Characterization of PM and PM in the South Coast Air Basin of Southern California: Part 2-Temporal Variations.

The South Coast Air Quality Management District (SCAQMD) conducted a 1-year special particulate monitoring study from January 1995 to February 1996. This monitoring data indicates that high PM and PM concentrations were observed in the fall (October, November, and December), with November concentrations being the highest. During the rest of the year, PM and PM masses gradually increased from January to September. Monthly PM mass varied from 20 to 120 |ig/m, and monthly PM mass varied from 13 to 63 |j.g/m. The PM-to-PM ratio varied daily and ranged between 22 and 96%. Two types of high-PM days were observed. The first type was observed under fall stagnation conditions, which lead to high secondary species concentrations. The second type was observed under high wind conditions, which lead to high primary coarse particles of crustal components. The highest 24-hr average PM concentration (226.3 |ig/m) was observed at the Fontana station, while the highest PM concentration (129.3 |ig/m) was observed at the Diamond Bar station.