Vehicle exhaust emissions | What comes out of a car exhaust? | RAC Drive (2024)

When you drive your car, lots of waste emissions come out of the exhaust pipe.

Whilst these are a necessary byproduct of running a combustion engine, exhaust emissions can be harmful to the environment, contribute to air pollution and cause serious publichealth problems.

Older diesel vehicles, in particular, are in the spotlight for the harmful emissions they produce as they’re seen to be more polluting than petrol cars. As a result, drivers of aging diesels are being discouraged from entering towns and cities by the introduction oflow emission zones.

In this comprehensive guide to car emissions, we look at what exactly comes out of your vehicle, how it affects you and what is being done to tackle exhaust fumes.

Jump to:

• What are vehicle exhaust emissions?
• Vehicle exhaust gases and pollutants
• The effects of breathing exhaust fumes
• What's being done to reduce exhaust emissions?
• What are the tests for exhaust pollutants?
• How else does my car cause pollution?
• How toxic is my car?

What are vehicle exhaust emissions?

Exhaust emissions are a mix of different gases and particles emitted by vehicles when the engine is running.

These emissions can reduce the quality of the air around us, particularly in big cities that are congested with cars.

The combination of exhaust fumes and other particulates released into the atmosphere are a major factor of global warming. According to the official transport and environment statistics 2022,transport is the largest emitting sector of greenhouse gasemissions, producing 24% of the UK’s total emissions in 2020. They also include dangerous pollutants and chemicals.

Theseemissions also include harmless chemicals such as oxygen, nitrogen and water.

CO2 is the one we’ve all heard of, but there are other less well-known substances coming from our cars that aredamaging.

Vehicle exhaust gases and pollutants

Cars emit a potent co*cktail of exhaust gases, many of which have harmful effects. They include:

• Carbon dioxide (CO2) – CO2 is a greenhouse gas, thought to be a major contributing factor to climate change. Although technically non-toxic, excessive volumes contribute towards ocean acidification.
• Carbon monoxide (CO) – This invisible gas is the result of incomplete combustion of fuel and is very toxic to humans. Most modern engines only produce tiny amounts of it thanks to efficient combustion processes, but older engines are bigger offenders.
• Nitrogen oxides (NOx) – Nitrogen oxides are produced in any combustion process. They are highly reactive and can contribute to smog when they come into contact with other airborne chemicals. Some manufacturers famously cheated NOx tests.
• Sulfur dioxide (SO2) – This is a colourless gas that smells like burnt matches and occurs naturally in crude oil used to refine petrol and diesel. It forms acids when burned, leading to engine corrosion and smog.
• Hydrocarbons (HC) – HCs escape from exhausts as unburnt fuel due to incomplete combustion. They also evaporate from the fuel tank and nozzle when you fill up at the petrol station.
• Benzene (C6H6) – This occurs naturally in petrol and diesel in very small quantities and is also emitted from vehicle exhausts as unburnt fuel. Benzene is a carcinogenic substance and high levels of inhalation can severely harm human health.
• Particulates – Diesel engines emit airborne particles of black soot and metal, known as particulate matter. Modern cars are fitted with diesel particulate filters (DPFs) to reduce the number of harmful particles being pumped out into the atmosphere.

Read more on emissions and clean air zones

• Clean Air Zones – what are they and where are they?
• The London Ultra Low Emission Zone (ULEZ): what you need to know
• The Bristol Clean Air Zone: What you need to know
• The Birmingham Clean Air Zone: what you need to know
• Euro 1 to Euro 6 guide – find out your vehicle's emissions standard
• Low Emission Zones: what you need to know
• 11 ways to reduce your driving emissions
• Is my car bad for the environment? A guide to vehicle exhaust emissions

The effects of breathing exhaust fumes

Pollutants from cars are linked to a range of health problems, from allergies and skin irritation to heart disease and respiratory problems such as asthma. Long-term repeated exposure to diesel exhaust fumes may also increase the risk of lung cancer, according to the World Health Organisation.

A blockage in your exhaust can lead to carbon monoxide poisoning. Breathing in CO can cause headaches, respiratory problems and even death if inhaled in large quantities. It’s particularly dangerous to children and people suffering from heart disease.

The amount of exhaust fumes people are exposed to varies greatly, but those living in densely-populated urban areas are most at risk of developing health problems linked to pollution.

What's being done to reduce exhaust fumes?

Thanks to advances in technology and policies designed to tackle climate change, emissions of CO2 and other car pollutants have been significantly reduced in recent years.

Car manufacturers are reducing exhaust emissions through improved engine and exhaust systemdesign, while catalytic converters and particulate filters are now standard on all new petrol and diesel cars. The Government has also pledged to ban the sale of new diesel and petrol cars by 2030 in a bid to encourage people to make the switch to electric vehicles.

Many cities around the world have introduced clean air zones to discourage the most polluting vehicles from entering them. London brought in its Ultra Low Emission Zone, andyou now need a Crit'Air clean air sticker to drive in France’s busiest cities.

• 11 ways to cut your driving emissions
• Electric and hybrid car reviews
• Euro 1 to Euro 6 guide – find out your vehicle's emissions standard

What are the tests for exhaust pollutants?

Since 1993, car manufacturers have had to comply with a series of European emissions standards that set maximum limits for harmful substances emitted by new cars.

The standards, which are different for petrol and diesel cars, have become increasingly stricter over time. The Euro 1 standard saw the introduction of catalytic converters and unleaded petrol for all cars. We’re now on Euro 6, which came into force in 2014 and slashes the permitted level of NOx for diesels.

Most vehicles also have an exhaust emissions test as part of their MOT and will fail if they’re found to be emitting too many harmful gases. When theMOT rules were updated in 2018, stricter guidelines were brought in for diesel cars, making it harder for them to pass.

How else does my car cause pollution?

It’s not only exhaust fumes that pollute the atmosphere. Brakes and tyres also contribute to harmful emissions.

Every time you drive a car, tiny fragments of particulate matter such as dust are released into the air from brake and tyre wear, as well as from the road surface.These particles enter the airstream and can have a damaging effect on people’s health. Plastic particles from tyres can also harm marine wildlife if they get deposited into water through sewers.

The Government wants to pass legislation to improve standards after a recent report by the Air Quality Expert Group said dust from car brakes and tyres will still pollute the air, even when cars are all-electric.

Is my car bad for the environment?

Out ofnon-commercial vehicles,gas-guzzling sports cars and some older SUVs are reportedlythe biggestoffenders when it comes to climate change.Owners of these vehicles usuallypay more road tax due to their motorshaving a larger engine, and emitting higher levels of CO2.

Their vehiclesmay even be banned from certain cities in Europe if they're driving particularly old and polluting models at times, so make suretofind out your vehicle's emissions standard and whether you'll be affected before you travel. At the other end of the spectrum, there’s no VEDto pay on fully electric cars with zero emissions.

One of the best ways to reduce emissions is to improve your fuel efficiency. That’s because the amount of CO2 produced by a vehicle is directly linked to how much fuel it consumes.

It makes sense to choose a car that is most efficient for your individual driving needs. For example, if you mainly drive short distances around town with the occasional longer distance, a plug-in hybrid is ideal, whereas if you undertake a range of different journeys, a petrol car might still be your best option.

Ultimately, switching to a more environmentally-friendly vehicle can save you hundreds of pounds a year in VEDand fuel. And the newer your car is, the better it is for the planet.

• How to save fuel - the ultimate guide
• Top nine alternative fuels for cars
• What is a hybrid car and should I buy one?

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