Wintertime PM2.5 and PM10 source apportionment at Sacramento, California

The chemical mass balance (CMB) model was applied to winter (November through January) 1991-1996 PM2.5 and PM10 data from the Sacramento 13th and T Streets site in order to identify the contributions from major source categories to peak 24-hr ambient PM2.5 and PM10 levels. The average monthly PM10 monitoring data for the nine-year period in Sacramento County indicate that elevated concentrations are typical in the winter months. Concentrations on days of highest PM10 are dominated by the PM2.5 fraction. One factor contributing to increased PM2.5 concentrations in the winter is meteorology (cool temperatures, low wind Speeds, low inversion layers, and more humid conditions) that favors the formation of secondary nitrate and sulfate aerosols. Residential wood burning also elevates fine particulate concentrations in the Sacramento area. The results of the CMB analysis highlight three key points. First, the source apportionment results indicate that primary motor vehicle exhaust and wood smoke are significant sources of both PM2.5 and PM10 in winter. Second, nitrates, secondarily formed as a result of motor-vehicle and other sources of nitrogen oxide (NOx), are another principal cause of the high PM2.5 and PM10 levels during the winter months. Third, fugitive dust, whether it is resuspended soil and dust or agricultural tillage, is not the major contributor to peak winter PM2.5 and PM10 levels in the Sacramento area.