Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2018-198
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
29 Mar 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Heterogeneous OH oxidation of secondary brown carbon aerosol
Elijah G. Schnitzler and Jonathan P. D. Abbatt Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
Abstract. Light-absorbing organic aerosol, or brown carbon (BrC), has significant but poorly-constrained effects on climate; for example, oxidation in the atmosphere may alter its optical properties, leading to absorption enhancement or bleaching. Here, we investigate for the first time the effects of heterogeneous OH oxidation on the optical properties of a laboratory surrogate of secondary BrC in a series of photo-oxidation chamber experiments. The BrC surrogate was generated from aqueous resorcinol, or 1,3-dihydroxybenzene, and H2O2 exposed to > 300 nm radiation, atomized, passed through trace gas denuders, and injected into the chamber, which was conditioned to either 15 or 60 % relative humidity (RH). Aerosol absorption and scattering coefficients and single scattering albedo (SSA) at 405 nm were measured using a photo-acoustic spectrometer. At 60 % RH, upon OH exposure, absorption first increased, and the SSA decreased sharply. Subsequently, absorption decreased faster than scattering, and SSA increased gradually. Comparisons to the modelled trend in SSA, based on Mie theory calculations, confirm that the observed trend is due to chemical evolution, rather than slight changes in particle size. The initial absorption enhancement is likely due to molecular functionalization and/or oligomerization, and the bleaching to fragmentation. By contrast, at 15 % RH, slow absorption enhancement was observed, without appreciable bleaching. A multi-layer kinetics model, consisting of two surface reactions in series, was constructed to provide further insights regarding the RH-dependence of the optical evolution. Candidate parameters suggest that the oxidation is efficient, with uptake coefficients on the order of unity, and the aerosol is very viscous, even at 60 % RH. At 15 % RH, the aerosol will be viscous enough to confine products of fragmentation, leading to their recombination, such that little bleaching is observed on the experimental timescale. These results further the current understanding of the complex processing of BrC that may occur in the atmosphere.
Citation: Schnitzler, E. G. and Abbatt, J. P. D.: Heterogeneous OH oxidation of secondary brown carbon aerosol, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-198, in review, 2018.
Elijah G. Schnitzler and Jonathan P. D. Abbatt
Elijah G. Schnitzler and Jonathan P. D. Abbatt
Elijah G. Schnitzler and Jonathan P. D. Abbatt

Viewed

Total article views: 581 (including HTML, PDF, and XML)

HTML PDF XML Total Supplement BibTeX EndNote
406 166 9 581 29 4 10

Views and downloads (calculated since 29 Mar 2018)

Cumulative views and downloads (calculated since 29 Mar 2018)

Viewed (geographical distribution)

Total article views: 581 (including HTML, PDF, and XML)

Thereof 580 with geography defined and 1 with unknown origin.

Country # Views %
  • 1

Saved

Discussed

Latest update: 18 Jun 2018
Publications Copernicus
Download
Short summary
Brown carbon (BrC) has significant but poorly-constrained effects on climate. In this work, we investigate the effects of OH radical on the optical properties of secondary BrC in a series of smog chamber experiments. At high relative humidity (RH), we find that the evolution of the particles is complex, exhibiting rapid absorption enhancement followed by slow bleaching. At low RH, bleaching does not occur. These results further our understanding of the highly variable evolution of ambient BrC.
Brown carbon (BrC) has significant but poorly-constrained effects on climate. In this work, we...
Share