Physical, Chemical and Optical Properties of Fine Aerosol as a Function of Relative Humidity at Gosan, Korea during ABC-EAREX 2005

Abstract

The water uptake by fine aerosol in the atmosphere has been investigated at Gosan, Korea during ABCEAREX 2005. The concentration of inorganic ion and carbon components, size distribution, and light scattering coefficients in normal and dry conditions were simultaneously measured for PM2.5 by using a parallel integrated monitoring system. The result of this study shows that ambient fine particles collected at Gosan were dominated by water-soluble ionic species (35%) and carbonaceous materials (18%). In addition, it shows the large growth of aerosol in the droplet mode when RH is higher than 70%. Size distribution of the particulate surface area in a wider size range (0.07-17 μm) shows that the elevation of RH make ambient aerosol grow to be the droplet mode one around 0.6 μm or the coarse mode one, larger than 2.5 μm. Hygroscopic factor data calculated from the ratio of aerosol scattering coefficients at a given ambient RH and a reference RH (25%) show that water uptake began at the intermediate RH range, from 40% to 60%, with the average hygroscopic factor of 1.10 for 40% RH, 1.11 for 50% RH, and 1.17 for 60% RH, respectively. Finally, average chemical composition and the corresponding growth curves were analyzed in order to investigate the relationship between carbonaceous material fraction and hygroscopicity. As a result, the aerosol growth curve shows that inorganic salts such as sulphate and nitrate as well as carbonaceous materials including OC largely contribute to the aerosol water uptake.

Keywords

• pm2.5
• size distribution
• hygroscopic growth
• growth curve
• scattering coefficient