Wintertime Cooling and a Potential Connection with Transported Aerosols in Hong Kong during Recent Decades

Hong Kong is susceptible to aerosols transported from the pearl river delta when the prevailing flow is from the west. The surface air temperature shows a wintertime cooling trend during recent decades in Hongkong, particularly during the midday hours. Differently, it shows a summertime warming trend during recent decades. By examining the distinct winter versus summer trends in midday hour temperature under low cloud cover conditions in Hong Kong from 1979–2014, we found a close relationship between the temperature reduction during midday hours and increased aerosol loading in winter but not in summer. The consistency in turning point for both the increase in aerosol loading and the variation in winter-summer temperature differences in the late 1980s also supports their strong association. Quantitatively, aerosols over Hong Kong during the study period reduced surface DSR and midday temperatures by approximately 30 W m^-2 and 2.1°C for low cloud cover cases.