An airshed is generally described as an area where the movement of air, and air pollutants, can be hindered by local geographical features such as mountains, and by weather conditions. The most obvious example in British Columbia is a mountain valley. Many B.C. communities have periods of unacceptable air quality, with adverse effects on human health, the environment and visibility.
These areas frequently experience temperature inversions, in which the air near the ground is colder than the layer of air above. This results in very stable conditions within the valley, such that pollutants released near the surface are confined to the airshed. In turn, these stable conditions can lead to high levels of air pollution.
The complex terrain and weather patterns in B.C. naturally divide the province into a number of airsheds, such as the Lower Fraser Valley, Okanagan Valley and Bulkley Valley. The larger Georgia Basin / Puget Sound airshed, which includes the Lower Fraser Valley, lies along the western coast of Canada and the United States.
Airshed Management Planning
Since air pollution knows no political boundaries, airshed activities may be focused on a single community or on a number of neighbouring communities faced with similar air quality problems and requiring similar action.
In some cases, airshed boundaries have followed political boundaries, to reflect the area in which there is support and authority for air quality action. This includes individual municipalities or regional districts, and multiple regional districts where there are common issues requiring solutions across a broader area.
Airshed plans and strategies to manage priority air contaminants are under development or being implemented in a number of communities in British Columbia. It also provides stakeholders with a clear understanding of community air-quality priorities and how future growth may be accommodated. In addition, an airshed plan ensures that the air quality goals of various levels of government are met. Community-based airshed plans are key to meeting B.C.'s obligations under the Canada-wide Standards for Particulate Matter and Ozone. To see if there is an air quality management strategy in your community visit your community or regional district website.
The Province has been broken into Air Zones for the purpose of reporting trends in air quality over time. In zones exceeding set contaminant levels, advanced airshed planning is suggested to provide actions to reduce air pollution levels. For more information learn about the Air Quality Management system.