Abstract
It has been previously established that photochemical smog occurring in the Pearl River Delta Region (PRD) was associated with stagnant meteorological conditions. However, the photochemical smog (17 July to 20 July 2005) induced by typhoon Haitang was associated with moderate wind speed and nonstagnant meteorological conditions. The dynamic process of this ozone episode was studied using an integrated numerical model, that is, a mesoscale meteorological model and Community Multiscale Air Quality (CMAQ) model. Model performance has been evaluated using both ground-based meteorological and air quality observations. Analysis of simulated wind fields and ozone budget has been performed. This dynamic process is summarized into three physical factors. First, the westerly wind placed Hong Kong directly downwind of the PRD emissions. Second, the convergence of wind flow stimulated a vertical local circulation near the surface layer. This recirculation allowed primary and secondary pollutants to accumulate. Third, the conditions of high air temperature and low humidity resulted in active photochemical reactions. These combined effects resulted in the formation of high ozone in this episode.
Highlights
Hong Kong is a subtropical coastal mega city located in the Pearl River Delta (PRD) region, which is one of the most rapidly urbanized and industrialized regions in China
Using an integrated modeling system, that is, Models3/Community Multiscale Air Quality (CMAQ), the formation mechanism of a high ozone episode that occurred in Hong Kong was examined
Simulation results provide a deeper understanding of the dynamics that contributed to photochemical smog
Summary
Hong Kong is a subtropical coastal mega city located in the Pearl River Delta (PRD) region, which is one of the most rapidly urbanized and industrialized regions in China. In the past two decades, air pollutant emissions from motor vehicles, power plants, industry, and infrastructure construction have been increasing due to rapid economic development. This has directly resulted in the deterioration of air quality as well as degradation in visibility. Lee et al [6] studied Hong Kong surface ozone episodes in the summer months between 1994 and 1999, while tropical cyclones dominated circulation patterns in the PRD and South/Central China regions. Huang et al [8] concluded that the synoptic patterns associated with tropical cyclones originating in the Western Pacific Ocean and the South China Sea were the most optimal weather conditions for the formation of ozone episodes in Hong Kong.
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