Analyzing Hygroscopic Particle Growth of West Antarctic Boundary Layer Aerosols during AWARE

The ARM West Antarctic Radiation Experiment (AWARE) included boundary layer aerosol measurements of humidified particle growth. Boundary layer aerosols can act as nuclei for cloud formation and have broader impacts on the Antarctic climate system by affecting albedo and other cloud properties. A humidified tandem differential mobility analyzer at McMurdo Station (77°5’S, 166°40’E) provided aerosol concentrations for five dry and humidified particle sizes with 90% relative humidity. These measurements provided particle growth factors, which are the ratio of the humidified and dry particle diameters for a specified relative humidity. The growth factors were also used to compute the single hygroscopicity parameter, k, a quantitative measure of water uptake and cloud condensation nuclei (CCN) activity. Measurements for this study were collected for two observational periods: 23 November – 20 December 2015 and 16 – 31 January 2016, for which local contamination events from diesel and aircraft were removed from the dataset. Statistical analysis conducted for the periods revealed consistent aerosol concentration distributions and hygroscopic properties with mean growth factor and k for all five dry diameter sizes (50, 100, 150, 200, 250 nm) of approximately 1.67 and 1.63 and k of 0.422 and 0.374 in the first and second periods respectively. Aerosol particles in the 100 – 150 nm dry diameter regime had notably larger hygroscopic growth as compared to larger particles in which growth distributions decreased in value with increased particle size. These hygroscopic measurements were consistent with particles that contain mixtures of ammonium, sulfate, salt, and organic components.