American Association for Aerosol Research - Abstract Submission

AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA

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Wavelength-dependent Complex Refractive Indices of Different Types of Secondary Organic Materials

PENGFEI LIU, Yue Zhang, Scot Martin, Harvard University

     Abstract Number: 74
     Working Group: Carbonaceous Aerosols in the Atmosphere

Abstract
For accurate quantifying aerosol optical properties, recent studies have emphasized the importance of obtaining improved knowledge of the complex refractive indices of the secondary organic materials (SOM). However, measurements of the complex refractive indices of SOM were typically limited to a few wavelengths, and the wavelength dependence is still not well understood. In this laboratory study, spectroscopic data of complex refractive indices of different types of SOM were obtained using a variable angle spectroscopic ellipsometer at wavelengths between UV (220 nm) and Near-IR (1200 nm). The SOM were generated from ozonolysis of monoterpene precursors alpha-pinene and d-limonene, and aromatic precursor catechol (Benzene-1,2-diol) using an aerosol flow tube reactor. The results show that both real and imaginary parts of different types of SOM decrease with increasing wavelength. The wavelength dependence is especially strong in the UV range. The real parts of the complex refractive index of catechol-derived SOM are slightly higher than that of monoterpene-derived SOM; the values are in the range from 1.53-1.58, 1.49-1.52 and 1.48-1.50 at the wavelengths 300, 550 and 1000 nm, respectively. Catechol-derived SOM has moderate light absorption in the UV range; the imaginary parts of complex refractive index are 0.017±0.001 and 0.002±0.0015 at the wavelengths 300 and 400 nm, respectively. By comparison, UV absorption of SOM derived from alpha-pinene and d-limonene is about an order of magnitude lower than that of catechol-derived SOM. Light absorption of studied SOM in visible and near-IR range is negligible. The new spectroscopic information about SOM complex refractive index is helpful for updating aerosol optical database for aerosol and gas satellite retrievals and atmospheric chemical modeling.