A photochemical model based on a scaling analysis of ozone photochemistry

A scaling-level model of a photochemical mechanism has been developed and integrated into an air quality model used to study ozone formation in an urban environment.; A scaling analysis was used to capture the internal workings of a photochemical mechanism using the OZIPR trajectory model to simulate a smog chamber for a wide range of precursor concentrations and a variety of environmental conditions.; A meteorological model and an emissions inventory were developed. These were incorporated into an air quality model used to explore the sensitivity of a regional ozone plume to environmental conditions and precursor concentrations. The air quality model consisted of a series of box models being advected by the mean wind, for a single day, where photochemistry of the precursors emissions was modeled using the similarity relationships developed from the scaling analysis. The chosen domain was the Lower Fraser Valley B.C., a complex coastal region that experiences moderate ozone episodes during summertime fair-weather conditions.; Emission fields were developed using published emission totals, four land-use categories and generic temporal emissions curves and were found to be comparable with fields based on more detailed inventories. Wind observations (speed and direction), from 53 stations, on a typical episode day, were interpolated to produce hourly wind fields. Mixing depths were determined using a simple slab model incorporating the interpolated wind fields and measured heat fluxes. The most problematic aspect of the model was determining the effects of pollutant build up in the boundary layer, prior to the modeling day. This was handled by emitting precursors into the boundary layer and advecting them, without chemical reactions, until steady state concentrations were reached. These were dependent on the choice of background concentrations used to initialize the pre-conditioning scheme and were set so resulting boundary layer NOx and VOC concentrations were in agreement with the limited available data and peak ozone concentrations were typical of recent episodes.; The model suggests: the region to be VOC limited; projected emissions reductions may not improve present episodic ozone concentrations, larger than anticipated reductions in NOx emissions, without equivalent additional VOC reductions, could increase episodic concentrations and future emissions reductions, stemming from TIER 2 LDV standards, which target NOx emissions to a greater extent than VOC emissions, may not result in appreciable changes in episodic ozone concentrations. These conclusions are intended to guide comprehensive modeling studies. (Abstract shortened by UMI.)...