Chemical Nature and Origins of Atmospheric Brown Carbon Aerosol

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Brown carbon (BrC) is a special class of light-absorbing organic matter in atmospheric aerosol that has potential direct and indirect climate effects. The formation of BrC is hypothesized to be related to the oxidation and/or oligomerization of organic compounds in biomass burning plumes or photochemical smog leading to relatively high-molecular weight (MW), low-volatility polycarboxylic compounds. This project seeks to better understand the chemical nature of BrC and address hypotheses regarding BrC sources. First, an unique analytical method that allows simultaneous thermal/optical characterization as well as mass spectrometric analysis (soft and hard ionization) of the evolved gases will be developed and applied to a comprehensive collection of standard and real-world aerosol samples. The method will integrate a carbon analyzer developed at the Desert Research Institute (DRI) in Reno,Nevada, enhanced for multi-elemental and spectral detection with photo-ionization time-of-flight mass spectrometers (TOF-MS) developed at the University of Rostock (UR). BrC and black carbon (BC) can then be quantified from spectral light absorption measurements and studied with molecular patterns/source signatures in gases evolved at different heating temperatures. The relationship of BrC to various organic groups will be investigated. A dynamic temperature ramping will be explored to better isolate BrC and other organic components for a more specific characterization. Finally, a library consisting of two-dimensional MS-thermograms for major aerosol types, including urban and rural environmental particulate matter and laboratory-generated combustion and secondary organic aerosol, will be established. This library will facilitate source attribution when coupled with advanced chemometric analysis.