Airborne quantification of Angolan offshore oil and gas methane emissions

Abstract. In September 2022, the METHANE-To-Go Africa (MTGA) scientific aircraft campaign, part of UNEP's International Methane Emissions Observatory (IMEO) Methane Science Studies, conducted the first methane (CH4) emissions measurements from the offshore oil and gas sector in West Africa. Using aircraft-based mass balance methods, we quantified trace gas emissions from all 57 Angolan offshore facilities, estimating total sector emissions and assessing 30 individual sites and 10 facility groups, thereby providing the first independent dataset for this previously unstudied region. Emissions were generally consistent across repeated measurements, but two facilities showed intermittent high emissions of 10 and 4 t h−1, significantly influencing total emissions. Older, shallow-water platforms emitted more than newer, deep-water floating production facilities. These findings suggest that production volume is a poor proxy for CH4 emissions, while age and maintenance status are more reliable indicators. Due to operational variability, regular monitoring remains essential, particularly for older facilities. We estimate total CH4 emissions at 16.9±5.3th-1, only 20 %–22 % of EDGAR and CAMS inventory estimates, but over twice the operator-reported values. Additional trace gas measurements (CO2, CO, C2H6, SO2, NOy, and aerosols) suggest CH4 stems primarily from fugitive emissions and venting, not combustion. The calculated carbon intensity of Angolan offshore oil and gas is 3.4±0.8 g CO2 eq MJ−1, with nearly equal contributions from CH4 and CO2. Notably, shallow-water platforms are CH4-dominated, while deep-water facilities mostly emit CO2. These results improve our understanding of greenhouse gas emissions from offshore production in a key oil- and gas-producing region.