Spatial and seasonal patterns of particulate matter less than 2.5 microns in the Sierra Nevada Mountains, California

This paper presents particulate matter data collected in the California southern Sierra Nevada Mountains (SNM) during 2002 to 2009 from the Central Valley (elevation 91 m) into the SNM (elevation 2 598 m). Annual average concentrations of particles smaller than 2.5 mu m in diameter (PM2.5) for all sites during this study ranged from 3.1 to 22.2 mu g m(-3). The highest elevation site experienced annual PM2.5 concentrations ranging from 3.1 to 4.6 mu g m(-3), while the lowest elevation site concentrations ranged from 18 to 22.2 mu g m(-3). PM2.5 generated from natural source emissions (background particulate matter) in the southern SNM was estimated to be 4.7 +/- 1.3 mu g m(-3). Higher elevation sites in the southern SNM exhibit a pattern of high PM2.5 in the summer as compared to the winter. For regulatory purposes, air quality throughout the southern Sierra Nevada is assumed to be similar to the Central Valley, which is currently in nonattainment. However, we determined that locations used in this study of elevations above 500 m in the southern SNM are actually in compliance with federal standards for PM2.5. Elevation and day of year appear to account for most of the variation in PM2.5 concentrations. Fires occurring during this study were typical of the size and intensity historically documented in this area of the SNM. We determined that while these fires impact air quality they do not appear to be a major driver in exceeding the United States Federal PM2.5 standard in the southern SNM.