SENSITIVITY ANALYSIS OF THE REQUIREMENTS OF RATE COEFFICIENTS FOR THE OPERATIONAL MODELS OF PHOTOCHEMICAL OXIDANTS FORMATION IN THE TROPOSPHERE

A local sensitivity analysis is performed on four chemical mechanisms describing the formation of photochemical oxidants in the troposphere. Indeed, large discrepencies do exist between the predictions of different mechanisms. For each mechanism studied and various realistic concentrations coming from field measurements each rate coefficient is varied according to three values: the median recommended value, the ceiling value and the bottom value, all other coefficients being kept at their median value. This calculation is repeated for each rate coefficient of each mechanism. Then the percentage of variation of the maximum concentration of five model species of practical concern are calculated with regard to the reference run for which all the rate coefficients are fixed at their median value. The results indicate that a restricted number of rate coefficients are sensitive within their uncertainty. Most often the same rate coefficients are sensitive whatever the mechanism is. However, the sensitivities of the reference compounds differ, H2O2 being very sensitive and HNO3 poorly sensitive. The limitations of this analysis is discussed. Based on these findings, a series of recommendations are made for future experimental kinetic studies.