Decade scale evolution of ozone air pollution in the lower Fraser Valley, B.C.

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Recent studies of ozone air pollution in the Lower Fraser Valley (LFV) of British Columbia over the past two decades have demonstrated marked spatio-temporal trends of ozone concentration. These trends consist of an eastward shift in the centroid of pollution, and overall reduction in the total number of exceedances, and have been in parallel with downward temporal trends in emissions of ozone precursors. It is assumed that the trends in precursors have been as a result of emissions reduction strategies contained in air quality management plans by Metro Vancouver and Fraser Valley Regional District. The pollution trends will be studied using numerical modelling studies based on composite meteorological conditions during observed episodes in the past. Episode selection will be made using criteria drawing from a meteorological cluster analysis. The modelling system will be run using emissions inventories from a sequence of years over the past two decades. The work will be based on a modelling system that has been demonstrated to be responsive to emissions changes (gross reductions in NOx and VOC, changes in chemical speciation and spatial and temporal shifts in emissions) that have occurred in the past, and are likely to occur in future. Models will be evaluated by demonstrating that they can successfully capture the decadal evolution of photochemical pollution in the LFV in relation to changes in emissions and meteorology. The response of ambient pollution to emissions changes will be investigated using chemical process analysis and spatio-temporal analysis of ozone plumes through the sequence studied. The overall study objective is to provide a policy relevant understanding of the relationship between ambient ozone and emissions of ozone precursors in the LFV. The work will be scientifically credible, will be based on methods appropriate to the tasks, and will be presented in ways that lead directly into the policy-making and regulatory realms.