Advances in the Separation and Detection of Secondary Organic Aerosol Produced by Decamethylcyclopentasiloxane (D 5 ) in Laboratory-Generated and Ambient Aerosol.

Decamethylcyclopentasiloxane (D 5 ), a common ingredient in many personal care products (PCPs), undergoes oxidation in the atmosphere, leading to the formation of secondary organic aerosol (SOA). Yet, the specific contributions of D 5 -derived SOA on ambient fine particulate matter (PM 2.5 ) have not been characterized. This study addresses this knowledge gap by introducing a new analytical method to advance the molecular characterization of oxidized D 5 and its detection in ambient aerosol. The newly developed reversed phase liquid chromatography method, in conjunction with high-resolution mass spectrometry, separates and detects D 5 oxidation products, enabling new insights into their molecular and isomeric composition. Application of this method to laboratory-generated SOA and urban PM 2.5 in New York City expands the number of D 5 oxidation products observed in ambient aerosol and informs a list of molecular candidates to track D 5 -derived SOA in the atmosphere. An oxidation series was observed in which one or more methyl groups in D 5 (C 10 H 30 O 5 Si 5 ) is replaced by a hydroxyl group, which indicates the presence of multistep oxidation products in ambient PM 2.5 . Because of their specificity to PCPs and demonstrated detectability in ambient PM 2.5 , several oxidation products are proposed as molecular tracers for D 5 -derived SOA and may prove useful in assessing the impact of PCPs-derived SOA in the atmosphere.