Characterization of PM_2.5and the major chemical components during a 1-year campaign in rural Guangzhou, Southern China

A 1-year campaign was conducted in the rural area of Guangzhou, a megacity in southern China, to collect fine particulate matter (PM2.5) from March 2012 to February 2013. The mass concentrations of PM2.5and the major chemical components including 6 water-soluble ions, organic carbon (OC), elemental carbon (EC), and 13 additional elements were measured. The annual average concentration of PM2.5was 44.2±25.8μg/m3. Sulfate was the most dominant component, accounting for 28.6% of PM2.5, followed by organic matter (21.9%). Both sea salt and crustal material accounted for only a small fraction of PM2.5(<5%). Seasonal enhancement of PM2.5was observed in autumn 2012, especially with high-PM2.5events (more than 100μg/m3) in October. The backward Lagrangian particle dispersion modeling (LPDM) and the cluster analysis of the back-trajectories indicate that the northern area is an important source region of long-range transport. An enhancement of PM2.5as well as sulfate, OC, and EC was observed in the samples with the influence of northern air masses. However, the footprint retroplume of the samples shows that the sources in the Pearl River Delta Region should also be considered, especially secondary aerosol formation and biomass/biofuel burning. Two high-PM2.5case studies show that both local and long-range transport can play important roles in the PM2.5elevation episode.