An analysis of trends in oxidant air quality in the south coast air basin of California

Abstract

Previous approaches for meteorological adjustment of oxidant trends were based on establishing a statistical or deterministic model between oxidant concentrations and meteorological parameters. This model was then used to remove the influence of meteorology. However, because of the simplistic forms of the models, they are not capable of removing meteorological effects for all years. To circumvent this problem, the daily peak oxidant trends have been determined based on fixed ranges of meteorological parameters, as well as on fixed parameter values using year-specific statistical models. Trends were determined for regional maxima, and at two specific sites Azusa and San Bernardino, over the high oxidant season from 1971 to 1979. The parameters selected to characterize the oxidant concentrations are the daily values of El Monte upperlevel temperature, maximum Ontario surface temperature, relative humidity, mixing height and wind speed. Fixed ranges or values of these parameters were further classified according to their high, moderate and low oxidant formation potential. Oxidant trends were determined for each classification. Between 1971 and 1979, for days with high oxidant formation potential, the oxidant trends are flat for Azusa, for San Bernardino and basinwide. For days with moderate and low oxidant formation potential, the trends are essentially flat, with minor variations depending on which approach is used to determine the trend.