AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Impact of Aerosol Acidity and Aerosol Liquid Water on Volatility and the Chemical Composition of SOA Formed from Alpha-Pinene Ozonolysis
MATTHIEU RIVA, Liine Heikkinen, Otso Peräkylä, Matti Rissanen, Mikael Ehn, University of Helsinki
Abstract Number: 98 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract The most abundant secondary organic aerosol (SOA) precursors are isoprene and monoterpenes, such as alpha-pinene. The formation of monoterpene-derived SOA has been qualitatively explained by gas-phase oxidation reactions of monoterpenes leading to condensable low-volatility products. Ozonolysis of alpha-pinene leads to the formation of multifunctional gas-phase products including alcohols, hydroperoxides, epoxides and carbonyls. Such compounds can then condense onto aerosol surfaces and contribute to SOA formation. Recent studies have highlighted the importance of multiphase chemistry, such as acid-catalyzed reactive uptake of epoxide products or decomposition of hydroperoxides, in SOA formation. Although many previous studies have characterized the oxidation of alpha-pinene and subsequent SOA formation, the coupled role of aerosol liquid water and acidity on the chemical composition and the physical-chemical properties of SOA remain uncertain.
In the present work, ozonolysis of alpha-pinene was systematically examined with varying composition and phase (i.e. effloresced/deliquesced) of seed particles. Size-selected ammonium sulfate aerosol particles (acidified and non-acidified) were injected into the chamber under dry or wet conditions to evaluate the importance of multiphase chemistry in the chemical composition of the monoterpene-derived SOA. Experiments were conducted at room temperature (27 ± 2°C) and atmospheric pressure in a 2-m3 Teflon chamber. Gaseous organic compounds were chemically characterized using two time-of-flight chemical ionization mass spectrometers (HR-ToF-CIMS) with iodide (I−) and nitrate (NO3−) ionization sources and a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). In addition, the particle-phase was chemically characterized using a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to an I−-HR-ToF-CIMS and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Hundreds of compounds, including highly oxidized products and oligomers, were observed in both gas- and particle phases. Thermograms of individual SOA constituents, reveal multiphase chemistry leading to an increase of the aerosol loadings and oligomers and impacting the aerosol volatility, especially in the presence of dry acidic particles.