Spectral Analysis of Brown Carbon Secondary Organic Aerosol from the IR to the UV

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Carbonaceous atmospheric aerosols, including black and brown carbon, impact climate through altering the optical properties of the atmosphere, and also by themselves undergoing further photochemical oxidation, in a poorly understood manner. This in turn may alter their own optical properties. The overall goal of this work is to improve the scientific basis for quantitatively modeling organic aerosol radiative effects. The results have application in remote sensing data retrieval algorithms, improving the reliability of radiative transfer models for aerosol and climate forcing calculations, and better understanding the impact of brown carbon (BrC) aerosol may have on atmospheric chemistry and climate. In previous work, University of Iowa researchers developed specialized laboratory optical capabilities to measure dust aerosol optical properties over the UV-Vis-IR spectrum, and have explored how physicochemical processing of aerosols alters those properties. Here they will further extend their experimental capabilities with a highly sensitive technique, cavity ring down laser spectroscopy (CRDS). This will be used to precisely measure the optical properties of the brown carbon (BrC) fraction of ambient and laboratory mimics of organic aerosols, across the visible and the mid-IR spectral range. How those properties may change as a result of UV photochemical processing will be further studied.