SURFACE OZONE PATTERN IN HONG-KONG

Surface ozone (O-3) and its precursors in rural and urban areas of Hon g Kong are analyzed through the seasonal, temporal, and spatial variat ion patterns. The seasonal O-3 shows a unique pattern with a major pea k in autumn and a trough in summer. The spring and winter seasons are the transition periods with a relatively small peak in spring. The sea sonal alternation of the prevailing oceanic and continental air masses , plus the climate system associated with the Asian monsoon system, ar e the governing factors for the temporal O-3 pattern in Hong Kong. The O-3 imported by these air masses is found to be the dominating factor for the fluctuation of ambient O-3 in Hong Kong. The aged air masses associated with the continental outflow from China carry with them ant hropogenic air pollutants emitted from the blooming industrial and urb an neighborhoods north of Hong Kong in Guangdong Province, China. Unde r favorable meteorological conditions for photochemical O-3 formation in southeast China, the O-3 level reaches a maximum in autumn. The abs ence of a local urban or a summer O-3 peak suggests that the local O-3 formation is not the dominant source of O-3 in summer. The absence of an elevated ground-level O-3 peak in the spring season is an indicati on that the stratospheric intrusion process of O-3 is not a significan t source of surface O-3 in Hong Kong. The authors' analysis also shows that the emission of O-3 precursors from motor vehicles and the compl ex topography within the territories has a local effect on the spatial O-3 distribution and diurnal O-3 pattern in Hong Kong.