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 PM2.5 showed an annual reduction trend with a rate of 8.58 μg m(-3) (p<0.01). The OC component of the PM2.5 reduced by 1.10 μg m(-3) yr(-1) (p<0.01), while the reduction rates of sulfur dioxide (SO2) and sulfate (SO4(2-)) were 10.2 μg m(-3) yr(-1) (p<0.01) and 1.72 μg m(-3) yr(-1) (p<0.01), respectively. In contrast, nitrogen oxides (NOx) and nitrate (NO(3-)) presented growth trends with rates of 6.73 μg m(-3) yr(-1) (p<0.05) and 0.79 μg m(-3) yr(-1) (p<0.05), respectively. The PM2.5 reduction was mainly related to the decrease of primary OC and SO4(2-), and the enhanced conversion efficiency of SO2 to SO4(2-) was related to an increase in the atmospheric oxidizing capacity and a decrease in aerosol acidity. The discrepancy between the annual trends of NOx and NO3(-) was attributable to the small proportion of NO3(-) in the total nitrogen budget. CAPSULE ABSTRACT: Understanding annual variations of PM2.5 and its chemical composition is crucial in enabling policymakers to formulate and implement control strategies on particulate pollution.