< Promoting change of mode in transport

summary

results

     Summary

A pollution monitoring and modelling study has been carried out on a low street canyon (height to width ratio = 0.53) in a suburb of Leeds, Headingly with the aim of determining the micrometeorological influences on pollution concentrations and dispersion.  Pollution monitoring was carried out under a variety of meteorological conditions, over ten separate days using a mobile atmospheric unit and measurements were taken for five pollutants, NO, NOx, CO, O3 and NO2, along with three meteorological variables, wind direction, wind speed and temperature.
Two models have been employed to simulate the flow, turbulence and concentration fields within the canyon: the CFD model code, Fluent and the empirical air quality management package, Airviro.
 

     Results

The results showed

• synoptic conditions control ambient pollution levels
• There was poor correlation between pollution concentrations and meteorological parameters and traffic flows in the canyon.
• The Fluent model predicted a transitional flow regime, between Wake- Interference flow and isolated roughness flow within the canyon.  This was an unexpected  result
• The highest turbulent Kinetic energy values were predicted to be found at roof level.
• Fluent and Airviro both over predicted CO concentrations when comparing their output to specific days.  The discrepancy was greatest at the windward.
• Airviro over predicted NOx concentrations by a large amount.

This study highlights the need for extensive experimental data, with measurements made at both side walls, from the base of the canyon up to the roof level, so that numerical models such as fluent can be correctly validated.