TRUE publication

Remote sensing of motor vehicle emissions in Paris

In 2017, Mayor Anne Hidalgo of Paris and Mayor Saddiq Khan of London jointly committed to making data on real-world vehicle pollutant emissions available to residents of those cities. In support of that aim, The Real Urban Emissions Initiative (TRUE) commissioned in-use vehicle testing campaigns in both cities, to be carried out using remote sensing technology.

In summer 2018, TRUE measured emissions from more than 180,000 vehicles on the road at three Paris sites. A newly published paper reports the results.

Among the study’s findings:

  • Nitrogen oxide (NOx) emissions from Euro 6 diesel cars on the streets of Paris were 4.8 times those of Euro 6 petrol cars and 6 times laboratory limits. On average, NOx emissions of Euro 6 diesel cars were only 18% lower than those of the oldest petrol cars, and many times higher than newer petrol cars’.
  • NOx emissions from petrol passenger cars in Paris decline in step with the emissions standard, but diesel cars show little improvement from Euro 2 through Euro 5 standards, and Euro 6 diesel cars only modest improvement.
  • In-use NOx emissions increase dramatically at high outside temperatures. NOx emissions of Euro 5 and Euro 6 diesel cars measured at ambient temperatures above 30 °C were 20% to 30% greater than at temperatures between 20 and 30 °C.
  • Euro 5 and Euro 6 diesel cars, which qualify for Crit’Air 2 classification and will be allowed to operate without restriction in the Paris low-emission zone (LEZ) until 2024, were responsible for an estimated 63% of total passenger vehicle NOx emissions in Paris during the field study.
  • Testing results for the newest diesel cars remain inconclusive. NOx emissions of Euro 6d-TEMP diesel cars observed in Paris were around 70% lower than diesel vehicles certified to earlier Euro 6 stages. But the number of vehicles measured was relatively small because few are yet on the road, no data is yet available on the durability of their emissions controls, and the testing raised questions about elevated NOx emissions at higher engine loads for these cars.
  • On average, NOx emissions of Euro VI city transit and coach buses were 59% and 84% lower, respectively, than Euro V buses’. On a fuel-specific basis (grams per kilogram of fuel consumed), Euro VI transit buses in Paris on average emit less NOx than Euro 6 diesel cars.
  • Fuel-specific emissions of carbon monoxide (CO), particulate matter (PM), and NOx from L-category vehicles (two- and three-wheelers) were on average significantly higher than from petrol cars. L-category vehicles certified to the most recent emissions standard (Euro 4) qualify for the Crit’Air 1 emissions classification and will be allowed to operate without restriction within Paris until 2030. Without new policies to reduce their exhaust emission limits or restrict circulation, the share of air pollution in Paris attributable to these vehicles may grow.