

The fallout from VW’s emissions scandal continues to cloud the future of so-called “clean diesel” technology in the United States, and the EPA has announced that as a result, it’s going to significantly bolster its emission testing. Specifically, the EPA is going to sweep the industry for so-called “defeat devices,” in partnership with the California Environmental Protection Agency and Canada’s own regulatory bodies. All manufacturers are required to submit vehicles for inspection, and the EPA notes that “Manufacturers should expect that this additional testing may add time to the confirmatory test process.”

One of the criticisms of environmental regulation testing leveled in both the US and Europe is that car manufacturers have long enjoyed a cozy relationship with the agencies that are expected to monitor them for appropriate compliance. The EPA appears to have been stung by these statements and is refusing to disclose exactly what kinds of tests it will be running in its search for defeat devices. We can guess, however, that it’s going to begin by focusing on other so-called “clean diesel” vehicles in the current fleets of other automakers. Whether it’ll be running additional tests on previous models of cars sold in the United States by automakers other than VW is still unknown; there’s evidence to suggest that VW isn’t the only company that’s been cheating on its test scores.

Clean diesel regulation

I’ve seen some questions raised about what the so-called clean diesel standards accomplish and a few commenters arguing that this type of regulation represents government overreach. It’s useful, I think, to revisit the question of what’s being regulated and why. While cars do emit carbon dioxide, CO2 emissions in cars isn’t what’s being discussed here. While the auto industry likes to claim that diesels produce less CO2 than gasoline vehicles, real-world studies have shown that the two are quite close in reality. Diesel vehicles have higher fuel efficiency that gasoline-powered cars, but a standard diesel engine produces far more particulates than a gasoline equivalent.

The problem with diesel engines is that they emit much more particulate matter than conventional gasoline cars. While heavy diesel engines are also regulated today, many of you probably recall driving behind heavy diesel vehicles like garbage trucks that emitted a literal cloud of brown-black exhaust every time they moved at a stoplight. That exhaust was full of soot, nitrogen oxide, and nitrogen dioxide (NO2 and NOx, respectively).

Both pollutants have been shown to cause lung inflammation, increased asthma, bronchitis, and may have negative impacts on fetal development. The high sulfur compounds in diesel fuel also contributed to acid rain, which is one reason why ultra-low sulfur diesel fuel has become much more popular in both the US and Europe.

Diesel emissions

The graph above shows NO2 levels across major European cities, where diesel cars generally outnumber gasoline. Air pollution is estimated to cause 400,000 premature deaths in Europe per year, and the primary source of that pollution is diesel fuel burned in vehicles.


The long and short of it is this: regulating the pollutants in diesel and gasoline fuels isn’t just about protecting the environment, but about protecting human health. The environmental standards implemented on both sides of the pond weren’t some immediate mandate that blindsided VW or other auto manufacturers — they were phased in gradually over a period of time, as the chart above shows.

Unfortunately, in Europe at least, the diesel industry as a whole hasn’t been meeting its own health standards. Tests performed by the ICCT and published by the BBC before the VW scandal even broke show that diesel vehicles in the EU were emitting far more particulate matter and NO2 than allowed by law.


This ongoing problem is why the ICCT commissioned the initial test study of US vehicles in the first place. The assumption was that vehicles that weren’t meeting Europe’s less-stringent standards, but passing the Tier2/Bin5 rate set by the California Air Resources Board must include additional technologies or adaptations that allowed them to do so. The idea that these vehicles weren’t passing in either country wasn’t considered. Now, it will be, and the solutions to the problem aren’t going to please a lot of VW owners.

That’s unfortunate, but it’s also a matter of public health. Vehicle exhaust isn’t a collection of unicorn farts and fairy dust that brings peace and love to anyone who encounters it. Regulating pollutants is a critical part of preventing damage to both human health and the wider environment. If automakers can’t build diesel vehicles that meet regulatory standards, it may mean that the regulations need to be redrawn — but emitting 20-40x more pollution than the law allows is not acceptable, either. In some cases, the diesel vehicles under inspection are failing to meet air quality standards from 30-40 years ago — and there’s simply no excuse for that.