Seasonal Trends of Aerosol Hygroscopicity and Mixing State in Clean Marine and Polluted Continental Air Masses Over the Northeast Atlantic

Five years of nearly continuous measurements aerosol hygroscopicity by a Humidified Tandem Differential Mobility Analyzer (HTDMA) at Mace Head research station are presented, making it the longest data set in marine environment and Northeast Atlantic region particular. The main goal this work was to examine seasonal patterns mixing state variety air masses. entire categorized into clean polluted continental sectors reveal contrasting physicochemical features. Distinct were revealed where sector significantly higher than that aerosol. median growth factors (GF) 1.67 1.31, respectively. Clean GF reached lowest values summer highest winter pointing an impact biological activity wind speed driven sea spray production hygroscopicity. Conversely, all sizes due decrease anthropogenic emission, enhanced photochemical aging, secondary inorganic formation. Wintertime aerosols both largely externally mixed, while summertime relatively internally mixed. A distinct subset near-hydrophobic Aitken mode particles smaller 50 nm diameter observed wintertime which most likely originated atmosphere based on evolution mass back trajectory clustering.