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> **UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON D.C. 20460**

> **OFFICE OF THE ADMINISTRATOR**
>
> **SCIENCE ADVISORY BOARD**

November 29, 2007

EPA-CASAC-08-003

Honorable Stephen L. Johnson

Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, NW

Washington, DC 20460

> Subject: Clean Air Scientific Advisory Committee's (CASAC) NO~X~ &
> SO~X~ Secondary NAAQS Review Panel's Consultation on EPA's *Draft Plan
> for Review of the Secondary NAAQS for Nitrogen Dioxide and Sulfur
> Dioxide* (September 2007 Draft)

Dear Administrator Johnson:

The Clean Air Scientific Advisory Committee (CASAC) NO~X~ & SO~X~
Secondary NAAQS Review Panel met on October 30, 2007 and has completed
its consultative review of EPA's *Draft Plan for Review of the Secondary
NAAQS for Nitrogen Dioxide and Sulfur Dioxide* (September 2007 Draft). A
consultation is conducted under the normal requirements of the Federal
Advisory Committee Act, which include advance notice of the public
meeting in the Federal Register. The CASAC uses a consultation as a
mechanism for individual technical experts to provide comments on the
Agency's draft plan for developing technical assessments as the basis of
the review of the secondary NAAQS review for NO~X~ and SO~X~. Written
comments provided by the individual Panelists are attached to this
letter. As this is a consultation, we do not expect a formal response
from the Agency.

We thank the Agency for the opportunity to provide advice early in the
NAAQS review process, and look forward to the review of the draft
Integrated Science Assessment in March 2008.

> Sincerely,
>
> /Signed/
>
> Armistead (Ted) Russell, Ph.D.
>
> Chair, CASAC NO~X~ & SO~X~ Secondary Review Panel

**Attachments**

Attachment A: Roster of CASAC NO~x~ & SO~x~ Secondary NAAQS Review Panel

Attachment B: Compilation of Individual Panel Member Comments on EPA's
*Draft Plan for Review*

*of the Secondary NAAQS for Nitrogen Dioxide and Sulfur Dioxide*
(September 2007 Draft)

Attachment A: Roster of CASAC NO~x~ & SO~x~ Secondary NAAQS Review Panel

**U.S. Environmental Protection Agency**

**Clean Air Scientific Advisory Committee**

**NO~x~ & SO~x~ Secondary NAAQS Review Panel**

**CASAC MEMBERS**

**Dr. Armistead (Ted) Russell** *(Chair)*, Professor, Department of
Civil and Environmental Engineering, Georgia Institute of Technology,
Atlanta, GA

**Dr. Ellis B. Cowling**, Emeritus Professor, Colleges of Natural
Resources and Agriculture and Life Sciences, North Carolina State
University, Raleigh, NC

**Dr. Douglas Crawford-Brown**, Professor and Director, Department of
Environmental Sciences and Engineering, Carolina Environmental Program,
University of North Carolina at Chapel Hill, Chapel Hill, NC

**Dr. Donna Kenski,** Director, Lake Michigan Air Directors Consortium,
Rosemont, IL

**PANEL MEMBERS**

**Dr. Praveen Amar**, Director, Science and Policy, NESCAUM, Boston, MA

**Dr. Andrzej Bytnerowicz**, Senior Scientist, Pacific Southwest
Research Station, USDA Forest Service, Riverside, CA

**Ms. Lauraine Chestnut**, Managing Economist, Stratus Consulting Inc.,
Boulder, CO

**Dr. Charles T. Driscoll, Jr.**, Professor, Environmental Systems
Engineering, College of Engineering and Computer Science, Syracuse
University, Syracuse, NY

**Dr. Paul J. Hanson**, Distinguished R&D Staff Member, Environmental
Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN

**Dr. Rudolf Husar**, Professor and Director, Mechanical Engineering,
Engineering and Applied Science, Center for Air Pollution Impact & Trend
Analysis (CAPITA), Washington University, St. Louis, MO

**Dr. Dale Johnson**, Professor, Department of Environmental and
Resource Sciences, College of Agriculture, University of Nevada, Reno,
NV

**Dr. Naresh Kumar**, Senior Program Manager, Environment Division,
Electric Power Research Institute, Palo Alto, CA

**Dr. Myron Mitchell**, Distinguished Professor and Director, College of
Environmental and Forestry, Council on Hydrologic Systems Science, State
University of New York, Syracuse, NY

**Mr. Richard L. Poirot**, Environmental Analyst, Air Pollution Control
Division, Department of Environmental Conservation, Vermont Agency of
Natural Resources, Waterbury, VT

**Mr. David J. Shaw**, Director, Division of Air Resources, New York
State Department of Environmental Conservation, Albany, NY

**Dr. Kathleen Weathers**, Senior Scientist, Institute of Ecosystem
Studies, Millbrook, NY

**SCIENCE ADVISORY BOARD STAFF**

**Ms. Kyndall Barry**, Designated Federal Officer, 1200 Pennsylvania
Avenue, NW

1400F, Washington, DC, Phone: 202-343-9868, Fax: 202-233-0643,
(barry.kyndall@epa.gov)

Attachment B: Compilation of Individual Panel Member Comments on EPA's
*Draft Plan for Review of the Secondary NAAQS for Nitrogen Dioxide and
Sulfur Dioxide* (September 2007 Draft)

[]{.mark}

Comments from CASAC NO~X~ & SO~X~ Secondary NAAQS Review Panel on EPA's

*Draft Plan for Review of the Secondary NAAQS for Nitrogen Dioxide and
Sulfur Dioxide* (September 2007 Draft)

[Comments from Dr. Praveen Amar 4](#__RefHeading___Toc182377117)

[Comments from Dr. Andrzej Bytnerowicz 6](#__RefHeading___Toc182377118)

[Comments from Ms. Lauraine Chestnut 9](#__RefHeading___Toc182377119)

[Comments from Dr. Ellis Cowling 11](#__RefHeading___Toc182377120)

[Comments from Dr. Douglas Crawford Brown
21](#__RefHeading___Toc182377121)

[Comments from Dr. Charles Driscoll 23](#__RefHeading___Toc182377122)

[Comments from Dr. Paul Hanson 25](#__RefHeading___Toc182377123)

[Comments from Dr. Rudolf Husar 27](#__RefHeading___Toc182377124)

[Comments from Dr. Dale Johnson 28](#__RefHeading___Toc182377125)

[Comments from Dr. Donna Kenski 32](#__RefHeading___Toc182377126)

[Comments from Dr. Myron Mitchell 36](#__RefHeading___Toc182377127)

[Comments from Mr. Richard Poirot 36](#__RefHeading___Toc182377128)

[Comments from Mr. David Shaw 43](#__RefHeading___Toc182377129)

[Comments from Dr. Kathleen Weathers 44](#__RefHeading___Toc182377134)

[]{#__RefHeading___Toc182377117 .anchor}[Comments from Dr. Praveen
Amar]{.underline}

EPA's Draft plan is a commendable effort on the part of EPA staff to
present in a short document the key policy-relevant issues, and then
describe how it will assess issues related to (1) science, (2)
risk-exposure, and (3) policy, as they inform the complex process of
establishing secondary standards for both NO~2~ and SO~2~.

The draft plan, to its credit, recognizes that we have arrived at the
current state of affairs in establishing separate NAAQS for SO~2~ and
NO~2~ in an ad hoc manner by historically considering "one pollutant" or
"one atmospheric or ecological issue" at a time. The goal of considering
the two pollutants in a joint "integrated" manner under the current
review process, because of the "science-entanglement" of both the
atmospheric processes and ecological effects of the two pollutants, is
worthwhile, but not without its own set of policy-related problems. For
example, such a "multi-pollutant/one atmosphere/diverse and variable
ecosystems" approach can easily lead to a policy-situation where one can
not make "some" necessary policy decisions unless one is ready to make
"all" decisions. For example, we should be careful that such an
"integrated" approach does not lead to *not* setting a nitrogen-based
standard in the context of eutrophication of water bodies in certain
regions of the US in the absence of complete information relating to
sulfur-based impacts.

The Draft Plan (page 1-13) notes that the role of ammonia "will be
considered," while it is "not the focus of this review." It goes on to
state that "a detailed discuss (sic) of these processes is included in
the PM review." I think it is important that ammonia also be the
***[focus]{.underline}*** of this review in the context of "total
nitrogen and total sulfur", and not just the oxidized forms of nitrogen
and sulfur. This means that its emissions at about five million tons per
year in the US (there is high level of uncertainty associated with this
estimate), location of its major sources in the US, its role in
long-range atmospheric transport and then deposition as ammonium sulfate
and ammonium nitrate, its chemistry in the atmosphere and in soils, and
its ecological impacts, all of these factors need to be the focus of
this effort. For example, questions like "Is NO~2~ a good indicator of
oxidized nitrogen in the atmosphere? Are there others?" may not even be
the right questions to ask if the focus is on total nitrogen and its
deposition to the ecosystems (oxidized and reduced). Same reasoning may
also be applicable to SO~2~/total sulfur.

The Draft Plan in all of its major Sections (key policy-relevant issues,
science assessment, risk/exposure assessment, and policy assessment)
does not discuss the issue of how the review process would evaluate the
critical load-based approach as an alternative to promulgating ambient
concentration-based standards. It appears to me that this is a major
oversight of the Draft Plan. For example, Chapter 8 (the science annex
on critical loads, July 2007 draft version) quotes the 2004 National
Research Council (NRC) report, " ... However, concentration-based
standards are inappropriate for some resources at risk from air
pollutants, including soils, groundwater, surface waters, and coastal
ecosystems. For such resources, a deposition-based standard would be
more appropriate. One approach for establishing such a deposition-based
standard is through the use of so-called "critical loads." At a minimum,
the Draft Plan should be revised to describe how it would address
critical load-based approach.

Finally, I will like the Draft Plan to be more explicit in how the
process of establishing secondary standards will address uncertainties
in inputs and outputs (emissions, CMAQ models, rate constants in
atmospheric chemistry processes, deposition maps, ecosystems modeling,
etc.) and how these uncertainties would affect the judgments that must
be made in recommending standards or range of standards. Each of the
many models that would be used in this process would generate outputs
with associated uncertainties that then will be used as inputs for
subsequent models across a set of linked modules (Appendix B of the
Draft Plan describes this process but at a very cursory level). There
are numerical and analytical methods available for propagating
uncertainty across modules for quantifiable sources of uncertainties.
For uncertainties that are difficult to quantify, there are
"scenario-based" methods that can be used to bound the results. However,
propagating uncertainty across models and modules represents only one
part of the puzzle: the results of these analyses require communication
to policy-makers and other interested stakeholders. Uncertainty
analyses, particularly multi-dimensional ones necessary for establishing
secondary standards for SO~2~ and NO~2~, can be difficult to communicate
and to understand, hindering their use in policy-making. To address
this, I suggest that the Draft Plan address the issue of quantifying
uncertainty in several models used in the review process and develop an
integrated uncertainty analyses and also develop communication tools to
explain the implications of uncertainty in decision making.

[]{#__RefHeading___Toc182377118 .anchor}[Comments from Dr. Andrzej
Bytnerowicz]{.underline}

**[General Comments]{.underline}**

Generally, the document is well written, logically structured, and can
serve as a good start of discussions on possible revision of the NO2 and
SO2 NAAQS. The first phase of the process (integrated review plan), as
well as three other phases (Integrated Science Assessment, risk exposure
assessment and policy assessment and rulemaking) are logically and
clearly presented.

It would be helpful to clarify what N pollutants should be discussed as
those which may have secondary (welfare) effects. In my opinion, in
regard to the oxidized N compounds, we should not discuss only **NOx**
(which is just a sum of NO2 and NO), but rather **NOy**, which includes
NOx and also other gases of a potential ecological importance such as
nitric acid vapor (HNO3) or peroxyacetyl nitrate (PAN) (Seinfeld and
Pandis, 1998, p. 71). It would be even better if we could use a term "N
gaseous compounds", since reduced species such as NH3 also have
pronounced ecological effects.

I would be even more comfortable with a term "welfare effects resulting
from deposition of criteria pollutants (NO2 and SO2) and their
transformation products" (p. 1-7, lines 22-23).

Changing climate should be considered in development of the secondary
NO2 & SO2 NAAQS as a modifier of the ecological effects of N and S
deposition. For example, in western ecosystems the effects of elevated
levels of N deposition or ambient ozone (increased above-ground biomass
production, reduced water availability, premature foliar senescence) can
be enhanced by elevated temperatures, drought or winds of higher speed
and frequency. All these factors may lead to catastrophic fires as those
from 2003 and these recently observed in southern California.

**[Specific Comments]{.underline}**

1\. Introduction

Generally Introduction is well written and offers a good basis for the
rest of the document.

However, in reference to my above statement, I suggest that on page
1-10, line 5, a change is made: "In addition to acidification, NOx and
**HNO3** act with ...". Alternatively, it could be changed to: "In
addition to acidification, **NOy** acts with..."

Page 1-12, line 12 --instead of considering NO2 and its transformation
products, it could be better to stress that NOy contributes to N loading
of ecosystems. If such a change is made, than HNO3, which provides large
proportion of oxidized N to ecosystems, especially in dry climate, would
be automatically included.

Page 1-13. It is a very important section emphasizing a need for
including reduced N compounds if deposition and ecological effects are
concerned.

Page 1-13, line 14 -- recent evidence suggests that fine particulate
matter can also reduce precipitation in mountainous areas of California
and elsewhere (Rosenfeld et al., 2007).

3\. Key Policy-Relevant Issues

Page 3-1, line 21 -- it is not scientifically correct to say
"particulate NOx and SOx". The authors probably had in mind N and S
aerosols, including fine particulate nitrate and sulfate.

4\. Science Assessment

Page 4-1, line 5, and the following text. Again, more precision is using
various chemical terms is needed. Criteria pollutants are SO2 and NO2,
not NOx and SOx. Maybe a term "SO2 & NO2 and their transformation
products" would be more appropriate.

Page 4-2 lines 4 and 5. I would like to suggest that also "gray"
literature, specifically reports, such as those from the UN ECE ICP
Forest and ICP Mapping and Modelling dealing with issues of Critical
Loads for S, N and acidity could also be considered. These reports have
been internally reviewed and may have an important practical value for
developing similar approaches in the US.

Page 4-1, lines 9 and 10. I would also consider recent information from
CASTNET and various passive sampler networks in US and Europe, on HNO3
concentrations. In some areas, information of ambient NH3 is also
becoming available (mostly from large-scale passive sampler networks).
Information on these two gases, which due to their high deposition
velocity provide significant amounts of N to ecosystems, could be quite
valuable.

Page 4-2, line 25 and 26. Ammonia (NH3) should also be added to the
proposed literature search.

Page 4-3, lines 8-21, again, I would like to emphasize again a potential
value of the ICP Mapping and Modelling and ICP Forests annual reports.

Page 4-3, lines 18 and 19. Modifying effects of the changing climatic
conditions (in western conditions, increasing temperature, reduced
precipitation and long -- term drought) or increasing background
concentrations of ambient ozone should be considered.

Page 4-5, lines 1 -- 16. Passive sampler networks (for HNO3, NH3, NO,
NO2 or SO2) can provide the receptor-level data that can be used for
validation of the deposition models. Use of geostatistics (such as
ArcGIS Geostatistical Analyst) may greatly help in translating point
data into landscape-level concentration surfaces.

5\. Risk /Exposure Assessment

Page 5-1, line 8 -- the recommended by NRC (2004) critical loads
approach for N, S ands acidity (already widely used in Europe) could be
considered. The US FS is already developing a strategy for measuring
parameters needed for calculation of CL for N & S on a network of
experimental forest and FS-managed LTER sites (21 sites altogether
nationwide).

Page 5-2, lines 5-10. Air pollution gradient studies or large-scale
monitoring/research networks linking information on air chemistry,
deposition and ecological responses could be considered.

Page 5-2, lines 11-15. Responses of ecosystems to N and S deposition in
mesic (East) and arid (West) climates are quite different and should be
better studied. Due to high diversity of the US ecosystems, an
understanding of the occurring changes on a continental scale may be
more difficult than in Europe. International cooperation with partners
in Europe and Asia may greatly help in understanding of N deposition
responses in two types of climate. In addition, responses of mountain
ecosystems (forests, sub-alpine and alpine) should be taken into serious
consideration. Since ecological effects of climate change in high
elevation forests have been very strong in recent years, interactions
with elevated N & S deposition and increasing background ozone
concentrations should be investigated.

[Literature:]{.underline}

Rosenfeld, D., J. Dai, X. Yu, Z. Yao, X. Xu, X Yang, C. Du. 2007.
Inverse relationship between amounts of air pollution and orographic
precipitation. *Science*, 315, 9 March 2007, 1396-1398.

Seinfeld, J., & S. N. Pandis. 1998. *Atmospheric Chemistry and Physics -
from Air pollution to Climate Change*. John Wiley and Sons, Inc., New
York, 1326 pp.

[]{#__RefHeading___Toc182377119 .anchor}[Comments from Ms. Lauraine
Chestnut]{.underline}

The draft plan gives a comprehensive overview of the ambitious
scientific review and policy assessment process planned by EPA for
determining what secondary standard might be appropriate, if any, for
the deposition related effects of NOx and SOx. I have just a few
questions and comments on the policy aspects of this plan.

How much needs to be known to provide a defensible basis for setting a
secondary standard for the deposition-related effects of NOx and SOx?

If all the questions articulated here could be answered then the
decisions about standards would be fairly straightforward. Difficulties
will arise, of course, because current science and analysis tools will
not be able to answer many of these important questions. Judgments will
be necessary about whether there is sufficient information to provide a
defensible basis for selecting a secondary standard. Does the secondary
standard language provide guidance on this issue? With the primary
standards, the presumption is to be protective of human health, but with
public welfare is the presumption the same? Public welfare is definitely
impacted by standards that impose costs; so how firm must the evidence
be that the standards prevent an adverse impact?

The plan mentions the need to assess the progress expected in reducing
deposition precursors as a result of the primary NAAQS (e.g., for PM and
ozone) and current regulations (e.g., CAIR), but this is an important
issue that perhaps deserves more attention. This review of a potential
secondary standard needs to acknowledge that other standards and
regulatory efforts are already underway that have reduced deposition
precursors and will reduce them further in the future. Theoretically, a
secondary standard could be based on a simple determination of what
level of exposure is sufficient to prevent adverse environmental
effects, independent of expected future emission levels. However, it is
a relevant policy question whether such standards are needed to prevent
expected future adverse effects or whether current standards and
regulatory efforts are sufficiently protective.

Defining what makes an effect "adverse."

Obviously, a key step in the standard setting process is determining
what effects are adverse. The draft mentions valuation studies as one
way to assess how adverse an effect may be. Although valuation (either
monetary or non-monetary) studies provide some metrics to measure
strength of preference, they do not alone provide sufficient information
about what effect may be adverse. Just because an effect has some
monetary value (either use or nonuse value), it is not necessarily
adverse.

The draft says little about what other methods may be useful in
assessing whether an effect is adverse. It seems like there may be many
ways to assess this from a biological perspective that would not
necessitate valuation. For example, acidification of lakes and streams
to the point that some aquatic species cannot survive in those waters
could be established to be an adverse effect without necessarily having
estimates of society's monetary valuation for preventing such effects. I
think the assessment will have to make the case regarding what
constitutes an adverse effect on the biological level regardless of what
valuation information may or may not be available.

Related to this is, I think, the issue of variations in sensitivity to
pollutants in different locations. Providing all locations the same
level of protection may well necessitate different standards in
different locations. Setting a uniform national standard at a level to
protect the most sensitive locations would likely be unnecessarily
costly. I'm glad to see language in the draft that seems to allow for
the possibility of standards that vary by location. However, the
assessment process will have to take into consideration the practical
policy implications of the long-range transport of the pollutants in
this case. Meeting a deposition-related standard in one location would
necessitate emission controls in many distant locations and this may
limit the practicality of having very fine tuned location specific
standards.

Repairing current injury versus maintaining current quality.

The draft mentions the need to assess how beneficial a standard might be
in terms of preventing or reducing ecological effects. This raises some
questions about how the standard setting process should take into
account ecological injury that has already occurred. With pollutants
that bioaccumulate or persist in the system for long periods of time, it
seems that a different standard might be needed in locations where
injury is already significant because lower exposures might be needed to
allow recovery to occur.

Critical load/carrying capacity versus full dose-response.

The draft plan describes all the information that would be needed for a
full assessment of the ecological benefits of changes in emissions of
NOx and SOx. Although a full quantitative benefits assessment would be
nice, it is going to be very difficult to do and may not be necessary.
Perhaps standards could be reasonably established based on less than a
full benefits assessment. This might be the case, for example, if
thresholds or limits could be determined based on the amount of exposure
a system could tolerate without suffering adverse effects. This would
need to be assessed in terms of ecosystem services and at what levels of
exposure these services could still be maintained by the system. This
would not necessarily require, however, the full quantification of the
dose-response relationship between levels of deposition and levels of
environmental response. The linkages between emissions and environmental
effects would have to be sufficient, however, to establish that there is
a causal link between anthropogenic emissions and adverse environmental
effects of deposition.

[]{#__RefHeading___Toc182377120 .anchor}[Comments from Dr. Ellis
Cowling]{.underline}

**Very General Comments on these NAAQS Review Processes**

Before dealing with the details of my specific assignment during the
October 30, 2007 CASAC Consultation on the Secondary (public-welfare
based) NAAQS for NOx and SOx, I would like to offer a few general
comments about these periodic NAQQS Review processes and the changes
that are being made in both the organization and focus of these reviews.

As described on pages 1-2 of the "Draft Plan" for the NOx and SOx
Secondary standards, the Clean Air Act of 1970 established two general
goals for management of air quality in the United States \-- protection
of human health and protection of public welfare. Section 108 of the CAA
directs the Administrator of EPA to identify and list "air pollutants"
that "in his judgment may reasonably be anticipated to endanger public
health and welfare" and to issue air quality criteria for those that are
listed -- hence the term "Criteria Pollutants."

Section 109 of the CAA further directs the Administrator of EPA to
propose and promulgate "Primary" National Ambient Air Quality Standards
to protect public health and "Secondary" National Ambient Air Quality
Standards to protect public welfare.

A secondary standard, as defined in Section 109, must "specify a level
of air quality the attainment and maintenance of which, in the judgment
of the Administrator, based on such criteria, is required to protect the
public welfare from any known or anticipated adverse effects associated
with the presence of \[the\] pollutant in the ambient air ..." The
welfare effects of concern include, but are not limited to "effects on
soils, water, crops, vegetation, man-made materials, animals, wildlife,
weather, visibility and climate, damage to and deterioration of
property, and hazards to transportation, as well as effects on economic
values and on personal comfort and well-being."

So far, the several Administrators of EPA since 1970 have:

1)  Identified six specific "Criteria Pollutants" -- carbon monoxide,
    ozone and other photochemical oxidants, sulfur dioxide, oxides of
    nitrogen, particulate matter, and lead -- which have thus been
    designated officially as requiring development and implementation of
    National Ambient Air Quality Standards;

2)  Emphasized protection of public health as the principal (and
    overwhelmingly important) *de facto* focus of concern within the
    Agency, and public welfare as a (rarely openly acknowledged) but
    distinctly less important *de facto* focus of concern;

3)  Established Secondary (public-welfare-based) NAAQS standards for all
    six criteria pollutants that almost always were identical in form
    (including level, indicator, statistical form, and averaging time)
    to the Primary (public- health based) NAAQS standards for each of
    these six criteria pollutants;

4)  Developed a long-standing tradition of dealing with these six
    specific air pollutants mainly on a "one-at-a-time" basis rather
    than collectively -- i.e., without strong attention to the frequent
    interactions and simultaneous occurrence of some of these pollutants
    as mixtures within the air in various parts of our country;

5)  Maintained a reluctant attitude about the concepts of ecologically
    based "Critical Loads and Critical Levels" developed in Europe as
    possible alternative or additional approaches to air-quality
    management in the US; and

6)  Maintained a long-standing general focus on the related concepts of:

> a\) "attainment counties and non-attainment counties,"
>
> b\) "attainment demonstrations" based on mathematical modeling of a
> limited number of exceedance events under extreme weather conditions,
> and
>
> c\) "local anthropogenic sources" as opposed to "both local and
> regional biogenic and anthropogenic sources of emissions."

In recent years, in contrast to several of the six ideas listed above,
EPA has shown increased willingness to think more holistically -- and in
more fully integrated ways -- about both the policy-relevant science and
the practical arts of air quality management aimed at protection of both
public welfare and public health. These shifts in both emphasis and
approach have included:

1.  Participation with other federal agencies and international bodies
    in discussions about the "One Atmosphere," "Critical Loads--Critical
    Levels," and "Multiple-Pollutant--Multiple Effects" concepts;

> 2\) Adoption of the "NOx SIP Call" in 1999 and both the "Clean Air
> Interstate Rule" (CAIR) and the "Clean Air Mercury Rule" (CAMR) in
> 2005 with their more balanced perspectives about both regional
> (interstate) and local sources of emissions and interactions among
> NOx, SOx, VOCs, "air toxics," and mercury in the formation,
> accumulation, and biological effects of "ozone and other photochemical
> oxidants," and fine, coarse, thoracic, and secondary aerosol
> particles;
>
> 3\) Recognition of both fine and coarse PM as complex and
> geographically variable mixtures of sulfate-, nitrate-, and
> ammonium-dominated aerosols; natural biogenic and anthropogenic
> organic substances; heavy metals including cadmium, copper, zinc,
> lead, and mercury; and some other miscellaneous substances;
>
> 4\) More frequent discussion about of the occurrence and both
> ecologically-important and public-health impacts of mixtures of air
> pollutants; and, most recently
>
> 5\) The unprecedented decisions to:
>
> A\) Prepare and publish in September 2007 a "*Draft Plan for*
> \[simultaneous\] *Review of the Secondary National Ambient Air Quality
> Standards for Nitrogen Dioxide and Sulfur Dioxide;*"
>
> B\) Include on page 2-1 of this "*Draft Plan*" a "*Proposed Schedule
> for Joint NOx and SOx Secondary Standard Review"* with a *"Final
> Integrated NO~2~/SO~2~ NAAQS Work Plan*" in December 2007 to be
> followed by preparation and CASAC review of similarly integrated
> NOx/SOx documents including:
>
> i\) an Integrated Science Assessment (ISA) to be issued in December
> 2008,
>
> ii\) a Risk/Exposure Assessment (R/EA) to be completed by July 2009,
>
> iii\) a Policy Assessment/Rulemaking document prepared in the form of
> an Advanced Notice of Proposed Rule Making (ANPR) in August 2009 and
> Final Rule Making to be completed by October 19, 2010; and
>
> C\) Separate the preparation and review of documentation, the required
> CASAC and public reviews, and (possibly also) the final
> decision-making processes for a Secondary (public-welfare-based) NAAQS
> from the (previously always dominating) Primary (public-health-based)
> NAAQS review processes.

**[Need for Policy Relevancy as the Dominant Concern in NAAQS Review
Processes]{.underline}**

In a May 12 2006 summary letter to Administrator Johnson, CASAC Chair,
Dr. Rogene Henderson, provided the following statement of purpose for
these periodic NAAQS review processes.

> "CASAC understands the goal of the NAAQS review process is to answer a
> critical scientific question: *"What evidence has been developed since
> the last review to indicate if the current primary and/or secondary
> NAAQS need to be revised or if an alternative level or form of these
> standards is needed to protect public health and/or public welfare?"*

During the past 18 months, CASAC has participated in reviews of three of
the existing six criteria pollutants -- particulate matter, ozone, and
lead. CASAC has also joined with senior EPA administrators in a
"top-to-bottom review" and the resulting recently-completed revision of
the NAAQS review processes. These two experiences have led to a
seemingly slight but important need for rephrasing and refocusing of
this very important "critical scientific question:"

> ***"What scientific evidence and/or scientific insights have been
> developed since the last review to indicate if the current
> public-health based and/or the current public-welfare based NAAQS need
> to be revised or if alternative levels, indicators, statistical forms,
> or averaging times of these standards are needed to protect public
> health with an adequate margin of safety and to protect public
> welfare?"***

With regard to the important distinction in purpose of the primary
(public health) and secondary (public welfare) NAAQS standards, it is
noteworthy that in all five cases in which a secondary NAAQS standard
has been established, the secondary standard has been set "Same as
Primary."

Thus, a second very critical scientific question that needs to be
answered \-- especially with regard to the present Joint Review of the
Secondary Standards for NOx and SOx, as well as the other four criteria
air pollutants is:

> ***"What scientific evidence and/or scientific insights have been
> developed since the last review to indicate whether, and if so, what
> particular ecosystem components or other air-quality-related public
> welfare values, are more or less sensitive than the populations of
> humans for which primary standards are established and for this reason
> may require a different level, indicator, statistical form, or
> averaging time of a secondary standard in order to protect public
> welfare."***

I hope these two "critical scientific questions" will be borne in mind
carefully as CASAC joins with the various relevant parts of the
Environmental Protection Agency in completing the upcoming reviews of
both the primary and secondary National Ambient Air Quality Standards
for NOx and SOx.

We now have the considerable advantage that a much more complete focus
can be achieved in the Integrated Science Assessment than has
historically been achieved in the encyclopedic Criteria Documents that
have been prepared during the years since 1970.

**Thus, I recommend that every chapter of the soon to be completed
NOx/SOx Integrated Science Assessment, the Risk/Exposure Assessment, and
the Policy Assessment/Rule Making documents** **contain a summary
section composed almost entirely of a series of very carefully crafted
statements of Conclusions and Scientific Findings that:**

1)  **Contain the distilled essence of the most important topics covered
    in each chapter, and**

2)  **Are as directly relevant as possible to the two Critically
    Important Scientific Questions written in bold italic type above**.

**In this connection, I call attention once again to the attached
"*Guideline for Formulation of Statements of Scientific Findings to be
Used for Policy Purposes.*"** These guidelines were developed and
published in 1991 by the Oversight Review Board for the National Acid
Precipitation Assessment Program. They are the best guides that I know
of for formulation of scientific findings to be used for policy
purposes.

**GUIDELINES FOR FORMULATION OF SCIENTIFIC FINDINGS**

###### TO BE USED FOR POLICY PURPOSES

The following guidelines in the form of checklist questions were
developed by the NAPAP Oversight Review Board to assist scientists in
formulating presentations of research results to be used in policy
decision processes.

1\) **IS THE STATEMENT SOUND?** Have the central issues been clearly
identified? [Does each statement contain the distilled essence of
present scientific and technical understanding of the phenomenon or
process to which it applies]{.underline}? Is the statement consistent
with all relevant evidence -- evidence developed either through NAPAP
research or through analysis of research conducted outside of NAPAP? Is
the statement contradicted by any important evidence developed through
research inside or outside of NAPAP? Have apparent contradictions or
interpretations of available evidence been considered in formulating the
statement of principal findings?

2\) **IS THE STATEMENT DIRECTIONAL AND, WHERE APPROPRIATE,
QUANTITATIVE?** Does the statement correctly quantify both the direction
and magnitude of trends and relationships in the phenomenon or process
to which the statement is relevant? When possible, [is a range of
uncertainty given for each quantitative result]{.underline}? Have
various sources of uncertainty been identified and quantified, for
example, does the statement include or acknowledge errors in actual
measurements, standard errors of estimate, possible biases in the
availability of data, extrapolation of results beyond the mathematical,
geographical, or temporal relevancy of available information, etc. In
short, [are there numbers in the statement? Are the numbers correct? Are
the numbers relevant to the general meaning of the
statement]{.underline}?

3\) **IS THE DEGREE OF CERTAINTY OR UNCERTAINTY OF THE STATEMENT
INDICATED CLEARLY?** [Have appropriate statistical tests been applied to
the data used in drawing the conclusion]{.underline} set forth in the
statement? If the statement is based on a mathematical or novel
conceptual model, has the model or concept been validated? Does the
statement describe the model or concept on which it is based and the
degree of validity of that model or concept?

4\) **IS THE STATEMENT CORRECT WITHOUT QUALIFICATION?** [Are there
limitations of time, space, or other special circumstances in which the
statement is true]{.underline}? If the statement is true only in some
circumstances, are these limitations described adequately and briefly?

5\) **IS THE STATEMENT CLEAR AND UNAMBIGUOUS?** [Are the words and
phrases used in the statement understandable by the decision makers of
our society]{.underline}? Is the statement free of specialized jargon?
Will too many people misunderstand its meaning?

6\) **IS THE STATEMENT AS CONCISE AS IT CAN BE MADE WITHOUT RISK OF
MISUNDERSTANDING?** Are there any excess words, phrases, or ideas in the
statement which are not necessary to communicate the meaning of the
statement? Are there so many caveats in the statement that the statement
itself is trivial, confusing, or ambiguous?

7\) **IS THE STATEMENT FREE OF SCIENTIFIC OR OTHER BIASES OR
IMPLICATIONS OF SOCIETAL VALUE JUDGMENTS?** Is the statement free of
influence by specific schools of scientific thought? Is the statement
also free of words, phrases, or concepts that have political, economic,
ideological, religious, moral, or other personal-, agency-, or
organization-specific values, overtones, or implications? [Does the
choice of how the statement is expressed rather than its specific words
suggest underlying biases or value judgments]{.underline}? Is the tone
impartial and free of special pleading? If societal value judgments have
been discussed, have these judgments been identified as such and
described both clearly and objectively?

8\) **HAVE SOCIETAL IMPLICATIONS BEEN DESCRIBED OBJECTIVELY?**
Consideration of alternative courses of action and their consequences
inherently involves judgments of their feasibility and the importance of
effects. For this reason, it is important to ask if a reasonable range
of alternative policies or courses of action have been evaluated? Have
societal implications of alternative courses of action been stated in
the following general form?:

\"[If this]{.underline} \[particular option\] were adopted [then
that]{.underline} \[particular outcome\] would be expected.\"

9\) **HAVE THE PROFESSIONAL BIASES OF AUTHORS AND REVIEWERS BEEN
DESCRIBED OPENLY?** Acknowledgment of potential sources of bias is
important so that readers can judge for themselves the credibility of
reports and assessments.

**My Assignment in this CASAC Consultation on the Draft Plan for**

**Review of the Secondary Standards for Nitrogen Dioxide and Sulfur
Dioxide**

My specific assignment in preparation for the October 30 , 2007 CASAC
Consultation on the Draft Plan as outlined in Chairman Ted Russell's
memo of 11 October 2007 is \-- *Key Policy Relevant Issues*. These
topics are covered primarily in Chapter 3 of the Draft Plan and are
summarized in the five Overarching Policy-Relevant Questions on pages
3-1 and 3-2 and the additional policy relevant scientific questions
presented in Chapters 4-6.

Chairman Russell also gave this same assignment to two other CASAC panel
colleagues \-- Lauraine Chestnut and Rich Poirot. Thus, I am very much
looking forward to comparing notes with both Lauraine and Rich during
our Consultation on October 30.

There are many parts of Chapter 3 and other parts of this Draft Plan
showing that both gaseous and particulate forms of the various oxides of
nitrogen and sulfur should be included among the "Pollutants of Concern"
in this review of the NOx and SOx Secondary standards. That is good.

As an ecologist, who is aware of the many different and important
adverse public-welfare effects of both oxidized and reduced forms of
reactive nitrogen, I was pleased to find that section 1.4.3 of Chapter 1
is titled "Ammonia" At first, I thought this might mean that EPA would
be willing to broaden its perspectives about the many, diverse, and very
significant adverse welfare effects of reactive nitrogen pollution by
adding ammonia, ammonium ion, and other reduced forms of reactive
nitrogen to the "Indicators of Concern" in this nitrogen and sulfur NOx
and SOx joint NAAQS review. But my hopes were quickly dashed by EPA's
apparent continuing preference (see page 1-13) to consider reduced forms
of nitrogen almost exclusively in the context of the PM review.

Many of us in the ecological community are well aware that atmospheric
deposition of nitrogen and sulfur oxides -- but also atmospheric
deposition of chemically reduced forms of these same elements
(especially ammonia and ammonium ion) \-- are causing a wide variety of
sometimes beneficial and sometimes adverse effects on terrestrial and
aquatic ecosystems in many parts of our country. These effects include:

1)  acidification of lakes, streams, soils, and both surface and ground
    waters;

2)  eutrophication of lakes, streams, and estuaries,

3)  hypoxia in some coastal and marine ecosystems,

4)  changes in biodiversity within some aquatic and terrestrial
    ecosystems,

5)  changes in reproduction and age-class distributions of fish
    populations,

6)  changes in the nutrient status of forest trees and natural
    grasslands that sometimes lead to increased growth and productivity
    but sometimes also cause increased susceptibility to pest and
    pathogens,

7)  decreases in frost hardiness in some forest tree species such as red
    spruce,

8)  nitrogen saturation of some forest soils, as well as

9)  decreases in visibility and increases in regional haze in urban and
    rural locations as well as in scenic vistas in wilderness areas and
    airports, and

10) increased deleterious effects on some building materials and
    historical monuments of various types.

These many and varied ecological and other public-welfare consequences
of nitrogen and sulfur pollution provide strong justification for
reexamination of the secondary NAAQS standards for both nitrogen and
sulfur. To be sure, inclusion of reduced as well as oxidized forms of
nitrogen and sulfur would require a very significant change in the
"Indicators of Concern" for either or both of the NOx and/or SOx NAAQS
standards.

But it is very clear that the wide range of adverse effects listed above
fit very well with the definition of "welfare effects" specified in
section 109 of the Clean Air Act \-- "effects on soils, water, crops,
vegetation, man-made materials, animals, wildlife, weather, visibility
and climate, damage to and deterioration of property, and hazards to
transportation, as well as effects on economic values and on personal
comfort and well-being."

Also, there is a very large body of accumulated scientific evidence
about many of the 10 different welfare effects listed above that have
been shown to be attributable to exposures to reduced as well as
oxidized forms of both nitrogen and sulfur. In fact, essentially all 10
of the important "Effects of Concern" listed above have been attributed
to- or at least are significantly influenced by- both reduced and
oxidized forms of nitrogen. Some of these same "Effects of Concern" also
are influenced by both reduced and oxidized forms of sulfur. This is
true for the 1^st^, 5^th^, 6^th^, 7^th^, 9^th^, and 10^th^ effects
listed above. Thus, it makes much logical sense -- and well-justified
scientific sense as well \-- for EPA to carefully consider the
possibility of broadening the definition of the "Indicators of Concern"
for the NAAQS for NOx and SOx to include both reduced and oxidized forms
of nitrogen \-- and perhaps also both reduced and oxidized forms of
sulfur \-- as a part of the presently proposed joint science assessment
for the secondary NAAQS for NOx and SOx.

Section 4.1 of this Draft Plan makes an important and well-reasoned
distinction between how the Agency plans to include welfare effects
caused by NOx and SOx "and their transformation products while still
residing in the ambient air" in the secondary PM NAAQS review, and thus
to include in the present "NOx and SOx secondary NAAQS joint science
assessment" the "welfare effects driven by the\[se\] pollutants or their
transformation products once deposited into the environment."

For all of the reasons outlined above, many of us in the ecological
community continue to believe that the US and other developed countries
of the world need to consider the establishment of an integrated total
reactive nitrogen approach in air-quality management.

Such an integrated total reactive nitrogen idea was considered in a 1997
EPA report titled "Nitrogen Oxides: Impacts on Public Health and the
Environment." This document was prepared by a team of scientists and
engineers led by Doug Grano in EPA's Office of Air and Radiation. Such
an integrated approach was also recommended in a 1998 review paper
titled "Optimizing air quality management in Europe and North America:
Justification for integrated management of both oxidized and reduced
forms of nitrogen" by Cowling et al (Environmental Pollution 102 S1
(1998) 599-608).

During the intervening years, a solid foundation of experimental work
and periodic reassessments of integrated total reactive nitrogen
approaches have been presented in a series of peer reviewed journal
articles and focused workshop and international conference reports
developed under the auspices of:

-   the 1^st^, 2^nd^, 3^rd^, and 4th International Nitrogen Conferences
    held in the US and abroad,

-   the International Fertilizer Industry Association,

-   the UN ECE Convention on Long Range Transboundary Air Pollution
    (LRTAP),

-   the European Commission's Clean Air for Europe program (CAFE),

-   the Nordic Council of Ministers, and

-   the International Nitrogen Initiative (INI).

The International Nitrogen Initiative
([www.initrogen.org](http://www.initrogen.org/)) was started in 2002 as
an outgrowth of the 2^nd^ International Nitrogen Conference. An
integrated nitrogen approach and management of nitrogen was proposed in
the Nanjing Declaration, which was an outgrowth of the 3rd International
Nitrogen Conference held in Nanjing in 2004.

The following peer reviewed articles and both workshop and conference
reports provide important parts of the scientific background for
consideration of integrated total reactive nitrogen strategies:

Erisman, J. W., W. de Vries, H. Kros, Oene Oenema, L. van der Eerden, H.
van Zeijts, and S. Smeulders. 2001. An outlook for an integrated
nitrogen policy. Environmental Pollution and Policy 4:87-95.

Galloway, J.N., J. D. Aber, J.W. Erisman, S.P. Seitzinger, R.W. Howarth,
and E.B. Cowling. 2003. The Nitrogen Cascade. Bioscience 53:341-356.

Erisman, J. W., P. Grennfelt, and M. Sutton. 2003. The European
perspective on nitrogen emission and deposition. Environment
International 29:311-325.

Erisman JW. 2004. The Nanjing Declaration on management of reactive
nitrogen. *BioScience* 54, 286-287.

Erisman, J.W., N. Domburg, W. deVries, B. deHaan, B., and K. Sanders.
2005. The Dutch N-Cascade in the European Perspective. Science in China
Series C. Life Sciences, 48(1): 1-10.

Erisman, J.W. 2007. Nitrogen and the Convention on Long-Range Transport
of Air Pollution.
[http://asta.ivl.se/Workshops/Saltsjobaden3/Background%20material/JWE_nitrogen%20and%20clrtap.doc](http://asta.ivl.se/Workshops/Saltsjobaden3/Background material/JWE_nitrogen and clrtap.doc)

Erisman, J.W., T. Spanger, M.A. Sutton, C. Askelssson, S. Amin-Hansjani,
H.V. Anderson, H. Apsimon, S. Belyazid, H. Fagerli, H. Harmens, M.
Havlikova, J.P. Hettelingh, K. Hicks, L. Horvath, N. Hutchings, M.
Maasikmets, M. Maione, S. Reis, and C. Stenby. 2007. Nitrogen --
integrated environmental policies. Working Group 5 Report,
<http://asta.ivl.se/Workshops/Saltsjobaden3/Conclusions/WG5.pdf>

Grennfelt, P., L. Lindau,. and J. Arnell. 2007. Air pollution and its
relationship to climate change and sustainable development: Linking
immediate needs with long term challenges. Main Conclusions from
\"Saltsjöbaden 3\" Workshop, Göteborg, Sweden, 12-14 March 2007.
<http://asta.ivl.se/Workshops/Saltjoboden3/Conclusions/Salt3_Final_conclusions_rev8juni.pdf>

Sutton, M.A., J. W. Erisman, and O. Oenema. 2007. Strategies for
controlling nitrogen emissions from agriculture: Regulatory, voluntary
and economic approaches. International Fertilizer Industry Association
International Workshop on Fertilization Best Management Practices,
Brussels, Belgium. March 2007.
<http://www.fertilizer.org/ifa/publicat/bap/2007_brussels_fbmp.asp>

Only one of these peer reviewed publications and detailed workshop and
conference reports are included among the References listed in Chapter 7
of the Draft Plan for Review of the Secondary NAAQS for NOx and SOx.

It is important to note that these emerging ideas about the need for an
"integrated total reactive nitrogen" approach also led to a recent
decision by the Science Advisory Board (SAB) of the USEPA to establish a
special committee of the Board to make a thorough study of reactive
nitrogen and its effects on public health and welfare. This committee is
titled the Integrated Nitrogen Committee (INC). It has been at work for
most of the past year and is led by Dr. James Galloway of the University
of Virginia. The 18 current members of the INC include a carefully
selected group of scientists and engineers with broad experience in both
air quality and water quality aspects of nitrogen pollution and its
management.

It is also noteworthy that during the 2007 "Solsjöbaden 3 Workshop"
cited above, the USEPA joined with other LRTAP signatory organizations
in proposing that a "Taskforce on Integrated Nitrogen" should be
established within the LRTAP Convention to explore integrated reactive
nitrogen strategies under the auspices of the LRTAP Working Group on
Strategies. In April 2007 the Executive Body of LRTAP decided to
implement this proposal in 2008 with leaders from the UK and the
Netherlands as co-chairs. This is the first time that an integrated
nitrogen approach has been approved for consideration on a political
level.

**Other Suggestions for Improvement of the Secondary NAAQS**

**NOx and SOx Documents Yet to Come**

Finally, permit me to offer the following additional suggestions for
improvement of the Integrated Science Assessment, Risk/Exposure
Assessment, and Policy Assessment/Rulemaking documents to be completed
with the present Draft Plan as an initial guide:

1)  The term "acidic deposition" used frequently in Chapter 1 should be
    replaced by the more accurate term "acidifying deposition" or at
    least the less misleading term "acid deposition." Gaseous ammonia,
    ammonium ion, and both ammonium sulfate and ammonium nitrate are all
    acidifying substances even though some are not acidic when they are
    being deposited from the atmosphere into ecosystems.

2)  The answers that will be given to the well-formulated and
    well-focused "overarching policy-relevant questions" listed on pages
    3-1 and 3-2 in Chapter 3 and the more detailed "policy-relevant
    questions" listed on pages 4-4 and 4-5, pages 5-5 and 5-6, and page
    6-3 will inevitably be incomplete and or misleading with regard to
    quantitative interpretation of the causal "Pollutants of Concern"
    and the principal "Effects of Concern" if gaseous ammonia, ammonium
    ion, and other reduced forms of reactive nitrogen in both wet and
    dry deposition are not included in the science assessment, risk
    assessment, and proposed rulemaking documents.

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

**Resolution from the Integrated Nitrogen Committee of the Science
Advisory Board**

**for Consideration by the CASAC Secondary NAAQS NOx and SOx Review
Panel**

During the ongoing meeting of the EPA Science Advisory Board's
Integrated Nitrogen Committee (INC) \-- meeting at SAB Headquarters in
Washington DC on October 29-31, 2007 \-- the several members and Chair
of the INC, Dr. James Galloway of the University of Virginia, asked me
(as the CASAC-designated liaison person to the Science Advisory Board's
Integrated Nitrogen Committee) to present the following Resolution
(which was developed and approved by the INC) for consideration during
the CASAC review of the NAAQS for NOx and SOx during our CASAC
Conference Call Consultation on October 30, 2007.

**Resolution**

The current air pollution indicator for oxides of nitrogen, NOx, is an
inadequate measure of reactive nitrogen in the atmospheric environment.
The SAB's Integrated Nitrogen Committee recommends that inorganic
reduced nitrogen (ammonia plus ammonium) and total oxidized nitrogen,
NOy, be monitored as indicators of total chemically reactive nitrogen.

[]{#__RefHeading___Toc182377121 .anchor}[Comments from Dr. Douglas
Crawford Brown]{.underline}

I am generally supportive of the plan laid out here. This is in part
because it is only a sketch of what will be done, and so there is little
with which I might disagree with respect to details, but also because I
think the choices made are wise ones. I agree with the plan to focus on
gaseous phase contaminants since the particulate ones are include in the
PM assessment, although I believe it will be VERY difficult to separate
out the effects of the gaseous and particulate phase NOx and SOx. I
agree with the effects being considered, including the decision to
reflect both direct effects and effects on natural services (although
the latter is by far the more contentious of these two classes of
effects). The stages of the assessment are also properly outlined.

I have some specific comments to offer at this point:

1\. I agree with the decision, outlined on pages 1-7 and 1-8, to bring
NOx and SOx into a linked assessment, as it will not be possible (I
believe) to separate their effects in any studies. But I also mentioned
above that it will prove equally difficult to separate the gaseous and
particulate phase effects.

2\. I was not completely clear, even after reading the document several
times, how atmospheric and non-atmospheric loadings will be assessed and
incorporated into the analysis. This includes the difficulty of
separating their attributable risks in the ecological studies that have
been conducted. But I agree with the need to focus on the atmospheric
loading, so long as this also includes loadings onto a surface that are
then washed to an ecosystem through run-off.

3\. On page 1-12, it seems to me that there is an assumption (lines
12-18) that all ecosystem changes that cause a shift in species are
adverse. I don't agree with this, and this will be a central question
when the assessment is performed.

4\. I liked the fact that the review is to be focused around a series of
"policy relevant questions" (as stated on page 3-1 at the top). This is
a wise choice because it will result in a document that can serve as the
basis for subsequent parts of the NAAQS process. The particular issues
described later in that paragraph are also the appropriate ones.

5\. Later on page 3-1, shouldn't the questions all make reference to
"gaseous phase ambient..." rather than the larger "ambient"?

6\. In the questions at the top of page 3-2, the authors mention
"effects we are trying to protect..." I assume they mean "effects we are
trying to protect against".

7\. On page 4-1, it is claimed that thousands of papers will be
evaluated. I rather doubt this. On page 4-2, some of the search terms
are "terrestrial ecosystems", aquatic ecosystems", etc. These will
return very large pools of studies, and so I wonder whether they
shouldn't always be paired by NOx and SOx in the search.

8\. The criteria on page 4-3 are good, although I note that criterion 6
is both the most important and by the far the most difficult to specify
procedurally.

9\. On page 4-4, there is mention (and on other pages later) of climate
change. It was not clear whether this was being included to try to
assess impacts in the future. If so, it must also be noted that climate
change will change transport patterns for pollutants.

10\. There are very strong reasons economists give for not believing
procedures that estimate the economic values of natural services (as
they have discussed with respect to the kind of assessments performed by
Bob Costanza). The Agency should be prepared to offer some counter
arguments to these critiques. Most of the critiques center on the fact
that existing natural services valuations are not actually rooted in
market phenomena.

11\. On page 5-1, lines 19 and 20, the claim is made that the
Administrator must make the final decision as to whether a given effect
is significantly adverse to warrant changing the standard. While I might
agree with this to some degree, I question whether the policy side will
understand the science well enough to know HOW adverse a given
ecological effect is. The science papers must present this case as well,
from a scientific perspective.

12\. On page 5-2, the authors ask "To what degree can assumptions be
made..." I don't know what this means. Assumptions can always be made. I
presume they mean "To what degree are assumptions supported by the
available science"?

13\. On page 5-3 (line 22), the authors mention normalizing all
ecosystems. I have no idea what this means. It is not the proper phrase.

14\. On page 5-4 (lines 25-30), the discussion of overlaying deposition
and impacts in GIS seems to me much too simplistic. At the least, some
sort of spatial correlational methodology will be needed.

15\. On page 6-1, lines 21-31, the issues being raised appear to me all
science questions, not policy questions. But the bulleted questions
presented on the next pages of this chapter are the appropriate ones for
the policy maker to ask of the science..

[Comments from Dr. Charles Driscoll]{.underline}

I appreciate the opportunity to comments on the EPA Draft Plan for
Review of the Secondary National Ambient Air Quality Standards for
Nitrogen Dioxide and Sulfur Dioxide. I received this document late (only
yesterday). The advantage is that I have had the opportunity to read
everyone else's comments. Many of the comments and thoughts that I have
are similar to those of others on the panel.

In general I am supportive of the document and approach. Some of these
comments amplify some of the comments of others on the panel.

**Reduced nitrogen**. I agree with the comments of many of the committee
members that reduced nitrogen should be included in the assessment.
Reduced nitrogen species (NH~4~^+^, NH~3~, organic N) make substantial
contributions to particulate matter in the atmosphere and to the total
nitrogen loading to ecosystems. Given the magnitude of these
contributions it seems that we should consider these emissions and
deposition as part of this assessment.

**Linked assessment of nitrogen and sulfur emissions**. I also agree
with the comments of many of the panel members that I very much support
the linked assessment of sulfur and nitrogen deposition, as there are
similar pathways for these materials and acidification effects are
related to the combined impacts of sulfur and nitrogen. That said in
addition to acidification effects, there are fertilization effects
associated with nitrogen that need to be assessed separately. Another
issue that may challenge the linked assessment of sulfur and nitrogen
may be how well the science is developed for each of these elements. I
may be off base here but my sense is that the science may be more
definitive for sulfur effects than nitrogen effects. This may be due to
the longer residence time of nitrogen in ecosystems and the more complex
ecosystem cycling of nitrogen.

**National vs regional control strategies.** I agree with some of the
panel members that there may be some advantages associated with a
regional approach to air quality management in the U.S. concerning
ecosystem effects. This approach was suggested by the NRC (2004).
However, there also appear to be disadvantages to this approach. I am
specifically thinking about the recent NO~x~ Budget Trading Program
(NBP) to control NOx emissions in the eastern U.S. I believe that this
rule was directed to control ozone in the East. However, there is a fair
amount of scientific literature suggesting nitrogen deposition effects
on the West. While there are some advantages associated with these
regional rules they rule the risk of ignoring environmental issues in
areas of the country where emissions are not controlled.

**Positive vs negative effects**. I endorse Dale Johnson's comments
about positive and negative effects. It is difficult to pass judgement
on what are positive and negative effects. I think we should simply
document change and let others decide what are the positive and negative
effects.

**Extent and rate of recovery.** One issue that I can imagine that will
be difficult to address is the extent and rate of "ecosystem recovery"
following reductions in emissions. There is a wide range of sensitivity
of ecosystems to inputs of atmospheric sulfur and nitrogen deposition.
With respect to acidification many ecosystems are naturally acidic due
to inputs of organic acids. In addition, the long-term monitoring
studies and modeling studies suggest that the recovery of ecosystems
following reductions will occur over extended time scales (e.g., many
decades). These two interrelated considerations will challenge our
ability to establish secondary standards for sulfur and nitrogen. Some
ecosystems are so sensitive that it is unlikely that they will ever
"recover" from emission reductions. Likewise, the recovery period for
some ecosystems will likely be so extended that this will create a
difficult situation.

**Methylation of mercury**. There is a bit of text on the linkage
between methylation of mercury and sulfur deposition, but this effect
and relative pH effect on fish should be addressed in the assessment.

Specific comments

1-9, line 28 I don't like the term occult deposition. Can this be
changed to cloud and fog deposition?

1-9, line 31 Should this be bio*geo*chemistry?

1-9, line 32 and below. Font change?

1-11 Figure title. Should the figure title be in caps or lower case?

1-11, line 12 Change levels to concentrations.

1-12, line 5 Decreases in *available* base cations...

1-12, line 11 and elsewhere Should section titles be in caps or lower
case.

1-12, line 21 On an annual basis, *atmospheric nitrogen deposition may
contribute* up to 40%\....

1-12, line 22-24. I do not understand these sentences.

1-12, line 29. ...addition, *increased phytoplankton growth in the water
column and on surfaces can attenuate light causing declines in*
submerged...

[]{#__RefHeading___Toc182377122 .anchor}[Comments from Dr. Paul
Hanson]{.underline}

I found the draft plan to be a concise yet fully developed plan for the
review of the policy-issues, science, and risk/exposure/policy
assessment of the welfare effects of NOx and SOx. The following comments
provide editorial comments and address some specific issues that should
be considered in the implementation of the final plan.

Specific comments:

Pages iv and v:

In the listing of terms the EPA might denote which terms represent legal
definitions within the context of the Clean Air Act or other regulatory
statutes versus those that are scientific consensus definitions.

The definition of biologically relevant indicator should be expanded and
clarified. As I read it I wondered if it might alternatively be a
measure of organism response to a stressor (essentially the opposite of
what is presented)? On the other hand, if it is intended to denote an
indicator of pollutant occurrence or exposure to which biological system
are known to respond this should be clarified. Is a biologically
relevant indicator the generic version of the chosen statutory 'form' of
NAAQS standards?

Page 1-1 lines 16 and 17 (also relevant to 1-8 line 20):

To avoid missing key science products that might be relevant to the
current evaluation of NOx science, the current science reviews should go
back prior to 1995 to around 1991. Much of the research summarized in
the previous NOx Air Quality Criteria Document was written and
summarized several years prior to the final publication data of 1995.

Section 1.4

Somewhere in this section the fertilization potential of forms of N
deposition for terrestrial ecosystems should be acknowledged. An
evaluation of the impacts of N deposition on organisms and ecosystems
will need to recognize that N-deposition responses through time can
proceed along a continuum of response from growth enhancing
fertilization to growth depressing conditions associate with advanced
level of N inputs. Excess N-deposition results when available N can't be
assimilated by existing vegetation or immobilized via soil buffering
capacities.

Figure 1-1 should include plant fertilization as an end point.

Section 1.4.2

The concept of 'excess N' demands a comprehensive understanding of the
biogeochemical cycle of N that will be location specific and able to
capture complex interplay between biological productivity and N uptake
potential and the biogeophysical processes that store and release forms
of N and acidity in soils. A key question for the science assessments
will be \-- Do current models have the capacity to handle this
complexity?

Section 4.1

Similar to the manner in which this section deals with NOx and SOx
contributions to particulate matter issues (it is summarized elsewhere),
Section 4.2 should also describe the issue of NOx as a tropospheric
ozone precursor. I assume that such a summary statement would conclude
that NOx as an ozone precursor is/ handled and discussed in the context
of the recent review and AQCD for photochemical oxidants. The dominant
role of NOx as an ozone precursor may, however, still be relevant in the
context a standard setting process for NOx and perhaps shouldn't be
completely excluded during this review.

Page 4-4 lines 25 and 26:

This statement seemed vague. I wasn't sure of the intent.

Page 4-5 lines 1 to 16:

A separate bullet on the nature and impacts of wet and dry deposition
might be highlighted. Some forms of wet and dry (gaseous) deposition
have direct access to biologically active plant interiors through
surface or stomatal uptake. This pathway should be contrasted with the
soil-mediated pathway for biological response.

Section 5.3

Section 5.3 and the questions it raises are very important and should be
fully evaluated by EPA and vetted in the review processes. As with other
criteria pollutants, it is an unfortunate fact that funding for the
continued development of mechanistic understanding of welfare effects is
limited. A comprehensive description of critical data gaps and research
needs is essential to justify and prioritize future research needs for
NO~x~ and SO~x~ welfare effects.

[]{#__RefHeading___Toc182377123 .anchor}[Comments from Dr. Rudolf
Husar]{.underline}

Overall, the draft review plan for the Secondary NAAQS for NOx and SOx
is sound and executable. In particular, the combination of NOx and SOx
review process is commendable. In essence, such an integrated review
plan is consistent with the multifaceted nature of welfare impacts.
Also, dividing the review into the four activities: integrated review
plan, science assessment, risk assessment and policy assessment is
appropriate. Below are specific comments and suggestions regarding the
draft plan:

**Linking of Science, Risk and Policy Assessments**:

In the review process, additional consideration should be given to the
interaction between the science, risk and policy assessments. In past
NAAQS assessments, these three assessments were conducted somewhat
independently following a linear causality chain: (1) Science assessment
determines the nature of the pollutants and their effects; (2) Risk
assessment draws on the science to quantify the risk: Policy/Regulation
is then developed based on the science and risk assessments. However,
policy making includes many other considerations beyond the science and
quantitative risk assessment. Therefore, in developing a policy-relevant
science and risk assessments could benefit from a more iterative
approach among these assessments. For example, the selection of
appropriate indicators might be influenced by the policy options that
are being considered.

**Comments on Science Assessment**:

-   In updating the observational evidence since the last NAAQS science
    review, special consideration should be given for the new
    satellite-based observations of NO2 and to a lesser degree SO2.

-   Similarly, the observational databases from surface monitoring
    networks should incorporate new data from the aerosol Speciation,
    AIRNOW and NOy networks.

-   The above new observations are of particular importance for the
    validation and improvement of the regional chemical transport models
    used in the assessments (CMAQ).

**Comments on Risk/Exposure Assessments**:

-   The heavy reliance on CMAQ model for assessment necessitates the
    validation and improvement of the CMAQ model performance. The
    marginal performance of CMAQ for non-sulfur species suggests
    considerable room for improvement.

-   The statistical analysis to generate concentration-deposition
    relationships is unclear. Providing further rationale for the
    approach would be beneficial.

**Comments on Policy Assessment:**

As indicated earlier, the policy assessment could provide considerable
guidance on both identifying policy relevant science, as well as
policy-relevant risk assessment. Therefore, making the policy assessment
more transparent and also more closely linked to other assessments would
be desirable.

[]{#__RefHeading___Toc182377124 .anchor}[Comments from Dr. Dale
Johnson]{.underline}

I have reviewed the Draft Plan for Review of the Secondary National
Ambient Air Quality Standards for Nitrogen Dioxide and Sulfur Dioxide,
and I have some substantial problems with this document as written.
Specifically, I find that the tone is entirely biased toward the
negative impacts of both SOx and NOx, whereas we have known for decades
that there are positive effects as well. I am more than a little amazed
that these considerations continue to fail to make it into review papers
and documents like this. In particular, I find absolutely no reference
to the possibility that increased deposition of NOx, which delivers the
one nutrient most commonly limiting to terrestrial vegetation, to
increased growth and/or ecosystem "health". This possibility has been
raised many times in various reviews (including some of my own, which I
am not pushing here, as they are now quite old). I can refer you to two
publications that have appeared on the scene since the 1990's that I
think are particularly significant. Kauppi et al (1992) evaluated forest
mensurational data for Europe over the period 1970 to 1990, and found,
contrary to what we were being told in the 1980's, that the growth of
European forests had been increasing, not decreasing, over this period.
They speculated that this could be due to better silviculture,
**increased nitrogen deposition**, and perhaps increasing levels of
atmospheric carbon dioxide. More recently, Magnani et al (2007)
concluded that forest net carbon sequestration in the Northern
Hemisphere "**is found to be overwhelmingly driven by nitrogen
deposition, largely the result of anthropgenic activities**". Given the
high visibility of increasing atmospheric carbon dioxide levels and
climate change, I am amazed that this kind of consideration is lacking
in the document. Yes, one could argue that the Magnani article is too
new to have made it in yet, but there is the Kauppi article as well as
several other older ones suggesting that N deposition enhances forest C
sequestration (see the Magnini article for these references). To be even
handed, the report should also consider the Nadelhoffer et al (1999)
article, which dismisses the possibility of nitrogen deposition
increasing forest growth by contending that it is mostly tied up in the
soil, given our experience in fertilizer studies. (I personally dispute
that, as nitrogen deposition, unlike fertilizer applied nitrogen, can be
directly taken up by foliage.)

I make these statements with absolutely no political axe to grind at all
-- I am NOT anti-environmentalist, and I am NOT in favor of allowing
pollutants to run rampant. And I most certainly do not deny the
existence of N-saturation and negative effects of too much N deposition
-- I have seen such things in my own research. My only motivation is
that this document give a balanced view of the effects of these
pollutants and consider both the pluses and minuses of them. I have been
making the same point in various meetings and reviews for a couple of
decades now. To not do so is to invite even more scathing review
comments from its detractors at a later time.

Specific Comments:

p\. 1-10, lines 5-8: Fertilizer is mentioned here, but only in a
negative context -- why do you suppose that people bother to manufacture
fertilizer then? To poison the environment or to promote positive growth
responses?

p\. 4-2, lines 24-26: I believe that the key words should include
"sulfur" and "nitrogen" as well. The key words listed here will
automatically steer toward negative pollutant effects and leave out
basics.

p\. 5-3, lines 21-32: This section comes the closest to an objective
evaluation in that it least considers the potential for nitrogen uptake.

p\. B-9, lines 11-23: Should include potential increases in C
sequestration here.

p\. B-14, Diagram: Amazing that the "Altering plant nutrients" box
mentions Ca, but not N! "Altering of Production" "Food and Fiber" and
"Carbon sequestration" are all shown here, but given that the only
reference is to Ca (presumably in a negative context), I presume that
only negative effects of N on all these results are being considered.

p\. B-16, Diagram: This diagram makes the most sense of anything I have
seen so far -- crop (or forest) yield increases with N fertilization,
but, inevitably, so does nitrate pollution. This is the kind of balance
that ought to be present in the entire document.

References:

Kauppi, P.E., Mielikäinen, K. and Kuusela, K., 1992. Biomass and carbon
budget of European Forests, 1971 to 1990. *Science,* 256: 70-74.

Högberg, P. 2007. Nitrogen impacts on forest carbon. Nature 447:
781-782.

Magnini, F., Mencuccini, M., Borghetti, M., Berbigier, P, Beringer, P.,
Delzon, S., Grelle, A., Hari, P., Jarvis, P.G., Kolari, P., Kowalski,
A.S., Lankreijer, H. Law. B.E., Lindroth, A., Loustau, D., Giovanni, M.,
Moncreiff, J.B., Rayment, M., Tedeschi, V., Valentini, R. and Grace, J.
2007. The human footprint in the carbon cycle of temperate and boreal
forests. Nature 447: 848-850.

Nadelhoffer, K. J., B. A. Emmett, P. Gundersen, O. J. Kjønaas, C. J.
Koopmans, P. Schleppi, A. Tietema, and R. F. Wright. 1999. Nitrogen
deposition makes a minor contribution to carbon sequestration in
temperate forests. Nature 398:145-148.

[]{#__RefHeading___Toc182377125 .anchor}[Comments from Dr. Donna
Kenski]{.underline}

Overall, this was an excellent plan for moving forward with a
comprehensive review of NOx and SOx effects on ecosystems. It was well
written and logically presented. I thought the posing of policy relevant
issues in Sec. 3 was particularly well done. There were two significant
shortcomings that I hope are addressed in the ISA. First, this plan
didn't explicitly mention any assessment of the spatial scales of
susceptible ecosystems. Some ecosystems and parts of the country are
more vulnerable than others to the effects of acidification and
deposition. These should be clearly identified and their degree of
susceptibility depicted, ideally with maps. Conceivably, a secondary
standard for deposition might be different for various parts of the
country, to adequately protect sensitive ecosystems but allow
flexibility for regions with more ecological resilience. The whole
process is crying out for a GIS analysis that could overlay and *really*
integrate the deposition data with the ecosystem data, emissions data,
valuation data, etc. -- i.e., build an atlas of relevant information.
Once that information is gathered together, GIS-based spatial analysis
tools can be used to extract many more insights from the collection of
data. Note that uncertainty in this spatial information can be
incorporated into this kind of analysis. Section 5.3 does mention that a
GIS approach will be used, but almost as an aside. It should play a much
more central role in the presentation and integration of findings in the
ISA.

Second, I'm confused about the extent to which NH3/NHx will be addressed
in the ISA. It rates a paragraph in section 1.4.3 that announces it will
be 'considered', but then it is barely mentioned again. It is
unrealistic to consider acidification effects of NOx and SOx without
NHx, which also plays an important role in acidification. Because the
chemistry of NOx and SOx are inextricably linked to NHx, it needs to be
addressed explicitly. I do not believe that it can be dismissed by
noting that its role in aerosol formation will be addressed in the PM
ISA. It plays an important role in total nitrogen deposition that has to
be discussed in detail here, in the context of all the important
species. It may well be that a more suitable secondary standard includes
all nitrogen species, not just NOx; thus to leave it out of the ISA
process would be a serious omission.

Science Assessment, p. 4-1, 2^nd^ and 3^rd^ paragraphs: It's not very
clear how this organization of the annexes will be done, with respect to
summarizing the thousands of studies. There is bound to be a good deal
of overlap among studies (since some studies will address more than one
effect being summarized---e.g., both acidification and nonacidification
effects) so having a well-thought out plan for presenting these that
minimizes duplication among the various annexes would be useful. Another
suggestion is to be rigorous in separating the discussion of new data
from the review of old studies -- this was a minor shortcoming CASAC
identified in the recent review of the NOx primary ISA that could be
avoided here.

Section 4.2.2: These criteria for evaluating the studies are eminently
reasonable. I would urge the authors to err on the side of being more
selective, rather than more inclusive, to keep the ISA and annexes to a
manageable size if there really are thousands of studies to review.

p\. 4-5: Is there a particular significance to the underscored text?
Item 2.g needs to be reworded; insert 'and' between pollution and
variations?

Sec. 5 and App. B: In several places this plan emphasizes that the
Administrator will make the final decision on the standard and judge
whether an effect is significantly adverse, factoring in the inherent
uncertainty in the information. Yet there doesn't seem to be a clear
plan for describing and quantifying uncertainty at the various stages of
this process, integrating that uncertainty across the process, or for
clearly identifying what is and isn't an adverse effect. Reasonable
people might disagree about what constitutes an adverse effect and how
to value it -- nitrogen deposition on a farm field might be seen as
favorable, while the same nitrogen deposition on an adjacent forest
might be considered adverse. The information in Appendix B on ecosystem
services and valuation presented an interesting framework for beginning
to make these assessments, but it wasn't clear who gets to make the
valuation decisions. Is EPA planning to conduct a survey? Or is this
data that's already been collected? If the valuation part of the
assessment is carried out correctly, it shouldn't be up to the
Administrator to judge whether an effect is adverse or not. The point of
the exercise is to take this judgment out of the policy realm and apply
a quantitative and nonsubjective method to determining value.

Sec. 6: Does this first paragraph (p. 6-1) mean that discussion of the
possible form of the standard won't be discussed in the ISA or REA? If
so, that is a distinct shortcoming. Analysis of the many options for
regulating deposition needs to be part of the ISA. There is no reason to
put it off to the last part of the process. It is nice to see that total
nitrogen is considered as a possible indicator, and that the seasonal
variability of deposition might justify a seasonal standard; temporal
variability was only briefly mentioned in the rest of the plan and yet
it might be an important risk driver. Similarly, as I noted above, it
seems reasonable to think that a standard might differ regionally due to
broad differences in ecosystem susceptibility. This concept is touched
on as well on p. 6-3, but the sooner these possible forms of the
standard are discussed the better.

Appendix B: This was a helpful description of the various tools, but
it's not clear how they all fit together, since the models cover a broad
range of spatial and temporal scales. Perhaps a schematic of the
modeling process would be useful.

p\. B-5: Not clear why this section on AIRQuest is here, whether
AIRQuest exists, or whether it is being developed as part of this
process. In any event, a database of national air quality monitoring
data already exists (EPA's AQS). However, it does not include much data
on non-criteria species like NH3, NO, NOx, etc. Those might need to be
gathered from other sources. In particular, data from Canada might be
useful, as well as satellite observations or special study data. The
Midwest RPO has collected ambient NH3 data for several years.

p\. B-14, line 18: what is WTP?

[]{#__RefHeading___Toc182377126 .anchor}[Comments from Dr. Myron
Mitchell]{.underline}

**GENERAL COMMENTS**

The document generally does a very good job of developing a protocol for
developing secondary national ambient air quality standards for nitrogen
dioxide and sulfur dioxide. The rationale for evaluating concomitantly
the interactions of nitrogen dioxide and sulfur dioxide needs to be
separated with respect to atmospheric versus other ecosystem processes.
Examining together sulfur and nitrogen chemical species in the
atmosphere due to the important linkages of these chemical species is a
useful approach.

Careful attention will be needed for quantifying the differential
effects of nitrogen and sulfur atmospheric inputs on ecosystem response.
The interactions of nitrogen and sulfur inputs in affecting soil,
microbial and plant processes differ between these elements. Their
respective biogeochemical transformations and fluxes are relatively
distinct from each other. It will be challenging to develop appropriate
metrics that capture the essential ecosystem features that determine: 1)
whether nitrogen and sulfur inputs by atmospheric deposition will be
lost or retained; and 2) the influence of these two elements and their
different chemical species on other factors including recovery from
acidification and loss of nutrients. This will be particularly important
for evaluating long-term effects on the availability of base cation
nutrients including calcium and magnesium.

The current document does not clearly address which soil chemical and
physical characteristics need to receive particular attention in the
development of standards and how spatial variation in these
characteristics will be incorporated in the determinations. For sulfur,
attention will be needed on the adsorption/desorption responses in
soils. In addition, the contribution of any internal S sources (both
organic sulfur mineralization and inorganic sulfur mineral weathering)
to sulfate fluxes in soil and the resultant differences in responses to
decreases in sulfur deposition in surface and ground waters will need
some consideration. In contrast for nitrogen, more attention will need
to focus on what soil features including how organic matter quality
affects microbial processes. This assessment will also need to be linked
to the role of vegetation both with respect to nitrogen cycling, but
also in affecting organic matter quality via organic matter inputs to
the soil.

It will be critical to look at other factors including climate change,
invasions of exotic species and the alterations of species composition
(especially wood vegetation) that will be occurring concomitantly with
changes in atmospheric deposition of sulfur and nitrogen. Such
considerations will be needed to help clarify other factors that will be
separating how other long-term trends are influencing ecosystem
response.

Information is provided on the CMAQ (Community Multi-Scale Air Quality)
model especially in Appendix B. A clear delineation of how the CMAQ
model compares and/or differ from other models including that being used
by CASTNET for estimating deposition at individual sites would help
unify various approaches that are evaluating atmospheric deposition. It
may also be useful to include some review of how these efforts
compliment or differ from efforts in other regions including those
taking place in Europe.

The consideration of ecosystem services as a factor to be evaluated in
developing the standards could be helpful. However, it will likely be
necessary to clearly identify early in the process of developing these
new standards those services that are most relevant with respect to the
effects of nitrogen and sulfur deposition.

**DETAILED COMMENTS**

Page 1-2, line 7: \"whose\" should generally be reserved for reference
to individuals. Replace with \"of which\".

Page 1-3, line 9: subscript x

Page 1-5, line 6: insert "ic" (acidic vs. acid)

Page 1-6, line 6: where is the beginning of the quoted statement?

Page1-8, line 1: subscripts here and throughout document.

Page 1-9, line 2: add an "s" to detail

Page 1-9, line15: replace "Once" with "After" and "complete" with
"completed"

Page 1-9, line 28: replace "or" with "and"

Page 1-9, line 30: consider "Deposition of other chemical species..."

Page 1-9, line 31: replace "biochemistry" with "biogeochemistry"

Page 1-9, line 32: from this point on the font changes through line 8 of
page 1-10.

Page 1-10, lines 1-3: consider separating these statements to read as

> "Acidification results in a cascade of effects that alter
> biogeochemical cycles and harm terrestrial and aquatic ecosystems.
> These effects include slower growth, the death of forest vegetation,
> and ..."

Page 1-10, line 5: replace "such as" with "including"

Page 1-10, line 8: disease is a very general term. Either be more
specific or delete.

Page 1-11: in the figure also include the charge on SO4 for soil
processes.

Page 1-11, line 9: should read "Acidic deposition"

Page 1-11, line 12: consider "toxic to both terrestrial and aquatic
biota"

Page 1-12, line 1: consider "organisms" vs. "species"

Page 1-12, line 7: could read "in the case of Ca, Mg and K, the role of
these essential..."

Page 1-12, line 8: could read "... nutrients especially in comparison
with Al concentrations have..."

Page 1-12, line 15: change to "more nitrogen-limited"

Page 1-12, line 16: could read "... changes in the ability of invasive
species to colonize..."

Page 1-12, line 20: "that is ultimately..."

Page 1-12, line 23: replace "places" with "locations"

Page 1-12, line 24-25: could read "... ecologically important, may play
a more important role than indicated by the annual average
concentrations."

Page 1-12, line 28: could read "other population changes which can
cascade throughout the food web."

Page 1-12, line 29: omit "off"

Page 1-12, line 30: "...which serves as an important..."

Page 1-13, line 7: replace "nitrogen" with "ammonium"

Page 1-13, line 10: replace "gives" with "increases"

Page 3-1, line 4: could read "In this review of the ecosystem-related
effects on public welfare related to NO~x~ and SO~x~..."

Page 3-1, line 6: replace "the" with "this"

Page 3-1, line 16: insert comma after "i.e."

Page 4-3, 4.2.2 includes questions so should this paragraph end with a
question mark?

Page 5-3, line 9: "correlation" would suggest a somewhat weak
statistical approach. Consider changing to "relationships"

Page 5-3, line 10: This would suggest a strong approach; see previous
comment.

Page 5-3, line 12: insert comma after "i.e."

Page 5-3, line 28: What is implied by soil type and characteristics?
Wouldn\'t it be better to use the more general term of \"soil
properties\"?

Page 5-3, lines 30-31: should read "... characteristics, which may help
assess sensitivities, include..."

Page 5-4, line 2: omit "a"

Page 5-4, line 26: replace "numerical" with "simulation"

Page 5-4, line 30: insert comma after "i.e."

Page 5-5, line 12: should read "Can deposition models..."

Page 5-5, line 12: Shouldn\'t occult deposition be included as well?

Page 5-5, line 26: should read "... into services being beneficial to
ecosystems."

Page 5-5, line 30: should read "... results in specific benefit to
ecosystems?"

Page 6-1, line 23: Abundance is a weak term. Would nitrogen availability
or another term be better?

Page 6-1, line 25: Can this be made more explicit.

Page 6-1, line 26: replace "depth of soils" with "soil characteristics"

Page 6-2, line 1: should read "... sulfate and other acidifying
components..."

Page 6-2, line 2: should read "soil constituents including sulfate..."

Page B-2: How does CMAQ compare and/or differ from the model being used
by CASTNET for estimating deposition at individual sites? Shouldn\'t the
document be consistent with respect to use of SI versus English units?
Elsewhere in the document \"miles\" are used.

Page B-9: paragraph B.1.3: Shouldn\'t those ecosystem services that will
be evaluated be clearly identified early in the process of developing
the new standards?

[]{#__RefHeading___Toc182377127 .anchor}[Comments from Mr. Richard
Poirot]{.underline}

**Comments on Chapter 3. (Key Policy-Relevant Issues)**

**1. Alternative Indicators.** There is very encouraging discussion in
Chapter 3 and elsewhere advocating broadened definitions of SOx and NOx,
and of possible new (secondary NAAQS) indicators for these pollutants --
separately or combined - to specifically include not just gaseous NO2
and SO2, but also (some of) their various transformation products.
However, the discussion of alternative indicators seems unnecessarily
vague, and might benefit from more specific examples. It's not clear how
far the Agency might actually be able (or willing) to depart from the
traditional practices of considering only direct effects of and/or
indicators based on gaseous NO2 and SO2. Could, for example, a new
indicator be:

-   Total atmospheric oxidized sulfur (sum of S from airborne SO2 and
    SO4)?

-   Total atmospheric oxidized nitrogen (sum of N from NOy & NH4NO3)?

-   Total (wet, dry and occult) deposition of oxidized atmospheric
    sulfur?

-   Total deposition of atmospheric nitrogen (or at least oxidized
    nitrogen)?

-   Exceedance (by X %) of critical load for atmospheric sulfur
    deposition?

-   Exceedance (by X %) of critical load for total sulfur + nitrogen
    deposition?

Has this current consideration of NAAQS indicators based on
transformation products of "criteria" pollutants has always been an
option, or is it inspired by the clarifying definition of welfare
effects added to Section 302 (h) of the 1990 CAAAA ("...whether caused
by transformation, conversion, or combination with other air
pollutants")?

The question of whether "total nitrogen deposition" -- including both
reduced and oxidized forms -- is on (or off) the table as a potential
indicator is of particular interest. Discussion under "Policy
Assessment" in Chapter 6 (P. 6-1ines 21-31) suggest that yes, it's on
the table (i.e. there's a potential to consider and possibly control
ammonia emissions here). If so, this should be identified up front as a
key science/policy issue in the ISI and not withheld from public
discussion until the (policy assessment) ANPR.

The possible use of critical loads (also explored in more detail in the
Chapter 6 discussion of the planned policy assessment) raises an
important question of whether site-specific conditions of receptor
locations could be incorporated as a component of a secondary NAAQS
indicator. Expressing a secondary NAAQS as a limit (absolute or %) by
which a critical load for S (or N or S+N) should not be exceeded might
allow for a "uniform" number to be applied nationally which would have
substantially different regional implications. Is this option on the
table?

A related question is whether separate standards might be applied to
different areas (for example Class 1 Wilderness areas as suggested on p.
5-3, line 32). Conceivably, it might be possible to specify, or propose
a process for identifying, "sensitive areas" where more stringent
standards might apply. This reminds me to point to an informative new
Forest Service-supported critical loads web resource at:
<http://nrs.fs.fed.us/tools/cl/home.htm> and to suggest that EPA might
do well to seek collaborative assistance from the FS and NPS in this
secondary NAAQS review.

**2. Sulfate & Nitrate Aerosols.** There's a clearly stated intention to
avoid consideration of public welfare (primarily visibility) effects of
sulfate and nitrate aerosols in this review -- but rather to address
these only in the upcoming PM review. The details of and reasons for
this separation aren't clear, and I don't see why a section focusing on
"the visibility effects of sulfate and nitrate aerosols" couldn't be
developed and copy/pasted into both the secondary SOx/NOx and the PM
ISIs (and environmental risk assessments). Good arguments could be made
on both sides of the issue of whether visibility effects can best be
addressed through secondary PM2.5 or secondary SOx & NOx standards (or
especially the combined sulfate+nitrate standards that seem to be on the
table here for deposition-related effects). But this interesting and
potentially illuminating science/policy discussion (and resulting policy
options) would be precluded by an advance decision that only one
approach will be considered.

The nature and logic of this division isn't stated very clearly. Page
3-1, lines 19-21, indicate that "this review will focus on the
ecosystem-related welfare effects that result from the deposition of
these pollutants and transformation products in the gas-phase...." Does
this mean that wet, occult and particle-phase deposition of these
pollutants will not be considered here? Do visibility effects from light
absorption by gaseous NO2 belong in the PM review? The first paragraph
on page 4-1 describes somewhat more clearly the intended division of
effects associated with pollutants suspended in the ambient air (only
considered under PM) vs. pollutants which have been deposited to the
environment (considered here). However, no justification is provided for
this division. Babs by NO2 still falls through the cracks,
particulate-phase NH4NO3 is often partially lost by PM2.5 mass
measurement methods and undergoes rapid and frequent transformations to
and from the gas phase. Sulfates + nitrates account for a majority of
visibility impairment nationally, are typically the most "anthropogenic"
(and controllable) of major PM and visibility-impairing species, are
(nearly) unique as water-absorbing PM species, greatly enhancing their
scattering efficiencies compared to most other species (although water
is intentionally disregarded in PM measurements). The aerosol
information is also a critical component of the S & N transformation,
transport, air quality characterization and deposition stories -- all of
which need to be included here even if aerosol effects are disregarded.
Conceivably a gas+aerosol, S+N indicator might correlate well with but
be easier to implement than one based on deposition or critical loads.

At a minimum, there needs to be a more clearly-stated (and convincing)
rationale for the predetermined avoidance of secondary aerosol effects.
A section focused specifically on sulfate+nitrate visibility effects (&
pro & con vs. an unspeciated PM2.5 indicator) should be included in the
PM document (and given high time priority, since that review lags this
one). This review should include a pointer to that section in the PM doc
(or just include it as an appendix here). But most importantly, there
needs to be a way to include consideration of aerosol effects in
developing alternative environmental exposure characterization and risk
assessments, such that a policy decision can be based on understanding
aerosol and other benefits of alternative deposition-based standards (or
deposition benefits of speciated aerosol + gaseous standards, etc.)

**3. Title IV and CAIR.** The CAA Title IV SO2 and NO2 emission cap and
trade program with its pending CAIR extension is the 800 lb. gorilla
lurking in the corner of the room, while the plan avoids making eye
contact. I think it would be important to include a discussion of these
programs in the Chapter 1 review of regulatory history, and to then
address some associated policy-relevant issues in Chapter 3. SO2 NAAQS
were last reviewed in 1988, following a decade of extensive, prioritized
acid rain research and just as the 1990 CAA details were being
developed. A (much) tighter secondary (and/or primary) NAAQS (for SO2
and/or its transformation products) would have been an effective way to
achieve the same emission reductions that have been achieved by Title IV
-- perhaps in a shorter time frame or in a way where environmental
benefits rather than polluter's profit margins were maximized. We seem
however to now be stuck indefinitely with an allowance-based cap and
trade program as the only way that SO2 and NOx emissions will be
controlled in the future (and EPA's former "Acid Rain" Division is now
the "Clean Air Markets" Division).

Air quality-based, deposition-based or effects-based standards are at
odds with an emissions-based trading program, since the latter approach
assumes all emissions are equal in space and time, while the former
approaches assume some locations or times are more important than
others. How revised NAAQS for SOx/NOx and transformation products might
interact with, complement or modify existing and future emissions
trading programs could be an interesting and informative area for future
science/policy discussions, and should be emphasized in this NAAQS
review cycle rather than avoided. Even if cap & trade remains our
preferred or exclusive control approach in the future, the timing and
magnitude of the cap(s) could and should be guided by health, welfare
and environmental protection needs. Consideration should also be given
to extension of or alternatives to these programs for the Western half
of the country, for which Title IV and CAIR have not reduced emissions.

In considering current and projected future environmental and other
welfare effects, and associated alternative secondary NAAQS, the Agency
will want to consider historical deposition burdens (generally declining
since the mid 1970s, well before Title IV) and projected future
reductions from CAIR (or other on-the-way programs). The environmental
responses -- first in concentration and deposition and later in
biological indices -- to recent (primarily) downward trends in emissions
can provide compelling evidence of causal relationships. And evaluation
of the rates and extent of biological recovery will want to take into
account both current and projected future loading rates.

**Specific Comments on Chapter 3**

P. 3-1, lines 17-24: You could change "particulates" in line 18 to
"transformation products" for a more inclusive term. Or if you intend
"NOx and SOx" here to mean all gaseous precursors and gaseous
transformation products, then this is inconsistent with the term "NOx
and SOx particles" in line 22. It's also unclear what "gas-phase" in
line 20 applies to. I assume you plan to consider effects contributed by
deposition of gaseous, particulate and precipitation-bound pollutants.

P. 3-1, lines 26&27: The term "ambient" on line 26 isn't quite right
unless you add "and their transformation and deposition products" after
"SOx" on line 27. I think you want to specifically include deposition
effects but avoid considering effects from the pollutants in the
"ambient" air (or at least that's what you say on page 4-1).

P. 3-2, line 1: You could add "soil and bedrock geology," after
"conditions,".

P. 3-2, line 6: You could add "or deposition" after "air quality".

P. 3-2, line 22: You could add "effects from" before "deposition" and
change "sulfates" to "sulfur compounds" (presumably you intend to
include effects from SO2 deposition).

P. 32, lines 30-31: The parenthetical expression relating to long-term
impacts from current and cumulative loadings is clearly relevant to a
NAAQS review, but isn't necessarily a subset of this bullet on effects
of varying meteorological & climatic conditions. I suggest breaking it
out as a separate bullet and putting it before the one that considers
met & climate variability (or long-term change).

**Comments on other sections**

Chapter 1

P. 1-4, lines 25-27: This 'logic' -- that there were insufficient data
to establish a quantitative relationship between SO2 and vegetation
effects -- seems to be necessarily based on an assumption that it was
necessary that gaseous SO2 be the indicator. Has this assumption changed
and why?

P. 1-5, lines 25-26: I don't think "premature and unwise" are accurate
descriptors (unless modified by the term "politically") for EPA's
reluctance to prescribe [any]{.underline} regulatory control program for
sulfur oxides in 1988 - considering that the Agency has estimated
(midrange estimate in 1999 report) economic benefits of the 1990 CAA
Amendments (which included the 10 million ton cap and trade SO2
reduction) of \$110 Billion, and currently estimates that incremental
benefits from additional future SO~2~ and NO~x~ reductions in from the
Clean Air Interstate Rule (CAIR) "will result in \$85 to \$100 billion
in health benefits and nearly \$2 billion in visibility benefits per
year by 2015 and will substantially reduce premature mortality in the
eastern United States." (<http://www.epa.gov/interstateairquality/> ).

I do think that at that point in time (1988), the Agency was
(understandably) politically reluctant to act because Congress was
actively debating 'acid rain control legislation' (& had been for the
preceding decade), and the Agency was working on an internal plan that
became the basis for the Title IV cap & trade provisions of the 1990 CAA
Amendments. Twenty years later, it appears that the predetermined policy
is that SO2 and NOx should be controlled primarily through
emissions-based cap & trade and not by effects-based NAAQS.

P.1-9, line 18: Generally, the clarity of this "science primer" section
would benefit from some editing, for example:

P.1-9, line 21: Change "generally accepted science" to something like
"the more recent peer-reviewed scientific literature"...

P. 1-9, line 25: You could delete "most", since air masses & met
influences acting on the formation of ozone are limited primarily to
sunny summer days, while reactions of SOx and especially NOx are also
important in clouds, at night, during winter, etc.

P. 1-10, line 2: You need something like "with" before "effects".

P. 1-11, line 11: add "," after "sediments".

P. 1-12, line 3: Add something like "Research on" before "Effects".

P. 1-12, line 7: Change "... and in the case of calcium, magnesium and
potassium, are essential ..." to something like "... and because
calcium, magnesium and potassium are essential ..."

P. 1-12, line 9: "correlated" is pretty weak. Could maybe change it to
"associated".

P.1-12, lines 22 & 23: No idea what the point is here, but I'm sure it's
not the "uncertainties" that cause greater relative contributions...

P. 1-12, line 24: I would change "... may be higher" to "can be
substantially higher" (of course episodic extremes are higher than
averages. Ain't no "may" about it).

P. 1-12, line 25: You could delete "over-" (or else delete "often").

P. 1-13, lines 7-9: This observation that formation of ammoniated
nitrate & sulfate aerosols extends the atmospheric lifetime (&
transport) of NH3/4 from a day to more than a week (prior to
deposition), helps illustrate the problem of avoiding discussion of
sulfate & nitrate aerosols from this NAAQS Review process.

Chapter 4

P. 4-1, lines 3-4: As indicated elsewhere, avoiding any "duplicating" of
topics intended to be addressed in the PM review doesn't necessarily
save any staff resources. A 'portable' section on the visibility effects
of sulfate and nitrate aerosols could be cheaply "duplicated" and
copy/pasted in both the SO2/NOx ISA and the PM ISA. It would make for
some interesting policy discussion (to include either here or in PM ISA
or both) to consider whether future visibility might be most efficiently
improved by secondary PM2.5 standards or by alternative secondary
indicators for sulfur & nitrogen oxides and their transformation
products. For example, an indicator of total oxidized atmospheric sulfur
(S from SO2 + SO4) might be worth considering (and would likely
correlate well with total S deposition), but may be precluded by this a
priori decision to separate aerosol phase transformation products of S &
N from their precursor gases and their deposition products.

P. 4-1 lines 9-12: This sentence needs work. If the subject is
"category", the (line 9) verb (line 10) should be "is" not "are", but
how does this category get to be "these processes" (line 11), and what
is it that "interacts" (line 12) with other PM components?

P. 4-3 line 8: Why not include "and Canadian", since their deposition is
often predominantly from US sources and we do have an AQ Agreement on
acid deposition. Generally, I think there will be a very useful body of
historical and continuing recent literature relating to critical loads
and similar approaches from both Canadian and European research groups
-- who are more generally more advanced in this area than we are. It
could be an especially limiting approach to focus here primarily on US
studies.

P. 4-5, line 15: You could add ", transport" after "chemistry"

P. 4-5, line 48: Might add a bullet or two relating to the (time lags
and) physical, chemical and ecological characteristics of "recovery"
from acidification and how the end points might differ from
pre-acidification conditions.

Chapter 5

P. 5-2, line 7: Might also consider including Southern Canada in some of
the US "mapping" exercises (for example forest sensitivity and surface
water mapping by NE Governors & Eastern Canadian Premiers).

P. 5-3, lines 10-20: In developing and comparing these gridded layers of
ambient concentration and deposition, it would be useful to include grid
layers aerosol SO4, NO3 & NH4 (regardless of whether visibility effects
are considered here), and might also be informative to include similar
gridded emission data and analyses (i.e. plots of the ratios of
deposition to emissions).

P. 5-3, line 29: Could add "current and historical" after "including".

P. 5-3, line 32: Could add ", National Parks and Fish and Wildlife
Refuges and National" between "Class I" and "Wilderness".

Chapter 6

P. 6-1, line 6-1: It's very encouraging to see the option of a "total
nitrogen" indicator (presumably to include deposition of all oxidized
[and reduced]{.underline} N). It's not clear in earlier sections of the
plan that this option is actually on the table, and that effects of NH3
& NH4 deposition will be fully considered. An interesting range of other
optional indicators (and receptor-specific modifiers) for biological
sensitivity to fertilization or acidification also seem to be presented
here for the first time (as exclusively policy considerations). The
technical foundations for use of these potential indicators should be
presented up front and in public in the ISI and evaluated in the
ecological risk assessment -- rather than considered only in the
Agency's internal policy assessment discussions.

P. 6-2, line 8: I'm not sure that determination of "adversity" is
exclusively a policy decision. Many of the various tools and methods for
assessing adversity are developed and evaluated in the scientific realm
and associated literature (albeit the dismal science). Presentation of
these techniques and their associated results should not be withheld
until the last-minute ANPR.

The concept of "sustainability" is a related topic which is a policy
consideration that would benefit from advance scientific illumination
(in might conceptually add a time dimension to the concept of
"adversity"). Are there ecosystems where the present state of
acidification is not currently resulting in "adverse" ecological
effects, but where the net rate of base cation removal from acid
deposition can't be sustained in the future?

[]{#__RefHeading___Toc182377128 .anchor}[Comments from Mr. David
Shaw]{.underline}

Number range CHAPTERI believe EPA's Draft Plan fairly presents the key
policy-relevant issues and the proposed method to review issues related
to science, risk-exposure and policy. The Draft Plan also recognizes the
significant regional variability in effects associated with this issue.

The Draft Plan states that the role of ammonia will be considered as
part of the analysis but does not contain specifics on how the role of
ammonia will be evaluated. The level of ammonia emissions in the United
States is substantial and in order to fully review the secondary NAAQS
for SO2 and NO2, its role in transport and subsequent deposition
formation needs to be fully understood and evaluated.

Substantial data from current studies of various ecosystems exists and
should be used as part of this review. Current data shows small, but
improved trends in aquatic chemistry and species. A thorough analysis of
these trends should be included in this review and factored into any
modeling provided as part of EPA's analysis.

[]{#__RefHeading___Toc182377134 .anchor}[Comments from Dr. Kathleen
Weathers]{.underline}

This draft plan is in places specific and in others quite vague,
necessarily; it is a draft plan. Nonetheless, while some of the sections
are rather straightforward and reasonably clear, the Risk/Exposure
section is significantly underdeveloped. It will be, ultimately, the
synthesis of research findings and understanding. Thus, among other
things, the development of a conceptual model as well as clearly
defining specific response variables will be critical to developing a
credible analysis to support this area of inquiry.

Below I have listed general as well as many specific comments on this
version of the draft.

First, I am encouraged that in 1995 the Acid Deposition Standard
Feasibility Report to Congress concluded that "establishing acid
deposition standards for sulfur and nitrogen deposition may at some
point in the future be technically feasible\..." The ability to relate
emissions, deposition and ecosystem effects seems to me still at the
core of the secondary effects assessment (see below).

A primary science and policy-relevant "tool" that was not explicitly
addressed is the importance of the environmental monitoring data and
programs that have been and will be necessary to detect long-term and
short-term secondary effects of NOx and SOx. Ultimately, this document
should identify what monitoring programs are necessary to determine the
efficacy of air quality related policy.

I applaud the efforts to combine the effects of pollutants. That said, I
think it very important to consider the emissions, deposition and
ecosystem effects of ammonia and ammonium as well, as was pointed to in
section 1.4.3. This review should continue to underscore the importance
of linked biogeochemical processes in considering effects of NOx and SOx
on ecosystems. Compartmentalizing analyses/assessment by chemical
species or particle size makes little sense from an ecosystem effects
standpoint.

Throughout (page 3-2 and beyond) the document, the importance of
receptor surfaces (i.e., landuse/landcover) in influencing atmospheric
deposition is under realized. "Ecosystem receptors" are considered
important to identify for their susceptibility to SOx and NOx in this
report, however, it is also important to recognize the importance of
receptor surfaces in affecting the deposition of gases and particles
(dry deposition), since dry deposition can contribute significantly to
total deposition (in many locations and for many chemical species
[\>]{.underline} 50% of total deposition).

Introduction:

The relative influence of ground-based vs tall stack-emitted SOx and NOx
vis-à-vis deposition should be noted.

The background (history) section is quite useful. Thank you for
including it.

**Section 1:**

1.4 Science Primer

line 21: what's the definition of "generally accepted science?" By whom?
How is it determined?

line 31: \..."[can]{.underline} initiate changes in\..."

Figure 1.1 might be modified for clarity. For example, the use of the
word "soil processes (e.g., nitrate, sulfate and NHx)" is confusing;
processes within the soil influence the rate of production or movement
of these ions. The arrow showing dry deposition depositing vertically to
land surface could be modified to indicate more realistic transfers
(horizontal deposition and/or deposition to trees). It might also be
worth modifying the size of the arrows (for fluxes) to indicate
(broadly) proportional contribution.

1.4.1

The beginning of this section could be made clearer and more linear.

1.4.3

I think it very important to include ammonia/ammonium as part of
discussion on nitrogen deposition, especially since it is becoming an
increasing issue in parts of the US (e.g., southeastern US). Salient
points from the PM review should be cross referenced in the NOx/SOx
report, at a minimum.

**Section 3:** It is important that dry deposition is considered part of
this review (the deposition of gases and particles).

**Section 4:** It would be helpful to include a list of the related
topics that will be addressed by the PM science assessment, just for
references.

Page 4-1. I assume that the data from US and Canadian federal monitoring
networks will be used as a basis to help\..."provide a better
understanding of the nature, sources, distribution\..." of air and
precipitation chemistry and deposition. If so, they should be noted as a
source of information in addition to peer reviewed literature.

How will the vast literature be distilled and/or weighted?

Give dates for the window in which published literature will be
considered (page 4-1).

Page 4-2: Deposition (atmospheric and acid deposition) should be used as
a search term. Also, a brief accounting of the relative numbers of
papers in each of the search categories would be instructive.

Page 4-3: I think the focus should be explicitly expanded to recent
studies in the US and abroad, especially like ecosystems in other
countries (Canada and the UK, for example).

It seems to me that the assessment of the scientific quality of studies
is redundant, at best, with peer review and may lead to subjectivity
and/or bias in deciding which studies are considered high quality and
which are not.

**Section 5:** This section's title addresses exposure (often synonymous
with deposition, it appears) and risk. The title is inconsistent with
the discussion below and should more accurately read: Exposure and Risk.

Page 5-1: The introductory paragraphs to this section are quite unclear.
Creating a conceptual model (i.e., figure) depicting the proposed steps
of the assessment would help. As I understand it, the goals are to
consider the effects of nitrogen and sulfur deposition (aka inputs) to
ecosystems. The response variables for ecosystems are functions (such as
productivity, rates of nutrient cycling), and the more general ability
of the ecosystem to produce clean water/air (i.e., goods and services
via the ecosystem functions noted above), and that these ecosystem
functions and services will be valued.

I could not tell what long-term trends would be assessed (line 14), nor
how such things as "biologically-relevant" indices or "sensitive"
ecosystems will be defined. Furthermore, in developing indices for
assessment, it would be useful to know what scientific criteria are
likely to be used by the Administrator when s/he makes "the final
decision as to whether an effect is significantly adverse," so that this
section can be made most useful and relevant to the process.

There is confusion throughout this section in regard to the use of the
terms exposure (does this mean ambient air concentrations of SOx and NOx
and their effects on ecosystems?) and deposition, and the quantity of N
and/or S delivered to ecosystems. Demonstrating the link between air
concentrations and deposition is of course critical to both exposure and
risk assessments and is a topic that it being actively researched.

Once again, the scope section might reiterate what the response
variables are. (Many of the potential questions to be posed are also
active areas of research.)

The topic of ecological recovery is a challenge. First, it must be
defined---is it biological? chemical? What are the measures? Recover to
what? Next, in regard to assessing standards, recovery may be especially
relevant in regard to thresholds: are there demonstrated exposures and
levels of deposition beyond which ecological recovery can, or cannot, be
achieved? Examining the literature for this country and abroad on the
determination of environmental thresholds for N and S deposition and
exposure will be important.

5.1 Assessment Approach

The goals here, once again, are to examine the relationships between
emission and deposition, and deposition and ecosystem effects (this goal
is stated in the Appendices, and see above). Thus, it seems important to
be clear, from the outset, about the suite of ecosystem effects
(response variables) to be considered (see comments above). Also,
bringing to bear all of the data and analyses available, from process
models as well as from monitoring programs and specific research
projects will be important, as suggested. There are published studies
for areas of the country showing relationships between emissions and
air/rain concentrations and, in some cases, wet deposition. As noted in
this document, deciding on the relevant time step for this analysis will
be important. For example, is annual or seasonal deposition sufficient
to determine welfare effects, or are hourly or daily data necessary? For
evaluating many ecosystem responses, the former might be the focus.

How does the CMAQ model compare to other estimates of total deposition
based on monitoring data? Does CMAQ take into account land use/land
cover? Do regions of high and low deposition line up, especially for
sensitive ecosystems, using different approaches?

Page 5-3, lines 10-20: It is unclear to me what analyses are being
proposed and how other data might be used in these analyses (e.g.,
precipitation, relative humidity, etc.).

There exist GIS-based maps of sensitive ecosystems as well as of
atmospheric deposition (e.g., www.ecosystems-research.com/fmi/reports).
Although I think that the idea of "normalizing" ecosystems is
interesting, data for the types of characteristics identified are
unlikely to be widely available and/or published. It may be instructive
to look at the BioScience articles on acid rain (2001) and nitrogen
(2003) that are a result of the ScienceLinks program as models for
synthesis.

Although the cluster analysis can group ecosystems together based on
certain characteristics, I underscore that it is critical that those
characteristics are relevant to the questions being asked. (I have seen
the method used in ways that are completely irrelevant to the process
being addressed).

**[Models]{.underline}**

I think it important to preface a model results or modeling section with
a general discussion on the purpose, utility, strengths and limitations
of the models used as part of this analysis. Rather than being
predictive, most models are best exercised as heuristic tools.

Also, there is no mention of the potential use of Day-Cent-Chem except
as part of a list. Further analysis of and emphasis on GIS-based models
should be considered