Hygroscopic properties and CCN characteristics of the aerosols measured at an island at the northwestern end of South Korea

Description

Aerosol total concentration (NCN), hygroscopic growth factor (GF), critical supersaturation (Sc), and CCN concentration (NCCN) were measured during August 8–30, 2009, at Baengnyeongdo (N 37°52’, E 124°53’), an island located at the northwestern end of South Korea where local anthropogenic disturbance is small and therefore suitable for monitoring Asian continental outflow. The Sc for aerosols of 81 and 110 nm mobility diameter was measured; monodisperse aerosols classified by a DMA were fed into both DMT CCN counter, whose supersaturation (S) varied over 0.07–1.3% range, and TSI CPC 3010; then the S was found where the NCCN/NCN ratio was at the mid-point. Such instrumentation setting required about 70 minutes of sampling time to obtain Sc measurement for one diameter. Since the local disturbance was small, required sampling time was short enough to obtain reliable Sc for most of the samples. GF at around 90% RH was measured by H-TDMA for 53, 113, 163, and 225 nm mobility diameters. The average hygroscopicity parameter kappa obtained from GF and Sc agreed within ±0.1, and the value was around 0.4~0.5 for most of the campaign. It is substantially higher than that obtained at the mega-city of Seoul, which was within the range of 0.01–0.21. The average NCCN was 4016±1437 cm-3, and the average NCCN/NCN ratio was 0.80±0.13. Both values are high compared to the ones measured about a year ago at Gosan (1421±783 and 0.53±0.17), located at the west coast of Jeju Island about 650 km south of Baengnyeongdo. Since both sites were strategically chosen for monitoring Asian continental outflow and identical instruments have been used over the same season, it is quite surprising to find such large differences between the two sites. More detailed analysis will be shown at the meeting.