Comprehensive Atmospheric Modeling of Reactive Cyclic Siloxanes and Their Oxidation Products
Nathan J. Janechek1,2, Kaj M. Hansen3, and Charles O. Stanier1,21Department 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
Received: 24 Dec 2016 – Accepted for review: 03 Jan 2017 – Discussion started: 06 Jan 2017
Abstract. Cyclic volatile methyl siloxanes (cVMS) 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 432 ng m−3. Peak oxidized D5 concentrations were significantly less, up to 9 ng 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.
Janechek, N. J., Hansen, K. M., and Stanier, C. O.: Comprehensive Atmospheric Modeling of Reactive Cyclic Siloxanes and Their Oxidation Products, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1159, in review, 2017.