An airshed is 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" (Government of British Columbia). The four participating Ports in the NWPCAS began working together in part because of their geographic location within the Georgia Basin-Puget Sound Airshed. As each port operates within the shared airshed, air pollutant emissions produced from one port can have an effect on air quality across the region. The Georgia Basin-Puget Sound Airshed includes both the watershed around the Strait of Georgia in British Columbia, Canada and north reaches of Whatcom County in Washington and the watershed surrounding the Puget Sound (Government of Canada).
