California Air Resources Board

Principal Investigator/Author: Christopher Cappa

Contractor: University of California, Davis

Contract Number: 17RD008

Project Status: Completed

Relevant CARB Programs: California State Implementation Plans, Criteria Air Pollutants

Topic Areas: State Implementation Plans (SIPs), Particulate Matter (PM), PM2.5

Research Summary:

Particulate matter (PM) 2.5 pollution in the San Joaquin Valley (SJV) remains the worst in California and the US, frequently exceeding the 24-hour and annual National Ambient Air Quality Standards. Previous studies show that PM2.5 in the SJV is dominated by ammonium nitrate and organic aerosols, with seasonal differences. However, process-level understanding is limited by a lack of chemically resolved PM2.5 measurementsthat occur both over a long period and with sufficient time resolution. This would allow assessment of trends over seasonal and day/night differences. More research is needed to understand and mitigate the emission sources, chemical pathways, and meteorological conditions contributing to PM2.5 pollution in the SJV.

This project provided insight into the effectiveness of current and future controls on primary and secondary pollution in an urban location that is not possible with current monitoring. The measurements were made using an Aerosol Chemical Speciation Monitor (ACSM). Researchers deployed an ACSM at the Fresno-Garland air quality monitoring site for two years. The ACSM collected continuous, sub-hourly measurements of non-refractory PM2.5 chemical composition, including particulate organic aerosols,particulate ammonium nitrate, particulate ammonium sulfate, and particulateammonium chloride.

This project provided an important new dataset against which the State Implementation Plan-appropriate models could be tested and compared in terms of their ability to accurately predict composition-specific diurnal patterns, pollution event buildup and dissipation, and composition-specific differences between weekdays and weekends. The results contributed to the refinement and development of effective and appropriate future PM2.5 control strategies for the SJV. It also provided a foundation upon which future long-term PM2.5 composition measurements could be made.

Keywords: particulate matter, PM, San Joaquin Valley, SJV, temporal resolution, PM reduction, air pollution, chemical composition, non-refractory PM2.5, emission sources, chemical speciation

Final Report: Please email research@arb.ca.gov to request the Final Report generated by this research contract.