Impact of wildfire smoke on atmospheric environment over the Southeast Atlantic during ORACLEs 2017

Abstract Smoke containing biomass burning aerosols (BBA) is emitted intensively from wildfires in Central Africa and transported across the Southeast Atlantic during the dry season, which imposes a notable influence on local radiative forcing and regional climate. To reduce the estimation uncertainty in models, constraints based on observations are required. The vertical distributions of biomass burning pollutants, including carbon monoxide (CO), black carbon (BC) and organic aerosol (OA), were characterized over the Southeast Atlantic, via aircraft measurements during the ORACLEs (ObseRvations of Aerosols above CLouds and their interaction) campaign in August 2017. A notable spatio-temporal difference in pollutants was found over the Southeast Atlantic due to their widespread occurrence. The detected smoke originated from wildfires in Central Africa and arrived above downwind regions via long range transport. High-CO layers mostly occurred at heights ranging from 1 to 5 km exhibiting uni- or bi-modal peaks, and their maximum concentration commonly exceeded 0.2 ppmv, and higher than 0.4 ppmv on certain days, while low-CO layers generally occurred above 5 km and below 1 km, with concentrations lower than 0.1 ppmv. Moreover, the vertical variation of pollutants was distinct across different latitude regions. The more northern the smoke occurrence, the higher the magnitude and altitude of the CO maxima. The biomass burning plumes in the northern, middle and southern regions mainly originated from Congo and North Zaire, South Zaire and Angola, Angola and Zambia, respectively. The pollutants in the downwind regions were also possibly influenced by the biomass burning state of flaming combustion over potential source areas and other physical and chemical processes during aging.