|Transboundary Air Quality|
|Introduction Air QualityAir Pollutants||EmissionsResearchCrossborder Collaboration||Crossborder ActivitiesInternational Air ProgramsEPA Region 10|
Air pollutants affect the health of our communities, our ecosystem, our economy, and our earth.
- Individuals breathe more than 11,000 liters of air each day, making air quality a critical component of human health (A Snapshot of Sustainability: State of the Fraser Basin Report (PDF, 24 pp.) Fraser Basin Council, 2003). Impacts from airborne pollutants range from eye, nose and throat irritation to decreased lung function and cancer.
- Contaminants in the air can damage farm crops and vegetation, reducing yields of economically important crops. In the US, agricultural losses due to ozone are estimated at between $1 billion and $3 billion annually ("The Smog Primer," Pollution Probe, Nugent, 2002).
- The reduction in visibility caused by the buildup of pollution particles in the air can have detrimental effects on tourism. For a single extreme visibility event, computer models estimate losses in future tourist revenue to be $7.45 million in the Greater Vancouver area and $1.32 million in the Fraser Valley. (The Impact of Visual Air Quality on Tourism Revenues in Greater Vancouver and the Lower Fraser Valley , McNeill and Roberge, 2000).
- Many sources of air pollution are also sources of greenhouse gas emissions. Increasing concentrations of these heat-trapping gases in the Earth's atmosphere contribute to climate change, with potentially far-reaching environmental, social and economic consequences.
Air pollutants in the Puget Sound
Ozone (O3)The amount of ground-level ozone in the ambient air is primarily the result of photochemical reactions between oxides of nitrogen and volatile organic compounds. Ozone and its precursors can be transported great distances. As a result, the highest ozone concentrations are often observed downwind of urban centers and at high elevations in rural areas, such as Surrey East in BC and Enumclaw, Washington. In those areas, the ozone precursors are not produced nearby but are transported to the site via air currents.
The highest concentrations of O3 for the year are recorded in the summer and are associated with short duration events or episodes. However, the analysis of ozone for the entire year shows a maximum in mean concentrations during the spring.
Ozone concentrations of 40 to 50 parts per billion (ppb) are often recorded at rural coastal locations during the spring and identified as “background” concentrations. These concentrations are caused by emissions from both natural and anthropogenic sources, including transport from outside the Basin.
Polluted airmasses travelling across the Pacific Ocean have been responsible for increasing surface ozone levels along the west coast by 10 ppb over the last two decades and are expected to increase ozone levels by several more ppb over the next decade.
Oxides of Nitrogen (NOx)
Rural areas are “NOx-limited” due to the relatively large amounts of naturally occurring VOC emissions and the small amounts of NOx emissions. Reducing ozone in rural areas may require large reductions in anthropogenic NOx emissions from urban areas.
Fine Particulate Matter (PM2.5)
Fine particulate matter is dominated by carbonaceous material. In urban areas, nearly 50 percent of the particle mass comes from combustion.
In Seattle, the three main sources contributing to PM2.5 are vegetative burning at 28 percent, mobile sources at 22 percent (diesel 18 percent; gasoline four percent), and secondary sulphate at 18 percent. The central Lower Fraser Valley shows mobile sources at 39 percent (diesel three percent; gasoline 36 percent), secondary nitrate at 29 percent and secondary sulphate at 13 percent. Farther east in the Valley, mobile sources contribute 30 percent (diesel seven percent; gasoline 23 percent), secondary nitrate accounts for 26 percent and secondary sulphate represents 14 percent of total PM2.5 emissions.
The annual average PM2.5 mass concentration within the PSGB air basin varies from six to eight µg/m3, except near the major urban centres of Seattle, Victoria and Vancouver, where averages are nine to 10 µg/m3. Particulate concentrations vary considerably by season, week and day.
Volatile Organic Compounds (VOCs)
Natural emissions of volatile organic compounds represent from one-third to one-half of the total VOC emissions in the Basin. The magnitude of natural emissions poses limits on achievable reductions in total VOC emission levels and on the effectiveness of nitrogen oxide emissions controls in reducing ambient PM and ozone concentrations.
Which air pollutants cause the smog that interferes with our region's mountain and ocean vistas?
SO2, organic carbon and NOx are the dominant pollutants responsible for degraded visibility in the Basin. SO2 and NOx are transformed in the atmosphere to sulphates and nitrates, which combine chemically with ammonia from agricultural sources and with sodium from natural marine emissions to form fine particulate matter.
How are pollutants measured?
Airborne chemicals and the associated meteorology are measured at a number of sites to quantify the air quality both in time and space. The ambient measurements are then compared against standards and objectives to gauge the success of air quality management strategies. Detailed measurements provide an indication of the composition of air pollutants, which leads to an understanding of the important chemical and physical processes creating the pollution, potential impacts on receptors and the key sources.