Effects of 20-100 nanometre Particles on Liquid Clouds in the Clean Summertime Arctic

Observations addressing effects of aerosol particles on summertime Arctic clouds are limited. An airborne study, carried out during July, 2014 from Resolute Bay, Nunavut, Canada, as part of the Canadian NETCARE project, provides an in-situ look into some effects of aerosol particles on liquid clouds in the clean environment of the Arctic summer.  Median cloud droplet number concentrations (CDNC) from 62 cloud penetrations are 10 cm^-3 for low-altitude cloud (cloud topped below 200 m) and 101 cm^-3 for higher-altitude cloud (cloud based above 200 m). The median lower activation size of aerosol particles is close to 50 nm diameter, and particles as small as 20 nm activated in the higher-altitude clouds consistent with generally higher supersaturations for those clouds inferred from comparison of the CDNC with cloud condensation nucleus measurements. Overall, particles with diameters from 20 nm to 100 nm exert a relatively strong influence on the CDNC within this exceedingly clean environment. CDNC formed on particles from natural sources, estimated using constraints on CO and particle mass concentrations, range between 16 cm^-3 and 160 cm^-3.  These observations offer the first wide-ranging reference for the aerosol cloud albedo effect in the summertime Arctic.