A preliminary study on measurements of black carbon in the atmosphere of northwest Qilian Shan.

Black carbon (BC) concentration and meteorological data are measured discontinuously from May 2009 to March 2011, at the Qilian Shan Station of Glaciology and Ecologic Environment (hereafter "QSSGEE"), located near the terminal of the Laohugou No.12 Glacier in northwestern Qilian Shan, China. We measured the daily, monthly and seasonal variations of BC concentration in the atmosphere and discussed the possible emission sources. Black carbon background concentration in this region varied in the range of 18-72 ng/m3 with the highest in summer and the lowest in autumn. The relations between BC concentration and surface wind direction indicated that BC concentration was higher when northwest wind prevails while lower when southeast wind prevails. Air masses backward trajectories showed the potential emission sources in the northwest. Significant positive correlations between daily mean BC concentration and relative humidity indicated that BC might be one of important cloud condensation nuclei. This hypothesis needs to be confirmed further through cloud microphysical features in this region.