A SENSITIVITY ANALYSIS OF OZONE FORMATION TO AMBIENT AIR COMPOSITION BY MEANS OF PHOTOCHEMICAL MODELS

摘要

The prediction of the atmospheric concentration of ozone and of other photochemical pollutants represents one of the major scientific challenges in the study of urban air qualify. To this aim, photochemical models are widely applied as support tools for regulatory purposes, but their results are known to be affected by several uncertainties, in boundary conditions, geographical and meteorological data and the chemical composition of emission and ambient air as well. Also the mechanism selected to describe the urban chemistry may lead to large differences in the model results. In this work, the influence of ambient air composition on the results of photochemical model has been studied using a simple Lagrangian trajectory model coupled with different chemical submodels (CB-IV and a simplified version of EMEP). To this aim a parametric sensitivity study of ozone with respect to its precursors' concentration was performed with reference to the same meteorological conditions and by simulating different scenarios characterized by specific emitted pollutants concentration. Rather than analyzing sensitivity by changing initial composition, an analytical local sensitivity concept has been applied; this allowed evaluation the influence of initial concentration on the predicted ozone concentration and to discriminate between VOC-sensitive and NOx-sensitive kinetic regimes. Finally, these results have been successfully compared with those obtained applying the concept of photochemical indicators (i.e. O_3/NOy and H_2O_2/HNO_3 ratios).