Hygroscopic Properties of Aerosol Particles in the Arctic

The hygroscopicity and volatility of aerosol particles in the Arctic were studied during the IPY-ICEALOT mission in March/April 2008 on board the R/V Knorr. A hygroscopicity tandem differential mobility analyzer (HTDMA) measured behind a thermodenuder scanning the temperature range 50-250C, thereby acquiring hygroscopic growth factors as a function of volatilization temperature. Every second scan the sample flow bypassed the thermodenuder and we measured ambient air. The sizes investigated by the HTDMA were 50, 100 and 150 nm, providing information of both Aitken and accumulation mode aerosol. On average during the cruise, the hygroscopic growth factors resembled those of ammonium sulfate. This is in line with data from a high resolution aerosol mass spectrometer (HR-AMS) which also sampled behind the thermodenuder, showing that the submicron aerosol was dominated by sulfate and oxygenated organics. The hygroscopic properties of the particles directly influence their size and therefore their radiative properties, and additionally determine the size at which a particle will activate and form a cloud droplet, contributing to the indirect cooling effect of the aerosol particles. A more detailed analysis will be performed, including case studies of continental outflow and comparisons with the HR-AMS and other chemical and physical measurements conducted on the ship.