Volkswagen seems to be bearing the brunt of the responsibility for the tests. And while VW admits to “unethical and repulsive” diesel emissions tests in 2014 on humans and monkeys, lets not forget that BMW and Daimler Mercedes were also involved in these same tests.

Joel Gunter, writing for BBC News:

The exact nature of the VW tests is not known, as their methodology and findings have not been made public, but two independent scientists who have conducted air pollution tests on human volunteers told the BBC that similar tests on humans are commonplace.

And

In typical emissions tests, participants spend up to two hours in a sealed environment chamber breathing diluted diesel fumes equivalent to the levels of air pollution in Beijing or Delhi.

They will usually spend about 90 minutes of that seated, and 30 minutes gently exercising on a stationary bike to keep up blood flow.

The same participants then return another day to complete the same process in clean air, for a control comparison. After both sessions, blood tests and other physical tests are carried out.