When Volkswagen’s diesel scandal broke in 2015, much was made of how the cars spewed the pollutant nitrogen oxide (NO x ) in dramatic excess of regulators’ standards during real-world driving. But that wasn’t what ultimately got VW Group in trouble with officials from the US Environmental Protection Agency (EPA) and European Union regulators. The key problem was that diesel VWs, Audis, and even Porsches included undisclosed “defeat devices,” or lines of code in the car’s software, that regulators didn’t know about. This code permitted the diesel cars to run cleaner in a lab than on the road.

In most cases, regulators know that vehicles will run dirtier during some real-world driving conditions than they do during the lab tests. They also know that lab tests are designed narrowly enough that automakers can exploit them. US regulators don't uniformly test emissions under real-world conditions (although the EPA conducted a review of diesel vehicles after the VW Group scandal).

A new study published in Nature has now calculated the effect of lax practices in regulation and come up with a body count—38,000 people around the world prematurely died in 2015 as a result of excess particulate matter (including NO x ) and ozone emissions from diesel vehicles.

Real-world consequences

In the US, federal emissions testing of light-duty vehicles (including passenger cars and some small commercial trucks) includes a 31-minute test in which an engine is hooked up to a dynamometer in a lab. The test administrators study tailpipe emissions from a cold start, then while the car is running, and finally after a hot start. There's room for an automaker to pass such a test without using secret software to turn on and off its emissions control system, as Volkswagen did.

In 2015, Ars spoke to a researcher from the University of Colorado Denver about the emissions compliance test. He noted that the testing conditions are well known to auto manufacturers before the day of the test, and manufacturers will even go so far as to hire drivers who can “drive” the car most efficiently while it’s hooked up to lab equipment to produce the lowest emissions possible. Since the amount of emissions a car gives off can be variable, regulators know that many diesels that pass the extremely narrow requirements of the EPA lab test will produce emissions in excess of what’s allowed while a real-world driver is, say, chugging up a steep hill or driving in cold temperatures.

The lax emissions tests aren't unique to the US: the authors of the Nature paper looked at 11 major vehicle markets including the US, the 28 European Union member states, Australia, Brazil, Canada, China, India, Japan, Mexico, Russia, and South Korea. Together, those regions represent 80 percent of the market for diesel vehicles. By tracking historical data on heavy-duty and light-duty diesel vehicle sales around the world, the authors were able to create “emission inventories.” They compared that data with emission data from more than 30 studies based on modeling and real-world testing of cars in the US, Europe, China, and Japan.

The authors found that “nearly one-third of on-road heavy-duty diesel vehicle emissions and over half of on-road light-duty diesel vehicle emissions are in excess of certification limits.”

Similar studies have been done to quantify the effects of the Volkswagen scandal in the US alone. In an October 2015 paper in Environmental Research Letters, researchers determined that the extra emissions from the nearly 500,000 diesel VWs and Audis sold in the US would cause about 60 premature deaths.

This recent study is larger in scope: it addresses a greater fraction of the estimated 4.4 million premature deaths from air pollution that occurred in 2015.

Luckily, there’s a way to prevent more premature deaths, and it means putting in place emissions regulations that have already been promulgated by the US and the EU. In the years since Volkswagen was caught flagrantly cheating to meet the bare minimum testing requirement, regulators have moved to make emissions testing more stringent. As of this year, EU regulators will require that vehicles meet certain emissions compliance levels during real-world driving tests.

“Adopting and enforcing next-generation standards... could nearly eliminate real-world diesel related NO x emissions in these markets,” the researchers wrote, adding that by 2040, the more stringent standards could help avoid about 174,000 deaths worldwide.

Critics might argue that if automakers can’t meet emissions standards without cutting corners now, they may not be able do it when the standards are even tighter. But the authors noted that recent tests showed “real-world NO x emissions in line with certification limits are technically achievable.”

Nature, 2017. DOI: doi:10.1038/nature22086 (About DOIs).