National Parks Conservation Association Logo

 June 29, 2020 

Andrew Wheeler, Administrator
Environmental Protection Agency
1200 Pennsylvania Avenue NW
Washington, D.C. 20460 

Submitted via

RE: Secondary National Ambient Air Quality Standards for Particulate Matter; Proposed Rule; Docket No. EPA-HQ-OAR-2015-0072 

Dear Administrator Wheeler,

We, the undersigned public lands and conservation organizations, strongly oppose the proposal to retain the current, inadequate secondary National Ambient Air Quality Standard for Particulate Matter and respectfully urge the agency to revise the proposal considering the decade of science it has ignored and propose a new rule in a new comment period to protect the public welfare.

The National Ambient Standards are fundamental public health and ecosystem safeguards – and fine particulate matter, PM2.5, is one of the most dangerous of our criteria pollutants, with no real known safe level of exposure for humans. In addition to fine particulate matter being a lethal air pollutant for humans to breathe, it is a primary driver of haze, or visibility impairment, while also negatively affecting many other ecosystem functions.

The Clean Air Act provides that welfare effects include impacts on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, visibility and climate. Effects also include damage to and deterioration of property and hazards to transportation, as well as effects on economic values and on personal comfort and well-being, whether caused by transformation, conversion, or combination with other air pollutants.

While the secondary National Ambient Air Quality Standards for PM2.5 ought to be independently and adequately evaluated and regulated, the Environmental Protection Agency (EPA) has failed to do so. The EPA must thoroughly review all recent science pertaining to the effects of fine particle pollution on the public welfare and consider and respond to all evidence submitted for the secondary standards. Indeed, all current Clean Air Scientific Advisory Committee (CASAC) members who offered comments on secondary standards specifically recommended that added expertise on PM welfare effects was needed.

PM2.5 is made of many different compounds which are all independently harmful to ecosystems and PM2.5 can be directly deposited on land and in the water, causing damage from acidification, eutrophication, and changes in soil and water chemistry. When deposited on plants, it can affect their ability to metabolize and photosynthesize correctly. Fine particulate matter is also a major cause of reduced visibility, or haze, in urban, rural and wilderness areas. Haze is one of the most visible manifestations of this air pollution.

Fine particles entering aquatic ecosystems can affect all organisms both directly and through bioaccumulation. Similar to mercury, PM2.5 can be absorbed by fish, frogs, snails, and other aquatic life, as these animals are consumed and the particulate matter travels up the food chain, increasing in concentration with each step up, ultimately to fish-eating predators including eagles, osprey, otters, pelicans, and grizzly bears. Those concentrations of PM2.5 have harmful health effects on our wildlife.

Nitrogen and sulfur gases emitted into the atmosphere can become particulate matter through a chemical transformation and when dissolved in water, become acid rain, creating devastating effects on our ecosystems, particularly in the eastern U.S. and in the Rocky Mountains at high elevations where ecosystems are more fragile. There are numerous negative ecosystem effects of acid deposition like depletion of soil nutrients, aluminum mobilization, and acidification in waters that lead to accelerated plant die-off, slower plant growth and damage to leaves and overall decreases in species diversity.

The EPA’s proposal to retain the current standard and 24-hour averaging time is not adequate for protecting the public welfare. In addition to revisiting the level itself, EPA must also reconsider the averaging times. For example, people do not perceive visibility impairment over a 24-hour period. When the public goes to a national park, wilderness area or other outdoor landscape, their experience can be as short as a 15-minute visit to a scenic vista to a multi-day stay at an urban park or mountain destination. Haze conditions can change over just a few hours. Therefore, EPA must select an averaging time that corresponds with its mandate to protect the public welfare.

The collective effects of fine particulate matter on our ecosystems and visibility are extensive and deeply problematic for the health and enjoyment of our national parks, our public lands and all of America’s wild places – places that bring enormous economic benefits to surrounding communities and behold values of our democracy in safeguarding our natural, cultural and historic heritage.

We urge EPA to revise its proposal for the secondary PM2.5 standard to reflect the science and base the standard on averaging times that are consistent with the Clean Air Act’s welfare requirements and then and reopen the comment period. The secondary standard must protect all aspects of public welfare from known or anticipated adverse effects from PM2.5. We thank you for your attention to and consideration of this critical matter.


Appalachian Mountain Club
Audubon Society of New Hampshire
Center for Biological Diversity
Chesapeake Bay Foundation
Coalition to Protect America’s National Parks
Evangelical Environmental Network
Great Old Broads for Wilderness
Minnesota Center for Environmental Advocacy
National Parks Conservation Association
Natural Resources Defense Council
Northeastern Minnesotans for Wilderness
The Lands Council
Utah Physicians for a Healthy Environment
Sierra Club
Southern Environmental Law Center
Western Watersheds Project
WildEarth Guardians
Wild Arizona
Young Evangelicals for Climate Action