The new index was created by the British company Emissions Analytics. The Equa Air Quality Index is based on the level of emissions of nitrogen oxides (NOx) in grams per kilometre emitted during our real-world tests. The index aligns the boundaries between ratings values as much as possible with recognisable points.

The new Equa Air Quality Index rating scheme has been launched to help clear customer confusion over real-world NOx emissions. It also allows manufacturers to demonstrate their vehicles’ clean credentials, and provide data to policymakers on progress in the drive to improve air quality.

The first set of over 440 ratings is now available online. The company will continuously add new vehicles to its database to form a compelling resource.

Nick Molden, chief executive of Emissions Analytics, said: “There’s a great deal of confusion among car buyers on the subject of pollutant emissions, but we’re able to deliver impartial and precise information to help them buy better. We’re also looking forward to working with the industry as a whole to highlight the best vehicles available.”

Recent reports have shown that real-world emissions can be four times or more higher than officially quoted NOx emissions figures. Designed to be clear and concise, the Equa Air Quality Index allows manufacturers and retailers to show how different models, whether diesel, petrol or hybrid, compare in the showroom.

The Equa Air Quality Index is intended to complement the forthcoming regulations for new vehicle certification, by monitoring vehicle performance when driven normally on roads; in effect keeping a watchful eye on the effectiveness of the new regulations. To ensure that the Equa Index remains robust and relevant, an advisory board of leading academic and industry experts has been assembled.

The board includes individuals from Imperial College London, King’s College London, the International Council on Clean Transportation and the University of Cambridge. Providing advice and guidance, as well as reviewing the test and rating methodology, the committee will provide input into the wider development of the programme.