An anonymous reader writes: The Guardian, citing a comprehensive set of data, reports that 97% of all modern diesel cars emit more toxic nitrogen oxide (NOx) pollution on the road than the official limit. A quarter of this voluminous number emits at least six times more than the limit. From the report, "Surprisingly, the tiny number of models that did not exceed the standard were mostly Volkswagens, the carmaker whose cheating of diesel emissions tests emerged last year sparked the scandal. Experts said the new results show that clean diesel cars can be made but that virtually all manufacturers have failed to do so. The new data, from testing industry leader Emissions Analytics (EA), follows the publication this week by the Department for Transport of emissions results for 37 vehicles, all of which emitted more NOx on the road than the official limit. But the new data covers more than 250 vehicles in more stringently standardised road conditions. EA found that just one of 201 Euro 5 diesels, the EU standard from 2009, did not exceed the limit, while only seven of 62 Euro 6 diesels, the stricter standard since 2014, did so. Diesel cars must meet an official EU limit for NOx but are only tested in a laboratory under fixed conditions. All vehicles sold pass this regulation but, when taken out on to real roads, almost all emit far more pollution. There is no suggestion that any of the cars tested broke the law on emissions limits or used any cheat devices. Mayoral candidates in London, the city with the worst air quality in Britain, have seized on the DfT data to call for tighter controls on polluting traffic -- including a ban on diesel cars."Caroline Pidgeon, the Lib Dem mayoral candidate, said: "The figures are exactly the reason why we need to speed up the introduction of the ultra-low emission zone so that it starts in 2018. Ultimately we will need to ban diesel vehicles from much of London and we need a mayor prepared to take these tough decisions and work with people to make these changes happen."