Whenever you burn any type of fossil fuel, whether its coal, gas or oil, you create a cocktail of by-products that are released into the atmosphere. Up to a point mother nature can compensate, but with a global population of 7.5 billion, Earth is struggling to cope with the rate at which our precious resources are being used up – as well as the rate at which the environment is being polluted.
The global population is very mobile; many of us use planes, trains, ships and cars to travel, while goods are transported vast distances. It’s reckoned that in 2010, for the first time ever, there were one billion cars in use around the world, each one pumping out an array of chemicals, most of them harmful to our health.
Air quality has become a massive issue over the past few months, with the private car getting the blame for much of the problem. All forms of transport have a part to play in polluting our air, and fossil fuels are at the root of the issue. Each time you start your car’s engine, this is what comes out of the exhaust and how it affects us:

• Nitrogen (N2), oxygen (O2) and water (H2O): not harmful to human health.
• Benzene (C6H6): toxic and carcinogenic; long-term exposure has been linked with leukemia.
• Carbon dioxide (CO2): not toxic but a powerful greenhouse gas.
• Carbon monoxide (CO): reduces the ability of blood to carry oxygen, can cause headaches, breathing problems or even death.
• Hydrocarbons (HC): react with nitrogen oxides to produce photochemical oxidants which cause breathing problems.
• Nitrogen oxides (NOx): react with hydrocarbons to produce ozone which can cause breathing difficulties.
• Particulate matter (PM) or soot: mainly associated with diesel engines. Gets lodged in lungs causing breathing problems.
• Sulphur dioxide (SO2): leads to acid rain and contributes to the formation of ozone.

It was 47 years ago that the first European exhaust emissions standard was introduced but it wouldn’t be until 1992, when the Euro 1 emissions standards were introduced, that decisive action was taken. This point was when catalytic converters became mandatory, and with it the need to analyse exhaust gases.
It was at this point that fuel injection became the norm on all mainstream production cars. Until then it was too costly and lacking in sophistication (as well as reliability) for mainstream use. While a whole host of other technologies were adopted to improve engine efficiency, this one feature allowed exhaust emissions to be cleaned up significantly.
However, it was still early days and the limits set were far from stringent. Initially the only tailpipe emissions checked were for hydrocarbons and carbon monoxide, while diesels were also tested for particulate matter. It was a good start though, and over the following quarter of a century ever tighter limits would be set, to the point where some emissions have been cut by up to 95 per cent.
Below are the half a dozen emissions standards that have been introduced so far. The first date is the point at which any new car submitted for type approval had to fall within the relevant Euro standard. The second date (in brackets) is the date from which any new car sold had to meet the standard. There’s usually a year or so between the car being introduced and it having to meet the rules when it’s sold.
Euro 1: July 1992 (January 1993)
From here on all cars had to have a catalytic converter and run on unleaded petrol, to cut carbon monoxide (CO) emissions.
Euro 2: January 1996 (January 1997)
The limits were cut for carbon monoxide, unburned hydrocarbons and oxides of nitrogen, with different emissions limits for petrol and diesel.
Euro 3: January 2000 (January 2001)
Carbon monoxide and diesel particulate limits were reduced and there were separate HC and NOx limits for petrol engines.
Euro 4: January 2005 (January 2006)
The focus was on cleaning up emissions from diesel cars, especially particulate matter and nitrogen oxides.
Euro 5: September 2009 (January 2011)
Particulate emissions for diesel cars were all cut further, with particulate filters essential to meet the new requirements. NOx limits were also reduced (by 28% compared with Euro 4) while there was now a particulates limit for direct-injection petrol engines. For all diesels type approved after September 2011 (and sold after January 2013), particulate emissions limits were cut further.
Euro 6: September 2014 (September 2015)
There was a big reduction in NOx emissions from diesel engines (67% compared with Euro 5), with petrol and diesel cars now having to comply with the same rules.
As you can see, for more than a decade the focus has been on cleaning up the exhaust emissions of diesel cars. So while petrol and diesel engines have always been subject to different limits, Euro 6 reduces that gap – in some cases to zero. For example, both types of engine have the same threshold for particulates and there’s almost parity on the nitrogen oxides front too – and since Euro 4, petrol cars are allowed to emit twice as much carbon monoxide as diesels.
Bizarrely, even though CO2 emissions have got all of the attention for many years, they’ve never been included in the exhaust gas tests. Despite this, car manufacturers have had to cut CO2 emissions significantly. Under Euro 6 regulations a manufacturer’s range must on average emit no more than 130g/km, and by 2020 this will be cut to just 95g/km.
While the aims of Euro 6 are laudable, the figures are achieved on test rig cycles that don’t replicate real-world driving. So while each of the Euro standards has brought down emissions of all sorts of chemicals, in the real world our cars are spewing out rather more than we’re being led to believe. And whichever way you look at that, it can’t be good.
Richard Dredge
April 2017