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This photo shows how researchers caught VW cheating on its emissions tests

Revelations that as many as 11 million Volkswagen cars have been cheating on their emissions tests have become big news this week. But the research that demonstrated that VW's diesel vehicles were generating excessive pollution has been publicly available for more than a year — ever since a team at West Virginia University published their findings in the spring of 2014.

Volkswagen reportedly programmed its vehicles to behave differently during emissions testing than in real-world driving conditions. To detect this, the West Virginia researchers developed a method for measuring a vehicle's emissions performance as it drove down the highway. Here's what it looked like:

(University of West Virginia)

This equipment rode around in the back of the vehicles they were testing, collecting gas from the exhaust pipe and analyzing it. The gear included an onboard generator, to make sure that the power demands of the testing equipment didn't change the performance of the engine.

Then they drove the vehicles up and down the West Coast, testing their performance in a variety of real-world driving conditions, from city streets to mountain roads. They found that one of the vehicles they tested (we now know it was a VW Jetta) was emitting 15 to 35 times the legal limit of nitrogen oxides, while another (a VW Passat) was emitting five to 20 times the limit.

At this point, the researchers didn't know why the cars were emitting so much pollution. But when they presented their results at a 2014 conference in San Diego, there were EPA officials in the audience. They picked up the investigation from there and eventually forced Volkswagen to admit that they had programmed the vehicles to cheat on emissions tests.