Low-emission cars checker

Want to buy a low-emission car? Our tests show that NOx exhaust emissions are plummeting but CO2 from many new cars is actually on the rise. Our free low-emissions checker will help you find the cleanest cars on the UK market.
Dino BurattiResearcher & writer

What is a low-emission car? Before the 2015 VW emissions scandal, also known as dieselgate, vehicle emissions largely focussed on CO2 (carbon dioxide).

But now we're more aware of pollutants like NOx (oxides of nitrogen), PM (particulate matter) and CO (carbon monoxide) and how poor air quality contributes to tens of thousands of premature deaths in the UK.

The good news is that our independent tests have found that, on average, the cars that meet the latest emission regulations (Euro 6d-temp and Euro 6d, explained in more detail below), are producing a fraction of the NOx and CO of the cars they replaced.

But to make things more complicated, our tests show that CO2 emissions from some new cars are actually going up, not down.

In a nutshell, we may be saving humanity's lungs at the expense of our planet's health. It also makes buying a low-emission car a lot more complicated.

It's not all doom and gloom though. Not only do we expect cars to become even more fuel efficient over the next few years as both combustion and hybrid technology is refined, there are some cars available today that strike a balance of low CO2 and low air pollutants such as NOx and CO. Our free low-emissions car checker, below, reveals CO, NOX and CO2 for hundreds of cars we've tested, so you can make an informed decision on your next purchase.


Want a car that produces zero, rather than low, emissions? You'll need to go fully electric. Take a look at our pick of the best electric cars


NOX, CO and CO2 car emissions checker

Our free low-emissions checker shows all emissions that our independent tests have measured for every car we've tested since 2012. This tool shows:

  • the car model and all engines we've tested in that car
  • the Euro emission legislation the car meets in official tests
  • the amount of NOx and CO each engine produced in Which? independent tests since 2012
  • the amount of CO2 we measured from the tailpipe for all cars Which? has tested since 2017 – this will be updated in the future to include all cars back to 2012.

CO2 figures are given in g/km, while NOx and CO emissions are rated from 'very low (trace)' to 'extremely high'. Scroll down to below the tool to find out more about what we consider to be ‘high’ and the consequences for those cars in our tests.

Car emissions checker – check by make and model

Every car we review is driven by our experts and put through our independent lab tests. As our lab tests are objective, you can trust our results. See our expert pick of the best cars.

Using our low-emission checker: high and low car emissions explained

New cars must meet the current emission regulation in official tests, otherwise they cannot be sold.

Our tests are tougher than the official ones, but we use the official Euro limits as benchmarks against our own test results to give them context.

Any engine that has a rating of ‘high’ produced more pollutants in our tests than the Euro 3 limit from 2001. So we withhold Which? Best Buy car status.

Euro limits are explained in more detail below. But, in brief, official emission regulations limit the amount of emissions such as NOx and CO in official tests.

(We updated our tests in 2017. Figures from our 2012-2016 test programme aren't directly comparable with figures from the current test programme.)

High and low car emissions in Which? tests explained

 Which? car emission levels explainedNOxCOEquivalent to
Extremely low (trace)Less than 0.015g/kmLess than 0.015g/kmNOx emissions are at least five times less than the current Euro 6 diesel limit. Or nearly seven times less than than Euro 6 petrol CO limit.
Very lowLess than 0.08g/kmLess than 0.05g/kmProduces less NOx than the current Euro 6 diesel limit
LowLess than 0.18g/kmLess than 0.5g/kmProduces less NOx than the Euro 5 diesel limit
MediumLess than 0.5g/kmLess than 1g/kmProduces less NOx than the Euro 4 diesel limit, or less CO than the Euro 6 petrol limit (CO petrol limit unchanged since Euro 4).
HighLess than 0.97g/kmLess than 2.72g/kmProduces more NOx than the Euro 3 diesel limit, or more CO than the Euro 3 petrol limit.
Extremely highMore than 0.97g/kmMore than 2.72g/kmProduces more NOx than the Euro 1 diesel limit, or more CO than the Euro 1 petrol limit.

Table notes:
1 Euro 1-6 limits are used for comparative purposes only, to place our own independent test results in context.
2 Which? tests are tougher than the official ones. Go to our guide on how Which? tests mpg and emissions to find out more.

Car emissions explained: how exhaust emissions affect us

Car emissions we measure in our tests can be divided into two main groups:

Air pollutants

NOx (oxides of nitrogen)

NOx is comprised of two gases: nitric oxide (NO) and nitrogen dioxide (NO2). Of the two, NO2 is the gas that causes us the most harm. It’s an irritant that can cause inflammation of our airways and can affect immune cells in the lungs. 

CO (carbon monoxide) 

CO has always been lethal in an enclosed space. But Defra now warns that excessive CO increases the risk for people with existing diseases that affect delivery of oxygen to the heart or brain, such as angina.

PM (particulate matter) 

These are tiny particles of solid and liquid matter. From cars, PM comes from the exhaust as well as from tyres and brakes as they wear down. 

Particles are measured in nanometres, and some are small enough to pass through the pores in our lungs. PM has been linked to cardiovascular and respiratory disease.

NOx and PM 

There are a number of difficulties in trying to get an accurate figure of how many premature deaths that air pollution from NOx and PM cause, and it's impossible to separate the effects of each emission. But a 2018 report by the Committee on the Medical Effects of Air Pollutants (COMEAP) puts the UK figure as an equivalent of 28,000 to 36,000 premature deaths from NO2 from NOx and PM combined, or 328,000 to 416,000 life years.

Greenhouse gas

CO2 (carbon dioxide) 

CO2 is a greenhouse gas linked to climate change and rising global temperatures. In our tests, we’ve found that CO2 from cars is rising, not falling. 

See our guide to CO2 from cars for more information.

Euro emissions explained

The Euro emission standards to date are explained below – click on each drop-down arrow to read the details.

Each Euro standard has two introduction dates: an early one for new type approvals, and a second one for all remaining new cars on sale.

A new type approval is typically a new generation of car. For instance, the 7th generation (or Mk7) version of the popular VW Golf (2013-2020) was replaced by a new generation of VW Golf (2020-) in 2020.

Compare car insurance

Find the right policy for your vehicle using the service provided by Confused.com

Get a quote now