Surface Ozone Pattern in Hong Kong

Abstract

Surface ozone (O3) and its precursors in rural and urban areas of Hong Kong are analyzed through the seasonal, temporal, and spatial variation patterns. The seasonal O 3 shows a unique pattern with a major peak in autumn and a trough in summer. The spring and winter seasons are the transition periods with a relatively small peak in spring. The seasonal alternation of the prevailing oceanic and continental air masses, plus the climate system associated with the Asian monsoon system, are the governing factors for the temporal O 3 pattern in Hong Kong. The O3 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 anthropogenic air pollutants emitted from the blooming industrial and urban neighborhoods north of Hong Kong in Guangdong Province, China. Under favorable meteorological conditions for photochemical O3 formation in southeast China, the O 3 level reaches a maximum in autumn. The absence of a local urban or a summer O3 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 O3 peak in the spring season is an indication that the stratospheric intrusion process of O 3 is not a significant source of surface O3 in Hong Kong. The authors’ analysis also shows that the emission of O 3 precursors from motor vehicles and the complex topography within the territories has a local effect on the spatial O3 distribution and diurnal O 3 pattern in Hong Kong.