AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Aerosol Optical Properties in the Ultraviolet Spectral Region during the Southern Oxidant and Aerosol Study
REBECCA WASHENFELDER, Alexis Attwood, Charles Brock, Steven G. Brown, University of Colorado and NOAA
Abstract Number: 209 Working Group: Air Quality and Climate in the Southeast US: Insights from Recent Measurement Campaigns
Abstract Optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength-dependence of aerosol extinction cross sections and complex refractive indices. In the case of brown-carbon, its wavelength-dependent absorption in the ultraviolet spectral region has been suggested as an important component of aerosol radiative forcing. During the Southern Oxidant and Aerosol Study in summer 2013, we deployed a new field instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector.
Biomass burning is thought to be one of the major sources of brown carbon aerosol, though direct ambient measurements of the optical properties of biomass burning aerosol, especially in the ultraviolet spectral region, remain sparse. Although the Southeast U.S. is typically less influenced by biomass burning during summer, there were three distinct biomass burning events measured during the SOAS 2013 field campaign. Here, we combine our wavelength resolved measurements of aerosol optical extinction with size distribution and composition data to better understand UV aerosol optical properties during these events. One of the key challenges is the separation of the aerosol absorbing and scattering components from a direct extinction measurement. Methods for separation of the real and imaginary parts of the refractive indices, and the challenges in doing so, will be discussed.