HYSPLIT and the Integrated Empirical Rate Model (IER) Solution

The ozone prediction method, a semi-empirical approach called the Integrated Empirical Rate (IER) model developed by Johnson (1984, 1989), is incorporated as the ozone calculation scheme. The IER model, based on outdoor smog chamber studies for conditions typical of Australian cities, is usually applied in conjunction with monitoring data, to evaluate the age of photochemical smog and to determine whether the air parcel is in the NOx -limited or light- limited regimes. In the light-limited regime, the smog produced is only a function of the accumulated incident light and the hydrocarbon concentration. In the NOx-limited regime, the concentration of smog produced is assumed to be independent of the amount of incident light and the smog concentration can only increase by increasing the amount of NO available. An updated version of the IER model by Azzi (1992) is used here which includes the loss of NOx to stable nitrate. The model is based upon the photo-stationary steady-state equation and its implementation within Hysplit is uncomplicated because the IER's integration of the smog produced is linear and contributions from each source can be added. More detailed information on the incorporation of IER into Hysplit is available elsewhere (Draxler, 2000).

Azzi, M.; Johnson, G.M. Notes on the derivation, The Integrated Empirical Rate Model, Version 2.2, 20 March 1992, CSIRO Division of Coal and Energy Technology, PO Box 136, North Ryde, NSW 2113, Australia.

Draxler, R.R. Meteorological factors of ozone predictability at Houston, Texas, J. Air & Waste Manage. Assoc. 50:259-271, 2000

Johnson, G.M. A simple model for predicting the ozone concentration of ambient air, In Proc. 8th Int. Clean Air Conf., 2, 715-731, Eds. H.F. Hartmann, J.N. O’Heare, J. Chiodo, and R. Gillis, Clean Air Soc. of Australia and New Zealand, Melbourne, Australia, 7-11 May 1984.

Johnson, G.M.; Quigley, S.M. A universal monitor for photochemical smog, Proceedings of the 82nd Annual Meeting of the Air and Waste Management Assoc., June 25-30, 1989, Anaheim, CA, Paper 89-29.8

Equation Overview

1) Smog Produced

[SP] = MIN { Time Integral 0->t (k1 [ROC], 4.09 [NOx] )}

2) Ozone produced and oxidized nitric oxide

[SP]t = [O3]t - [O3]o + [NO]o - [NO]t

3) Photostationary state equation

[O3]t = k1 [NO2]t / k4[NO]t

4) Definition of NOx

[NOx]t = [NO]t + [NO2]t