Volkswagen's shocking admission that they designed software to cheat EPA emissions tests, and thereby emit 15-35 times as much poisonous nitrogen oxides (NOx) as is legally allowed (and very possibly killing thousands of people), is by now well known. But how is this technology supposed to work?
Professor Martyn Poliakoff explains below. The problem with NOx formed during diesel combustion is that they are free radicals, meaning they each have an unpaired electron. This makes them extremely reactive — so if you breathe them in, they'll tear up your lungs (and in the open air, form smog and particulates). But that suggests a solution: get something to react with the NOx before it reaches the atmosphere. One low-emissions diesel engine design does just that, with a tank of urea — inject it into the exhaust stream, and the NOx is reduced to nitrogen, water, and carbon dioxide. It works great, but it reduces the efficiency of the engine, which is likely why VW cheated. Watch the full explanation below. Ryan Cooper
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