ANALYSIS OF NUMERICALLY MODELLED LOCAL CONCENTRATION GRADIENTS IN STREET CANYONS: IMPLICATIONS FOR AIR QUALITY MONITORING J.M. Crowther 1, D. Mumovic 2, Z. Stevanovic 3 1 School of the Built and Natural Environment, Glasgow Caledonian University 2 The Bartlett, Faculty of the Built Environment, University College, London 3 Institute of Nuclear Sciences, University of Belgrade

Objectives of this study To analyse numerically modelled, local concentration gradients in street canyons To make recommendations for the positioning of air quality monitoring stations

Cases Studied 1.A single street canyon 2.A staggered cross-road 3.An idealised complex configuration of several street canyons

Methodology PHOENICS with different turbulence models: –Standard k-epsilon –Renormalisation group k- model –Chen-Kim modification of k- model –Two-scale k-

Validation Comparison with air quality data collected for Glasgow city Council, Scotland Wind tunnel data from the University of Hamburg, Germany

Incompressible, Steady-state Navier Stokes equations k = turbulence kinetic energy per unit mass U i = mean velocity, u i = turbulence velocity P = pressure, = density, μ = dynamic viscosity t = turbulent viscosity

Pollutant Transport Equations Turbulence Contribution to the Pollutant Flux Conservation of Pollutants D = Laminar Diffusivity, C = Turbulent Schmidt No.

General Transport Equation Property with source S and diffusivity

Standard k- Turbulence Model k =1.0, =1.314, C 1 =1.44, C 2 =1.92, C = 0.09

RNG k- Turbulence Model k =0.7914, =0.7914, C 1 =1.42, C 2 =1.68, C = o = 4.38, = 0.012

Chen-Kim k- Turbulence Model k = 0.75, =1.15, C 1 =1.15, C 2 =1.9, C 3 = 0.25, C = 0.09

Two-scale k-ε Turbulence model

Two-Scale k- Turbulence Model Parameters

Case 1: Single Street Canyon Hope Street, Glasgow Three-dimensional: wind direction at normal incidence Ref. Mumovic & Crowther, 2002 Four different turbulence models Longitudinal single vortex

Standard k- model Single Street Canyon Pollutant Dispersion Case 1

RNG k- model Single Street Canyon Pollutant Dispersion Case 1

Chen-Kim k- model Single Street Canyon Pollutant Dispersion Case 1

Two-Scale k- model Single Street Canyon Pollutant Dispersion Case 1

Comparison of a wind- tunnel study (Pavageau & Schatzmann, 1999) with the RNG turbulence model Case 1 Single Street Canyon

Case 2: Staggered Cross-Road University of Hamburg wind-tunnel test Ref Mumovic, Crowther & Stevanovic, 2003a Ref. Mumovic, Crowther & Stevanovic, 2003c

Case 2 Staggered cross-road

Case 2 Staggered cross-road, Section B-B

Case 2 Staggered cross-road, Section A-A

Case 3: Complex Configuration of Street canyons Wind-tunnel study University of Hamburg Ref. Crowther, Mumovic & Stevanovic, 2003a, b

Experimental Geometry

Model Grid for Wind-Tunnel Simulation

Case 3 Complex configuration of street canyons: vertical plane at centre of 5th cavity

Case 3: Concentration distribution in the mid-height horizontal cross-section of the 5th cavity

Experimental Concentration Contours: Horizontal Cross-Section, Mid-Height, 5 th Canyon

Local Concentration Gradients

Factors for Location of Monitoring Equipment Practicality of Location Practicality of Location Level of Turbulence Level of Turbulence Local Concentration Gradients Local Concentration Gradients Suitable Location Suitable Location