Particulate Matter in California: Part 2―Spatial, Temporal, and Compositional Patterns of PM_(2.5), PM_(10-2.5), and PM_(10)

摘要

Geographic and temporal variations in the concentration and composition of particulate matter (PM) provide important insights into particle sources, atmospheric processes that influence particle formation, and PM management strategies. In the nonurban areas of California, annual-average PM_(2.5) and PM_(10) concentrations range from 3 to 10 μg/m~3 and from 5 to 18 μg/m~3, respectively. In the urban areas of California, annual-averages for PM_(2.5) range from 7 to 30 μg/m~3, with observed 24-hr peaks reaching levels as high as 160 μg/m~3. Within each air basin, exceedances are a mixture of isolated events as well as periods of elevated PM_(2.5) concentrations that are more prolonged and regional in nature. PM_(2.5) concentrations are generally highest during the winter months. The exception is the South Coast Air Basin, where fairly high values occur throughout the year. Annual-average PM_(2.5) mass, as well as the concentrations of major components, declined from 1988 to 2000. The declines are especially pronounced for the sulfate (SO_4~(2-)) and nitrate (NO_3~-) components of PM_(2.5) and PM_(10) and correlate with reductions in ambient levels of oxides of sulfur (SO_x) and oxides of nitrogen (NO_x). Annual averages for PM_(10-2.5) and PM_(10) exhibited similar downwind trends from 1994 to 1999, with a slightly less pronounced decrease in the coarse fraction.