Implementing spatial variance in the rate of photolytic breakdown of NO2 in urban street canyons

Sammanfattning: In this study a module for calculating the solar exposure of individual fluid cells was developed to more accurately represent the effect of photolysis on the pollutant dispersion in an urban street canyon. The module was tested and validated on 12 different cases, each with a different geographical location, time of year and/or time of day. It was used for four parallel simulations performed on a street canyon model representing a real-life street canyon in Gothenburg, Sweden, each one using a differ- ent model for NO2 photolysis. NOx and O3 levels were measured and compared at street level, mid-canyon level, and sky level, with results showing negligible differ- ence between models using partial sunlight and no sunlight, while showing signifi- cant difference between the partial sunlight model and the uniform sunlight model. We conclude from our results that simulations without any modeling of photolytic reactions are sufficient for accurately predicting NO and O3 levels, but fail to accu- rately predict NO2 levels, while simulations utilizing a solar model with uniform photolysis throughout the simulated domain are sufficient for accurately predicting NO and NO2 levels, but fail to accurately predict O3 levels. For any study placing an emphasis on both NO2 and O3 levels within the domain, it is our recommendation to incorporate a non-uniform solar model. Such a model was developed for this thesis, and aims to be integrated into the OpenFOAM framework in the future.