Characteristics Of Chemical Elements In Atmospheric Particulates And Cloudwater At Mount Hengshan

In order to understand the regional background concentrations of trace elements in atmospheric particulate matter and cloud water in southern China, and explore the interaction between atmospheric particles and cloud water and the trend of cross-border transfer of pollutants, Hengshan meteorological station was chosen as the sampling location. From March to May2009,192cloud water samples and42total suspended particles (TSP) samples were collected, and the concentrations of SO42-and trace elements (Fe, Al and Pb, Mn, As, Ba, Cu, Ni, Se,, of Cd, Sb and Cr) were determined using IC-2500and ICP-MS, respectively.The results showed that concentrations of Fe and Al were highest in the atmospheric particulates at Mount Hengshan, accounted for more than80%of the total content of all elements measured, while concentrations of other elements were lower. Dust storms played an important role in the concentrations of TSP and Fe, Al, Mn, Ba, Ni and Cr. Solubility of Se, Cd, As were high, and it was easy for them to migrate to the aqueous phase. On the contrary, Fe and Al were difficult to dissolve into the the aqueous phase and their mobility and bioavailability were low, which were mostly present in the particle phase. TSP concentrations in southern China were lower than those in the northern areas, but compared to the developed countries it was more seriously polluted. Observation stations in China (including Mount Hengshan, Mount Taishan and Daihai) concentrations of As and Se in TSP were much higher than the values in the developed countries, and more attentions should be paid.Trace element concentrations in cloud water at Mount Hengshan were higher than those in the foreign background sites as a whole. During the observation period, variation of liquid water content (LWC) in cloud water was large, and the LWC increased firstly and then reduced with and the duration of the cloud events. The LWC in cloud water had a certain impact on concentrations of trace elements. As a whloe, the higher the LWC, the lower the concentrations. The high acidity of cloud water at Mount Hengshan would promote the dissolution of trace elements from the particle phase to aqueous phase, and might enhance the activities of trace elements in carbonate phase, oxidisable and reducible part which were originally relatively stable. The bioavailability of trace elements raised, which increased the pollution level of trace elements in cloud water.Influencing of the solubility of various compounds, acidity of cloud water, particle size, and so on, trace elements in TSP and cloud water showed different concentration distribution characteristics. Because trace elements in cloud water were mainly from the dissolution of aerosols, the initial samples of cloud events and aerosols just before the cloud events showed a good correlation. SO42-in cloud water was mainly from the dissolution of aerosols at Mount Hengshan, and contribution of oxidation in aqueous phase was only accounting for19.2%. The scavenging efficiency of cloud water for As, Pb and Cd in TSP were higher than other elements, and they were more easily cleared, while Fe, Al, Ba and Sb were difficult to clear out. Solubility of trace elements in atmospheric particulates played an important role in their scavenging efficiency. In addition, scavenging efficiencies may also be affected by many factors, including particle size distribution, LWC of cloud water, acidity, and so on.Through comparative analysis of trace elements concentrations of atmospheric particulate matter in different regional sites, we could find that in Northeast and North China, Fe, Al, Mn, and As, Se concentrations were of a high level; trace element concentrations were relatively high in the eastern and southern districts, and concentrations of Pb, Cu, Cr which came from traffic and industrial sources of pollutants were high; pollutants from dust and natural sources were the main components in the western region, and trace element concentrations in the aerosols were low as a whole. Influencing of different characteristics of regional industrial distribution in different districts and weather conditions at Mount Hengshan, contributions of air masses from different regions to trace element concentrations in cloud water at the observation site were quite different.