Source contributions to the regional distribution of secondary particulate matter in California

Source contributions to PM2.5 nitrate, sulfate and ammonium ion concentrations in California's San Joaquin Valley (SJV) (4-6 January 1996) and South Coast Air Basin (SoCAB) surrounding Los Angeles (23-25 September 1996) were predicted using a three-dimensional source-oriented Eulerian air quality model. The air quality model tracks the formation of PM2.5 nitrate, sulfate and ammonium ion from primary particles and precursor gases emitted from different sources though a mathematical simulation of emission, chemical reaction, gas-to-particle conversion, transport and deposition. The observed PM2.5 nitrate, sulfate and ammonium ion concentrations, and the mass distribution of nitrate, sulfate and ammonium ion as a function of particle size have been successfully reproduced by the model simulation. Approximately 45-57% of the PM2.5 nitrate and 34-40% of the PM2.5 ammonium ion in the SJV is formed from precursor gaseous species released from sources upwind of the valley. In the SoCAB, approximately 83% of the PM2.5 nitrate and 82% of the PM2.5 ammonium ion is formed from precursor gaseous species released from sources within the air basin. In the SJV, transportation related sources contribute approximately 24-30% of the PM2.5 nitrate (diesel engines similar to 13.5-17.0%, catalyst equipped gasoline engines similar to 10.2-12.8% and non-catalyst equipped gasoline engines similar to 0.3-0.4%). In the SoCAB, transportation related sources directly contribute to approximately 67% of the PM2.5 nitrate (diesel engines 34.6%, noncatalyst equipped gasoline engine 4.7% and catalyst equipped gasoline engine 28.1%). PM2.5 ammonium ion concentrations in the SJV were dominated by area (including animal) NH3 sources (16.7-25.3%), soil (7.2-10.9%), fertilizer NH3 sources (11.4-17.3%) and point NH3 sources (14.3-21.7%). In the SoCAB, ammonium ion is mainly associated with animal sources (28.2%) and catalyst equipped gasoline engines (16.2%). In both regions, the majority of the relatively low PM2.5 sulfate (< 5 mu g m(-3)) is associated with upwind sources. Most of the locally generated sulfate is emitted from diesel engines and high-sulfur fuel combustion processes in both modeling domains. Emissions control programs should target the sources listed above to reduce PM2.5 concentrations. (c) 2005 Elsevier Ltd. All rights reserved.