Concurrent observations of air pollutants at two sites in the Pearl River Delta and the implication of regional transport

Abstract. An intensive field measurement study was conducted simultaneously at a site within the inland Pearl River Delta (PRD) region (WQS) and a site in Hong Kong (TC) between 22 October and 1 December 2007. Ambient air pollutants measured included O3, NOx, CO, SO2, NMHCs, and carbonyls. The purpose is to improve our understanding of the interplay among local and regional air pollutants in the Hong Kong area, and the influence of regional transport on local air pollutants. The results indicate that the mean levels of air pollutants at the WQS site were much higher than those at the TC site, except NOx. Elevated CO levels were measured when the northerly monsoons enhanced mixing ratios at both sites, whereas high O3 episodes were usually observed when weather systems were relatively stable. Thirteen O3 episode days (daily O3 peak in excess of 122 ppbv) were monitored at WQS during the study period, while only 2 days were recorded at TC. The diurnal variations of air pollutants at the two sites were found to be rather different, suggesting different local and regional contributions. Ratio analyses for VOCs revealed that the air masses arriving at WQS were more aged than those arriving at TC, confirmed by the back trajectories analysis. In addition, the influence of regional transport from eastern China on the primary pollutants of Hong Kong was noticeable, whereas the air masses from the inland PRD region (e.g. Dongguan) had significant influence on the air pollutants at WQS. These results confirm that regional transport of air pollution has a complex and significant impact on local air pollutants in this region.