AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Relating Chemical Evolution of Laboratory Generated SOA to Optical Properties
STEPHEN ZIMMERMAN, Justin Dingle, Alexander Frie, Justin Min, Roya Bahreini, University of California, Riverside
Abstract Number: 785 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Atmospheric particles directly influence the global radiative budget by absorbing and scattering solar radiation. Particulate matter formed from oxidation of various gaseous precursors, otherwise known as secondary organic aerosol (SOA), influence the optical properties of bulk aerosol. In this study, laboratory generated SOA is formed via photooxidation of α-pinene (AP) and 1-methylnaphthalene (1-MNPH) with hydroxyl radical (OH.) in an atmospheric smog chamber, at high and low concentrations of hydrocarbons and nitrogen oxides (NOx). An Aerodyne mini-aerosol mass spectrometer (mAMS) is used to obtain fast, size-resolved, non-refractory chemical composition and mass concentrations of organic and nitrate submicron particles while online optical properties are measured by a Cavity Attenuated Phase-Shift (CAPS) spectrometer and Photoacoustic Extinctiometer (PAX). High resolution analysis is performed to determine contributions of CxHy+, CxHyO+, and CxHyOz>1+ ion families. Fractional contribution of CxHyOz>1+ increases with photooxidation from both compounds and is greater for 1-MNPH, suggesting SOA becomes more highly oxygenated. Fractional contribution of CxHyO+ decreases for AP and remains constant for 1-MNPH. Contribution of oxygenated vs. hydrocarbon-like ions at key fragments (e.g., m/z 43, 44, 55, 57) is also tracked to capture the effect of aging on the mass spectral characteristics of SOA. Distribution of f44 vs. f43 in triangle space indicates a larger contribution of semi-volatile oxygenated organic aerosol (SV-OOA) products from AP precursor, while SOA products of 1-MNPH oxidation over time move towards the low-volatility oxygenated organic aerosol (LV-OOA) region. Decreasing ratio of NO2+/NO+ after addition of NO suggests growth of organo-nitrates. Changes in chemical signatures will be used to examine the observed variabilities in SOA mass absorption coefficient (MAC), single scattering albedo (SSA), and Ångström exponent of extinction.