A new study by MIT researchers, published this month in Atmospheric Environment, finds that in Europe, 10 major auto manufacturers produced diesel cars, sold between 2000 and 2015, that generate up to 16 times more NO_x emissions on the road than in regulatory tests—a level that exceeds European limits but does not violate any EU laws.

The researchers estimate that these excess emissions will cause approximately 2,700 premature deaths per year across Europe. These health effects, they found, are “transboundary,” meaning that diesel emissions produced in one country can adversely affect populations in other countries, thousands of kilometers away.

We find that 70% of the total health impacts from excess NO_x are due to trans-boundary emissions. For example, 61% of the impacts in Germany of total excess NO_x emissions are caused by emissions released in other countries. These results highlight the need for a coordinated policy response at the European level. In addition, we find that total emissions accounting for country-specific fleet mixes and driving behaviors vary between manufacturers by a factor of 10 and mortality impacts per kilometer driven by a factor of 8.

—Chossière et al.

The 10 manufacturers’ excess emissions may not be a result of unlawful violations. Instead, the team writes that “permissive testing procedures at the EU level and defective emissions control strategies” may be to blame.

According to the report, if all 10 auto manufacturers were to improve their emissions control technologies to perform at the same level as the best manufacturer in the group, this would prevent up to 1,900 premature deaths per year.

There are many times the number of diesel cars in Europe compared to the US, partly because the EU started pushing diesel for environmental reasons, as it produces less carbon dioxide emissions compared with [gasoline]. It’s a case where diesel has probably been beneficial in terms of climate impacts, but it’s come at the cost of human health.

— Steven Barrett, the Raymond L. Bisplinghoff Professor of Aeronautics and Astronautics at MIT and corresponding author of the study

The researchers considered 10 major auto manufacturers of diesel cars sold in Europe, for which lab and on-road emissions data were available: Volkswagen, Renault, Peugeot-Citroën, Fiat, Ford, General Motors, BMW, Daimler, Toyota, and Hyundai. Together, these groups represent more than 90% of the total number of diesel cars sold between 2000 and 2015, in 28 member states of the EU, along with Norway and Switzerland.

For each manufacturer, the team calculated the total amount of excess emissions produced by that manufacturer’s diesel car models, based on available emissions data from laboratory testing and independent on-road tests. They found that overall, diesel cars produce up to 16 times more NO_x emissions on the road than in lab tests.

They then calculated the excess emissions associated with each manufacturer’s diesel car, by accounting for the number of those cars that were sold between 2000 and 2015, for each country in which those cars were sold.

The team used GEOS-Chem, a chemistry transport model that simulates the circulation of chemicals and particles through the atmosphere, to track where each manufacturer’s excess NO_x emissions traveled over time. They then overlaid a population map of the EU onto the atmospheric model to identify specific populations that were most at risk of exposure to the excess NO_x emissions.

Finally, the team consulted epidemiological work to relate various populations’ NO_x exposure to their estimated health risk. The researchers considered four main populations in these calculations: adults with ischemic heart disease, stroke, chronic obstructive pulmonary disease, and lung cancer.

Overall, they estimated that, each year, 2,700 people within these populations will lose at least a decade of their life due to exposure to excess NO_x emissions from passenger cars. They broke this number down by manufacturer and found a wide spread of health impact contributions.

Significant differences arise between manufacturers, with an average of 58 and 52 additional premature mortalities per million vehicles on the road attributed to Renault and GM cars, respectively, which corresponds to an average 33 and 36 premature mortalities per 10 billion vehicle-kilometers traveled (VKT). BMW and PSA vehicles show the lowest mean excess NO_x emissions, estimated to result in an additional 13 and 18 premature mortalities per million cars (or 4.6 and 9.6 premature mortalities per ten billion VKT) on average, respectively.

Overall, mean relative health impacts per VKT vary by a factor of 8 among manufacturers, while impacts by car vary by a factor of 4.5 between manufacturers. We note that if the vehicles from all manufacturers in a given Euro standard category emitted at the best-performing manufacturer’s level in the category, all other things being equal, approximately 1900 annual premature mortalities would be avoided.

—Chossière et al.

For each country, the team also compared the excess emissions that it produced itself, versus the number of premature deaths that its population incurred, and found virtually no relationship. That is, some countries, such as Poland and Switzerland, produced very little NO_x emissions and yet experienced a disproportionate number of premature deaths from excess emissions originating in other countries.

Barrett says this transboundary effect may be due to the nature of NO_x emissions. Unlike particulate matter which mostly settles out in the local area, NO_x is first emitted as a gas, which can be carried easily by the wind across thousands of kilometers, before reacting with ammonia to form particulates, a form of the chemical that can ultimately cause respiratory and cardiac problems.

There’s almost no correlation between who drives [diesel cars] and who incurs the health disbenefits, because the impacts are so diffuse through all of Europe.

—Steven Barrett

Resources

• Guillaume P. Chossière, Robert Malina, Florian Allroggen, Sebastian D. Eastham, Raymond L. Speth, Steven R.H. Barrett (2018) “Country- and manufacturer-level attribution of air quality impacts due to excess NOx emissions from diesel passenger vehicles in Europe,” Atmospheric Environment, Volume 189, Pages 89-97 doi: 10.1016/j.atmosenv.2018.06.047