Collaborative Research: Impact of Changing Volatile Organic Compounds (VOC) to NOx Ratios on Secondary Organic Aerosol Formation

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A large, state-of-the-art, dual 90-m3 environmental chamber, designed for low-NOx experiments at the University of California, Riverside (UCR) will be used to simulate atmospheric photochemical production of secondary organic aerosol (SOA) from four aromatic species--those present in the Carter ambient reactive organic gas (ROG) surrogate mixture and those used in state-of-the-art computational modules; the Cal Tech Atmospheric Chemistry Module and the Model to Predict the Multi-phase Partitioning of Organics (CACM/MPMPO); to simulate SOA formation. The series of experiments, which includes single and binary mixtures of the aromatic hydrocarbons, will explore the chemical mechanisms leading to SOA formation and be used to improve the CACM/MPMPO modules.The SOA formation from aromatic hydrocarbons appears to be underpredicted grossly in current air quality models due, at least in part, to the dependence on experimental data from chambers utilizing excessively high NOx concentrations. This work develops the necessary chemical mechanisms to improve estimation of SOA formation locally, regionally, and globally. The predictive models will then be available to the larger scientific community in assessing gas-to-particle conversion processes. The scenarios evaluated in this project provide critical insight into the role of aromatic species in the atmosphere and the impacts of changing ROG to NOx ratio through dilution and/or regulation. Improved chamber data will be available to the entire community through websites and peer-reviewed literature. The project will involve undergraduate and graduate researchers at UC Riverside and a graduate researcher at Rice. A temporary graduate student exchange is will cross-train modeling oriented students from Rice with laboratory oriented students from UCR.