Dependence of Summertime Surface Ozone on NOx and VOC Emissions Over the United States: Peak Time and Value

Abstract

AbstractWe apply the Regional chEmistry and trAnsport Model to analyze summertime O3 observations over the contiguous United States. We show that the evaluation of simulated timing of surface ozone maximum with observations provides another independent constraint on the model in addition to O3 concentrations. Over regions with massive biogenic isoprene emissions,O3 peak values are sensitive to the emissions of NOx but not VOCs; however, O3 peak time is sensitive to isoprene emissions and increasing isoprene emissions leads to earlier peak time. By such relationships and model evaluation with the observations, we find that the underestimation of soil NOx emissions leads to a low bias of simulated O3 peak value in the south, while the overestimation of biogenic isoprene emissions results in earlier than observed O3 peak time in the central, south, and southeast regions. The latter is corroborated by the evaluation using Ozone Monitoring Instrument observations of HCHO tropospheric columns.