The Effects of Humidity on Atmospheric Aerosols.

This Dissertation is composed of four papers concerning the effects of relative humidity on atmospheric aerosols. The first describes the construction and testing of a large thermal diffusion cloud chamber and dichotomous separator intended for the segregation of the sub-micrometer atmospheric aerosol into two fraction on the basis of the individual particle's ability to act as a cloud condensation nucleus (CCN). The second discusses the result of an experiment done with this apparatus on the urban aerosol of Seattle. The third describes the optical and aerodynamic properties of the dry aerosol produced by the evaporation of solution droplets composed of a deliquescent salt. The fourth demonstrates a method for improving the size resolution of measurements made on these aerosols by either aerodynamic or optical means: this is done by humidifying the aerosol to a known relative humidity above the deliquescent point prior to sizing.