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Measurement of the water cycle in mixed ammonium acid sulfate particles
Abstract A single ammonium-hydrogen-sulfate particle is levitated in an evacuated quadrupole trap at room temperature and the temperature of an attached tube containing bulk water is slowly cycled introducing then removing water vapor. With increasing pressure the particle dissolves in stages, then grows as a solution droplet by water absorption. With decreasing pressure the droplet supersaturates, crystallizes, then dehydrates completely to return to its initial state. Particle mass, and thus composition, is measured continuously with an electrostatic balance. Twenty-six cycles were studied as solute composition ranged from ammonium bisulfate through letovicite to ammonium sulfate in roughly equal steps. Composition was changed in situ by reaction with ammonia at low partial pressure. With solute composition characterized by x = [NH4]/[SO4], deliquescence was found to occur at water activity a w = 0.394−0.029 (x− 1) for 1 ⩽ x < 1.5 and a w = 0.710−0.023(x−1.5) for 1.5 ⩽ x < 2. Particle growth occurs at deliquescence and subsequently is in excellent agreement with that predicted in a model proposed by Tang for dissolution of a two-component mixed solute. Water activities of the solution droplets are measured up to a w = 0.9. The results are compared with those predicted by the Zdanovskii-Stokes-Robinson method of interpolation from binary data and with those obtained using the mixing rule of Meissner and Kusik. Particle crystallization from supersaturated solution is analyzed thermodynamically using measured water activities, the Gibbs-Duhem equation, and classical nucleation theory. The specific free energy barrier to crystallization, ΔG/n, is found to increase from near zero to 0.04 eV as composition ranges from x = 1 to 2, where n is the number of formula units in the critical nucleus. New phase diagrams are presented and used to discuss the dynamics of mixed sulfate particles in the atmosphere.
Measurement of the water cycle in mixed ammonium acid sulfate particles
Abstract A single ammonium-hydrogen-sulfate particle is levitated in an evacuated quadrupole trap at room temperature and the temperature of an attached tube containing bulk water is slowly cycled introducing then removing water vapor. With increasing pressure the particle dissolves in stages, then grows as a solution droplet by water absorption. With decreasing pressure the droplet supersaturates, crystallizes, then dehydrates completely to return to its initial state. Particle mass, and thus composition, is measured continuously with an electrostatic balance. Twenty-six cycles were studied as solute composition ranged from ammonium bisulfate through letovicite to ammonium sulfate in roughly equal steps. Composition was changed in situ by reaction with ammonia at low partial pressure. With solute composition characterized by x = [NH4]/[SO4], deliquescence was found to occur at water activity a w = 0.394−0.029 (x− 1) for 1 ⩽ x < 1.5 and a w = 0.710−0.023(x−1.5) for 1.5 ⩽ x < 2. Particle growth occurs at deliquescence and subsequently is in excellent agreement with that predicted in a model proposed by Tang for dissolution of a two-component mixed solute. Water activities of the solution droplets are measured up to a w = 0.9. The results are compared with those predicted by the Zdanovskii-Stokes-Robinson method of interpolation from binary data and with those obtained using the mixing rule of Meissner and Kusik. Particle crystallization from supersaturated solution is analyzed thermodynamically using measured water activities, the Gibbs-Duhem equation, and classical nucleation theory. The specific free energy barrier to crystallization, ΔG/n, is found to increase from near zero to 0.04 eV as composition ranges from x = 1 to 2, where n is the number of formula units in the critical nucleus. New phase diagrams are presented and used to discuss the dynamics of mixed sulfate particles in the atmosphere.
Measurement of the water cycle in mixed ammonium acid sulfate particles
Spann, J.F. (author) / C.B., Richardson (author)
Atmospheric Environment ; 19 ; 819-825
1984-10-10
7 pages
Article (Journal)
Electronic Resource
English
Copper Corrosion Caused by Ammonium Sulfate and Sodium Sulfate Particles
| British Library Online Contents | 2002
Copper Corrosion Caured by Ammonium Sulfate and Sodium Sulfate Particles
| British Library Online Contents | 2002