Fig. 2: d-BrC tar balls abundant in smoke plumes.
From: Shortwave absorption by wildfire smoke dominated by dark brown carbon
a, TEM image of a d-BrC tar ball abundant in the smoke plumes sampled at altitudes ranging from ground to 10 km. Identification of these tar balls involves use of secondary electron imaging at low accelerating voltage and low working distance29. b, Relative abundance of d-BrC tar balls and BC as a function of sampling altitude along the smoke plume height. The total number of particles analysed was n = 3,837. c, High-angle annular dark field (HAADF) image48 of a single d-BrC tar ball with a diameter of ~290 nm sampled close to a fire. d, HAADF images of multiple d-BrC tar balls with diameters of 70 nm, 150 nm and 185 nm. A Nion HERMES scanning TEM28 was used for acquiring these images. e, HAADF image of a tar ball with a diameter of ~50 nm, acquired simultaneously with EEL spectra. f, Variation in the real (n) and imaginary (k) refractive index across the diameter of the tar ball. The data points corresponding to the diameter of the tar ball are highlighted in e with the cyan-coloured line. The n and k values, corresponding to wavelengths of λ = 450 nm, 550 nm and 650 nm, remained consistent for all the three wavelengths for EEL spectra collected >10 nm from the particle edges. The particles show a high degree of material homogeneity and uniformity in refractive index across their physical cross sections.
