Woodsmoke and air pollution

Sitting in front of a roaring fire on a chilly winter night may be romantic, but unless you have an advanced-combustion wood stove or fireplace insert, significant quantities of more than 100 pollutants associated with woodsmoke could be making their way into your home and the outside air. Several of these chemicals are carcinogenic, and linked with risks to human health and the environment.

The burning of residential fuel wood is an important source of air pollution in Canada, according to a 1995 emissions inventory released by Environment Canada and other members of a federal-provincial task force on emissions inventories and projections. The inventory shows that residential fuel wood combustion is responsible for about 25 per cent of fine particulates found in Canada's air pollution, 15 per cent of volatile organic compounds, and 10 per cent of carbon monoxide.

Residential fuel wood combustion is a significant source of fine particulate emissions in the Atlantic provinces and the Northwest Territories. Ontario, Manitoba and British Columbia also receive significant volumes of air pollution from residential wood burning, which is a concern in many urban areas of the country where usage is concentrated. In mountainous regions of British Columbia, weather patterns exacerbate the problem by trapping smoke near ground level in populated valleys for extended periods of time.

How are these pollutants created? If you watch wood burn, you will see that flames appear over only a portion of the log, while smoke issues from different areas. This smoke is a complex mix of particulates and volatile incomplete combustion products that are being distilled out of the wood. These incomplete combustion products include volatile and semi-volatile organic compounds as well as carbon monoxide, polycyclic aromatic hydrocarbons (PAHs) and other toxic chemicals. Fine particulates can cause eye and throat irritations, headaches, allergies and aggravate cardio-respiratory problems.

In conventional fireplaces and wood stoves, large volumes of these unburned compounds are sent directly up the chimney and into the atmosphere. One way of minimizing emissions from wood burning is to maintain a healthy fire-with a chimney temperature of 150-200^oC considered optimum for combustion. Reducing the air flow by closing dampers or burning fresh wood with a high moisture content reduces the combustion temperature and greatly increases the formation of creosote and atmospheric pollutants. Dark or smelly smoke rising from a chimney is an indication that the fire is not hot enough, and is releasing large quantities of emissions.

Key features of a conventional wood stove.

An even more effective way to reduce pollutants is to use these clean burning practices with an advanced-combustion appliance. Such appliances have two simultaneous combustion zones-the first at wood level, where conventional burning takes place, and the second in the area immediately above, where volatiles are temporarily detained by a deflector and burned off before leaving the combustion chamber. Advanced-combustion wood stoves certified under Canadian Standards Association or United States Environmental Protection Agency performance standards reduce toxic emissions, emit 80-95 per cent fewer particulates, and are up to 20 per cent more fuel efficient than conventional models.

Environment Canada has helped promote these technologies by providing support to change-out projects in communities in British Columbia, New Brunswick and Nova Scotia, where retailers provide people with financial incentives to swap their old wood-burning appliances for new, high-efficiency ones. Hundreds of households have made a switch as a result of these projects, which also included seminars and workshops on better burning techniques. A similar effort involving Environment Canada, the Hearth Products Association of Canada and several other organizations is currently running in Eastern Ontario.

The results of the 1995 emissions inventory will be helpful in making more accurate assessments of the environmental impacts of emissions from residential wood burning in Canada, and in assisting decision-makers in the development of guidelines aimed at reducing air pollution in the future.

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