On the local and regional influence on ground-level ozone concentrations in Hong Kong

摘要

Hong Kong is a densely populated city situated in the fast developing Pearl River Delta of southern China. In this study, the recent data on ozone (O_3) and related air pollutants obtained at three sites in Hong Kong arc analy/ed to show the variations of O_3 in urban, sub-urban and rural areas and the possible regional influences. Highest monthly averaged O_3 was found at a northeastern rural site and lowest O_3 level was observed at an urban site. The levels of NO_x, CO, SO_2 and PM_(10) showed a different spatial pattern with the highest level in the urban site and lowest at the rural site. Analysis of chemical species ratios such as SO_2/NO_x and CO/NO_x indicated that the sites were under the influences of local and regional emissions to varying extents reflecting the characteristics of emission sources surround the respective sites. Seasonal pattern of O_3 is examined. Low O_3 level was found in summer and elevated levels occurred in autumn and spring. The latter appears different from the previous result obtained in 1996 indicating a single maximum occurring in autumn. Principal component analysis was used to further elucidate the relationships of air pollutants at each site. As expected, the O_3 variation in the northeastern rural area was largely determined by regional chemical and transport processes, while the O_3 variability at the southwestern suburban and urban sites were more influenced by local emissions. Despite the large difference in O_3 levels across the sites, total potential ozone (O_3 + NO_2) showed little variability. Cases of high O_3 episodes were presented and elevated O_3 levels were formed under the influence of tropical cyclone bringing in conditions of intense sunlight, high temperature and light winds. Elevated O_3 levels were also found to correlate with enhanced ratio of SO_2 to NO_x, suggesting influence of regional emissions from the adjacent Pearl River Delta region.