How should we address model
uncertainty in the assessment of
major infrastructure projects?
Emma Gibbons
3
• Model uncertainty in industrial assessments
• Model uncertainty in highways & airport assessments
• Discussion
Outline
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Assessment of model uncertainty in industrial assessments
• Meteorological data
• Buildings
• Terrain
• Coastal effects
• Wind turbines
• Model type
• Background concentrations (all assessments)
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Industrial assessments: meteorological data
• 5 years of met data
• Monitoring station
PC (µg/m3)
at point of
max impact
2011 2012 2013 2014 2015
LT NO2 0.78 0.68 0.75 0.68 0.85
LT PM10 0.06 0.05 0.05 0.05 0.06
1hr NO2 11.4 14.4 12.0 12.6 15.4
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Industrial assessments: buildings
• Buildings
Point of
max impact2015 PC (µg/m3)
Without With
LT NO2 0.46 0.85
LT PM10 0.03 0.06
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Industrial assessments: terrain
• Terrain
Point of
max impact2015 PC (µg/m3)
Without With
LT NO2 0.85 0.94
LT PM10 0.06 0.07
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Industrial assessments: wind turbines
• Wind turbines
Point of
max impact2014 PC (µg/m3)
Without With
LT NO2 0.74 0.79
LT PM10 0.23 0.24
1hr NO2 36.9 96.5
24hr PM10 12.7 12.8
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Industrial assessments: model type
• ADMS vs AERMOD
Point of max
impact2015 PC (µg/m3)
ADMS AERMOD
LT NO2 0.94 0.36
LT PM10 0.07 0.03
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All assessments: background concentrations
Sources – Defra, LAQM, PCM, site-specific monitoring
Data – Monitoring station, data availability
• Background concentrations
NO2
PM10
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Assessment of model uncertainty in road assessments
• Traffic data
• Reliability of input data
• Extent of reliability area
• Timing of traffic counts
• Congestion
• Meteorology
• Assessment years
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Assessment of model uncertainty in road assessments
• Urban street-scape
Canyons, traffic lights, bus stops, queuing, tall buildings, car parks.
Canyon Concentration (µg/m3)
Without With
LT NO2 4.9 10.3
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Assessment of model uncertainty in road assessments
• Model verification
Compare predicted and measured pollutant concentrations to validate the air
quality model and adjust where required
• Consideration of uncertainty in air quality trends
Use of tools to take account of future pollutant projections for Highways
England schemes – IAN 170/12
IAQM position statement on vehicle NOx emissions
CURED v2A – AQC tool
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Assessment of model uncertainty in airport assessments
• Traffic data
• Meteorology
• Assessment years – climate change, background concentrations, road transport emissions