Cloud Condensation Nuclei Activity at Jeju Island (Korea) in Spring

Abstract

We measured the number concentrations of cloud condensation nuclei (CCN) and the size distributions of CCN/CN (CN: condensation nuclei) ratios at supersatura- tions (SSs) of 0.097, 0.27, 0.58, and 0.97% at Jeju Island, Korea during March-April 2005. We made simultaneous measurements of aerosol inorganic ions, water-soluble or- ganic carbon (WSOC), organic carbon (OC), and elemental carbon (EC) inPM2.5. The CCN/CN ratios increased with in- creasing particle diameter, and the diameter at CCN/CN=0.5 was defined asD50. D50 represents the activation dry diame- ter of atmospheric particles. The averageD50 at SS=0.097% and 0.97% was 136±17nm and 31±3 nm, respectively. The temporal variation of D50 at SS=0.097% was correlated with the mass fraction of water-soluble components (inor- ganic ions + WSOC), indicating that the temporal variation of CCN activity was mainly controlled by changes in the water-soluble components fraction. The critical dry diam- eter (Dcrit), which is the threshold dry diameter for CCN activation, was calculated from the observed aerosol chemi- cal compositions by K¨ The D50 at SS=0.097% was correlated (r2=0.48) with cal- culated Dcrit, although Dcrit was larger than D50 by 20–29% on average. The systematic difference betweenD50 andDcrit could be caused by the size dependence of the aerosol chem- ical compositions or surface tension lowering caused by the mixing of water-soluble organic compounds. This difference ohler theory for comparison withD50. corresponds to a 27±14% uncertainty in the CCN number concentration estimated from the observed particle number size distribution.