An anonymous reader quotes a report from The Guardian: Emissions from diesel cars – even newer and supposedly cleaner models -- increase on hot days, a new study has found, raising questions over how cities suffering from air pollution can deal with urban heat islands and the climate crisis. Research in Paris by The Real Urban Emissions (True) initiative found that diesel car emissions of nitrogen oxides (NOx) rose by 20% to 30% when temperatures topped 30C -- a common event this summer. Emissions from a range of vehicles were found to be many times higher than those declared by manufacturers in laboratory tests, confirming earlier findings following the 2015 Dieselgate scandal, in which Volkswagen cars were found to emit 40 times more NOx on the road than during laboratory tests. Certain pollutants from motorcycles -- often considered a cleaner alternative to four-wheeled vehicles -- were also found to "greatly exceed" averages for both petrol and diesel cars. Yoann Bernard of the International Council on Clean Transportation, which carried out the study, said real NOx emissions had been found to be up to 18 times higher than those recorded in vehicle manufacturers' tests, even in newer vehicles that are supposed to be cleaner.
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