Aerosol Chemical Characterization and Seasonal Variability at the Helmos Hellenic Atmospheric Aerosol and Climate Change Mountain Station

Abstract Observations of PM 1 nonrefractory species (NRS) were performed for a 12 month period at the high‐altitude Helmos Hellenic Atmospheric Aerosol and Climate Change ((HAC) 2 ) station at 2,314 m a.s.l. using real‐time online mass spectrometry. Aerosol‐cloud interactions were studied as well as influence from the planetary boundary layer (PBL) and air mass origin. Source apportionment was performed on the combined data set of organic species and inorganic ions to track the sources of PM 1 . Five factors were identified in all seasons; three factors composed mainly of organic aerosol (OA) (one primary‐related and two secondary OA) and two mainly of inorganic species (ammonium nitrate and ammonium sulfate). A 10‐fold increase in mass concentration levels was found during the summer compared to winter time, whereas PBL‐influenced aerosol mass concentration was up to 6 times higher than free tropospheric (FT). In‐cloud aerosol was found to vary between autumn and winter due to different cloud formation pathways between the two seasons. In autumn, in‐cloud scavenging resulted in much lower concentration levels compared to clear sky conditions, whereas in winter in‐cloud periods resulted in similar or even increased mass concentration for some species. Differentiation of interstitial aerosol from dried cloud droplets, possible by exploiting their variable penetration through the external PM 10 inlet during cloud events (in‐cloud regimes), showed that during winter time the fraction of the interstitials to dried droplets was much higher compared to autumn time.