Hygroscopic growth of ultrafine ammonium sulphate aerosol measured using an ultrafine tandem differential mobility analyzer

An ultrafine tandem differential mobility analyzer has been developed for measurements of the hygroscopicity of ultrafine aerosol particles, between 8 and 50 nm in mobility diameter. In this paper, the main operation features of the device are presented along with a detailed evaluation for the limits of its operation. The instrument is suitable for both laboratory-generated and atmospheric aerosol measurements. Hygroscopic growth data are presented for ammonium sulphate particles in the ultrafine size range, and comparisons are made with both experimental literature data and with theory. The data include determination of hygroscopic growth curves, deliquescence behavior, and hysteresis. These data will find applications in studies of the formation and growth of atmospheric aerosols.