Extrapolation techniques used in the solution of stiff odes associated with chemical kinetics of air quality models

The solution of chemical kinetics is generally the most computationally intensive step in atmospheric air quality models. The incorporation of ever more complex chemical mechanisms and physicochemical phenomena into these models stimulates the search for more accurate and efficient numerical ODE integration methods. We report here on a new method based on Richardson extrapolation to solve the chemical kinetics in air quality models. The extrapolation method presents high accuracy consistently for wide ranges of ROG/NOₓ ratios. The method is robust during sunrise and sunset transitions, when the rate of change of concentrations of a number of photochemically driven species is the greatest. In addition, the extrapolation algorithm is one of the most efficient computationally tested.