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Puget Sound Georgia Basin Air Quality

Transboundary Air Quality
Introduction Air QualityAir Pollutants EmissionsResearchCrossborder Collaboration Crossborder ActivitiesInternational Air ProgramsEPA Region 10

Puget Sound Georgia Basin air quality is largely determined by two factors:

  • the emission of air pollutants into the atmosphere
  • the atmospheric conditions that transport, transform, disperse and deposit these airborne pollutants.
Sources of pollutants
  • Point sources: Industrial complexes associated with the petroleum industry, manufacturing plants and combustion-driven electricity generation are examples of point sources of pollutants.
  • Area sources: Small businesses such as dry cleaners and auto body shops, home heating (including woodstoves) and outdoor burning are examples of area sources. These types of numerous small sources are particularly significant to the emission inventory in residential and suburban areas. Emissions generated by agriculture and forestry practices such as windblown dust from tillage, ammonia from animal wastes and prescribed burning of crop residue are also classed as area sources and can be important contributors to the total inventory.
  • Mobile sources: Mobile sources of emissions include on-road vehicles, off-road vehicles, rail, marine vessels and aircraft.

Natural Sources

Natural sources of atmospheric chemicals are very important to the overall emissions inventory and to the understanding of air quality in the Basin. The largest source of natural emissions is vegetation, particularly trees. Both deciduous and coniferous trees produce gaseous chemicals. The quantity of these emissions depends on the time of year and local weather conditions. In the spring, under sunny skies and warm temperatures, trees produce tonnes of gaseous emissions per day (Moran and Makar, 2001). Other important sources of natural emissions are marine areas and bogs.

For more information on biogenic emissions from trees, visit "Choosing the Right Tree to Improve Urban Air."

Atmospheric conditions

Map of airshed regionThe atmospheric characteristics and meteorological conditions that dictate the transport, dispersion and deposition of airborne chemicals are strongly influenced by the topography of the Basin. The Georgia Basin is dominated by the west-to-east axis of the Lower Fraser Valley, the northwest-to-southeast Strait of Georgia and the west-to-east Strait of Juan de Fuca. This is in contrast to the well-defined north-south alignment of the Puget Sound airshed. The southern portion of the Puget Sound airshed is affected by air flowing through the Chehalis Gap from the Pacific Ocean. Both airsheds are influenced by the flow of air up and down “tributary” valleys and mountain slopes.

Periods of stagnation often occur in the summer and winter, causing higher measurements of ozone and fine particulate matter (PM) and poorer visibility than in other periods.

Airborne chemicals from the Eurasian continent and California have been observed to add to the overall mixture of pollution within the Basin. Air pollutants from sources outside of the Basin are usually well-dispersed by the time they arrive, adding a small, but measurable, amount to the ozone and PM ambient concentrations. Certain weather patterns cause periods of stagnation simultaneously in both airsheds, effectively isolating one from the other. Windflow patterns that are established during these stagnant periods do not allow air pollutants to flow between airsheds.


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