The effect of complex black carbon microphysics on the determination of the optical properties of brown carbon. Issue 2 (23rd January 2015)

• Record Type: Journal Article
• Authors: Liu, Dantong; Taylor, Jonathan W.; Young, Dominque E.; Flynn, Michael J.; Coe, Hugh; Allan, James D.
• Is Part Of: Geophysical research letters. Volume 42:Issue 2(2015:Jan.)
• Page Start: 613
• Page End: 619
• Publication Date: 2015-01-23
• Subjects: brown carbon -- black carbon -- microphysics -- Mie -- RDG; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2014GL062443
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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 London 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 m 2 /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. Key Points: Source‐specific optical properties evaluated in different model approaches Particle morphology is major model sensitivity This sensitivity is acute for larger BC core and thicker coating thickness