Sources of long-lived atmospheric VOCs at the rural boreal forest site, SMEAR II

Abstract

Abstract. In this study a long-term volatile organic compounds (VOCs) data set, measured at the SMEAR II (Station for measuring Ecosystem–Atmosphere Relations) boreal forest site at Hyytiälä, Finland during the years 2006–2011, was investigated. VOC mixing ratios were measured using proton transfer reaction mass spectrometry. Four-day backward trajectories and the Unmix 6.0 receptor model were used for source area and source composition analysis. Two major forest fire events, one in Eastern Europe and one in Russia, took place during the measurement period. The effect of these fires was clearly visible in the trajectory analysis, lending confidence to the method employed with this data set. Elevated volume mixing ratios (VMRs) of non-biogenic VOCs, e.g. acetonitrile and aromatic VOCs, related to forest fires were observed. Ten major source areas for long-lived VOCs (methanol, acetonitrile, acetaldehyde, acetone, benzene and toluene) were identified at the SMEAR II site. The main source areas for all the targeted VOCs were Western Russia, Northern Poland, Kaliningrad and Baltic countries. Industrial areas in Northern Continental Europe were also found to be source areas for certain VOCs. Both trajectory and receptor analysis showed that air masses from Northern Fennoscandia were less polluted with both the VOCs studied and with other trace gases (CO, SO2 and NOx) than areas of Eastern and Western Continental Europe, Western Russia and Southern Fennoscandia.