The Generic Reaction Set (GRS) model by Azzi (1993,1994) is a semi-empirical approach, but it is written in terms of a non-steady state chemical mechanism using the reaction rate equations for the seven species. The GRS is not limited by the photo-stationary steady-state assumption of the IER model. Unlike the IER model, the implementation of the GRS model within the framework of a meteorological transport and dispersion model is non-linear and requires adding the precursor contributions from all sources before integration. The GRS model has been evaluated by Venkatram (1994) and Tonnesen and Jeffries (1994). The core subroutines used in HYSPLIT to compute ozone formation using the GRS were developed by Martin Cope, Victoria EPA, and later modified by G.D. Hess, BMRC, BoM, Melbourne, Australia. The key to properly linking a Lagrangian model with Eulerian chemistry is the conversion of particle mass to concentration and then back to particle mass after the chemistry has been applied. The method of Stein (2000) is used in the HYSPLIT-GRS module.

Azzi, M.; Johnson, G.M. Airtrak: new developments, Clean Air 1993, 27, 191-193.

Azzi, M.; Johnson, G.M.; Cope, M. An introduction to the generic reaction set photochemical smog mechanism, In Proceedings of the International Conference of Clean Air Soc. of Aust. and N.Z. 1992, 2, 451-462.

Stein, A. Incorporation of detailed chemistry into a three-dimensional Lagrangian-Eulerian hybrid model, Atm. Environ. 34: 4361-4372.

Tonnesen, S.; Jeffries, H.E. Inhibition of odd oxygen production in the carbon bond four and generic reaction set mechanisms, Atmos. Environ. 1994, 28, 1339-1349.

Venkatram, A.; Karamchandani, P.; Pai, P.; Goldstein, R. The development and application of a simplified ozone modeling system (SOMS), Atmos. Environ. 1994, 28, 3665-3678.

Equation Overview

1) Radical production from photo-oxidation of ROC

2) Oxidation of nitric oxide by radicals

3)  Photolysis of nitrogen dioxide to nitric oxide

4) Nitric oxide-ozone titration reaction

5) Radical pool sink through recombination to stable products

6) Sink for nitrogen dioxide to stable gaseous nitrates

7) Sink for nitrogen dioxide to stable non-gaseous nitrates