Sensitivity of ozone concentrations to VOC and NO x emissions in the Canadian Lower Fraser Valley

Abstract

The SAPRC90 chemical mechanism module implemented in CALGRID is updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. The kinetic and mechanistic parameters of lumped VOC reactions recalculated using the LFV emissions profiles are noticeably different from those based on default emissions profiles, indicating the importance of tailoring the parameters to specific regions. The sensitivities of ozone concentrations to total and speciated VOC and NO x emissions as well as to the NO 2 NO x ratios are determined. Significant VOC model species are identified based on the impact of their emissions on ozone formation in the LFV. Of note is the importance of the emissions of a lumped class of aromatics, ARO2, which contains mostly isomers of xylene and trimethylbenzene and is derived chiefly from the use and distribution of gasoline fuels. The ARO2 emissions make the largest contribution of all model VOC species to the ozone levels in the urban plume. The results indicate that reduction of AR02 emissions alone could achieve significant reduction of ozone levels in the LFV. Base case emissions of NO x (NO or NO 2) in the LFV contribute negatively to the ozone formation. Any overestimation of NO x or underestimation of VOC in the emissions inventory could cause underestimations of ozone levels by photochemical models.