Global CO emissions and drivers of atmospheric CO trends constrained by MOPITT satellite observations

Abstract. Carbon monoxide (CO), an important atmospheric pollutant produced from incomplete combustion and hydrocarbon oxidation, significantly influences atmospheric chemistry and air quality. Accurate quantification of its global emissions and the underlying drivers of atmospheric trends is essential for understanding and improving global environmental conditions. Using 20 years (2003–2022) of satellite observations from the Measurement of Pollution in the Troposphere (MOPITT) instrument, here we analyze changes in global CO emissions and atmospheric concentrations. The a posteriori simulations show improved consistency with independent surface and aircraft measurements compared to the a priori simulations. Sensitivity analyses further confirm that inferred emissions remain robust against uncertainties associated with satellite vertical sensitivity and variations in hydroxyl radical (OH) concentrations. Our results indicate a substantial decline in global anthropogenic CO emissions of 14–17 % (approximately 85–110 Tg) over the two-decade period, largely driven by reductions in the United States, Europe, and eastern China. In contrast, biomass burning emissions exhibited strong interannual variability, with recent increases in Northern Hemisphere high-latitude forests. A key finding is that rising biomass burning emissions have offset about 37 % of the global anthropogenic emission reduction (47 % in the Northern Hemisphere alone), underscoring the considerable moderating influence of wildfires on atmospheric composition trends. This study provides a comprehensive assessment of global CO emissions and the mechanisms governing atmospheric CO trends, offering a scientific basis for integrated policies addressing both climate change and air pollution.