Relationship between intraseasonal variations of air pollution and meteorological variables in Hong Kong

Abstract

Intraseasonal variation is an important component in monsoon regions to which Hong Kong belongs. This study investigates the relationship between intraseasonal variations of air quality and precipitation, wind direction and wind speed in Hong Kong. The intraseasonal variations are depicted by fluctuations with period of 3–90 days. Air quality is represented using the air pollution index of 14 air quality monitoring stations. Meteorological variables, including precipitation, wind speed and wind direction, are measured at the Hong Kong Observatory. It is found that the relationship between intraseasonal variations of air pollution and meteorological factors displays a strong seasonal dependence. Comparison between 2010 and 2011 indicates that the intraseasonal relationship varies largely from year to year. While more precipitation tends to favour better air quality, the statistical relationship between intraseasonal precipitation and air quality variations is not necessarily robust. Although wind speed increase usually enhances the dispersion of air pollutants, leading to an improvement in air quality, the statistical relationship on intraseasonal variations is not robust in some seasons. While northerly is the dominant wind direction for air quality worsening in Hong Kong, severe air pollution can occur under other wind directions in some unusual situations. The complexity of the intraseasonal relationship indicates that the relative importance of different factors in Hong Kong air quality change varies from season to season and from year to year, and that the large-scale background change may modulate the roles of factors in air quality change.