Articles | Volume 17, issue 14
Atmos. Chem. Phys., 17, 8725–8738, 2017
Atmos. Chem. Phys., 17, 8725–8738, 2017

Research article 18 Jul 2017

Research article | 18 Jul 2017

Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data

Christopher Chan Miller1, Daniel J. Jacob1,2, Eloise A. Marais1, Karen Yu2, Katherine R. Travis2, Patrick S. Kim1, Jenny A. Fisher3, Lei Zhu2, Glenn M. Wolfe4,5, Thomas F. Hanisco4, Frank N. Keutsch2,6, Jennifer Kaiser7,a, Kyung-Eun Min8,9,b, Steven S. Brown9,10, Rebecca A. Washenfelder8,9, Gonzalo González Abad11, and Kelly Chance11 Christopher Chan Miller et al.
  • 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 2School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 3School of Chemistry and School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia
  • 4Atmospheric Chemistry and Dynamics Lab, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 5Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
  • 6Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
  • 7Department of Chemistry, University of Wisconsin Madison, Madison, WI, USA
  • 8Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 9Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 10Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
  • 11Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
  • anow at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • bnow at: School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, South Korea

Abstract. Glyoxal (CHOCHO) is produced in the atmosphere by the oxidation of volatile organic compounds (VOCs). Like formaldehyde (HCHO), another VOC oxidation product, it is measurable from space by solar backscatter. Isoprene emitted by vegetation is the dominant source of CHOCHO and HCHO in most of the world. We use aircraft observations of CHOCHO and HCHO from the SENEX campaign over the southeast US in summer 2013 to better understand the CHOCHO time-dependent yield from isoprene oxidation, its dependence on nitrogen oxides (NOx  ≡  NO + NO2), the behavior of the CHOCHO–HCHO relationship, the quality of OMI CHOCHO satellite observations, and the implications for using CHOCHO observations from space as constraints on isoprene emissions. We simulate the SENEX and OMI observations with the Goddard Earth Observing System chemical transport model (GEOS-Chem) featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NOx conditions following the isomerization of the isoprene peroxy radical (ISOPO2). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NOx conditions due to prompt CHOCHO formation. SENEX vertical profiles indicate a free-tropospheric CHOCHO background that is absent from the model. The OMI CHOCHO data provide some support for this free-tropospheric background and show southeast US enhancements consistent with the isoprene source but a factor of 2 too low. Part of this OMI bias is due to excessive surface reflectivities assumed in the retrieval. The OMI CHOCHO and HCHO seasonal data over the southeast US are tightly correlated and provide redundant proxies of isoprene emissions. Higher temporal resolution in future geostationary satellite observations may enable detection of the prompt CHOCHO production under low-NOx conditions apparent in the SENEX data.

Short summary
The use of satellite glyoxal observations for estimating isoprene emissions has been limited by knowledge of the glyoxal yield from isoprene. We use SENEX aircraft observations over the southeast US to evaluate glyoxal yields from isoprene in a 3-D atmospheric model. The SENEX observations support a pathway for glyoxal formation in pristine regions that we propose here, which may have implications for improving isoprene emissions estimates from upcoming high-resolution geostationary satellites.
Final-revised paper