Chemical Characteristics And Transport Of PM2.5at Mt. Lu

Atmospheric fine particulate matters (PM2.5) which are crucial factors resulting in haze, have significant effect on human health and climate change and have become the most serious atmospheric environmental problems in China at present. In this research, PM2.5samples were collected at Mt. Lu (1165m a.s.l), and chemical components of soluble/total trace elements and water soluble ions were measured. Bio-availability of trace elements and the influence factors of secondary ions were analysed, as well as the source and atmospheric transport of PM2.5at Mt. Lu.The monitoring campaign was divided into2periods: Aug.2011-Sep.2011and Mar.2012-May.2012. Indicators of PM2.5mass concentration, total/water soluble trace elements (including Be, Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, Pb) and water soluble ions (including Na+, NH4+, K+, Mg2+, Ca2+, SO42-, NO3-, F", Cl", NO2-) were analysed.During the period of observation, the average mass concentration of PM2.5was55.66±19.18μg/m3, comparable with other mountains’observed value and much lower than that of urban site. The main total trace elements were Al>Fe>Zn> Pb>Ba>As≈Mn, while water soluble trace elements were Zn>Al>Fe>Ba>Pb>Mn>As. The concentration of crustal elements were moderate, while Ba has a remarkable high concentration value. There were varying temporal variation discrepancies of each element, but the crustal elements were more impacted by dust weather than anthropogenic elements obviously.Enrichment factor(EF) analysis indicated that the trace elements were more enriched in water soluble part than their total state. Source of particulate matter was found to be the most essential factor influencing element solubility by analysing the relationship of solubility, EF value and concentration of each element, and the correlation of crustal element and solubility conformed to logarithmic inverse relationship while anthropogenic element had scarcely any relation with solubility, indicating the solubility of crustal elements was more likely to be impacted by element concentration. Because of high solubility and EF value, anthropogenic elements were more hazardous to human health and ecology environment than crustal elements.The predominant ions in PM2.5were SO42-(15.91±8.05μg/m3), NH4+(5.50±3.15μg/m3)fNO3-(1.17±1.48μg/m3), accounting for about93%of the total ion concentration. All ions’ concentration values except lower NO3-concentration were comparable with other similar mountain sites, however, concentrations of SO42-and NH41+were even higher than urban and rural sites. The spring and summer NO3-/SO42-ratio were0.12and0.04, far less than1, suggesting more PM2.5contribution of stationary emission like coal-fired power plant than mobile emission as vehicle exhaust. SO42-and NH41+had a highest correlation, which combined mainly as (NH4)2SO4and less NH4HSO4, while correlations between NO3-and other ions were much poor. Meanwhile, K+had good relevance with SO42-and NH41+, indicating the influence of biomass burning to PM2.5at Mt. Lu.Concentrations of SO42-and NH41+were higher during summer than spring, but NO3-was on the contrary. Meteorological factors were observed to effect secondary ions significantly, with less contribution of gas precursors. Photochemical reaction rate of SO2and NO2were accelerated by solar radiation during summer, and air temperature could effect NO3-much greater than SO42-. In addition, humidity had some contribution to liquid phase formation of SO4-, but no effect to NO3-. NH4+were mainly formed by neutralization with acidic components in PM2.5.Five main sources of PM2.5at Mt. Lu were identified using Principal component analysis, which were combustion emission, soil dust, vehicle emission, non-ferrous metal smelting and secondary nitrate. As the air trajectory analysis showed, Local air mass (L) and Northeast air mass (NE) effected PM2.5remarkably. North air mass (N) which originated from the north desert, made the highest contribution to crustal element but lower to secondary ions. Due to high pollution of industrial activity, NE mass brought PM2.5with vast water soluble ions and industrial elements. East air mass (E) which come from china east sea and went throught Yangtze River Delta region brought plenty of ions but few trace elements. Effected by summer monsoon, South air mass (S) had little influence on PM2.5except the element Ba. The highest frenquency of PM2.5(31.9%) were brought by L mass,which contributed to abundent SO42-, probably due to in situ oxidation of regional SO2. This study introduced the characteristics of trace elements and water soluble ions in PM2.5at Mt. Lu comprehensively, analysed the influence of different air mass, and had significant importance for researching the form transformation and transpot rules of air pollutants at high altitudes.