RTCA18

1. Real world measurements of
ammonia emissions from
vehicles
Rebecca Rose
Routes to Clean Air, 30th October 2018

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• Sources of ammonia emissions in UK (NAEI):
– >80% of from agriculture
– <2% from road transport
• But road transport is a significant source of ammonia in
urban areas
– Co-emission with NOx so could be important for
secondary formation of ammonium nitrate
– Impacts on nitrogen deposition
• National emissions of NH3 are regulated (NECD,
Gothenburg Protocol etc.) and ammonia emissions from
vehicles have the potential to be regulated
Ammonia emissions
Road transport Agriculture
Source: http://naei.beis.gov.uk/data/gis-mapping

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• Combustion engines emit very little ammonia.
• Technologies introduced to reduced to reduce NOx emissions from vehicles can have the unintended
consequence of increasing ammonia emissions.
• Three-way catalysts fitted to petrol vehicles since 1991 are designed to chemically reduce NOx to nitrogen,
but ammonia can be formed by when reduction does not stop at N2 but continues to NH3.
• Selective catalytic reduction (SCR) uses ammonia (from urea) to reduce NOx in the exhaust gas of diesel
vehicles. Urea injection is actively managed - too little urea and excess NOx is emitted, too much urea and
excess NH3 is emitted (“ammonia slip”).
• Remote sensing used to measure ammonia emissions from vehicles in the real-world.
Ammonia emissions from vehicles

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Vehicle Emission Remote Sensing
• Measurements made using OPUS Inspection RSD5000
instrument:
– UV/Infrared beam to measure emissions – different
gases absorb in different wavelength regions
– Measure NO, NO2 (hence NOx), CO, HC, PM and NH3
– 100 scans in 0.5 seconds of exhaust plume
– Emissions expressed as ratios to CO2 and through
combustion equations, grammes of pollutant per unit fuel
(mostly commonly g/kg)
– Measure speed and acceleration of each vehicle
• Photograph each vehicle to obtain number plate
– Detailed cross reference with SMMT-derived
databases…more than 80 vehicle characteristics, down
to the colour of the vehicle!

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• We have ~300,000 measurements from >20 different measurement
locations across UK
• Sample a range of different driving conditions (speeds, acceleration,
gradients) and vehicle types
• Use a vehicle power model to convert the remote sensing
measurements in g per kg fuel to real-world g per km emission factors
that can be aligned with COPERT emission factors
• Can go beyond COPERT emission factor categories
– Road gradient
– Acceleration
– Temperature
– Vehicle manufacturer and model
• Work in progress
Vehicle Emission Remote Sensing

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Real-world ammonia emissions: Overview
• NH3 emissions are higher for petrol vehicles than diesel vehicles
* All results presented are provisional

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• Previous studies show that emissions of NH3 increased with the requirement for petrol cars to be fitted with
three-way catalyst since 1993 (Euro 1 onwards)
• Real-world emissions measurements demonstrate that NH3 emissions are lower for newer vehicles
• Measured emission factors are significantly higher than COPERT emissions factors
Ammonia from petrol vehicles
Car Van

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• Use most recent MOT mileage
• Evidence that ammonia emissions from Euro 3/4 petrol cars increase with vehicle
mileage
• Suggests TWC becomes more reducing as mileage increases
Ammonia from petrol cars: effect of vehicle mileage

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Harwell Campus measurements of cold start emissions
Off site
Onto site

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• Evidence that petrol cars above Euro 2 have higher NH3 emissions with cold engines
• Fuel rich mixture on engine start up favours the formation of ammonia over TWC
• Likely to be important for urban NH3 emissions and concentrations of NH3 and formation
secondary PM (nitrates)
Cold start effects on NH3 emissions

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Ammonia emissions from diesel cars – technology dependence
• Increase in NH3 emissions for newer
diesel cars

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Ammonia emissions from diesel cars – technology dependence
SCR
All
LNT
• Increase in NH3 emissions for newer diesel
cars
• A range of technologies are used to meet Euro
6 emissions limits for NOx
• Lean NOx trap (LNT): reduction of NOx by
hydrocarbons
• SCR: reduction of NOx by ammonia
• SCR is more effective at reducing NOx
• Increase in NH3 emissions for Euro 6 cars is
driven by the use of SCR
• Heavy duty vehicles also show some evidence
of increased emissions for Euro 5 and 6
vehicles consistent with the use of SCR

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Ambient ammonia measurements in urban areas
• Ammonia monitoring from National Ammonia Monitoring
Network (NAMN)
• Few sites in urban areas
• Trend to decreasing ammonia concentrations at urban traffic
and urban background sites
• Consistent with reductions in ammonia from new petrol cars as
the dominant source of ammonia in roadside and urban areas

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Role in formation of secondary aerosols
• Trend to decreasing concentrations of ammonium aerosol concentrations at urban traffic
and urban background sites, consistent with reductions in ammonia concentrations in an
environment where secondary ammonium PM formation is ammonia limited
• Contributes to reductions required to achieve WHO guideline values for PM2.5

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• Emissions of NH3 from petrol cars are higher than emissions from diesel cars (by a factor of 5-10+
depending of the Euro standard)
• Emissions from petrol cars decline with Euro standard and Euro 3/4 petrol cars show evidence of increased
NH3 emissions as mileage increases
• Cold start emissions from petrol cars are significantly higher than hot exhaust emissions – likely to be
important in urban areas
• Emissions from diesel vehicles have increased with the introduction of SCR to reduce NOx emissions
• Trends in ambient measurements of ammonia and secondary nitrate particulates show evidences of
reductions in concentrations of both species in recent years. This is consistent with a decline in emissions of
ammonia from vehicles driven by reductions in emissions from petrol vehicles
Summary

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• Diesel car sales are declining in light of bad publicity around diesel vehicles, while sales of petrol cars are
increasing
• Aging effects on the emissions for the newest vehicles are unknown
• Ammonia emissions from diesel vehicles have increased from new vehicles as a result of the use of SCR
to reduce emissions of NOx
Potential for increases in NH3 emissions from road transport
• Euro VI emissions standards for heavy duty diesel vehicles includes an ammonia concentration limit of 10
ppm
• Euro 7 emissions standards for light duty vehicles may include a limit for ammonia emissions
May combat increases in NH3 emission for diesel vehicles and provide additional controls for petrol
vehicles – continued measurements required
• Increase in electric and hybrid vehicle fleet uptake will lower overall NH3 emissions from road transport
Looking to the future

17. Rebecca Rose
Ricardo Energy & Environment
Rebecca.rose@ricardo.com
https://ee.ricardo.com/air-quality/case-studies/remote-sensing-blog-2