ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-6363-2010 Brown carbon in tar balls from smoldering biomass combustion Chakrabarty R. K. 1 Moosmüller H. 1 Chen L.-W. A. 1 Lewis K. 2 Arnott W. P. 2 Mazzoleni C. 3 4 Dubey M. K. 4 Wold C. E. 5 Hao W. M. 5 Kreidenweis S. M. 6 Division of Atmospheric Sciences, Desert Research Institute, Reno, NV, 89512, USA Department of Physics, University of Nevada, Reno, NV, 89557, USA Department of Physics, Michigan Technological University, MI, 49931, USA Geochemistry and Climate Focus Team, Los Alamos National Laboratory, NM, 87547, USA Fire Sciences Laboratory, USDA Forest Service, Missoula, MT, 59808, USA Department of Atmospheric Sciences, Colorado State University, CO, 80523, USA 13 07 2010 10 13 6363 6370 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/6363/2010/acp-10-6363-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/6363/2010/acp-10-6363-2010.pdf

We report the direct observation of laboratory production of spherical, carbonaceous particles – "tar balls" – from smoldering combustion of two commonly occurring dry mid-latitude fuels. Real-time measurements of spectrally varying absorption Ångström coefficients (AAC) indicate that a class of light absorbing organic carbon (OC) with wavelength dependent imaginary part of its refractive index – optically defined as "brown carbon" – is an important component of tar balls. The spectrum of the imaginary parts of their complex refractive indices can be described with a Lorentzian-like model with an effective resonance wavelength in the ultraviolet (UV) spectral region. Sensitivity calculations for aerosols containing traditional OC (no absorption at visible and UV wavelengths) and brown carbon suggest that accounting for near-UV absorption by brown carbon leads to an increase in aerosol radiative forcing efficiency and increased light absorption. Since particles from smoldering combustion account for nearly three-fourths of the total carbonaceous aerosol mass emitted globally, inclusion of the optical properties of tar balls into radiative forcing models has significance for the Earth's radiation budget, optical remote sensing, and understanding of anomalous UV absorption in the troposphere.

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