Methane is among the most important greenhouse gases in the Earth’s atmosphere, causing rapid global warming. A recent study indicates that tropical methane emissions explain a large fraction of the global atmospheric methane growth (Feng et al., 2022). The relatively short lifetime of methane of about a decade makes methane emissions an attractive target of short-term climate change mitigation strategies. The sources of methane in Africa are quite diverse (e.g. gas/oil production and transport, wetlands, landfills, geological seepage, livestock and rice paddies) and the emissions of each of those sources are often poorly quantified. The determination of methane emissions is a main focus for African countries, as was recently shown by the signing of the Global Methane Pledge (following COP26) by 24 African countries. However, methane emissions reported to the UNFCCC bear large uncertainties (Deng et al., 2022). Those reported from Africa are based on only a few in situ observations, due to the lack of infrastructure and logistical hurdles in collecting emission data. There is a clear need to improve upon the current estimates, for which satellite observations are potentially very useful.
Emissions of nitrogen oxides (NOx) from soils and hydrocarbon emissions from vegetation in the Tropics (biogenic volatile organic compounds, BVOC) contribute substantially to the global budget of these species. BVOCs are key drivers of tropospheric chemistry through their impacts on ozone, aerosols and the oxidising capacity of the atmosphere. However, large uncertainties reside in BVOC and soil NO emission estimates mostly due to the complex mechanisms driving the emissions and to the paucity of local observations. Since BVOC emissions are the dominant source of formaldehyde (HCHO) over African rainforests, spaceborne HCHO columns can be used to better quantify this source. Moreover, the use of satellite NO2 data provides valuable information on the spatial distribution and magnitude of the natural sources of NOx over Africa at an unprecedented spatial resolution.
Within IMPALA, we will combine Sentinel-5p satellite data with state-of-the-art models and sophisticated inversion algorithms to estimate the emissions of methane as well as biogenic hydrocarbon and natural NOx emissions over Africa. Both qualitative and quantitative constraints on biosphere/atmosphere exchanges and anthropogenic emissions will be provided. This information is relevant not only for a better scientific understanding of climate forcing and biosphere-climate-air quality interactions, but also for local stakeholders and for environmental and agricultural agencies. IMPALA capitalises the long-term expertise of the consortium in emission estimation from space observations.