Trends and source apportionment of atmospheric heavy metals at a subarctic site during 1996–2018

Atmospheric trace elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn) in particulate matter have been measured since 1996 at Pallas, a subarctic site in Finland. The results indicate a very low level of pollution as the concentrations were among the lowest measured in Europe. The annual average concentration during the whole time series (1996–2018), from the lowest values to the highest, was Co < Cd < Cr < As < V < Ni < Cu < Mn < Pb < Zn < Al < Fe, ranging from 0.02 to 20 ng m−3. For the priority elements As, Cd, Ni and Pb, the annual average concentration was 0.10, 0.02, 0.21 and 0.65 ng m−3, respectively, in 2018. The concentrations were compared with the results from three other sites in Finland, and a clear south-to-north decreasing gradient was found for most elements except for Ni, which was found to be mostly associated with emissions from the Kola Peninsula together with the trace elements of Cu, As and Co, as confirmed by the source apportionment analysis using positive matrix factorization. Cd, Pb, V and Zn were attributed to long-range transported (LRT) pollutants originating from combustion while Al, Fe and Mn were related to the soil origin. Gaseous Hg was included in the source analysis and was found in a separate LRT and marine factors. Considering the full time series, a trend analysis showed statistically significant decreasing trends for As, Cd, Co, Cu, Ni, Pb and V up to 64% in the whole period. Since 2010, six elements (Cd, Co, Ni, Pb, V, Zn) have continued the positive development of declining trends (P < 0.05) with changes between 25% and 53% during the period. No statistically significant increasing trends were observed for the studied elements.