It’s been all over the news this week – Volkswagen have admitted to cheating emissions tests and have recalled millions of cars around the world. Exactly how they have achieved this remains unclear, but stock prices in the company have plummeted and its reputation may never recover from this scandal.
But what emissions have VW been illegally controlling, and what is there to worry about?
Well, this article on the Chemistry World website explains everything.
It would seem that VW have been using sophisticated software to control NOx emissions during testing – leading to up to 40 times more NOx being released outside of testing. NOx – nitrogen oxide and nitrogen dioxide – are extremely hazardous to health, and have been linked to many respiratory issues. It can also cause smog and ground-level ozone to be produced, further risking public health.
The production of nitrogen oxides is difficult to avoid – at the high temperatures found within car engines, nitrogen and oxygen in the atmosphere will inevitably react. They must instead by cleaned up post-combustion, which is achieved through the ‘lean NOx trap’, or selective catalytic reduction (SCL). The NOx trap involves using alkali earth oxides to convert the NOx emissions into nitrates, whilst SCL injects urea into the exhaust, which evaporates and reacts with the NOx gases in a zeolite catalyst to form nitrogen and water. Neither method is perfect, as the NOx trap continually uses fuel to keep itself clear, and SCL can fail when cars are stuck in traffic, as the exhaust temperature isn’t high enough for the required reactions to take place.
The unfortunate reality for car manufacturers is that lower NOx emissions generally means lower fuel economy, greater wear and tear on engine parts or higher cost for the consumer, all of which they want to avoid. There’s a real worry amongst experts and customers alike that this will lead to manufacturers building engines specifically to pass lab tests, which might not perform nearly as well on real road situations. This could prove catastrophic for the environment, and will diminish trust completely in the sector, and is unfortunately what appears to have happened in VW’s case.
Obviously, there’s a real need for improved technology in this area, so that the challenge of lowering NOx emissions whilst maintaining a high-quality car can be conquered once and for all.