Document ID: EPA-HQ-OAR-2007-1145-0055
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2008-11-24T05:00Z

November 10, 2008

N3615 (2350)

Docket No. EPA-HQ-OAR-2007-1145

U.S. Environmental Protection Agency

Mail code 2822T

1200 Pennsylvania Ave., N.W.

Washington, D.C.    20460

Dear Sir/Madam:

These comments are submitted on behalf of the National Park Service
(NPS) in response to the U.S. Environmental Protection Agency’s (EPA)
August 29, 2008, Federal Register Notice for review and comment of the
Draft Risk and Exposure Assessment (REA) Report for Review of the
Secondary National Ambient Air Quality Standards (NAAQS) for Oxides of
Nitrogen and Oxides of Sulfur.  These comments reinforce and supplement
comments submitted by NPS at the October 1-2, 2008, Clean Air Scientific
Advisory Committee (CASAC) Review Panel’s meeting in Research Triangle
Park, NC, and reflect our general support for EPA’s approach to
setting secondary standards for oxides of sulfur and nitrogen.

The NPS manages over 388 areas covering more than 84 million acres
including many of the most unique and beautiful ecosystems in our
country.  National parks represent a legacy from Americans today to
generations of Americans yet to come.  As a nation, we have promised to
leave these extraordinary places of discovery and power in a condition
that is unimpaired so that they will continue to serve the needs of
society to connect to authentic places for their educational,
recreational, spiritual, and restorative values.   Yet in many parks,
stresses from outside park boundaries have degraded resources. 
Deposition of air pollutants has acidified streams, reduced
biodiversity, and altered nutrient cycling in soils.  Some streams in
Shenandoah and Great Smoky Mountains National Parks are acidified and
brook trout populations have been lost.  Throughout the National Park
System, ecosystems are experiencing changes ranging from subtle to the
extreme as a result of pollutant deposition.  Alpine lakes and meadows
in Rocky Mountain National Park, a park most people would consider
pristine, are being significantly altered by nitrogen deposition.  These
effects are occurring despite the fact that these parks are attaining
the Secondary NAAQS for nitrogen oxides (NOx) and sulfur oxides (SOx),
standards established to protect public welfare.  As the Risk and
Exposure Assessment details, these harmful effects extend well beyond
national parks, including many sensitive ecosystems across the country. 
Current standards are clearly not providing the requisite level of
protection required by the Clean Air Act.  For this reason, we are
supportive of EPA’s effort to develop a secondary standard that is
linked to ecological response.

The approach EPA is now proposing is innovative as it suggests
expressing the secondary standard in terms of ecological indicators and
endpoints linked to atmospheric concentrations.  Secondary standards
based strictly on atmospheric concentrations of NOx and SOx have failed
because there are no direct links between concentrations of these
pollutants and ecosystem responses.  Rather, it is the amount of
nitrogen and sulfur compounds deposited into an ecosystem that affects
response.  The scientific literature has clearly defined relationships
between deposition and many types of ecosystem responses.  Ecosystem
models are routinely used to predict the amount of deposition that will
result in a given effect.  EPA has relied on this extensive knowledge
base to develop a well-reasoned conceptual model of the possible
structure of a secondary standard based on an ecological indicator’s
response to deposition.  The model illustrates the relationship between
an ecosystem indicator, atmospheric and ecological variables,
deposition, and atmospheric concentrations of nitrogen and sulfur
compounds.   In this model, the secondary standard would be based on a
“standard level” established to protect an ecological indicator. 
For example, for acid-neutralizing capacity, or ANC, a standard level of
100 microequivalents per liter would protect most streams and lakes from
acidification.  Ecosystem models can predict the amount of deposition
that would maintain this ANC in an area, given bedrock and watershed
characteristics, while atmospheric models can predict the concentrations
of NOx and SOx that would result in that amount of deposition for a
selected area.   This approach provides a uniform level of protection to
ecosystems while recognizing that deposition, meteorology, and other
factors vary across regions, providing flexibility in implementation.  

The National Park Service believes this approach to be reasonable and
soundly based on ecosystem science, and in accord with the intent of the
Clean Air Act to protect public welfare.  EPA has indicated that, in the
next draft of the REA, ecological indicators for terrestrial
acidification and nutrient nitrogen enrichment of aquatic and
terrestrial ecosystems will be examined.  We believe that this is
essential.  ANC is a very useful indicator for aquatic acidification,
and setting a reasonable standard level of ANC, such as the 100
microequivalents per liter noted above, would protect most streams and
lakes from acidification.  However, in some areas of the country,
notably the Rocky Mountain region, lakes and streams are affected by
nitrogen nutrient enrichment long before acidification effects are seen.
 For example, in Rocky Mountain National Park, modeling predicted that
high elevation aquatic ecosystems would experience episodic
acidification at a total nitrogen deposition level of 6.6 kilograms per
hectare per year; aquatic ecosystem eutrophication in the same areas
occurs at nitrogen levels as low as 1.5 kilograms per hectare per year
(wet deposition).  Other areas in the Rocky Mountains appear to have
similar responses to very low levels of nitrogen.  In these areas, an
indicator related to enrichment is far more meaningful than ANC, the
indicator for acidification, as a standard based solely on ANC would be
relatively useless for protection of these areas.  We strongly encourage
EPA to consider this as they evaluate appropriate indicators and further
develop this conceptual model for ecological standards.  

 

Finally, because the standards for SOx and NOx will be tied to an
ecological endpoint(s), EPA recognizes that they could allow for varying
SOx and NOx concentrations nationally, given the spatial variability in
environmental and biological factors that drive ecological response.  
As mentioned previously, we believe that this type of approach is
necessary in order to protect ecosystems that have been or will be
damaged at current levels of pollution.  We realize that this innovative
approach to standard setting will also require an innovative approach to
demonstrating and achieving NAAQS compliance relative to traditional
attainment/nonattainment designations.  Recognizing that the process is
still underway, we suggest that EPA also consider regional approaches or
initiatives aimed at attaining the standard as they further develop the
conceptual model. Current examples of collaborative regional or
multistate initiatives that target a specific air quality issue include
the Ozone Transport Commission and the Regional Planning Organizations
developed under the Regional Haze Rule.    

If you have any questions, please contact me at (303) 969-2074.

Sincerely,

Christine L. Shaver

Chief, Air Resources Division

bcc:

WASO: Julie Thomas McNamee

ARD-DEN: John Bunyak, Policy, Planning, and Permit Review Branch

                     John Vimont, Research and Monitoring Branch

ARD-DEN:EPorter:ep:11/10/08:x2617:EPA REA NOxSOx.Ltr.Doc

 Hartman, M.; Baron, J. S.; Ojima, D. S.; Parton, W. J. (2005) Modeling
the timeline for surfacewater acidification from excess nitrogen
deposition for Rocky Mountain National Park [abstract]. In: Abstracts of
the George Wright Society biennial conference on parks, protected areas,
and cultural sites; March; Philadelphia, PA.

 Baron, J. S. (2006) Hindcasting nitrogen deposition to determine
ecological critical load. Ecol Appl. 16: 433-439.

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