AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Refractive Index of Secondary Organic Aerosols Formed from Oxidation of Alpha-Pinene, Longifolene, Phenol and 1-Methylnaphthalene
JUSTIN DINGLE, Stephen Zimmerman, Alexander Frie, Justin Min, Roya Bahreini, University of California Riverside
Abstract Number: 736 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Secondary organic aerosols (SOA) formed in the atmosphere through oxidation processes play an important role in the perturbation of radiative forcing; however optical properties of SOA are still poorly characterized. In this study, we report on the complex refractive index (RI) of SOA formed from oxidation of α-pinene, longifolene, phenol and 1-methylnaphthalene. Experiments were conducted in a Teflon film chamber under varying NOx conditions, with the utilization of hydroxyl radicals to initiate oxidation of the precursor compounds. Optical scattering and absorption coefficients (βscat and βabs respectively) at 375 nm were measured using a Photoacoustic Extinctiometer (PAX-375) and aerosol size distributions were measured with a Scanning Electron Mobility Sizer (SEMS). In order to determine SOAs’ RI, scattering and absorption coefficients of aerosols corresponding to the average measured size distributions were calculated at 3 min intervals using Mie Theory and initial guesses for the real (n) and imaginary (k) components of RI. This calculation was repeated through an iterative process to minimize the least-squares deviation functions defined for the optical coefficients (Spinder and Riziq 2007). For the biogenic precursors, α-pinene and longifolene, n values for the SOA produced ranged from 1.39-1.68, with increasing values observed later in the experiment, but showed minimal k values indicating mostly scattering SOA. Exposure to NO decreased n values by ~2.7% for α-pinene and longifolene, with the k values remaining constant at 0.001-0.002 during NO exposure. In contrast, for the aromatic precursors, phenol and 1-methylnaphthalene, n values increased from 1.40 to 1.44 and 1.44 to 1.52, respectively. Additionally, brown carbon was formed with k values increasing with oxidation from 0.010 to 0.017 and 0.003 to 0.008, respectively.