Urban Air Pollution and Its Photochemistry Studied by Laser Spectroscopic Methods

Abstract

This work compares approaches both of mathematical and physical modelling of pollutant dispersion in simulated atmospheric boundary layer (ABL) with results of remote sensing of atmospheric pollutants. Measurements were performed over a highway outside a city and in an urban street canyon with extensive traffic under different meteorological conditions (autumn versus summer period). Time-resolved spatial distributions of pollutants (NO2 and O3) were measured by the combined DIAL (differential absorption light detection and ranging)/SODAR (sound detection and ranging) method and using spot analyzers appropriately located on the leeward and windward sides near the urban street canyon bottom. Qualitative agreement was found between the results obtained by remote sensing in the real atmosphere and those obtained by physical modelling in the simulated atmosphere of a wind tunnel for the autumn period. On the other hand, the analysis of the monitoring results and outputs of the physical modelling shows disagreement for the summer period. Besides neglecting the thermal effect during the sunny period, chemical reactions or photochemical processes taking place in the street canyon can affect the dispersion and distribution of pollutants very significantly. To improve the description of the system investigated, the Computational Fluid Dynamics (CFD) environment was tested for a basic implementation of photochemical reactions into the commonly used mathematical models of turbulence and dispersion processes as well.