Abstract
Cyclic volatile methyl siloxanes (cVMS) are high-production chemicals present in many personal care products. They are volatile, hydrophobic, and relatively long-lived due to slow oxidation kinetics. Evidence from chamber and ambient studies indicates that oxidation products may be found in the condensed aerosol phase. In this work, we use an oxidation flow reactor to produce ~ 100 μgm-3 of organosilicon aerosol from OH oxidation of decamethyl-cyclopentasiloxane (D5) with aerosol mass fractions (i.e., yields) of 0.2-0.5. The aerosols were assessed for concentration, size distribution, morphology, sensitivity to seed aerosol, hygroscopicity, volatility and chemical composition through a combination of aerosol size distribution measurement, tandem differential mobility analysis, and electron microscopy. Similar aerosols were produced when vapor from solid antiperspirant was used as the reaction precursor. Aerosol yield was sensitive to chamber OH and to seed aerosol, suggesting sensitivity of lower-volatility species and recovered yields to oxidation conditions and chamber operation. The D5 oxidation aerosol products were relatively non-hygroscopic, with an average hygroscopicity kappa of ~ 0.01, and nearly non-volatile up to 190 °C temperature. Parameters for exploratory treatment as a semi-volatile organic aerosol in atmospheric models are provided.
Highlights
Cyclic volatile methyl siloxanes are high-production chemicals (OECD Environment Directorate, 2004) present in many personal care products such as lotions, hair conditioners, and antiperspirants (Horii and Kannan, 2008; Wang et al, 2009; Lu et al, 2011; Dudzina et al, 2014; Capela et al, 2016)
This study adds to the short list of laboratory confirmations where aerosol formation from OH oxidation of D5 has been observed and provides one of the first assessments of particle morphology
A further confirmation of atmospheric relevance was conducted by verifying that similar aerosols were produced when vapor from solid antiperspirant was used as the reactant
Summary
Cyclic volatile methyl siloxanes (cVMS) are high-production chemicals (OECD Environment Directorate, 2004) present in many personal care products such as lotions, hair conditioners, and antiperspirants (Horii and Kannan, 2008; Wang et al, 2009; Lu et al, 2011; Dudzina et al, 2014; Capela et al, 2016). Cyclic siloxanes are volatile (Lei et al, 2010), relatively unreactive, and hydrophobic molecules (Varaprath et al, 1996) composed of a Si–O ring backbone with two methyl groups bonded to each Si. The most prevalent cVMS in personal care products is decamethylcyclopentasiloxane (D5) (Horii and Kannan, 2008; Dudzina et al, 2014; Lu et al, 2011; Wang et al, 2009).
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