High ozone concentrations have become the major summertime air quality problem in China. Extensive in situ observations are deployed for developing strategies to effectively control the emissions of ozone precursors, that is, nitrogen oxides (NO_X =NO+ NO_2) and volatile organic compounds (VOCs). The modeling analysis of in situ observations often makes uses of the dependence of ozone peak concentration on NO_X and VOC emissions, because ozone observations are among the most widely available air quality measurements. To extract more information from regulatory ozone observations, we extend the ozone-precursor relationship to ozone peak time in this study. We find that the sensitivities of ozone peak time and concentration are complementary for regions with large anthropogenic emissions such as China. The ozone peak time is sensitive to both VOC and NO_X emissions, and the sensitivity is nearly linear in the transition regime of ozone production compared to the changing ozone peak concentration sensitivity in this regime, making the diagnostics of ozone peak time particularly valuable. The extended ozone-precursor relationships can be readily applied to understand the effects on ozone by emission changes of NO_X and VOC and to assess potential biases of NO_X and VOC emission inventories. These observation constraints based on regulatory ozone observations can complement the other measurement and modeling analysis methods nicely. Furthermore, we suggest that the ozone peak time sensitivity we discussed here to be used as a model evaluation measure before the empirical kinetic modeling approach (EKMA) diagram is applied to understand the effectiveness of emission control on ozone concentrations.
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