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 observations from the same region and period, are used to identify and characterize a nonurban ozone (O-3) pollution episode in China. Because of the influence of the Asian Monsoonal Circulation, high O-3 concentrations were not observed 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 period 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 concentrations were observed at all four monitoring sites located in eastern China. Meteorological conditions during the episode were characterized by the presence of a strong and stationary high-pressure ridge over eastern China; synoptic conditions quite similar to those observed during regional O-3 pollution episodes over the United States, Canada, and Europe. An updated version of the Regional Acid Deposition Model (RADM) driven by meteorological fields derived from the Regional Climate Model (RegCM) and spatially disaggregated anthropogenic emissions prepared by the Chinese Academy of Meteorological Sciences is used to simulate 3 months of the observed O-3 data from China. Comparisons between observations and model calculations indicate that the model is able to reproduce some of the key features of the O-3 distribution 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 simulations suggest that peak O-3 concentrations during this episode would respond to changes in NOx and VOC emissions in a spatially inhomogeneous manner. In general, rural areas in southern China tend to be NOx-limited, but rural areas in northern China tend to be VOC-limited. The Yangtze Delta region, where the highest O-3 concentrations were observed and predicted to occur, was found to be transitional between VOC and NOx limitation.