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Trifluoroacetic Acid from Degradation of HCFCs and HFCs: A Three-Dimensional Modeling StudyTrifluoroacetic acid (TFA; CF3 COOH) is produced by the degradation of the halocarbon replacements HFC-134a, HCFC-124, and HCFC-123. The formation of TFA occurs by HFC/HCFC reacting with OH to yield CF3COX (X = F or CI), followed by in-cloud hydrolysis of CF to form TFA. The TFA formed in the clouds may be reevaporated but is finally deposited onto the surface by washout or dry deposition. Concern has been expressed about the possible long-term accumulation of TFA in certain aquatic environments, pointing to the need to obtain information on the concentrations of TFA in rainwater over scales ranging from local to continental. Based on projected concentrations for HFC-134a, HCFC-124, and HCFC-123 of 80, 10, and 1 pptv in the year 2010, mass conservation arguments imply an annually averaged global concentration of 0.16 micro g/L if washout were the only removal mechanism for TFA. We present 3-D simulations of the HFC/HCFC precursors of TFA that include the rates of formation and deposition of TFA based on assumed future emissions. An established (GISS[Harvard/ UCI) but coarse-resolution (8 deg latitude by 10 deg longitude) chemical transport model was used. The annually averaged rainwater concentration of 0.12 micro g/L (global) was calculated for the year 2010, when both washout and dry deposition are included as the loss mechanism for TFA from the atmosphere. For some large regions in midnorthern latitudes, values are larger. 0.15-0.20 micro g/L. The highest monthly averaged rainwater concentrations of TFA for northern midlatitudes were calculated for the month of July, corresponding to 0.3 - 0.45 micro g/L in parts of North America and Europe. Recent laboratory experiments have suggested that a substantial amount of vibrationally excited CF3CHFO is produced in the degradation of HFC-134a, decreasing the yield of TFA from this compound by 60%. This decrease would reduce the calculated amounts of TFA in rainwater in the year 2010 by 26%, for the same projected concentrations of precursors.
Document ID
20000011663
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kotamarthi, V. R.
(Atmospheric and Environmental Research, Inc. Cambridge, MA United States)
Rodriquez, J. M.
(Atmospheric and Environmental Research, Inc. Cambridge, MA United States)
Ko, M. K. W.
(Atmospheric and Environmental Research, Inc. Cambridge, MA United States)
Tromp, T. K.
(Atmospheric and Environmental Research, Inc. Cambridge, MA United States)
Sze, N. D.
(Atmospheric and Environmental Research, Inc. Cambridge, MA United States)
Prather, Michael J.
(California Univ. Irvine, CA United States)
Date Acquired
August 19, 2013
Publication Date
March 20, 1998
Publication Information
Publication: Journal of Geophysical Research
Publisher: American Geophysical Union
Volume: 103
Issue: D5
ISSN: 0148-0227
Subject Category
Environment Pollution
Report/Patent Number
Paper-97JD02988
Distribution Limits
Public
Copyright
Other

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