AAAR 30th Annual Conference
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Myoseon Jang

A Predictive Model for UV-Visible Absorption Spectra of SOA

Min Zhong, Myoseon Jang

University of Florida

     Abstract Number: 165
     Last modified: April 1, 2011

     Working Group: Aerosol Physics

Abstract
A predictive model for the UV-visible absorption spectra of secondary organic aerosol (SOA) has been developed for the SOA produced from the photochemical oxidation of toluene and alpha-pinene in the presence of NOx. The predictive model for the absorption spectra of SOA has two primary parts: a predictive SOA mass model and a semiempirical quantum chemistry model. The SOA mass is predicted using the PHRCSOA (Partitioning Heterogeneous Reaction Consortium Secondary Organic Aerosol) model developed by Cao and Jang [Environ. Sci. Technol., 2010, 44, 727]. The SOA chemical composition predicted by the kinetic model (MCM) used in the PHRCSOA model was used in the calculation of the SOA absorption spectrum. The SOA absorption spectrum was obtained by taking the sum of the spectrum of each SOA product and the individual spectra were each calculated using the semiempirical NDDO (Neglect of Diatomic Differential Overlap) method. SOA was generated from the photochemical reaction of toluene or alpha-pinene in the presence of NOx (24-107ppb) using a 2 m3 indoor Teflon film chamber. The model underestimates the intensity of UV-visible spectra of both toluene SOA and alpha-pinene SOA compared to measured spectra. The modelís predictions were improved upon including a small fraction (1.54% - 3.24 wt%) of a light absorbing conjugated structure. Both the measurement and theoretical predictions show that the absorption spectrum of toluene SOA is much stronger than that of alpha-pinene SOA. The absorption spectrum of toluene SOA is enhanced with increasing NOx concentrations, while that of alpha-pinene SOA is not affected by NOx concentrations.

 
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