Fig. 3: Saturation of lensing-induced absorption enhancement in pyroCb cloud.
From: Light absorption enhancement of black carbon in a pyrocumulonimbus cloud
A Population-averaged absorption enhancement (Eabs) at 532 nm wavelength by BC-containing particles from urban sources, wildfire sources, and within a pyroCb plume. We find that extremely thick coatings on BC inside the pyroCb cloud cause higher Eabs when compared to BC from urban and wildfire sources. The solid black line in (A) shows a sigmoidal fit of Eabs measurements for wildfire BC made by ref. 30, with shaded areas representing 95% confidence intervals. Boxes in (A) show the inter-quartile range, whiskers represent 5th and 95th percentiles, and lines represent median values. We find that Eabs plateaus at ∼2.0, providing an upper limit for absorption enhancement by atmospheric BC. This plateau is visualized in (B–D), which shows the strength of the induced electric field as light passes through the BC core of a particle which is representative of a particle inside the pyroCb plume (B), a non-pyroCb wildfire particle (C), and an urban BC particle (D). Black contours in (B–D) represent the silhouette of coatings on the BC particles. We find that increasing RBC beyond ∼12 does not lead to significant increases in the average strength of the induced electric field (\(\bar{{{\mbox{E}}}}\)). This is demonstrated in (E), which shows the change in \(\bar{{{\mbox{E}}}}\) per unit change in RBC (Δ\(\bar{{{\mbox{E}}}}\)/ΔRBC). We find that Δ\(\bar{{{\mbox{E}}}}\)/ΔRBC decreases significantly as the value of RBC increases, and thus does not lead to significantly increased absorption.
