Impact of South American biomass burning emissions on elevated South Atlantic upper tropospheric ozone

Abstract

During the SOUTHTRAC mission in autumn 2019 elevated mixing ratios of carbon monoxide (CO), carbon dioxide CO2, nitrogen oxide (NO) and total reactive nitrogen NOy were observed during a flight at the beginning of October. The potential plume extended over more than 1000 km (15° latitude) east of the Brasilian coast at altitudes of 13 km in the upper troposphere. In-situ measurements showed elevated ozone in this plume (≈ 100 ppbv), being 20–40 ppbv higher than during a previous flight in early September at exactly the same flight route. For the plume flight positive correlations of ozone and pollutants (CO, NO, NOy) indicate ozone production in these pollution layers. Lagrangian Analysis shows, that the observed air masses were strongly affected by biomass burning over Amazonia. A combined analysis of a chemical Lagrangian box model and a global chemistry climate model (EMAC) revealed that ozone production from biomass burning predominantly caused the ozone enhancements. The effect is intensified by NOx produced from lightning. Upward transport of the plumes happened ≈ one week before the flight, allowing ozone to be formed and enhanced by 25 % compared to the September flight. Estimate of the potential climate impact show, that the biomass burning produced ozone has an impact on the radiation budget, namely a spatially and regionally localized radiative flux disturbance of up to 250 mW m−2 at the tropopause and 150 mW m−2 at the top of the atmosphere.