Secondary organic aerosol formation from the oxidation of decamethylcyclopentasiloxane at atmospherically relevant OH concentrations

Decamethylcyclopentasiloxane (D5,C10H30O5Si5) is measured at parts per trillion (ppt) levels outdoors and parts per billion (ppb) levels indoors. Primarily used in personal care products, its outdoor concentration is correlated to population density. Since understanding the aerosol formation potential of volatile chemical products is critical to understanding particulate matter in urban areas, the secondary organic aerosol yield of D5 was studied under a wide range of OH concentrations and, correspondingly, OH exposures using both batch-mode chamber and continuously run flow tube experiments. These results were comprehensively analyzed and compared to two other secondary organic aerosol (SOA) yield datasets from literature. It was found that the SOA yield from the oxidation of D5 is extremely dependent on either the OH concentration or exposure. For OH concentrations of less than or similar to 10(7) molec. cm(-3) or OH exposures of less than or similar to 2 x 10(11) molec.s cm(-3), the SOA yield is largely < 5 % and usually similar to 1 %. This is significantly lower than SOA yields previously reported. Using a two-product absorptive partitioning model for the upper bound SOA yields, the stoichiometric mass fraction and absorptive partitioning coefficients are, for the first product, proportional to(1) = 0.056 and K-OM,K-1 = 0.022 m(3) mu g(-1); for the second product, they are proportional to(2) = 7.7 and K-OM,K-2 = 4.3 x 10(-5) m(3) mu g(-1). Generally, there are high SOA yields (> 90 %) at OH mixing ratios of 5 x 10(9) molec. cm(-3) or OH exposures above 10(12) molec.s cm(-3).

Automated summary

Decamethylcyclopentasiloxane (D5) is a chemical compound commonly used in personal care products. Its concentration outdoors and indoors is correlated to population density. The formation of secondary organic aerosol (SOA) from the oxidation of D5 is highly dependent on the concentration or exposure of hydroxyl radicals (OH).