THE ADMINISTRATOR OF THE ENVIRONMENTAL PROTECTION AGENCY 

The Honorable Darrell O'Neal Sr. 

Chairman ofNorthem Arapaho Tribe 

P.O. Box 396 

Ft. Washakie, Wyoming 82514 

Dear Chairman O'Neal: 

WASHINGTON, D.C. 20460 

\:DEC l S 2014 

I would like to summarize the U.S. Environmental Protection Agency's recent action to address fineparticle pollution on your reservation. As required by the Clean Air Act, the EPA has determined which 

areas are meeting the national ambient-air-quality standards for fine-particle pollution and which areas 

must take steps to reduce emissions that contribute to violations of the standard. 

The EPA on December 14, 2012, strengthened the annual, health-based fine-particle standard from 15.0 

micrograms per cubic meter (j.!g/m3

) to 12.0 jlg/m3. Thousands of scientific studies have linked exposure 

to these tiny particles- approximately 1/30th the size of a human hair - with serious health problems 

including premature death in people with heart and lung disease, nonfatal heart attacks and increased 

hospital admissions and doctor and emergency-room visits for respiratory and cardiovascular disease. 

I appreciate the information you and your staff have shared with the EPA throughout this process to 

assess fine-particle-pollution levels in communities across your reservation and the impact of emission 

sources that could be contributing to unhealthy air. After considering your recommendations, reviewing 

the most recent certified fine-particle air-quality data for your reservation and evaluating factors to 

assess contribution to nearby levels of fine-particle pollution, I have determined that no area within the 

Northern Arapaho Tribe reservation violates the 2012 standard or contributes to a nearby violation ofthe 

standard. As a result, the EPA is designating all of the Northern Arapaho Tribe reservation 

"unclassifiable/attainment." 

Because air-quality monitoring for 2014 is nearly complete, the EPA, at a tribe's request, will evaluate 

the status of an area based on its annual fine-particle-monitoring data for 2012-14. lfyou would like the 

EPA to re-evaluate any areas within your reservation, please submit complete, quality-assured and 

certified air-quality data for 2014 to the EPA by February 27, 2015. 

I recognize that the EPA shares responsibility with the states and tribes for managing particle-pollution 

levels. Efforts by states and tribes to attain the 1997 and 2006 fine-particle-pollution standards are 

already working to reduce unhealthy levels of fine-particle pollution. In addition, current and upcoming 

federal standards and safeguards, including pollution-reduction rules for power plants, vehicles and fuels 

will ensure steady reductions of fine-particle pollution and will protect public health in communities 

across the nation. 

This paper is printed with vegetable-oil-based inks and is 100-percent postconsumer recycled material chlorine-free-processed and recyclable. 
Together we have made considerable progress in reducing fine-particle pollution. Nationwide monitored 

levels of fine-particle pollution have fallen 34 percent since 2000 when we first began such monitoring 

for particles of this size. I am confident this progress will continue as we work toward our shared goal of 

clean air. 

For additional information about these designations, please visit www.epa.gov/pmdesignations. 

Sincerely,