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

We apply the Regional chEmistry and trAnsport Model to analyze summertime O-3 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 O-3 concentrations. Over regions with massive biogenic isoprene emissions,O-3 peak values are sensitive to the emissions of NOx but not VOCs; however, O-3 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 O-3 peak value in the south, while the overestimation of biogenic isoprene emissions results in earlier than observed O-3 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. Plain Language Summary Surface ozone, which is produced by nitrogen oxides and volatile organic compounds in the daytime, adversely affects human health and vegetation growth. Observed ozone concentrations can be used to evaluate nitrogen oxides and volatile organic compound emissions by using their relationships with ozone concentrations. In this study, we show that the time when ozone reaches its daily maximum (peak time) is also related to nitrogen oxides and volatile organic compound emissions. We use a three-dimensional model to simulate ozone daily maximum concentrations (peak value) and peak time in July 2011 over the contiguous United States. Through model sensitivity analyses, we find that ozone peak values are more sensitive to nitrogen oxide emissions, while ozone peak time is more sensitive to volatile organic compound emissions in the eastern United States. By such relationships and the comparison between observations and model results, we find that the underestimation of soil nitrogen oxides emissions leads to a low bias of simulated ozone peak value in the south, while the overestimation of biogenic isoprene emissions results in earlier than observed ozone peak time in the central, south, and southeast regions. The simulated formaldehyde columns, which are higher than satellite measurements, confirm the latter.