Improvement of a Simple Dispersion Model for Calculations of Urban Background Concentrations

A simple dispersion model for calculation of urban background concentrations, similar to the one used for Copenhagen in Denmark, has been developed for Sweden (SWE-BUM). The model calculates concentration on a 1 x 1 km grid and is, within the national Air Quality system SIMAIR, operationally applied for 150 cities in Sweden. In this study, a simple stability parameterisation is implemented in the calculation of the vertical dispersion parameter, since stability plays an important role for Swedish conditions with cold climate and small towns. Furthermore, the meteorology is corrected in order to represent urban conditions. The model is evaluated against monitoring data from 13 cities in Sweden. The performance is improved in the new model version; when comparing the calculated NO2 concentrations with measurements, 95 % of the data points are within ±50 % for the new model version in comparison with 41 % for the original model. However, the improved model still doesn’t succeed to fully reproduce the highest daily and hourly peaks of concentrations.