Clarity from A to E Finding a clean, low emission car made easy

The AIR Index rates cars by the level of harmful NOx emissions they produce from A (the best) to E (the worst) providing reliable comparative results to car buyers and policy makers.

At least two different vehicles of each type, sold and on the road, are sourced independently from the car makers and then tested, in the same on-road test, with the emissions results used for the published AIR Index.

AIR Index Rating Urban NOx What does this mean?
A 0 - 80 mg/km Low levels of NOx emissions using the latest technology to improve air quality in towns and cities.
B 80 - 168 mg/km Moderate levels of NOx emissions with technology reducing the impact on air quality in towns and cities.
C 168 - 270 mg/km High levels of NOx emissions impacting air quality in towns and cities.
D 270 - 600 mg/km Very high levels of NOx emissions contributing to poor air quality in towns and cities.
E 600+ mg/km Extreme levels of NOx emissions with the worst impact on air quality in towns and cities.
Clarity from A to E

In addition to the emissions rating in the AIR Index and basic vehicle information to identify the vehicle correctly, the results include the official Euro emissions standard and CO2 emissions. This enables users to filter vehicles in the same Euro standard rating to be ranked by the AIR Index and find the car with lowest levels of NOx emissions to minimise the impact on air quality.

For specific vehicle comparisons cars can be pinned together and compared. Searches are also possible by vehicle class and, for fleet managers and policy makers, connection via API is also available.

The AIR Index addresses popular misconceptions and confusion about vehicle choices following the 'Dieselgate' scandal. Some diesel engines actually produce lower NOx emissions than petrol engine variants and the AIR Index provides clarity when making car buying decisions.

All vehicles tested for the AIR Index technically meet the European emission standards required at the time of delivery such as Euro 4, 5 or 6, even if the real-world emissions are higher. The AIR Index A-to-E rating provides a deeper, more realistic, independent assessment of the actual emissions of each car.

Car buyers can now make informed choices in the vehicles they buy, whether new or used. Policy makers can use fair comparative emissions results to ensure their policies are robust, fair and optimal in effectively improving air quality. Car makers have the opportunity to regain consumer trust by ensuring car buyers can use independent comparative results that show how they compete to deliver cleaner cars.

Test Methodology

Independent testing to the latest European CEN Workshop Agreement methodology for comparable emissions.

The AIR Index rating categorises vehicles in bands, based upon NOx emissions data measured during on-road tests. Testing each vehicle in urban conditions to the same test provides comparable NOx emissions levels that more accurately reflect the contribution to urban air quality than existing tests performed in a laboratory.

AIR ensures that the AIR Index is only obtained from tests that follow the latest European CEN Workshop Agreement CWA 17379. This was developed in public, by scientists and stakeholders. The methodology ensures that the test procedure is consistently applied to different vehicles so that the data collected from different tests provides comparable emissions data.

Only specialist test centres capable of carrying out tests in accordance with CWA 17379, accredited to ensure appropriate standards and test equipment, are able to provide test results for an AIR Index.

Only AIR is able to use results derived from the independent vehicle tests, conducted inline with CWA 17379, which classifies vehicles from A-to-E under the AIR Index rating.


You can read more about CWA 17379 here.

On-road independent emissions tests

Not all cars pollute in the same way

Whether they are diesel, petrol, hybrid or electric, the most accurate way to measure harmful emissions is to test cars on the road in actual driving conditions. Every car with a published AIR Index rating is tested in accordance with the CWA 17379 methodology ensuring a series of strictly controlled, independently conducted tests using Portable Emissions Measurement Systems (PEMS) equipment.

We source the cars
At least two different vehicles, of each type, sold and on the road are sourced independently from car makers for the tests which lead to the AIR Index rating. Each vehicle must have travelled between 3,000km and 100,000km from new to ensure data collected is comparable.
On-road, real urban driving
The exact test cycle driven each time will differ due to the nature of traffic flows and driving styles. To ensure comparability of results between vehicles, at least five 10km trips must be completed for each model with an average speed between 20km/h and 40km/h on paved streets, and meeting a range of other dynamic criteria including acceleration and braking rates. These trips typically can take around 20 minutes each to complete. The AIR Index rating is created from the average of the data, taking into consideration the trip-to-trip variability.
The power of PEMS
Portable Emissions Measurement Systems (PEMS) testing involves advanced scientific test equipment to be attached the vehicle. It is a very similar procedure to that which is required of car makers when type-approving a new model for sale on EU roads. The test equipment is set up, maintained, operated and calibrated to the same strict standards. All AIR Index testing takes place with air temperatures between 10C and 20C on routes including hills, with acceleration and deceleration rates in full compliance with CWA 17379.
Cars Tested

Confidence through transparency

The development of the AIR Index has been led by a global alliance of scientists and organisations committed to reducing harmful vehicle emissions by providing car buyers and policy makers with a trusted and independent way to evaluate each car model.

It is not practical to test every variant of every model to be rated for the AIR Index, but there is an ongoing programme underway to evaluate as wide a range of vehicles as possible according to the CWA 17379 methodology. If there is a particular vehicle you would like to see tested, please let us know by sending an email to testme@allowair.org for us to consider.

We also include partial ratings for models which have not yet completed testing in full compliance with CWA 17379 . These are displayed in the search results with the relevant AIR Index rating 'greyed out' as they are not full AIR Index ratings, but they do provide an indication of the expected result once a second vehicle has been tested.

The CEN Workshop Agreement CWA 17379 was initiated by Nick Molden of Emissions Analytics, which has tested more than 2,000 vehicles, including over 1,000 in Europe since 2011. Together with test data from several other organisations and companies, independent from car makers, the AIR Index has been created reflecting this extensive experience.

About AIR

The alliance created to reduce the harmful effects of vehicle emissions on air quality

AIR is a global not-for-profit organisation that empowers car buyers and policy makers to reduce vehicle emissions and improve air quality by providing an independent, trusted, on-road vehicle emissions ratings for cars: the AIR Index. AIR was formed in 2017 by Nick Molden, founder of Emissions Analytics, and Massimo Fedeli of Fair Play Consulting, and is an alliance of scientists, regulatory experts, and people and organisations committed to addressing pollutant emissions from vehicles.

Members and supporters of AIR enable the organisation to provide information which is:

  • COMPARABLE: Based on the most thorough assessment of on-road driving conditions enabling genuine comparability between vehicle models, makes and manufacturers, both new and old.
  • ACCESSIBLE: Data is publicly available, transparent and free of charge.
  • STANDARDISED: Based on a European CEN Workshop Agreement CWA 17379 to deliver standardised emissions ratings across all markets and regions providing a truly global rating system.
  • INDEPENDENT: Created to be the most comprehensive, independently endorsed , vehicle testing and ratings available in the market place
  • STANDARDISED: Available now.

Join us in the AIR alliance

Sign up as a supporter, it’s free and we’ll keep you updated with news about the latest AIR Index ratings, policy updates and events.