Absorption Properties of Organic Aerosols from Biomass Burning Tied to Their Black Carbon Content

Summary

Atmospheric aerosols can directly affect Earth’s energy balance by reflecting incoming solar radiation (a cooling effect), absorbing incoming radiation (a warming effect), and emitting infrared. The net overall effect depends most strongly on whether the aerosols absorb or reflect solar radiation. Black carbon is an example of a strongly absorbing aerosol that is also an important global warming agent; one-third of the global black carbon budget is due to biomass burning. Climate models typically treat black carbon as the only organic absorbing aerosol, but in reality other organic aerosols can absorb solar radiation, although typically not as strongly as black carbon. These partly absorbing aerosols are often referred to as brown carbon.

Brown carbon has not been treated in detail in climate models because its absorption properties and composition are highly variable. In collaboration with scientists at Carnegie Mellon University and the University of Montana, an Atmospheric System Research-funded team of scientists at Los Alamos National Laboratory recently made discoveries that will make it easier for climate modelers to more accurately represent both black and brown carbon emissions from biomass burning as part of the simulations. They conducted a set of laboratory experiments that quantified the absorption properties of emissions from a range of common biomass fuels as well as diesel. They showed that the absorption properties of brown carbon from biomass burning depends more on burn conditions than fuel type and that compounds with extremely low volatility are responsible for the absorption. These results should enable climate models to treat both black and brown carbon and quantify how fires contribute to warming now and in the future.

References

Saleh, R., E. S. Robinson, D. S. Tkacik, A. T. Ahern, S. Liu, A. C. Aiken, R. C. Sullivan, A. A. Presto, M. K. Dubey, R. J., Yokelson, N. M. Donahue, and A. L. Robinson. 2014. “Brownness of Organics in Aerosols from Biomass Burning Linked to Their Black Carbon Content,” Nature Geoscience 7, 647-50. DOI: 10.1038/ngeo2220.