State-Variable and Representativeness Errors Conceal “Clean Diesel” Harm: Methodologically Fallacious ACES Research

In 2015 authors of four joint US-government and auto-and-oil-industry studies, ACES, claimed to have done the first comprehensive evaluation of lifetime exposure to new-technology-diesel exhaust (NTDE-2007), so-called “clean diesel” required by US emissions standards for year-2007 and later heavy-duty trucks. ACES claimed to have found no evidence that NTDE-2007 causes lung cancer. However, since at least 2012, the World Health Organization (WHO), International Agency for Research on Cancer, American Public Health Association, and many other scientists say any diesel exhaust, especially diesel particulate matter, causes lung-cancer, cardiovascular, and neurological problems. Who is right about diesel exhaust, ACES or WHO? This question is important both because the US and other governments cite ACES research in their diesel-exhaust standard-setting, and because the auto and oil industries use ACES conclusions to claim new diesel exhaust is virtually harmless. This article (1) begins the task of assessing the ACES-versus-WHO scientific debate. It (2) Argues that the ACES research is fatally flawed because it neither studies what it claims nor does so in an unbiased way. Instead the article (3) shows that ACES research (3.1) relies on state-variable biases (in focusing mainly on NO2 and mass, not also on DPM and particle size/number), and (3.2) exhibits representativeness errors (in using only the healthiest animals, too-small sample sizes, and non-lifetime exposures). Despite some ACES strengths, the article (4) concludes that because ACES fails to fully assess the worst NTDE-2007 harm and typical exposures to typical subjects, therefore it draws no valid conclusions about NTDE-2007 harm.