AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Modeling NOx-dependent Chemistry During Organic Aerosol Aging with the 2D-VBS
WAYNE CHUANG, Neil Donahue, Carnegie Mellon University
Abstract Number: 512 Working Group: Aerosol Chemistry
Abstract Organic compounds in the vapor phase undergo extensive chemistry in the atmosphere, resulting in more oxygenated species with higher polarities and lower vapor pressures than the parent species. These products can partition between the vapor and aerosol phases to produce secondary organic aerosols (SOA) and are modeled using the two-dimensional volatility basis set (2D-VBS), which tracks their oxidation states (O:C) along with their volatilities. However, current 2D-VBS implementations do not account for the NOx dependence of organic oxidation chemistry. Polluted air masses from urban areas tend to have higher levels of NOx. Reactions between NO and organo-peroxy radicals (RO2) will change the organic product distribution compared to low-NOx oxdiation. These differences have been treated in the simpler 1D-VBS but not in the 2D-VBS, where composition is tracked in addition to volatility. Organic nitrates, which can be 30-40% of the total high-NOx products, can be accounted for by creating a second layer of the 2D-VBS. High- and low-NOx products can then be treated with separate oxidation “kernels”. A parameter β is introduced to represent the fraction of RO2 that react with NO. Within the model, β is used as a form of mixing of the SOA yields from each condition. This extension of the 2D-VBS produces an atmospherically relevant model of organic aerosols aging and SOA formation, which we will illustrate with box-model simulations of chamber experiments, extrapolated to residence times typical of regional photochemical smog events.