AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Evolution of Optical Properties of Brown Carbon Aerosols as a Function of Atmospheric Aging
BENJAMIN SUMLIN, Robert Pattison, Rajan Chakrabarty, Washington University in St Louis
Abstract Number: 531 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Long-lasting smoldering phases of wildfires emit large amounts of brown carbon (BrC) aerosol, a component of organic carbon which absorbs incoming solar radiation in the near ultraviolet visible spectrum. There is a currently a large gap in our knowledge of intensive optical properties of BrC aerosols, and how these properties evolve as a function of atmospheric processing. With increase in atmospheric residence time, these aerosols could be subjected to physicochemical alterations which could in turn affect their radiative properties. In this study, a Potential Aerosol Mass (PAM) reactor was used to simulate atmospheric oxidation processes on timescales ranging from one to several days. Smoldering combustion of Alaskan peat land samples was conducted at the Washington University Biomass Burning Chamber, and the emitted BrC aerosols were “aged” to different timescales using a PAM reactor under the combined influence of OH, O3, and UV light. Photoacoustic spectrometers with integrated nephelometers were used to measure in real-time the absorption and scattering coefficients and single scattering albedo of the aerosols at 375, 405, 532, 671, and 1047 nm wavelengths. In addition, a three-wavelength TSI nephelometer (450, 550, and 700 nm) was used to measure the mean hemispherical backscatter fraction and asymmetry parameter. Electron microscopy analysis of the BrC aerosols revealed a spherical morphology, which facilitated the calculation of their index of refraction using Lorenz-Mie theory. This talk will provide a comprehensive comparison of the measured optical properties of both fresh and aged BrC aerosols in the 375 – 1047 nm (UV-Vis-IR) spectrum.