Ricardo developed an air quality modelling system called RapidAIR to model pollution in cities. It processes traffic data from models very quickly to calculate emissions and concentrations. Leicestershire County Council procured RapidAIR to model road traffic pollution across the county and help assess impacts on air quality and determine mitigation needs. RapidAIR customizations were made to ingest LCC's traffic model outputs. The model converts road links to area sources to model concentrations at high resolution. It can also account for street canyons. RapidAIR was used to model NOx concentrations in Leicester in 2014 from road traffic and background sources. The model provides results very quickly and can model hypothetical scenarios like COVID-19 impacts on traffic and air quality.

1. Delivering ExcellenceThrough
Innovation &Technology
1July 2017Unclassified - Public Domain© Ricardo plc 2017
Demonstrating the development of a county wide
road traffic pollution model with Leicestershire
County Council
Dr Scott Hamilton, Ricardo
Dr Nicola Masey, Ricardo
Dr Sonny Tolofari, Leicestershire County Council
Alex Gray, Leicestershire County Council
Data and the interface between
traffic and air quality models
in partnership with
NOx in Leicester, 2014

2. 2© Ricardo plc
• The project with Leicestershire County Council (LCC)
• Modelling air pollution in a city, what sources need to be considered?
• RapidAIR- our technical solution to this problem
• Traffic data processing
– Converting traffic model outputs to emission model inputs without losing information
• Why did LCC want to procure RapidAIR?
• Demo of some outputs for Leicester
• Example use case
• Conclusions
This talk

3. Delivering ExcellenceThrough
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3July 2017Unclassified - Public Domain© Ricardo plc 2017
The project with Leicestershire County Council
• First use of RapidAir beyond Ricardo’s own internal use for consultancy services
• First time that the software has been licenced to an organisation as a free-standing product for its in-house use
• Ricardo gratefully acknowledges Leicestershire as a foundation client and for funding this project
• Includes use of RapidAir for the Council’s 7 District-based micro-simulation models

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Air quality modelling in a city

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Built by Scott and Nicola
Rapid Atmospheric Impulse
Response (RapidAIR) is our air
quality modelling system
designed for use in cities. It’s
really fast which makes it very
useful for policy/scenario work.
Scott.Hamilton@ricardo.com
Nicola.masey@ricardo.com
Method
GUI
Scenario analysis
Academic rigour
Large domains with high resolution
National scale ‘what if’
testing – COVID example
Beijing

6. 6© Ricardo plc
• Speed- the model can convert a ‘new’ traffic model to
concentrations of air pollutants in minutes
• Reproducibility- the simplicity and high degree of
automation in the system makes it straightforward to
audit
• Recognised platform- wanted a Defra recognised air
quality module to be integrated to its unified
Transport Modelling system to help assess air quality
impacts of growth on a County-wide scale as part
fulfilment of its statutory Development Management
and Transport Authority duties, and determine the
right levels of mitigation that might be needed to
achieve the objectives of sustainable development.
• Consistency- potential to use the system in smaller
scale assessments County wide
• Close coupling to traffic models- a custom module
developed on behalf of LCC consumes the outputs of
the traffic models ‘direct’ so there is no information
loss
Why did LCC want to procure RapidAIR?

7. Delivering ExcellenceThrough
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7July 2017Unclassified - Public Domain© Ricardo plc 2017
RapidAIR customisation for Leicestershire County Council

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• Custom processing added (python) which can process and calculate emissions from the outputs of traffic
models e.g. VISSIM, SATURN
• The following data needs to be provided for each link from the transport models:
– Average traffic flow for period
– Fraction of flow attributed to cars, LGV, HGV and buses for the period
– Average speed for the period
• The ‘period’ could be annual average or hourly (provided full 24 hours of information is available)
• The traffic model outputs must be accompanied by a spatially accurate shapefile of the road network
Traffic data processing for Leicestershire
Inputs
Link-based
flows and
Speeds
(.csv or
.shp)
+
Spatially accurate
shapefile of road network
RapidEMS traffic processor + emissions calculations Outputs
Link-based emissions

9. Delivering ExcellenceThrough
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9July 2017Unclassified - Public Domain© Ricardo plc 2017
Illustrative workflow for Leicestershire County Council
implementation of RapidAIR

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We start with roads as line sources, process the
traffic model, and compute emissions for each
link using the RapidAIR emission model
A key benefit of RapidAIR is the
decoupling of computation time
from the number of sources
There is no computational
difference between 100 and 1
million sources/road links-
normally this would mean a
10,000 x the computational effort
It can accommodate any spatial
resolution of traffic activity
representation from the traffic
models
Number of road links in
the traffic model
Leicester city centre

11. 11© Ricardo plc
Then we convert the line
sources to area sources
A key benefit of RapidAIR is the
decoupling of computation time
from the number of sources
In terms of the area sources
there is no computational
difference between 100,000 and
100 million sources so it can
handle very detailed emission
geometries
It can accommodate any spatial
resolution of emission
representation that has been
derived from the traffic model
Number of area sources
in the dispersion model
~120,000

12. 12© Ricardo plc
Then we work out which links
fall within street canyons
Street canyons are generated by
measuring the perpendicular
distance from the road centre to
the nearest building on each side
The height is sampled from the
buildings and written to the
canyon geometry
Any canyons that don’t have an
average height of >5m are
removed
The polygons act as ‘decision
boundaries’ for where to switch
on a canyon-specific dispersion
model
Number of street
canyons in the model
~400

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13July 2017Unclassified - Public Domain© Ricardo plc 2017
Background NOx in Leicester (2014)

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µg/m3
Background concentrations
without any road source
contributions are derived from
Defra data
What is left is a mix of
pollution from sources like
industry, domestic, other
types of transportation and
some other less important
sectors
In the air quality model these
are treated as absolute
values which provide the
background to the road
concentrations from the
dispersion model.

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15July 2017Unclassified - Public Domain© Ricardo plc 2017
Road NOx in Leicester (2014)

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Road NOx 2014
µg/m3
≥
In this example there is a discrete
prediction from RapidAIR in every 3m2
cell which in this case is ~24 million
locations
The model can accommodate around
1 billion locations (bounded by RAM
on the machine running the model)
This uncovers another advantage-
RapidAIR computational effort is also
decoupled from the number of
receptor points. Any of the 24 million
cells in the map can be sampled to get
a concentration value
The map represents a lossless
translation of the information in the
traffic model

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17July 2017Unclassified - Public Domain© Ricardo plc 2017
Total NOx in Leicester (2014)

18. 18© Ricardo plc
Total NOx 2014
µg/m3
≥
Now the model is complete and we need
to verify the model concentrations
against observed values (to be
completed…). RapidAIR has a validation
scheme to handle this
Once we have corrected for any biases,
and investigated any issues with the
emissions inventory, the next step is to
convert concentrations to NO2 and
compare with standards (RapidAIR has a
simple chemical scheme to handle this)
The workflow shown implied here is
pretty fast- we could get from traffic
model to concentrations in 30 min or less
(the computation is only a few minutes)
When the model has been bias corrected
we can proceed to scenarios which can
be iterated very quickly

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19July 2017Unclassified - Public Domain© Ricardo plc 2017
Use case example- COVID 19 impact on traffic pollution (UK scale)

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Pre-lockdown road NOx
µg/m3

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In lockdown road NOx
~70%
µg/m3

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• RapidAIR has worked very well for us as an internal air quality modelling system
• This is the first deployment of our previously internal model RapidAIR outside Ricardo
• We are very grateful to LCC for their support and vision
• The model is going through its final calibration with the strategic traffic model inputs, and will be put
to use at LCC as soon as that is complete
• When the microsimulation model results are available they will be integrated
• I’m really looking forward to seeing what LCC’s team do with the system!
Conclusions

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23July 2017Unclassified - Public Domain© Ricardo plc 2017
Scott Hamilton- scott.hamilton@ricardo.com
Nicola Masey- nicola.masey@ricardo.com
Sonny Tolofari- Sonny.Tolofari@leics.gov.uk
Alex Gray -Alex.Gray@leics.gov.uk
Thanks for listening
in partnership with
NOx in Leicester, 2014