Abstract
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.
Highlights
Both sulfur and primary particle emissions have been decreasing largely all over Europe (Kupiainen and Klimont, 2006; Vestreng et al, 2007; Smith et al, 2011), resulting in improved air quality, decreased acid fallout (Berge et al, 1999) and weakened direct radiative forcing by aerosols (Liepert and Tegen, 2002)
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
We aim to address the following questions: (1) is the signature from decreased Kola emissions observable in new particle formation (NPF) characteristics and associated trends?, (2) what are the relative roles of the decreasing SO2 concentration and decreasing value of condensation sink on NPF?, (3) how do changes in primary particle emissions, NPF and subsequent aerosol growth influence cloud condensation nuclei concentrations?, and (4) how does the situation in eastern Lapland differ from that reported for western Lapland where the influence of Kola is expected to be much smaller
Summary
Both sulfur and primary particle emissions have been decreasing largely all over Europe (Kupiainen and Klimont, 2006; Vestreng et al, 2007; Smith et al, 2011), resulting in improved air quality, decreased acid fallout (Berge et al, 1999) and weakened direct radiative forcing by aerosols (Liepert and Tegen, 2002). Kyrö et al.: Effect of decreasing sulfur emissions from Kola Peninsula (Hamed et al, 2010; Makkonen et al, 2012). The SMEAR I station (Station for Measuring Ecosystem– Atmosphere Relations) (Hari et al, 1994) was established in 1991 to measure the impact of Kola sulfur emissions on the forests in eastern Lapland. Värriö Subarctic Research Station is located about 800 m south of SMEAR I
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