Fig. 1: African smoke transport and characteristic black carbon mass size distributions.

a Geography of African biomass burning smoke transport across the Atlantic into the Amazon, b locations of ground-based and aircraft measurements analyzed in this study, and c, d characteristic differences in the shape of refractory black carbon (rBC) mass size distributions of African vs South American smoke. In (a), the Atlantic trade winds north and south of the intertropical conversion zone are shown by means of a backward trajectory ensemble (2011-2020, HYSPLIT model, 10 days) starting at 200 m above ground at ATTO. The fire map represents the average density of fires detected by the satellites Aqua and Terra from 2011 to 2020. In (b), the relevant locations include ATTO³³ as well as several flight segments in heavy biomass burning smoke during the aircraft missions ACRIDICON-CHUVA in Sep 2014¹⁸ and CAFE-Africa in Aug and Sep 2018³⁴. In (c), the rBC mass size distributions as a function of rBC core mass equivalent diameter (d_MEV) during event periods under predominant African (20 - 23 Jan and 03 - 09 Feb 2020) vs predominant South American (28 Jul - 11 Aug 2020) smoke influence at ATTO are compared. In (d), the ATTO rBC mass size distributions from (c) (gray and green shadings) are shown in combination with the aircraft rBC mass size distributions (symbols) for the flight segments in (b). The rBC mass size distributions were normalized to the area under the curves. Solid lines are the median, and shadings are the range between the 5th and 95th percentiles of 3 h (ATTO) and 10 seconds averages (aircraft). For statistics and further information refer to Supplementary Fig. 4.