DELIQUESCENCE BEHAVIOR OF MULTICOMPONENT AEROSOLS

The deliquescence behavior of multicomponent aerosols has been studied extensively by measuring the particle size or weight growth at contro lled relative humidities. To our knowledge there has been no experimen tal investigation of the chemical composition of the aerosol surface a s a function of relative humidity, which is extremely important in und erstanding a number of issues in atmospheric chemistry and physics. Ra pid single-particle mass spectrometry (RSMS) has been used in this wor k to explore the deliquescence behavior of particles generated from Na Cl/KCl, NaCl/NaNO3, and (NH4)(2)SO4/NH4NO3 mixed solutions and then co nditioned at different relative humidities. Thermodynamic predictions of the crystallization/deliquescence behavior of each mixture were als o given. For NaCl/KCl and NaCl/NaNO3 mixtures, the data were generally consistent with thermodynamic analysis and earlier investigations. Th e results indicate that as the ambient relative humidity reaches the d eliquescence point of the system, the chemical composition of the part icle surface changes gradually with increasing relative humidity until the particle transforms completely to an aqueous droplet. The observe d deliquescence began at relative humidities somewhat lower than that predicted by equilibrium thermodynamics. This is probably due to the c racks on the particle surface. The deliquescence behavior of (NH4)(2)S O4/NH4NO3 mixtures observed was very complicated and was generally not consistent with thermodynamic predictions.