Greenhouse gas column observations from an EM27/SUN portable spectrometer in Uganda

The natural ecosystems of tropical Africa represent a significant store of carbon, and play an important but uncertain role in the global atmospheric budgets of carbon dioxide and methane. Recent studies using satellite data have concluded that unusually heavy rainfall over East Africa in late 2019 led to additional methane emissions equivalent to over a quarter of the growth in global CH4 emissions in 2019 (Lunt et al 2021), and that the tropical Africa region dominates net carbon emission across the tropics (Palmer et al 2019). These conclusions, as well as those of other studies looking at the tropical African carbon and methane cycles, rely on the accuracy of satellite datasets and atmospheric transport models over a region where there are no independent observations available to confirm their robustness and validity. Here we present the first ground-based observations of greenhouse gas (GHG) column concentrations over tropical East Africa, obtained using the University of Leicester EM27/SUN spectrometer during its deployment in Jinja, Uganda, on the northern shore of Lake Victoria. Thanks to an automated weatherproof enclosure designed by the Technical University of Munich (Heinle and Chen 2018, Dietrich et al 2021) we operated the instrument remotely and near-continuously for a three month period in early 2020, observing total atmospheric column concentrations of carbon dioxide and methane along with other gases of interest including water vapour and carbon monoxide. In this presentation we describe the instrument setup and the data obtained during this period, processed using tools developed under the COCCON project (COllaborative Carbon Column Observing Network, Frey et al 2019), and demonstrate the value that these ground-based GHG column measurements can contribute towards diagnosing the carbon and methane budget for the tropical East Africa region. A main focus here is on the evaluation of CO2 data from OCO-2, and CH4 from Sentinel 5P TROPOMI - datasets previously used in the studies of Palmer et al 2019 and Lunt et al 2021 respectively - and interpret these comparisons with our ground-based observations in the light of simulated total columns from the GEOS-Chem atmospheric chemistry transport model and the CAMS (Copernicus Atmospheric Monitoring Service) reanalyses.     «

The natural ecosystems of tropical Africa represent a significant store of carbon, and play an important but uncertain role in the global atmospheric budgets of carbon dioxide and methane. Recent studies using satellite data have concluded that unusually heavy rainfall over East Africa in late 2019 led to additional methane emissions equivalent to over a quarter of the growth in global CH4 emissions in 2019 (Lunt et al 2021), and that the tropical Africa region dominates net carbon emission acro...     »