# Gas-Particle Distribution of D5 Oxidation Products in New York City during Summertime

## TL;DR

This study examines how D5 oxidation products, like D4TOH, distribute between gas and particles in New York City's air during summer.

## Contribution

The study provides the first ambient measurement of D4TOH's gas-particle distribution and identifies better tracers for D5-derived SOA.

## Key findings

- D4TOH showed high positive sampling artifacts on quartz filters, averaging 86%.
- After correction, D4TOH was found in fine particles in 5 of 12 sampling periods with an average particle-phase fraction of 13%.
- Polysiloxanols, as further oxidation products, are predominantly in the particle-phase and are better tracers for D5-derived SOA.

## Abstract

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%, n = 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%, n = 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.