CAREER: Towards a Better Understanding of Ambient Semi-volatile Organic Aerosol: Investigation of Thermodynamic Properties of Multi-component Organic Aerosols

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The goal of this project is to obtain empirical parameterizations of thermodynamic properties of multi-component organic aerosol to be used in chemical transport models. The main hypothesis is that volatility of an organic compound in a mixture is a function of the carbon number and the polarity of this compound, as well as those of the mixture; and that volatility of the total mixture can be predicted using a simplified matrix containing binned data on the carbon number and polarity of each of the compounds in the mixture. Prediction of ambient semi-volatile organic aerosol remains highly problematic and air quality models often do not agree with observations. The lack of understanding of the partitioning of semi-volatile compounds between the gas and the complex aerosol matrix is one of the main reasons for this discrepancy.In this study the equilibrium thermodynamic properties of multi-component aerosols will be investigated under controlled laboratory conditions as well as in the field. In the laboratory experiments model mixtures of organic compounds as well as modified ambient aerosols will be tested. The ambient aerosols will be modified in a controlled way by adding known amounts of different organic substances of known thermodynamic properties and variable molecular weight and polarity. The equilibrium gas/aerosol partitioning in a temperature range relevant to ambient conditions will be investigated using the Integrated Volume Method (IVM), developed in the principal investigator's (PI) laboratory. The results will be used to derive equilibrium vapor pressures and activity coefficients of test compounds as a function of their carbon number and polarity and to determine the minimum number of bins along these dimensions that will adequately represent ambient aerosol volatility.This project will improve the understanding, predictions and control of the major fraction of ambient aerosol, which is relevant for public health and global climate change. The educational and outreach component will be directed at a wide audience in order to help educate the public about the current environmental problems related to air pollution and help attract students to environmental science and engineering. Special attention will be given to attracting and retaining under-represented groups, such as women and minorities. The project will include an educational outreach component with hands-on experience for middle school students; summer research projects will be offered to students from the North Carolina School of Science and Math, for graduate and undergraduate students at Duke University and North Carolina Central University (NCCU), an Historically Black University. The research results will be disseminated via conferences and peer-reviewed publications. To reach a wider audience the PI plans to utilize the power of social media tools, such as Facebook groups, to share the research results and engage the community directly.