Seasonal, regional and vertical characteristics of high carbon monoxide plumes along with their associated ozone anomalies as seen by IAGOS between 2002 and 2019

In-situ measurements from IAGOS are used to characterise extreme values of carbon monoxide (CO) in the troposphere between 2002 and 2019. The SOFT-IO model, combining the FLEXPART lagrangian dispersion model with emission inventories over the footprint region is used to identify the origins of the CO in the sampled plumes. The impact of biomass burning and anthropogenic emissions on such CO plumes are characterised through CO mixing ratios and simultaneously recorded ozone (O ₃) ones.

In the Northern Hemisphere, maximum of CO are reached in DJF in the lower troposphere because of the elevated anthropogenic emissions and reduced convective activity of the season. Due to the low photochemistry and the fresh age of the air mass the O₃ values of these plumes are low. CO plumes in the upper troposphere result from intense emissions and efficient vertical transport, peaking during JJA. Among the anomalies detected in the UT in JJA, the ones with the higher associated O₃ values are the ones associated with biomass burning emissions. The middle troposphere combines the two previous vertical levels with contributions from both local emissions and long-range transport. The emission regimes and meteorological conditions are fundamentally different within the troposphere over Africa. Convection is no longer the limiting factor and the transport of the CO plumes is driven by the ITCZ shift, trade winds and the upper branch of the Hadley cell redistributing the pollution to higher latitudes.