Driving tests

What is vehicle exhaust pollution?

When vehicles burn fuel they don’t do it efficiently and it creates undesirable compounds which we call pollution. Vehicle manufacturers are constantly striving to make their engines more efficient with the optimum goal of burnt fuel just producing water, nitrogen and carbon dioxide.

Governments have passed standards for engine emissions since 1992 when Euro 1 was released. Compared with Euro 1, the current Euro 6 levels are up to 96% less emissions in some of the compounds.

Euro 1 emission limits (1992):

  • CO (carbon monoxide) – 2.72 g/km (petrol and diesel)
  • HC+ NOx (hydrocarbons and nitrogen oxides) – 0.97 g/km (petrol and diesel)
  • PM  (atmospheric particulate matter) – 0.14 g/km (diesel only)

Euro 6 (or Euro VI) emission limits (2015) (petrol):

  • CO – 1.0 g/km
  • HC – 0.10 g/km
  • NOx – 0.06 g/km
  • NMHC (non-methane hydrocarbons) – 0.0068 g/km
  • PM (atmospheric particulate matter) – 0.005 g/km (direct injection only)
  • PM  (number of particles) – 6.0×10 ^11/km (direct injection only)

Euro 6 emission limits (diesel):

  • CO – 0.50 g/km
  • HC+ NOx – 0.17 g/km
    NOx – 0.08 g/km
  • PM – 0.005 g/km
  • PM – 6.0×10 ^11/km

Gases and particulates explained

Nitrogen oxides

NO and NO2 are released from exhausts. They:

  • are harmful to human health, causing asthma and lung irritation
  • can cause acid rain
  • react with hydrocarbons to produce ground-level ozone
  • are produced during high-temperature combustion
  • contribute to the formation of particulate matter in the atmosphere.

Carbon monoxide

It is:

  • Colourless, odourless and tasteless
  • toxic to animals above 35 parts per million
  • a temporary atmospheric pollutant until it combines to form ground-level ozone
  • produced when fuel isn’t completely burnt



  • are tiny particles such as diesel soot that are released into the air
  • damage lungs
  • contribute to smog.



  • are one of the causes of smog
  • are produced when fuel isn’t fully burned
  • are produced when fuel evaporates when in the fuel tank



  • emitted in unburnt fuel
  • toxic and carcinogenic
  • linked with leukemia with long-term exposure

Pollution problems with older types of fuel


Lead used to be added to fuel to create leaded petrol (hence why we have unleaded petrol now). It interferes with the production of red blood cells, causes high blood pressure and inhibits development in children. Lead no longer appears in exhaust emissions except in a handful of countries that still use leaded petrol. It affects the performance of catalytic converters.

Sulphur dioxide

Sulphur dioxide contributes to the formation of ozone and particulate matter. It’s naturally present in petrol at the refining process and is removed. It affects the performance of catalytic converters.

Vehicle emissions standards in New Zealand

Most vehicles imported into New Zealand must meet approved emissions standards unless they’re either more than 20 years old, are a special interest vehicle, or it’s a car, van or off-road vehicle you’ve owned in another country and you are emigrating here.

Detailed explanations of the emissions standards accepted in New Zealand are available here.

As your vehicle’s engine wears out it may start to produce more emissions. When you take it for a Warrant of Fitness test it will be check to see if it produces smoke. If it does, you may need to get a proper emissions test done.

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Darren has written over 3000 articles about driving and vehicles, plus almost 500 vehicle reviews and numerous driving courses. Connect with him on LinkedIn by clicking the name above

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