Retrieval of Glyoxal from the Ozone Monitoring Instrument: Implications for Volatile Organic Compound Emissions Constraints

Abstract

Glyoxal (CHOCHO) and formaldehyde (HCHO) are short lived products of non-methane volatile organic compound (NMVOC) oxidation. Satellite HCHO observations have been used extensively for constraining NMVOC emissions, but the use of space-based CHOCHO observations has been limited by inconsistencies with ground based observations, and a limited understanding of CHOCHO yields from NMVOC species. This thesis describes a new satellite retrieval of CHOCHO for the Ozone Monitoring Instrument (OMI). The GEOS-Chem chemical transport model is used to interpret the new OMI observations, and understand relationships between CHOCHO and HCHO for different NMVOC sources. Previous work suggest that CHOCHO retrievals are highly sensitive to the position of the spectral window chosen for fitting. The fit window dependence is systematically tested on real and simulated OMI spectra. The observed dependence is consistent with a combination of errors from reference cross section uncertainties and spectral features due to the Ring effect. The retrieval minimizes interferences with NO2, water vapor, and surface absorption from sand, and is more consistent with surface observations. The new retrieval reveals a hotspot of CHOCHO over the Pearl River Delta, China. By applying a plume model to wind segregated OMI data, it is shown that CHOCHO and HCHO enhancements are consistent with current NMVOC emissions inventories. The CHOCHO hotspot can be mainly attributed to aromatic NMVOCs from industrial solvent emissions. Observations of CHOCHO and HCHO from the SENEX aircraft campaign over the Southeast US are used to constrain the CHOCHO yield from isoprene. SENEX and OMI satellite observations are simulated with GEOS-Chem, featuring a new chemical mechanism for CHOCHO formation from isoprene. The SENEX observations provide support for a new prompt-formation pathway under low-NO_x conditions. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and model, with some departure under low-NOx conditions due to the new pathway. OMI CHOCHO and HCHO 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 enhancement under low-NOx conditions apparent in the SENEX data.