Comparison of the Yield and Chemical Composition of Secondary Organic Aerosol Generated from the OH and Cl Oxidation of Decamethylcyclopentasiloxane

Cyclic volatile methyl siloxanes (cVMS) that are emitted from industrial processes and consumer products often dominate the burden of volatile organic compounds (VOCs) in occupied spaces. cVMS may contribute to oxygenated VOC and secondary organic aerosol (SOA) formation following oxidation by gas-phase radicals in both indoor and outdoor source regions. Several recent studies examined the SOA formation potential of decamethylcyclopentasiloxane (D5) following exposure to hydroxyl radicals (OH) and found that this reaction generates SOA in high yield following multiple days of oxidative aging. Chlorine atoms (Cl) may compete with OH for the oxidative loss of D5 in indoor and outdoor source regions with active chlorine chemistry, but the SOA formation potential of D5 + Cl reactions has not been studied. Here, we characterized the yield and chemical composition of SOA generated from Cl oxidation of D5 in an oxidation flow reactor (OFR) under dry [relative humidity (RH) < 5%] and humid (RH = 40%) conditions and compared results to the yield and composition of SOA generated from OH oxidation of D5. D5 was oxidized using integrated OH and Cl exposures (OHexp and Clexp) ranging from 1.1 x 1012 to 8.2 x 1012 cm-3 s and from 1.6 x 1010 to 1.6 x 1012 cm-3 s, respectively. Like OH, Cl facilitated multistep SOA oxidative aging over the range of OFR conditions that were studied, with maximum SOA mass yields of 1.5 and 1.3 obtained following OH and Cl oxidation of D5 under humid conditions. These results suggest that indoor and outdoor source regions that are significantly influenced by chlorine chemistry may enhance the atmospheric SOA formation potential of D5.