I expect you’re wondering about emissions, seeing as they’re kind of in the news at the moment. Most of us have been (since the changeover in the motor tax system in 2008 anyway) aware that cars that burn petrol or diesel – or indeed any liquid or gas fuel – generate emissions – it’s why we have exhaust pipes. Basically, burn anything and you’ll get emissions. Smoke from a fire, for example.


At the moment, when we say emissions, we generally mean carbon dioxide, or CO2. Burning almost any solid or liquid fuel generates CO2, simply because as we burn the stuff, the carbon molecules in it are released and they bond with oxygen on their way out. CO2 is everywhere – we even generate some just by breathing, and green-leafed plants draw it in to create fuel to keep growing.

So why all the fuss over emissions? Because it is almost incontrovertibly proven that human activity is causing the Earth’s climate to change, principally because in the past centuries that we’ve been burning wood, coal and oil CO2 is being pumped up into the atmosphere, trapping heat and moisture that would normally escape into space. It’s warming things up, melting ice caps and glaciers and generally causing havoc. You can argue the toss over how much human activity is contributing to background natural processes, but the science is pretty convincing.


So, with all of the billions of cars on the road pouring gases into the atmosphere, it was finally felt in the 1990s (in Europe) that some sort of standard should be put on what cars can emit what gases. That was the beginning of the Euro regulations, which govern and set the limits that car makers have to design their engines around. Breach the limits and you can’t legally sell your cars in Europe. The first set of regulations, Euro1, came into force in 1992 and they’ve been getting progressively tougher since then. We’re currently working to Euro6 regulations, which came into force in September 2014.

European Emission Standards

With me so far? Good. So, with the fixation on CO2 emissions, it was natural that diesel engines would be encouraged. Diesel engines, thanks in part to their greater thermal efficiency (basically, they waste less of the energy from their fuel as heat) makes them more economical than a petrol engine (as anyone who’s switched over to diesel will know) and they have CO2 emissions that are around 15 per cent lower, pound for pound.

So, governments across Europe subsidised diesel fuel prices and encouraged – through tax systems – car makers to make more diesels and car buyers to buy more diesels. You need proof? Look at the Irish market. In 2007, the year before the tax system changed, 71 per cent of the cars we bought were petrol-powered. Since then, the reverse has been true – we buy 71 per cent diesel now.


So that’s great, right? We’re all saving ourselves money and saving the planet as we go. Great.

Not quite. You see, diesel fuel, by its nature, is dirty stuff. It’s far less refined than petrol, which you’ll know if you’ve ever seen the clouds of black smoke from an old, badly maintained diesel car. That smoke is not just unsightly and a bit smelly, either – it’s swarming with stuff that’s seriously bad for your health. Particulate emissions – tiny, almost invisible flakes of sooty, unburned diesel – are highly carcinogenic and have been linked to rises in rates of lung cancer. Worse again, diesels emit a lot of nitrogen oxides, commonly known as NOx. NOx is not really a greenhouse gas, as such, but it’s positively lethal – linked to thousands of deaths worldwide every year thanks to the fact that it can trigger both asthma and respiratory disease.

CO2 might be bad for the environment but NOx and particulates are bad for everything living on the planet. So, the regulators got tough on NOx and particulates and car makers had to come up with ways to clean up diesel exhausts. Particulates are defeated by particulate traps (otherwise known as DPF’s/Diesel Particulate Filters) – fine mesh honeycombs of metal in your exhaust that filter these particles out before they reach the outside air. They’re a great invention but they can be troublesome – you need to generate heat in the exhaust to keep them clean and functioning, and many low-mileage diesel drivers have found out the hard way that short journeys won’t get enough heat into the system to clean the traps, resulting in expensive exhaust system failures and replacements.

How DPF works

NOx can be treated in a couple of ways. You can fiddle with the fuel injection and combustion cycle, but that tends to make the engine less responsive and a bit thirstier. Or you can treat the exhaust gases as they are pumped out, by squirting a fine mist of liquid urea (often marketed under the name AdBlue) into the exhaust, which sets off a chemical reaction  that converts nitrogen oxides into nitrogen, water and tiny amounts of carbon dioxide.

So, once again we’re all good, right? Technology saved the day?

I’m afraid not. You see, it has been revealed that at least one major car maker had been cheating on its emissions tests. Those tests were American ones, carried out by the Environmental Protection Agency (EPA) and they care far more about NOx than CO2. It turned out that the car maker in question had installed clever software in its cars, which would alter the engine’s performance while in the testing laboratory, to dramatically reduce the car’s emissions of NOx. Test passed, the software switches off, the car becomes more lively to drive but the owner is blithely unaware that they’re now pumping NOx into the air, potentially at 40 times the legal limit. That’s why emissions have been so much in the news lately!

What does this mean for you, the driver? Well, that’s still an unfolding story really. If one car maker was cheating, chances are other car makers were doing something similar, and while the European rules on emissions are strict, the actual tests are much less so – allowing car makers to (entirely legally) use every trick they can come up with to make their cars perform as well as they can on the test. They take out spare tyres to save weight, tape up body gaps to aid wind resistance, even disconnect alternators to reduce power drain on the engine. Ever wonder why your car can never match the fuel economy figures printed in the brochure? That’s why!

The emergence of outright cheating rather changes things though. Without question, oversight of these tests and their stringency are going to be seriously ramped up. Car makers will have to hit ambitious new targets of cleanliness and we, potentially, are going to have to pay higher tax rates as the testing loopholes are closed off.

Perhaps we should all just switch to electric cars after all…