International Collaboration in Chemistry: Chemical Nature and Origins of Atmospheric Brown Carbon Aerosol

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The Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation supports the research Professors Judith C. Chow, Lung-Wen Anton Chen and Douglas H Lowenthal who submitted an International Collaboration in Chemistry (ICC) proposal. They seek to better understand the chemical nature of brown carbon (BrC) and address the hypotheses regarding BrC sources through an international collaboration between U.S. and German researchers. Brown carbon is a special class of light-absorbing organic matter in atmospheric aerosols that has direct and indirect effects on the Earth's radiation balance. BrC is believed to derive from the oxidation and/or oligomerization of organic compounds in biomass burning plumes and photochemically-formed secondary organic aerosol. This project improves understanding of the BrC's chemical nature and its sources by perfecting and applying a new measurement method. This method combines thermal/optical characterization of source and ambient aerosol samples with mass spectroscopic detection of the evolved gases using soft and hard ionization methods. A thermal/optical carbon analyzer developed at the Desert Research Institute (DRI) is enhanced for multi-elemental and spectral detection with photo-ionization time-of-flight mass spectrometers (TOF-MS) developed at the University of Rostock (UR) in Germany. 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 temperatures. The relationship of BrC to organic groups, particularly carboxyls observed in higher temperature fractions (likely originating from high-MW polycarboxylic acids), will be investigated. A library consisting of two-dimensional MS-thermograms for major aerosol types, including laboratory-generated model aerosols, real-world fresh and aged source emissions, and source mixtures from urban and non-urban environments will be established. This library will facilitate source attribution when coupled with advanced chemometric analyses. The derived profiles can be applied to global emission inventories that currently contain only a BC component for modeling the global radiation balance.Broader impacts of this study include: 1) increasing academic exchanges between U.S. and German universities; 2) training doctoral candidates in both countries to enhance the environmental workforce; 3) research experiences for environmental science instructors from Nevada high schools and community colleges; and 4) improving the ability to better model effects of BC and BrC as short-term climate forcers by improving their regional and global emission estimates.