ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-24435-2010 Importance of secondary sources in the atmospheric budgets of formic and acetic acids Paulot F. 1 Wunch D. 1 Crounse J. D. 2 Toon G. C. 3 Millet D. B. 4 DeCarlo P. F. 5 Vigouroux C. 6 Deutscher N. M. 7 González Abad G. 8 Notholt J. 9 Warneke T. 9 Hannigan J. W. 10 Warneke C. 11 12 de Gouw J. A. 11 12 Dunlea E. J. 12 De Mazière M. 6 Griffith D. W. T. 7 Bernath P. 8 Jimenez J. L. 12 13 Wennberg P. O. 1 Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, USA Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA University of Minnesota, Department of Soil, Water and Climate, St. Paul, Minnesota, USA Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland Belgisch Instituut voor Ruimte-Aëronomie, Brussels, Belgium School of Chemistry, University of Wollongong, Wollongong, Australia Department of Chemistry, University of York, York, UK Institute of Environmental Physics, Bremen, Germany National Center for Atmospheric Research, Boulder, Colorado, USA Aeronomy Laboratory, NOAA, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA 20 10 2010 10 10 24435 24497 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/10/24435/2010/acpd-10-24435-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/24435/2010/acpd-10-24435-2010.pdf

We present a detailed budget of formic and acetic acids, two of the most abundant trace gases in the atmosphere. Our bottom-up estimate of the global source of formic and acetic acids are ~1200 and ~1400 Gmol/yr, dominated by photochemical oxidation of biogenic volatile organic compounds, in particular isoprene. Their sinks are dominated by wet and dry deposition. We use the GEOS-Chem chemical transport model to evaluate this budget against an extensive suite of measurements from ground, ship and satellite-based Fourier transform spectrometers, as well as from several aircraft campaigns over North America. The model captures the seasonality of formic and acetic acids well but generally underestimates their concentration, particularly in the Northern midlatitudes. We infer that the source of both carboxylic acids may be up to 50% greater than our estimate and report evidence for a long-lived missing secondary source of carboxylic acids that may be associated with the aging of organic aerosols. Vertical profiles of formic acid in the upper troposphere support a negative temperature dependence of the reaction between formic acid and the hydroxyl radical as suggested by several theoretical studies.

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