Trends of ambient fine particles and major chemical components in the Pearl River Delta region: Observation at a regional background site in fall and winter

In the fall and winter of 2007 to 2011, 167 24-h quartz filter-based fine particle (PM2.5) samples were collected at a regional background site in the central Pearl River Delta. The PM2.5showed an annual reduction trend with a rate of 8.58μgm-3(p<0.01). The OC component of the PM2.5reduced by 1.10μgm-3yr-1(p<0.01), while the reduction rates of sulfur dioxide (SO2) and sulfate (SO42-) were 10.2μgm-3yr-1(p<0.01) and 1.72μgm-3yr-1(p<0.01), respectively. In contrast, nitrogen oxides (NOx) and nitrate (NO3-) presented growth trends with rates of 6.73μgm-3yr-1(p<0.05) and 0.79μgm-3yr-1(p<0.05), respectively. The PM2.5reduction was mainly related to the decrease of primary OC and SO42-, and the enhanced conversion efficiency of SO2to SO42-was related to an increase in the atmospheric oxidizing capacity and a decrease in aerosol acidity. The discrepancy between the annual trends of NOxand NO3-was attributable to the small proportion of NO3-in the total nitrogen budget. Capsule abstract: Understanding annual variations of PM2.5and its chemical composition is crucial in enabling policymakers to formulate and implement control strategies on particulate pollution.