Radiative Absorption Enhancements Due to the Mixing State of Atmospheric Black Carbon

Dark Forcing Soot, or black carbon, is a ubiquitous atmospheric pollutant whose warming effect might be second only to carbon dioxide. When black carbon is emitted, it combines with other aerosols to form heterogeneous mixtures. Models have predicted that internal mixing of black carbon with other materials can double the amount of radiation absorbed. Cappa et al. (p. 1078 ) report that in situ measurements of the enhancement of radiation absorption by these mixed black carbon–containing particles in the atmosphere show a much smaller effect. Thus, many climate models may be overestimating the amount of warming caused by black carbon emissions.