Formation of Aqueous SOA From Water-Soluble Gaseous Products of Monoterpene Oxidation
MATT ZARAGOZA, Lisa Wingen, Sergey Nizkorodov, Annmarie Carlton, University of California, Irvine
Abstract Number: 92
Working Group: Aerosol Chemistry
Abstract
Aqueous secondary organic aerosol (aqSOA) refers to compounds that are produced by the chemical transformations of small organic molecules into less volatile molecules in aqueous environments, such as cloud droplets and wet aerosols. The amount and impact of aqSOA produced from gaseous products of oxidation of common volatile organic compounds (VOCs) are still highly uncertain. A large fraction of these VOC oxidation products can be classified as water-soluble organic carbon (WSOCg), and they can undergo aqueous photochemical processing upon exposure to ultraviolet radiation in aqueous environments to generate aqSOA. This project aims to quantify the mass yields and chemical composition of aqSOA from gaseous products of alpha-pinene oxidation. A mixture of alpha-pinene oxidation products was generated in an oxidation flow reactor using the hydroxyl radical (•OH) as the primary oxidant. The oxidation products were passed through a Teflon 0.2 μm filter to remove particulate matter, allowing only gaseous oxidation products to pass through. A glass mist chamber was used to partition WSOCg into aqueous mist droplets, mimicking atmospheric aqueous environments. Aqueous WSOCg samples were irradiated with 254 nm radiation in presence of H2O2 in order to simulate •OH-driven aging over various time periods. Photooxidized samples were atomized, and AMS and SMPS instruments were used to determine aqSOA mass yields and chemical composition. Separately, an Orbitrap high-resolution mass spectrometer was used to measure the formula distribution of aqSOA compounds, and a total organic carbon analyzer was used to quantify the changes in dissolved organic mass concentration. There was a noticeable increase in particle-phase mass concentration for both the AMS and SMPS as photooxidation time increases, indicating the formation of aqSOA. Results from this experiment will help models better describe aqSOA formation from the aqueous processing of water-soluble alpha-pinene oxidation products.