We, the undersigned, are public health and medical professionals who call on you to protect our patients, our communities and our nation from ozone pollution by adopting the most protective national ambient air quality standard of 60 parts per billion (ppb).

The Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to set the primary national air quality standard to accurately reflect the state of the science and to protect the public health, including those most vulnerable to the effects of air pollution, with an adequate margin of safety.  There is a robust body of scientific evidence that supports the adoption of a more protective standard of 60 ppb.  Clearly, the evidence show that the current standard of 75 ppb does not protect the public health.

EPA’s panel of expert science advisors, the Clean Air Scientific Advisory Committee (CASAC), has reviewed the scientific evidence in the EPA Integrated Science Assessment, the Health Risk and Exposure Assessment and the Policy Assessment and has unanimously concluded that “there is clear scientific support for the need to revise the standard.” We also agree with CASAC’s unanimous expert opinion that at “70 ppb there is substantial scientific evidence of adverse effects,” and that adopting a standard of 60 parts per billion “would certainly offer more public health protection than the levels of 70 ppb or 65 ppb and would provide an adequate margin of safety.” (CASAC letter to Administrator McCarthy, dated June 26, 2014).

Controlled human exposure studies have repeatedly demonstrated that some healthy adults experienced reduced lung function and increased airway inflammation following exposures to concentrations of 60 ppb and below (Adams, 2002 and Adams, 2006 Brown et al., 2008 and Kim et al, 2011). The chamber studies establish the strongest evidence that concentrations above 60 ppb provide significant risk not only to many healthy adults, but most critically, to vulnerable and susceptible populations, including children, seniors and people with asthma and other chronic lung diseases.

Six large epidemiological studies in the U.S. and Canada provide further real-world evidence that a standard of either 70 ppb or 65 ppb fails to provide adequate protection, as recognized in the Policy Assessment. These studies (Bell et al., 2006; Cakmak et al., 2006; Dales et al., 2006; Katsouyanni et al., 2009, Stieb et al, 2009) reported positive and statistically significant associations from the most serious health threat—premature death—as well as from hospital admissions and emergency department visits.  In the majority of locations where increased risk was found, the ozone levels would have met the weaker standards of either 70 or 65 ppb, but would not meet a standard set at 60 ppb.

The combined evidence demonstrates that the EPA’s proposed range of 65 to 70 ppb would not provide adequate protection for the large at-risk populations, nor even for all healthy adults. EPA’s Integrated Science Assessment identifies children, the elderly, outdoor workers and people with asthma as more susceptible to ozone than the general population. However, EPA also identified research that indicated that others, including people with low socioeconomic status, may face increased risk.

The primary ozone standard is crucial to protecting the public health. The current ozone standard clearly puts far too many people at risk. Therefore, we urge you to adopt the most protective level for the ozone national ambient air quality standard of 60 parts per billion.