AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Modeling the Formation and Evolution of Secondary Organic Aerosol in a Potential Aerosol Mass (PAM) Chamber
Shuang Chen, WILLIAM BRUNE, Paul Davidovits, Andrew Lambe, Timothy Onasch, Pennsylvania State University
Abstract Number: 170 Working Group: Aerosol Chemistry
Abstract A model was set up to simulate the formation and evolution of secondary organic aerosol (SOA) in a Potential Aerosol Mass (PAM) chamber, a small flow-through 15L cylinder containing ultraviolet lights that produce a highly oxidizing environment. The hydroxyl (OH) levels are high enough that a few minutes in the chamber is equivalent to 0.6 to 15 days in the atmosphere. The model framework was based on the two-dimensional volatility basis set approach (2D-VBS), in which all organic oxidized products in the model were distributed on the 2D space of volatility and oxygen-to-carbon (O:C) ratio. First-generation organic products from the oxidation of a precursor were modeled with the use of the VBS parameters from previous experimental studies. The O:C ratios of these products were assigned based on the measurements at low OH exposure. Further homogeneous and heterogeneous oxidation was assumed for all organic products. Both functionalization and fragmentation processes were included in the model. The model predictions of SOA yields and O:C ratios were compared with the experimental data of the PAM chamber. The results showed that at the same levels of OH exposure, the predicted SOA concentrations generally agree well with the measurements. Sensitivity analysis indicated that the model predictions of O:C ratio and SOA concentrations were most sensitive to the fragmentation branching ratio of the products and the rate coefficient of the reactions of semi-volatile products with OH.