This document discusses how certain vehicles, termed "gross emitters", can significantly contribute to local air pollution even though they meet emissions standards. It notes that 3.9% of trucks emit 50% of NOx emissions and that gross emitters include older vehicles as well as those with tampered emissions systems. The document then outlines Cambustion's work developing portable sensors to detect high NOx emissions from passing vehicles and identifies situations where legitimate selective catalytic reduction (SCR) systems used to reduce diesel NOx can still emit high levels, such as during cold starts. It warns that tampered SCR systems may emit large amounts of untreated NOx and discusses the health impacts of NOx exposure on cyclists and children.

1. How “gross emitting” vehicles
can spoil local air quality
Mark Peckham & Jamie Parnell

2. Why worry about gross emitters?
2
• 3.9% of trucks emit 50% of all NOx *
• Significant contribution to urban pollution hot spots
• Modern diesel vehicles can be very clean
• Even “good” vehicles can emit high levels of NOx under certain conditions
• Some gross emitters may be “legitimate” (older models), some may have been tampered with
• Nominally clean Euro 6 vehicles may gain access to CAZ on the basis of their number plate but then
produce large amounts of pollution
* CARB 2020 PEAQS project

3. Cambustion’s background (founded 1987)
3
• Fast response analyzers to measure transient emissions (cold start, gear changes etc)
• Development work with engine companies to develop catalytic converter systems
• Recent adaptation of products to measure transient ambient air quality

4. Roadside measurements of passing gross emitter
4

5. Portable ambient NO&NO2 detection system
5

6. Typical roadside NOx data set
6

7. Interest in identifying “gross emitters”
7
• Law enforcement and government to catch
SCR system “defeat devices”
• Local government to check which vehicles
are polluting the most (in Clean Air Zones)

8. SCR (Selective Catalytic Reduction) for lowering diesel NOx
8
Converts NO to NO2
NH3 + NO2 reacts to
nitrogen and water
Ammonia “slip catalyst”
NOx sensor
Must be hot (>~180C) to work efficiently

9. NOx tailpipe ppm comparisons, TfL West London route
9
Instantaneous [NOx] (ppm)

10. Cumulative NOx comparisons TfL route
10
Euro 5 diesel, 937mg/km:
no NOx catalyst
Euro 6b PHEV petrol, 95mg/km
– two 3-way catalysts
Euro 6d-TEMP diesel,
60mg/km – SCR

11. Modern SCR additional measures
11
Converts NO to NO2
NH3 + NO2 reacts to
nitrogen and water
NH3 “slip catalyst”
NOx sensor
Must be hot (>~180C) to work efficiently
“Post-injection”
of fuel
“NOx adsorber”
temporarily traps NOx
until system warms up

12. Portable fast response NO&NO2 analyzer for pursuit
12

13. “Pursuit” measurements
13

14. Chase study of bus stop manoeuvre
14

15. When & where legit SCR systems can emit…
15
Cold start and first few minutes of driving
• Leaving home
• Leaving place of work
• Leaving car parks
• Leaving bus depot (e.g. 60% of NOx from a 2 hour journey emitted within first 5 mins)
After long periods of deceleration or idle
• Accelerating away from the foot of a hill
• Bus stops (!)
• Pulling away from traffic lights
• Sudden acceleration in congested traffic

16. The effect of speed bumps on NOx
16

17. Defeat devices (emulators)
17

18. Why tamper with an SCR system?
18
• No more SCR maintenance costs
• Pass MOT (warning lights suppressed)
• No need to buy any more AdBlue
• Claims of better fuel economy (save fuel) through disabling of catalyst heating etc
…but can still enter CAZs if number plate allows

19. Tampered-with SCR system
19
Converts NO to NO2
NH3 + NO2 reacts to
nitrogen and water
NH3 “slip catalyst”
NOx sensor
A tampered-with SCR system may end up emitting a large proportion of primary NO2

20. Cyclist NOx exposure
20

21. Child exposure to NOx
21

22. msp@cambustion.com
jparnell@cambustion.com
Thank you
https://www.cambustion.com/industries/air-quality