American Association for Aerosol Research - Abstract Submission

AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA

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A New Experimental Approach toward Determining Cloud Nucleating Activities of Haze Particles

SHUNSUKE NAKAO, Sonia Kreidenweis, Colorado State University

     Abstract Number: 560
     Working Group: Aerosols, Clouds, and Climate

Abstract
The atmospheric aqueous phase plays an important role in the interactions between atmospheric particles, cloud droplets, and gas-phase compounds. The presence of an aqueous phase may enhance secondary organic aerosol (SOA) formation from water-soluble organic compounds that are too volatile to partition to an organic phase solely based on volatility. Water may affect formation of oligomers, acting as a plasticizer that reduces organic aerosol viscosity. The hygroscopicity of an aerosol can be determined by measuring its activity in serving as a cloud condensation nucleus. A common experimental approach to evaluation of cloud-nucleating activity is to remove the aqueous phase before measurement, due to the technical need to know the amount of (dry) solute in the aerosol for correlation with the measured critical supersaturation. However, the drying step may lead to uncertainties such as changes in aerosol phase/shape, loss of semi-volatile compounds, and incomplete drying. This study eliminated the drying step, utilizing an additional chemical measurement to account for the presence of the aqueous phase. A humidity-controlled differential mobility analyzer was used to produce mono-disperse, equilibrated wet aerosol, and subsequently cloud nucleating activities and chemical compositions of wet particles were measured. The evaluation of this experimental approach using inorganic salts and low-volatile/semi-volatile organic compounds will be presented.