An investigation of air-pollutant patterns under sea-land breezes during a severe air-pollution episode in Hong Kong

In this study, air-pollutant concentrations at a number of stations are analyzed during a severe air-pollution episode in Hong Kong on 29 and 30 December 1999. It is found that high levels of NOx, RSP and SO2 emitted from vehicles and the power plants in Hong Kong are mainly responsible for this episode. O-3 concentrations are much lower than the background values, indicating the chemical scavenging of O-3 caused by its precursor emissions from traffic and other sources in Hong Kong. Under the calm synoptic conditions, air-pollutant patterns are governed by the interaction of local circulations, the complex topography and the stabilities. During daytime, air pollutants are redistributed by several sea-breeze circulations developing in Hong Kong from different directions. Meanwhile, several convergence zones created by the different wind systems are found to be situated over some urban areas and new towns in the western part of Hong Kong. This significantly traps air pollutants in these locations. During the nighttime, the stably stratified flow over the complex topography leads to complex airflow patterns with light winds, consequently leading to pollutant accumulations. These mechanisms explain the main features of temporal and spatial variations of air-pollutant concentrations in Hong Kong. (C) 2002 Elsevier Science Ltd. All rights reserved.