Exposures in homes constitute the major part of exposures to airborne pollutants experienced through the human lifetime. They can constitute from 60 to 95% of our total lifetime exposures, of which 30% occurs when we sleep. The airborne pollutants constituting these exposures have sources outdoors and indoors. Pollutants having sources outdoors penetrate building envelope through cracks, gaps, slots and leakages, as well as through open windows and ventilation systems. Indoor pollutant sources include humans and their activities related with hygiene, house cleaning, food preparation, laundry, etc.; building construction materials, furnishing, and decoration materials; mould, bacteria, and fungi; tobacco smoking and combustion processes; as well as pets and pests. Studies have measured over 250 fifty pollutants in the indoor air in homes. Volatile organic compounds (VOCs) have the highest airborne concentrations in homes due to higher volatility however other pollutants impact occupant health as well. Indoor concentrations vary from home to home as well as over time in a given home.
Exposure controls should be designed to minimize health hazards and avoid unwanted odours. To do this, we must identify the pollutants driving the health risks and identify the best control strategies for those pollutants. High concentrations are not necessarily indicative of a health hazard. Pollutant concentration data alone cannot be used to identify pollutants driving health hazards. Toxicity varies widely from pollutant to pollutant and extensive research has been undertaken to link exposures levels of specific pollutants to specific adverse health outcomes. Toxicology and epidemiology have traditionally been used to link concentrations/exposures to health outcomes. However, in-silico and in-vitro based assessments of toxicity are gaining prominence.
Several studies have attempted to prioritize pollutants for mitigation in the indoor environment based on the prevalence of disease in the community, occupant exposure estimates, and the research derived links between exposures and health outcomes. The key pollutants identified as driving chronic health impacts include: PM2.5 (particulate matter with a diameter less than 2.5 microns), mould/moisture, radon, environmental tobacco smoke (ETS), formaldehyde and acrolein. To reduce the exposure of contaminants different control strategies can be applied. The most effective are (1) source control and reduction of pollutant sources and (2) enclosure and encapsulation of sources. Ventilation plays a key role in reducing exposures that cannot be controlled by these measures. Effective local ventilation, such as cooker/range hoods, are critical for removing pollutants from periodic high emission sources such as cooking. Other contaminants can be removed by making use of mixing ventilation or displacement ventilation. The correct amount of ventilation is still an area of debate.
The following top five research needs were identified in a pair of workshops held by the Air Infiltration and Ventilation Centre (AIVC) and its partners in 2012: (1) Impact of user behaviour on the control of indoor environmental quality; (2) Development, implementation and harmonization of new, advanced methods for monitoring indoor air quality and its effects on health and comfort in buildings; (3) Development of ways to increase the accountability of building contractors, designers, producers, constructors and installers; (4) Tools and methods for ensuring a robust and performance-based design, operation and maintenance of building systems while maintaining good indoor air quality; and (5) Quantification of health and comfort outcomes in terms of public health and economic criteria. Workshop participants recommend that these research needs be addressed quickly so that indoor air quality (IAQ) and health in highly energy efficient buildings are not compromised. It is also of utmost importance to benchmark systematically differences in exposure to pollution sources and their associated health risks in buildings having different occupancy and purpose, from traditional through energy-retrofitted buildings to highly energy-efficient buildings to create reference points for further development. The tighter building envelopes of energy-efficient buildings will reduce adventitious ventilation and increase the need for designed ventilation systems to provide good IAQ. New materials in homes may also introduce new pollutants of concern.
These topics can be used for a number of purposes: they can guide research directions and the priorities of public, private, national and international agencies supporting research, they can be used to develop innovative solutions and they can indicate policy needs. Policies should be aligned, integrated, and harmonized with regulations and standards for highly energy efficient buildings and indoor environmental quality, and consistent requirements should be developed for any of their crosscutting and overlapping criteria.