AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Explaining Changes in SOA Optical Properties by Evaluating Chemical Characteristics of Chamber-Derived SOA
STEPHEN ZIMMERMAN, Justin Min, Justin Dingle, Roya Bahreini, University of California, Riverside
Abstract Number: 661 Working Group: Aerosol Chemistry
Abstract Atmospheric particles directly influence the global radiative budget by absorbing and scattering light. Particulate matter formed from gases in the atmosphere, otherwise known as secondary organic aerosol (SOA), influence the optical properties of bulk aerosol. This presentation explores changes in the chemical properties of SOA formed under various experimental conditions in an environmental smog chamber. Individual chamber experiments showcase high and low concentrations of alpha-pinene, toluene, and 1-methylnaphthalene exposed to an oxidizing radical, hydroxyl (OH$^-) or chloride (Cl$^-). Furthermore, these series of experiments are conducted under NO$_x-free, intermediate, and high-NO$_x conditions. An Aerodyne mini-aerosol mass spectrometer (mAMS) is used in this study to obtain fast, size-resolved, non-refractory chemical composition of submicron particles. The data obtained by the mAMS is analyzed to produce mass concentrations of SOA, nitrate, and chloride. High-resolution analysis is performed to determine contributions of C$_xH$_y$^+,C$_xH$_yO$^+, and C$_xH$_yO$_z$^+ ions, from which elemental ratios of O:C and H:C are calculated. Additionally, the effect of aging on the mass spectral characteristics of SOA is tracked by observing the evolution of the contribution of oxygenated vs. hydrocarbon-like ions at key fragments (e.g., m/z 43, 55, 57). Variability of these parameters with oxidation condition, HC/NO$_x ratio, and O$_x (NO$_x + O$_3) are studied in order to explain the observed variabilities in SOA mass absorption efficiency (MAE), single scattering albedo (SSA) and Angstrom exponent of extinction.