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Info box: "Aircraft induced Ozone"

Keywords:
  • Aircraft
  • Ozone
  • UTLS
  • medium lifetime
  • Seasonal cicle
  • Steady state
 Input parameter:
  • Lifetime: 360d / 1y
  • Emission rate: 30-60e9 molecules cm**-2 s**-1
  • Emission source:
    • Process: Catalytic photochemical reaction chain
      initiated by NOx emissions from civil aircraft
    • Geographical distribution:
      Mainly Europe, North America, and the "flight corridor" in between
    • Altitude: 200hPa ~ 12km
  • Start distribution: Zero
  • Simulation time: 6 years
Vocabulary: As mentioned in the introduction page every NOx molecule emitted causes the production of a bunch of ozone molecules, a process which parameterised in the model simulation such a way that the chemical ozone source coincides with the locations of NOx emissions.

Model results:

  • Concentrations:
    ~ 12 - 17 ppbv in the flight corridor
    ~ 2 - 6 ppbv at the earth's surface
  • Spatial variability:
    Gradients around the emission sources smooth down with time in the longitudinal direction. A relatively steep gradient persists between the Northern and Southern Hemisphere as well as in the vertical profile.
    The reason: the lifetime of ozone is still about half as long as the so called "interhemispheric exchange time" and the higher wind velocities in the flight corridor region (the reason why they fly there) causes a faster mixing up there. Prevailing windirection is always in longitudinal direction towards east, which explains the preferred zonal distribution pattern.
  • Steady state:
    Approximately reached after four years - see station diagram.
  • Seasonality:
    Well pronounced in the source region:
    Annual maxima during NH summer - minimum in January.
    Very small amplitude at ground. Local maxima in December over Mainz and a reverse behaviour at Tasmania.
    The reason for that is obviously a stronger interhemispheric exchange in high altitudes in summer by the model dynamics. Chemical "aircraft ozone" production at ground level or elsewhere remote from the main "aircraft NOx" source can be excluded because of the low "aircraft NOx" concentrations there.
  • Conclusion:
    The longer lifetime of ozone leads to less variability in "aircraft ozone" concentration in space and in time compared to that of "aircraft NOx". I.e. "aircraft ozone" can even reach the eart's surface at small but significant amounts.
  • Other remarks:
    These model results cannot be validated by measurements, because in reality it is not possible to discriminate between "aircraft NOx / ozone" and those from other sources. However the role of numerical models can be seen as a tool to test hypotheses and simulate scenarious which are rather complex under simplifying assumptions.