Characterization of Particulate Matter in California.

The size, composition, and concentration of particulate matter (PM) vary with location and time. Several monitoring/sampling programs are operated in California to characterize PM less than 2.5 and 10 µm in aerodynamic diameter (PM and PM). This paper presents a broad summary of the spatial and temporal variations observed in ambient PM and PM concentrations in California. Many areas that have high PM concentrations also have relatively high PM concentrations, and data indicate that a significant portion of the PM air quality problem is caused by PM To develop effective plans for attaining the ambient PM standards, improved understanding of these unique problems is needed. Since 1989, pollution control efforts-whether specifically targeted for particulate matter or indirectly via controls on gaseous emissions-have caused annual average PM and PM concentrations to decline at most sites in California.