CARB Research Seminar

This page updated August 13, 2018

Improving Chemical Mechanisms for Ozone and Secondary Organic Carbon

Photo of Christopher Cappa, PhD.

Christopher Cappa, Ph.D., University of California, Davis

August 31, 2018
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Photochemical air quality models are the primary tool for determining the limiting precursors for various secondary pollutants in California air sheds. This project was designed to update and comprehensively evaluate the detailed chemical processes in an air quality model for the formation and prediction of ozone and secondary organic aerosol (SOA). The statistical oxidation model (SOM) was used to explore the role of multi-generational oxidation chemistry and quantify the effects of laboratory chamber vapor wall losses on SOA formation, which was not accounted for in previous studies. Accounting for wall losses significantly increases the projected SOA concentrations in air quality models in Southern California and elsewhere. The research has led to fundamental changes in the direction of further research on the characterization of environmental chambers and their impact on SOA formation estimates and helped further SOA air quality model development. The ozone formation potentials of over one thousands volatile organic compounds were also updated using current (2010) rather than historical (1988) environmental conditions. Some significant changes were observed in the updated ozone formation potential values (mostly increased), but the relative rank order did not changed greatly from previous updates.

The key finding of this research project addressed several critical areas on the formation and aging of SOA and provided a better foundation for the description and modeling of SOA. An improved and more up-to-date model of chemical processes will enable air quality modelers to improve predictions of ozone and SOA formation and their influence on ambient conditions in California.

Speaker Biography

Christopher Cappa is a Professor and Vice Chair of the Civil and Environmental Engineering Department at the University of California, Davis, and is currently a Chancellor's Fellow. He received his B.S. in Chemistry from Hope College in 2000, and earned his Ph.D. from the University of California, Berkeley in Physical Chemistry in 2005. Since starting at UC Davis in 2007, the work in Prof. Cappa’s group has entailed a mix of laboratory experiments, field measurements and conceptual model development. He has focused on understanding the formation and properties of organic aerosol particles, interactions between particles and water, and the relationship between composition and the light absorption and extinction properties of atmospheric aerosols. He is currently leading projects funded by NSF, the Department of Energy Atmospheric Systems Research Program, US EPA, and NOAA to develop clearer linkages between particle composition (including organic components) and optical properties.

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for the seminars please view the Main Seminars web page