METO 637

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METO 637

• Lesson 9

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Mans impact on the Stratosphere

• The concern over a loss of stratospheric ozone is
  that this will lead to an increase in ultraviolet
  radiation at the ground, especially those
  wavelengths near 300 nm.
• The next figure shows the so-called action
  spectra for biological response. The action
  spectra also follows closely the absorption
  spectra for DNA, which leads to the dissociation
  of the DNA molecule. This could lead to cell
  mutations skin cancer.
• We identify a spectral intervals of interest,
  UV-B from 280 to 315 nm.
• Although skin cancer gets most of the publicity,
  it also impacts the biota.

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DNA absorption and the solar flux at the surface
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Human death due to skin melanoma
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Supersonic Aircraft

• First real concern was the role of supersonic
  transport (SST) which were to fly in the
  stratosphere. These aircraft emit water vapor,
  CO, and NOX directly into the stratosphere, where
  they could accumulate over two years.
• The NO comes from heating the air at high
  temperatures
• N2 energy ? N N
• N O2 ? NO O
• O N2 ? NO N
• The reaction rates can become large at high
  temperaures, e.g. in the cylinders of
  automobiles. This cycle is known as the
  Zeldovich mechanism.
• The water vapor and CO come from the oxidation of
  the aviation fuel.
• Initially a projected fleet of 500 aircraft
  emitting 1.2E9 kg of NO per year was assumed.

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Supersonic Aircraft

• Initially it was thought that the injected water
  vapor was the major problem , after the work of
  Bates and Nicolet. These reactions are
• OH O3 ? HO2 O2
• HO2 O ? OH O2
• net reaction O O3 ? O2 O2
• And
• OH O3 ? HO2 O2
• HO2 O3 ? OH O2
• Net O3 O3 ? 3O2
• In the US this concern led to the formation of
  the CIAP program (Climatic Impact Assessment
  Program).

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Supersonic Aircraft

• Then Paul Crutzen (theorist) put forward the NOX
  catalytic cycle and Harold Johnson (laboratory
  chemist) showed that the reaction rates would
  make the catalytic cycle significant.
• These reactions are
• NO O3 ? NO2 O2
• NO2 O ? NO O2
• net reaction O O3 ? O2 O2
• The fleet of 500 SSTs would have led to a
  reduction in the global ozone column of about 12.

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Potential atmospheric impacts of aircraft
emissions
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Measured and calculated NOx emission indices
from aircraft
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Typical fuel consumption in Kg
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History of calculations of ozone loss from SSTs
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Rockets and the Space Shuttle

• Solid fuel rockets are used as launch vehicles,
  and to boost the Space Shuttle in its early
  stages of flight.
• The oxidizer used in these rockets is ammonium
  perchlorate.
• HCl is released into the stratosphere, which
  can begin the chlorine catalytic cycle.
• Aluminum is added to the rocket fuel to boost
  thrust, and the rocket exhaust also contains
  aluminum oxide particles, which could contribute
  to heterogeneous chemistry. The following
  reaction is known to occur on aluminum particles
• ClONO2 HCL ? Cl2 HNO3
• In general the amount of HCl released is small
  compared to natural sources of chlorine.