Articles | Volume 11, issue 22
Atmos. Chem. Phys., 11, 11867–11894, 2011

Special issue: MILAGRO/INTEX-B 2006

Special issue: Megacities: air quality and climate impacts from local to...

Atmos. Chem. Phys., 11, 11867–11894, 2011

Research article 30 Nov 2011

Research article | 30 Nov 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

A. Fried1, C. Cantrell2, J. Olson3, J. H. Crawford3, P. Weibring1, J. Walega1, D. Richter1, W. Junkermann4, R. Volkamer5, R. Sinreich5, B. G. Heikes6, D. O'Sullivan7, D. R. Blake8, N. Blake8, S. Meinardi8, E. Apel2, A. Weinheimer2, D. Knapp2, A. Perring9, R. C. Cohen9, H. Fuelberg10, R. E. Shetter2, S. R. Hall2, K. Ullmann2, W. H. Brune11, J. Mao12, X. Ren13, L. G. Huey14, H. B. Singh15, J. W. Hair16, D. Riemer13, G. Diskin17, and G. Sachse17 A. Fried et al.
  • 1The National Center for Atmospheric Research, Earth Observing Laboratory, 3450 Mitchell Lane, Boulder, CO, USA
  • 2The National Center for Atmospheric Research, Atmospheric Chemistry Division, 3450 Mitchell Lane, Boulder, CO, USA
  • 3NASA Langley Research Center, Hampton, VA, USA
  • 4Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
  • 5The University of Colorado, Dept. of Chemistry, Boulder, CO, USA
  • 6The University of Rhode Island, Narragansett, RI, USA
  • 7United States Naval Academy, Annapolis, MD, USA
  • 8University of California, Irvine, Irvine, CA, USA
  • 9University of California, Berkeley, Berkley, CA, USA
  • 10Florida State University, Tallahassee, Florida, USA
  • 11Pennsylvania State University, University Park, PA, USA
  • 12Harvard University, Cambridge, MA, USA
  • 13University of Miami, Miami, Fl, USA
  • 14Georgia Institute of Technology, Atlanta, GA, USA
  • 15NASA Ames Research, Moffett Field CA, USA
  • 16NASA Lidar Applications Group, Langley Research Center, Hampton, VA, USA
  • 17NASA Langley Research Center, Hampton, VA, USA

Abstract. Detailed comparisons of airborne CH2O 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 CH2O, 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 CH2O. 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 CH2O 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 CH2O 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 CH2O produced from unmeasured and multi-generation hydrocarbon oxidation compounds, particularly methylglyoxal, 3-hydroxypropanal, and butan-3-one-al.

Final-revised paper