Can Urban Ozone Generation be Modeled Correctly Based on Major Gaseous Atmospheric Reactions?

A simple model based on inorganic atmospheric gaseous constituents to investigate ozone generation in urban areas is proposed. We performed simulation using the STELLA software for a late summer episode in Los Angeles (LA) metropolitan area. Wind, temperature, solar irradiance and relative humidity were the meteorological inputs to the model, which are extracted from Typical Meteorological Year (TMY3) dataset. Constant values of the inputs simplified momentum, mass, and energy conservation laws to the balance of the related properties' budget in the lateral boundaries. The quantity of pollutants was estimated based on their inflow and outflow from chemical reactions, anthropogenic emissions and convection. Photochemical reaction rates were determined by parameterization of their relationship to the zenith angle. Other chemical reaction rates were extracted from the reported experimental data obtained from chemical reactors or by parameterization of their relationship to temperature from collision theory. The model simulated the diurnal variation of ozone concentration, with a significant increase and gradual decrease of ozone concentration before and after noon, respectively. A sensitivity analysis of the response of ozone concentration to temperature produced controversial results compare to other models and experimental data. This means that the diurnal variation was driven by the photolysis reactions, and improving the model would require the inclusion of other sources of the ground state oxygen atoms as well as the emission of Volatile Organic Compounds (VOCs). The role of VOCs is formation of radical intermediates that convert NO to NO2, and this increase in the NO2/NO ratio results in increasing the ozone concentration.