OCO-2 Observations of Africa Fire CO2 Emissions

Fire CO₂ fluxes play a major role in the terrestrial biosphere, the global carbon budget, and the long-term carbon cycling of fire-prone ecosystems. African fires account for roughly 50% of global fire carbon (C) fluxes, largely emitted into the atmosphere as CO₂ and CO. Disentangling fire CO₂ emissions from total CO₂ and CO fluxes remains a challenge, due to large uncertainties in combusted biomass density and combustion efficiency (CO₂:CO). Major savanna and grassland ecosystems fire events during the OCO-2 era provide ideal case studies for testing current understanding of African fire C emissions. We use MOPITT CO to characterize the role of fire CO₂ enhancements in OCO-2 CO₂ measurements during September-October 2014. We constrain the combustion efficiency of southern Africa fires by retrieving CO₂:CO total dry-column CO₂ concentrations from OCO-2 and MOPITT total dry-column CO. We also performed a benchmark OSSE, based on the CMS-Flux atmospheric transport and chemistry analysis of CO₂ and CO. We find that OCO-2 MOPITT CO₂:CO (1:30) are almost a factor of 2 higher than the OSSE true and retrieved CO₂:CO values (1:18 and 1:16). Our findings indicate that southern Africa fire CO₂:CO values are higher than previously assumed. We hypothesize that the higher-than-expected CO₂:CO values are due to fire fuel dryness and composition. We anticipate that CO₂:CO observations will provide an important global constraint on the estimation and attribution of continental-scale CO₂ fluxes and on the processes controlling fire C emission variability.