Cyclic Siloxane Oxidation over North America: Quantifying the Strength and Properties of Widespread Silicon from Personal Care Products
Abstract
Cyclic volatile methyl siloxanes (cVMS) are present in personal care and consumer products such as antiperspirants. Their environmental fate is mainly volatilization to air, followed by oxidation at time scales of approximately one week. cVMS has been studied for decades as a potential long-range transport organic pollutant. However, recently, the research focus has shifted to evaluating its role as a source of secondary aerosols, its role as an ozone precursor, its role as an indoor air pollutant, and its role as an anthropogenic marker compound. The shift is a result of laboratory, field, and model evaluation of its aerosol formation potential, and further by the growing realization of the importance of volatile chemical products, including personal care products, in atmospheric chemistry.
We present related laboratory and modeling studies which investigate and quantify, for both precursors and secondary aerosol particles, critical aspects of environmental loading, transport, and aerosol formation capacity for this anthropogenic compound class. These include laboratory aerosol generation in an Oxidation Flow Reactor (OFR), and physical and chemical particle characterization (concentration, size distribution, morphology, chemical composition, aerosol yield, volatility, and CCN formation potential). Analyzed aerosols contained spherical primary particles, aggregate formation, and elemental composition consistent with aerosols derived from cVMS. Measured aerosol yields at OH exposures equivalent to aging of 12-40 days were 20-50% with typical aerosol number concentrations of 300,000 cm-3, up to 200 μg m-3 of aerosol mass, and diameters of 60-80 nm. Particles had low hygroscopicity with kappa Köhler (κ) values of 0.01. The cVMS compounds and their oxidation products were added to the CMAQ 3D photochemical grid model. Typical concentrations, seasonal variability, spatial patterns, and vertical profiles for parent compounds and secondary species were quantified over North America during four separate seasons. The paper will summarize our experimental results, place this research into context with the geochemical cycle for Si and discuss implications for aerosol measurement and modeling at indoor, urban, and remote locations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A52C..08S
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0368 Troposphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES