Meteorological and chemical characteristics of the photochemical ozone episodes observed at Cape D'Aguilar in Hong Kong

As in many metropolitan areas around the world, air pollution in Hong Kong is an increasing concern. In this paper the authors present the observations of ozone (O3) pollution episodes made at a nonurban coastal location in Hong Kong. Four O3episodes were observed in 1994, during which hourly averaged O3concentrations exceeded 100 ppbv and in one case reached 162 ppbv. Recirculation of urban air caused by the reversal of surface winds was found to be an important mechanism for transporting the "aged" urban plumes to the monitoring site. Concurrent measurements of CO, SO2, NO, and O3provided an insight to the chemical characteristics of the air masses, and the chemical data appeared to suggest that the high levels of O3during the episodes were produced in the urban plumes that were mainly characteristic of vehicle emissions. The relationship between O3and CO in two of the episodes may be represented by a linear approximation, and a nonlinear relationship between O3and CO was found in another. Ozone levels observed at the nonurban site were higher than those at two urban locations.