Chemical characterization and formation of secondary organosiloxane aerosol (SOSiA) from OH oxidation of decamethylcyclopentasiloxane

Abstract

Cyclic volatile methyl siloxanes (cVMS) are anthropogenic chemicals emitted by consumer and industrial products. Evidence from laboratory and ambient studies indicates that cVMS contributes to the formation of secondary organosiloxane...

Advances in the Separation and Detection of Secondary Organic Aerosol Produced by Decamethylcyclopentasiloxane (D5) in Laboratory-Generated and Ambient Aerosol

“…Their compositional changes from D 5 (Table ) correspond to the replacement of 1, 2, 3, and 4 methyl groups with hydroxyl groups. This oxidation series is consistent with prior OFR experiments ,, and indicates the production of multiple generations of D 5 oxidation products in the OFR experiments. Here, the substitution of one methyl group with a hydroxyl group represents a single oxidation step and generates the first-generation oxidation product, and this pattern continues for subsequent generations.…”

“…Reasonable formulas were assigned based on the following criteria: (a) elemental composition falls in the range of C 0-30 H 0-90 O 0-30 Si 0-20 N 0-10 , (b) theoretical m/z values fall within the ±5 ppm of the observed m/z value, and (c) observed isotope distributions agreed within 50% with the theoretical isotope distributions for A+1, and A+2 peaks. The most abundant isotopes of Si, including 28 Si at 92.2%, 29 Si at 4.7%, and 30 Si at 3.1%, show a unique isotopic pattern in the mass spectrum for oVMS.…”

“…1-Hydroxynonamethylcyclopentasiloxane (D 4 TOH) has been identified as the major D 5 -derived oVMS product . The gas-particle partitioning of D 4 TOH may depend on aerosol composition and varies with aerosol concentration, humidity, and temperature. , Hundreds of additional oVMS products were observed in aerosols collected from D 5 oxidation in laboratory oxidation experiments. ,− These products included ring-opened products, monomers, and dimers. Oxidation introduced functional groups to the VMS, including silanol, silyl alcohol, carboxylic acid, formate esters, and carbonyls.…”

“…Measurements of oVMS in ambient aerosol have been limited by their expectedly low concentrations, lack of authentic standards for identification and quantification, and the capabilities of analytical methodology. While high-resolution mass spectrometry coupled to direct sample infusion with electrospray ionization (ESI) and aerosol mass spectrometry have proven useful in identifying Si-containing molecular formulas of oVMS with high accuracy, ,− these techniques are unable to resolve oVMS isomers. Additionally, these techniques measure the components of aerosol samples simultaneously, which may hinder the detection of components at low concentrations, particularly in complex environmental matrices.…”

“… 19 , 26 Hundreds of additional oVMS products were observed in aerosols collected from D 5 oxidation in laboratory oxidation experiments. 20 , 27 − 29 These products included ring-opened products, monomers, and dimers. Oxidation introduced functional groups to the VMS, including silanol, silyl alcohol, carboxylic acid, formate esters, and carbonyls.…”