HR: 11:44h
AN: A22A-07    [Abstracts]
TI: Changes in Ozone Due to Reductions in Precursor Emissions: Application of the Adjoint Sensitivity Analysis Procedure
AU: * Martien, P T
EM: martien@ce.berkeley.edu
AF: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710 United States
AU: Harley, R A
EM: harley@ce.berkeley.edu
AF: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710 United States
AB: Control of oxides of nitrogen (NO$_x$) and volatile organic compounds (VOC) can significantly shift the sensitivities of ozone production and, subsequently, alter the contribution of emission source regions. Understanding these changes is critical for designing effective ozone control measures as the magnitude and ratio of precursor emissions change over time. However, because of the complexity of transport and chemistry in an urban airshed and because of the large number of parameters that can change, such shifts have been difficult to quantify. This study developed a new modeling tool, the Adjoint Sensitivity Analysis Procedure (ASAP), to efficiently predict all input data sensitivities in a three-dimensional Chemistry-Transport Model. The ASAP was applied to Southern California during a summertime air pollution episode to quantify the effects of changes in precursor emissions on ozone sensitivities. Using ASAP, we generated ranked lists of sensitivities of ozone to all emissions and all reaction rate coefficients. The ranked lists enabled us to quantify the effect of NO$_x$ and VOC emission reductions on chemical dynamics. For example, we found that a 50% reduction in NO$_x$ emissions increased ozone, but also shifted the chemistry from a VOC sensitive to a NO$_x$ sensitive regime as evidenced by the finding that ozone sensitivity to NO$_x$ emissions shifted from strongly negative to positive. Furthermore, the relative importance of NO$_x$ emissions increased compared to VOC emissions. Radical initiation in the reduced NO$_x$ case, with its higher relative abundance of VOC species, was found to be less important relative to the base case as evidenced by the drop in ranking of the sensitivity of ozone to the rate coefficients of radical initiation reactions. Changes in the distribution and sign of the adjoint function for emitted species revealed changes in the ozone source apportionment due to changes in emissions. For example, with a 50% reduction in NO$_x$ emissions, the adjoint function for nitric oxide (NO) remained positive for sources offshore and downwind of an inland receptor location, but switched from negative to positive for onshore sources, indicating a switch to a positive contribution to ozone.
DE: 0322 Constituent sources and sinks
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting