| Summary: | Trace gas concentrations have been measured at Sevettijärvi in Finnish Lapland from 8 January 1992 to 10 July 2002. The maximum hourly SO2 concentrations decreased from around 500 ug m–3 in the first two years of the monitoring to 200–300 ug m–3 in the mid 1990s. The annual average SO2 concentrations decreased from about 5 ug m–3 to 3–4 ug m–3 during the same period when taking into account the years for which the data coverage was above 85%. For NO2 and O3 no clear trends were observed. The sources of all three trace gases were investigated using wind measurements and in the case of NO2 also using back trajectories. The analysis indicated that the source areas of NO2 and SO2 are to the east and north-east of the site, i.e., at Nikel-Zapolyarnyj industrial areas in Kola Peninsula, Russia. In addition to these, NO2 transported from other industrial and urban areas in Europe can also be observed at Sevettijärvi.
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