PNNL

Abstract

Atmospheric particulate black carbon (BC) leads to warming of the Earth’s climate. Many models that include forcing by BC assume that non-BC aerosol species internally mixed with BC enhance BC absorption, often by a factor of ~2. However, such model estimates have yet to be clearly validated through atmospheric observations. Here, we report on direct measurements of the absorption enhancement (Eabs) of BC in the atmosphere around California and find that it is negligible at 532 nm and much smaller than predicted from theoretical calculations that are uniquely constrained by observations, suggesting that the warming by BC may be significantly overestimated (factor of 2) in many climate models. Additionally, non-BC particulate matter is found to contribute ~10% to the total absorption at 405 nm.