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Fourier transform-infrared studies of thin H2SO4/H2O films: Formation, water uptake, and solid-liquid phase changesFourier transform-infrared (FTIR) spectroscopy was used to examine films representative of stratospheric sulfuric acid aerosols. Thin films of sulfuric acid were formed in situ by the condensed phase reaction of SO3 with H2O. FTIR spectra show that the sulfuric acid films absorb water while cooling in the presence of water vapor. Using stratospheric water pressures, the most dilute solutions observed were greater than 40 wt % before simultaneous ice formation and sulfuric acid freezing occurred. FTIR spectra also revealed that the sulfuric acid films crystallized mainly as sulfuric acid tetrahydrate (SAT). Crystallization occurred either when the composition was about 60 wt% H2SO4 or after ice formed on the films at temperatures 1-4 K below the ice frost point. Finally, we determined that the melting point for SAT depended on the background water pressure and was 216-219 K in the presence of 4 x 10(exp -4) Torr H2O. Our results suggest that once frozen, sulfuric acid aerosols in the stratosphere are likely to melt at these temperatures, 30 K colder than previously thought.
Document ID
19950039659
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Middlebrook, Ann M.
(University of Colorado, Boulder, CO United States)
Iraci, Laura T.
(University of Colorado, Boulder, CO United States)
Mcneill, Laurie S.
(University of Colorado, Boulder, CO United States)
Koehler, Birgit G.
(University of Colorado, Boulder, CO United States)
Wilson, Margaret A.
(University of Colorado, Boulder, CO United States)
Saastad, Ole W.
(University of Colorado, Boulder, CO United States)
Tolbert, Margaret A.
(University of Colorado, Boulder, CO United States)
Hanson, David R.
(National Oceanic and Atmospheric Administration, Boulder, CO United States)
Date Acquired
August 16, 2013
Publication Date
November 20, 1993
Publication Information
Publication: Journal of Geophysical Research
Volume: 98
Issue: D11
ISSN: 0148-0227
Subject Category
Environment Pollution
Accession Number
95A71258
Funding Number(s)
CONTRACT_GRANT: NSF ATM-92-96067
CONTRACT_GRANT: NAG2-760
Distribution Limits
Public
Copyright
Other

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