Hygroscopic properties of atmospheric aerosol in Riverside, California

The hygroscopic properties of atmospheric aerosol were investigated by performing in‐situ optical measurements under controlled temperature and relative humidity conditions. Complementary measurements included ambient relative humidity and aerosol filter sampling. Measurements were performed in Riverside, California during the months of August and September, 1983. Experimental results indicate that ambient aerosol particles, with diameters less than 2 μm, exhibited deliquescence between 73 and 78% relative humidity during 52% of the measurements. During a one‐week intensive sampling period, ambient aerosol particles existed as droplets during 86% of the tests and were dry during the balance of those measurements. When ambient aerosol droplets were detected, they were supersaturated with respect to solute concentration during 71 % of tests and were otherwise subsaturated with respect to solute concentration. 1987 Blackwell Munksgaard