Abstract
Abstract. Tropospheric glyoxal and formaldehyde columns retrieved from the SCIAMACHY satellite instrument in 2005 are used with the IMAGESv2 global chemistry-transport model and its adjoint in a two-compound inversion scheme designed to estimate the continental source of glyoxal. The formaldehyde observations provide an important constraint on the production of glyoxal from isoprene in the model, since the degradation of isoprene constitutes an important source of both glyoxal and formaldehyde. Current modelling studies underestimate largely the observed glyoxal satellite columns, pointing to the existence of an additional land glyoxal source of biogenic origin. We include an extra glyoxal source in the model and we explore its possible distribution and magnitude through two inversion experiments. In the first case, the additional source is represented as a direct glyoxal emission, and in the second, as a secondary formation through the oxidation of an unspecified glyoxal precursor. Besides this extra source, the inversion scheme optimizes the primary glyoxal and formaldehyde emissions, as well as their secondary production from other identified non-methane volatile organic precursors of anthropogenic, pyrogenic and biogenic origin. In the first inversion experiment, the additional direct source, estimated at 36 Tg/yr, represents 38% of the global continental source, whereas the contribution of isoprene is equally important (30%), the remainder being accounted for by anthropogenic (20%) and pyrogenic fluxes. The inversion succeeds in reducing the underestimation of the glyoxal columns by the model, but it leads to a severe overestimation of glyoxal surface concentrations in comparison with in situ measurements. In the second scenario, the inferred total global continental glyoxal source is estimated at 108 Tg/yr, almost two times higher than the global a priori source. The extra secondary source is the largest contribution to the global glyoxal budget (50%), followed by the production from isoprene (26%) and from anthropogenic NMVOC precursors (14%). A better performance is achieved in this case, as the updated emissions allow for a satisfactory agreement of the model with both satellite and in situ glyoxal observations.
Highlights
Glyoxal (CHOCHO) and formaldehyde (HCHO) are shortlived intermediate products in the oxidation of non-methane volatile organic compounds (NMVOCs) emitted by vegetation, fires and anthropogenic activities
This study aims at determining the global distribution and strength of the glyoxal continental sources
The results show that our conclusions regard- The a priori global CHOCHO source is estimated at ing the magnitude of the UVOC source and the agreement 134 Tg/yr
Summary
Glyoxal (CHOCHO) and formaldehyde (HCHO) are shortlived intermediate products in the oxidation of non-methane volatile organic compounds (NMVOCs) emitted by vegetation, fires and anthropogenic activities. They are directly emitted during fossil fuel and biofuel combustion and biomass burning. This study aims at determining the global distribution and strength of the glyoxal continental sources To this purpose, we utilize synergistically HCHO and CHOCHO satellite columns in a twocompound inverse modelling framework based on the adjoint of the IMAGES model (Muller and Stavrakou, 2005). Note that the focus of this study is limited to continental regions due to an inherent difficulty to retrieve CHOCHO columns over the oceans (interference with liquid water absorption (Wittrock et al, 2006)), and to the fact that the HCHO columns over oceanic regions lie close to the detection limit of the instrument
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