1) The document compares air pollution modeling using ADMS-Roads and CFD modeling to analyze the impact of a proposed 10-story building on nitrogen dioxide (NO2) concentrations in a street canyon. 2) ADMS-Roads predicted a 20 μg/m3 increase in annual mean NO2 concentrations with the proposed development, while CFD modeling found smaller increases or decreases depending on wind direction and speed. 3) Overall, CFD modeling indicated a small 0.01% decrease in annual mean NO2 concentrations with the proposed development when accounting for different wind conditions.

1. Modelling Street Canyons:
Comparison of ADMS-Roads
and CFD Modelling
Dr Austin Cogan

2. What is a street canyon?

3. Canyons within ADMS-Roads

4. Islington Case Study
10-storey building proposed - would create a street canyon
Application Site

5. ADMS-Roads Results
Figure 1: Predicted Annual Mean Nitrogen Dioxide Concentrations in the Street Canyon for With
and Without the Proposed Development in 2019 (µg/m3). View is looking northeast
along the Road.
20 µg/m3 increase in NO2

6. Different building heights
Figure 2: Predicted Annual Mean Nitrogen Dioxide Concentrations in the Street Canyon for With
and Without the Proposed Development in 2019 (µg/m3). View is looking northeast
along the Road.
Proposed Building
Height
Max NO2
Increase
(µg/m3)
2-Storey 1.1
3-Storey 5.4
4-Storey 15.4
5-Storey 16.7
6-Storey 17.3
7-Storey 17.8
8-Storey 18.5
9-Storey 18.9
10-Storey 20.0
Increase Necessary
for Adverse Impact
0.6

7. Predictions outside canyon
No Scheme
Height(m)
Road Transect (North to South)
Dramatic step-changes can have big consequences in model results
With Scheme
10 Storey
Building
Height(m)
Road Transect (North to South)
Figure 3: Predicted Annual Mean Nitrogen Dioxide Concentrations inside and outside the Street
Canyon for With and Without the Proposed Development in 2019 (µg/m3). View is
looking northeast along the Road.

8. Figure 4: Illustration of air flow predicted with CFD Modelling
Canyons within CFD Modelling
Both ADMS and CFD Modelling provide a representation of a very
complex environment and both have limitations
CFD advantages: urban landscapes, wind speed and wind direction
CFD disadvantages: cost and computational time

9. Wind Analysis
Figure 5: Wind Rose for London City Airport Meteorological Station in 2016 showing the
Frequency (number of hours) for each Wind Direction (10 degree sections) and
Wind Speed (m/s)
Most wind from SW
Also some from NW
and 90º

10. Wind Analysis
Figure 6: Wind Rose for London City Airport Meteorological Station in 2016 showing the Percentage Contribution of each
Wind Direction (10 degree sections) and Wind Speed (m/s) to the Predicted Annual Mean Nitrogen Dioxide
Concentrations at the Existing Properties for the Without and With Scheme Scenarios
Largest contributions from 210-250º
Also some NW (300º, 320º and 330º) and 90º
Decided 90º, 240º and 320º as well as 5 m/s and 3m/s
Without Scheme With Scheme

11. CFD Model Setup
Buildings within 200 m of site
modelled
Based on OS Mastermap data and
Google Street View
Figure 7: Illustration CFD Model Steup

12. CFD Model Results
Scenario Without Scheme With Scheme % Change
90º, 5m/s at 10 m 23 6 -74%
240º, 5m/s at 10 m 23 8 -65%
320º, 5m/s at 10 m 145 19 -87%
90º, 3m/s at 10 m 23 10 -57%
NOx concentrations
predicted on the building
façade (blue area)
Table 2: Predicted values at the building façade with and without the scheme for each wind scenario
Figure 8: Proposed Development and Receptors

13. CFD Model Visualisation
90º, 5m/s at 10 m
Development shields buildings from the wind
Figure 9: Visualisation of results for the scenario of 90º, 5m/s at 10 m height

14. CFD Model Visualisation
240º, 5m/s at 10 m
Development acts to channel air along the road
Figure 10: Visualisation of results for the scenario of 240º, 5m/s at 10 m height

15. CFD Model Visualisation
320º, 5m/s at 10 m
Development causes less re-circulation
Figure 11: Visualisation of results for the scenario of 320º, 5m/s at 10 m height

16. CFD Model Visualisation
Difference in wind speed
Similar pattern
Reduced dispersion with slower wind
Figure 12: Visualisation of results for the scenarios of 90º at 5m/s and 3m/s at 10 m height

17. Summary
Both ADMS and CFD Modelling provide a representation of a very
complex environment and both have limitations
CFD advantages:
• urban landscapes
• wind speed
• wind direction
Other considerations:
• Choice of receptor locations / canyon characteristics
• What happens to the displaced pollution? Any wider issues?
• Consideration of domain size
• Model verification?
CFD disadvantages:
• cost
• computational time

18. Head Office
23 Coldharbour Road, Bristol BS6 7JT
Tel: 0117 974 1086
London Office
12 Airedale Road, London SW12 8SF
Tel/Fax: 020 8673 4313

19. Bristol Case Study
Figure 13: Wind Rose for Filton Airfield Meteorological
Station for six years combined (2010, 2011,
2012, 2014, 2015 & 2016)
Existing
Sensitive
Property
New Building Proposed

20. CFD Results
30º, 5m/s at 10 m
157% increase in NOx
Proposed building shields the road from the cross wind, reducing the dispersion
of emissions

21. CFD Results
210º, 5m/s at 10 m
19% increase in NOx
Proposed building restricts local flow across the road, keeping the stagnant flow
near the sensitive property

22. CFD Results
255º, 5m/s at 10 m
12% decrease in NOx
Proposed building acts to funnel air along the road, helping to disperse
emissions

23. Analysis of CFD Results
Description Value Reference
30 Degree Wind Direction
A Without Scheme Road-NOx Concentration (µg/m3) 7 CFD Modelling
B With Scheme Road-NOx Concentration (µg/m3) 18 CFD Modelling
C Change in Road-NOx Concentration (µg/m3) 11 B - A
D Wind Directions Associated 10 – 70 -
E Total No. of Hours Associated a 8,811 -
F % of Hours Associated b 17 -
G Total Cumulated Without Scheme Road-NOx (µg/m3) 61,677 A × E
H Total Cumulated With Scheme Road-NOx (µg/m3) 158,598 B × E
210 Degree Wind Direction
I Without Scheme Road-NOx Concentration (µg/m3) 58 CFD Modelling
J With Scheme Road-NOx Concentration (µg/m3) 69 CFD Modelling
K Change in Road-NOx Concentration (µg/m3) 11 J - I
L Wind Directions Associated 180 – 230 -
M Total No. of Hours Associated a 10,260 -
N % of Hours Associated b 20 -
O Total Cumulated Without Scheme Road-NOx (µg/m3) 595,080 I × M
P Total Cumulated With Scheme Road-NOx (µg/m3) 707,940 J × M
255 Degree Wind Direction
Q Without Scheme Road-NOx Concentration (µg/m3) 129 CFD Modelling
R With Scheme Road-NOx Concentration (µg/m3) 114 CFD Modelling
S Change in Road-NOx Concentration (µg/m3) -15 R - Q
T Wind Directions Associated 240 – 300 -
U Total No. of Hours Associated a 15,877 -
V % of Hours Associated b 30 -
W Total Cumulated Without Scheme Road-NOx (µg/m3) 2,048,133 Q × U
X Total Cumulated With Scheme Road-NOx (µg/m3) 1,809,978 R × U
Overall
Y Without Scheme Road-NOx Concentration (µg/m3) 77.40 (G + O + W) / (E + M + U)
Z With Scheme Road-NOx Concentration (µg/m3) 76.59 (H + P + X) / (E + M + U)
% Change in NOx Concentration -0.01 Z - Y
Table 1: Derivation of the Change in NO2 Concentrations
a Wind speeds of 2 m/s and above
have been used to determine the
number of hours. Below 2 m/s the
wind is quite calm, which is not
represented by the CFD model.
b The wind directions modelled do not
account for all wind directions. 17,660
hours (34%) of hours are not
accounted for by the CFD modelling.
These wind directions relate to the
northwest and southeast, which have
low frequencies compared to other
directions.