Physical Properties of Secondary Photochemical Aerosol from OH Oxidation of a Cyclic Siloxane

Nathan J. Janechek, Rachel F. Marek, Nathan Bryngelson, Ashish Singh, Robert L. Bullard, William H. Brune, Charles O. Stanier
2018 Atmospheric Chemistry and Physics Discussions  
<p><strong>Abstract.</strong> 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 ~<span class="thinspace"></span>100<span class="thinspace"></span>µg<span
more » ... an class="thinspace"></span>m<sup>&amp;minus;3</sup> of organosilicon aerosol from OH oxidation of decamethylcyclopentasiloxane (D<sub>5</sub>) with aerosol mass fractions (i.e. yields) of 0.2&amp;ndash;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 or from hair conditioner was used as the reaction precursor. Aerosol yield was sensitive to chamber OH, indicating an interplay between oxidation conditions and the concentration of lower volatility species. The D<sub>5</sub> oxidation aerosol products were relatively non-hygroscopic, with average hygroscopicity kappa of ~<span class="thinspace"></span>0.01, and nearly non-volatile up to 190<span class="thinspace"></span>°C temperature. Recommended parameters for treatment as a semi-volatile organic aerosol in atmospheric models are provided.</p>
doi:10.5194/acp-2018-748 fatcat:3neb5lu6jjgvvjqjkazsoubjvq