379 The SOA Formation Model Combined with Semiempirical Quantum Chemistry to Predict UV-Vis Absorption of Secondary Organic Aerosols

Monday, 7 January 2013
Exhibit Hall 3 (Austin Convention Center)
Min Zhong, University of Florida, Gainesville, FL; and M. Jang, A. Oliferenko, G. G. Pillai, and A. R. Katritzky

A new model to predict the UV-visible absorption spectrum of secondary organic aerosol (SOA) has been developed. The model consists of two primary parts: a SOA formation model and a semiempirical quantum chemistry method. The mass of SOA 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 chemical composition is estimated using a combination of the kinetic model (MCM) and the PHRCSOA model. The absorption spectrum is obtained by taking the sum of the spectrum of each SOA product calculated using a semiempirical NDDO (Neglect of Diatomic Differential Overlap)-based method. SOA was generated from the photochemical reaction of toluene or α-pinene under different NOx levels (low NOx: 24~26ppm, middle NOx: 49ppb, high NOx 104~105ppb) using a 2 m3 indoor Teflon film chamber. The model simulation reasonably agrees with the measured absorption spectra of α-pinene SOA but underestimates toluene SOA for high and middle NOx conditions. The absorption spectrum of toluene SOA is moderately enhanced with increasing NOx concentrations, while that of α-pinene SOA is not affected. Both measured and calculated UV-visible spectra show that the light absorption of toluene SOA is much stronger than that of
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