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) NOX & SOX

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) NOX & SOX 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 NOX and SOX. 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 NOX & SOX Secondary Review Panel 

Attachments 

Attachment A: Roster of CASAC NOx & SOx 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 NOx & SOx Secondary NAAQS Review Panel 

U.S. Environmental Protection Agency 

Clean Air Scientific Advisory Committee 

NOx & SOx 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) 

Comments from CASAC NOX & SOX 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 

Comments from Dr. Andrzej Bytnerowicz......................................................................... 6 

Comments from Ms. Lauraine Chestnut............................................................................. 9 

Comments from Dr. Ellis Cowling ................................................................................... 11 

Comments from Dr. Douglas Crawford Brown................................................................ 21 

Comments from Dr. Charles Driscoll ............................................................................... 23 

Comments from Dr. Paul Hanson..................................................................................... 25 

Comments from Dr. Rudolf Husar.................................................................................... 27 

Comments from Dr. Dale Johnson.................................................................................... 28 

Comments from Dr. Donna Kenski .................................................................................. 32 

Comments from Dr. Myron Mitchell................................................................................ 36 

Comments from Mr. Richard Poirot ................................................................................. 36 

Comments from Mr. David Shaw..................................................................................... 43 

Comments from Dr. Kathleen Weathers........................................................................... 44 

3
Comments from Dr. Praveen Amar

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 NO2 and SO2. 

The draft plan, to its credit, recognizes that we have arrived at the current state of affairs 

in establishing separate NAAQS for SO2 and NO2 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 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 NO2 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 SO2/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 so4
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 SO2 and NO2, 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. 

5
Comments from Dr. Andrzej Bytnerowicz

General Comments

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

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. 

6
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. 

7
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, subalpine 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:

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. 

8
Comments from Ms. Lauraine Chestnut

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 

9
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 doseresponse 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. 

10
Comments from Dr. Ellis Cowling

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; 

11
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 “MultiplePollutant–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 NO2/SO2

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 

12
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

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 recentlycompleted 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. 

13
14

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? 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? 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? 

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 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? 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? 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? 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 [particular option] were adopted then that [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.

15
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 

16
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 wellbeing.” 

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 1st, 5th, 6th, 7th, 9th, and 10th 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). 

17
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 1st, 2nd, 3rd, 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) was started in 2002 as an 

outgrowth of the 2nd 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

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

18
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_rev8

juni.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. 

19
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. 

20
Comments from Dr. Douglas Crawford Brown

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. 

21
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.. 

22
Comments from Dr. Charles Driscoll

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 (NH4

+

, 

NH3, 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 NOx 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. 

23
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 biogeochemistry? 

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... 

24
Comments from Dr. Paul Hanson

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? 

25
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 NOx

and SOx welfare effects. 

26
Comments from Dr. Rudolf Husar

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. 

27
Comments from Dr. Dale Johnson

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 antienvironmentalist, 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?

28
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. 

29
Comments from Dr. Donna Kenski

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, GISbased 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, 2nd and 3rd 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. 

30
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?

31
Comments from Dr. Myron Mitchell

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 

32
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” 

33
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 NOx and SOx...” 

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.” 

34
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? 

35
Comments from Mr. Richard Poirot

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. 

36
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.) 

37
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. 

38
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

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 SO2 and 

NOx 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. 

39
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 

40
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 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. 

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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?

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Comments from Mr. David Shaw

I 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. 

 

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Comments from Dr. Kathleen Weathers

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 > 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 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. 

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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 

46
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 

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 

47