Secondary Organic Aerosol and Gas-Phase Products from Chlorine-Initiated Oxidation of Decamethylcyclopentasiloxane (D5)

KRISTI MCPHERSON, Nirvan Bhattacharyya, Lea Hildebrandt Ruiz, Pawel K. Misztal, University of Texas at Austin

     Abstract Number: 132
     Working Group: Aerosol Sources and Constituents of Emerging Importance and Their Impacts across Spatial Scales

Abstract
Decamethylcyclopentasiloxane (D5) is a ubiquitous gas phase pollutant emitted by personal care products and observed in concentrations of up to 1100 ng m^-3 outdoors and 56,000 ng m^-3 indoors. While D5 itself is considered non-toxic, the impacts of its oxidation products on air quality and health are less clear. Investigations of D5 oxidation by hydroxyl radicals (OH) have shown the potential for secondary organic aerosol (SOA) formation; however, D5 oxidation by chlorine radicals (Cl) and its potential to form SOA has not been as thoroughly studied. Experiments on Cl-initiated D5 oxidation in this work have shown that at high chlorine concentrations, which can occur in indoor environments, SOA yields range from 30% to 170%. This work also investigates gas phase products, which included D5 rings with various functional group substitutions, C_wH_xO_ySi_z fragments, and chlorinated species. Other findings include evidence for Cl-initiated oxidation of D5 under LED lighting conditions (which simulate indoor lighting conditions) and potential issues with detecting Si-containing particles in the Aerosol Chemical Speciation Monitor (ACSM). The effect of NO_x on this reaction system was also examined.

The Cl-initiated oxidation of D5 was studied in seeded chamber experiments with varying D5 and Cl₂ concentrations. Particle and gas-phase products were analyzed with an ACSM, a Scanning Electrical Mobility Spectrometer (SEMS), an Iodide-mode Chemical Ionization Mass Spectrometer (I-CIMS) with a Filter Inlet for Gases and Aerosols (FIGAERO), a Proton-Transfer-Reaction Mass Spectrometer (Vocus-2R-PTRMS), and monitors for O₃, NO_x and NO₂.