Low and high NOx chemical regimes in an urban environment

In this work, a chemistry-transport box model, derived from the CHIMERE model, is used in order to examine the existence of different chemical regimes, known as the low NOx and high NOx regimes, and the existence of multiple equilibria in an urban environment. From an operationnal point of view, the existence of chemical regimes of low NOx and high NOx type and of multiple equilibria is of paramount importance for the effectiveness of the air quality policies. For the urban photochemical system under consideration, we determine the equilibria associated with primary pollutant emissions varying in a range of values typical of the parisian urban area. The influence of several variables on these regimes is also studied, through the following parameters: wind speed, upstream ozone concentration, cloudiness.