Measured Spectra of the Hygroscopic Fraction of Atmospheric Aerosol Particles

Abstract

The relation between dry diameter (X0) and critical supersaturation (Sc) for atmospheric submicron aerosol particles is investigated using a long term air sampling program at Rolla, Missouri. The particles are passed through an electrostatic aerosol size classifier, and then through an isothermal haze chamber. Results are reported in terms of an apparent volume fraction of soluble material, ?v defined such that for particles composed only of ammonium sulfate and water insoluble compounds, ?v is the actual volume fraction of soluble material. The probability distribution of ?v is found to be approximately Gaussian in the ?v range 0.2 to 1.3. The mean ?v is 0.5, for electrostatic aerosol classifier settings of 0.2, 0.3, and 0.4 ?m diameter.