In 2010 Henry Miller and James Enstrom seriously wrote a piece in Forbes Magazine where they completely deny all scientific evidence of adverse health effects ultrafine diesel soot is causing.
So what's the deal: It must be the affiliation with the Hoover Institution, like many so called conservative and libertarian think tanks they just ignore scientific evidence. It's not just the cooked up Tea-Baggers who lack understanding, but quite often we see high profile people who just seem to live in a bubble.
Henry Miller, a physician and molecular biologist, is a fellow at Stanford University's Hoover Institution. James Enstrom is an epidemiologist and physicist at the UCLA Jonsson Comprehensive Cancer Center.
http://www.forbes.com/2010/06/08/california-diesel-regulation-pollution-opinions-columnists-henry-i-miller-james-e-enstrom_2.html
PS. As indicated in the comment below, Engstrom has taken money from Philip Morris in the past, which somehow underlines his credentials...