The Integrated Empirical Rate Model

The Integrated Empirical Rate (IER) Model is a description of the formation of photochemical smog in the urban atmosphere. It is a key component of the AIRTRAK monitoring system which executes the model in real time from ambient monitoring data, in which case no emissions inventory data are required (Johnson & Quigley 1989). The model was derived from extensive chamber studies by colleagues at CSIRO Energy Technology (See, e.g., ECOS article about smog in Sydney and AIRTRAK. Contact merched.azzi@csiro.au).

The IER model is used in our prognostic Lagrangian particle model, LADM, to predict concentrations of nitrogen dioxide and ozone downwind of a chimney. A more detailed smog model called the Generic Reaction Set, and of which the IER model is a solution, has also been developed (Azzi et al. 1992). An extended version of GRS is used in the air pollution model, TAPM, a new general purpose prognostic air pollution model from CSIRO. An extended GRS is also used in the Australian Air Pollution Forecasting System.

According to the Integrated Empirical Rate Model (see Johnson 1984) there are two regimes in the formation of photochemical smog in an air parcel:

• a light-limited regime in which the smog produced [SP] is a function of the cumulative sunlight exposure expressed in terms of the rate coefficient for NO2 photolysis, the concentration of reactive compounds (ROC), and temperature (Wratt et al. 1990, Wratt et al. 1992);

• a NOx-limited regime in which sufficient light has been incident on the air parcel that smog production effectively ceases.

Species concentrations are all measured in volume/volume units such as ppb.
At any time and location, they are:

     [SP] = smog produced
  [NO2] = nitrogen dioxide
    [NO] = nitric oxide
     [O3] = ozone, including background [O3bg]
[SNGN] = stable non-gaseous nitrogen products (loss)
  [SGN] = stable gaseous nitrogen products (loss)
  [ROC] = the concentration of reactive compounds in the air
 [NOxo] = concentration of nitrogen oxides as it would be if the nitrogen oxides were treated as a conserved species

      = 4.09
      = activity coefficient (~ 0.0067 in urban air)
     k1f = temperature corrected actinic flux expressed as the rate coefficient for photolysis of NO2.

    [NOx] = [NO] + [NO2]
  [NOxo] = [NOx] + [SGN] + [SNGN]
[SMOG] = [O3] + [NO2] + [SGN]
       [SP] = [O3] + [NOo] - [NO] - [O3bg].

[SNGN] = min([NOxo], P[SP])
   [SGN] = min(([NOxo] - [SNGN]), Q[SP])

REFERENCES

Azzi M., G. Johnson, M.Cope (1992). An introduction to the Generic Reaction Set Photochemical Smog Model. In Proceedings of the 11th International Conference of the Clean Air Society of Australia and New Zealand, Eds. P. Best, N. Bofinger, and D. Cliff, 2, pp. 451-462.

Johnson G. (1984). A simple model for predicting the ozone concentration of ambient air. In Proc. 8th International Conference of the Clean Air Society of Australia and New Zealand, Eds. H. Hartmann, J. O'Heare, J. Chiodo, and R.Gillis, 2, pp. 715-731.

Johnson, G.M. and S.M. Quigley (1989). A universal monitor for photochemical smog. In: Proc. 82nd Annual meeting of the Air and Waste Management Assoc., Paper 89-29.8, 18 pages.

Johnson, G.M., S.M. Quigley and J.G. Smith (1990). Management of photochemical smog using the AIRTRAK approach. In International Clean Air Conference 1990, Auckland, New Zealand. March 25-30, The Clean Air Society of Australia and New Zealand. Editor Philippa Gibson pp. 209-214.

Wratt, D.S., M.G. Hadfield, M. Jones and G.M. Johnson (1990). Predicting the impact of a proposed gas fired power station on photochemical pollution levels around Auckland. In International Clean Air Conference 1990, Auckland, New Zealand. March 25-30, The Clean Air Society of Australia and New Zealand. Editor Philippa Gibson pp. 159-164.

Wratt, D.S., M.G. Hadfield, M.T. Jones, G.M. Johnson and I. McBurney (1992). Power stations, oxides of nitrogen emissions, and photochemical smog: a modelling approach to guide decision makers. Ecological Modelling, 64, pp. 185-203.

CONTACTS

For more information, e-mail: peter.manins@csiro.au or peter.hurley@csiro.au

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Modified: May 22, 2008

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