The impact of biomass burning on upper tropospheric carbon monoxide: A study using MOCAGE global model and IAGOS airborne data

Abstract. In this paper the fate of biomass burning emissions of carbon monoxide is studied with the global chemistry transport model MOCAGE and IAGOS airborne measurements for the year of 2013. The objectives are firstly to improve their representation within the model and secondly to analyse their contribution to carbon monoxide concentrations in the upper troposphere. At first, a new implementation of biomass burning injection is developed for MOCAGE, using the latest products available in GFAS biomass burning inventory on plume altitude and injection height. This method is validated against IAGOS observations of CO made in fire plumes, identified thanks to the SOFT-IO source attribution data. The use of these GFAS products lead to improved MOCAGE skill to simulate fire plumes originating from boreal forests wildfires. It was also shown that this new biomass burning injection method did not change upper tropospheric carbon monoxide concentrations elsewhere on the globe as the previous one was already satisfying. Then, MOCAGE performances were evaluated in general in the upper troposphere in comparison to the IAGOS database, and were shown to be very good, with very little bias and good correlations between the model and the observations. Finally, we analyse the contribution of biomass burning to upper tropospheric carbon monoxide concentrations. This was done by comparing simulations were biomass were toggled on and off in different source regions of the world to assess their individual influence. The two regions contributing the most to upper tropospheric CO were found to be the boreal forests and equatorial Africa, in accordance with the quantities of CO they emit each year and the fact that they undergo fast vertical transport: deep convection in the tropics and pyroconvection at high latitudes. It was found that biomass burning contributes for more than 11 % on average on the CO concentrations in the upper troposphere, and up to 50 % at high latitudes during the wildfire season.