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Info box: "Road Traffic induced NOx"

Keywords:
  • Road traffic
  • Nitrogen oxide
  • Planetary boundary layer
  • Short lifetime
  • Seasonal cicle
  • Steady state
Input parameter:
  • Lifetime: 1d
  • Emission rate: 10 - 50e9 molecules cm**-2 s**-1
  • Emission source:
    • Process: Road traffic exhaust
    • Geographical distribution:
      Mainly Europe, North America, and some minor sources in South Africa, Asia (Russia, India, Japan), Australia, and South America.
    • Altitude: 1000hPa ~ Surface level
  • Start distribution: Zero
  • Simulation time: 13 month
Vocabulary: Model results:
  • Concentrations:
    ~ 600pptv - 2 ppbv it the major source regions
  • Spatial variability:
    High gradients around the emission sources
  • Steady state:
    Reached after several days: Already most of Jan 2000 looks like Jan. 2001.
  • Seasonality:
    Most obvious feature: Seasonality in variability at e.g. Mainz - see station record.
    The PBL over the NH continents is averagely about 3 times as high in summer compared to winter. This causes the pollution ("road traffic NOx" in this study) to be mixed in a larger volume of air with the result of lower concentrations. Enhanced turbulence and convective activity cause the rapid variability of the record during the months March through October. In contrast the air flow at 12km altitude is rather laminar except for some short events, when the "fasten your belt" sign flashes up ;-) .
  • Conclusion:
    Short lifetime of a species results in high spatial variability and a rapid levelling into steady state.
  • Other remarks:
    The lifetime of NOx at surface level is even shorter than that at heigh altitudes, which together with the turbulence in the PBL explanes the high variability in the station records. The lover curves represent Mount Zugspitze (3000m) and Tasmania (SH). They do not see much of the traffic NOx but well the consequences, which will turn out in the corresponding ozone simulation (next exercise). Like in the aircraft scenario the chemistry of NOx is only parameterised in form of a lifetime in this simple exercise.