Field Measurements of Carbonaceous Aerosol and Secondary Aerosol Tracers for Volatile Methyl Siloxanes in New York City

JOSIE WELKER, Jeewani Meepage, Saeideh Mohammadi, Christopher Brunet, Hanalei Lewine, Rachel Marek, Keri Hornbuckle, Eleanor Browne, Charles Stanier, Elizabeth Stone, University of Iowa

     Abstract Number: 443
     Working Group: Carbonaceous Aerosol

Abstract
Volatile methyl siloxanes (VMS) are known environmental pollutants from personal care products (PCP). In the atmosphere, they are oxidized to form oxidized volatile methyl siloxanes (oVMS) that can partition to form secondary organic aerosol (SOA). This study aims to quantify oVMS in gas and aerosol phases to establish their gas-particle partitioning in ambient air. Fine particle (PM_2.5) and gas phase samples were collected on the rooftop of the City University of New York Advanced Science and Research Center located in northern Manhattan, New York City from July 7 to August 3, 2022. PM_2.5 was collected on to precleaned quartz fiber filters and semi-volatile gases were collected onto precleaned polyurethane foam filters (PUF) at a sampling frequency of 12 hours. PM_2.5 samples were analyzed for elemental carbon (EC) and organic carbon (OC) concentrations using thermal-optical methods. OC concentrations ranged from 2.2 μg/m³ – 7.4 μg/m³ with a daytime average of 4.7 μg/m³ and a nighttime average of 4.5 μg/m³, while EC concentrations ranged from 0.16 μg/m³ – 0.56 μg/m³ with a daytime average of 0.29 μg/m³ and a nighttime average of 0.37 μg/m³. OC/EC ratios ranged from 5.8 – 27. The higher average daytime OC/EC ratio (17) compared to average nighttime (13) suggests photochemical SOA formation during the daytime. A thermal-desorption gas chromatography mass spectrometry (GCMS) method is being developed to examine tracers of PCP-derived SOA, while solvent extraction GCMS methods will be used to analyze these tracers in the gas phase. This research will inform our understanding of the temporal variation in the magnitude of PCP-derived SOA in ambient air through the gas-particle partitioning of oVMS.