The developments of the Streamlined- PCM as a tool for screening the impact of road - traffic policy actions on No2 concentrations

1. The development of the Streamlined-PCM as
a tool for screening the impact of road-traffic
policy actions on NO2 concentrations
Dr. Michel Vedrenne
DMUG 16, London – 19th April 2016

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• The assessment of the effectiveness of emission abatement measures is essential for informing
policy making. The objective is to select measures with the highest mitigation potential at the
lowest possible cost.
• The Pollution Climate Mapping (PCM) model provides support to DEFRA in selecting those
measures; however it requires several weeks to carry out the full emissions calculations,
emissions mapping and concentration modelling required to test the effect of measures.
• In order to make well-informed decisions in a shorter timeframe, DEFRA required a simplified
version of the PCM to model a range of road-traffic scenarios.
• The Streamlined PCM has been built as an approximation of the full PCM model using data from
the National Atmospheric Emissions Inventory (NAEI). The results of the tool have a base which is
consistent with the compliance assessment and baseline projections of the full PCM model.
• It has a number of limitations compared to the full PCM model and it is not intended to be a
substitute. Furthermore, the Streamlined PCM requires data produced by the full PCM so it is not
an independent model. Streamlined PCM should be regarded as a screening tool.
Background and model purpose
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• The Streamlined PCM is a tool that enables the quantification of the effect of measures applied to
different aspects of road traffic on the emissions of nitrogen oxides (NOx) and the annual mean
concentration of nitrogen dioxide (NO2).
• The Streamlined PCM has the capacity to assess the impact of measures applied at different
spatial scales including national, local authority, specific geographic areas or the individual road
level
• The tool combines a simplified road traffic emissions model that relies on the National Atmospheric
Emission Inventory (NAEI) for emissions and a parameterisation of the Pollution and Climate
Mapping (PCM) model for ambient concentrations.
• According to the specific abatement measures, the relevant activity variables, fleet compositions
and emission factors are combined to calculate NOx emissions and variation ratios with respect to
a reference scenario.
• The estimation of NOx emissions is carried out for 18,346 road links in 406 local authorities of the
United Kingdom and the change in NO2 concentrations for 9,336 roads for which compliance with
Directive 2008/50/EC is assessed.
Description of the Streamlined PCM
DMUG 16

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The technical report of the Streamlined PCM was published
by DEFRA on the 26th November 2015. It is available from
the UK-Air website:
https://uk-air.defra.gov.uk/library/reports?report_id=882
Description of the Streamlined PCM
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The Streamlined PCM tool estimates the effect of NO2 abatement measures to be assessed by comparing a
scenario against a baseline. The baseline corresponds to a fully-characterised reference situation of
emissions. Any additional measure or set of measures beyond those already included in the baseline will
correspond to a scenario.
To characterise the effect of any measure with the Streamlined PCM, it should be modelled as a set
of variations (fi) with respect of the baseline scenario for one or more of the following variables (Vi):
• Activity variables (flows/veh·km by vehicle and fuel type – annual average daily flows).
• Fleet composition variables (fleet mix by vehicle and fuel type – in terms of Euro standards).
• Petrol-to-diesel fuel split.
• Emission factors, including the possibility of changing conformity factors.
𝑓𝑖 =
𝑉𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 − 𝑉𝑏𝑎𝑠𝑒𝑙𝑖𝑛𝑒
𝑉𝑏𝑎𝑠𝑒𝑙𝑖𝑛𝑒
The formulation of the adjustment factors (fi) within the framework of the Streamlined PCM defines
measures that seek to reduce the impact of the relevant variables are negative, while those that aim
to increase them are positive. Translating a measure in terms of a set of adjustment factors is a task
that requires careful identification of the degree to which variables change.
Design principles of the Streamlined PCM
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Structure of the Streamlined PCM
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fF
fC
fEF
Flow
Database
Composition
Database
EF
Database
Cars
Buses
Coaches
HGVs
Motorc.
LGVs
Pre Euro
Euro 1
Euro 2
Euro 4
Euro 3
Euro 5
Euro 6
Petrol Diesel
Hybrid
Baseline
Scenario(s)
Reduction %
Baseline
Scenario(s)
Reduction
NO2 LV Comp.
Emissions
Concentrations
Roads
(Census)
Local
Authorities
Streamlined PCM
Adjustment
Factors
Users
Compliance
Measure
Emission Reduction
Flowchart of the spreadsheets of the Streamlined PCM
Mapping
NAEI

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Structure of the Streamlined PCM (Emissions Module)
The Streamlined PCM contains information on the different road-traffic variables that are likely of
being affected by a given abatement measure, which then combine to estimate the NOx emissions of
road traffic. All these variables are sourced directly from the NAEI or the PCM data and are referred
to 2020.
• Vehicle types. Passenger cars (petrol and diesel), LGVs (small and large, petrol and diesel),
Buses, Coaches, Rigid HGVs, Articulated HGVs, Motorcycles and Mopeds.
• Emission factors. Emission factors and speed-dependent functions from COPERT (v.4.11) are
included in the tool, taking into account the engine size/weight of the vehicle, and for buses and
coaches the load and the slope of the roads (30 road types). Fractions of primary NO2 for each of
the considered vehicles and fuel types are also provided.
• Fleet composition. Euro standard composition in terms of vehicle-kilometres for the different
vehicle types and road types. Compositions are available for two types of locations: London and
the rest of the UK and for three types of roads: motorways, urban roads and rural roads.
• Activity variables. Traffic counts for the considered vehicle types in the form of annual average
daily flows (AADFs) for 18,346 georeferenced roads projected to 2020 using the NAEI projections.
DMUG 16

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Structure of the Streamlined PCM (Concentration module)
The Streamlined PCM is also able to estimate the annual mean
concentrations of NO2 as a function of the variation in the NOx emissions
for 9,336 roads. The estimation of concentrations is made through a
parameterisation of the results of the full PCM model, which combines the
following variables :
• Background road traffic area source (Brdarea) – NOx concentration
(μg/m3).
• Background non-road tr. area source (Bnondrarea) – NOx concentration
(μg/m3).
• Background point source (Bpoints) – NOx concentration (μg/m3).
• Background rural (Brural) – NOx concentration (μg/m3).
• Roadside increment – NOx concentration (μg/m3).
• Background local oxidant from road traffic area sources
(Brdarealocalolx – ppb).
• Background local oxidant non-road traffic sources (Bnonrdarealocalox –
ppb).
• Roadside increment local oxidant (Rlocalox – ppb).
• Regional oxidant (Regionalox – ppb).
NO2 roads 2013
NO2 back. 2013
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Appearance of the Streamlined PCM
Application
Geography
Tool
Controls
Adjustment Factor Tables
(to be populated by user)
Other
Controls I/O Tabs
Microsoft Excel® frontend of the Streamlined PCM
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Performance comparison with full PCM
The Streamlined PCM calculates roadside concentrations only; the full PCM model calculates both
roadside and background concentrations. It can take into account the specific changes in emissions of
minor roads and cold starts on backgrounds. The contribution of road transport area sources is scaled
using the proportional change at the roadside in Streamlined PCM. The contribution of non-road transport
sources remains unchanged.
Results from the Streamlined PCM have been compared with the full PCM model for 4 clean air zone
(CAZ) type scenarios in 2020. The mean differences between the two models along with the 5th, 25th, 50th,
75th and 95th percentiles of the differences are provided below (in μg/m3).
The differences between both models range from 0.15-0.25 μg/m3 across the 4 CAZ types. As expected,
differences and limitations between the two models exist, but the results from both models are very close.
The Streamlined PCM is producing larger changes than the full PCM model.
CAZ Type A B C D
Mean -0.15 -0.20 -0.25 -0.16
P5 -0.67 -0.71 -0.73 -0.64
P25 -0.18 -0.24 -0.29 -0.18
P50 -0.06 -0.11 -0.16 -0.09
P75 0.00 -0.04 -0.08 -0.03
P95 0.12 0.07 -0.02 0.14
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Demonstration of the Streamlined PCM
“What is the effect of switching diesel cars for Euro 6 petrol cars in the roads of Norwich in 2020?”*
DMUG 16
Modelling assumptions
• Two change percentages of diesel
vehicles are modelled: 20% and 50%.
• The measure will apply exclusively to the
roads considered by the Streamlined PCM
in the Norwich District.
• The composition specified in Streamlined
PCM for a non-London area in 2020
applies to all the considered roads in the
Norwich District.
• Variables to be affected in Streamlined
PCM: fleet compositions and diesel/petrol
split for passenger cars.
• Effects on minor roads, neighbouring
roads, and cold starts are not considered.
• The effects of the measure will be
noticeable for all the roads in Norwich. The
measure does not affect flows, speeds or
other variables.
Fleet compositions pre- and post-measures (2020)
*This is a hypothetical example for the purposes of demonstrating the
model, it was not commissioned by Defra and it does not reflect Defra’s
thinking.

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DMUG 16
Baseline NOx emissions in Norwich District (2020) – [t/yr]
*Note: the colour map is different to the one used in PCM official reports for
illustrative purposes only.

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DMUG 16
Baseline NO2 annual means in Norwich District (2020) – [μg/m3]
*Note: the colour map is different to the one used in PCM official reports for
illustrative purposes only.

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DMUG 16
Demonstration of the Streamlined PCM
20% diesel cars to Euro 6 petrol – [t/yr] 50% diesel cars to Euro 6 petrol – [t/yr]
NOx Emissions in Norwich District (2020) 20% change 50% change
Emissions after measures 71.3 t/yr 60.4 t/yr
Emission reduction 7.3 t/yr 18.2 t/yr
Reduction percentage 9.27% 23.18%

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Demonstration of the Streamlined PCM
20% diesel cars to Euro 6 petrol – [μg/m3] 50% diesel cars to Euro 6 petrol – [μg/m3]
Roadside NO2 Ann. Mean in Norwich District (2020) 20% change 50% change
Maximum annual mean after measures 25.8 μg/m3 23.3 μg/m3
Maximum annual mean reduction 1.5 μg/m3 4.0 μg/m3
Reduction percentage 5.8% 14.6%

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Streamlined PCM is …
• A national-level screening tool based on the full PCM model that estimates the effect of
road-transport measures on NOx emissions and NO2 concentrations.
• A resource used by DEFRA for the quick investigation of the effectiveness of mitigation
measures with regards to compliance with Directive 2008/50/EC.
• Comparable results with the full PCM model for road transport measures.
Streamlined PCM is not ...
• A substitute or an independent model from the Pollution Climate Mapping model.
• An alternative to national, regional or local air quality modelling.
• An air quality model in itself.
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Conclusions

17. Dr. Michel Vedrenne
30 Eastbourne Terrace
W2 6LA London
United Kingdom
michel.vedrenne@ricardo.com