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, Frank N. Keutsch6, Jennifer Kaiser6,a, Kyung-Eun Min7,8,b, Steven S. Brown8,9, Rebecca A. Washenfelder7,8, Gonzalo González Abad10, and Kelly Chance101Department 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, University of Wisconsin Madison, Madison, WI, USA 7Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA 8Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA 9Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA 10Harvard-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
Received: 23 Nov 2016 – Accepted for review: 28 Nov 2016 – Discussion started: 29 Nov 2016
Abstract. Glyoxal (CHOCHO) is produced in the atmosphere by oxidation of volatile organic compounds (VOCs). It is measurable from space by solar backscatter along with formaldehyde (HCHO), another oxidation product of VOCs. 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 time-dependent yields from isoprene oxidation, their dependences on nitrogen oxides (NOx ≡ NO + NO2), the behaviour of the CHOCHO-HCHO relationship, the quality of OMI satellite observations, and the implications for using satellite CHOCHO observations as constraints on isoprene emission. We simulate the SENEX and OMI observations with the GEOS-Chem chemical transport model 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 emission. 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.
Miller, C. C., Jacob, D. J., Marais, E. A., Yu, K., Travis, K. R., Kim, P. S., Fisher, J. A., Zhu, L., Wolfe, G. M., Keutsch, F. N., Kaiser, J., Min, K.-E., Brown, S. S., Washenfelder, R. A., González Abad, G., and Chance, K.: Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1042, in review, 2016.