A.B., Princeton University (1979) Ph.D., University of California-Berkeley (1987) Postdoctoral Fellow, Colorado State University (1988); Postdoctoral Fellow, University of California-Berkeley (1989)

Analytical Chemistry/Physical Chemistry

We are currently focusing our efforts on three main areas of research: Charge- and proton-transfer phenomena in molecular clusters Heterogeneous atmospheric chemistry mediated by solid aerosol particles Real-time environmental mass spectrometry An important facet of our work is the development of new experimental approaches using a variety of instrumentation, including laser sources. We often employ computational methods to supplement the experimental results. We are particularly interested in systems that are relevant to environmental and atmospheric chemistry. The diverse nature of our work calls for a multidisciplinary approach and much of the research is carried out in collaboration with colleagues in chemistry, physics and engineering. We also benefit from our association with the Optical Science and Technology Center (OSTC) and the Center for Global and Regional Environmental Research (CGRER). Charge- and proton-transfer in clusters Clusters, consisting of two or more molecules bound together by intermolecular forces, represent an ideal system to investigate the details of various chemical processes. The cluster environment can also result in unique, supramolecular chemistry that is vastly different from the behavior of the isolated molecules. We form isolated cluster species in a low temperature molecular beam that is coupled to a specialized time-of-flight mass spectrometer (TOFMS). We have developed an array of powerful laser analysis methods that couple multiphoton ionization probes with mass-specific detection to study cluster photochemistry. We are investigating clusters that exhibit an intermolecular charge-transfer (CT) absorption band due to the transfer of an electron from a donor to an acceptor molecular orbital. Electron transfer is a fundamental concept in chemistry with significant implications for both basic and applied science. We are especially interested in the identification of new processes that may play a role in atmospheric chemistry. For instance, photofragmentation of O2 clustered with an alkene to produce O atoms, an important atmospheric radical species, is enhanced by at least three orders of magnitude compared to the isolated oxygen molecule; alkene-O2 alkene+-O2- alkene-O2* alkene + O + O We are also investigating proton-transfer systems that exhibit a so-called low barrier hydrogen-bond, which is of great importance in the structure of biomolecules and in enzyme kinetics. Heterogeneous atmospheric chemistry on aerosol particles We are interested in chemistry that is mediated by aerosol particulates suspended in the troposphere, particularly soot from combustion processes and mineral aerosols from windborne soil. Our unique experimental approach is to study the chemistry of the isolated aerosols, as opposed to more traditional bulk studies. We have constructed a large volume atmospheric reaction chamber to monitor gas-aerosol interactions at pressure, temperature and relative humidity conditions found in the troposphere. We utilize a FTIR, a fiber-optic UV/Vis spectrometer, a fast-sampling mass spectrometer, and lasers to probe the chemistry. As part of our collaborative effort, the experimental information we obtain regarding reaction probabilities and product branching serves as input to sophisticated computer models of atmospheric chemistry. The results of the models provide feedback so that we may target the most sensitive and critical systems in our experiments. Real-time mass spectrometry We are actively developing real-time mass spectrometric methods for field and laboratory studies in environmental and atmospheric chemistry. For example, airborne biological particulates, such as microorganisms and microbial products, are sampled into a modified TOFMS. The isolated particles are size-selected using a laser scattering method and then probed using a combination of laser wavelengths. The resultant mass spectrum is used to identify and classify the particle with fast time resolution. Our approach will greatly aid studies of inhalation toxicology in contaminated settings, which require knowledge of the size-correlated chemical speciation as well as details regarding the distribution of airborne microorganisms. A similar instrument will be used to detect species absorbed onto the surface of aerosol particles in our atmospheric reaction chamber. We are also applying a novel mass sensitive technique to the study of aqueous photochemistry in rain and surface waters.

Preszler Prince, A.; Grassian, V.H.; Kleiber, P.D.; Young, M.A. Heterogeneous Conversion of Calcite Aerosol by Nitric Acid. Physical Chemistry Chemical Physics 2006, 5, 622-634. Hudson, P.K.; Gibson, E.R.; Young, M.A.; Kleiber, P.D.; Grassian, V.H. A Newly Designed and Constructed Instrument for Coupled Infrared Extinction and Size Distribution Measurements of Aerosols. Aerosol Science and Technology 2007, 41, 701-710. Curtis, D.B.; Aycibin, M.; Young, M.A.; Grassian, V.H.; Kleiber, P.D. Simultaneous Measurement of Light Scattering Properties and Particle Size Distribution for Aerosols: Application to Ammonium Sulfate and Quartz Aerosol Particles. Atmospheric Environment 2007, 41, 4748-4758. Hudson, P.K.; Young, M.A., Kleiber, P.D.; Grassian, V.H. Coupled Infrared Extinction And Size Distribution Measurements of Several Non-Clay Components of Mineral Dust Aerosol (Quartz, Calcite, and Dolomite). Atmospheric Environment 2008, 42, 5991-5999. Cwiertny, D.M.; Young, M.A.; Grassian, V.H. Heterogeneous Chemistry and Photochemistry of Mineral Dust Aerosol. Annual Reviews of Physical Chemistry 2008, 59, 27-51. Navea, N.G.; Stanier, C.O., Young, M.A.; Grassian, V.H. Heterogeneous Uptake of Octamethylcyclotetrasiloxane (D4) and Decamethylcyclopentasiloxane (D5) onto Mineral Dust Aerosol Under Variable RH Conditions. Atmospheric Environment 2009 43, 4060-4069. Kleiber, P.D.; Grassian, V.H.; Young, M.A.; Hudson, P.K. T-Matrix Studies of Aerosol Particle Shape Effects on IR Resonance Spectral Line Profiles and Comparison with an Experiment. Journal of Geophysical Research 2009, 114, doi:10.1029/2009jd012710. Meland, B.; Kleiber, P.D.; Grassian, V.H.; Young, M.A. Correlated IR Spectroscopy and Visible Light Scattering Measurements of Mineral Dust Aerosol. Journal of Geophysical Research 2010, 115, doi:10.1029/2010JD014389. Hudson, P.K.; Young, M.A., Kleiber, P.D.; Grassian, "V.H. Infrared Extinction and Size Distribution Measurements of Mineral Dust Aerosol" a book chapter in Fundamentals and Applications of Aerosol Spectroscopy, Eds. J.P. Reid and R. Signorell 2010 CRC Press. Chen, H.; Stanier, C.O.; Young, M.A.; Grassian, V.H. A Kinetic Study of Ozone Decomposition on Illuminated Oxide Surfaces. Journal of Physical Chemistry A 2011, 115, 11979-11987.