A nonurban ozone air pollution episode over eastern China: Observations and model simulations

Air quality data gathered from five nonurban sites in China over a 12-month period from August 1994 to August 1995, along with meteorological observat ions from the same region and period, are used to identify and characterize a nonurban ozone (O-3) pollution episode in China. Because of the influenc e of the Asian Monsoonal Circulation, high O-3 concentrations were not obse rved at the nonurban sites during the summer months. However, enhanced O-3 concentrations were observed during the other seasons, especially the fall and early winter. A more detailed inspection of the O-3 data during the per iod from October 15, 1994, to January 15, 1995, indicated the occurrence of a multiple-day episode in late October/early November when high O-3 concen trations were observed at all four monitoring sites located in eastern Chin a. Meteorological conditions during the episode were characterized by the p resence of a strong and stationary high-pressure ridge over eastern China; synoptic conditions quite similar to those observed during regional O-3 pol lution episodes over the United States, Canada, and Europe. An updated vers ion of the Regional Acid Deposition Model (RADM) driven by meteorological f ields derived from the Regional Climate Model (RegCM) and spatially disaggr egated anthropogenic emissions prepared by the Chinese Academy of Meteorolo gical Sciences is used to simulate 3 months of the observed O-3 data from C hina. Comparisons between observations and model calculations indicate that the model is able to reproduce some of the key features of the O-3 distrib ution and its relationship to the concentration of one primary pollutant (i .e., sulfur dioxide) provided the comparison is made using averaging times of several days or more. However, simulation of day-to-day variations in O- 3 at a given site was poorly correlated with observations. Model simulation s suggest that peak O-3 concentrations during this episode would respond to changes in NOx and VOC emissions in a spatially inhomogeneous manner. In g eneral, rural areas in southern China tend to be NOx-limited, but rural are as in northern China tend to be VOC-limited. The Yangtze Delta region, wher e the highest O-3 concentrations were observed and predicted to occur, was found to be transitional between VOC and NOx limitation.