Abstract:

 Based on the observational mass concentrations of surface ozone and its precursors (NO, NO₂, and CO) in Xi’an, the temporal variation of ozone pollution was analyzed, and the correlation analysis and fitting equations between ozone and some meteorological parameters were carried out. The results showed that the highest ozone concentration occurs in summer due to the effect of local photochemical reaction of ozone, and the number of pollution days caused by O₃-8h accounts for 1/3 of the total number of pollution days. In winter, the photochemical reaction of ozone becomes weak, but the emissions of its precursors increase, which results to the largest NO, NO₂, and CO concentrations. Diurnal variation of ozone concentrations is characterized by one peak around 16:00 and a low level at night, while the concentrations of NO, NO₂, and CO are lower at daytime and higher at  the night, showing two peaks for their diurnal variations. Ozone has a positive correlation with temperature and wind speed and a negative correlation with relative humidity. The concentrations of NO, NO₂, and CO have a negative correlation with wind speed. Under the control of the northeasterly, northerly, and easterly flows, ozone concentration usually increase due to the pollutant transport from the upwind direction. The fitting degree of ozone mass concentration and meteorological parameters in summer is high, which means the routine meteorological parameters can be used to predict the evolution of ozone concentration.