Characterizing the Hygroscopicity of Asian Continental Outflow Aerosols Measured During Four Field Campaigns at Island Coastal Sites in Korea

In order to characterize hygroscopicity of aerosols in Asian continental outflow, H-TDMA data obtained during the summer 2006, spring 2007, summer-autumn 2008 and summer 2009 field campaigns at the coastal sites in two remote islands in Korea were analyzed. The size-CCN measurement was made in the latter two campaigns. Submicron aerosol size distribution, cloud condensation nuclei (CCN) concentration and CCN number fraction were also measured for all campaigns. Average CCN concentrations at 1.0% supersaturation (S) for all the campaigns were over 2500 cm-3 and such high concentrations suggest that the islands were under continental influence for most of the campaign periods. Occasional aerosol growth events observed during each campaign also support the idea that the islands were under continental influence. Based on mixing state and size-resolved hygroscopicity information from H-TDMA, CCN closure was attempted for the two campaigns with sufficient simultaneous data in 2007 and 2008, with relative error of -8%±13% and -6%±24%, respectively. The size-CCN measurement showed larger hygroscopicity compared to H-TDMA measurement and resulted in relative error of 12%±33% when such information was used for the closure. The discrepancy between the two methods remains unanswered at this point. Several additional CCN closure was attempted with constant hygroscopicity of pure ammonium sulfate (κ=0.61), aged continental conditions (κ=0.3) based on review of previous worldwide measurements and campaign-averages for each campaign. It was found that while the closures can be achieved within average relative error of 20% (except for pure ammonium sulfate assumption) by such prescribed hygroscopicity information, the standard deviations of relative errors were mostly larger and the degrees of disagreement especially for CCN concentrations below 1000 cm-3 was always significantly larger than the aforementioned closures utilizing simultaneously measured hygroscopicity information.