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Title: Study on an ozone episode in hot season in Hong Kong and transboundary air pollution over Pearl River Delta region of China
Authors: Lam, KS 
Wang, TJ
Wu, CL
Li, YS 
Keywords: Air quality modeling
Photochemical smog
Transboundary transport
Issue Date: 2005
Publisher: Pergamon Press
Source: Atmospheric environment, 2005, v. 39, no. 11, p. 1967-1977 How to cite?
Journal: Atmospheric environment 
Abstract: An ozone (O 3) episode that occurred in Hong Kong during 18-22 August 1999 was investigated. This episode lasted nearly 2 days with Typhoon Sam located at 500 km away from Hong Kong in the southeast. The maximum ground-level concentration of O 3 reached 334 μg m -3, which violated the Hong Kong Air Quality Objective for O 3 (240 μg m -3, 1 h). The visibility was reduced to 3.2 km and UV radiation was reduced by 50%. Investigations of local meteorological factors revealed that cloudless sky with high temperature and weak wind was responsible for the formation of O 3, which was trapped by sea-breeze circulations developed under stable atmospheric conditions. Backward trajectories indicated that transboundary transport induced by synoptic northwest wind due to the cyclone system played a critical role in this episode. It carried aged air mass of O 3 as well as its precursors from areas with heavy emissions. The PATH (Pollutants in the Atmosphere and their Transport over Hong Kong) model system was used to simulate the flow field and O 3 concentration. The computed results were basically consistent with field observations. Comparison with measurements showed that the model generally performed well in simulating flow structure over coastal complex terrain. The computed O 3 peaks at most stations were underestimated by 10%, which might be due to the uncertainty in NO x and VOC emission inventory in the study region. The H 2O 2/HNO 3 ratio of 0.8-1.2 was identified to be the transition value for separating NO x- and VOC-sensitive regimes of O 3 chemistry. A process analysis further revealed the importance of horizontal transport in all physical and chemical evolution phases. Sensitivity study suggested that regional transport contributed to 60-90% of O 3 level at urban and rural areas of Hong Kong during the study period.
ISSN: 1352-2310
EISSN: 1873-2844
DOI: 10.1016/j.atmosenv.2004.11.023
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