Hazy Days of Winter

Smog - that heavy blanket of air pollution - is synonymous with hot and hazy days in the city when stepping outside for a breath of "fresh air" is something to be avoided. Smog, however, can also be a problem in the winter, not only in cities, but in rural regions as well. The explanation lies both in the types of air pollutants that can create smog, as well as the conditions that promote its formation.

Smog refers to a noxious mixture of gases and particles in the air that reduces visibility and is linked to adverse health and environmental impacts. High summertime smog levels in Canada are typically associated with a mixture of ground-level ozone (formed in the air in the presence of sunlight through the mixing of nitrogen oxides and volatile organic compounds) and particulate matter (PM) (tiny liquid and solid particles that become suspended in the air).

Since high levels of ground-level ozone generally occur under warm conditions, the main constituent of winter smog is particulate matter. Winter smog usually forms in stagnant air, so valleys and other regions where the local landscape tends to restrict air movement can be particularly susceptible. In some cases, high smog levels in winter are also associated with a temperature inversion, an atmospheric condition where cold air is trapped at ground level by a layer of warmer air above.

Causes of Winter Smog

The principle source of PM in the winter is wood heating, which is why winter smog can be a problem in both urban and rural areas. Wood is used in more than three million Canadian homes as either a primary or secondary heat source. Its continuing popularity is not only due to its ready availability in many regions, but also to the "comforting and cosy" atmosphere it creates in the home.

In addition to PM, wood smoke is known to contain more than a hundred other pollutants. Wood smoke pollutants, even at relatively low levels, can cause breathing difficulties and other health problems, especially for those with chronic conditions such as asthma.

Another significant source of winter smog is vehicle exhaust. Under stagnant air conditions, the combustion of fossil fuels to power personal, recreational, commercial and industrial vehicles can load the air with PM, volatile organic compounds, carbon monoxide, nitrogen oxides and other pollutants, which can also have significant impacts on human health. In colder months the proportion of commuters who travel by car in Canada increases from 73 per cent to 81 per cent (Statistics Canada, 2006 Household and Environment Survey).

Protecting our Air

The federal government is working to reduce emissions from vehicles by promoting sustainable transportation options and improved land use and by developing regulations for vehicles and engines. Most recently, the government announced plans to regulate the fuel consumption of new cars and light trucks, beginning with the 2011 model year. Efforts such as these can have significant positive effects on air quality, acid rain and climate change.

Federal, provincial, territorial and some regional governments monitor air pollution at stations across the country and communicate levels to the public through their air quality websites and through the Meteorological Service of Canada. Longer term averages and trends in air quality are reported annually through the Canadian Environmental Sustainability Indicators (CESI) initiative.

The CESI air quality indicators focus on ground-level ozone and fine particulate matter (PM2.5), which is PM that is less than 2.5 microns in size. From a health perspective, these particles are of greatest concern because the are sufficiently small to reach the finer structures of the lung. Due to technical challenges in collecting reliable data in the winter, the PM2.5 indicator is currently limited to the warm season (April 1-September 30). However, work is under way to address these challenges so that winter PM2.5 levels can be reported to the public and tracked through CESI as well.

Resources for You

Numerous other resources are available to provide the necessary support, information and guidance for individuals and communities to improve the quality of our air. These offer ways to help Canadians make more environmentally friendly choices, access financial support, explore opportunities to participate and become more active in promoting the clean air message. They include:

• Clean Air Day
• The Consumer - Environmental Choice Program
• Energy Efficiency Initiatives
• Transportation Outreach
• Residential Wood Heating Guidelines
• Citizen Monitoring
• The Canadian Pollution Prevention Information Clearinghouse

By taking advantage of these and the many other initiatives and resources, all Canadians can help improve the quality of the air we breathe throughout the year.

For information on the Canadian Environmental Sustainability Indicators initiative or to view the full CESI annual reports (Highlights and more in-depth Feature reports), which include the CESI air quality indicators, visit the Government of Canada's Sustaining the Environment and Resources for Canadians web site.