HR: 1340h
AN: A23B-1255    [Abstracts]
TI: Deliquescence Measurements of Potassium Salts
AU: * Freney, E J
EM: efreney@asu.edu
AF: Arizona State University, School of Earth and Space Exploration and Department of Chemistry & Biochemistry, Tempe, AZ 85281, United States
AU: Martin, S T
EM: smartin@seas.harvard.edu
AF: Harvard University, School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Cambridge, MA 02138, United States
AU: Buseck, P R
EM: pbuseck@asu.edu
AF: Arizona State University, School of Earth and Space Exploration and Department of Chemistry & Biochemistry, Tempe, AZ 85281, United States
AB: Potassium compounds such as KCl, K₂SO₄, and KNO₃ are salts resulting from biomass burning. With time the number of aerosol particles containing KCl decreases, and the number of particles containing KNO₃ and K₂SO₄ increases. The transformation of KCl to K₂SO₄ and KNO₃ with aging of the smoke could lead to changes in the hygroscopic properties of the smoke particles and thus their cloud-nucleating potential. Similar reaction mechanisms are likely to be involved in the conversion of KCl in smoke particles as occur for NaCl in sea salt. Little experimental work has been published on the hygroscopic properties of potassium salts because of their high DRH values. Instruments that are commonly used to measure hygroscopic properties such as differential mobility analyzers or electrodynamic balances do not operate accurately at RH > 90%. Here we present data describing the hygroscopic properties of several fresh potassium salts, as well as laboratory generated mixed salts, using transmission and scanning electron microscopes (TEM and SEM). Both microscopes have environmental chambers that enable study of the interaction of water with single particles. DRH values for KCl, KNO₃ and K₂SO₄ were found to be 86%, 92%, and 97%, respectively. KNO₃ particles formed by atomization appear rounded and undergo continuous hygroscopic growth without a distinct deliquescence point. Similar results have been published for NaNO₃. In contrast, when KNO₃ powder is ground in a mortar and pestle and placed in the SEM, the grains appear euhedral and have a DRH at 92%, in agreement with literature values. It appears that KNO₃ particles formed by atomization will readily take up water at RH values below their DRH. Our results indicate that the hygroscopic properties of KNO₃ particles are influenced by their histories. Water associated with aged or mixed particles at RH's less than their DRH will affect how these particles uptake and react with gases.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting