Assessing Ozone-Precursor Relationships Based on a Smog Production Model and Ambient Data

Abstract

A semi-empirical model, Johnson’s smog production model (SFM), which relates precursor emissions to ozone levels and estimates the relative effectiveness of volatile organic compounds (VOC) and NO_x emission controls, has been evaluated and a modified version of SPM has been introduced. Both versions have been applied to routine data from 1989–1991 in five areas in the United States. In particular, extent parameters, which reveal the relative merit of VOC and NO_x controls in reducing high ozone levels, have been calculated. Preliminary applications of SPM reveal interesting features with respect to VOC vs. NO_x controls in reducing high ozone levels. For hourly data with ozone ≥0.08 ppm, distributions of extent parameters resulting from the modified SPM show the effectiveness of VOC controls at more monitoring sites than those from Johnson’s SPM; however, relative features between the two versions are similar. On the other hand, for hourly data with ozone ≥0.12 ppm, the two SPM versions show very similar relative effectiveness of VOC and NO_x controls with chosen values of model parameters. To improve the credibility of SPM, the range of validity of relationships between maximum smog produced or maximum ozone and NO_x concentrations must be determined, and the parameters in these relationships must be better determined for typical VOC mixtures. Another essential parameter, which determines the fractional loss of NO_Y (NO and its oxidation products) from the gas phase must be better determined.