Natural emissions of VOC and NOx over Africa constrainted by
TROPOMI HCHO and NO2 data using the MAGRITTEv1.1 model
Opacka, B., Stavrakou, T.,
Müller, J.-F., De Smedt, I., van Geffen, J., Marais, E. A.,
Horner, R. P., Millet, D. B., Wells, K. C. and Guenther, A. B.: 2025,
Atmos. Chem. Phys. 25, 2863-2894.
doi: 10.5194/acp-25-2863-2025
Abstract
Natural emissions (vegetation, soil, and lightning) are the dominant sources
of non-methane biogenic volatile organic compounds (BVOCs) and nitrogen
oxides (NOx == NO + NO2) released into the atmosphere over Africa. BVOCs and
NOx interact with each other and strongly impact their own chemical
lifetimes and degradation pathways, in particular through their influence on
hydroxyl radical levels. To account for this intricate interplay between NOx
and VOCs, we design and apply a novel inversion setup aiming at simultaneous
optimization of monthly VOC and NOx emissions in 2019 in a regional
chemistry-transport model, based on Tropospheric Ozone Monitoring Instrument
(TROPOMI) HCHO and NO2 satellite observations. The TROPOMI-based inversions
suggest substantial underestimations of natural NOx and VOC emissions used
as a priori in the model. The annual flux over Africa increases from 125 to
165 Tg yr-1 for isoprene, from 1.9 to 2.4 TgN yr-1 for soil NO emissions,
and from 0.5 to 2.0 TgN yr-1 for lightning NO emissions. Despite the NOx
emission increase, evaluation against in situ NO2 measurements at seven
rural sites in western Africa displays significant model underestimations
after optimization. The large increases in lightning emissions are supported
by comparisons with TROPOMI cloud-sliced upper-tropospheric NO2 volume
mixing ratios, which remain underestimated by the model even after
optimization. Our study strongly supports the application of a bias
correction to the TROPOMI HCHO data and the use of a two-species constraint
(vs. single-species inversion), based on comparisons with isoprene columns
retrieved from the Cross-track Infrared Sensor (CrIS).
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created: 10 March 2025
last modified: 10 March 2025