Gas-phase acid precipitation chemistry: Simulations and analysis

A method of analysis based on a Taylor series integration of final model outcomes with respect to initial model parameters is used to study the behaviour of a gas-phase photochemical reaction mechanism. Acid precipitation reactions are examined using the first and second order sensitivities of the results of several simulations towards the initial conditions used in the reaction model. It is found that the chemicals whose initial values have the greatest influence on acid precipitation chemistry are: ;The behaviour of the radicals during the interval of integration can have a profound effect on the outcome of the simulation. This is in contrast to earlier studies, which used only sensitivity coefficients for analysis. Radicals are characterized by very fast chemical interactions which cause them to remain in a steady state throughout a simulation. Their concentrations at any instant in time are thus solely dependent on the concentrations of the non-radicals at that instant. The radicals and their effects are modelled using the pseudo steady-state approximation, in which the rates of change of the radicals are set to zero and their concentrations result from the solution of a set of non-linear equations.