A Study of the Relationship of Chemical Composition and Humidity to Light Scattering by Aerosols

Abstract

A chemically pure aerosol of defined size distribution exhibits a unique growth pattern due to adsorption of water vapor, and to hygroscopic and/or deliquescence effects which are dependent upon relative humidity and which can be followed by measuring light scattering by the aerosol. A number of pure aerosols were produced artificially in the laboratory, subjected to a controlled humidity environment, and the magnitude of their light scattering coefficient measured continuously over a wide range of relative humidity (20–90%) with an integrating nephelometer. The results obtained can be applied to similar measurements on ambient air to yield qualitative chemical information and to determine the amount of visibility degradation which may be attributed to the association of water vapor with atmospheric aerosols. Examples of light scattering-relative humidity relationships for atmospheric aerosols are given. Abstract A chemically pure aerosol of defined size distribution exhibits a unique growth pattern due to adsorption of water vapor, and to hygroscopic and/or deliquescence effects which are dependent upon relative humidity and which can be followed by measuring light scattering by the aerosol. A number of pure aerosols were produced artificially in the laboratory, subjected to a controlled humidity environment, and the magnitude of their light scattering coefficient measured continuously over a wide range of relative humidity (20–90%) with an integrating nephelometer. The results obtained can be applied to similar measurements on ambient air to yield qualitative chemical information and to determine the amount of visibility degradation which may be attributed to the association of water vapor with atmospheric aerosols. Examples of light scattering-relative humidity relationships for atmospheric aerosols are given.