Light attenuation cross-section of black carbon in an urbanatmosphere in northern China

Fine particulate matter (PM2.5) samples were collected over two years in Xi&rsquo;an, China to investigate the relationships between the aerosol composition and the light absorption efficiency of black carbon (BC). Real-time light attenuation of BC at 880&nbsp;nm was measured with an aethalometer. The mass concentrations and elemental carbon (EC) contents of PM2.5 were obtained, and light attenuation cross-sections (&sigma;ATN) of PM2.5 BC were derived. The mass of EC contributed &sim;5% to PM2.5 on average. BC &sigma;ATN exhibited pronounced seasonal variability with values averaging 18.6, 24.2, 16.4, and 26.0&nbsp;m2/g for the spring, summer, autumn, and winter, respectively, while averaging 23.0&nbsp;m2/g overall. &sigma;ATN varied inversely with the ratios of EC/PM2.5, EC/[SO42&minus;], and EC/[NO3&minus;]. This study of the variability in &sigma;ATN illustrates the complexity of the interactions among the aerosol constituents in northern China and documents certain effects of the high EC, dust, sulfate and nitrate loadings on light attenuation.</p

Impact of Meteorological Parameters and Gaseous Pollutants on PM2.5 and PM10Mass Concentrations during 2010 in Xi’an, China

Mass concentrations of PM2.5 and PM10 from the six urban/rural sampling sites of Xi&rsquo;an were obtained during two weeks of every month corresponding to January, April, July and October during 2010, together with the six meteorological parameters and the data of two precursors. The result showed that the average annual mass concentrations of PM2.5 and PM10 were 140.9 &plusmn; 108.9 &micro;g m&ndash;3 and 257.8 &plusmn; 194.7 &micro;g m&ndash;3, respectively. Basin terrain constrains the diffusion of PM2.5 and PM10 concentration spatially. High concentrations in wintertime and low concentrations in summertime are due to seasonal variations of meteorological parameters and cyclic changes of precursors (SO2 and NO2). Stepwise Multiple Linear Regression (MLR) analysis indicates that relative humidity is the main factor influencing on meteorological parameter. Entry MLR analysis suggests that SO2 from local coal-burning power plants is still the primary pollutant. Trajectory cluster results of PM2.5 at BRR indicate that the entrained urban pollutants carried by the westerly or winter monsoon forms the dominant regional pollution sources in winter and spring. Ultraviolet (UV) aerosol index verified the source and pathway of dust storm in spring.</p