A.R. Ravishankara

A.R. Ravishankara
Office: NOAA
Office Phone: 303 497 5821
Group Website: http://www.esrl.noaa.gov/csd/
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Assistant Professor & CIRES Affiliate

Ph.D.: University of Florida, 1975
Postdoctoral Fellow:University of Maryland, 1976
Feodor-Lynen Fellowship by Alexander von Humboldt Foundation (since 2005)
Environmental Chemistry Fellowship by Henry & Camille Dreyfus Foundation (2002-2004)
Marie Curie Research Training Grant by the European Commission (1998-2000)
Erasmus Scholarship by the European Commission (1992-1993)

Kinetics and Photochemistry of Atmospheric Systems

Professor Ravishankara's research is aimed at understanding the chemistry of Earth's atmosphere as it is today and as it may be in the future. The results of his research help elucidate how man's activities affect our air and provide information on how to preserve our environment. Current research interests include climate change (greenhouse effect), and regional air quality, and stratospheric ozone changes.

Our laboratory investigations of gas-phase processes are important in Earth's atmosphere. Since free radicals are the key players in Earth's oxidative atmosphere, their reactions are studied to obtain the temperature and pressure dependencies of the rate coefficients, to identify products of reactions, and to determine the reaction mechanisms. Since Earth's atmosphere is driven by the input of solar radiation, photochemistry plays a crucial role in determining its composition. Therefore, photochemistry of small molecules is studied to understand how they break apart upon light absorption. Most of the kinetic and photochemical studies are carried out using spectroscopic techniques. Therefore, electronic spectra of small transients are studied to enable their detection. Such characterization also allows monitoring these species in the atmosphere. Pulsed photolysis or discharge flow methods are used for kinetics experiments. Detection of the reacting species is carried out using laser-induced fluorescence, resonance fluorescence, long-path UV/visible absorption, and photoionization or chemical ionization mass spectrometry. Recently, the technique of cavity ring down spectroscopy has also been extensively used.

It is now abundantly clear that reactions between closed shell molecules on surfaces and transport of molecules into drops play critical roles in atmospheric chemistry. Therefore, reactions of closed shell molecules and free radicals are studied on various atmospheric substrates or their surrogates. Reactive uptake into liquid water and sulfuric acid is also investigated. The modifications to the substrates caused by their exposure to atmospheric species is investigated. A tubular flow reactor, an aerosol flow tube, or other such devices are used in conjunction with detection methods such as chemical ionization mass spectrometry and laser-induced fluorescence to investigate these processes.

Aerosols are now known to be one of the most important forcing agents for climate and also for modifying atmospheric composition. Therefore, the physical and chemical properties of aerosols are investigated in the laboratory and in the real atmosphere.

Finally, measurements of atmospheric constituents are key to find out what is in the atmosphere and check our understanding of the processes. The nitrate radical (NO3) and nitrogen pentoxide (N2O5) are measured using a newly developed cavity ring down spectrometer. Using this instrument, NO3 and N2O5 are being measured in-situ to elucidate the chemical processes that take place during night and to understand the implication of night time processes to atmospheric composition and effects on the Earth system.

Selected Publications

Y. Matsumi, F.J. Comes,G. Hancock, A. Hofzumahaus, A.J. Hynes, M. Kawasaki, and A.R. Ravishankara, "Quantum yields for production of O(1D) in the ultraviolet photolysis of ozone: Recommendation based on evaluation of laboratory data", J. Geophys. Res., 107, 2002.

G. Feingold, G. J. Frost and A. R. Ravishankara, "The role of NO3 in sulfate production in the wintertime northern latitudes", J. Geophys. Res., 107, No. D22, 4640, doi:10,1029, 2002.

S. S. Brown, H. Stark and A. R. Ravishankara, "Cavity ring-down spectroscopy for atmospheric trace gas detection: Application to the nitrate radical NO3) Applied Physics B, 75, 173-182, 2002.

S. S. Brown, H. Stark, S. J. Ciciora, R. J. McLaughlin and A. R. Ravishankara "Simultaneous In-situ Detection of Atmospheric NO3 and N2O5 via Cavity Ring-Down Spectroscopy", Review of Scientific Instruments, 73, 3291-3301, 2002.

A. R. Ravishankara, E.J. Dunlea, M.A. Blitz, T.J. Dillon, D.E. Heard, M.J. Pilling, R.S. Strekowski, J.M. Nicovich, and P.H. Wine, "Redetermination of the rate coefficient for the reaction of O(1D) with N2", Geophys. Res. Letters, 29, 35-1-35-4, 2002.

R. K. Talukdar, E. J. Dunlea, S. S. Brown, J. S. Daniel and A. R. Ravishankara "Kinetics of O23+g) Reaction with H2 and an Upper Limit for OH Production" J. Phys. Chem. A, 106, 8461-8470, 2002.

A R Ravishankara, "Ozone Photochemistry", Encyclopedia of Atmospheric Sciences, September 2002.