Centre for Atmospheric Chemistry
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Browsing Centre for Atmospheric Chemistry by Subject "air pollution"
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Item Open Access Evaluation of an Air Quality Simulation of the Lower Fraser Valley. Part II: Photochemistry(Elsevier, 1997) Hedley, M.; McLaren, R.; Jiang, W.; Singleton, D.L.The photochemical component of an advanced modelling system for use in pollution control studies is evaluated. Results of a case study for July 1985 in the Lower Fraser Valley region of British Columbia are used to test the performance of the modelling system during an ozone episode. Time series of surface trace pollutant concentrations are used to validate the model prediction. A quantitative analysis of the model errors shows that the modelling system adequately predicts the photochemistry without arbitrary adjustments to the emissions inventory. Improved performance of the ozone forecast would likely be obtained, however, if the non-methane organic compound emissions were increased in urban areas. The mechanistic parameters were shown to be very sensitive to the emissions profile, although the net impact of the parameter changes on ozone production was minor in this case.Item Open Access Sensitivity of Ozone Concentrations to Rate Constants in a Modified SAPRC90 Chemical Mechanism Used for Canadian Lower Fraser Valley Ozone Studies(Elsevier, 1997) Jiang, W.; Singleton, D.L.; McLaren, R.; Hedley, M.The SAPRC90 chemical mechanism implemented in CALGRID is modified and updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. Explicit reactions related to biogenic emissions and alternative fuels are added. The sensitivity of ozone formation to rate parameters in the mechanism is determined for an episode specific trajectory which originates under relatively clean marine conditions and passes over the urban core of Vancouver during the morning rush hour. Of the 137 reactions in the modified mechanism, the rate constants of 44 reactions are found to have a high sensitivity on ozone formation. The 44 reactions are further divided into general sensitive reactions, for which rate constant changes near the base case values have observable effects on maximum ozone concentrations, and limit-sensitive reactions, for which rate constant changes of more than an order of magnitude are required to have an observable impact on ozone concentrations. For the sensitive reactions, both ozone sensitivity coefficients for small changes (20%) in the rate constants and effects on ozone caused by large rate constant changes (factors of 0, 0.5, and 2) are calculated. Of note is the importance of several photolysis reactions and the reactions of OH with a class of reactive aromatics, including xylenes, on ozone concentrations in the LFV.Item Open Access Sensitivity of Ozone Concentrations to VOC and NOx Emissions in the Canadian Lower Fraser Valley(Elsevier, 1997) Jiang, W.; Singleton, D.L.; Hedley, M.; McLaren, R.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 NOx emissions as well as to the NO2/NOx 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 NOx(NO or NO2) in the LFV contribute negatively to the ozone formation. Any overestimation of NOx or underestimation of VOC in the emissions inventory could cause underestimations of ozone levels by photochemical models.