AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Refractive Index of Secondary Organic Aerosols from Oxidation of alpha-pinene and 1-methyl-nathalene
JUSTIN DINGLE, Stephen Zimmerman, Justin Min, Roya Bahreini, University of California Riverside
Abstract Number: 82 Working Group: Aerosol Chemistry
Abstract Optical properties of secondary organic aerosols (SOA) formed in the atmosphere are still poorly characterized. In this study, we report on the complex refractive index (RI) of SOA formed from oxidation of alpha-pinene and 1-methyl-nathalene. Experiments will be conducted in a Teflon film chamber, under varying relatively humidity and NO$_x conditions, with the utilization of chlorine and hydroxyl radicals to initiate reactions of the precursor compounds.Optical extinction coefficient (beta$_(ext)) at 632 nm will be measured using a Cavity Attenuated Phase Shift extinction monitor (CAPS-PM$_(ex)), while absorption and scattering coefficients (beta$_(scat) and beta$_(abs) respectively) at 375 nm will be measured using a Photoacoustic Extinctiometer (PAX-375). Additionally, aerosol size distributions will be measured with a Scanning Electron Mobility Sizer (SEMS). In order to determine SOA’s RI, scattering (at 375 nm and 632 nm) and absorption coefficients (at 375 nm) of aerosols corresponding to the average measured size distributions will be calculated at 5 min intervals, using Mie Theory and initial guesses for the real (n) and imaginary (k) components of RI. In this calculation, it is assumed that SOA is non-absorbing at 632 nm. Values of RI will then be varied and calculations will be repeated until the comparison between the measured and calculated optical coefficients results in a minimum value for the modified Chi-square (Chi$^2) functions. Trends in the optimum values of n and k for different hydrocarbons and oxidation conditions will be investigated.