AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Evolution of Brown Carbon Aerosol Optical Properties Induced by Heterogeneous OH Oxidation
ELIJAH G. SCHNITZLER, Jonathan Abbatt, University of Toronto
Abstract Number: 722 Working Group: Aerosol Chemistry
Abstract Heterogeneous OH oxidation of a brown carbon (BrC) surrogate was investigated in a series of photooxidation chamber experiments. The BrC surrogate was generated from aqueous 1,3-dihydroxybenzene (10 mM) and H2O2 (10 mM) exposed to >300 nm radiation, atomized, passed through a series of trace gas denuders, and injected into the chamber. Following aerosol injection, H2O2 was continuously bubbled into the chamber; an hour later, the chamber was irradiated with black-lights (UV-B) to produce OH. Before irradiation, aerosol absorption and scattering at 405 nm, measured using a photoacoustic spectrometer, decreased due only to deposition and dilution, and single scattering albedo (SSA) was steady. In the presence of gas-phase OH, absorption first briefly increased, despite continued particle losses, and SSA decreased. Subsequently, absorption decreased faster than scattering, and SSA increased uniformly. No particle growth occurred, because trace gases were removed before particle injection, and the evolution of the BrC optical properties cannot be attributed to the size-dependence of Mie scattering and absorption. Consequently, this evolution reflects changes in the imaginary part of the refractive index of the aerosol. Furthermore, heterogeneous OH oxidation of a large azo dye (Reactive Yellow 2) results in colour loss without the initial colour enhancement observed for BrC. Colour enhancement followed by colour loss is consistent with the photochemical evolution of other BrC surrogates in the bulk aqueous phase and likely corresponds, chemically, to functionalization followed by fragmentation.