Water soluble fraction of Asian dust particles

The volume fraction (ε) of water soluble material in atmospheric aerosol particles is an important parameter related to their hygroscopicity and activation processes to form cloud and ice particles. To estimate ε of coarse dust particles, confocal scanning laser microscope was applied to measure the volume difference of individual particles before and after water dialysis directly. Individual particles (sphere equivalent diameter approx. 1–8 μm) of Asian reference dusts (CJ1 and CJ2) and atmospheric coarse particles during four Asian dust events were analyzed to ascertain ε. Median values of ε for CJ1 and CJ2 were, respectively, 29% and 13% with no size trend. Median values of ε for coarse aerosol particles during four dust events were 18–42%, which show nearly pure (low ε) to aged (higher ε possibly attributable to addition of sea salts and other water soluble salts) Asian dust. Dust particles with high ε are potentially important for acting as giant CCN. Therefore the aging of dust particles during transport might enhance the number of giant CCN over the North Pacific.