PNNL

Abstract

Pyrocumulonimbus (pyroCb) firestorm systems have been shown to inject significant amounts of black carbon (BC) to the stratosphere with a residence time of beyond eight months. A distinguishing feature of BC-containing particles residing within pyroCb clouds is their thick surface coatings made of condensed water vapor and organic matter. When coated with non-refractory materials, BC’s absorption is enhanced, yet the absorption enhancement factor (Eabs) for pyroCb BC is not well constrained. Here, we perform particle-scale measurements of BC mass, morphology, and coating thickness from inside a pyroCb cloud and quantify their Eabs using an established particle-resolved BC optics model. We find that Eabs for BC asymptotes to ~2.0 with increasing coating thickness. This value could denote the upper limit of Eabs for thickly coated BC in the atmosphere. Our results provide observationally constrained parameterizations of BC absorption for improved radiative transfer calculations of pyroCb events.