Integrated studies of a photochemical smog episode in Hong Kong and regional transport in the Pearl River Delta of China

Air pollution in Hong Kong has close relations to synoptic systems, especially continental high Pressure in cold season and tropical storms in the warm season. Here, it case study was performed of the characteristics of a photochemical pollution episode during March 27-31, 2000, in which the maximum concentrations of ozone (O-3), nitrogen oxides (NOx), carbon monoxide (CO), respirable Suspended particulates (RSP)and sulphur dioxide (SO2) reached 265 mu gm(-3). 2166 mu gm(-3) roadside), 5405 mu gm(-3), 349.3 mu gm(-3) and 221 mu gm(-3), respectively. The O-3/CO and O-3/NOx ratios were found to be 0.1 and 6.29, respectively, at rural site without significant correlation. At all urban site, moderate negative correlation was observed for O-3, CO, NOx, where the ratios of O-3/CO and O-3/NOx were relatively lower (0.03 and 0.21, respectively). The episode lasted 2 d in the Hong Kong territory and the Pearl River Delta (PRD) region. Synchronous meteorological and air monitoring data were adopted for analysis with focus on concentration variability, weather pattern, mechanisms of local photochemical production and regional transport. Our results indicate that clear skies with high temperature and low humidity Caused by the strong high-pressure system over South China as well as local emissions were attributable to the high O-3 level observed. In addition, backward trajectories and the O-3/NOx, O-3/CO ratios provided evidence that regional transport did play an important role in the formation of the episode. The MM5/STEM-2K1 and TAPM model systems were used to simulate the regional and urban O-3 pattern in PRD and Hong Kong. The modeling surface concentrations of O-3 were compared with the measurement front Hong Kong air quality monitoring network. which showed that the ground O-3 level was Underestimated 10-20% due to the uncertainty in emission data, simple chemical mechanism as well as MM5 meteorological prediction. Sensitivity Study revealed the strong cross-border transport over PRD region. which accounted for 50-90% of the observed O-3 level at nighttime and 40-70% at daytime in Hong Kong territory depending on site locations.