Impact of typical meteorological conditions on air pollution over Pearl River Delta in autumn

Through analyzing the observed air quality index (AQI), pollutant concentrations, meteorological observations, synoptic charts and the WRF mesoscale numerical weather prediction results together, the impacts of weather conditions and meteorological characteristics on air pollution over the Pearl River Delta in October 2014 were investigated. Comparison with observations showed that WRF was able to reproduce temporal and spatial variations of ground-level and upper meteorological elements, with the correlation coefficient between simulated and observed average surface temperature, relative humidity and wind speed at nine cities of 0.90, 0.87 and 0.78, respectively. Analysis of all three pollution episodes in October showed that the bottom of the high-pressure control type and uniform pressure control type are the main meteorological factors of air pollution in the PRD. Low wind speed (<2 m·s^-1) and pollutant transport along with the northerly wind led to the increase of the pollutant concentrations in the PRD. In addition, O₃ was the primary pollutant when the relative humidity (RH) was lower than 65%, while PM_2.5 became the primary pollutant when the RH was higher than 70%. The photochemical reaction during high temperature conditions also caused the increase of air pollution in the PRD.