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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-270
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
28 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Secondary Organic Aerosol from Atmospheric Photooxidation of Indole
Julia Montoya1, Jeremy R. Horne2, Mallory L. Hinks1, Lauren T. Fleming1, Veronique Perraud1, Peng Lin3, Alexander Laskin3, Julia Laskin4, Donald Dabdub2, and Sergey A. Nizkorodov1 1Department of Chemistry, University of California, Irvine, CA 92697, USA
2Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697, USA
3Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, USA
4Physical Sciences Division Pacific Northwest National Laboratory, Richland, WA 99354, USA
Abstract. Indole is a heterocyclic compound emitted by various plant species under stressed conditions or during flowering events. The formation, optical properties, and chemical composition of secondary organic aerosol (SOA) formed by low-NOx photooxidation of indole were investigated. The SOA yield (1.1 ± 0.3) was estimated from measuring the particle mass concentration with a scanning mobility particle sizer (SMPS) and correcting it for the wall loss effects. The SOA particles were collected on filters and analysed offline with UV-Vis spectrophotometry to measure the mass absorption coefficient (MAC) of the bulk sample. The samples were visibly brown and had MAC values of ~7 m2/g at λ = 300 nm and ~2 m2/g at λ = 400 nm, comparable to strongly absorbing brown carbon emitted from biomass burning. The chemical composition of SOA was examined with several mass spectrometry methods. The direct analysis in real time mass spectrometry (DART-MS) and nanospray desorption electrospray high resolution mass spectrometry (nano-DESI-HRMS) were used to provide information about the overall distribution of SOA compounds. High performance liquid chromatography, coupled to photodiode array spectrophotometry and high resolution mass spectrometry (HPLC-PDA-HRMS) was used to identify chromophoric compounds. Indole derivatives, such as tryptanthrin, indirubin, indigo dye, and indoxyl red were found to contribute significantly to the visible absorption spectrum of indole SOA. The potential effect of indole SOA on air quality was explored with the airshed model, which found elevated concentrations of indole SOA during the afternoon hours contributing considerably to the total organic aerosol under selected scenarios. Because of its high MAC values, indole SOA can contribute to decreased visibility and poor air quality.

Citation: Montoya, J., Horne, J. R., Hinks, M. L., Fleming, L. T., Perraud, V., Lin, P., Laskin, A., Laskin, J., Dabdub, D., and Nizkorodov, S. A.: Secondary Organic Aerosol from Atmospheric Photooxidation of Indole, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-270, in review, 2017.
Julia Montoya et al.
Julia Montoya et al.
Julia Montoya et al.

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Short summary
Various plant species emit a compound called indole under stressed conditions or during flowering events. Our experiments show that indole can be oxidized in the atmosphere to become a brownish haze containing well know indole derived dyes, such as indigo dye. An airshed model that includes indole chemistry shows that indole aerosol makes a significant contribution to the total aerosol burden and to visibility.
Various plant species emit a compound called indole under stressed conditions or during...
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