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

Authors

Christopher C. Miller, Harvard University
Daniel J. Jacob, Harvard University
Eloise A. Marais, Harvard University
Karen Yu, Harvard University
Katherine R. Travis, Harvard University
Patrick S. Kim, Harvard University
Jenny A. Fisher, University of WollongongFollow
Lei Zhu, Harvard University
Glenn M. Wolfe, NASA Goddard Space Flight Center, University of Maryland
Frank N. Keutsch, University of Wisconsin-Madison
Jennifer Kaiser, University of Wisconsin-Madison
Kyung-Eun Min, University of Colorado, National Oceanic and Atmospheric Administration
Steven S. Brown, National Oceanic and Atmospheric Administration, University of Colorado
Rebecca A. Washenfelder, National Oceanic and Atmospheric Administration
Gonzalo Abad, Harvard-Smithsonian Center For Astrophysics
Kelly Chance, Harvard-Smithsonian Center For Astrophysics

RIS ID

114615

Publication Details

Miller, C. Chan., 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., Brown, S. S., Washenfelder, R. A., Abad, G. & Chance, K. (2017). Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data. Atmospheric Chemistry and Physics, 17 8725-8738.

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 (NO_x ≡ 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.