AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Fluorescence, Photobleaching, and Molecular Level Analysis of Brown Carbon Aerosol
HYUN JI LEE, Paige Aiona, Sergey Nizkorodov, Alexander Laskin, Julia Laskin, University of California, Irvine
Abstract Number: 159 Working Group: Aerosol Chemistry
Abstract Brown carbon (BrC) compounds can either be directly emitted from combustion sources as primary organic aerosol (POA)(Bond et al., 2006) or be formed in the atmosphere through multi-phase reactions, such as aging of secondary organic aerosol (SOA) mediated by ammonium sulfate (AS)(Galloway et al., 2009). Chemical composition and atmospheric transformations of both primary and secondary BrC are highly uncertain. This presentation will discuss the molecular level composition, absorption spectra, fluorescence spectra, and the mechanism of photodegradation of several different types of BrC. The secondary BrC samples included products of reaction between AS and chamber-generated SOA or methylglyoxal, as well as SOA prepared by high-NOx photooxidation of aromatic compounds. The primary BrC samples included aerosol produced by wood combustion. In all cases, the evolution of the absorption and fluorescence spectra of aqueous extracts of BrC were measured during irradiation by a known flux of UV or visible light. The compositional changes between the aged and photobleached samples were characterized by liquid-chromatography coupled to a photodiode array detector and to a high-resolution electrospray ionization mass spectrometer (LC-UVVIS-ESI/HRMS). Photodegradation of BrC occurs on atmospherically relevant time scales and significantly changes its absorption properties. In contrast, the molecular level composition of BrC exhibits only subtle changes suggesting that the optical properties of BrC are controlled by minority compounds. The fluorescence of BrC is significant in some cases, and it can be potentially mistaken for bioaerosols in fluorescence-based methods. Overall, the results demonstrate a high degree of variability in optical properties and dynamic nature of atmospheric BrC.
Bond et al. Light Absorption by Carbonaceous Particles: An Investigative Review. Aerosol Science and Technology, 2006, 40, 27.
Galloway et al. Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions. Atmos. Chem. Phys., 2009, 9, 3331.