Chemical composition of the background aerosol at two sites in southwestern and northwestern China: potential influences of regional transport

摘要

Concentrations of organic carbon (OC), elemental carb on (EC), selected trace elements and water-soluble (WS) ions were determined for samples collected from August 2004 to February 2005 to assess the aerosol background at two remote sites in China. The OC and EC concentrations in PM10 from near the Tibetan Plateau at Zhuzhang (ZUZ) were comparable with other background sites, averaging 3.1 and 0.34 mu g m(-3), respectively, with no pronounced seasonality. At Akdala (AKD) on northern margin of the Zhungaer Basin, the average concentrations were similar (mean OC 2.9 mu g m(-3) and EC = 0.35 mu g m(-3)), but the concentrations were higher in winter. The aerosol mass at both, sites was dominated by OC and SO42-, but a stronger contribution from soil dust was observed at AKD. At ZUZ, NO3- showed a unique weather-related fluctuation in PM10 with a periodicity of similar to 1 week. Anthropogenic sources in the Sichuan Basin and southeastern Yunnan Province evidently influence ZUZ in summer and autumn while pollutants from Russia and the China-Mongolia border affect AKD nearly all year. The identification of these upwind sources demonstrates that transboundary transport needs to be taken into account when assessing air quality in remote parts of China.