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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 13 | Copyright
Atmos. Chem. Phys., 17, 8357-8370, 2017
https://doi.org/10.5194/acp-17-8357-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Jul 2017

Research article | 10 Jul 2017

Comprehensive atmospheric modeling of reactive cyclic siloxanes and their oxidation products

Nathan J. Janechek1,2, Kaj M. Hansen3, and Charles O. Stanier1,2 Nathan J. Janechek et al.
  • 1Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, USA
  • 2IIHR Hydroscience and Engineering, University of Iowa, Iowa City, IA 52242, USA
  • 3Department of Environmental Science, Aarhus University, Roskilde, Denmark

Abstract. Cyclic volatile methyl siloxanes (cVMSs) are important components in personal care products that transport and react in the atmosphere. Octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and their gas-phase oxidation products have been incorporated into the Community Multiscale Air Quality (CMAQ) model. Gas-phase oxidation products, as the precursor to secondary organic aerosol from this compound class, were included to quantify the maximum potential for aerosol formation from gas-phase reactions with OH. Four 1-month periods were modeled to quantify typical concentrations, seasonal variability, spatial patterns, and vertical profiles. Typical model concentrations showed parent compounds were highly dependent on population density as cities had monthly averaged peak D5 concentrations up to 432ng m−3. Peak oxidized D5 concentrations were significantly less, up to 9ng m−3, and were located downwind of major urban areas. Model results were compared to available measurements and previous simulation results. Seasonal variation was analyzed and differences in seasonal influences were observed between urban and rural locations. Parent compound concentrations in urban and peri-urban locations were sensitive to transport factors, while parent compounds in rural areas and oxidized product concentrations were influenced by large-scale seasonal variability in OH.

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Gas-phase cyclic volatile methyl siloxanes and their oxidation products, which are likely precursors to secondary organic aerosol, were modeled using an atmospheric transport model over North America. Typical concentrations, spatial patterns, seasonal variability, and vertical profiles were quantified. Urban parent compound concentrations were sensitive to transport factors, while rural parent and oxidized product concentrations were sensitive to large-scale seasonal variability in OH.
Gas-phase cyclic volatile methyl siloxanes and their oxidation products, which are likely...
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