AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Experimental Characterization and Lung Cytotoxicity of Secondary Aerosol from D5 Cyclic Siloxane Oxidation
NATHAN JANECHEK, Benjamin King, Nathan Bryngelson, Rachel Marek, Andrea Adamcakova-Dodd, Traci Lersch, Kristin Bunker, Gary Casuccio, William Brune, Peter Thorne, Keri Hornbuckle, Jennifer Fiegel, Charles Stanier, University of Iowa
Abstract Number: 472 Working Group: Aerosol Chemistry
Abstract Cyclic volatile methyl siloxanes are anthropogenic chemicals present in personal care products such as antiperspirants and lotions. These are volatile chemicals that are readily released into the atmosphere by product use. Due to their emission and relatively slow kinetics of their major transformation pathway (reaction with hydroxyl radicals (OH)), these compounds are present in high concentrations in indoor environments and widespread in outdoor environments. While the parent compounds have been well-studied, the oxidation products have received much less attention, with almost no ambient measurements or experimental physical property data. We report physical properties of aerosols generated by reacting the cyclic siloxane D5 with OH using a Potential Aerosol Mass (PAM) photochemical chamber. The particles were characterized by SMPS, imaging and elemental analysis using both Scanning Electron Microscopy and Transmission Electron Microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDS and TEM-EDS), volatility measurements using Volatility Tandem Differential Mobility Analyzer (V-TDMA), and hygroscopicity measurements using a Droplet Measurement Technologies Cloud Condensation Nuclei Counter (DMT-CCN). Aerosol yield sensitivity to D5 and OH concentrations, residence time, and seed aerosols were analyzed. SEM-EDS and TEM-EDS analysis show spherical particle morphology with elemental composition consistent with aerosols derived from cyclic siloxane sources. Measured aerosol yields were 20-50% with typical aerosol concentrations 300,000 particles cm-3, up to 200 μg m-3, and diameters of 30-90 nm. Particles experienced little diameter change after heating up to 200°C suggesting low volatility, while particle activation was retarded compared to ammonium sulfate suggesting moderate hygroscopicity in line with other secondary organics. Cellular toxicity was tested by exposing A549 lung epithelial cells to the generated aerosols using an in vitro air-liquid interface exposure system. No significant difference in cell viability could be attributed exclusively to the aerosol species. No increases were observed in biomarkers of inflammation and oxidative stress.