Monitoring and modelling carbon monoxide concentrations in a deep street canyon: application of a two-box model

Carbon monoxide concentrations were monitored at 3, 10 and 30 meters in a deep street canyon with an aspect ratio of (H/W) ≈ 5.8 and were modelled using a two–box model developed in a previous CFD study. The monitoring campaign lasted 5 days, from 11th to 15th July, 2011. The turbulent kinetic energy at the rooftop level and traffic flow was also measured in the same period. Experimental data were used to evaluate parameters (mass transfer velocities and overall mass transfer velocity) of the box model. The daily pattern shows a significant increase of the overall mass transfer velocity from 9:00 to 11:00 and a decrease until 14:00. Turbulent kinetic energy measured at the rooftop level seems to play a major role with respect to wind velocity in determining the mass transfer between the canyon and the atmosphere above. The evaluation of the overall mass transfer velocity contributes to the use of operational street canyon dispersion models in the case of deep street canyons.