Very cleanest cars revealed: new A+ rating from the EQUA Index

Emissions Analytics’ EQUA Index ( has been revealing the cleanest and most efficient cars since it launched in 2016. Since then, technology and vehicle performance have improved to a point that a new class of even cleaner vehicles can now be revealed.

On 17 October, the Mayor of London, in collaboration with Emissions Analytics, launched an online Cleaner Vehicle Checker ( with a new EQUA Aq A+ rating for those vehicles with the very lowest emissions of nitrogen oxides (NOx). This identifies 105 Euro 6 petrols meeting this more stretching standard and 11 diesel engines from four manufacturers.

To achieve the A+ rating a vehicle must emit no more than 0.060 grams per kilometre of NOx across the real, on-road EQUA Index test, made up of equal proportions of urban, rural and motorway driving. This is 25% more stringent than the A rating of no more than 0.080 grams per kilometre. It is also significantly tougher than emissions required under the new, official Real Driving Emissions (RDE) regulation, under which 0.168 g/km (180% higher) are allowed until 2021.

A recent study, conducted by Imperial College London on behalf of the campaign group Allow Independent Road-testing (AIR,, concluded that RDE and the EQUA Index tests are broadly similar in how demanding they are on the vehicle.

The new A+ rating illustrates dramatically the challenge that diesel engines face, but also shows that they shouldn’t be automatically consigned to the history books. Not that many years ago, governments encouraged car buyers to opt for diesel cars in order to reduce carbon dioxide (CO2) emissions. However, the NOx emissions were much higher (often five times higher, and more than the petrol cars they replaced), and even the CO2 emissions were higher than the official figures suggested (often 40% or more adrift).

With the progress in standard “full” hybrid technology – ignoring for a moment plug-in hybrids – the newest models now delivers Mpg comparable with diesels. This in-turn means that on average CO2 as well as NOx emissions are lower too – the best of both worlds.

Does this spell the end for diesel passenger cars? Maybe. The loss of confidence in the automotive industry combined with the political narrative, nationally and locally, may be hard to correct. Consider the new Volkswagen Passat 1.6 litre diesel, with an EQUA Aq rating of A+, an EQUA CO2 rating of B and EQUA Mpg of 52.6 mpg. Compared to the latest Hyundai Ioniq petrol hybrid with EQUA Aq of A+, EQUA CO2 of A and EQUA Mpg of 58.1 mpg. The diesel has impressively low NOx emissions, but the hybrid is beating it on fuel economy and CO2 emissions.

So, the battle between diesels and hybrids is on. Can diesels shrug off the legacy of those Euro 6 diesels still on the market with EQUA Aq H ratings (12 or more times the regulatory NOx limit)? Does the current performance of hybrids obviate the need for alternative powertrains to meet urban air quality goals? Whatever happens, the EQUA Index will be tracking through its independent, real-world test programme.

The EQUA Index data can be accessed for free at There are four ratings for each vehicle: EQUA Aq rating for NOx; EQUA CO2 for carbon dioxide; EQUA CO for carbon monoxide; and EQUA Mpg for fuel economy. In publishing the EQUA Aq A+ ratings, the boundaries for categories B to H have not been changed.