Abstract
Abstract. Both observations and a 3-D chemical transport model suggest that surface ozone over populated eastern China features a summertime trough and that the month when surface ozone peaks differs by latitude and region. Source-receptor analysis is used to quantify the contributions of background ozone and Chinese anthropogenic emissions on this variability. Annual mean background ozone over China shows a spatial gradient from 55 ppbv in the northwest to 20 ppbv in the southeast, corresponding with changes in topography and ozone lifetime. Pollution background ozone (annual mean of 12.6 ppbv) shows a minimum in the summer and maximum in the spring. On the monthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbv in June north of the Yangtze River and in October south of it, which explains the peaks of surface ozone in these months. The summertime trough in surface ozone over eastern China can be explained by the decrease of background ozone from spring to summer (by −15 ppbv regionally averaged over eastern China). Tagged simulations suggest that long-range transport of ozone from northern mid-latitude continents (including Europe and North America) reaches a minimum in the summer, whereas ozone from Southeast Asia exhibits a maximum in the summer over eastern China. This contrast in seasonality provides clear evidence that the seasonal switch in monsoonal wind patterns plays a significant role in determining the seasonality of background ozone over China.
Highlights
Many nations set ambient air quality standards for surface ozone and regulate anthropogenic emissions of ozone precursors in order to protect public health and vegetation from the adverse effects of ozone pollution
The peak month of surface ozone differs by latitude and region, changing from October in the Pearl River Delta (PRD) to May in the Yangtze River Delta (YRD) and to June in the North China Plain (NCP)
With confidence in the model’s ability in simulating key features of ozone observed upwind, downwind and over China, we apply model sensitivity analyses to decompose total surface ozone (TO) into contributions from total background ozone (TBO), natural background (NBO), pollution background (PBO), and the enhancement from Chinese anthropogenic pollutants (CPO)
Summary
Many nations set ambient air quality standards for surface ozone and regulate anthropogenic emissions of ozone precursors in order to protect public health and vegetation from the adverse effects of ozone pollution. The present study uses a 3-D global model of tropospheric chemistry (GEOS-Chem) and its nested-grid version over East Asia to investigate some general features of the seasonal and spatial variations of surface O3 over China and to identify contributions of various source types (natural and anthropogenic) and regions (domestic and foreign) to its spatial distribution and seasonality. The modeling approach follows Fiore et al (2002) and is similar to the concept of source-receptor analysis which describes the sensitivity of surface ozone to a change in emissions from a source region or source category Based on this modeling approach, the following relationships will hold for surface ozone of the standard simulation (referred hereafter as to total ozone or TO): TO = TBO + CPO, where TBO = NBO + PBO. We focus on the nested-grid model results for 2001 and 2006 when observations were available
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