Atmospheric Chemistry and Space Physics
During the past three decades there has developed a growing public
awareness of the interrelation between human activity and the
atmosphere. In recent years this has evolved an urgency that is
leading to major international research efforts to prepare for the
political and economic decisions that need to be made.
SRI's research in Atmospheric Chemistry and Space Physics contributes
to understanding of atmospheric processes through active programs in
all three cornerstone areas: field observations, modeling and
simulation, and laboratory measurements.
Table of Contents
- Atmospheric Fate of Anthropogenic Substances
- Heterogeneous Atmospheric Chemistry
- Reliable Models of Ozone-Depletion Chemistry
- Aeronomy: Photochemistry of Terrestrial and
Planetary Atmospheres
- Atmospheric Interactions of Spacecraft
- Ionospheric and Space Sciences
1. Atmospheric Fate of Anthropogenic Substances
Industrial activity results in release of wide variety of chemicals
to the atmosphere. Some of these chemicals are benign, others are
effectively destroyed by natural processes in the atmosphere, and some
result in damaging air pollution, acid rain, ozone depletion, or are
implicated as promoting potential global climate changes. Increasingly
restrictive
regulations motivate careful assessment of atmospheric impact
and development of new technologies with reduced emissions.
SRI scientists and engineers assist clients through testing and
monitoring protocols that track pollutants in the environment.
Laboratory experimental procedures are used to understand
chemical transformations. Optical and sampling techniques are
developed for remote and point monitoring of pollutants and
transport through the atmosphere.
Principal Investigators
2. Heterogeneous Atmospheric Chemistry
Heterogeneous chemistry plays a crucial role in the chemical balance
of the atmosphere. Perhaps the most dramatic illustration is the
appearance each spring of the Antarctic ozone hole.
SRI scientists conduct laboratory investigations to quantify the
kinetics of atmospherically important chemical reactions on the
surfaces of ice crystals, nitric- and sulfuric-acid aerosols, and
soot particles. We use a low pressure Knudsen cell flow reactor to
measure uptake coefficients, solubility, reaction probabilities, and
branching ratios. Our
pioneering studies were a leading source of the information needed to
understand the catalytic effect of polar stratospheric clouds on
the chlorine-ozone chemistry that results in Antarctic ozone
depletion.
Principal Investigators
Representative Projects and Publications
- M.A. Tolbert, M.J. Rossi, R. Malhotra, and D.M. Golden, Science
238, 1258 (1987).
- C.M. Reihs, D.M. Golden, and M.A. Tolbert, J. Geophys. Res.
95, 16,545 (1990).
- L.R. Williams, J.A. Manion, D.M. Golden, and M.A. Tolbert,
J. Appl. Met. 33, 785 (1994).
- L.R. Williams, D.M. Golden, and D.L. Huestis, J. Geophys. Res.
100, 7329 (1995).
3. Reliable Models of Ozone-Depletion Chemistry
Computer models of the atmosphere form the primary basis upon which
public policy decisions rely. A realistic and usable model must be
"mechanistic" rather than purely "empirical" because we need to be
able to extrapolate beyond the range of conditions currently
obtaining in the atmosphere, and even more importantly, because we need
to be able to make "cause" and "effect" judgements.
SRI scientists are using advanced computer programs and techniques
(developed in earlier work on combustion chemistry) to quantify the
reliability of existing models of depletion of ozone by compounds
such as CFCs. A second benefit of this work is identification of the
specific processes that are most in need of further laboratory or field
investigation, based on a combination of the estimated uncertainty of
existing mechanism parameters and the calculated sensitivity of the
atmospheric chemistry with respect to these processes.
Principal Investigators
4. Aeronomy:
Photochemistry of Terrestrial and Planetary Atmospheres
Solar radiation is the power source of the atmosphere. At the same
time, the atmosphere is a filter that protects us from harmful
ultraviolet radiation. The ozone shield in the stratosphere comes from
oxygen atoms produced by photodissociation of diatomic oxygen
molecules. Above the ozone layer, all molecules are affected by the
unfiltered sunlight, resulting in complex and interesting
photochemistry involving atoms, radicals, and excited states.
SRI scientists perform theoretical and laboratory investigations
of the spectroscopy and chemical reactions of the ground and excited
states of species such as oxygen and nitrogen atoms, hydroxyl (OH)
radicals, nitric oxide (NO), ozone, carbon dioxide, and oxygen and
nitrogen molecules. We use the resulting understanding to interpret
optical field observations made from the ground, rockets, and
spacecraft.
Principal Investigators
Representative Projects and Publications
- Studies on Excited States of N2
- Charge Transfer Collisions in Ionospheres, Exospheres,
Magnetospheres, and Interstellar Clouds
- Telescope Studies of Terrestrial and Planetary Nightglows
- Low-Temperature Hydrocarbon Photochemistry: CH3 +
CH3 Recombination in Giant Planet Atmospheres
- Dissociative Recombination in Planetary Ionospheres
- D.L. Huestis and T.G. Slanger, J. Geophys. Res. 98, 10,839
(1993).
- M.J. Dyer, G.W. Faris, P.C. Cosby, D.L. Huestis, and T.G. Slanger,
Chem. Phys. 171, 237 (1993).
- D.L. Huestis, et al. Can. J. Phys. 72, 1109 (1994).
- C.W. Walter, P.C. Cosby, and H. Helm, Phys. Rev. A 50,
2930 (1994).
- K. Knutsen, M.J. Dyer, and R.A. Copeland, J. Chem. Phys.
101, 7415 (1994).
- R.A. Copeland, M.J. Dyer, D.L. Huestis, and T.G. Slanger,
Chem. Phys. Lett. 236, 350 (1995).
- D.L. Huestis, "Radiative Transition Probabilities," in Atomic,
Molecular, and Optical Physics Handbook, G.W.F Drake, Ed.
(AIP Press, Woodbury NY, 1996).
- T. G. Slanger, D. L. Huestis, D. E. Osterbrock, and J. P.
Fulbright, Science 277, 1485-1488 (1997).
5. Atmospheric Interactions of Spacecraft
Man-made objects produce disturbances as they travel through or
re-enter the earth's upper atmosphere. At high altitudes, the
space shuttle and earth-orbiting satellites collide with ambient
atmospheric components, principally oxygen atoms and nitrogen molecules,
resulting in the phenomenon called "spacecraft glow." At lower
altitudes, hypersonic vehicles produce high temperature bow shocks
that heat the vehicle surface and produce characteristic optical
signatures.
SRI scientists perform laboratory experimental investigations and
computer model simulations of the chemical kinetics of radical formation,
electronic excitation, collisional quenching, and radiative emission.
These studies have led to improved mechanistic understanding and
interpretation of atmospheric observations. We have helped elucidate
the contributions to spacecraft glow of the OH radical and nitrogen
dioxide molecule. Our investigations of reentry shock-heating have
illustrated the importance of non-equilibrium chemical kinetics and
the requirement for measurement of state- and quencher-specific rate
coefficients.
Principal Investigators
Representative Projects and Publications
- R.A. Copeland and T.G. Slanger, Geophys. Res. Lett. 17,
2341 (1990).
- G.A. Raiche and D.R. Crosley, J. Chem. Phys. 92, 5211 (1990).
- U.E. Meier, G.A. Raiche, D.R. Crosley, D.J. Eckstrom, and G.P.
Smith, Appl. Phys. B 53, 138 (1991).
6. Ionospheric and Space Sciences
SRI scientists and engineers use incoherent scatter radar, satellite
and optical instruments, and radiowave diagnostics to investigate
the fundamental processes governing the nature of the upper
atmosphere and space environment. We also manage national space
research facilities.
Principal Investigators
- Jeffrey P. Thayer, E-mail: <jeffrey.thayer@sri.com>
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