Driver Knowledge Tests

What is car pollution and car emissions?

Air pollution by vehicles is caused by exhaust emissions that are a result of incomplete combustion of fuel in an engine. In a perfect world, fuel would be burnt completely and only water, carbon dioxide and nitrogen would be released, but in reality some quite toxic and harmful gases and particles are created.

Nitrogen oxides

Known as NOx the main compounds are NO (nitric oxide) and NO2 (nitrogen dioxide). They are produced during high-temperature combustion and, once released, contribute to the formation of particulate matter in the atmosphere. They impact human health as they can cause asthma and lung irritation. Nitrogen oxides react with hydrocarbons to produce ground-level ozone and can cause acid rain.


Hydrocarbons are produced both when fuel is not fully burnt and when fuel evaporates as it sits in the petrol tank. Hydrocarbons are one of the causes of smog which inhibits plant growth and damages respiratory tissues (i.e. your lungs).


Benzene is released by evaporation of fuel and when it’s burnt. Long term exposure is implicated in leukemia and anaemia.

Carbon monoxide

Colourless and odourless, it occurs naturally in the atmosphere. At low levels it’s harmless, but at concentrations above 35 parts per million it is toxic. It is a temporary atmospheric pollutant until it combines to form ground-level ozone. It is produced when fuel isn’t burnt completely.


Particulates are tiny particles of dust, salts, soot and other toxic compounds. There are three size classes

  • Fine – less than 2.5 micrometers in diameter
  • Coarses – less than 10 micrometers in diameter
  • Total – all others up to about 50 micrometers.

They reduce visibility and cause irritation in the lungs and throat. They contribute to bronchitis and asthma.

You can be fined for driving a smoky vehicle – one that creates pollution – and you can also report smoky vehicles. See these EPA guidelines for how to do it.

Less common pollutants

With the phasing out of leaded petrol, lead is no longer the issue that it once was. Lead causes many health problems, particularly in children where it can inhibit brain development. Only a handful of countries still use leaded petrol (Algeria, Yemen and Iraq).

Sulphur dioxide used to be an emissions from burning fuel but it is now removed in the refining process.

Vehicle emissions standards

Vehicles imported into Australia must meet emissions standards. Worldwide the commonly accepted standard is Euro X. Currently Euro VI (Euro 6) is the latest. It was created in September 2014. The Euro standards were initiated in 1992 and since then some pollutants have had their levels cut by 96%.

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 released) – 0.14 g/km (diesel only)

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

  • CO (carbon monoxide) – 1.0 g/km
  • HC (hydrocarbons) – 0.10 g/km
  • NOx (nitrogen oxides) – 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 released) – 6.0×10 ^11/km (direct injection only)

Euro 6 emission limits (diesel):

  • CO (carbon monoxide) – 0.50 g/km
  • HC+ NOx (hydrocarbons and nitrogen oxides) – 0.17 g/km
    NOx (nitrogen oxides) – 0.08 g/km
  • PM (atmospheric particulate matter) – 0.005 g/km
  • PM (number of particles released) – 6.0×10 ^11/km

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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