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Interim Review of the Subsonic Assessment Project Management, Science, and Goals (1997) / Chapter Skim
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Atmospheric Effects
Pages 5-10

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From page 5...
... One of the most important potential consequences of aircraft emissions' effects on the troposphere is the possible alteration of climate through perturbations of ozone and aerosol concentrations. Ozone is highly reactive chemically, and is also a strong specific greenhouse gas that absorbs atmospheric radiation in the troposhere.
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From page 6...
... When averaged zonally, O3 production prevails, and because of ozone's long lifetime in the upper troposphere, current models predict an increase in O3 as a result of aircraft emissions everywhere in the upper troposphere (Ehhalt and Rohrer, 1995; Brasseur et al., 1996~. The unperturbed NOx concentration field, however, is poorly known and poorly understood: Available measurements are insufficient to characterize well the background distribution of NOx, and other source processes that introduce NOx into the upper troposphere (namely, lightning, convective transport from the boundary layer, and input from the stratosphere)
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From page 7...
... The size distributions, compositions, and concentrations of aerosol particles reflect a dynamic balance among source, transport, evolution, and removal mechanisms that vary in both space and time. (For instance, some particles and gases are injected from the atmospheric boundary layer into the upper troposphere and lower stratosphere by deep convection.
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From page 8...
... Particles that scatter light effectively at relative humidities below saturation, yielding direct radiative effects, are usually about 0.1 to 10 ,um in diameter; normally they dominate the aerosol mass concentration in the upper troposphere. One subset of the total aerosol population, which can grow into cloud droplets through the condensation of water vapor at typical cloud supersaturations, is called cloud condensation nuclei (CCN)
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From page 9...
... Such measurements were recently attempted in a specific location in the SASS project's Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) program, as well as under the German Advanced Technologies Testing Aircraft Systems (ATTAS)
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From page 10...
... · Increase efforts to characterize the size and properties of soot particles emitted under ambient operating conditions. · Pursue direct interactions with aircraft manufacturers and air carriers to identify a workable joint strategy for using the commercial air fleet as platforms for measurements of both aerosol and gas-phase species.
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Key Terms

  • current uncertainties
  • radiative effects
  • chemical reactions
  • lower stratosphere
  • aircraft emissions

  • lowermost stratosphere
  • aircraft exhaust
  • sulfuric acid
  • particle size
  • indirect effect

  • boundary layer
  • background aerosol
  • cloud droplets
  • optical properties
  • ice crystals

  • radiative properties
  • water vapor
  • aerosol particles
  • removal mechanisms
  • particles form

  • cloud forcing
  • aerosol mass
  • direct radiative
  • specific location
  • background distribution

  • sass research
  • free troposphere
  • reactive trace
  • local formation
  • surface radiation


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