Understanding CO in the Most Remote Atmosphere: Direct Emissions and Secondary Chemistry

Carbon Monoxide (CO) is a product of incomplete combustion and is often used as a tracer for anthropogenic pollution and forest fires. CO is also produced from methane and VOC oxidation by the hydroxyl radical (OH), especially in the remote atmosphere. It is lost through oxidation by OH.

In this study we use aircraft profiles of CO observed during the Atmospheric Tomography (ATom) mission over the Atlantic and Pacific oceans (from 65S to 85N) to test our understanding of the budget of CO. We find that the latitudinal gradient in each ocean basin shows different seasonal trends (summer vs winter) and we examine the drivers of these differences using the wide range of chemical species measured during ATom. We compare background CO (defined using various tracers measured during ATom) with the CO output from an ensemble of models to evaluate the baseline CO of these models and use the CO enhancement above this background to investigate emissions from biomass burning and anthropogenic sources. By comparing the observed CO concentrations to the CO calculated from a range of models we can get a better understanding of the model uncertainties and biases.

Finally, we compare our CO observations from ATom with the CO profiles from the Pacific (HIPPO flights, 2009-2011) and long-term CO observations (1990-2017) from coastal tower sites to examine long term trends in the CO observations and put the ATom flight data into a longer-term context.