Other gas plot

This shows the emissions of CH4, N2O, CO, NOx, VOx, SOx, and the concentration and radiative forcing of CH4, N2O and tropospheric Ozone.

  • Java Source Code

    Curves

    (from Oghga Module)

    Emissions

  • Green: Methane (CH4)
  • Brown: Nitrous Oxide (N2O)
  • Grey: Carbon Monoxide (CO)
  • Yellow: NOx (=NO, NO2, NO3)
  • Purple: Volatile Organic Carbons
  • Blue: SOx (=SO2, SO3)

    Concentration

  • Green, Brown: CH4, N2O as above
  • Grey: Tropospheric Ozone (O3T)

    Radiative Forcing

  • Green, Brown, Grey: CH4, N2O, O3T as above
  • Light-green: stratospheric water vapour from CH4
  • Yellow: Stratospheric Ozone (O3S)
  • Purple: CFCs total
  • Blue: HFCs total
    (See F-gas plot for more details regarding CFCs, HFCs and O3S).

    The sum of the radiative forcings above, is shown by the "other gas" curve on the radiative forcing plot.

    Units

  • Emissions are in teragrams (=megatons) per year
  • Concentrations are in parts per billion (or Dobson Units for ozone)
  • Radiative Forcing is in Watts per m2 Note, emissions and concentrations units are 1000 times smaller than on the carbon cycle plot! However the warming effect per molecule is much greater.

    Discussion

    (Note also Oghga Module -how it works)

    Changing the emissions

    The emissions for all these gases are prescribed by the SRES scenarios. They may also be reduced by mitigation, depending on the option you select from the "Other Gas" menu (top panel).

    See also:

  • Other Gas Emissions Menu
  • SRES Scenarios
  • Mitigation Module.

    Note these formulae also apply to all the HFCs, but not to the CFCs, HCFCs fixed by the Montreal protocol

  • See F-gas plot.

    Lifetimes

    These gases are destroyed by chemical oxidation in the atmosphere, unlike CO2 which is absorbed into the ocean and biosphere sinks.

    The atmospheric lifetime of CH4 is just under a decade (depending on OH, see below), whilst the lifetime of N2O is just over a century (similar to CO2).

    Choose "2000 fixed" from the "Other Gas menu" to see the effect of different lifetimes (CH4 and O3T concentrations level off rapidly, N2O much more slowly).

    CO, NOx, VOC, Ozone and Hydroxyl radicals

    Carbon Monoxide (CO) and Volatile Organic Carbons (VOC) are produced mainly by incomplete fossil fuel combustion (e.g. in cool engines or with insufficent oxygen), whilst NOx is produced mainly by the reaction of atmospheric nitrogen and oxygen in very hot engines. These gases have no direct influence on radiative forcing, but contribute to the formation of tropospheric ozone (O3), which is the an important greenhouse gas, the next after methane.

    Note that we need ozone in the stratosphere where it protects us from ultraviolet radiation, but not so much in the troposphere where it causes adverse health impacts and photochemical smog.

    CO, NOx, VOC and CH4 also affect the production of reactive hydroxy radicals (OH). These play a major role in atmospheric chemistry, including the oxidation of CH4 and the HFCs. Consequently CH4 has an effect on its own lifetime.

    The atmospheric chemistry leading to formation and destruction of O3 and OH is very complicated, with dozens of transient species and reactions which are difficult to measure. The distribution of these gases is also highly variable over space and time. So this model uses some simple formulae taken from an IPCC workshop (Prather et al) (see Ogha Module.). Note that these may not be valid beyond the range of SRES scenarios for which they were calibrated.

    Minor radiative forcing effects

    The model also accounts for the overlap in the radiative forcing of CH4 and N2O, and the small cooling effect of water vapour produced by the oxidation of methane in the stratosphere.

    Atmospheric Aerosols

    This plot also shows Sulphate emissions (SOx), which lead to the production of sulphate aerosols, whose cooling effect is shown and discussed in the radiative forcing plot.

    Black carbon and organic carbon aerosols may also be calculated as a function of CO emissions (see Oghga Module).

    Comparison with IPCC predictions

    This model may be checked against data from IPCCTAR-WG1-SRESappx. See
  • Comparison with IPCC predictions
  • radiative forcing plot.

    Future Development

    Controls should be added to experiment with varying emissions of each gas seperately, and also to see the sensitivity to the OH chemistry feedback.