ARB Research Seminar

This page updated June 19, 2013

Wintertime Particulate Matter in the San Joaquin Valley: Concentrations, Mechanisms, and Sources

Jorn Dinh Herner, Ph.D., Research Division, California Air Resources Board

November 20, 2007
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA



The San Joaquin Valley in California has one of the most severe particulate air quality problems in United States. During wintertime meteorological inversions trap pollutants near the surface and allow the buildup of particulate matter near the surface. This seminar will present the results from field sampling that took place as part of the California Regional PM10/2.5 Air Quality Study (CRPAQS) during the winter 2000/2001. Samples were collected using filter-based methods, cascade impactors, and real time particle sizers. Samples were collected both in the San Joaquin Valley and along the California Coast to determine local and transported PM. Size segregated chemical speciation and modeling was used to infer sources and mechanisms of particle formation in the San Joaquin Valley.

The 24hr National Ambient Air Quality Standard for PM2.5 (particulate matter with aerodynamic diameter less than 2.5 Ám) was exceeded by almost a factor of three during the study. PM2.5 was dominated by ammonium nitrate, while the ultrafine fraction, PM0.1, was completely dominated by carbon species. Analysis of size and composition of the size segregated ambient particulate matter suggest that two particle types exist in the San Joaquin Valley; hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. These particle types exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode. These findings have implications both when considering exposure and strategies to reduce ambient PM levels in the San Joaquin Valley.

Speaker Biography

Jorn Dinh Herner, Ph.D., works in the Research Division at the California Air Resources Board (ARB). His research interests include ultrafine particulate matter found both in ambient and emitted from combustion. Recent work at ARB include characterizing emissions from heavy duty diesel vehicles, especially the effect of aftertreatment devices such as diesel particulate filters and NOx scrubbers. An additional interest is laboratory sampling methodologies. As a graduate student Dr. Herner worked on the California Regional PM10/2.5 Air Quality Study (CRPAQS) analyzing the size and composition distribution of ambient particulate matter in the San Joaquin Valley. Prior to his work on particulate matter Dr. Herner was employed in private industry remediating contaminated groundwater.

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