Even Clean Diesel Exhaust Has Health Risks: MIT Study

Even Clean Diesel Exhaust Has Health Risks: MIT Study

Diesel’s several charms are being outweighed by continuing bad news about the apparent health of effects of emissions from diesel engine vehicles. The latest potential diesel backbreaker is a study out of Europe that shows 10 automakers built diesel cars through 2015 that emitted up to 16 times the pollution on highways, in real-world daily driving, as in test labs that were supposed to replicate daily conditions. But the dirty diesels don’t violate any current European Union laws because the laws focus on lab tests.

There was a big variation in pollution output among the diesel makers selling in Europe. Toyota, Hyundai, and BMW “were associated with fewer early deaths” from NOX emissions. The study says 2,700 people each year will have their lives shortened by at least a decade because of the extra pollutants.

BMW diesels have a lesser impact. But still, an impact, the study says. Here, a BMW 335d that can go New York City to Miami on two tanks of fuel.
BMW diesels have a lesser impact. But still, an impact, the study says. Here, a BMW 335d that can go New York City to Miami on two tanks of fuel.

“There’s No Safe Level” of NOX Pollutants (Except Zero)

This study focused on nitrogen oxide (NOX) emissions. The gas is part of diesel exhaust. Combine it with ammonia in the air and tiny particles are formed that — like diesel vehicles — are capable of traveling long distances. Inhaled, the particles may lodge in the lungs and may cause asthma, respiratory disease, and pulmonary and cardiac conditions. NOX emissions also contribute heavily to smog, which has bad connotations for the health of mammals. (This specific study did not look at diesel soot particles, typically formed from incomplete combustion.)

“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,” says Steven Barrett, a professor of aeronautics and astronautics at MIT and the study’s lead author. The study is in the current issue of Atmospheric Environment (paywall) and summarized in MIT News.

Researchers found a transboundary effect to NOX pollution, meaning the potential victims of excessive NOX pollution included people from areas outside where the bulk of NOX emissions emanated. Poland and Switzerland emit few NOX emissions but have a disproportionate amount of premature deaths, the research found:

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 percent 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 NOx emissions on the road than in lab tests. …

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 NOx emissions from passenger cars. They broke this number down by manufacturer and found a wide spread of health impact contributions: Volkswagen, Renault, and General Motors produced diesel cars associated with the most yearly premature deaths, each numbering in the hundreds, while Toyota, Hyundai, and BMW were associated with fewer early deaths.

“The variation across manufacturers was more than a factor of five, which was much bigger than we expected,” Barrett says.

Diesel carries a price premium but also packs in 10% more BTUs than gasoline.
Diesel carries a price premium but also packs in 10% more BTUs than gasoline.

Is There Any Good News About Diesel?

Diesel continues to be better at reducing carbon dioxide emissions, which is the scientist way of saying diesel cars get better fuel economy. Carbon dioxide is a byproduct of combustion and is produced in direct proportion to how much fuel is burned. Because of its economy, you go longer between fill-ups. Diesel vehicles with 20-gallon tanks can get 600 to 800 miles of highway driving. They routinely beat the EPA’s highway economy estimates in US testing.

Barrett, the study’s author, says cleaner diesel may not be the answer: “The solution is to eliminate NOx altogether,” he says in the MIT News report. “We know there are human health impacts right down to pre-industrial levels, so there’s no safe level. At this point in time, it’s not that we have to go back to [gasoline]. It’s more that electrification is the answer, and ultimately we do have to have zero emissions in cities.”

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