and depend upon the type and age of
the vehicle. In Europe, the newest
diesel cars are subject to the Euro 6
emissions standard, which was introduced
in 2015 and allows just 80 milligrams of
NOx to be emitted per kilometre driven.
That’s substantially less than the previous
Euro 5 standard, which permitted 180
milligrams per kilometre.
Unfortunately, the laws of physics
mean that the temperatures and
pressures at which a diesel engine runs
most efficiently and delivers the most
energy also happens to be the conditions
that convert the maximum amount of
oxygen and nitrogen into NOx. That
means that building one is a trade-off
between power, fuel efficiency and clean
emissions. To sell more of their cars,
manufacturers like to boost the first
two, but to be allowed to sell cars they
have to allow for the third.CLEAN IT UP
Catalytic converters only work in petrol
cars, but there are similar technologies
available for diesel. Mercedes-Benz cars
inject a f luid called urea that converts
NOx into less harmful substances, but
the tank of f luid has to be periodically
refilled. Volkswagen instead invested in
a sponge-like technology that soaks up
the polluting gases – details on how it
works are sketchy, but it’s thought that
PHOTO: GETTY X3, ALAMYwhen activated this filter lowers engineVolkswagen cars emitted lower NOx levels during tests, then went back to belching out higher amounts when the test was overperformance. That, it seems, may be
why the company decided to cheat.
It is, however, relatively simple to fix
the cars. A software update is all that’s
needed, which reactivates the filter.
Volkswagen says that about 11 million
cars worldwide, including 8.5 million in
Europe, are affected and must be
recalled to apply the fix. Making things
right is costing the company about
US$5.3bn, and that’s before fines from
regulators and legal action are taken into
account. Unsurprisingly, the company’s
shares have fallen by almost a third since
the news broke.“SINCE 2011 WE’VE BEEN
PUBLISHING RESULTS
SHOWING THAT DIESEL CARS IN
REAL DRIVING WERE EMITTING
HIGH AMOUNTS OF NITROGEN
OXIDES”The news that Volkswagen had been
cheating in the tests didn’t come as a
surprise to Dr James Tate, a lecturer at
the Institute for Transport Studies at the
University of Leeds. For years, he’s
been collecting data on theSCIENCE