Chemical Composition and Sources of Aerosols in Finnish Arctic: 1964 - 2008

BC particles strongly absorb solar radiation and impact the Earth's climate. In fact, BC may be the second largest contributor to global warming after greenhouses gases. However, the magnitude of the climate forcing by BC is quite uncertain, with a global average value estimated up to + 1.1W m-2 [Bond et al., 2013]. Direct long-term atmospheric measurements in the Arctic are required to evaluate the BC trends, variability and contributions from local as well as distant regional sources. Such information will permit the development of a strategy to minimize its impact on the climate. In this paper we report the measurements of concentrations of black carbon, [BC], SO4, methane sulfonic acid (MSA) and trace elements in filters collected weekly for 47 consecutive years at Kevo, Finland (69o 45' N and 27o 02' E) from 1964-2010. The data provides the longest record of direct measurement of these particulate species, and should be invaluable in assessing the impact of changes in emissions from nearby as well as distant sources. BC concentrations were determined in individual filters using thermal-optical and optical methods. The mean winter, spring, summer, and autumn [BC] were, 339, 199, 127, and 213 ngm-3, respectively. Annual [BC] decreased from 645 in 1965 to 82 ngm-3 in 2010, a nearly 8-fold decrease. There was a sharp decrease in concentrations after 1988, around the time of the collapse of the USSR. An overall decreasing trend was observed for all anthropogenic elements except lead where there was a decline that reflects the shift to unleaded gasoline. The 47-year complete data set will be analyzed by Positive Matrix Factorization (PMF). The receptor modeling results will be connected with back trajectory data in a Potential Source Contribution Function (PSCF) analysis to determine possible source areas. The combination of PMF and PSCF will identify sources and their geographic locations. Initial PSCF results with MSA show the Barents Sea and related areas as the source region while BC and sulfate come largely from Russia and Eastern Europe. The sulfate concentrations parallel the changes in estimated emission rates in Europe and Russia, but the BC concentration/emissions relationships are less clear. MSA has a weak but statistically significant correlation with the sea surface temperature anomaly within the areas identified by the PSCF analysis suggesting responses to temperature changes by the phytoplankton dimethyl sulfide emissions.