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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. D6, 4047, doi:10.1029/2001JD000689, 2002

Formation of photochemical air pollution in central California 1. Development of a revised motor vehicle emission inventory

Linsey C. Marr

Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA

Douglas R. Black

Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA

Robert A. Harley

Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA

Abstract

Photochemical air pollution problems have proved difficult to understand and control in central California. A major source of uncertainty is the rate of precursor volatile organic compounds and NO_x emissions, especially from motor vehicles. We develop alternative emissions estimates for on-road motor vehicles in 1990, using fuel sales data, emission factors measured in on-road studies, and ambient pollutant ratios, for a region that includes the San Francisco Bay and San Joaquin Valley air basins and Sacramento County. Fuel-based emissions estimates are compared with predictions of California's most recent motor vehicle emission factor model (EMFAC) and with an inventory that has been used in previous regional-scale photochemical modeling studies. The fuel-based inventory contains 10–50% less CO, 40–100% more nonmethane organic compounds, and 10–20% less NO_x than estimated both by EMFAC and the photochemical modeling inventory. We also describe new temporal distributions of vehicle emissions by hour and day of week. Diesel trucks, a major source of NO_x, have a broad midday peak in emissions on weekdays, in contrast to passenger vehicles, which show morning and afternoon commuter peaks. While passenger vehicle travel is similar on weekdays and weekends, diesel truck activity and emissions decrease by 70–80% on weekends. Vehicle emission rates and their temporal patterns are linked to a regional photochemical air pollution episode that spans a weekend in August 1990.

Published 28 March 2002.

Index Terms: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry.

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Citation: Marr, L. C., D. R. Black, and R. A. Harley (2002), Formation of photochemical air pollution in central California 1. Development of a revised motor vehicle emission inventory, J. Geophys. Res., 107(D6), 4047, doi:10.1029/2001JD000689.

Copyright 2002 by the American Geophysical Union.