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

Abstract

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 (NO x ≡ NO + NO 2 ), 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 (GEOSChem) featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NO x conditions following the isomerization of the isoprene peroxy radical (ISOPO 2 ). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHO-CHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NO x 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 isoPublished by Copernicus Publications on behalf of the European Geosciences Union. 8726 C. Chan Miller et al.: Glyoxal yield from isoprene prene 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-NO x conditions apparent in the SENEX data.

The 2005–2016 Trends of Formaldehyde Columns Over China Observed by Satellites: Increasing Anthropogenic Emissions of Volatile Organic Compounds and Decreasing Agricultural Fire Emissions

“…Values exceed 15 × 10 15 molecules cm −2 in megacity clusters, such as in the North China Plain (NCP), Pearl River Delta, Yangtze River Delta (YRD), and the Sichuan Basin. Also shown in Figure are the HCHO production rates from anthropogenic, biogenic, and open fire VOCs, as estimated by applying 1‐day HCHO production yields under high‐NO x conditions (Chan Miller et al, ) to emissions of individual VOCs from the bottom‐up MEIC, MEGAN, and FINN inventories, respectively. The 1‐day HCHO yields of individual VOCs and their contributions to the mean HCHO columns over China in May–September are listed in Table S1.…”

“…Note the lower scale for open fire emissions. The HCHO 1‐day yields from oxidation of different VOC species are from Chan Miller et al (), as given in Table S1. The May–September total HCHO production amounts during 2005–2016 from each source type in eastern China (east of 103°E, covering the map domain) are shown inset.…”

“…The simulated trend of HCHO columns in eastern China relative to 2005 is 1.0% a −1 , very similar to the trend of 1.1% a −1 with varying NO x emissions ( Figure S3b). This is because the prompt HCHO yield is relatively insensitive to NO x emission changes in the high-NO x regime (Chan Miller et al, 2017).…”

“…Biogenic emissions by vegetation, in particular of isoprene, are an additional source of VOCs (Fu & Liao, ; Guenther et al, ). A number of studies have used HCHO observations from space to infer VOC emissions and test inventories (Palmer et al, ; Stavrakou et al, ; Zhu et al, ), including specifically for China (Cao et al, ; Chan Miller et al, ; Fu et al, ). De Smedt et al () found a 3% a −1 HCHO increase over China between 1997 and 2009 that they attributed to changes in VOC emissions.…”

High-resolution inversion of methane emissions in the Southeast US using SEAC<sup>4</sup>RS aircraft observations of atmospheric methane: anthropogenic and wetland sources

“…We use a nested version of GEOS-Chem as described by Kim et al (2015) with 0.25 • × 0.3125 • horizontal resolution over the North America window and adjacent oceans (9.75-60 • N, 130-60 • W), driven by GEOS-FP assimilated meteorological data from the NASA Global Modeling and Assimilation Office (GMAO). The same version of the GEOS-Chem has been applied to simulation of other chemical observations from the SEAC 4 RS campaign (Kim et al, 2015;Fisher et al, 2016;Marais et al, 2016;Travis et al, 2016;Zhu et al, 2016;Yu et al, 2016;Chan Miller et al, 2017). The boundary conditions for the nested-grid simulation are from a 4 • × 5 • global simulation by using methane emissions optimized with three years of GOSAT satellite data.…”