Chemical characterization of aerosols at the summit of Mountain Tai in Central East China

摘要

PM2.5 and TSP samples were collected at the summit of Mountain Tai (MT) (1534 m a.s.l.) in spring 2006/2007 and summer 2006 to investigate the characteristics of aerosols over central eastern China. For comparison, aerosol samples were also collected at Tazhong, Urumqi, and Tianchi in Xinjiang in northwestern China, Duolun and Yulin in northern China, and two urban sites in the megacities, Beijing and Shanghai, in 2007. Daily mass concentrations of TSP and PM2.5 ranged from 39.6–287.6 μg m?3 and 17.2–235.7 μg m?3 respectively at the summit of MT. Averaged concentrations of PM2.5 showed a pronounced seasonal variation with higher concentration in summer than spring. 17 water-soluble ions (SO42, NO3, Cl, F, PO43, NO2, CH3COO, CH2C2O42, C2H4C2O42, HCOO, MSA, C2O42, NH4+, Ca2+, K+, Mg2+, Na+), and 19 elements of all samples were measured. SO42, NO3, and NH4+ were the major water-soluble species in PM2.5, accounting for 61.50 % and 72.65 % of the total measured ions in spring and summer, respectively. The average ratio of PM2.5/TSP was 0.37(2006) and 0.49(2007) in spring, while up to 0.91 in summer, suggesting that aerosol particles were primarily comprised of fine particles in summer and of considerable coarse particles in spring. Crustal elements (e.g., Ca, Mg, Al, Fe, etc.) showed higher concentration in spring than summer, while most of the pollution species (SO42, NO3, K+, NO2, NH4+, Cl, organic acids, Pb, Zn, Cd, and Cr) from local/regional anthropogenic emissions or secondary formation presented higher concentration in summer. The ratio of Ca/Al suggested the impact of Asian dust from the western deserts on the air quality in this region. The high concentration of K+ in PM2.5 (4.41 μg m3) and its good correlation with black carbon (r = 0.90) and oxalic acid (r = 0.87) suggested the severe pollution from biomass burning, which was proved to be a main source of fine particles over central eastern China in summer. The contribution of biomass burning to the fine particle at MT accounted for 7.56 % in spring and 36.71 % in summer, and even reached to 81.58 % on a day. As and Pb were two of the most enriched elements. The long-range transport of aerosols spread the heavy pollution from coal-mining/coal-ash to everywhere over China. Anthropogenic air-pollution was evidently rather severe at MT, though it has been declared by UNESCO to be a World Heritage site.