AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Mixing of Secondary Organic Aerosols from Terpenes: Eff ects of Relative Humidity, Temperature and Oxidation State
QING YE, Mary Alice Upshur, Ellis Shipley Robinson, Regan Thomson, Ryan Sullivan, Franz Geiger, Neil Donahue, Carnegie Mellon University
Abstract Number: 430 Working Group: Single Aerosol Particle Studies - Techniques and Instrumentation
Abstract While practically all chemical transport models assume instantaneous ideal mixing of organic constituents from various sources, very few experimental studies have been performed to prove this assumption. Specifically, direct investigation on mixing of semi-volatile organic compounds (SVOCs) produced from secondary organic aerosol (SOA) formation is scarce. In this work, we study mixing dynamics of SOA generated from mono-terpenes (alpha-pinene and limonene) and a sesquiterpene (beta-caryophyllene), with a focus on probing any diffusion or volatility limitation that may influence effective absorption of SVOCs. By using isotopically labeled precursors and quantitative single particle mass spectrometry, we are able to separate different SOA populations after we combine them into a uniform container. We then analyze their mixing via SVOC exchange. We will also explore the mixing process under various atmospherically-relevant temperatures, relative humidities and oxidation states.
Our preliminary results show that SOA from alpha-pinene ozonolysis is able to uptake SVOCs on a timescale shorter than one hour, indicating that there are no significant diffusion barriers in the condensed phase. By quantifying the extent of vapor exchange, we show that SOA from alpha-pinene ozonolysis contains 20%{40% effective semi-volatile material depending on the total SOA concentration. However, SOA from ozonolysis of beta-caryophyllene resists SVOC uptake under low and moderate RH on the timescale of several hours. At 50% RH, the resistance diminishes and mixing occurs. This work, complemented by existing SOA rheological studies in the literature, will provide valuable information to the treatment of SOA partitioning in chemical transport models, and ultimately improve our prediction of air quality and climate change.