CCN Activity and Hygroscopicity of Water Soluble Organic Carbon Extracted from Ambient Aerosol

Due to its atmospheric abundance and well-appreciated complexity, the contribution of water soluble organic particulate matter to the role of aerosol in cloud microphysics is both difficult and critical to assess. To complement and constrain more common laboratory and model based approaches to this issue, we performed measurements on Water Soluble Organic Carbon (WSOC) samples isolated from ambient aerosol. Briefly, this procedure consisted of collecting and combining several day-long, high-volume PM 2.5 filter samples; extracting the water soluble fraction; isolating the organic portion of the water soluble fraction using XAD 4 and XAD 8 HPLC column resins; and atomizing this resultant WSOC sample for CCN activity and hygroscopicity measurements. These measurements were conducted using a custom H-TDMA and an SMPS paired with a DMT-CCN counter. WSOC extracts were generated and analyzed from three locations: Mount Rainier National Park, summer, 2009; Acadia National Park, summer, 2011; Storm Peak Laboratory, Steamboat Springs, Colorado, summer, 2011. The average water interaction parameter, ‘kappa', was determined from both the hygroscopicity and CCN activity measurements for each project (given as hygroscopicity based ‘kappa'/CCN activity based ‘kappa'): Mount Rainier, 0.05/0.075; Acadia, 0.13/0.15; Storm Peak, 0.083/0.09. Our presentation will focus on adapting and contrasting these results to other current approaches.