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A New Parameterization of H2SO4/H2O Aerosol Composition: Atmospheric ImplicationsRecent results from a thermodynamic model of aqueous sulfuric acid are used to derive a new parameterization for the variation of sulfuric acid aerosol composition with temperature and relative humidity. This formulation is valid for relative humidities above 1 % in the temperature range of 185 to 260 K. An expression for calculating the vapor pressure of supercooled liquid water, consistent with the sulfuric acid model, is also presented. We show that the Steele and Hamill [1981] formulation underestimates the water partial pressure over aqueous H2SOI solutions by up to 12% at low temperatures. This difference results in a corresponding underestimate of the H2SO4 concentration in the aerosol by about 6 % of the weight percent at approximately 190 K. In addition, the relation commonly used for estimating the vapor pressure of H2O over supercooled liquid water differs by up to 10 % from our derived expression. The combined error can result in a 20 % underestimation of water activity over a H2SO4 solution droplet in the stratosphere, which has implications for the parameterization of heterogeneous reaction rates in stratospheric sulfuric acid aerosols. The influence of aerosol composition on the rate of homogeneous ice nucleation from a H2SO4 solution droplet is also discussed. This parameterization can also be used for homogeneous gas phase nucleation calculations of H2SO4 solution droplets under various environmental conditions such as in aircraft exhaust or in volcanic plumes.
Document ID
19990063745
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Tabazadeh, Azadeh
(NASA Ames Research Center Moffett Field, CA United States)
Toon, Owen B.
(Colorado Univ. Boulder, CO United States)
Clegg, Simon L.
(East Anglia Univ. Norwich, United Kingdom)
Hamill, Patrick
(San Jose State Univ. CA United States)
Date Acquired
August 19, 2013
Publication Date
August 1, 1997
Publication Information
Publication: Geophysical Research Letters
Publisher: American Geophysical Union
Volume: 24
Issue: 15
ISSN: 0094-8534
Subject Category
Environment Pollution
Report/Patent Number
Paper-97GL01879
Distribution Limits
Public
Copyright
Other

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