Extended Data Fig. 3: Number density spectrum of soot along with the particle size from K-Pg boundary layer.

It indicates a median diameter of 0.22 μm (Toon et al., 2016³⁹; Wolbach et al., 1985²⁰). Concerning the aerosol life cycle and processes, coagulation is one of the crucial microphysical mechanisms that might pose as important for the transport of aerosols in the atmosphere. Nanometric particles below 0.1 μm, that is, 0.015 μm < D_p < 0.052 μm⁷⁹, whose range is referred to as the Aitken-mode (within the cyan dashed lines), are formed by two processes: (i) condensational growth on existing aerosol particles, and (ii) coagulation due to the random particle collisions. These nanometric particles can further grow into larger particles or chains, resulting in the so-called accumulation-mode (0.056 μm < D_p < 0.26 μm)⁷⁹ (within the red dashed lines) where the coagulation can occur especially at high particle concentrations following the K-Pg impact. The median diameter of soot (0.22 μm^20,39) in our simulations are prominently larger than the Aitken-mode interval, while lying within the range of accumulation-mode.