Variations and vertical profiles of trace gas and aerosol concentrations and CO2 exchange in eastern Lapland

Abstract

This article presents results of measurements performed at Varrio environmental research station in Finland during 1992 to 1995. The aim of the station is to obtain more information on air quality as influenced by the Kola industrial areas and the effects on photosynthesis in subarctic climate. The diurnal and annual characteristics and correlations of measured species and their profiles were analyzed. Trace gas (SO2, O3, CO2) and particle concentrations, profiles and weather characteristics were measured continuously, and CO2 exchange of pine twigs was measured during summer periods using an automatic cuvette system. Practically, no local sources of pollutants existed in Varrio, however regularly occurring episodes of sulphur dioxide were observed during northeasterly winds. These events were presumed to be caused by transport from the Kola industrial areas. Some of the pollutant sources were located less than 200 km away from Varrio. Trajectories related to some typical pollution conditions are presented. Single episodes of SO2 and aerosols usually occurred simultaneously, but not always. Mean SO2 concentrations were lower during summer due to more effective deposition of SO2, sulfur dioxide conversion into sulfate and vertical mixing of air. The mean aerosol concentrations were higher during the summer than during the winter. An annual and a weak diurnal cycle were observed in ozone concentrations. The ozone concentrations in Varrio were not strongly dependent on the wind direction, and signs of long-range transport could not be clearly seen. Profile measurements of gases and particles showed the deposition to and emission from plants and soil. The carbon dioxide gradient was quite strong during the summer, which was related to the photosynthetic activity of the plants. A gradient in the ozone concentrations was also observed. The dependency of CO2 exchange on irradiation was clear.