Environmental, physical/analytical chemistry: gas/particle processes of tropospheric significance; mass spectrometry; laser-based analysis techniques.
Ph.D., , University of California, Davis
B.S., , University of California, Davis
Postdoc, Physical Chemistry, University of California, Berkeley
Awards and Academic Honors
ACS San Diego Distinguished Scientist Award
Fellow, American Geophysical Union
Fellow, American Academy of Arts and Sciences
Director, NSF Center for Aerosol Impacts on Climate and the Environment
ACS Creative Advances in Environmental Science and Technology
UCSD Faculty Sustainability Award
Fellow, American Association for the Advancement of Science
Selected as Member of EPA PM2.5 Clean Air Scientific Advisory Board
ACS Analytical Chemistry Arthur F. Findeis Award
Kenneth T. Whitby Award
GAeF Smoluchowski Award
National Science Foundation Special Creativity Award
University of California, Berkeley; American Society for Mass Spectrometry Award
National Science Foundation Young Investigator
We are working as part of a new Center funded by NSF, the Center for Aerosol Impacts on Climate and the Environment (NSF-CAICE)--see http://caice.ucsd.edu for further details and updates.
Our research involves making measurements of atmospheric aerosol chemistry and developing and using new analytical methods for these measurements. Aerosols occur in the environment in a variety of forms: clouds of ice or water droplets, salt particles from ocean spray, and smoke from a variety of combustion sources. They play an enormous role in our daily lives from affecting visibility and global climate change to endangering our health. Due to applications in research, medicine, and industry, there is great scientific interest in aerosols, however relative to their gas phase counterparts, limited information exists regarding their complex chemistry.
Conventional analytical methods for analyzing aerosols involve isolating particles on filters with subsequent analysis performed in the laboratory. These isolation processes often disturb the aerosol and thus render the data questionable because the particles evaporate or react before analysis. In order to overcome these difficulties, we developed aerosol-time-flight mass spectrometry (ATOFMS). This represented the first analytical technique capable of providing the precise size and chemical composition of individual aerosol particles in real time. Some examples of aerosol systems which we are characterizing in the laboratory using ATOFMS include suspended dust, sea salt, and a variety of combustion particles. Most recently, we developed a much smaller ATOFMS which has been flown over Colorado, northern and southern California, and most recently the Caribbean. In field studies, we strategically position our transportable instruments at sites that allow us to monitor the evolution of single particles in the atmosphere over time. In regional and international studies, these instruments are being used to study the direct effect of aerosols on visibility, pollution levels, cloud formation, and the global radiation balance.
Another major thrust of our research involves the development of new techniques for the analysis of organic species in aerosol particles. This is an extremely complex problem as there are hundreds of organic species in particles yet only 10-20% of the mass has been identified. We are approaching this problem by using tunable laser wavelengths and selective reagent ions in chemical ionization.
Another area of interest involves using an ATOFMS instrument as an on-line probe for monitoring heterogeneous gas-particle reactions in the laboratory. The ATOFMS is interfaced to a flow tube where heterogeneous reactions of tropospheric concern are simulated. Aerosols of known size and composition are created and reacted under controlled conditions. The fundamental question of which factors (i.e. size, composition, charge) influence heterogeneous gas-particle reactions are being addressed.
Controlled laboratory studies such as these assist in sorting out data obtained from atmospheric studies, complicated by the numerous chemical processes occurring at any time. The information obtained will be used to generate new models for atmospheric processes which will be directly applicable in efforts to control ozone depletion, improve air quality, and develop an understanding of the impact of aerosols on global climate.
Primary Research Area
Atmospheric and Environmental
Picture of aircraft-ATOFMS (Shirley)
Schematic of ATOFMS which can collect information on aerosol size, chemistry, and optical properties.
- Moffet, R.C. and K. Prather, In-situ measurements of the mixing state and optical properties of soot with implications for radiative forcing estimates. Proceedings of the National Academy of Science, (2009). 106(29): p. 11872-11877.
- Pratt, K.A., L.E. Hatch, and K.A. Prather, Seasonal Volatility Dependence of Ambient Particle Phase Amines. Environ. Sci. Technol., (2009). 43: p. 5276-5281.
- Prather, K.A., C.D. Hatch, and V.H. Grassian, Analysis of Atmospheric Aerosols. Annual Review of Analytical Chemistry, (2008). 1: p. 485-514.
- Sullivan, R.C., S.A. Guazzotti, D.A. Sodeman, and K.A. Prather, Direct observations of the atmospheric processing of Asian mineral dust. Atmospheric Chemistry and Physics, (2007). 7: p. 1213-1236.
- Ault, A.P., M.J. Moore, H. Furutani, and K.A. Prather, Impact of Emissions from the Los Angeles Port Region on San Diego Air Quality during Regional Transport Events. Environmental Science & Technology, (2009). 43(10): p. 3500-3506.
- Moffet, R.C., B. de Foy, L.T. Molina, M.J. Molina, and K.A. Prather, Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry. Atmospheric Chemistry and Physics, (2008). 8(16): p. 4499-4516.
- Moffet, R.C., X.Y. Qin, T. Rebotier, H. Furutani, and K.A. Prather, Chemically segregated optical and microphysical properties of ambient aerosols measured in a single-particle mass spectrometer. Journal of Geophysical Research-Atmospheres, (2008). 113(D12).
- Pratt, K.A., J.E. Mayer, J.C. Holecek, R.C. Moffet, R.O. Sanchez, T.P. Rebotier, H. Furutani, M. Gonin, K. Fuhrer, Y.X. Su, S.A. Guazzotti, and K.A. Prather, Development and Characterization of an Aircraft Aerosol Time-of-Flight Mass Spectrometer. Analytical Chemistry, (2009). 81(5): p. 1792-1800.
- 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, In situ detection of biological particles in cloud ice-crystals. Nature Geoscience, (2009). 2(6): p. 398-401.
- Spencer, M.T., L.G. Shields, and K.A. Prather, Simultaneous measurement of the effective density and chemical composition of ambient aerosol particles. Environmental Science & Technology, (2007). 41(4): p. 1303-1309.