ARB Research Seminar

This page updated June 19, 2013

Development of the SAPRC-07 Chemical Mechanism and Updated Ozone Reactivity Scales

Photo of William P. L. Carter, Ph.D.

William P. L. Carter, Ph.D., Air Pollution Research Center and College of Engineering Center for Environmental Research and Technology, University of California, Riverside

August 28, 2007
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


An updated version of the SAPRC-99 chemical mechanism, designated SAPRC-07, has been developed. This includes a complete update of the rate constants and reactions based on current data and evaluations, reformulated aromatics mechanisms, a representation of chlorine chemistry, a reformulated method to represent peroxy reactions that is more appropriate for modeling secondary organic aerosol formation, and improved representations for many types of VOCs. This mechanism was evaluated against the result of ~2400 environmental chamber experiments carried out in 11 different environmental chambers, including experiments to test mechanisms for over 120 types of VOCs. The performance of the mechanism in simulating the chamber data was comparable to SAPRC-99, with generally satisfactory results for most types of VOCs but some increases in biases in simulations of some mixture experiments. The mechanism was used to derive an update to the MIR and other ozone reactivity scales for almost 1100 types of VOCs. The average changes in relative MIR values was about 10%, with >90% of the VOCs having changes less than 30%, but with larger changes for some types of VOCs, including halogenated compounds. Recommendations are given for future mechanism development research.

Speaker Biography

William P. L. Carter, Ph.D., holds a joint emeritus appointment at the Air Pollution Research Center and the College of Engineering Center for Environmental Research and Technology (CE-CERT) at University of California, Riverside. His research concerns the gas-phase atmospheric reactions of volatile organic compounds (VOCs) and the assessment of ozone and other impacts of VOCs in the atmosphere. This includes developing chemical mechanisms for airshed models, conducting environmental chamber experiments to evaluate and improve these mechanisms, and utilizing them in airshed models to develop ozone reactivity scales for VOCs. Chemical mechanisms he has developed are being used in airshed models for a number of research and regulatory applications. Ozone reactivity scales he developed have been incorporated several VOC emissions regulations in California.

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