Water Uptake Ability of Atmospheric Aerosols

Atmospheric aerosols have a direct impact on global climate and human health. Because aerosols are integral to the formation of clouds, it is important to understand their behavior in the atmosphere. An important property of aerosols is their ability to take on water in the atmosphere and increase in diameter or to act as cloud condensation nuclei (CCN). The diameter at which an aerosol will grow into a cloud droplet under specified conditions is known as its activation diameter. Experimental analysis of the activation diameters of certain organic aerosols has yielded inconsistent results among researchers. This may be due to aerosols which contain residual water and thus activate at smaller diameters than would be predicted for dry aerosols. In this work, many common organic atmospheric aerosols have been prepared in the lab and viewed under a scanning electron microscope. They were produced by atomizing a solution where the liquid droplets were subsequently dried with silica gel diffusion drying tubes. One aerosol, L-glutamic acid, surprisingly still appeared wet under the microscope ? conditions of near perfect dryness. To verify this, generated aerosols were viewed on both a hydrophilic and hydrophobic surface. Aerosols that were still wet were larger and spread out on the hydrophilic surface but were smaller and beaded up on the hydrophobic surface. Several aerosols, including glutaric and malonic acid, were found to contain residual water even after being sent through the drying tubes. Continuing research will be devoted to further drying of the wet aerosols to compare activation diameters of wet versus dry aerosols.