Temporal variability of trace metal mobility of urban participate matter from Beijing - A contribution to health impact assessments of aerosols

摘要

The total element concentration and the chemical fractionation of 18 elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Rb, Sr, Ti, V, Zn) in total suspended particulate matter (TSP) from Beijing, China, were studied for a period of three years (July 2005-May 2008, n = 35). Additionally, particulate matter smaller than 2.5 urn (PM_(2.5)) was included in the study (February 2005-September 2007, n = 32). A chemical sequential extraction scheme according to Fernandez Espinosa et al. (2002) was applied to assess the speciation and potential mobility of the elements. Four different fractions were distinguished, which can be classified as: (fl) water-extractable, (f2) bound to carbonates, oxides and reducible metals, (f3) bound to organic matter, oxidisable and sulfidic metals, and (f4) residual fraction. The chemical speciation results illustrated that potential toxic metals like Zn (41%), Cd (40%), Mn (32%), and As (29%) were detectable to a high percentage in the water-soluble fraction (fl) of TSP samples and consequently are especially harmful to the environment and exposed people. Lead and Cu in TSP samples showed highest extractability in fraction f2 (53% and 23%, respectively) and can also be considered as mobile with a negative impact on the environment and the human health. Fine particles (PM_(2.5)) showed comparable results with sometimes higher percentages in the highly mobile fraction fl, for example for As (52%). Anthropogenic sources, such as industry and traffic, played an important role for overall atmospheric pollution throughout the year. Additionally, these more or less constant emissions were superimposed by seasonal sources, especially coal combustion in winter and geogenic dust in spring. Coal combustion proved to be a source especially relevant for the toxic and mobile elements Cd, As and Pb. The study illustrated that special attention has to be taken to the mentioned elements and their related sources for health impact assessments and when planning mitigation measures for urban atmospheric pollution and for providing a sustainable development of cities and megacities.