Long-term trends of the black carbon concentrations in the Canadian Arctic -: art. no. D15203

During the winter and spring the North American Arctic is impacted by anthropogenic black carbon (BC) in "Arctic Haze'' pollution from sources mainly located in Europe and Russia. This black carbon, while suspended in the atmosphere and in surface snow, has a significant effect on radiative forcing of the Arctic atmosphere. Routine ground-level observations of aerosol black carbon by optical absorption have been made at a Canadian Arctic location, Alert (82.5degreesN, 62.5degreesW), Nunavut since 1989. A 3-year intensive study was conducted to compare BC obtained by the thermal analysis and optical absorption methods, so that the seasonal variations in the "operational'' absorption cross sections of the aerosol could be determined. A time series analysis indicated that black carbon concentrations undergo a strong seasonal variation superimposed upon a long-term trend. The latter shows a decrease of about 55% in BC concentrations between 1989 and 2002 at Alert. Factors responsible for these trends such as changes in emissions and atmospheric transport support the hypothesis that BC emissions from the former USSR are mostly responsible for the observed decreasing trend. Transport from other sectors such as North America and Europe are not as prevalent at Alert.