Mass and isotopic concentrations of water-insoluble refractory carbon in total suspended particulates at Mt. Waliguan Observatory (China)

Abstract

Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon (WIRC) component of total suspended particulates (TSP), collected weekly during 2003, as well as from October 2005 to May 2006 at the WMO-GAW Mt. Waliguan (WLG) site. The overall average WIRC mass concentration was (1183±120)ng/m3 (n=79), while seasonal averages were 2081±1707 (spring), 454±205 (summer), 650±411 (autumn), and 1019±703 (winter) ng/m3. Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer, although WIRC concentrations were typically higher, especially in winter and spring. The δ13C PDB value (−25.3±0.8)‰ determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion. No seasonal change in δ13C PDB was evident. The average percent Modern Carbon (pMC) for 14C in WIRC for winter and spring was (67.2±7.7)% (n=29). Lower pMC values were associated with air masses transported from the area east of WLG, while higher pMC values were associated with air masses from the Tibetan Plateau, southwest of WLG. Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event.