ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-11867-2011 Detailed comparisons of airborne formaldehyde measurements with box models during the 2006 INTEX-B and MILAGRO campaigns: potential evidence for significant impacts of unmeasured and multi-generation volatile organic carbon compounds Fried A. 1 Cantrell C. 2 Olson J. 3 Crawford J. H. 3 Weibring P. 1 Walega J. 1 Richter D. 1 Junkermann W. 4 Volkamer R. 5 Sinreich R. 5 Heikes B. G. 6 O'Sullivan D. 7 Blake D. R. 8 Blake N. 8 Meinardi S. 8 Apel E. 2 Weinheimer A. 2 Knapp D. 2 Perring A. 9 Cohen R. C. 9 Fuelberg H. 10 Shetter R. E. 2 Hall S. R. 2 Ullmann K. 2 Brune W. H. 11 Mao J. 12 Ren X. 13 Huey L. G. 14 Singh H. B. 15 Hair J. W. 16 Riemer D. 13 Diskin G. 17 Sachse G. 17 The National Center for Atmospheric Research, Earth Observing Laboratory, 3450 Mitchell Lane, Boulder, CO, USA The National Center for Atmospheric Research, Atmospheric Chemistry Division, 3450 Mitchell Lane, Boulder, CO, USA NASA Langley Research Center, Hampton, VA, USA Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany The University of Colorado, Dept. of Chemistry, Boulder, CO, USA The University of Rhode Island, Narragansett, RI, USA United States Naval Academy, Annapolis, MD, USA University of California, Irvine, Irvine, CA, USA University of California, Berkeley, Berkley, CA, USA Florida State University, Tallahassee, Florida, USA Pennsylvania State University, University Park, PA, USA Harvard University, Cambridge, MA, USA University of Miami, Miami, Fl, USA Georgia Institute of Technology, Atlanta, GA, USA NASA Ames Research, Moffett Field CA, USA NASA Lidar Applications Group, Langley Research Center, Hampton, VA, USA NASA Langley Research Center, Hampton, VA, USA 30 11 2011 11 22 11867 11894 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.net/11/11867/2011/acp-11-11867-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/11867/2011/acp-11-11867-2011.pdf

Detailed comparisons of airborne CH<sub>2</sub>O measurements acquired by tunable diode laser absorption spectroscopy with steady state box model calculations were carried out using data from the 2006 INTEX-B and MILARGO campaign in order to improve our understanding of hydrocarbon oxidation processing. This study includes comparisons over Mexico (including Mexico City), the Gulf of Mexico, parts of the continental United States near the Gulf coast, as well as the more remote Pacific Ocean, and focuses on comparisons in the boundary layer. Select previous comparisons in other campaigns have highlighted some locations in the boundary layer where steady state box models have tended to underpredict CH<sub>2</sub>O, suggesting that standard steady state modeling assumptions might be unsuitable under these conditions, and pointing to a possible role for unmeasured hydrocarbons and/or additional primary emission sources of CH<sub>2</sub>O. Employing an improved instrument, more detailed measurement-model comparisons with better temporal overlap, up-to-date measurement and model precision estimates, up-to-date rate constants, and additional modeling tools based on both Lagrangian and Master Chemical Mechanism (MCM) runs, we have explained much of the disagreement between observed and predicted CH<sub>2</sub>O as resulting from non-steady-state atmospheric conditions in the vicinity of large pollution sources, and have quantified the disagreement as a function of plume lifetime (processing time). We show that in the near field (within ~4 to 6 h of the source), steady-state models can either over-or-underestimate observations, depending on the predominant non-steady-state influence. In addition, we show that even far field processes (10–40 h) can be influenced by non-steady-state conditions which can be responsible for CH<sub>2</sub>O model underestimations by ~20%. At the longer processing times in the 10 to 40 h range during Mexico City outflow events, MCM model calculations, using assumptions about initial amounts of high-order NMHCs, further indicate the potential importance of CH<sub>2</sub>O produced from unmeasured and multi-generation hydrocarbon oxidation compounds, particularly methylglyoxal, 3-hydroxypropanal, and butan-3-one-al.

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