The US Environmental Protection Agency has been fighting a controversial campaign against very fine airborne particulates called PM2.5s. Studies showed that they were linked to premature deaths, especially in vulnerable populations. One of the EPA's most powerful opponents has been the American Trucking Association, which does not want to see tough restrictions on PM2.5 emissions included in proposed Clean Air legislation.

An independent team of 31 scientists led by Professor Daniel Krewski carried our an exhaustive review of both the methodology and science of two key studies, and was also able to replicate their findings. According to the EPA’s John Bachmann, the agency now has a very powerful case for strict regulation.