Statistical analysis of winter ozone events

Abstract

We have developed quadratic regression models that predict the daily ozone concentration in either the Uintah Basin (UB) of Utah, USA, or the Upper Green River Basin (UGRB) of Wyoming, USA. Sites selected for study are ozone stations near the towns of Ouray, Utah, in the UB and Boulder, Wyoming, in the UGRB. Input data for the UB model are daily values of lapse rate, snow depth, solar angle, temperature, and the number of consecutive days under inversion conditions. The UGRB model also requires the wind speed. Standard errors are 10 and 5 ppb for the UB and the UGRB, respectively. The models have been optimized to predict seasonal exceedances of the National Ambient Air Quality Standard (NAAQS), i.e., the number of times each season that the daily maximum in the eight-hour running average exceeds 75 ppb, and they perform in this regard to an accuracy of ±1 day. (However, Ouray is not at this time a regulatory site for judging compliance with federal law.) We predict that any given winter will be NAAQS compliant with 44 % odds in the UB and with 60 % odds in the UGRB. We have estimated the ozone production for each winter in the UB since 1950, under the assumption that precursor emissions are at modern values.