Open AccessFormation of photochemical air pollution in central California 1. Development of a revised motor vehicle emission inventory
Author(s) -
Marr Linsey C.,
Black Douglas R.,
Harley Robert A.
Publication year - 2002
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd000689
Subject(s) - emission inventory , environmental science , truck , san joaquin , diesel fuel , air pollution , air quality index , bay , pollution , meteorology , pollutant , atmospheric sciences , vehicle miles of travel , environmental engineering , oceanography , waste management , transport engineering , automotive engineering , chemistry , geography , ecology , engineering , organic chemistry , geology , soil science , biology
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.