AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Experimental Characterization of Secondary Aerosol from D5 Cyclic Siloxane Oxidation
NATHAN JANECHEK, Nathan Bryngelson, Traci Lersch, Kristin Bunker, Gary Casuccio, William Brune, Charles Stanier, University of Iowa
Abstract Number: 319 Working Group: Aerosol Chemistry
Abstract Cyclic siloxanes are anthropogenic chemicals present in personal care products such as antiperspirants. These are volatile chemicals that are readily released into the atmosphere by personal care product use. Since personal care products used by people are the primary source of cyclic siloxanes, population density strongly determines concentrations, with urban and indoor environments having the greatest concentrations. In the atmosphere, cyclic siloxanes undergo reaction with atmospheric hydroxyl radicals (OH) forming oxidation products that can form aerosol species. While the parent compounds have been well studied, the oxidation products have largely been unexplored, no ambient measurements or physical property data are currently available. More importantly, ultrafine particles are known to adversely affect human health, and cyclic siloxanes may represent an important source of ultrafine particles due to ubiquitous use and high exposure potential indoors. Therefore, understanding the behavior of the aerosol species is important. In this work, we characterize generated cyclic siloxane particles in order to provide thermodynamic parameters important to understand the secondary aerosol formation. The Potential Aerosol Mass (PAM) photochemical chamber is used to oxidize the cyclic siloxane D5 to generate aerosol species. The particles are characterized by imaging with Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDS), and volatility, hygroscopicity, and yield data are measured. Volatility data was collected using a Volatility Tandem Differential Mobility Analyzer (V-TDMA) which heats the particles. Comparing shifts in particle size, vapor pressure and enthalpy of vaporization are estimated. Hygroscopicity (water uptake) data was collected using a Droplet Measurement Technologies Cloud Condensation Nuclei Counter (DMT-CCN), using Kohler theory the hygroscopicity parameter is calculated. PAM chamber conditions of OH production, residence time, gas phase concentrations, and seed aerosols are varied to determine the sensitivity to aerosol yield.