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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Feb 2019

Research article | 01 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

Siyang Li1, Xiaotong Jiang1, Marie Roveretto3, Christian George2,3, Ling Liu1, Wei Jiang1, Qingzhu Zhang1, Wenxing Wang1, Maofa Ge4, and Lin Du1 Siyang Li et al.
  • 1Environment Research Institute, Shandong University, Binhai Road 72, Qingdao 266237, China
  • 2School of Environmental Science and Engineering, Shandong University, Binhai Road 72, Qingdao 266237, China
  • 3University of Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
  • 4State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

Abstract. Photosensitizing compounds containing brown carbon can absorb UV light and transfer that energy to low volatile organic compounds at the surface of aqueous particles. To better understand the reactivity and photochemical aging processes of organic coating on the aqueous aerosol surface, we have simulated the photosensitized reaction of organic films made of several long chain fatty acids in a Langmuir trough in the presence or absence of irradiation. Several chemicals (imidazole-2-carboxaldehyde and humic acid), PM2.5 samples collected from the field and secondary organic aerosols samples generated from a simulation chamber were used as photosensitizers to be involved in the photochemistry of the organic films. Stearic acid, elaidic acid, oleic acid and two different phospholipids with the same carbon chain length and different degrees of saturation i.e., 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) were chosen as the common organic film-forming species in this analysis. The double bond (trans and cis) in unsaturated organic compounds has an effect on the surface area of the organic monolayer. The OA monolayer possessing a cis double bond in an alkyl chain is more expanded than EA monolayers on artificial seawater that contain a photosensitizer. Monitoring the change in the relative area of DOPC monolayers has shown that DOPC does not react with photosensitizers under dark conditions. Instead, the photochemical reaction initiated by the excited photosensitizer and molecular oxygen can generate hydroperoxidation in the DOPC monolayers, accompanied by an increase in the molecular area. The DSPC monolayers did not yield any photochemical oxidized products under the same conditions. The spectra measured with polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) were also consistent with the results of a surface pressure-area isotherm. Here, a reaction mechanism explaining these observations is presented and discussed. The results will contribute to our understanding of the processing of organic aerosol aging that controls the aerosol composition.

Siyang Li et al.
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Siyang Li et al.
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Short summary
We stimulated the photochemical aging of organic film coated on aqueous aerosol in the presence of imidazole-2-carboxaldehyde, humic acid, atmospheric PM2.5 sample and secondary organic aerosol sample from laboratory. The unsaturated lipid mixed with photosensitizer under UV irradiation produced hydroperoxides, leading to the surface area increase of organic film. Our results reveal the modification of organic film on aqueous aerosol have potential influence on the hygroscopic growth of droplet.
We stimulated the photochemical aging of organic film coated on aqueous aerosol in the presence...