1Department of Physics, University of Helsinki, Helsinki, Finland
2Air Quality Research, Finnish Meteorological Institute, Helsinki, Finland
3Department of Physics, Tampere University of Technology, Tampere, Finland
4Department of Environmental Sciences, University of Helsinki, Helsinki, Finland
5Department of Real Estate, Planning and Geoinformatics, Aalto University, Espoo, Finland
6Department of Applied Environmental Science and Bert Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
7Airmodus Oy, Pietari Kalmin katu 1 F 1, 00560 Helsinki, Finland
8Department of Forest Sciences, University of Helsinki, Helsinki, Finland
Received: 16 Sep 2013 – Discussion started: 26 Nov 2013
Abstract. The smelter industry in Kola Peninsula is the largest source of anthropogenic SO2 in the Arctic part of Europe and one of the largest within the Arctic domain. Due to socio-economic changes in Russia, the emissions have been decreasing especially since the late 1990s resulting in decreased SO2 concentrations close to Kola in eastern Lapland, Finland. At the same time, the frequency of new particle formation days has been decreasing distinctively at SMEAR I station in eastern Lapland, especially during spring and autumn. We show that sulfur species, namely sulfur dioxide and sulfuric acid, have an important role in both new particle formation and subsequent growth and that the decrease in new particle formation days is a result of the reduction of sulfur emissions originating from Kola Peninsula. In addition to sulfur species, there are many other quantities, such as formation rate of aerosol particles, condensation sink and nucleation mode particle number concentration, which are related to the number of observed new particle formation (NPF) days and need to be addressed when linking sulfur emissions and NPF. We show that while most of these quantities exhibit statistically significant trends, the reduction in Kola sulfur emissions is the most obvious reason for the rapid decline in NPF days. Sulfuric acid explains approximately 20–50% of the aerosol condensational growth observed at SMEAR I, and there is a large seasonal variation with highest values obtained during spring and autumn. We found that (i) particles form earlier after sunrise during late winter and early spring due to high concentrations of SO2 and H2SO4; (ii) several events occurred during the absence of light, and they were connected to higher than average concentrations of SO2; and (iii) high SO2 concentrations could advance the onset of nucleation by several hours. Moreover, air masses coming over Kola Peninsula seemed to favour new particle formation.
Revised: 31 Mar 2014 – Accepted: 03 Apr 2014 – Published: 05 May 2014
Kyrö, E.-M., Väänänen, R., Kerminen, V.-M., Virkkula, A., Petäjä, T., Asmi, A., Dal Maso, M., Nieminen, T., Juhola, S., Shcherbinin, A., Riipinen, I., Lehtipalo, K., Keronen, P., Aalto, P. P., Hari, P., and Kulmala, M.: Trends in new particle formation in eastern Lapland, Finland: effect of decreasing sulfur emissions from Kola Peninsula, Atmos. Chem. Phys., 14, 4383-4396, doi:10.5194/acp-14-4383-2014, 2014.