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Physical chemistry of the H2SO4/HNO3/H2O system - Implications for polar stratospheric cloudsPolar stratospheric clouds (PSCs) play a key role in stratospheric ozone depletion. Surface-catalyzed reactions on PSC particles generate chlorine compounds that photolyze readily to yield chlorine radicals, which in turn destroy ozone very efficiently. The most prevalent PSCs form at temperatures several degrees above the ice frost point and are believed to consist of HNO3 hydrates; however, their formation mechanism is unclear. Results of laboratory experiments are presented which indicate that the background stratospheric H2SO4/H2O aerosols provide an essential link in this mechanism: These liquid aerosols absorb significant amounts of HNO3 vapor, leading most likely to the crystallization of nitric acid trihydrate (NAT). The frozen particles then grow to form PSCs by condensation of additional amounts of HNO3 and H2O vapor. Furthermore, reaction probability measurements reveal that the chlorine radical precursors are formed readily at polar stratospheric temperatures not just on NAT and ice crystals, but also on liquid H2SO4 solutions and on solid H2SO4 hydrates. These results imply that the chlorine activation efficiency of the aerosol particles increases rapidly as the temperature approaches the ice frost point regardless of the phase or composition of the particles.
Document ID
19930072552
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Molina, M. J.
(NASA Ames Research Center Moffett Field, CA, United States)
Zhang, R.
(NASA Ames Research Center Moffett Field, CA, United States)
Wooldridge, P. J.
(NASA Ames Research Center Moffett Field, CA, United States)
Mcmahon, J. R.
(NASA Ames Research Center Moffett Field, CA, United States)
Kim, J. E.
(NASA Ames Research Center Moffett Field, CA, United States)
Chang, H. Y.
(NASA Ames Research Center Moffett Field, CA, United States)
Beyer, K. D.
(MIT Cambridge, MA, United States)
Date Acquired
August 16, 2013
Publication Date
September 10, 1993
Publication Information
Publication: Science
Volume: 261
Issue: 5127
ISSN: 0036-8075
Subject Category
Geophysics
Accession Number
93A56549
Funding Number(s)
CONTRACT_GRANT: NSF ATM-90-17150
CONTRACT_GRANT: NAG2-632
Distribution Limits
Public
Copyright
Other

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