研究领域

Analytical Chemistry/Environmental Chemistry/Nano Chemistry/Mass Spectrometry Studies of the Interactions of Atmospheric Trace Gases/Particles/and Clouds with the Biosphere and Cryosphere

Atmospheric chemistry impacts global climate, regional air pollution, and human health. Air-surface interactions are important components of global atmospheric and biogeochemical cycles. Chemical reactions occur in the environment between trace gases, within aqueous solutions (e.g. cloud droplets), within particles, and on surfaces (e.g. snow, ice, atmospheric particles, vegetation). Atmospheric particles, often ~3 nm to 10 microns in diameter, are constantly evolving, complex mixtures that interact with radiation, form cloud droplet and ice crystals, and deposit onto surfaces. Primary atmospheric particles are emitted from a variety of natural and anthropogenic sources (e.g., dust, bacteria, sea spray, soot) and undergo heterogeneous and particle-phase reactions during transport. Secondary organic aerosol, formed primarily from the oxidation of trace level volatile organic compounds and subsequent gas-particle partitioning, is a dynamic chemical mixture, wherein each particle can contain thousands of organic compounds, the vast majority of which remain unidentified. Given the complexity and evolving nature of atmospheric particles, their measurement represents an analytical challenge and has resulted in significant uncertainties in our understanding of particle formation, evolution, and environmental impacts and fate. The Pratt group focuses on studies of interactions between atmospheric trace gases, particles, and clouds using novel mass spectrometry techniques. In particular, we tackle the major uncertainties that exist in our understanding of atmospheric aerosols with respect to interactions between urban pollution and trace gas emissions from forests, as well as feedbacks associated with sea ice loss in the Arctic. We use a field-portable single-particle mass spectrometer to measure the size and chemistry of individual particles in real-time. Trace gas composition is measured using a field-portable on-line chemical ionization mass spectrometer, as well as gas chromatography coupled with mass spectrometry. To study the molecular composition of high molecular weight organics, electrospray ionization coupled with high-resolution mass spectrometry is used to probe ambient samples. These measurements of trace gases, aerosols, and cloud water are complemented by one-dimensional modeling of chemical reaction mechanisms and kinetics to examine and predict chemistry versus altitude and time. These studies will improve our understanding of the feedbacks between natural aerosol sources, anthropogenic emissions, and the Earth system for future climate and air quality predictions. Representative Publications Pratt, K.A., K. D. Custard, P.B. Shepson, T.A. Douglas, D. Pohler, S. General, J. Zielcke, W.R. Simpson, U. Platt, D.J. Tanner, L.G. Huey, M. Carlsen and B.H. Stirm. 2013. Photochemical production of molecular bromine in Arctic surface snowpacks. Nature Geoscience. 6: 351-356. Pratt, K.A., L.H. Mielke, P.B. Shepson, A.M. Bryan, A.L. Steiner, J. Ortega, R. Daly, D. Helmig, C.S. Vogel, S. Griffith, S. Dusanter, P.S. Stevens and M. Alaghmand. 2012. A one-dimensional model study of individual reactive biogenic volatile organic compounds and their contributions to organic nitrates above a mixed forest. Atmospheric Chemistry & Physics. 12: 10125-10143. Pratt, K.A. and K.A. Prather. 2012. Mass spectrometry of atmospheric aerosols - Recent developments & applications. Part II: On-line mass spectrometry techniques. Mass Spectrometry Reviews. 31: 17-48. Pratt, K.A., C.H. Twohy, S.M. Murphy, R.C. Moffet, A.J. Heymsfield, C.J. Gaston, P.J. DeMott, P.R. Field, T.R. Henn, D.C. Rogers, M.K. Gilles, J.H. Seinfeld and K.A. Prather. 2010. Observation of playa salts as nuclei in orographic wave clouds. Journal of Geophysical Research. 115: doi:10.1029/2009JD013606. Pratt, K.A., P.J. DeMott, J.R. French, Z. Wang, D.L. Westphal, A.J. Heymsfield, C.H. Twohy, A.J. Prenni and K.A. Prather. 2009. In-situ detection of biological particles in cloud ice crystals. Nature Geoscience. 2: 398-401. Pratt, K.A., J.E. Mayer, J.C. Holecek, R.C. Moffet, R.O. Sanchez, T. Rebotier, H. Furutani, M. Gonin, K. Fuhrer, Y. Su, S. Guazzotti and K.A. Prather. 2009. Development and characterization of an aircraft aerosol time-of-flight mass spectrometer. Analytical Chemistry. 81: 1792-1800.

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Dependence of the vertical distribution of bromine monoxide in the lower troposphere on meteorological factors such as wind speed and stability. P. K. Peterson, W. R. Simpson, K. A. Pratt , P. B. Shepson, U. Frie?, J. Zielcke, U. Platt, S. J. Walsh, and S. V. Nghiem. Atmospheric Chemistry and Physics, 2015, 15: 2119-2137. Impacts of Aerosol Aging on Laser Desporption/Ionization in Single-Particle Mass Spectrometers. Lindsay E. Hatch, Kerri A. Pratt ,J. Alex Huffman, Jose L. Jimenez, and Kimberly A. Prather. Aerosol Science and Technology, Vol. 48, Iss. 10, 2014. Temporal and spatial characteristics of ozone depletion events from measurements in the Arctic. J. W. Halfacre, T. N. Knepp,P. B. Shepson, C. R. Thompson, K. A. Pratt, B. Li, P. K. Peterson, S. J. Walsh, W. R. Simpson, P. A. Matrai, J. W. Bottenheim, S. Netcheva, D. K. Perovich, and A. Richter Atmospheric Chemistry and Physics,2014, 14: 4875-4894. Studying Bromine, Ozone, and Mercury Chemistry in the Arctic. Nghiem, S., P. Clemente-Colon, T. Douglas, C. Moore, D. Obrist, D. Perovich, K. Pratt, I. Rigor, W. Simpson, P.B. Shepson, A. Steffen and J. Woods, EOS,Transactions American Geophysical Union, 2013, 94: 289-291. Organosulfates in cloud water above the Ozarks’ isoprene source region. Pratt, K.A., M.N. Fiddler, P.B. Shepson, A.G. Carlton and J.D. Surratt, Atmospheric Environment, 2013, 77: 231-238. Photochemical production of molecular bromine in Arctic surface snowpacks. Pratt, K.A., K. D. Custard, P.B. Shepson, T.A. Douglas, D. P?hler, S. General, J. Zielcke, W.R. Simpson, U. Platt, D.J. Tanner, L.G. Huey, M. Carlsen and B.H. Stirm, Nature Geoscience, 2013, 6: 351-356. Improvements to an empirical parameterization of heterogeneous ice nucleation and its comparison with observations. Phillips, V.T.J., P.J. DeMott, C. Andronache, K.A. Pratt, K. Prather, R. Subramanian, and C. Twohy, Journal of the Atmospheric Sciences, 2013, 70: 378-409. Contributions of individual reactive biogenic volatile organic compounds to organic nitrates above a mixed forest. Pratt, K.A., L.H. Mielke, P.B. Shepson, A.M. Bryan, A.L. Steiner, J. Ortega, R. Daly, D. Helmig, C.S. Vogel, S. Griffith, S. Dusanter, P.S. Stevens and M. Alaghmand, Atmospheric Chemistry & Physics, 2012, 12: 10125-10143. A disjunct eddy accumulation system for the measurement of BVOC fluxes: Lab characterizations and field deployment. Edwards, G.D., D.K. Martins, T. Starn, K.A. Pratt and P.B. Shepson, Atmospheric Measurement Techniques, 2012, 5: 2115-2132. Seasonal comparisons of single-particle chemical mixing state in Riverside, CA. Qin, X., K.A. Pratt, L.G. Shields, S.M. Toner and K.A. Prather, Atmospheric Environment, 2012, 59: 587-596. Importance of aerosol composition, mixing state and morphology for depositional ice nucleation: A combined field and laboratory approach.. Baustian, K.J., D.J. Cziczo, M.E. Wise, K.A. Pratt, G. Kulkarni, A.G. Hallar and M.A. Tolbert, Journal of Geophysical Research, 2012, 117: doi:10.1029/2011JD016784. Ice in Clouds Experiment – Layer Clouds. Part 2: Testing characteristics of heterogeneous ice formation in lee wave clouds. Field, P.R., A.J. Heymsfield, B.J. Shipway, P.J. DeMott, K.A. Pratt, D.C. Rogers, J. Stith and K.A. Prather, Journal of the Atmospheric Sciences, 2012, 69: 1066-1079. In situ, airborne instrumentation: Addressing and solving measurement problems in ice clouds. Baumgardner, D., L. Avallone, A. Bansemer, S. Borrmann, P. Brown, U. Bundke, P. Chuang, D. Cziczo, P. Field, M. Gallagher, J.-F. Gayet, A. Heymsfield, A. Korolev, M. Kr?mer, S. Lance, P. Lawson, G. McFarquhar, S. Mertes, O. M?hler, M. Petters, K. Pratt, G. Roberts, D. Rogers, O. Stetzer, J. Stith, W. Strapp, C. Twohy and M. Wendisch, Bulletin of the American Meteorological Society, 2012, 93: E529-E534. Mass spectrometry of atmospheric aerosols – Recent developments & applications. Part II: On-line mass spectrometry techniques. Pratt, K.A. and K.A. Prather, Mass Spectrometry Reviews, 2012, 31: 17-48. Mass spectrometry of atmospheric aerosols – Recent developments & applications. Part I: Off-line mass spectrometry techniques. Pratt, K.A. and K.A. Prather, Mass Spectrometry Reviews, 2012, 31: 1-16. Flight-based chemical characterization of biomass burning aerosols within two prescribed burn smoke plumes. Pratt, K.A., S.M. Murphy, R. Subramanian, P.J. DeMott, G.L. Kok, T. Campos, D.C. Rogers, A.J. Prenni, A.J. Heymsfield, J.H. Seinfeld and K.A. Prather, Atmospheric Chemistry & Physics, 2011, 11: 12549-12565. Quantitative determination of biogenic volatile organic compounds in the atmosphere using proton-transfer reaction linear ion trap mass spectrometry. Mielke, L.H., K.A. Pratt, P.B. Shepson, S.A. McLuckey, A. Wisthaler, and A. Hansel, Analytical Chemistry, 2010, 82: 7952-7957. Ice initiation by aerosol particles: Measured and predicted ice nuclei concentrations versus measured ice crystal concentrations in an orographic wave cloud. Eidhammer, T., P.J. DeMott, A.J. Prenni, M.D. Petters, C.H. Twohy, D.C. Rogers, J. Stith, A. Heymsfield, Z. Wang, K.A. Pratt, K.A. Prather, S.M. Murphy, J.H. Seinfeld, R. Subramanian, and S.M. Kreidenweis, Journal of the Atmospheric Sciences, 2010, 67: 2417-2436. Relationships of biomass burning aerosols to ice in orographic wave clouds. Twohy, C.H., P.J. DeMott, K.A. Pratt, R. Subramanian, G.L. Kok, S.M. Murphy, T. Lersch, K.A. Prather, J.H. Seinfeld, A.J. Heymsfield and Z. Wang, Journal of the Atmospheric Sciences, 2010, 67: 2437-2450. In-situ chemical characterization of aged biomass burning aerosols impacting cold wave clouds. Pratt, K.A., A.J. Heymsfield, C.H. Twohy, S.M. Murphy, P.J. DeMott, J.G. Hudson, R. Subramanian, Z. Wang, J.H. Seinfeld and K.A. Prather, Journal of the Atmospheric Sciences, 2010, 67: 2451-2468.