Aerosol Growth and Chemical Compositions from Heterogeneous Processing of Organic Compounds

Scientific questions to be addressed in this project include (1) what is the chemical mechanism of heterogeneous processing of different classes of oxygenated organic compounds on inorganic, organic, and soot aerosols, (2) what is the dependence of heterogeneous processing on gaseous reactant concentrations, RH, reaction time, and particle acidity and size, (3) what are synergetic effects between the first- and later generations of low and semi-volatile organic compounds (VOC) oxidation products and effects of the presence of oxidants in the particle phase, and (4) how can laboratory measurements be used to aid interpretation of ambient measurements and simulations of atmospheric organic particulate matter (PM)? Heterogeneous processing will be studied by exposing monodisperse aerosols in a flow reactor and particles deposited in an optical cell to low gaseous concentrations of representative products from VOC oxidation, including alpha-dicarbonyls, aldehydes, and alcohols. Experiments will also be conducted in a Teflon chamber with aerosols exposed to organic compounds generated in situ from photo-oxidation of VOCs. Secondary organic aerosol (SOA) growth will be quantified from concurrent measurements of the particle size, mass, density, and chemical compositions along with the gaseous organic concentrations. Seed particles will be chosen to represent primary and secondary atmospheric aerosols under conditions of different relativity humidity (RH), acidity, and reaction times. The changes in the particle size and mass due to heterogeneous processing will be measured using a combination of tandem differential mobility analyzer (TDMA) and differential mobility analyzer - aerosol particle mass analyzer (DMA-APM). Concentrations of gaseous reactants will be monitored by ion drift - chemical ionization tandem mass spectrometry (ID-CIMS/MS). The chemical composition of aerosol particles will be characterized using thermal desorption - ion drift - chemical ionization tandem mass spectrometry (TD-ID-CIMS/MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance (NMR) spectrometry, and matrix-assisted laser desorption/ionization - time-of-flight mass spectrometry (MALDI-TOFMS).

Persistent exposure to elevated levels of particulate matter has adverse effects on human health. Also, aerosols play an important role in regulating the solar radiation intake in the earth-atmosphere system. Understanding of formation and growth of organic aerosols represents a frontier in atmospheric chemistry and aerosol research. The information on formation and chemical compositions of organic aerosols generated from this project can be employed to assess human-health effects including respiratory and cardiovascular diseases. Hence, this research not only will advance our knowledge of organic aerosol formation, but also will be beneficial to the public by identification of potential human health and climate issues and to policy-decision makers in developing effective control strategies for ambient particulate matter. The project will provide interdisciplinary research opportunities for undergraduate students and graduate students in the areas of organic chemistry and atmospheric sciences. They will have the opportunity to present their work at conferences and build connections within the two scientific communities, as part of their education and training on global environmental change research.