Source apportionment of sulphate in the High Arctic by a 10 yr-long record from Gruvebadet Observatory (Ny-Ålesund, Svalbard Islands)

A long-term study of the chemical composition of Arctic aerosol has been carried out at the Gruvebadet Observatory located in Ny-Ålesund since 2010. The PM10 aerosol has been collected continuously every year on a daily/2-day basis, each covering at least the spring and summer months, and the ionic content was evaluated using simultaneously three IC-systems. In order to determine the contribution of different sources (sea spray, crustal, biogenic and anthropogenic) to the total sulphate budget, specific markers and characteristic marker-to-sulphate ratios were used (Na+, Ca2+ and methanesulphonate). The obtained data set was then compared with the one from the Zeppelin Observatory, also located in Ny-Ålesund. The anthropogenic fraction resulted to be the major component, reaching the highest value in March and April during the Haze period, followed by the sea salt, biogenic and crustal ones. The comparison between the two datasets confirms the seasonal trend of these fractions even though some differences in magnitude were observed, likely due to discrepancies in the timing and resolution of sampling campaigns. The temporal profile of the anthropogenic fraction, evaluated in both sites, showed no evident continuous trend from 2010 to 2019, although the 2017-19 period revealed higher concentration with respect to the previous years. Focusing on single months, two opposite trends in the sulphate budget along 10 years were observed for March against April and September. Whereas a decrease was observed in March, April and September showed an increase in the monthly mean concentration values. Finally, the correlation between the non-sea salt non-crustal sulphate fraction and ammonium was evaluated. An increase in the ammonia neutralizing effect, resulting in a decrease in aerosol acidity, was observed at GVB, from the 2010 to 2017, then stabilized. Conversely, a decrease in the concentration of ammonia was found in ZEP since 2015, leading to an increase of the nssSO42-/NH4+ ratio in the same period.