Low-emission cars checker

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.

Our low-emissions car checker 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 tailpipe emissions? Take a look at our pick of the best electric cars. 

NOX, CO and CO2 car emissions checker

Our 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 2012

CO2 figures are given in g/km, while NOx and CO emissions are rated from 'very low (trace)' to 'extremely high'.

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.

Car emission levels 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 these cars cannot be Which? Best Buys.

Note that we updated our tests in 2017. Figures from our 2012-2016 test programme aren't directly comparable with figures from the current test programme.

The table below explains how we rate rank emission levels in our tests.

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.

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