German automakers Volkswagen, BMW and Daimler backed studies that exposed humans and monkeys to exhaust fumes and nitrogen dioxide, the Washington Post reports. European Research Group on Environment and Health in the Transport Sector (EUGT), which conducted the studies in 2014, never published results.

Why it matters: Experiments reportedly forced monkeys to "inhale exhaust fumes from a Volkswagen Beetle car and an older pickup truck for several hours in an attempt to prove the Beetle’s clean emission standards." Human subjects "were asked to inhale nitrogen dioxide (NO2), a gas that is primarily emitted through traffic," according to the Post.