Abstract
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.
Highlights
Though volatile organic compounds (VOCs) are present only in trace amounts in the atmosphere, their presence can drive the formation of pollutants such as secondary organic aerosol and ozone
We present absolute mixing ratios of HCHO and CHOCHO observed during daytime flights in the southeastern United States (SE US) and discuss the observed relationships of RGF with observed VOC precursors and anthropogenic influence
HCHO was measured at 1 Hz by the NASA In Situ Airborne Formaldehyde (ISAF) instrument (Cazorla et al, 2015), which is based on the FIber Laser-Induced Fluorescence (FILIF) technique (Hottle et al, 2009; DiGangi et al, 2011; Kaiser et al, 2014)
Summary
Though volatile organic compounds (VOCs) are present only in trace amounts in the atmosphere, their presence can drive the formation of pollutants such as secondary organic aerosol and ozone. The impact of VOC emissions on tropospheric chemistry depends on the speciation of emitted VOCs and their degradation pathways. As many as 105 different species of VOCs are estimated to have been measured in the atmo-. J. Kaiser et al.: Ratio of glyoxal to formaldehyde sphere (Goldstein and Galbally, 2007). While an air mass will usually contain a large variety of VOCs, often a particular species or subset of species (e.g., biogenics) will dominate the photochemistry, giving rise to the production of a range of oxygenated VOCs (OVOCs). OVOCs can provide downstream constraints on the rates and pathways of VOC oxidation
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