Gas-Particle Distribution of D ₅ Oxidation Products in New York City during Summertime

Personal care products can release decamethylcyclopentasiloxane (D₅) to the atmosphere, where it oxidizes to form 1-hydroxynonamethylcyclopentasiloxane (D₄TOH). This oxidation product subsequently can partition to the particle-phase to form secondary organic aerosol (SOA). The gas-particle distribution of D₄TOH has been studied in the laboratory but has yet to be established in ambient air. This study examines the gas-particle distribution of D₄TOH and related oxidation products in New York City during the summertime of 2022 using medium volume air samplers, solvent extraction, and gas and liquid chromatography mass spectrometry methods. Positive sampling artifacts constituted the majority of D₄TOH observed on quartz fiber filters (54-100%, averaging 86%, <i>n</i> = 12), indicating the high potential for particle-phase D₄TOH to be overestimated. After artifact correction, D₄TOH was observed in fine particles in 5 of the 12 sampling periods, with its particle-phase fraction averaging 13%. Because D₄TOH is predominantly in the gas phase, it makes a minor contribution to D₅-derived SOA during summertime. Further oxidation products of D₅, including di, and tetrasiloxanols are predominantly in the particle-phase (>77%, <i>n</i> = 4) during summertime and have relatively small positive artifacts. These polysiloxanols provide evidence of D₅-derived SOA in the urban aerosols and are more suitable tracers for D₅-derived SOA than D₄TOH in summertime because of their higher particle-phase fractions.