Simplified kinetics of tropospheric ozone

Though air quality modelling has reached a stage of extreme complexity, this simple model is intended to demonstrate how the basic mechanism of tropospheric ozone can be explained with a very simple dynamics, if the model is adjusted to the field situation with the aid of an efficient parameter calibration algorithm. The scope of this paper is to propose a simple kinetic model to describe the interactions of NO, NO2 and O3 in a polluted urban atmosphere where the presence of free radicals disrupts the basic Leighton cycle, which otherwise provides a stable cycle among these three species. The key feature of the model is the inclusion of the free radical concentrations, which are extremely difficult to measure, in the reaction kinetics. The model thus obtained is very simple and easy to calibrate. After describing its structure, it is tested with data taken from a smog chamber and a real urban environment, in which the kinetics of the pollutants are known to prevail over air mass movements. In both cases, a satisfactory agreement between data and model response is obtained, with consistent parameter values.