Chemical composition and size distribution of wintertime aerosols in the atmosphere of Mt. Hua in central China

Abstract

TSP, PM10 and size-segregated aerosols were collected at the summit (2060 m, a.s.l.) of Mt. Hua in central China during the winter of 2009, and determined for organic (OC) and elemental carbon (EC), pH of water-extracts and inorganic ions. OC in TSP and PM10 are 6.9 ± 2.9 and 5.9 ± 2.5 μg m−3, while EC in TSP and PM10 are 0.9 ± 0.6 and 0.9 ± 0.5 μg m−3, respectively. SO42−, NO3−, NH4+ and Ca2+ are major ions in PM10 with concentrations of 5.8 ± 3.7, 2.7 ± 1.6, 1.6 ± 0.9 and 1.5 ± 0.7 μg m−3, respectively. OC/EC ratios (8.2 ± 3.1 in TSP and 6.6 ± 1.8 in PM10) at the mountaintop are 2–4 times higher than those in lowland surface, suggesting an enhanced transformation of organics from gas- to solid- phase because of an increased photochemical oxidation and/or an increased condensation due to lower temperature, as well as an increased organic input from mountain plant emission. Air mass backward trajectories showed that compared with those derived from north/northwest China aerosols transported from the south contained higher concentrations of SO42− and NH4+ and lower concentrations of Ca2+. Size distributions of NH4+ and K+ presented as an accumulation mode with a peak at 0.7–1.1 μm, in contrast to Ca2+ and Mg2+, which maximized at the size 4.7–5.8 μm as a coarse mode. SO42− and NO3− showed a bimodal pattern with a large peak at the range 0.7–1.1 μm and a small peak at the size of 4.7–5.8 μm, whereas Na+ and Cl− displayed a bimodal pattern with two equivalent peaks in the fine (<2.1 μm) and coarse (≥2.1 μm) ranges. pH values of the water-extracts demonstrate that aerosols originate from southern China are more acidic than those from the north/northwest, and the particles with a diameter of 0.7–1.1 μm are most acidic.