Articles | Volume 15, issue 13
Atmos. Chem. Phys., 15, 7571–7583, 2015
Atmos. Chem. Phys., 15, 7571–7583, 2015

Research article 13 Jul 2015

Research article | 13 Jul 2015

Reassessing the ratio of glyoxal to formaldehyde as an indicator of hydrocarbon precursor speciation

J. Kaiser1, G. M. Wolfe2,3, K. E. Min4,5,a, S. S. Brown5,6, C. C. Miller7, D. J. Jacob7,8, J. A. deGouw4,5, M. Graus4,5, T. F. Hanisco3, J. Holloway4,5, J. Peischl4,5, I. B. Pollack4,5, T. B. Ryerson5, C. Warneke4,5, R. A. Washenfelder4,5, and F. N. Keutsch1,b J. Kaiser et al.
  • 1Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
  • 2Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
  • 3Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
  • 5Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
  • 6Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
  • 7Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
  • 8School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
  • anow at: School of Environmental Science and Engineering, Gwangju Institute for Science and Technology, Gwangju, Korea
  • bnow at: School of Engineering and Applied Sciences and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA

Abstract. The yield of formaldehyde (HCHO) and glyoxal (CHOCHO) from oxidation of volatile organic compounds (VOCs) depends on precursor VOC structure and the concentration of NOx (NOx = NO + NO2). Previous work has proposed that the ratio of CHOCHO to HCHO (RGF) can be used as an indicator of precursor VOC speciation, and absolute concentrations of the CHOCHO and HCHO as indicators of NOx. Because this metric is measurable by satellite, it is potentially useful on a global scale; however, absolute values and trends in RGF have differed between satellite and ground-based observations. To investigate potential causes of previous discrepancies and the usefulness of this ratio, we present measurements of CHOCHO and HCHO over the southeastern United States (SE US) from the 2013 SENEX (Southeast Nexus) flight campaign, and compare these measurements with OMI (Ozone Monitoring Instrument) satellite retrievals. High time-resolution flight measurements show that high RGF is associated with monoterpene emissions, low RGF is associated with isoprene oxidation, and emissions associated with oil and gas production can lead to small-scale variation in regional RGF. During the summertime in the SE US, RGF is not a reliable diagnostic of anthropogenic VOC emissions, as HCHO and CHOCHO production are dominated by isoprene oxidation. Our results show that the new CHOCHO retrieval algorithm reduces the previous disagreement between satellite and in situ RGF observations. As the absolute values and trends in RGF observed during SENEX are largely reproduced by OMI observations, we conclude that satellite-based observations of RGF can be used alongside knowledge of land use as a global diagnostic of dominant hydrocarbon speciation.

Final-revised paper