Seasonal and spatial variability of surface ozone over China: contributions from background and domestic pollution

摘要

Both observations and a 3-D chemical transport model suggest that surfaceozone over populated eastern China features a summertime trough and that themonth when surface ozone peaks differs by latitude and region.Source-receptor analysis is used to quantify the contributions of backgroundozone and Chinese anthropogenic emissions on this variability. Annual meanbackground ozone over China shows a spatial gradient from 55 ppbv in thenorthwest to 20 ppbv in the southeast, corresponding with changes intopography and ozone lifetime. Pollution background ozone (annual mean of12.6 ppbv) shows a minimum in the summer and maximum in the spring. On themonthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbvin June north of the Yangtze River and in October south of it, which explains thepeaks of surface ozone in these months. The summertime trough in surfaceozone over eastern China can be explained by the decrease of backgroundozone from spring to summer (by ?15 ppbv regionally averaged over easternChina). Tagged simulations suggest that long-range transport of ozone fromnorthern mid-latitude continents (including Europe and North America)reaches a minimum in the summer, whereas ozone from Southeast Asia exhibitsa maximum in the summer over eastern China. This contrast in seasonalityprovides clear evidence that the seasonal switch in monsoonal wind patternsplays a significant role in determining the seasonality of background ozoneover China.