Aerosol Phase Transformation and Growth in the Atmosphere

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  • 1 Environmental Chemistry Division, Brookhaven National Laboratory, Upton, New York
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Abstract

The dynamic behavior of hygroscopic multicomponent aerosols under the influence of changing relative humidity in the atmosphere is investigated. Laboratory measurements of the deliquescence humidity as a function of temperature between 5° and 35°C are carried out with single aerosol particles individually suspended in an electrodynamic cell. The single-particle levitation cell is placed in a vacuum chamber that can be evacuated and backfilled with water vapor. The phase transformation of the aerosol particle is monitored by laser light scattering, and the relative humidity at the transition point is determined by directly measuring the water vapor pressure in the cell. Results are obtained for aerosol particles composed of binary mixtures of NACl, KCl, NaNO3, Na2SO4, and (NH4)S2SO4, which are common constituents of ambient aerosols. The measured temperature and composition dependence of the deliquescence properties agrees well with a theoretical model based on thermodynamic considerations. A study of aerosol particles containing more than two inorganic salts shows that the system is too complex for the present theoretical analysis. Further work is needed in order to elucidate and predict the complex nature of multicomponent aerosols.

Abstract

The dynamic behavior of hygroscopic multicomponent aerosols under the influence of changing relative humidity in the atmosphere is investigated. Laboratory measurements of the deliquescence humidity as a function of temperature between 5° and 35°C are carried out with single aerosol particles individually suspended in an electrodynamic cell. The single-particle levitation cell is placed in a vacuum chamber that can be evacuated and backfilled with water vapor. The phase transformation of the aerosol particle is monitored by laser light scattering, and the relative humidity at the transition point is determined by directly measuring the water vapor pressure in the cell. Results are obtained for aerosol particles composed of binary mixtures of NACl, KCl, NaNO3, Na2SO4, and (NH4)S2SO4, which are common constituents of ambient aerosols. The measured temperature and composition dependence of the deliquescence properties agrees well with a theoretical model based on thermodynamic considerations. A study of aerosol particles containing more than two inorganic salts shows that the system is too complex for the present theoretical analysis. Further work is needed in order to elucidate and predict the complex nature of multicomponent aerosols.

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