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Assessment of the impacts of brown carbon (BrC) requires accurate determination of its physical properties, but a model must be invoked to derive these from instrument data. Ambient measurements were made in L ondon at a site influenced by traffic and solid fuel (principally wood) burning, apportioned by single particle soot photometer data and optical properties measured using multiwavelength photoacoustic spectroscopy. Two models were applied: a commonly used Mie model treating the particles as single-coated spheres and a Rayleigh-Debye-Gans approximation treating them as aggregates of smaller-coated monomers. The derived solid fuel BrC parameters at 405 nm were found to be highly sensitive to the model treatment, with a mass absorption cross section ranging from 0.47 to 1.81 m2/g and imaginary refractive index from 0.013 to 0.062. This demonstrates that a detailed knowledge of particle morphology must be obtained and invoked to accurately parameterize BrC properties based on aerosol phase measurements.
Liu, D., J. W. Taylor, D. E . Young, M. J. Flynn, H. Coe, & J. D. Allan (2015) Theeffect of complex black carbon microphysics on thedetermination of theoptical properties of brown carbon, GEOPHYSICAL RESEARCH LETTERS (Early View).