Thought Leaders

Investigating the Pollution from Volkswagen Engines

Recently, it was exposed that Volkswagen had programmed their engines to 'cheat' emissions tests to appear less polluting than they truly are. However, research conducted at the University of Manchester shows that Volkswagen are not the only problem and emissions testing needs to be stricter across the board. AZoM spoke to Dr. Rami Alfarra, from the Centre of Atmospheric Science, about his research into diesel emissions and the myriad of secondary pollutants formed by them.

Firstly, please could you tell me about your research and why you think it's important?

The main motivation behind our research has come from the observation that pollution levels in the UK and across Europe have been consistently high despite the introduction of increasingly stringent emissions regulations. This was a puzzling observation. The concentration of certain pollutants was not coming down, as would be expected based on regulations. One of the obvious sources of pollution in towns and cities is combustion engines used in the traffic sector.

Over the past few years, there’s been a drive, in the UK and Europe, towards more diesel cars because of their fuel efficiency and their supposedly greener reputation. Currently in the UK about 35 percent of the light duty fleet in the UK is diesel.

To evaluate the emissions caused by diesel engines we have set up a project known as Combustion Particles in the Atmosphere, which is funded by the UK Natural Environment Research Council. In this project, we have been looking at emissions coming from a diesel engine, under different speed and load conditions.

In addition to the primary emissions that directly come out of the tailpipe we wanted to investigate what happens to the pollution once it is in the atmosphere. The atmosphere itself is a big reactor driven by solar radiation, which initiates chemistry.

As a result, compounds that are emitted into the atmosphere become subject to a series of chemical reactions, which lead to the formation of secondary pollution and affect air quality.

Can you describe how your experiment worked? What set-up did you use to simulate the atmosphere?

We have set up a standard 1.9 litre diesel engine connected on a rig to a dynamo-meter, which allows us to run the engine under different speed and load conditions. We have also modified the exhaust of the engine to include a catalytic convertor and a silencer.

This engine was then coupled to our existing photo-chemical aerosol chamber. This is a University of Manchester facility made of an 18 cubic meter Teflon bag housed in a controlled environment. The chamber is fitted with lights that simulate the solar spectrum at ground level.

The Aerosol Chamber at the University of Manchester

In the atmosphere, there are numerous sources of pollution. It's very hard to isolate specific pollutants or de-couple processes. However, in this setup we can be sure that we are looking at one source and see what happens to the pollution emitted from it under realistic atmospheric conditions.

Our setup allows us to study the atmospheric transformations that occur to a single compound known to be emitted from a specific source, as well as studying whole emissions from a known source such as a diesel engine.

You mentioned that secondary pollution is bad for the environment. How is this formed?

They are formed through chemical reactions initiated by solar radiation involving a series of chemical reactions between nitrogen oxides, which are primary pollutants from combustion processes and other gases in the atmosphere that come from a number of sources including combustion. The combination of the gaseous compounds, nitrogen oxide and solar radiation leads to the formation of secondary pollutants.

When I say secondary, I mean things that did not exist in the atmosphere or were not emitted directly from a specific primary source; instead they are produced as a result of chemical reactions in the atmosphere. Secondary pollution includes for example secondary particulate matter and ozone.

What exactly are the health implications of high pollution levels?

High levels of particulate matter have been associated with higher numbers of hospital admissions related to respiratory as well as cardiovascular diseases. Particulate matter can be very problematic depending on their size and composition; the smaller they are the deeper they can penetrate into the lungs and cause problems. A number of chemical components of particulate matter have been shown to be carcinogenic.

Regarding gaseous pollution such as ground level ozone for example, it has been found to cause irritation to the eye, nose and throat, and it can cause damage to plants and crops. Nitrogen dioxide is highly toxic and has been linked with respiratory problems.

It's often claimed that, in general, diesel engines are greener than Petrol engines. Do you think there's any truth behind that claim?

I think there is some truth in that claim but it actually mixes two issues up. One issue is related to global warming, which is directly related to CO2 emissions. Another issue is related to air quality and health problems.

Image Credits: Egon Zitter/

Diesel engines have been promoted in recent years as a greener option because they are known to be more efficient in terms of fuel consumption. It gives you more miles per gallon when compared to petrol engines. The logic there is burning less fuel produces less CO2. So, when it comes to global warming, diesel emissions are possibly “greener” than petrol.

However, diesel engines produce more nitrogen oxides and particulate matter than petrol engines. It is the emission of nitrogen oxides and particulate matter, and the associated formation of secondary pollution, that leads to air quality problems in towns and cities. So because of air quality and health impacts I’d say that, overall, diesel engines aren’t greener.

How the current EU car emissions testing methods work?

Vehicles are driven over a standard test cycle. They put cars on a dynamo-meter where you can get the wheels of the car spinning whilst the rest of it is stationary. Then emissions are measured and expressed in grams of pollutants per kilometre driven. Each new car model has to be tested this way. Thousands of vehicles are produced each year and pretty much most of them pass.

Image Credits: Lu Yao/

This doesn't necessarily say that the current testing is accurate. The test itself contains a prescribed set of conditions which don’t really fully represent real-world driving habits and conditions.

For example the acceleration in the test is smooth, whilst in real life some drivers accelerate rapidly and aggressively, and that changes the emissions. Also, the cold start when you first turn the engine on is highly polluting and it's not currently represented in the test cycle. Basically, there is a strong mismatch between the current test conditions and real-world driving conditions.

The test cycle needs to be more representative of real driving conditions. Real world, on-road testing is probably a more realistic way of characterising real emissions.

How would you suggest the level of pollution the engines produce be reduced?

I can think of at least two areas to focus on; engine performance and exhaust post treatment. These involve improving the engine efficiency in terms of fuel consumption and burning conditions and the technologies to capture or convert the emissions in the exhaust pipe before being emitted into the atmosphere.

Image Credits: Paolo Bono/

The recent Euro standards now require the inclusion of a diesel particulate filter. This captures most of the black carbon particulate matter, which comes directly from the engine. These have been shown to work well for dealing with primary particulate matter, but have no effect on gaseous emissions.

Catalytic convertors are used to reduce gaseous emissions and have been shown to work well with a range of pollutants, but less well with nitrogen oxides. More needs to be done to improve the ability of catalytic convertors to clean emissions of nitrogen oxides.

Your experimental setup is sophisticated and it wouldn't be available to most people. Is there a more basic method of roughly determining how polluting a car or engine is?

Yes, for primary emissions which come out of the tailpipe, there are existing methods. These methods can be used to measure particulate matter and how much gaseous pollution, such as nitrogen oxides, is produced. This can all be done using available technology.

The more sophisticated part of our setup is to do with investigating the secondary pollution with our simulation chamber, which is a more substantial infrastructure.

Over the course of your research have you encountered any methods of reducing atmospheric pollution, or is it simply a case of having cleaner engines and fewer vehicles on the road?

Well to begin with, of course, cleaner engines and fewer of them on the roads would be an ideal way of reducing the sources of pollution.

Until this becomes a reality, we need to think about other ways to help mitigate the problem. For example, traffic flow and management in towns and cities. This is an area we should think about more; to come up with smarter ways of controlling the flow of traffic in order to reduce the number of times cars stop and start. Ensuring a better flow of traffic through towns and cities should help reduce emissions.

Image Credits:

Of course, we as individuals should try, when possible, to use public transportation and other means of commuting and cut down on unnecessary journeys.

Finally, how are you planning to use the results of your research and do you have anything else in the area that you’re planning to investigate?

We have already started to disseminate our results through conferences and are now in the process of doing so through peer reviewed publications. We will also present a final report to our funding agency, the Natural Environment Research Council. We have been in communication our findings with the the media to make sure that our findings are available in the public domain.

In terms of what we are also planning to investigate, we would like to look at different types of engines, and to look at the formation of secondary pollution from Petrol cars. Although petrol cars produce less NOX they produce a lot of other gases that can form secondary pollutants. Other areas of interest include wood combustion and we are hoping to be investigating it using a similar setup, subject to the availability of funding.

Ultimately we would like to secure funding to use our setup to directly look at the health effect of these pollutants. This would ideally happen through collaboration with colleagues in the medial field who can examine the toxicology of pollution on human lung cells. This is an area we'd like to expand into so we can begin to fully understand the implications of primary and secondary pollution on human health.

University of Manchester - VW Emissions Research/YouTube

About Dr. Rami Alfarra

Dr. Rami Alfarra

Rami Alfarra is a scientist at the National Centre for Atmospheric Science and a Research Fellow at the University of Manchester. Rami completed a PhD degree in atmospheric science at University of Manchester in 2004, where he worked on a ground breaking analytical technique to measure the chemical composition and size distribution of atmospheric particulate matter in real time.

As a post-doctoral scientist at Paul Scherrer Institute in Switzerland (2005-2008), Rami managed a field, chamber and controlled emission programme to characterise and quantify particulate matter throughout Switzerland.

In 2009, Rami joined the UK National Centre for Atmospheric Science and has since then been managing and conducting research on chamber studies of the formation and transformation of secondary organic aerosols from man-made and natural sources. Rami received the 2008 Swiss Academy of Sciences Atmospheric Chemistry and Physics Award.

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.

Jake Wilkinson

Written by

Jake Wilkinson

Jake graduated from the University of Manchester with an integrated masters in Chemistry with honours. Due to his two left hands the practical side of science never appealed to him, instead he focused his studies on the field of science communication. His degree, combined with his previous experience in the promotion and marketing of events, meant a career in science marketing was a no-brainer. In his spare time Jake enjoys keeping up with new music, reading anything he can get his hands on and going on the occasional run.


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  1. David Moore David Moore United States says:

    Very small engines for gas cars seem to be a simple solution to both particulates and CO2 and of course driving them fewer miles. Think Honda CRX and geo metro from the 1990s and Smart car and For Two now.

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