HR: 10:50h
AN: A22A-03 INVITED     [Abstracts]
TI: Weekly and Decadal Changes in NO$_{x}$ Emissions and Tropospheric Ozone
AU: * Marr, L C
EM: lmarr@vt.edu
AF: Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, 411 Durham Hall, Blacksburg, VA 24061 United States
AU: Harley, R A
EM: harley@ce.berkeley.edu
AF: Department of Civil and Environmental Engineering, University of California, Hearst Field Annex B66, Berkeley, CA 94720 United States
AB: Variations in air pollutant emissions and ambient concentrations on both weekly and decadal time scales can be used to test our understanding of atmospheric responses to changes in anthropogenic forcing. Combining records of fuel sales and on-road measurements of vehicle activity and emissions, we have estimated motor vehicle emissions by hour and day of week, separately for gasoline and diesel-powered vehicles. Between 1990 and 2000, emissions of nitrogen oxides (NO$_{x}$) from motor vehicles in California decreased by more than 30%. However, NO$_{x}$ emissions from heavy-duty diesel trucks actually increased by over 40%, offsetting some of the reductions in light-duty vehicle emissions. During the past two decades, the occurrence of higher ozone levels on weekends, a phenomenon known as the weekend effect, has become more widespread in California. The effect impacted 11% of surface observation sites in 1980-84 and 38% in 1995-1999. Results of chemical transport modeling show that the primary cause of the weekend ozone effect is the large decrease in NO$_{x}$ emissions due to a ~75% reduction in diesel truck traffic on weekends. Areas where ozone formation is VOC-sensitive therefore can experience higher ozone concentrations on weekends. Long-term (decadal) changes in anthropogenic emissions have produced a shift towards greater VOC-sensitivity, and the weekend ozone effect has grown more prevalent because diesel trucks now account for over 50% of total motor vehicle NO$_{x}$ emissions.
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting