nationally determined minimum guidelines based on the presence of people only (CO2 concentration). There seem to be a discrepancy between current standards and end-users wishes and demands. Because, even though those standards and guidelines are met, the quality of the indoor air, as experienced by the occupants, may often still not be acceptable and can cause health and comfort problems.Minimum ventilation rates based mainly on body odour (with CO2 as an indicator) and to some extent on primary emissions from some building materials, are not preventing occupants and visitors of a space developing health symptoms (asthma, etc) and/or comfort complaints (odour, irritation).
From the state of the art it was concluded that defining indoor air quality is difficult. Considering the status of our knowledge with respect to emission, indoor air and human perception, it is not surprising that there are considerable difficulties with defining effective standards and guidelines for good indoor air quality. Also it is understandable that discussions on how much ventilation is sufficient to prevent noxious odour and spread of disease, that have origins in the beginning of the 19th century, are on-going (see Figure 1).
Some facts and problems underlying the conclusions of the state of the art are listed below and described elsewhere in more detail:
- The emission behaviour of sources is complex
- Indoor and source surface chemistry create “new” often unidentified compounds, not (yet) accounted for in current standards and guidelines
- The material constituents and moisture retention characteristics of a product determine the risk for microbial growth
- The HVAC systems can be a source of pollution as well, if poorly designed, operated and/or maintained, which is not always acknowledged
- To truly evaluate an exposure, all routes of exposure (both physiological and psychological) should be taken into account. Individuals will react differently to the same exposure
- There are diverse techniques available to indicate the IAQ people are/were exposed to
- It is difficult to relate symptoms to IAQ evaluations
- Some compounds may have adverse effects on their own while others, seemingly harmless, become harmful when they interact with each other or over time. Some compounds behave differently in a mixture than single
- Problems with IAQ are not only source related, but also building process related.
Figure 1 shows the recommended minimum ventilation rate changed over the years: from 2 l/s per person by Tredgold in 1836, to 14 l/s per person by Billings in 1895, back to 4.7 l/s person in 1936 by Yaglou to 7.5 l/s person in 1983. The current recommended minimum ventilation rate by ASHRAE is 2.5 l/s per person added with 0.3 l/s.m2 for single person cellular offices (10 m2) and 4 l/s person added with 0.4 l/s.m2 for single person cellular offices (10 m2) by CEN.