The best method to improve IAQ is to reduce air contaminants by eliminating their source.  Many common biological and chemical contaminants including mould, asbestos and volatile organic compounds (VOCs) have sources that can be easily controlled or removed altogether.

Indoor wood burning is one major source of poor indoor air quality.  When wood is burned it often undergoes incomplete combustion, resulting in the release of smoke and particulates to the air.  Contaminants found in wood smoke include particulate matter, carbon monoxide, VOCs, dioxins, furans, and polycyclic aromatic hydrocarbons (PAHs).  Many of these compounds cause breathing difficulty and can even result in chronic asthma (1). 
 
Vehicle exhaust is also a substantial contributor to poor indoor air quality. Many families choose to idle the family vehicle in the garage, and often some of these vehicle fumes travel into the house.  Vehicle exhaust contains a number of air pollutants including carbon monoxide, carbon dioxide, VOCs, ozone, and fine particulate matter, as well as some residual unburned gasoline.  In additional to their negative impact on human health, some of these contaminants are greenhouse gases that contribute to global warming.  While all vehicle idling should be kept to a minimum, any idling that does occur should be outdoors and away from entrances to homes and other buildings.

Indoor moisture contributes to poor air quality by promoting the growth of mould and release of mould spores into the air.  Inhalation of these spores can cause chronic asthma, allergic reactions, respiratory infection, and acute toxic poisoning (2).  Mould can be prevented or controlled by regulating the humidity level indoors and drying any wet materials within 48 hours.  The presence of any visible mould on surfaces should be cleaned immediately (3).

Often overlooked sources of indoor air contaminants are building materials and furnishings, which can emit contaminants such as formaldehyde, VOCs, radon and lead.  This source is best controlled through the careful selection of products that are known to contain and/or emit very low levels of these contaminants.  For more information on this subject, please see the webpage for Low Emitting Materials. 

Sources:
¹ Environment Canada (Clean Air Online), 2008.  Residential Wood Heating (webpage).
² North Carolina Department of Health and Human Services, 2009. Mold and Human Health: Health effects of indoor mold (webpage).
³ Health Canada, 2009. Mould: Get rid of it! (webpage).