Study: All Diesel Tests Understate Real-World Emissions

Government certification tests around the world routinely understate real-world emissions from diesels by more than 50%, according to a global study published on Monday in Nature.

The 17-page report asserts that the additional pollution that results caused some 107,600 premature deaths worldwide in 2015, the year analyzed by the researchers.

The study emphasizes that excess pollution is a result of imprecise government standards and not necessarily wrongdoing on the part of diesel manufacturers.

The study looks at on-the-road diesel emissions of nitrogen oxides (NOx)—pollutants linked to respiratory problems—from vehicles in 11 markets that represent 80% of the global diesel sales. The work was done by an 11-member team of researchers from the Council on Clean Transportation, the University of Colorado, Environmental Health Analytics, Stockholm Environment Institute and International Institute for Applied Systems Analysis.

The report calculates that on-the-road diesels generate 55% of all NOx emissions emitted by surface transportation. The worldwide fleet covered by its analysis emitted 14.4 million tons of NOx during real-world usage in 2015 compared with a government laboratory-certified level of 9.4 million tons.

The researchers estimate that heavy-duty trucks and buses contribute three-fourths of excess NOx. That proportion jumps to 90% for such vehicles in Brazil, China, the European Union, India and the U.S.

Tough emission standards in Europe and the U.S. have dramatically reduced soot and most other emissions from diesels. But the report notes that achieving regulatory limits for NOx—the challenge that triggered Volkswagen’s diesel emission cheating scandal—has been technically feasible but more difficult.