Aerosol hygroscopicity influenced by seasonal chemical composition variations in the Arctic region

In this study, we quantified aerosol hygroscopicity parameter using aerosol microphysical observation data (κ phy ), analyzing monthly and seasonal trends in κ phy by correlating it with aerosol chemical composition over 6 years from April 2007 to March 2013 at the Zeppelin Observatory in Svalbard, Arctic region. The monthly mean κ phy value exhibited distinct seasonal variations, remaining high from winter to spring, reaching its minimum in summer, followed by an increase in fall, and maintaining elevated levels in winter. To verify the reliability of κ phy , we employed the hygroscopicity parameter calculated from chemical composition data (κ chem ). The chemical composition and PM 2.5 mass concentration required to calculate κ chem was obtained through Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) reanalysis data and the calculation of κ chem assumed that Arctic aerosols comprise only five species: black carbon (BC), organic matter (OM), ammonium sulfate (AS), sea salt aerosol less than a diameter of 2.5 μm (SSA 2.5 ), and dust aerosol less than a diameter of 2.5 μm (Dust 2.5 ). The κ chem had no distinct correlation but had a similar seasonal trend compared to κ phy . The κ chem value followed a trend of SSA 2.5 and was much higher by a factor of 1.6 ± 0.3 than κ phy on average, due to a large proportion of SSA 2.5 mass concentration in MERRA-2 reanalysis data. This may be due to the overestimation of sea salt aerosols in MERRA-2 reanalysis. The relationship between monthly mean κ phy and the chemical composition used to calculate κ chem was also analyzed. The elevated κ phy from October to February resulted from the dominant influence of SSA 2.5 , while the maximum κ phy in March was concurrently influenced by increasing AS and Dust 2.5 associated with long-range transport from mid-latitude regions during Arctic haze periods and by SSA mass concentration obtained from in-situ sampling, which remained high from the preceding winter. The relatively low κ phy from April to September can be attributed to low SSA 2.5 and the dominance of organic compounds in the Arctic summer. Either natural sources such as those of marine and terrestrial biogenic origin or long-range-transported aerosols may contribute to the increase in organic aerosols in summer, potentially influencing the reduction in κ phy of atmospheric aerosols. To our knowledge, this is the first study to analyze the monthly and seasonal variation of aerosol hygroscopicity calculated using long-term microphysical data, and this result provides evidence that changes in monthly and seasonal hygroscopicity variation occur depending on chemical composition. • Arctic aerosol hygroscopicity quantified using 6 years of microphysical data. • Arctic aerosol hygroscopicity exhibits seasonality. • High spring hygroscopicity attributed to sea salt, ammonium sulfate, and dust aerosol. • Low summer hygroscopicity linked to reduced sea salt and raised organic compounds.