Measurements of cloud condensation nuclei and droplet activation kinetics in pollution-influenced arctic air masses during the spring and summer of 2008 (NASA ARCTAS / NOAA ARCPAC)

The Arctic is a climatically sensitive region of the globe; clouds and pollution persist for long periods of time, but little is known of their properties. As part of the 2008 International Polar Year, numerous field experiments were conducted in the Arctic to better understand all the components of the Arctic climate system. We present in-situ aircraft measurements of cloud condensation nuclei (CCN) from the NASA ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and NOAA ARCPAC (Aerosol, Radiation, and Cloud Processes affecting Arctic Climate) campaigns. CCN counters and aerosol sampling instruments were deployed on board the NASA DC-8, NASA P-3B, and NOAA WP-3D aircraft with over 50 combined flights representing a sampling region from Alaska to Greenland. During the spring intensive, aircraft sampled pristine arctic air, aged pollution transported from the mid-latitudes, and aged biomass burning plumes. During the summer, fresh and aged Canadian forest fire plumes were primarily sampled. Both CCN number concentration and activation kinetics were analyzed to determine whether organics present in the aerosol influence hygroscopicity and the activation kinetics. The data suggest that organics can have a strong influence on droplet growth kinetics (particularly for fresh biomass burning plumes and pollution layers transported from the mid-latitudes). The water-soluble organics also contribute significantly to the hygroscopicity, as including their effects dramatically improves CCN closure.