The Helmos Hellenic Atmospheric Aerosol & Climate Change station (or simply Helmos Mt) is operated by the National Center for Scientific research “Demokritos” (NCSR-Demokritos). The Aroania (or Helmos) mountainous region is a unique and optimal location for targeted studies of aerosol-cloud interactions. Aroania, situated in the Achaea Prefecture of Greece and is the 3rd highest mountain in the Peloponnese (summit at 2340 m amsl.) and hosts a NCSR-Demokritos monitoring station situated at 2314 m amsl. A unique characteristic of the Helmos High Altitude Monitoring Station (2314 m, 42°N 05' 30'', 34°E 14' 25'') is that it is a typical free tropospheric background site with very low influence from the surface polluted layers (Collaud Coen et al., ACP, 2018) and lies in a cross-road of different air masses (continental, Saharan, long-range biomass burning, volcanic, etc.).