Cyclic volatile methyl siloxanes (cVMSs) are important components inpersonal care products that transport and react in the atmosphere.Octamethylcyclotetrasiloxane (D), decamethylcyclopentasiloxane(D), dodecamethylcyclohexasiloxane (D), and their gas-phaseoxidation products have been incorporated into the Community Multiscale AirQuality (CMAQ) model. Gas-phase oxidation products, as the precursor tosecondary organic aerosol from this compound class, were included to quantifythe 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 modelconcentrations showed parent compounds were highly dependent on populationdensity as cities had monthly averaged peak D concentrations up to432 ng m. Peak oxidized D concentrations weresignificantly less, up to 9 ng m, and were located downwind ofmajor urban areas. Model results were compared to available measurements andprevious simulation results. Seasonal variation was analyzed and differencesin seasonal influences were observed between urban and rural locations.Parent compound concentrations in urban and peri-urban locations weresensitive to transport factors, while parent compounds in rural areas andoxidized product concentrations were influenced by large-scale seasonalvariability in OH.
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