‘Diesel cars emit more air pollution on hot days’
September 11 2019 01:02 AM
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Guardian News and Media / Paris

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.
Launching its latest report, True said it used hi-tech remote-sensing equipment to measure emissions from more than 180,000 vehicles being driven on roads in the French capital during three weeks in summer 2018.
The tests, carried out with the approval of the city’s mayor, Anne Hidalgo, used a beam of light to analyse the exhaust plumes of vehicles as they passed, with automatic number plate recognition linking the measurement to specific models.
More than 370,000 such measurements taken in the UK, France and other countries have been compiled into a new rating system by True.
The vehicles were tested on three roads in Paris’s 12th and 13th arrondissements – not the most central – and most were passenger cars and light commercial vehicles.
The sample also included buses, motorcycles, mopeds and lorries.
The aim, as with a similar study in London the previous year, was to measure the real emissions of vehicles on the road in a range of different driving and traffic conditions.
The latest findings will come as no surprise to Parisians, who returned to work last week after the long summer holiday.
Car lobbies dismiss residents’ complaints about asthma and allergies as anecdotal evidence and contest city hall’s measures to discourage car use in the city centre.

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