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expert comments on VW emissions scandal, vehicle emissions testing and air pollution

The car manufacturer Volkswagen has said that up to 11 million of its vehicles may have been affected by the rigging of emissions tests of its cars.


Dr Karl Ropkins, Vehicle Emissions and Air Quality Researcher, University of Leeds, said: 

“Obviously, we do not know the full details because this matter is the subject of on-going legislative action in the US.

“However, what we do know is that a comparative study [1] identified large differences between the real world vehicle emissions of some vehicles manufactured by VW and the levels the same vehicle emitted during the regulatory tests used by the US.

“The regulatory tests measure the emission rates of species including CO2, and NOx across a defined range of driving activities (collectively known as a drive cycle), which must remain below limits set by regulatory bodies.The US vehicle emissions regulation test procedures, like similar tests elsewhere including the UK, are intended to minimise the impact of traffic-related pollution, so this is an important issue.

“However, the gap between on-road and test measurements is not itself the big news. The much more important issue is that this looks like a deliberate attempt to circumvent the test procedures.

“Both US Environmental Protection Agency (EPA) and the State of California Air Resources Board (ARB) have issued compliance letters to this effect [2-3] and VW have now publically apologised.

“It looks like about 11 million vehicles worldwide are going to be recalled as part of corrective measures [4].This supports the earlier ICCT statement on the subject [5], which recognises this as an issue that had significant international as well as US implications.

“Legal actions of this nature are highly delicate, and we are unlike to hear too many details for a while, if ever.

“However, we do know the US EPA are describing this as both a “sophisticated software algorithm” and, more importantly a “defeat device”, their legislative terminology for a device intended to deliberately circumvent the test procedures. They go on to describe the defeat device as “installed software” in the vehicle’s on-board management system that operated a “switch” that applies a different engine management map in situations where testing is detected. The parameters used by the switch were listed as including “the position of the steering wheel, vehicle speed, the duration of the engine operation and barometric pressure” and they used the wording “precisely track.”

“This claim (if proven) suggests a much more sophisticated attempt to cheat the test than that encountered in the late 1990s, when previously other vehicle manufacturers were the subject of a similar action [6], and that was an action that resulted in the biggest settlement of its day.”





[4] See e.g.




Prof. James Longhurst, Professor of Environmental Science, and Director of the Air Quality Management Resource Centre, UWE Bristol, said 

“VW have admitted to having deliberately designed and manufactured vehicles with a device to render inoperable the emission control system of diesel cars sold in the USA.  The USEPA have issued a Notice of Violation of the Clean Air Act whilst the California Air Resources Board is issuing an In use Compliance Letter to VW. VW have deliberately set out to deceive and in so doing have put at risk public health from increased air pollution.

“All vehicle manufacturers must now seek to regain the trust of consumers by demonstrating that they have not engaged in such practices either in the US, the EU or other markets.  The utmost transparency is now required.

“Emissions of nitrogen oxide (NOx) remain a major problem in the US and the EU. Concentrations of NOx have not fallen as much as expected despite the introduction of new technology on vehicles. If the deliberate bypassing of emission control systems is more widespread than just VW diesel sales in the US then it may help explain what has been observed in measurements of air pollution in cities.”


Dr Jo Barnes, Air Quality Management Resource Centre, UWE Bristol, said:

“All the coverage I have seen has been about the business impact of this scandal on VW, but very little appears to have been said about the impacts that this apparently blatant transgression of emissions testing procedure will have had on public health. If it is shown that this has also been occurring in Europe, I would have thought there would be a strong case for governments to seek compensation from culpable vehicle manufacturers against the millions of pounds/euros of public funding that has been spent trying to address local air pollution. We are aware that a large proportion of new vehicles were failing to achieve the latest Euro emission standards in real-world driving conditions and that the purely test-bed cycle emissions testing was flawed, but that tests were actively and knowingly manipulated in this way is criminal. Perhaps it is not surprising that profit margins take precedence over public health, but with transport emissions the main contributor to urban air pollution, resulting in nearly 10,000 early deaths a year in London alone and hugely decreasing quality of life for children, the elderly and those with pre-existing health complaints, the public should be utterly outraged by this news.”


Prof. Ian Colbeck, Professor of Aerosol Science, University of Essex, said:

“It has been observed for some time that real world driving conditions do not deliver the emission reductions shown in the laboratory. The European Commission will require real world tests in 2017.

“It has recently been estimated that the impact of NO2, the pollutant in question, on mortality is equivalent to 23,500 deaths every year in the UK.”


Prof. Alastair Lewis, Professor of Atmospheric Chemistry, University of York, said:

“It remains to be seen whether the specific VW tactic used to pass tests in the US has also been applied in the UK or Europe more widely.

“What is established is that virtually all new vehicles in recent years appear to emit substantially more NOx in the real-world than they do when tested in labs, irrespective of manufacturer. VW appear to have been caught red-handed, but it would seem highly likely that others have also played dubious games to pass emissions tests. Optimising vehicles to function at their best under test cycle conditions occurs also for fuel economy and CO2 testing as well.

“There are many possible strategies that could be applied to help give a vehicle lower emissions during a test, including optimising the fuel combustion process specifically for the test cycle speeds and acceleration, limiting power output when on test, through to the more extreme VW case of apparently only selectively switching on a sophisticated emissions reduction system.  The test cycles are very formal and well established, so priming a vehicle to sense when it is being tested is potentially quite straightforward, for example are only its drive wheels turning, is the acceleration unnaturally smooth, or constant speeds too precise for a human driver? That said the test cycles in Europe are to be toughened up and made to be more like real world driving so this may well make gaming the system more difficult.

“Ultimately if a new vehicle cannot pass the emissions standard in the US or Europe for its particular type and size then it can’t be sold, so there are very major consequences for manufacturers.

“The reasons the tests are conducted is ultimately so that air pollution can be managed appropriately. Emissions data from manufacturers is used by Governments to simulate future air pollution levels and set policy.  Over time more modern fleets were predicted to have lower emissions and hence urban pollution levels would improve. Estimates made a decade ago indicated that the UK would be on downward trend in NOx in city centres. But this was based on cars emitting NOx at the rates suggested by the manufacturers test data, and the reality is that NOx has effectively plateaued in most cities, and in many places above the European air quality standards.”




Declared interests

Dr Karl Ropkins: “I was not directly involved in this study on either side and I have no relevant interests that should be declared other than the facts that I work in the sector and that I do know a number of those more directly involved.”

Prof. Ian Colbeck: Member of Institute of Physics, Royal Meteorological Society, International Society of Indoor Air Quality and Climate, Aerosol Society.  Grants funding: NERC, EU.  Voluntary appointments: Essex Air Quality Consortium.

Prof. Alastair Lewis: Employed by National Centre for Atmospheric Science and University of York.  Funding from NERC, Defra and DECC for air pollution research, member of the Defra Air Quality Expert Group.

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