Explicit diagnosis of the local ozone production rate and the ozone-NOx-VOC sensitivities

In the troposphere, ozone is a harmful gas compound to both human health and vegetation. Ozone is produced from the reaction of NOx (NO + NO2) and VOCs (volatile organic compounds) with light. Due to the highly nonlinear relationships between ozone and its precursors, proper ozone mitigation relies on the knowledge of chemical mechanisms. In this study, an observation-based method is used to simulate ozone formation and elucidate its controlling factors for a rural site on the North China Plain. The instantaneous ozone production rate is calculated utilizing a box model using the dataset obtained from the Wangdu campaign. First, the model was operated in a time-dependent mode to calculate the ozone production rate at each time stamp. The calculated ozone formation rate showed a diurnal average maximum value of 17 ppbv/h (1-h diurnal averaged). The contribution of individual peroxy radicals to ozone production was analyzed. In addition, the functional dependence of calculated P(O3) reveals that ozone production was in a NOx-limited regime during the campaign. Furthermore, the missing peroxy radical source will further extend NOx-limited conditions to earlier in the day, making NOx limitation dominate more of a day than the current chemical model predicts. Finally, a multiple scenarios mode, also known as EKMA (empirical kinetic modeling approach), was used to simulate the response of P(O3) to the imaginary change in precursor concentrations. We found that ozone production was in the NOx-limited region. However, the use of NO2 measured by the molybdenum converter and/or the absence of a peroxy radical source in the current chemical model could over-emphasize the VOC-limited effect on ozone production.