Indoor Air Cartoon Journal, February 2019, Volume 2, #47

Several materials in the indoor environment remove pollutants from indoor air passively or actively. Some of these materials are designed to do so while others are not intended to do so. For example, HVAC filters are designed to remove pollutants from the air actively. Some materials on building interior surfaces remove pollutants passively while others, by being on indoor surfaces contribute to deposition of gas phase pollutants.

Whatever the case may be, the efficiency of these materials in removing pollutants from indoor air without causing any discomfort depends on their cleanliness. Pollutants deposited on the indoor surfaces could cause health problems when they are introduced back to the gas phase. Some of the accumulated pollutants could also participate in surface chemistry to form new products on the surfaces. Depending on the environmental condition, relative humidity (RH) or temperature level, air movement across the surface or human disturbance of the surfaces, pollutants may be reintroduced back to indoor air, while these materials may still be performing sink effect. A good cleaning or replacement of “dirty” sink materials will reduce the pollution source effect.

Air cleaning system can also provide a sink effect. For example, the ionizer system can be effective in reducing particulate matter concentration if they are designed, operated, and appropriately maintained. Poor maintenance, causing degradation, of the ionizer system even if designed and operated adequately could lead to the emission of ozone which is dangerous to human health. The ozone-initiated chemistry that occurs afterward will further compromise human health. Ventilation system when designed, operated, and appropriately maintained could help to maximize the benefits inherent in ventilation. The degradation of ventilation systems due to poor maintenance, even when designed and operated appropriately, could cause the system to introduce unwanted pollutants of outdoor origin into the indoor environment.

Therefore, when the sink becomes the source, or sink becomes a poor sink, pollutants concentration – hazard – in the indoor environment increases. The presences of building occupants where the “hazard” is present leads to exposure. Increase in exposure increases vulnerability. Increase in “hazard” and or “vulnerability” increases the risk of the human developing indoor air quality related health problems. Therefore, maintenance should be taken seriously to ensure a sink does not become a poor sink or source of pollutants. Maintenance culture is mainly due to human behaviour. Human assumption drives thinking. Thinking drives human behaviour. The assumption is a difficult engineering problem to solve. This is because if people are ready to do maintenance, a wrong assumption will make them unwilling to carry it out. What are the typical assumptions that hinder your maintenance culture? To what extent could poor maintenance culture increase indoor air risk, hazard, and vulnerability?

Do you want to know more about how building materials or systems could be a source and sink to appreciate the importance of maintenance? Read Batterman and Burge (1995) and Beko et al. (2007).