Transcript Document 7896308

DIMER PHOTOCHEMISTRY IN THE
PALEOATMOSPHERE
E. C. Zipf
University of Pittsburgh
([email protected])
&
Sheo S. Prasad
Creative Research Enterprises
([email protected])
28 April 2000
• Dimer Photochemistry may have
been very important in the
prebiological paleoatmosphere
before the advent of the biological
photosynthesis
• May have influenced the
evolution of the primitive marine
life and also of the O3 layer during
the time period when the O2 layer
was developing
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 1
DIMER PHOTOCHEMISTRY WAS IMPORTANT DUE
TO LOW ATMOSPHERIC TEMPERATURES
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Illustration for the era of O2 level = 10-4 present
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 2
IN O2-DEFICIENT PALEOATMOSPHERE DIMER
PHOTOCHEMISTRY MAY HAVE DONE THINGS
NOT POSSIBLE IN THE PRESENT ATMOSPHERE
With O2 being at 10-5 to
10-3 PAL (Present
Atmospheric Level), the
chemically significant
UV penetrated the
region where dimer
population is
appreciable.
Flux at the ground for various O2 levels
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 3
NOX PRODUCTION: AN EXAMPLE OF IMPORTANT
ROLE OF DIMER PHOTOCHEMISTRY IN
PALEOATMOSPHERE
O2•N2 + hv (200-250 nm)  NO +NO
• Laboratory experiments put wavelength averaged
quantum yield () at   3.3 x 10-2 NO /photon
• Also dimerization might facilitate the spin forbidden
absorption of these photons by O2 of the O2•N2 dimer
• N & NO2 as the primary products are ignored since
N+ NO2  N2O + O
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 4
TOTAL NOX PRODUCTION RATE WAS
SUBSTANTIAL
• Assuming -averaged 
was valid for each
wavelength bin
•Note, the total NOX
production rate was
considerable at even the
ground level
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 5
LET US PUT THE DIMER NOX PRODUCTION IN A
PROPER PERSPECTIVE
• The N2O + O(1D)  NO +NO was insignificant due to
deep penetration of the UV
• Lightning is thought to be the only important source
of NOX in the post-bolide impact era
• The dimer source, however, may have been 50 to 100
times larger than the lightning source
• The dimer was thus the most important NOX source in
the post-bolide prebiological paleoatmosphere
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 6
THIS DIMER CHEMISTRY MAY HAVE AFFECTED
THE EVOLUTION OF LIFE IN OCEAN AND LAND
• Since it was a global tropospheric source, it was
particularly effective in providing nutrients to marine
life in the post-bolide impact era
• It may have created a low-altitude paleoionosphere
that modified the electrical properties of the
Precambrian atmosphere.
• It may have influenced the pace of formation of the O3
shield over the biosphere when the O2 was growing
from its prebiological level to the present level
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 7
CONCLUDING REMARKS
• The dimer photochemistry may have been
quite important in the prebiological
paleoatmosphere
• It is therefore hoped that this presentation
will motivate the key measurements- the
wavelength dependence of the quantum
yield
28 April 2000
Creative Research Enterprises’ Presentation
EGS2000/ST9-02 Paper # ST029
Slide 8