Motor vehicles and air quality

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Vehicle emissions •
Are petrol and diesel emissions different? •
Drive smart and keep in tune

Motor vehicles produce emissions that can affect human health and the environment.

Vehicle emissions can be a significant contributor to air pollution in urban areas within the Waikato region, dependent on urban population and traffic density.

Vehicle emissions

Motor vehicles produce a range of contaminants that can affect the environment and human health. These include:

nitrogen dioxide (NO2)
fine particles (PM10 and PM2.5)
carbon monoxide (CO)
sulphur dioxide (SO2)
carbon dioxide (CO2) - a greenhouse gas associated with climate change
volatile organic compounds (VOCs) - partly burnt fuel

The main sources of NO2 are the burning of fossil fuels (for example, coal, gas and oil) and motor vehicle emissions. In urban areas the main source of NO2 is motor vehicle emissions. NO2 is therefore a useful indicator for the impact of vehicle emissions on air quality and is used as a general proxy for air pollution from motor vehicles. The recent Health and Air Pollution in New Zealand study (HAPINZ 3.0) found that NO2 from motor vehicles accounts for over half the health and social costs associated with air pollution.

A traffic monitoring and modelling investigation in Hamilton in 2025 predicted the highest NO2 concentrations at locations closest to the road edge with concentrations reducing rapidly with distance away from the road source. However, other local factors such as street canyons, high density of heavy commercial vehicles or road gradients can impact the drop off with distance that occurs, and so in some locations concentrations remain higher further from a road where dispersion is limited or emissions are elevated.

Are petrol and diesel emissions different?

Petrol and diesel engines work in slightly different ways and burn different fuels, so they produce different exhausts.

Compared with petrol engines, diesel engines produce smaller amounts of unburnt and partially burnt fuel (hydrocarbons and carbon monoxide) but can produce more nitrogen oxides and large amounts of smoke (fine particulates). These particles consist of soot, hydrocarbons, sulphur-based chemicals and volatile organic compounds (VOCs).

Heavy duty diesel vehicles, such as trucks, can be very polluting because they produce large amounts of particulates and nitrogen oxides. Diesel exhaust has also been shown to be a probable cause of cancer.

Drive smart and keep in tune

You can help reduce the amount of air contaminants polluting our air by reducing the number of times you use a motor vehicle:

Carpool.
Use public transport (trains, buses and shuttles).
Cycle or scooter.
Walk.

If you do need to use a private motor vehicle to get around, make sure you drive smart and keep it in tune.

We all need to reduce the amount of air contaminants in order to reduce their damaging effects. If your engine is producing high levels of contaminants, it’s not burning fuel as well as it could. This costs you money and damages the environment.

The way you drive and how well you look after your engine can affect how much air pollution comes from your vehicle. It can also help you save on fuel costs!
- Drive smoothly – accelerate slowly.
- Travel light – don’t carry unnecessary loads.
- Plan ahead – avoid short trips and unnecessary use of your vehicle.
- Don’t overfill your fuel tank.
- Don’t idle the engine unnecessarily.
- Use air conditioning sparingly.
- Ensure that the vehicle you buy is fuel-efficient.
Reduce smoke from diesel engines:
- Use moderate accelerations rather than wide-open throttle accelerations.
- If the engine starts to slow down, shift to a lower gear.
- Back off the accelerator when climbing a hill or towing a heavy load. The extra fuel used with a wide-open throttle under load conditions is just making smoke, not power.
Petrol vehicles

Maintain and tune your engine as recommended by the manufacturer. Many faults can increase contaminants in the exhaust, for example:
- a rich idle mixture or incorrect air/fuel ratios
- a dirty air filter
- an incorrectly adjusted carburettor
- defective spark plugs or worn distributor contacts
- a faulty ignition coil
- improper timing
- vacuum leaks, burned valves, worn rings and head gasket leaks.
Diesel vehicles

Too much diesel exhaust smoke can indicate engine problems. Follow these tips to reduce smoke and keep your diesel vehicle well maintained:
- Clean or change your air filter regularly.
- Change your engine oil at least as often as the manufacturer’s recommendation. Dirty engine oil becomes thick. This causes excessive engine and turbocharger wear.
- Maintain your engine’s fuel injection system (as recommended by the manufacturer). This includes changing the fuel filter at recommended intervals, regularly draining the water/fuel separator, having injectors checked, cleaned or replaced and the fuel injection pump maintained as needed.