Effects of subgrid segregation on ozone production efficiency in a chemical model

Ozone production efficiency is a parameter used for evaluating the effect of anthropogenic NOx on tropospheric ozone. For this work, zero-dimensional simulations were run to compare the differences in ozone production efficiency when air masses of different origin were separated and when they were merged. The purpose of the simulations was to estimate whether coarsely resolved models might under or overpredict ozone production due to their blending of air masses of different origin. Cases were run for several combinations of air mass origin, different latitudes, times of year, air mass dilution ratios and initial gas concentrations. The main result of this study is that integrated ozone production may be overpredicted by as much as 60% in coarse-model grid cells exposed to different air masses. Under certain conditions, such as in rather finely resolved urban airshed models, ozone production may actually be underpredicted by about 20% in mid-latitudes during summer. The results imply that large-scale global models may have a difficult time correctly predicting ozone concentrations near, for instance, urban/free tropospheric boundaries, a conclusion supported by other studies examining parameters other than ozone production efficiency.