In this paper, seasonal variation, diuranl and duration characteristics of ozone episodes in the urban and rural areas of Hong Kong are presented. The seasonal behavior of ozone episodes in this subtropical and coastal city is observed to be different from those measured in other parts of the world. Ozone episode spikes occur throughout the year with distinct and higher frequencies found in late summer and early autumn months (Aug-Oct). There are also frequent episodes in spring and winter months. Elevated ozone concentrations occur throughout the diurnal cycle and persist for only a short period. Higher frequencies are observed from early aftermoon to early evening (>60 ppb) and ligh ozone concentrations (>80 and 100 ppb) are found in the afternoon. The synoptic meteorological and weather conditions associated with these episode days can be classified into six main categories.
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