UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD December 23, 2008

EPA-CASAC-09-004

The Honorable Stephen L. Johnson

Administrator U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. Washington, DC 20460

Subject: Peer Review of EPA’s Risk and Exposure Assessment to Support the Review of the Secondary National Ambient Air Qua lity Standard for Oxides of Nitrogen and Sulfur: First Draft

Dear Administrator Johnson:

The Clean Air Scientific Advisory Committee (CASAC) NO

x & SO

x Secondary National Ambient Air Quality Standards (NAAQS ) Review Panel held a public meeting on October 1-2, 2008 to review EPA’s Risk and Exposure Assessment to Support the Review of the Secondary National Ambient Air Quality Standard for Oxides of Nitrogen and Sulfur: First Draft (see Enclosure A for the Panel roster). The Panel discussed its draft report on November 19, 2008 at a public teleconference. The Panel’s draft report was reviewed and approved by the chartered CASAC at the public teleconference on December 19, 2008 (see Enclosure B for the CASAC roster).

Overall, the Panel found the first draft of the Risk and Exposure Assessment (REA) document to be a credible beginning in the deve lopment of the assessments needed to support future rule-making. The Panel recognizes the tim e constraints under which the present first draft REA was prepared and that much of the analyses and the subsequent interpretation have yet to be completed (e.g., Chapter 7 is focused primarily on acidifying deposition and Chapter 8 only begins to explore how a secondary NAAQS might be structured). The Panel has many suggestions for strengthening the document in re sponse to the Agency’s charge questions.

Individual comments from the Panel me mbers are provided in Enclosure C.

The Panel strongly supports the up-front incl usion of a policy-focused interpretation of each of the key scientific findings in the In tegrated Science Assessment (ISA). These policy interpretations should be included in an Executive Summary, as well as in the applic able sections of the REA. As discussed in pr ior reviews of the ISA and Scope and Methods documents, it is critical that the REA give attention to all forms of reactive nitrogen (Nr, which includesoxidized, chemically-reduced and organic nitrog en forms) deposition because all forms can

contribute to both acidifi cation and nutrient enri chment of ecosystems. Moreover, the science indicates that ecological effect s could be ameliorated by decreasing deposition of any of those forms. From a scientific standpoint, this intri cate relationship indicate s that the applicable NAAQS standard(s) should addr ess total reactive nitrogen de position. Thus, the Panel affirms that science-based secondary NAAQS standards for nitrogen and sulfur should consider the ecological consequences of total Nr deposit ion. However, it is noted that the present interpretation of the re gulatory authority of EPA recognizes only oxidized forms of nitrogen and

sulfur as Criteria Pollutants. The Panel re commends that the EPA move forward with establishing scientifically-based standards that effectively protect the environment, while recognizing the current re gulatory constraints.

Scope of the Review

1. Chapters 1 and 2 provide the background, history, and fram ework for this review, including a discussion of our focus on the four key ecological e ffect areas (aquatic acidification, terrestrial acidification, aqua tic nutrient enrichment , terrestrial nutrient enrichment). Is this review appropriately focu sed in terms of characterizing the important atmospheric and ecologic variables that in fluence the deposition and, ultimately, the ecologic impacts of nitrogen and sulfur? Do es the Panel have any further suggested refinements at this time?

Chapters 1 and 2 of the REA begin to satisfy the goals of providing a clear and correct framing of the issues, providing a coherent method for reaching conclusions required in the NAAQS review process, summarizing the releva nt policy questions a nd building on the ISA. The appropriate effects are considered in th e REA and the potential relationships between atmospheric deposition and ecological effects are outlined.

The Panel commends EPA on its use of figur es and diagrams throughout Chapters 1 and 2: such illustrations help orient the reader a nd provide a framework for discussion. It would be helpful if Figure 1.4-1 was accompanied by descripti ons in the text that explain how well each of the steps can be executed, what the major unc ertainties are, and where each component is addressed in the later parts of the REA. Such modifications would assist in guiding the reader through the material in the documen t. It would also be beneficial for the Agency to include a paragraph on the central concept of N and S “loa ding" because this con cept is pivotal to the document. Similarly, the concept of “N satura tion” needs to be introduced earlier in the

document with a clear delineation of how this co ncept is, or should be, used in evaluating the effects of N loadings. There should be greater coherence between the text, figures and policy statements with respect to reduc ed and organic forms of N: both forms of N are mentioned here and in the ISA, and are important contributors to the effects being e xhibited by ecosystems in response to N deposition. In the present version of the REA, the chemistry figures and the policy questions essentially address only the oxidized form. The material should be modified to address chemically-reduced and organic nitrogen.

Discussions of uncertainty in Section 2.4 are generic and qualit ative: it is unclear when uncertainty is being discussed and when variability is the real issue. The document needs to be

2explicit that variability and uncertainty are two important but different concepts, with different impacts on establishing secondary NAAQS. The issu e of uncertainty needs to be paramount in the discussion of monitoring networks. The sp arse data from the existing network, the relationship between ambient con centrations and dry deposition and our understanding of cloud water deposition introduce significant uncerta inty in estimates of to tal deposition. The Panel recommends that Chapters 1 or 2 address uncerta inty with a discussion of the implications on EPA’s ability to perform the assessments out lined in Chapters 7 and 8. Additionally, the uncertainty issue should extend to the discussi on of climate change, for which there are both beneficial and adverse effects of atmospheri c Nr in ambient air and deposition. The REA is unclear on how a change in the secondary NAAQ S will affect climate change and in what

direction. If the science is uncerta in on the level and direction of effects on climate, it should be clearly stated in the REA.

Exclusion of non-ecological publ ic welfare effects of NO

x and SO

x (e.g., effects of N- and S-containing particulate matter on visibility degradation and c limate change, materials damage)

continues to be an area of concern for the Panel. To ensure that the current REA meaningfully represents an assessment of environmental crite ria, EPA should state clearly in which Agency

documents the omitted NO

x /SO

x welfare effects will be treated and provide a short synopsis of the key non-deposition effects in a ppropriate locations in the REA.

The Panel recognizes that including a discus sion of the potential primary NAAQS (i.e., based on public health) for NO

x and SO

x , and the current PM NAAQS, is premature at present. However, future drafts of the REA should include an analysis of how the estimates of ecological exposure and risk are impacted by the range of primary standards under c onsideration and if the respective primary NAAQS would (or would not) be adequately protective of the full range of environmental risks. Of particular concern is that in the past, th e secondary NAAQS for a number of pollutants has been set identical to th e primary NAAQS. As noted later in this letter, the Panel finds the proposed approach for a secondary NO

x -SO

x NAAQS to be innovative, but has concerns about its feasibility. Given the challenges the Agency may face with rulemaking and implementation, a policy decision coul d be to once again set the secondary NO

x and SO

x NAAQS to be identical to thei r respective primary NAAQS. We recommend a full assessment of the implications of making such a decision.

Air Quality Analyses

1. To what extent are air quality characteriza tions and analyses presented in Chapter 3 technically sound, clearly communicated, appropriately characterized, and relevant to the review of the secondary NAAQS for NO

x and SO

x ?

2. Section 3.2.1 describes an approach for evaluat ing the spatial and temporal patterns for nitrogen and sulfur deposition and associated ambient concentrations in the case study locations. This draft document includes th e analysis for the Adir ondacks case study. Does the Panel agree with this approach and should it be applied to the other Case Study

Areas?

33. Section 3.2.2 describes the rela tive contributions of ambien t emissions of nitrogen and ammonia to nitrogen deposition for the case st udy areas. To what extent is the approach taken technically sound, clearly communi cated, and appropriately characterized?

The general nature of Question 1 leads the Panel to both addr ess the question and also to provide general comments on the current air qua lity analyses. Assuming the many and important missing “placeholder” sections ar e satisfactorily completed, the ai r quality characterizations and analyses presented in Chapter 3 should provi de a reasonably sound and clearly communicated

characterization of estimates of deposition of total re active nitrogen and acidifying species to the specific case study areas. The Chapter, when comp leted, should also provide information that is relevant to potential revisions to the current secondary NAAQS for NO

x and SO

x .

Given that most of Chapter 3 is devoted to the presentation of model results from the Community Multiscale Air Quality (CMAQ) model and Response-Surface Model (RSM), a major limitation of the current chapter is the ab sence of any evaluation of model performance on simulated levels and atmospheric deposition rates of the various forms and phases of sulfur- and Nr-containing chemical species. It is critical th at EPA complete the placeholders that relate to model/measurement comparisons and the characteri zations of uncertainty in model results. For example, plots of spatial and temporal variabil ity with measurements would convey how well the model captures the spatial and te mporal patterns. Per the panel’s previous recommendations on the ISA, much of the needed evaluation of the CMAQ model should be included in the ISA.

There is also a need – either in the ISA or here in the REA – for a more detailed description of the RSM and an evaluation of its performance for the S and N species. With the relatively extensive sets of air quality, atmospheric depos ition and environmental measurements available for the Adirondacks, this may be a good case stu dy area in which to evaluate model performance prior to extending this approach to other case study areas.

The complex terrain in sections of the Ad irondacks also raises concerns. It is not appropriate to compare the 12-km spatial resolu tion of the modeled deposition with the spatial patterns in actual deposition (i ncluding orographic precipitat ion increases and cloud water deposition) or the spatial patterns in sensitive species and ecosyst ems. A sensitivity analysis of variations within selected Adirondack model grid cells could help evaluate the importance of spatial variability, scale and resultant effects on deposition estimates.

The Panel was pleased to note the efforts of the Agency to link the atmospheric models (relating emissions to deposition) with watershe d or landscape models (relating deposition to environmental effects). The disparity in the tim e scales between atmospheric (i.e., CMAQ) and watershed models is a major issue. Atmosphe ric models typically provide predictions at relatively fine time scales (e.g., hourly) over a single year, while the watershed models often provide results on scales ranging from decades to centuries. To the extent possible, it would be helpful if CMAQ could be run for a number of recent years (2002-2006), varying both meteorology and emissions, to provide a better un derstanding of inter-annual variability and longer-term spatial patte rns. This would provide a more robust basis for model-to-measurement and model-to-model comparisons.

4Assuming the model evaluations indicate r easonable performance for most of the chemical species of concern, the Panel recommends that the model results (for both sulfur and reactive nitrogen species) be used to generate a number of maps that illustrate the spatial

distributions of:

• emissions (preferably interpolated to better illustrate high-emitting regions),

• atmospheric concentrations (gaseous and aerosol and combined species),

• deposition (wet, dry, total S, total N, oxidi zed N, chemically-reduced N, etc.), and

• ratios of deposition to atmospheric con centrations and deposition to emissions. The Panel recommends that the maps have a c onsistent spatial resolu tion (e.g., 36 km) over the contiguous United States and a finer resolution over the case study areas. Such maps would provide the reader a more direct understanding of the spatial re lationships that exist between emission location, ambient concentrations and th e resulting deposition. The maps would also be useful in proposing a struct ure for a secondary NAAQS.

In addition to these maps, the Panel recomm ends the EPA use scatter plots of gridded

model results to further illust rate the key relationships betw een the deposition metrics most

relevant to environmental effects and alternat ive air quality metrics upon which the secondary NAAQS might be based. The scatte r plots could also be used to provide information relevant to uncertainty analysis.

Case Study Analyses

Before dealing with the specifi c charge questions w ith regard to the Case Study Analyses, the Panel offers the following general comments . The proposed use of ec ological indicators that can be linked to varying severi ty or magnitudes of effects (a nd related losses in ecosystem services) goes beyond the concept of estimating cr itical loads at which ecosystems experience no effects according to present knowledge. An impo rtant consideration as these indicators are selected and further developed is how to describe effect indicators of varying severity rather than just providing a "no-effects" threshold. A contin uum of effect indicators will provide important information on the range of adverse responses, and quantifying the response indicators to various emissions and deposition levels will be important for the eventual assessment of what ecological effects are considered to be adverse. A separate section may be needed to discuss the ecological implications of various levels of acid neutralizin g capacity (ANC) and associated effects, and its application to evaluating effects of acidify ing deposition. This disc ussion should include a

consideration of the im plications for moving beyond single crit ical load “no-effects threshold” approaches to more comprehensive approaches that offer varying degrees of ecosystem protection within specified leve ls of statistical probability.

The modeling approaches used to develop crit ical loads for these case studies are very different. Evaluating these differe nt approaches could be very instructive. In particular, a

discussion of the relative merits of dynamic models vs. steady st ate models in these specific applications is needed. For example, MAGIC doe s not effectively simulate watershed nitrogen dynamics, so if watershed nitrogen dynamics is an important component of the critical load there will undoubtedly be some errors. Most forest ecosystems currently are losing exchangeable cations and accumulating S and N, so by definition they are not steady-state systems. Applying a steady-state model to such systems is problem atic as a critical loads assessment tool.

5In the case study Attachments, the discus sions of varying amounts of ANC and their associated effects on ecosystem function differ from what is presented in the main chapters of the REA document. A more consistent approach is needed for setting the ANC limits of concern with respect to ecosystem sensitivity to acidifica tion and recovery from acidification. The panel suggests that full protection of fish species (set at 100 μ eq/L) should be considered in the case study scenarios.

It would be useful and instru ctive to include an N-limited site among the case studies. Possible systems would be the ra pidly-growing and N-demanding Douglas-fir forest ecosystem in the Pacific Northwest or a loblolly pine domin ated forest stands in the Southeastern US. For better understanding of the regional effects of N deposition in th e southern Sierra Nevada, EPA should consider a comparison of responses in mi xed conifer forests (e.g., the Kings River Project area) as compared to ANC changes in the nearby lakes of the sub-alpine and alpine zone (e.g., such as leaching of nitrate to streams, liche n species composition, and invasion of invasive grasses).

Additionally, it may be useful to include an up-front discussion of how the acidity of the solid phase of the soil affects soil solution acidit y which can in turn affect surface water acidity. In an already acid soil (whether acidic due to natural or anth ropogenic processes), soil solution acidity can increase or d ecrease instantaneously with the in troduction or removal of mineral acid anions (such as sulfate, nitrate, or chloride) wi thout any change in the soil solid phase. This is sometimes referred to as the “intensity eff ect” and is described in Reuss and Johnson (1986) 1

. In contrast, acidification of th e solid phase of the soil can take a long time and is usually not reversible without liming.

1. Attachment 2 presents a GIS analysis to defi ne geographical areas that are sensitive to acidification and nutrient enrichment. Are the national geospatial datasets chosen adequate to identify sensitive areas? Are th ere other data sets that have not been identified by this analysis that we shoul d consider? Does the panel agree with this approach or can they suggest alternatives?

The selected datasets and the general GIS appr oach are appropriate for this analysis, and

the Panel has no recommendation for additional data sets to consider. The period of coverage and spatial representativeness (e.g., the lichen data base) are possibly important limitations that

should be noted.

2. Attachment 3 presents our current progr ess on evaluating the effect of aquatic acidification in the Adirondacks. It descri bes the use of the MAGIC model to evaluate

ANC levels in selected streams and lakes in Adirondacks and Shenandoahs. To what extent is the approach taken technically sound, clearly co mmunicated, and appropriately
characterized?

1 Reuss J.O., and D.W. Johnson. 1986. Acid Deposition and the Acidification of Soil and Water. Chapter 7.5: Capacity versus Intensity. Ecological Studies No. 59. Springer-Verlag, New York, Pages 71-72.)

6The selection of the Adirondacks and the Sh enandoah Park as case study areas and the use of MAGIC as the modeling tool are appropriate; however, this section needs to be edited for clarity. At present, it is genera lly confusing, especially the mode ling approach and descriptions

of MAGIC and ASTRAP models. Numerous errors make it difficult to fully assess technical

merits of the discussion in Attachment 3.

ANC has been selected as a metric to quantify the current acidic conditions and biological impacts because, in many studies, it was found to be the most appropriate single indicator of the biological response of aquatic communities in the acid-sensitive ecosystems and it is relatively easy to simulate using wate rshed biogeochemical models. Based on the ANC values and fish populations responses, five cl asses of biological responses (acute, severe, elevated, moderate and low concerns) have been developed and can by used for evaluation of risk assessment using the critic al loads concept. As suggested above, for a higher level of protection of fish species EPA should consid er using a more conservative value of 100 μ eq/L

instead of 50 μ eq/L.

Some comparisons of these case study result s with other efforts to evaluate acid deposition/biogeochemical responses in each of these sites (especially the Adirondacks) would

be useful to indicate eith er differences from or support for these modeling efforts.

3. Attachment 4 presents our current progre ss on evaluating the effect of terrestrial acidification. It outlines a pl an to use the Simple Mass Bala nce Model to evaluate current deposition on forest soil A NC for sugar maple in Kane Experimental Forest and red spruce in Hubbard Brook Experimental Forest . To what extent is the approach taken technically sound, clearly communicate d, and appropriately characterized?

The selection of the study ar ea is reasonable. Attachment 4 is highly uneven. Substantial detail has been provided in some cases, while br oad generalizations are made in others. It is

difficult for the reader to ascertain the salient points in this chapter.

4. Attachment 5 presents our current progress on evaluating the effect of aquatic nutrient enrichment. It outlines a plan to evaluate how changes in nitrogen deposition affect the eutrophication index in two estuaries: Ch esapeake Bay and Pamlico Sound. The analysis will model one steam reach (Potomac River and Neuse River) to determine the impact on the eutrophication index for the estuary. To what extent is the appr oach taken technically sound, clearly communicated, and ap propriately characterized?

The approach is appropriatel y characterized. The Chesapeake Bay has been the focus of considerable efforts relating to the effects of nitrogen load ing on eutrophication. Extensive investigations have been made to identify Nr sources within bot h the very large airshed and the much smaller watershed areas of the Chesapeake region. However, a poten tial drawback of the choice of both the Chesapeake Bay and Pamlico S ound areas is that for both areas atmospheric nitrogen deposition is no t likely to be the dominant component of the total nitrogen loading, and thus may not be as sensitive to atmospheri c deposition changes as ot her ecosystems where deposition is the major source of nitrogen loadin g. Future assessments should consider including

7case studies of watersheds where atmospheric deposition provides a greater proportion of the total N loading.

5. Attachment 6 presents our current progress on evaluating the effects of terrestrial nutrient enrichment. It describes an approach to evaluate the effects of N deposition on the Coastal Sage Scrub community in Ca lifornia and mixed conifer forests in San

Bernardino and Sierra Nevada Mountains. To what extent is the approach taken technically sound, clearly communicate d, and appropriately characterized?

The selection of coastal sage scrub (CSS) and mixed coni fer forest ecosystems is appropriate. Attachment 6 provides a comprehensiv e review of existing scientific knowledge for these two ecosystems and the findings have b een clearly communicated. For development of critical loads for CSS, accumula tion of biomass of invasive gra sses (critical level for occurrence of catastrophic fires) could be considered. For the mixed conifer forests, change in lichen communities is a good indicator for ecosystem eff ects at the low end and nitrate leaching to surface water is a good indicator at the hi gh end of total Nr deposition loads.

Additional Effects

1. In this chapter, we have presented result s from some initial qualitative analyses for additional effects including the impact of sulfur deposition on mercury methylation, the impact of nitrous oxide on climate change, and the impact of nitrogen deposition on carbon sequestration. Are these ef fects sufficiently addressed in light of the focus of this review on the other targeted effects in terms of ava ilable date to analyze them?

These descriptions and level of detail in Chapter 6 seem ade quate, but the relevant issues go beyond those associated with carbon sequestra tion, mercury methylation and nitrous oxide emission changes. The chapter would be much improved by providing a short summary that

describes additional welfare effects of SO

x and NO

x for which deleterious impacts are expected (e.g., effects on visibility, climate and materials; as well as the de position-related terrestrial and aquatic effects on which the REA currently focuses). Additional information is needed as to the effect of changes in pH on merc ury concentrations in fish and other organisms. This summary should indicate both the importance of these ecosy stems to individual regi ons and, in the context of the entire United States, the overall adverse ecological impacts. In c onsidering the impacts of nitrogen deposition on carbon sequestration, the positive (e.g., increased forest growth and harvestable timber production) and the negative relationships need to be considered and presented in a balanced fashion.

Synthesis and Integration of the Case Study Results into the Standard Setting Process

1. The purpose of Chapter 7 is to summarize th e Case Study results and characterize the relationship between levels of an ecologica l indicator and the associated degree of ecologically adverse effects. To what extent is this approach c haracterized at this point of the review? Does the Panel have any furthe r suggested refinements at this time?

Chapter 7 remains in a very early stage of development; thus it is difficult to provide summary comments on the overall content and dire ction of this chapter. The Chapter ends

8abruptly and seems incomplete. Section 7.3 shou ld be completed and a discussion of linkages between ecological indicators and adverse effects in terrestrial ecosystems is needed (similar to section 7.3.1 focusing on ANC in freshwater systems).

In general terms, the outline and material in cluded in the Chapter are appropriate to the intended summary. Table 7.1 will be very important in its final form in future drafts of the REA and thus EPA should carefully consider its conten ts. The initial statement at the beginning of Section 7.2 strikes the right bala nce between important effects wh ile recognizing their variable and localized nature. As appropr iate throughout Chapter 7 (and the entire REA), the wording

should be scrutinized so that the reader is clear when NO

x and SO

x versus total S or N deposition are the real drivers for the effects being consider ed. In the summarized cases, the key metric is total deposition irrespective of the original ch emical forms of the airborne S and N inputs.

Considerations in the Structure of the NOx/SOx Secondary Standard

1. Chapter 8 begins to explore how a secondary NAAQS might be structured to address the targeted ecological effects discussed in the risk assessment. The next draft of this

document will include one or more examples of how this struct ure might be used to relate specific levels of air qualit y indicators with a correspondi ng ecological indicator for a given location and/or scenario. To what ext ent is the described approach technically sound, clearly communicated and appropriately char acterized at this point of the review? Does the Panel have any further sugg ested refinements at this time?

As noted previously, the Panel views that, sc ientifically, a NAAQS standard developed to protect ecological systems should focus on to tal acidifying deposition and excess nutrient enrichment, both of which include chemically -reduced, organic and oxidized forms of total reactive nitrogen. The current constraints have led EPA to focus on developing a combined

ambient standard that is limited to sulfur and nitrogen oxides, but which may accommodate

indirect consideration of cont ributions from other forms of reactive nitrogen as well. The proposed approach is scientific ally well-founded: it is designed to lead to atmospheric deposition rates that will protect at least some (and perhaps many) of the target ecosystems as measured by specific ecosystem-based indicators of adverse ecological effects (e.g., ANC). While the approach does not directly include ta rgeted decreases in atmospheric deposition of reduced or organic forms of nitrogen, the appr oach does include consideration of chemically reduced and organic nitrogen loadings as part of the already existi ng conditions that contribute to acidification and nutrient enrichment of sensitive ecosystems. As such, the approach could provide for a substantial decrease in some of the adverse ecologi cal effects of acidification and

nutrient enrichment in various part of the United States.

The Panel concludes that the approach presen ted is novel and environmentally relevant. The description should be clarifie d and more detail should be pr ovided, specifically with regard to how the approach could be implemented in some of the proposed Case Study Areas. EPA should clarify how the approach would promote controlling chemically-reduced and oxidized nitrogen loadings as a means to decreasing ecologi cal acidification and nutrient enrichment.

Currently, the discussion in Chapter 8 on es tablishing an appropriate linkage between

910 ambient air concentrations and ecosystem effect s, and the importance of spatial and temporal scales, is limited. The Chapter should show how the proposed approach di rectly addresses the Panel’s concerns that, from a scientific pers pective, the resulting environmentally-focused standard would include all reactive N deposition. Further, the Panel has concerns about the feasibility of implementing a standard base d on this approach. There are a number of complications that need to be addressed so as to fully inform policy-makers, particularly in preparation for the development of an appropr iate Advanced Notice of Proposed Rule Making (ANPR). Critical issues that need to be elaborated upon include:

1. whether (or how) a standard w ill integrate the multiple indicators identified in the case studies,

2. what are the appropriate spatial scales fo r each indicator and sensitive ecosystem,

3. how varying levels of protection required by different ecosystems can be accommodated,

and

4. what level of protection is being provided to various ecosystems under alternative levels

and forms of the standards.

The REA as a whole needs to show how the re sults of the case studies (specifically, the relationships between the observed chemical a nd biological changes and N and S atmospheric deposition) can be linke d to the traditional NO

x , SO

x and PM standards that are based on ambient concentrations. It is imperative th at this additional linkage informa tion is incorporated in the next draft of Chapter 8.

In summary, the CASAC Panel was pleased to review this first draft of the Risk and Exposure Assessment to Support the Review of the Secondary National Ambient Air Quality Standard for Oxides of Nitrogen and Sulfur . The Agency’s venture in to new territory in the consideration of multi-pollutant standards is laudable. Shifting to standards that focus on ecological effects and employ metrics that are speci fically relevant to ecosystems will have some inherent complexities and difficulties, and the Panel looks forward to following and contributing to the evolution of suggested approaches.

Sincerely,

/Signed/ /Signed/

Dr. Armistead (Ted) Russell, Chair Dr. Jonathan M. Samet, Chair

CASAC NO

x & SO

x Secondary Clean Air Scientific Advisory Committee NAAQS Review Panel

EnclosuresEnclosure A



### U.S. Environmental Protection Agency Clean Air Scientific Advisory Committee

NO

x 

### & SO

x 

### Secondary NAAQS Review Panel

CHAIR

Dr. Armistead (Ted) Russell , Professor, Department of Civ il and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA

PANEL MEMBERS

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

Dr. Andrzej Bytnerowicz , Senior Scientist, Pacific Southw est Research Station, USDA Forest Service, Riverside, CA

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

Dr. Douglas Crawford-Brown , Professor Emeritus, Department of Environmental Sciences and Engineering, University of North Caro lina at Chapel Hill, Chapel Hill, NC

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 Sta ff 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 & Tr end Analysis (CAPITA), Washington University, St. Louis, MO

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

Dr. Donna Kenski , Data Analysis Director, Lake Mi chigan Air Directors Consortium,
Rosemont, IL

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

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

11Mr. Richard L. Poirot , Environmental Analyst, Air Pollutio n 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, Fa x: 202-233-0643, (barry.kyndall@epa.gov)

12Enclosure B



### U.S. Environmental Protection Agency Clean Air Scientific Advisory Committee

CHAIR

Dr. Jonathan M. Samet , Professor and Chair, Department of Preventive Medicine, University of Southern California, Los Angeles, CA

MEMBERS

Dr. Joseph Brain , Philip Drinker Professor of Envir onmental Physiology, Department of Environmental Health, Harvard School of Public Health, Ha rvard University, Boston, MA

Dr. Ellis B. Cowling , University Distinguished Professo r At-Large Emeritus, Colleges of Natural Resources and Agricultur e and Life Sciences, North Caro lina State University, Raleigh,

NC

Dr. James Crapo , Professor of Medicine, Department of Medicine, National Jewish Medical and Research Center, Denver, CO

Dr. H. Christopher Frey , Professor, Department of Civ il, Construction and Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, NC, USA

Dr. Donna Kenski , Data Analysis Director, Lake Mi chigan Air Directors Consortium,
Rosemont, IL

Dr. Armistead (Ted) Russell , Professor, Department of Civ il and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA

SCIENCE ADVISORY BOARD STAFF

Dr. Holly Stallworth , Designated Federal Officer, 1200 Pennsylvania Avenue, NW, Washington, DC, Phone: 202-343-9867, Fa x: 202-233-0643, (stallworth.holly@epa.gov)

13Enclosure C

Comments received:

Dr. Praveen Amar....................................................................................................................... 15 Dr. Andrzej Bytnerowicz ............................................................................................................ 17

Ms. Lauraine Chestnut............................................................................................................... 20 Dr. Ellis B. Cowling .................................................................................................................... 22 Dr. Douglas Crawford-Brown ................................................................................................... 30

Dr.Charles T. Driscoll ................................................................................................................. 33

Dr. Paul J. Hanson ...................................................................................................................... 43

Dr. Rudolf Husar ........................................................................................................................ 49

Dr. Dale W. Johnson ................................................................................................................... 52

Dr. Donna Kenski ........................................................................................................................ 55

Dr. Naresh Kumar ...................................................................................................................... 62 Dr. Myron J. Mitchell ................................................................................................................. 65

Mr. Richard Poirot ..................................................................................................................... 84

Mr. David Shaw .......................................................................................................................... 89

Dr. Kathleen C.Weathers ........................................................................................................... 93

14

### Dr. Praveen Amar

The charge is to respond to Questions #2 and 3 re lated to air quality an alyses. Specifically, the two questions are reproduced here:

Question # 2 : Section 3.2.1 describes an appr oach for evaluating the spatial and temporal patterns for nitrogen and sulfur deposition and associated ambient concentrations in the case study locations. This draft document includes th e analysis for the Adirondacks Case Study. Does the Panel agree with this approach and should it be applied to the other Case- Study Areas?

Question # 3 : Section 3.2.2 describes the relative contributions of ambient emissions of nitrogen and ammonia to nitrogen deposition for the case-study areas. To what extent is the approach taken technically sound, clearly communi cated, and appropriately characterized?

Question # 2 Response:

The approach outlined in Section 3.2.1 should prove to be useful in that it does propose to do a complete analysis of spatial and temporal patterns of concentrati ons and deposition of sulfur and nitrogen compounds (dry oxidized nitrogen, dry redu ced nitrogen, wet oxidized nitrogen, wet reduced nitrogen, dry sulfur deposition and wet su lfur deposition). However, the analyses at the present time are based only on CMAQ predic tions (text says “CMAQ data”; “CMAQ predictions” is more appropriate) are only for one year (2002), and for just one case-study location (Adirondacks).

1. At a minimum, before one can answer the ques tion “Does the Panel agree with this approach and should it be applied to other case-study ar eas?” with a reasonable level of confidence, the proposed approach needs to include an independent as well as corroborative (by comparing it to model-predicted re sults) analysis that is based on measured data for this case-study region (as well as the remaining case -study regions). It appears that modeled CMAQ results are reasonable, but it will increase the confidence in this approach if the measured data from NADP and CASTNet (a nd other networks in the Adirondacks region and other regions) corroborate the modeled predictions.

2. It is also important that before this approach is applied to other cas e-study areas, that the placeholders on Page 3-53 and 3-54 be complete d. I would recommend that the analysis of

inter-annual variation in N and S (for the years 2002-2006) depos ition as well as uncertainty analysis (Section 3.2.1.5) be firs t completed for Adirondacks regi on before similar analyses are done for the other four case-study regions.

3. Once the measured deposition data analyses are completed, Section 3.2.1 should include a brief evaluation/comparison of CMAQ predicti ons for the four nitrogen and two sulfur components. As a part of this evaluation, the measured precipitation data and modeled (from MM5?) precipita tion data (amounts and spatial pattern s) should be compared. This

15is important since the modeled results in S ection 3.2.1 indicate str ong correlations between amount of precipitation and wet deposition.

4. A general comment on presentation of results on dry deposition of N and S: This section

needs to be more clear and explicit that we only estimate dry deposition (whereas we measure wet deposition) and therefore conclu sions on total deposition (wet and dry) and on the relative contribution of each pathway have a level of uncertainty that is hard to determine, but needs to be acknowledged (f or example, in Section 3.2.1.5 on Uncertainty).

Question # 3 Response:

This question involves the description of relati ve contributions of ambient emissions of NOx and ammonia to deposition of nitrogen (tot al nitrogen deposition (TND), oxidized nitrogen deposition (OND), and reduced nitrogen deposit ion (RND)) for the eight case-study regions. It asks if the approach used is technically sound, clearly communicated, and appropriately

characterized. Here are some comments:

1. The “model of the model” or the RSM (Response-Surface Model) applied to CMAQ needs a more friendly description on how it works. On Page 3-55, the text makes an effort but does not succeed in explaining wh at (and how) exactly RS M does. It appears that RSM is like an “instrumented CMAQ” mode l in that it “represents the outputs of the CMAQ model using statistical pr edictions.” It is not clear to me what exactly these statistical predictions are. It might be us eful to compare the “w orkings” of RSM with, say, Direct Decoupled Method (DDM) or other “process” models (that evaluate the

relative contribution of various processes embedded in the model on model predictions). Has the RSM approach been applied by the general scientific and policy/regulatory

communities outside the US EPA?

2. To the extent RSM is essentially based on th e “brute-force” appro ach of “zeroing out” NOx or ammonia emissions (recognizing there are some residual emissions for NOx that include international sources and lightning, and, for NH3, they include international, non-anthropogenic and point source emissions), I am not sure this is the right approach to accurately answer Question # 3. Are there more appropriate approaches that do not “unduly stress” the CMAQ model that can be tter address this question of relative

contributions?

3. It is not clear to me how the twelve “emissi on control factors” on Page 3-56 were actually applied in the model. Were the emissions zer oed out only for the case-study region or for the whole modeling domain?

16

### Dr. Andrzej Bytnerowicz

Question 2 – Current progress on evaluation the e ffects of aquatic acidification in the

Adirondacks and Shenandoah. To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized?

Selection of the Adirondack Mountains and Shenandoah National Park for estimation of ecological effects and risks caused by acidifying deposition of N and S is well justified. The two areas experience high levels of deposition, are characterized by a high density of anthropogenically acidified lakes and streams, and there is a well documente d record of chemical and biological changes from many studies w ith their results published in peer-reviewed

literature.

The proposed approach is logical and technically sound. The wet deposition data comes from the NADP/NTN networks operational in the Adirond acks since 1978 and in the Shenandoah since 1980. Current conditions were evaluated by a 3 step process that assessed trends in surface water

SO 4 2- , NO 3 - and ANC concentrations; the percent of watershed bodies th at have different degree of acidity; and the percent of water bodies receiving N & S depos ition above the harmful levels (exceedance of critical loads). Biological e ffects of acidity caused by atmospheric N & S deposition are measured at the individual level as fitness and at the community level as species richness and community structure. ANC has been selected as a metric to quantify the current acidic conditions and biological impacts because in many studies it was found to be the best single indicator of the biologi cal response of aquatic commun ities in the acid-sensitive ecosystems. Relationship between ANC and number of fish species showed that at the ANC

values of 50-100 μ eq/L, species richness begins to declin e. Based on the ANC values and fish populations responses, five classes of biological responses (acute, severe, elevated, moderate and low concerns) have been developed and can by us ed for evaluation of risk assessment using the critical loads concept.

It will be interesting to see complete results of the planned evaluations.

Specific comments:

Page 32, Figure 5.1-2 - why there is such a high di fference in the “severe” category between the observed and MAGIC modeled outputs?

Page 33, Figure 5.1-3 – change ANC units to μ eq/L. In the same figure – why not to use more

conservative value of 100 μ eq/L instead of 50 μ eq/L as the thres hold of protection?

Question 5 – Current progress on evaluating the effects of terrestrial nutrient enrichment for coastal sage scrub and mixed conife r forests of California. To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized?

17Selection of coastal sage scr ub (CSS) and mixed conifer fore st ecosystems is appropriate because: (a) these ecosystems have high geographi c coverage and are located in the important wildland–urban interface I highl y populated areas, (b) they encomp ass a strong gradient of N deposition from the low, background le vels up to the highest levels recorded in the US, (c) these ecosystems have been investigated for a long time from a perspec tive of interactive effects of atmospheric deposition, climate change fire a nd other stressors, (d) results of these investigations are well documented in the peer-reviewed literature.

If the goal of this chapter was to review the cu rrent state of science for these two case studies, than the approach taken was technically sound and findings have been clearly communicated. However, if results of these two case studies were supposed to show how the relationships between the observed chemical and biological ch anges and N atmospheric deposition (possibly expressed as critical loads) c ould be linked to the concentratio n-based NOx/SOx standards, then the used approach was not inadequate and should be revised.

The chapter provides a comprehens ive review of the existing scientific knowledge for these two case studies. GIS maps show modeled N deposition in portion of California encompassing the two selected ecosystems, CSS threat from fire, and the presence of acidophyte lichens. Three-dimensional maps illustrating loss of CSS in re lation to different levels of fire threats or N deposition could greatly help in developing a probabilistic appr oach to the evaluation of N deposition risks to important California ecosystems.

For development of CL for CSS, in addition to biodiversity changes or changes in lichen communities, accumulation of biomass of invasive grasses (critical level for occurrence of catastrophic fires) could be considered (Anderson, 1982; Sci fres and Hamilton, 1993; Gimeno et al., 2009; Minnich and Franco-Vizcaino, 2009). Fo r more information on this subject please

contact Drs. Richard Minnich and Edith Allen, UC Riverside. For the mixed conifer forests, on the low end of N deposition changes in lichen communities, and on its high end, nitrate leaching to surface water, are good end points for CL esti mates. Other, such as possible changes in understory biodiversity changes could al so be considered and explored.

Data on N deposition levels was obtained from the NADP and CASTNET networks and modeled N deposition distribution from the CMAQ model runs for 2002, which were based on the 12 km grids. As the authors of this analysis suggest, results from the 4 km grid would greatly improve accuracy of predicted relationships between N deposition and the biological effects.

Some data for the main drivers of N dry deposit ion in the San Bernardino Mountains, gaseous

HNO 3 and NH 3 from passive samplers have already been published (Bytnerowicz et al, 2007). More results on distribution of N nitrogenous gases monitored with passive samplers in southern

California and southern Sierra Nevada are currently being prep ared for publication (Andrzej Bytnerowicz, unpublished).

Suggestion: For better unders tanding of regional (southern Sierra Nevada) effects of N deposition, comparison of responses in mixed coni fer forests (Kings Rive r Project) such as leaching of nitrate to streams, lichen species composition, and invasi on of invasive grasses, could be compared to ANC changes in the nearby lake s of the sub-alpine and alpine zone.

18Specific comments:

Page 13, 1 st paragraph – also high levels of NH 3 and NH 4 + are deposited to CSS of southern

California.

Page 29, Figure 3.1-1. Scale for N deposition is too coarse – a bracket 6.83-70.04 kg N/ha/yr is not acceptable.

Page 33, 1 st paragraph – bark beetle s hould be added as important stressor in the mixed conifer forest ecosystem.

Page 44 and 45, section 5.2 – for the mixed conifer forest also changes of species composition of the under story vascular plants should be considered.

Page 45, list of questions – in regard to respons es of lichens to N deposition, effects of oxidized vs. reduced N should be considered. This may be of interest because there is a potential shift

towards less reduced N due to the movement of dairy farms from the Los Angeles Basin to California Central Valley.

References:

Anderson, H. E. 1982. Aids to determining fuel models for estimating fire behavior. USDA

Forest Service Intermountain Fo rest and Range Experiment St ation, General Technical Report INT-122, Ogden, Utah. http://www.fs .fed.us/rm/pubs_int/int_gtr122.pdf

Bytnerowicz, A., M. Arbaugh, S. Schilling, W. Fraczek, D. Alexander, P. Dawson (2007) Air pollution distribution patterns in the San Bernardino Mountains of southern California: a 40-year perspective. TheScientificWorldJOURNAL 7(S1) , 98–109. DOI 10.1100/tsw.2007.57.

Gimeno, B. S., Yuan, F., Fenn, M. E., Meixner, T. 2009. Management options for mitigating nitrogen (N) losses from N-saturated mixed-conifer forests in California. In: A. Bytnerowicz, M. Arbaugh, A. Riebau and C. Andersen (eds). W ildland Fires and Air Pollution, Developments in Environmental Sciences, Vol 8, Elsevier, Amsterdam, pp. 425-455.

Minnich, R. A., Franco-Viscaino, E. 2009. A pr obabilistic view of chaparral and forest fire regimes in southern California and no rthern Baja California. In: A. Bytnerowicz, M. Arbaugh, A. Riebau and C. Andersen (eds). W ildland Fires and Air Pollution, Developments in Environmental Sciences, Vol 8, Elsevier, Amsterdam, pp. 339-364.

Scifres, C.F., Hamilton, WT. 1993. Prescribed Bu rning for Brushland Management: The South Texas Example. Texas A & M University Press, College Station.

19

### Ms. Lauraine Chestnut

Charge question 1: Scope of the review There seems to be some ambiguity regarding use of the term “sensitive.” It sometimes seems to mean an ecosystem that is vulnerable but not nece ssarily harmed at current or historic deposition rates, and other times it seems to mean that harm is occurring at current exposures. To me, the

word sensitive fits better for the former than fo r the latter. For there to be harmful effects it would seem to require both se nsitivity and exposure. Thus, the selected case studies are appropriately selected as not just sensitive, but currently being affected by N and/or S deposition.

Pages 2-7 to 2.8

Descriptions of ecosystem services reduced or degraded as a result of harmful effects on ecosystem functions are not only important i nputs into economic valu ation and cost-benefit analysis, they are important in helping policy makers and the public unde rstand the significance of the effects on the ecosystems.

It is important to recognize that economic valuation is best considered rela tive to an alternative. In figure 2.3-2 it is unclear what an economic value to “maintain” an ecosystem would be without specifying what would ha ppen if some action were not taken. There may be a value to prevent a specified amount of degradation or a va lue to obtain a specified improvement, but the value to simply “maintain” is probably ambiguous.

Page 2-13

This discussion of uncertainty is pretty weak. One important note is that variability is not the same thing as uncertainty. There may be a lot of variability in how diffe rent ecosystems respond to the same amount of N/S deposit ion but it may be able to specify this variability with a great deal of certainty.

It is important to acknowledge uncertainty, but a critical thing here is how to determine when there is enough known to be able to set reasonable standards. The uncertainty issue will need to be taken up again when the analysis is furthe r along. A key question is whether there is enough confidence in the results that they are useful to assist policy de cision-making. This requires more than just listing sources of uncer tainty, but necessitates an assessm ent of the significance of the uncertainty and how it affects the results.

Case studies

The proposed use of ecological indi cators that can be linked to varying levels of effects (and related losses in ecosystem servi ces) goes beyond the idea of estim ating critical loads at which ecosystems experience no effects. This does not co me through in the current draft until Chapter 7, and is a missing perspective in the various ca se study appendices. An important consideration

20that has to be made as these indicators are selected is their ability to be linked to effects of varying severity rather than defining simply a "no effects" threshold, because this will be important information for the eventual assessment what effects are adverse.

The REA ultimately needs to describe the significance of the effects on ecosystem function and

services at current levels of e xposure and at alternativ e levels of exposure that might be achieved

with alternative standards in the case study areas. Selecting an y secondary standard probably requires more than a determination of a “safe” leve l because the standard needs to protect against adverse effects, not just any effects. The case stu dy analyses seem to be headed in this direction and I look forward to seeing this furt her fleshed out in the second draft.

Chapter 8

An important issue is that is not yet addressed is how the analysis will deal with spatial scale in defining a potential standard. This is complicated by expected va riability in eco logical response to deposition in different locations even within a case study ecosystem. It is unlikely to be reasonable or even feasible to set a standard to protect the most sensitive ecosystems (or components of an ecosystem). The scale decisions can be somewhat analysis driven in that the results may show reasonable categories or groupi ngs, such as X% of lakes in the Adirondacks

that would have an ANC of 50 or 100 at various ambient co

21

### Dr. Ellis B. Cowling

My individual comments on the August 2008 Firs t External Review Draft of the Risk and Exposure Assessment (REA) for the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur are or ganized below in response to each of the several Charge Questions posed the Pa nel in preparation for the Oc tober 1-2, 2008 CASAC meeting. As you will see, somewhat more detailed attention has been given to the five Charge Questions on Case Study Analyses and the recently received Ch apters 7 and 8 than to other parts of this Risk and Exposure Assessment as requested by the Chair.

Scope of the Review

2. Chapters 1 and 2 provide the background, hi story, and framework for this review, including a discussion of our focus on the four key ecological effect areas (aquatic acidification, terrestrial acidification, aquatic nutrient enrichment, terrestrial nutrient enrichment). Is this review appropriately focused in terms of characterizing the important atmospheric and ecologic variables that influe nce the deposition and, ultimately, the ecologic impacts of nitrogen and sulfur? Does the Panel have any further suggested

refinements at this time?

My most serious reservation about the analysis framework for Chapters 1 and 2 is that chemically reduced forms of nitrogen (NHx), organic forms of nitrogen (NCx), and total reactive nitrogen (Nr) all are not included in the specific wording of any of the 20 policy-re levant questions that are said to constitute the framework for this review on the effects of nitrogen and sulfur pollution on acidification and nutrient enrichment of aqua tic and terrestrial ecosystems in the US.

This reservation is surprising in view of the very comprehe nsive analysis regarding the importance of chemically reduced forms of reactive nitrogen contained in the Integrated Science Assessment (ISA) document and also in view of the October 31, 2007 Resolution from the Science Advisory Board’s Integrated Nitr ogen Committee (INC) which makes the following strong assertion from the INCs Committee’s examin ation of much of the same body of evidence

reviewed in the ISA:

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

Please note the roster of current members of the SA B’s Integrated Nitrogen Committee whose collective competence with regard the public welfare and public hea lth effects of reactive nitrogen is very similar to the collective competence of the CASAC Panel selected to review Secondary NAAQS for Oxides of Nitrogen and Oxides of Sulfur as can be seen in the Determination Memo at http://yosemite.epa.gov/sab/sabproduct .nsf/02ad90b136fc21ef85256eba00436459/c83c30afa465 6bea85256ea10047e1e1!OpenDocument&TableRow=2.1#2

.

22The conclusionary statements written in bold-type in Chapter 4 of the ISA indicate that:

“The evidence is sufficient to infer a causa l relationship between “acidifying deposition” (which includes NHx, and NCx, as well as NOx ) and the following adverse acidification

effects: a) “changes in biogeochemistry rela ted to terrestrial ecosystems,” b) “changes in terrestrial biota,” c) “changes in biogeochemistry rela ted to aquatic ecosysytems,” d) “changes in aquatic biota.”

Also, “The evidence is sufficient to infer a cau sal relationship between Nr (reactive nitrogen) deposition (which also includes NHx, NCx, and NOx) and the following additional ecologically

adverse nutrient- enrichment effects: e) “alteration of biogeochemical cycling of N in terrestrial ecosystems,” f) “alteration of biogeochemical cycling of C in terrestrial ecosystems,” g) “alteration of biogeochemical flux of N 2 O in terrestrial ecosystems,” h) “alteration of biogeochemical flux of CH 4 in terrestrial ecosystems,” i) “alteration of species richness, species co mposition and biodiversity in terrestrial ecosystems,” j) “alteration of the biogeochemical cycling of N,” k) “alteration of the biogeochemical cycling of C,” l) “alteration of N 2 O flux in wetland ecosystems,” m) “alteration of CH 4 flux in wetland ecosystems,” n) “alteration of species richness, specie s composition and biodiversity in wetland ecosystems,” o) “alteration of biogeochemical cycling of C in freshwater aquatic ecosystems,” p) “alteration of species richness, species co mposition and biodiversity in freshwater aquatic ecosystems,” q) “alteration of the biogeochemical cycling of N in estuarine aquatic ecosystems,” r) “alteration of the biogeochemical cycling of C in estuarine aquatic ecosystems,” s) “alteration of species richness, species composition and biodiversity in estuarine aquatic ecosystems,”

“The evidence is sufficient to in fer a causal relationship between: t) “exposure to NO, NO 2 , and PAN and injury to vegetation” and s) “exposure to HNO 3 and changes to vegetation.”

On the basis of this substantial body of accumu lated evidence, I recommend that a schematic diagram similar to Figure 1.3-1 be included in Chapter 1 of the Second Draft REA document to illustrate the “cycle of reactive, chemically reduced nitrogen species.” I also recommend that: a) Chemically reduced (NHx) and also organic fo rms (NCx) of total reactive nitrogen also be included among the nitrogen pollutants of concern in many of the 20 policy-relevant questions listed in Section 1.4 on pages 1-17 th rough I-20 in Chapter 1 of this First Draft REA, and b) Appropriate answers about both chemically reduced (NHx) forms of total reactive nitrogen, and, if possible also organic forms (NCx) of total react ive Nitrogen (Nr), be presented in Chapters 2, 3, and 4 of th e Second Draft REA when it is completed.

23Air Quality Analyses

4. To what extent are air quality characterizations and analyses presented in Chapter 3 technically sound, clearly communicated, approp riately characterized, and relevant to the review of the secondary NAAQS for NOx and SOx?

With the exception of the major reservations stat ed in answer to the Charge Questions about the Scope of the Review, I believe that the an alyses presented in Chapter 3 are technically sound, clearly communicated, and appropriately characterized.

5. Section 3.2.1 describes an approach for evalua ting the spatial and temporal patterns for nitrogen and sulfur deposition and associated ambient concentrations in the case study locations. This draft document includes the analysis for the Adirondacks case study. Does the Panel agree with this approach and should it be applied to the other Case Study Areas?

The approach used for evaluating the spatial a nd temporal patters for of N and S deposition and associated ambient concentration seems very reasonable to me. This approach proved to be useful in the Adirondacks Case study and I expect it to be reasonable for other case studies as well.

6. Section 3.2.2 describes the relative contributions of ambient emissions of nitrogen and ammonia to nitrogen deposition for the case study areas. To what extent is the approach taken technically sound, clearly communica ted, and appropriately characterized?

I presume from examining the figures and associated text for the data presented on pages 3-63 through 3-112 that this question should have read:

” Section 3.2.2 described the relative contributions of chemically oxidized and chemically reduced forms to total reactive nitrogen for the Case Study areas. To what extent is the approach taken technically sound, ...etc.”

On the assumption that my presumption is correct, I consider this combination of modeling and measurement approaches to be reasonable. But I must confess that it took me a very long time to finally understand the rationale behind the statemen t on lines 10-12 on page 3-13 that “In order to calculate total nitrogen (by which I suppose the author meant deposition of total reactive nitrogen) the two chemical species from the Na tional Atmospheric Deposition Program (NADP) (i.e., NO3- and NH4+) were added together and then added to the total dry deposition values estimated from the Community Multiscale Air Quality model (CMAQ).

It also took me a very long time to understand what was meant by the term “zero-out of NOx emissions” as used in most of the figure captions on pages 3-63 through 3-112) and periodically in the

associated text.

With regard to the questions of “clearly communi cated and appropriately characterized” I offer the following comments:

1) What a delight it was to find the following firm statement on lines 15-20 on page 3-70:

“Figures 3.2-42 examines the relative impact of emissions on NH 3 of the deposition of total reactive nitrogen. Figure 3.2-42 shows that NH 3 emissions represent a significant contribution to total reactive nitrogen in most case study areas, although the impact varies by season and by area. The smallest impact of NH 3 , 10% occurs in the Potomac ca se study area in February. The

24largest impact of NH 3 , 73% occurs in the Neuse Case stud y in July. The Neuse case study has the largest overall impact of from NH 3 of any of the case study areas, across all four seasons.”

2) On lines 6 and 7 also on page 3-63 (and another case on lines 9 and 10 on page 3-71) we find three very confusing sentences that reveal clearly why EPA’s constant use of the terms “reduce,” “reducing” and “reduction” is so often confusing and ambiguous:

“One possibility is that reducing NOx reduces HNO 3 , which limits ammonium nitrate (NH 4 NO 3 ) formation (and for existing aerosol, a reduction in HNO 3 shifts the equilibrium towards the gas phase), thereby increasing the lifetime of NH 3 . A net increase in NH 3 /NH 4 results. Because the deposit velocity of NH 3 is much higher than the deposition of NH 4 + aerosol, dry deposition of

NH

x increases.

The terms “reduce,” “reducing” and “reduction” have both chemical and numerical meanings. Fortunately we have the unambiguous terms “d ecrease” and ”decreasing” which have only a single (always numerical) meaning. So why not use the unambiguous term “decrease” instead of the word “reduce” when our intended meaning is numerical and thus reserve the term “reduce” for its chemical meaning?

Is this what was meant by the sentence quoted above?

“One possibility is that decreasing emissions of NOx decreases air concentrations of HNO 3 , which limits ammonium nitrate (NH 4 NO 3 ) formation (and for existing aerosol, a decrease in

HNO 3 emissions shifts the equilibrium towa rds the gas phase), thereby increasing the atmospheric lifetime of gaseous NH 3 . A net increase in the ratio of gaseous NH 3 to NH 4 + aerosol in the atmosphere results. Because the deposit velocity of gaseous NH 3 is much larger than the deposition velocity of NH 4 + aerosol, dry deposition of NH

x increases.

Case Study Analyses

1. Attachment 2 presents a GIS analysis to defi ne geographical areas that are sensitive to acidification and nutrient enrichment. Are the national geospatial data sets chosen adequate to identify sensitive areas? Are the re other data sets that have not identified by this analysis that we should consider? Does the Panel agree with approach or can they suggest alternatives?

I have only limited experience with the several data bases that we re used in the GIS analysis used in an attempt to define geographic areas that are sen sitive to acidification. Thus I have only limited professional experience on which to base a detailed judgment in response to this question.

Nevertheless, my general impression derived from study of the summary map on page 18 of Attachment 2, and my general awareness of so il, vegetation, surface and ground waters, and the topographical, meteorological, and climatic factors that are relevant to acidification and nutrient enrichment, lead me to conclude that the GIS approach used is generally sound. I know of no additional data sets that should be included in this analysis.

2. Attachment 3 presents our current progress on eval uating the effect of aquatic acidification

in the Adirondacks. It describes the use of the MAGIC model to evaluate ANC levels in

selected lakes and streams in the Adirondack s and Shenandoah. To what extent is the approach taken technically sound, clearly commu nicated, and appropriately characterized?

25I have no direct experience on which to base an in formed judgment in response to this question. However, several of my colleagues tell me that th e MAGIC model is very appropriate for these kinds of analyses.

3. Attachment 4 presents our current progress on evaluating the effect of terrestrial acidification. It outlines a plan to use th e Simple Mass Balance Model to evaluate current deposition levels on forest soil ANC for sugar maple in the Kane Experimental Forest and red spruce in the Hubbard Brook Experimental Forest. To what extent is the approach taken technically sound, clearly communica ted, and appropriately characterized?

I have studied Attachment 4 with considerable care and consider that the approach taken so far (since this is still a work in progress) is technically sound, clearly communicated, and appropriately

characterized.

4. Attachment 5 presents our current progress on evaluating the effect of aquatic nutrient enrichment. It outlines a plan to evaluate how changes in nitrogen deposition affect the eutrophication index in two estuaries: the Chesapeake Bay and Pamlico Sound. The analysis will model one stream reach (Potomac River and Neuse River) to determine the impact on the eutrophication index for the est uary. To what extent is the approach taken technically sound, clearly communicate d, and appropriately characterized?

I have studied attachment 5 with reasonable care a nd conclude that the appr oach taken in this case also is technically sound, clearly communicated, and appropriately characterized.

5. Attachment 6 presents our current progress on e valuating the effects of terrestrial nutrient enrichment. It describes an approach to evaluate the effects of nitrogen deposition on the Coast Sage Scrub community in California and in mixed conifer forests in the San Bernardino and Sierra Nevada Mountains. To what extent is the approach taken technically sound, clearly communicate d, and appropriately characterized?

I have no experience with any of the western state ecosystems that are discussed in Attachment 6. Thus I have no professional experience on which to base an informed response to this question.

Additional Effects

1. In this chapter, we have presented result s from some initial qualitative analyses for additional effects including the impact of sulfur deposition on mercury methylation, the impact of nitrous oxide on climate change, and the impact of nitrogen deposition on carbon sequestration. Are these effects sufficiently add ressed in light of the focus of this review on the other targeted effects in terms of available date to analyze them?

Chapter 6 provides a useful overview of the impact of sulfur deposition on methylation of mercury which seems to me to be very worthy of consider ation with regard to setting appropriate limits on the amount of air emission of sulfur oxides that should be permitted in various regions of the US. I see little reason for worry about nutrient enrichment or acidification effects of carbon sequestration. I do believe, however, that nitrous oxide emissions s hould be incorporated in EPA’s review of the NAAQS for nitrogen pollution and its effects on terrestrial and aquatic ecosystems.

Synthesis and Integration of Case Study Result s into the Standard Setting Process (Chapter 7)

1. The purpose of Chapter 7 is to summarize the Case Study results and characterize the relationship between levels of an ecologica l indicator and the associated degree of

26ecologically adverse effects. To what extent is this approach technically sound, clearly communicated and appropriately characterized at this point of the review? Does the Panel have any further suggested refinements at this time?

I believe that the attempt being made in Chapter 7 to building a scientifically sound linkage between carefully selected ecological indicators and the exte nt and magnitude of ecologically adverse effects is a very complicated but very desirable goal.

During my initial readings of Chapter 7, and even more Chapter 8 during the few days between their availability to CASAC on September 23 and the CASA C meeting on October 1 and 2, it appeared to me that EPA was deliberately trying to build a case for making a modest decrease in emissions of nitrogen oxides (NOx -- which is already recognized as a Criteria Pollutant ) –and of course would help decrease the adverse acidification and nutrient enrichment effects of total acidifying deposition and of total reactive nitrogen -- without also ha ving to develop the very challenging regulatory case for “listing” ammonia and ammonium ions” as Criteria Pollutants.

At that time, my “seat-of-the-pants” inclination was to believe that the extent of decrease in reactive nitrogen pollution loads that are needed to protect sensitive terrestrial and aquatic ecosystems of this country probably cannot be achieved without taking steps to also include significant decreases in the amounts of chemically reduced and perhaps also organic forms of total reactive nitrogen.

During the CASAC meeting in the Research Triangl e Park on October 1 a nd 2, 2000, however, and also during the EPA Science Advisory Board’s In tegrated Nitrogen Committee (INC) Workshop held in Washington DC on October 29 and 30, 2008, I began to see several things much more clearly:

1) EPA already has full regulatory authority to limit air concentrations of oxides of nitrogen in order to protect sensitive ecological sy stems from adverse effects,

2) The regulatory and political obstacles that would have to be overcome in order to “list” ammonia and ammonium ion as Criteria Pollutants are extraordinarily large,

3) It would not be possible to meet the court-ordered regulatory deadlines for completion of the current NOx and SOx Secondary NAAQS Standard re views if an attempt were made to overcome these very imposing regulatory and political obstacles,

4) It would be possible to consider the amounts of NHx and NCx as part of the “already existing

conditions that lead to acidification and nutrient enrichment of sensitive aquatic and terrestrial ecosystems,”

5) It should be possible to determine what technically achievable extent of decrease in emissions of NOx might be sufficient to protect some if not a ll sensitive ecosystems in various parts of the US from the adverse ecological effects caused by reactive-nitrogen-induced acidification and nutrient enrichment of aquatic and terrestrial ecosystems, and

The present drafts of Chapters 7 and 8 indicate that OAQPS is seeking first to determine, within

EPA’s present regulatory structure, if decreases in emissions of nitrogen oxides (NOx) -- which are already recognized as a Criter ia Pollutant -- coul d achieve an adequate decrease in the

adverse acidification and nutrient enrichment effe cts of N pollution that are now occurring in various parts of the United States.

27During our CASAC discussions w ith OAQPS on October 2, 2008, we were assured that Chapters

7 and 8 of the Second Draft REA will deal much more completely with the combined causal effects of both chemically reduced (NHx) and chemically oxidized forms of reactive nitrogen (NOx).

Considerations in the Structure of the NOx/SOx Secondary Standard (Chapter 8)

1. Chapter 8 begins to explore how a secondary NAAQS might be structured to address the targeted ecological effects discussed in the assess ment. The next draft of this document will include one or more examples of how this structu re might be used to relate specific levels of air quality indicators with a corresponding ecologi cal indicator for a given location and/or

scenario. To What extent is the descri bed approach technically sound, clearly communicated and appropriately characterized at this point of the review? Does the Panel have any further suggested refinements at this time?

In Section 8.1 – Possible Structure of a Secondary Standard – the diagram in Figure 8.1-1 was especially informative of the approach that is currently bein g considered by OAQPS. The example given was based on the ecological indicator ANC (acid neutralizing cap acity) and assumed that the pollutants of concern were not only the chemically oxides form of reactiv e nitrogen (NOx) and sulfur (SOx) , but also the chemically reduced forms of reactive nitrogen (NHx).

The attached diagrams were developed by Ted Ru ssell in his role as Chair of the CASAC NOx/SOx Secondary Standards Review Panel for presentation to the SAB’s INC Committee during the INC Workshop in Washington DC on October 30, 2008. These two diagrams were designed to show how OAQPS might include an estimate of chemically reduced nitrogen as one of the “already existing

conditions” that lead to acidification and/or nutrient en richment of aquatic and terrestrial ecosystems, and thus to provide a basis for calculating the amount by which nitrogen oxide deposition would need to be decreased in order to achieve an appropriate critical load for acidification effects and a similarly appropriate critical load for nutrient enrichment.



## Integrating Across Species Contribution to

Acidification: A Proposed EPA Approach...

ANC Deposition

Load Atmospheric

Concentrations What is regulated

Total acidifying

deposition Indicator
Physical

Regulatory

Acceptable depositional rate

Deposition from reduced N

Dep NOx – C NOx Dep NOx

– C SOx Allowed NOx+SOx deposition Current

Allowed

28

## Applied to Nutrient Enrichment

? (your thoughts?) Deposition

Load Atmospheric

Concentrations What is regulated

Total Nutrient Load Indicator

Deposition from

reduced N Allowable R

n load

Non-atmospheric load

Allowed NOx deposition

29

### Dr. Douglas Crawford-Brown

I am charged primarily with Scope of the Revi ew, and so my comments are primarily on that issue. The specific Charge Question addressed is:

“Scope of the Review: Chapters 1 and 2 provide the background, history and framework for this review, including a discussion of our focus on the four ecological e ffect areas (aquatic acidification, terrestrial acid ification, aquatic nutrient enri chment, terrestrial nutrient enrichment). Is this review appropriately focu sed in terms of characterizing the important atmospheric and ecologic variables that influe nce the deposition and ultimately the ecologic impacts of nitrogen and sulphur? Does the panel have any further suggested refinements at this

time?”

This review also considers Chapters 7 and 8, as th ese are the core of the document in regards to an eventual regulatory decision.

As with my review of th e ISA, my conclusion here is that th e REA does in fact satisfy the goal in the Charge Question, subject to the comments below. The correct effects are considered (there may be more effects one could note, but the ones considered here are the most significant and are likely to bound the areas of concern adequately), and the correct relationshi ps to atmospheric and ecologic variables are considered (again to the extent these ar e needed to draw the primary conclusions). The document is well written, be ing easy to follow and nicely organized, although the wheels fall off a bit – or are not even present - in Chapters 7 and 8). The authors have culled the most important conclusions from an immense literature, focusing the reader properly onto the key findings. A theme that will emerge below, howev er, is my feeling that the available data and analyses may support the need for consider ing a reduced NAAQS for NOx and SOx, but is insufficient to suggest the actual ambient levels needed to avoid demonstrably adverse effects (which I contrast with effects alone, which ma y or may not be sufficient to deem adverse).

This document would benefit greatly from an Ex ecutive Summary similar to the one in the ISA. There is a large amount of information here, but it can be boiled down to a few key conclusions. My fear is that failing to do that, the authors may find specific parts of the document picked in the policy process because they support a desire d conclusion and policy solution. There needs to be a concise and unambiguous statement of the key scientific conclusions, and an Executive Summary is exactly the place to put these.

I found Chapter 1 very well writte n. The document lays out the relevant policy questions and even relates these (in contrast to past documents) clearly to th e task of deciding whether the NAAQS needs to be revised and, if so, how the information would be used to do that.

Figure 1.4-1 is quite interesting, but it also lays clear the one glaring prob lem with a secondary NAAQS, since the key element is the Ecologica l Effect Function. I don’ t see where such a function is sufficiently well establ ished to allow use in setting a secondary standard, other than perhaps as an analogue to an effects threshol d in non-cancer human heal th risk assessment,

30probably with some margin of safety inherent in it due to the inability to draw a proper line

between effect and adverse effect.

Chapter 2 begins by listing the appropriate effects, and I agree with the se lection of these based on the information in the ISA. Table 2.1-1 is particularly useful in providing a road map to the material in the entire document. In the previous draft, I was unclear as to the purpose of the case studies. In the present draft, this point is clearer, and I agree w ith the idea that given the very large inhomogeneity in both exposure conditions and species across different geographic areas,

the best that can be done is to select a few representative but sensitive regions and determine

where the ambient levels would need to be to protect these. The one thing missing is a clear statement as to how unique thes e case study areas are. One can’t set national standards based on a few outliers in the national distribution, and I believe a better case can be made in the document as to why these particular areas studied are not in the extr emes of the tail of inter-site distributions of sensitivity.

I particularly like the structure of the asse ssment outlined in the seven steps. While the committee may have disagreements over specific methodological issues, these seem to me the appropriate steps and an innovati ve way to get at the issue of a secondary NAAQS that relies maximally on available data. I fully support the EPA staff in this choice of framework, even if in the end they must execute it somewhat more qualitatively than might be desired. The point is that it is the right way to be thinking about the NAAQS.

The ecosystem services discussion in Chapter 2 wa s interesting to read. It presented the subject well, and it is evident to me that ecosystem services is one lens through which to view a secondary NAAQS (although it doesn’t capture issues such as inherent rights of other species). My problem lies in a disconnect between the deta iled discussion of ecosystem services and the specific Ecological Effect Functions in Figure 1. 4-1. I don’t believe the document, or even the current state of the science, allows for developm ent of such a Function ne eded to determine how much a specific ecosystem service is impacted by a given N or S loading, or how adverse is a given decline in ecosystem service. I wouldn’ t be inclined to suppor t a position that says any decline is automatically adverse; the same app lies to my position on human health imapcts. Due to this methodological and comput ational gap, the Ecosystem Services discussion in Chapter 2 comes off as more interesting th an truly informative – a good idea that can’t quite be pulled off when the data are analyzed.

The uncertainty discussion, as in almost all of th e REAs we have reviewe d, is quite generic and qualitative. But given the nature of this exercise , I am not sure a more quantitative approach to uncertainty would inform the final decision. Th is is because, while there are quantitative uncertainties having to do with the data and m odelling, an equally importa nt uncertainty is the conceptual relationship between the case studies a nd any sort of statement about the impact of a

national standard.

As Chapters 3, 4 and 5 are outside my area of ex pertise, especially with respect to specifying where the staff should look for representative but sensitive case study areas, I don’t provide comments here, other than to note that Chapters 4 and 5 are of little use given their sketchy

nature.

31The heart of the REA is found in Chapters 7 and 8. Table 7.1-1 agrees with the information provided in Chapter 1, so at leas t the methodology is consistent on this point. The framework of thinking laid out in this Chapte r is appropriate, although provided here in much too sketchy a form for me to agree or disagree with how it is being executed. There re main two areas in which substantial disagreement can arise between individuals reviewing the document: (1) the methodological steps in calculati ng impacts on a given case study s ite and (2) drawing summary

conclusions across sites. At the moment, the document does not fu lly clarify the first, and the

second issue is dealt with more through aspirations than any clear approach. But I must withhold judgment until the final report is prepared. The staff is at least headed in the right direction, have a proper roadmap in front of them and have th e expertise on hand to ca rry out these tasks.

In Chapter 8, the phrase “uniform level of ecosy stem protection” occurs, and seems to become a key idea in how a NAAQS might be considered. This idea really needs more of an explanation. Given the high levels of inhomogeneity, and the f act that the conclusions rest ultimately on case studies of sensitive areas, and the quite diverse kinds of effects being considered, I don’t understand what is meant by a “uniform level of ecosystem protection”. It surely doesn’t mean

that the level of effect will be the same across all ecosystems in the country, or even that the same ambient level will produce the same level of effect everywhere, or that the effects will be equally adverse in some deeper sense. And ther e is no common metric to which all these diverse effects can be reduced. So, just what does it mean?

Again, Figure 8.1-1 is the right kind of structure, but I don’t see how the Ecological Effect Function will be developed as anything other than a threshold model. And I don’t see where a margin of safety is recognized or introduced. But it is still the right concep tual approach if it can be pulled off methodologically.

Much of the discussion in Section 8.2 seems to me of a policy nature, belonging in a much earlier chapter. It almost comes across as being filler here while the st aff tries to figure out exactly how they will execute the ambitious st eps in Figure 8.1-1. I re commend moving it to the front of the REA in either Chapter 1 or 2.

The rest of the Chapter 8 strikes me as a lot of scie ntific detail with little to connect it all to the final calculations. I can’t comment on many of the equations proposed, because they relate more to environmental transport a nd fate than to effects. But it is evid ent to me that ther e is still a large gap between methodologies to estimate deposition a nd methodologies to relate these loadings to any specific effect that will drive a NAAQS.

32

### Dr. Charles T. Driscoll

The document “Risk and Exposure Assessment for Review of Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur” is an effort by U.S. EPA staff to provide and discuss a framework for establishing secondary sta ndards of nitrogen oxides (NO

x ) and sulfur dioxide (SO 2 ). Overall, I found the framework thought provoking and an interesting path forward in the establishment of secondary standards. While I enjoyed reviewing the document, there were several general technical issues that I am concerned about. There are several wording and grammatical problems in th e text that should be addressed before the document is more widely circulated. Finally, there are numerous small technical and wording problems in the document. I have organi zed my comments around these three issues.

Unfortunately, the document is not complete. Majo r sections are missing or partially complete. It is really a waste of time to conduct a review of such a larg e and complex document when the document is incomplete.

Technical Issues:

1. Case studies and modeling approach. I think the approach of using case studies to address the framework for secondary standa rds is a good and appropriate one. I also generally think the specific case studies that are advanced in the RE A are appropriate and helpful. I generally endorse the approach used. There are a few general

comments/issues I would like to address.

The case studies for aquatic effects in the Ad irondacks and the Shenandoah Park regions, terrestrial effects on red spru ce and sugar maple in the East and terrestrial effects on coastal sage scrub and conifer forests in Calif ornia seem appropriate. I also like the two

estuarine sites to evaluate coastal effects. I do have some concerns with the estuarine studies. First, it appears that the entire es tuary watershed will not be evaluated (i.e., Chesapeake-Potomac; Pamlico; Neuse). Will this be a problem or is the scope of doing the entire watershed just too great for this assessment? More problematic is conducting analysis for two watersheds that are in fairly close proximity? Although there is considerable information for Chesapeake Bay and Pamlico Sound, wouldn’t it make more

sense to conduct one of these case studies at a site with more contrasting features, with different land cover, climatic or N sources ? I would think intere st’s would be best served by either selecting a northern estuar y (e.g., Gulf of Maine, Long Island Sound) or a Gulf estuary as a second site.

The other general technical comment is that th e approaches used to develop critical loads for these case studies are very different. Ev aluating these different approaches could be very instructive but also problematic. I lik e the approach proposed of using a dynamic

acidification model for the Adirondack a nd Shenandoah case studies. Note, however, that MAGIC does not effectively simulate wate rshed nitrogen dynamics. So if this is an

33important component of the cri tical load, there will undoubtedly be some errors. I find it disconcerting that for the terrestrial acidifica tion assessment a steady-state model is being used. First, is it a good idea to use a dyna mic model for the aquatic assessment and a steady-state model for the terrestrial assessmen t? While I agree with the authors that critical loads are a steady-state phenomenon, eco systems are not. Forest ecosystems are losing exchangeable cations and presumably accumulating sulfur and nitrogen. This makes these systems by definition not a steady-state and increasingly sensitive to inputs of acidic deposition. While the application of a steady-state model is easy, it would seem to be problematic as an assessment tool. There are clear limitations in using a steady-state model for critical loads assessments. Finall y, I don’t understand how the

critical loads will be determined for the co astal and terrestrial nutrient case studies.

SPARROW is a statistical model and it is not clear how this can be used to evaluate greater and lower N loads.

2. Nitrogen saturation. Throughout the text, N saturation is referred to. However, I could not find any discussion of this phenomenon in th e introductory sections. It is discussed in the ISA but not (that I coul d find) in the REA. A brief summary of N saturation might be helpful.

3. Time scale disconnect. There appears to be a disconnect between the time scales used for the atmospheric modeling and the effect s assessments. Ecosystem effects of air pollutants are largely manifested over decades to multiple decades. Certainly the simulations conducted by MAGIC are conduc ted with what I believe to be the appropriate temporal perspective. I be lieve the time-scale for nutrient effects on ecosystems similarly have a long-term persp ective. In contrast, the deposition/CMAQ analysis seems to be largely focused on a s hort-term or seasonal perspective. Why? There seems to be a complete disconnect in the atmospheric and effects modeling concerning time-scale of analysis. Isn’t the primary concern here ecological effects? Do seasonal or monthly patterns in air concen tration or deposition have any relevance for this long-term analysis of ecosystem effects?

4. Climate. I am a bit surprised that no discussi on is given to changing climate. The framework to be developed is examining effect s that will play out over the next decades. It is projected that climate will also change substantially over the same period. Climate change will affect hydrology and ecosystem response to air pollution. Climate change

should be mentioned and needs to be addressed in future assessments.

5. Establishing standards around ambient air concentrations. In Chapter 8, limited

discussion was advanced in establishi ng ecosystem effects around ambient air

concentrations. While I can see that this mi ght be a desirable objective, as we currently have primary standards and some quasi secondary standards based on ambient air concentrations. However, for ecosystem effects, I do not see this approach as workable.

I think the standard needs to be based u ltimately on total sulfur and total nitrogen deposition. There are many species of sulfur and nitrogen all wh ich contribute to ecological effects but having different resi dence times in the atmosphere. These residence times vary in time and space. The ke y driver of ecological effects is long-term

34total deposition. Establishing standards around ambient air concentrations would seem

to be intractable.

6. Spatial variability in sensitivity. I’m not sure if this cons ideration is relevant for the nutrient case studies, however, the acidific ation case studies will exhibit considerable spatial variability in sensitiv ity to acidic deposition. Ther e is a range of ecosystem sensitivity to acidification from highly sensi tive to highly insensitive. How will this range of ecosystem response to acidic depos ition be addressed when establishing the critical load? Will all ecosystems be protected? 90%, 50%. Some discussion of this consideration would be helpful.

Written Document Considerations:

1. Written perspective. The document is written from the “we” perspective (i.e., we did this..., we analyzed that...). I find this appr oach somewhat disconcerting. The reason being it is not clear who owns the document. Is this EPA’s document or the contractor’s

document? Who are we? I would like to see the document altered.

2. Typos, errors, writing mistakes. As with the last draft of the ISA, the REA (and the 2 nd
draft of the ISA) is filled with mistakes and typos. I point out many of these in my specific comments (see below). However, these are by no means all the mistakes. This document needs to be carefully read, proof read and edited for consistency and to

eliminate the mistakes.

3. Redundancy. There are many redundant sections in the document. This makes a very long document, longer than it needs to be. The document should be edited to eliminate

the redundant text.

4. Tense. The REA switches back and forth from the past to present tenses. I can see writing in either tense. However, the docum ent should be edited so it is written in a

consistent tense.

Specific comments:

Page 1-2, line 16 Units of ANC μeq/L?

Page 1-11, line 24 I don’t agree with the statement. Most published studies document inputs of oxidized and reduced N. A few don’t, but

most do.

Page 1-12, line 10 Space missing.

Page 1-12, line 13 I would change the wordi ng. Acidification is an environmental effect due primarily to sulfur and secondarily nitrogen in most

environments.

35Page 1-13, line 12 As above, need to define N saturation.

Page 1-13, line 19 Change air to atmosphere.

Page 1-15, line 22 alpine

Page 1-16, line 12 It is incorrect to state th at watersheds conducive to methylation are

found in the northeastern U.S. and southeastern Canada. They are found all over. See Figure 6.1-3.

Page 2-2, table 2.1-2 Under aquatic acidific ation also include hydrologic flow paths under sensitivity variable.

Page 2-4, line 15 Eliminate comma

Page 3-7 I would like to see this sec tion expanded to include a section of background (pre Industrial Revol ution) deposi tion, including sulfate, nitrate, ammonium and basic cation deposition.

Page 3-8 I would like to see a brief description of organic N deposition, including sources.

Page 3-9, thru 12 There is a summary of sp atial deposition patterns. The discussion of how these maps are produced is in the section that follows (3-12). The methods section shou ld be moved in front of the maps. Also, the maps are generated for 2002. Some discussion should be given as how represen tative this year is, given year-to-year variability in deposit ion. Moreover, it is critical to clarify on the deposition maps th e units of mass (e.g., Kg N/ha-yr or kg NO 3 /ha-yr).

Page 3-12, line 10 data are ...

Page 3-13, line 1 data were...

Page 3-13, line 6 Change to... kg/ha-yr.

Page 3-13, line 7 data were...

Page 3-16, line 5 Need to clarif y the time interval kg/ha-yr?

Page 3-16, table 3.2-2 It is not clear what this table is. Some additional text is necessary.

Page 3-19 It would be helpful to put the Adirondack Park and the

Shenandoah National Park boundari es and the Chesapeake and

36Pamlico watershed areas on the ma p so the reader can understand the scope of the analysis re lative to the total resource.

Page 3-25, line 7,8 Change to... kg N-ha/yr.

Page 3-35, line 12 Change to... fairly uniform.

Page 3-36, figure 3.2-14 Why show figures of both monthly and seasonal deposition? Isn’t

this redundant?

Page 3-38, figure 3.2-16, 17, 18, 19 These figures are difficult to read and are they really helpful?

Page 3-40, line 4 Change to... generally uniform...

Page 3-50, lines 3, 17 and Page 3-51, line 6 Change...drop to decrease

Page 3-50, figure 3.2-28 and elsewhere Aren’t the monthly patterns in wet deposition st rongly driven by the quantity of precipitation? Wouldn’t patterns for a different year with different precipitation pa tterns be different? As a result, this temporal section is misleadi ng because it is strongly affected by the meteorology for that year. If true, why in clude all this analysis? As a minimum, this f act should be clarified and some data provided on 2002 as a reference year.

Page 6-1, line 3-4 Rephrase. Every wetla nd has sulfate. The production of methyl mercury is largely mediated by sulfate reducing bacteria.

Page 6-1, line 22 Also phosphorus (or N) can be important as it regulates aquatic productivity and therefore mercury concentrations in aquatic organisms (Driscoll et al. 2007).

Page 6-2, line 4 Change to...Industrial Revolution.

Page 6-2, line 28 This sentence needs to be clarified. Ionic mercury can be reduced and evaded and separately methyl ated. Methyl mercury is not

reduced. Where does this 1-2% come from? The extent of methylation is highly variable from ecosystem to ecosystem.

Page 6-4, line 14-16 Why is methane needed ? Why do you need HgS in the equation? Define MeHg +

.

Page 6-4, line 20 Al so anoxic conditions.

37Page 6-4, last paragraph There are other studie s that probably should be cited (Branfireun et al. 1999), (Jeremiason et al. 2006).

Page 6-5, line 12 Change to...m ethylation can occur within.

Page 6-5, figure 6.1-2 Hg can also be supplied from sediments.

Page 6-6, line 3 Change to... anoxia, sulfate).

Page 6-6, line 5 Change to... response, hydrology, nutrient loading, limnology).

Page 6-10, line 4 Is this really true? I do not believe it. % methyl mercury is highly variable. Need to correct.

Page 6-12, line 5 Change to... oxidizing NH 4 +

.

Page A3-1, line 15 Subscript 2.

Page A3-1, line 20 hydrogen ion, and Al n+

.

Page A3-1, line 20 and throughout the document

I don’t think the writers of th is document understand the concept of buffering capacity. Buffering cap acity is the resistance of a system to changes in pH. I would recommend eliminate using the term here and elsewhere or change the phrasing to use it correctly.

An alternative could be acid ne utralizing capacity or acid-base

status.

Page A3-2, 1 st paragraph I suggest addi ng a sentence or two about

immobilization/mobilization of SO 4 2- and NO 3 - by plants/soil organic matter.

Page A3-2, line 10 There are numerous chemical indicators.

Page A3-2, line 12 NO 3 - , Al n+

Page A3-2, line12 Change to... of base cations; and ANC.

Page A3-2, line 27 Change to... precip itation enters the soil and soil water to

emerge...

Page A3-2, line30 K + + Na + + NH 4 + ) – (SO 4 2- + NO 3 - + ...) in (μeq/L)

Page A3-3, line 5 Change to... low pH.

38Page A3-3, line 6 Change to... This is th e acid neutralizing capacity (ANC), or the

...

Page A3-5, line 4 acidic surfac e waters (14%; ANC<0 μeq/L).

Page A3-5, line 26 United States

Page A3-6, line 24 Need to define the time and mass basis of deposition (e.g., kg

SO 4 /ha-yr or kg S/ha-yr).

Page A3-7, line 12 Change to... weathe ring rates and limited neutralizing of acid inputs.

Page A3-8, line 5 Again need to defi ne the time and mass basis of deposition.

Page A3-9, line 19 Al n+

Page A3-9, line 21 with limited leaching

Page A3-9, line 23 EPA-administered Long-Term Monitoring (LTM) program.

Page A3-15, line 12 SO 4 2-

Page A3-16, line 9 comma

Page A3-16, line 19 it’s the acid neutralizing capacity of a ...

Page A3-16, line 21 The acid ne utralizing capacity of a ...

Page A3-17, line 3 20 μeq/L (limited protection)

Page A3-16, line 12 This sentence makes no sense. At ANC = 0 μeq/L a water is chronically acidic.

Page A3-17, line 8 Sub and super script

Page A3-20, line 5 Units should be eq/ha-yr.

Page A3-20, line 7,8 I would eliminate the term occult deposition simply call it cloud and fog deposition.

Page A3-20, line 10 Units meq/m 2 -yr

Page A3-22, line 24 This description needs to be expanded or clarified. There are

more than 200 NADP sites.

39Page A3-28. line 25 in the catchment

Page A3-29, line 19 400 meq/m 3

Page A3-29, line 24 The titles used for these cl asses should be consis tent with the titles

established in table 4.1-1 on A-14.

Page A3-33 There needs to be some discussion on the time and nitrogen retention assumptions used to obtain critical loads.

Page A4-1 I would change the title to Forest Acidification Case Study.

Page A4-1, line 17 hydrogen ions

Page A4-1, line 19 where strong acids

Page A4-4 Should also consider citi ng the recent paper by (Warby et al. (in press)) attached), which shows wide spread soil acidification in the

Northeast.

Page A4-5, line 14 This statement needs to be reworded. Al mobilization occurs under low % base saturation and high concentrations of acid

anions. The statement as it stands is incorrect.

Page A4-9, line 18 Should be (Driscoll et al. 2001).

Page A4-10 It would be helpful to cite the study by (St. Clair et al. 2005) which shows decreases in foliar antioxidant enzymes in sugar maple in response to lower foliar and soil Ca 2+ in Pennsylvania.

Page A4-19, line 1 Again need to specify the mass and time basis of deposition.

Page A4-28, line 10 acidi ty input neutralized by

Page A4-28, line 18 parties

Page A4-49 Need to indicate the units of the figure.

Page A4 References Should be BioScience.

Page A5-18, 1 st paragraph Need to use metric units.

Page A5-26, line 6 Need to define Nr.

Page A5-30 SPARROW is a steady-state model. Will need to demonstrate how you can use it.

40Page A5-55, line 7 were from

Page A5-58, line 6, 8 Does the SAV coverage really have this le vel of significant figures?

Page A6-10, line 1 Change to... Mediterranean climate. This climate is...\

Page A6-25, line 16 result of long-term elevated N deposition rather than pulses

Page A6-42, line 7 data are

Page 7-3, line 12 Change to... where strong acids are

Page 7-11, line 2 catchment to neutralized acid anion deposition is known as acid neutralizing capacity.

Page 8-1, line 14 There cannot possibly be a uniform level of ecosystem protection due to the inherent variability in ecosystem sensitivity.

Page 8-4, figure 8.1-1 Add climate as a variable/fixed factor.

Page 8-5, line 2 What is meant by the point of deposition?

Page 8-8, line 14 What about forest acidification?

Page 8-8, line 14 How can you say whether precipitation occurs or not. Is there a location where precipitation does not occur? Rewrite sentence.

Page 8-10, line 24. Do you mean deposition is expressed or an equivalence basis? Please clarify.

Page 8-11, line 4 This sentence make s no sense and should be rewritten.

Page 8-14, line 1 data are

Page 8-14, line 20 Do you me an equivalence ratio?

References:

Branfireun, B. A., N. T. Roulet, C. A. Kell y, and J. W. M. Rudd. 1999. In situ sulphate stimulation of mercury methylation in a borea l peatland: Toward a li nk between acid rain and methylmercury contamination in remo te environments. Global Biogeochemical Cycles 13 :743-750.

41Driscoll, C. T., Y.-J. Han, C. Y. Chen, D. C. Evers, K. F. Lambert, T. M. Holsen, N. C. Kamman, and R. K. Munson. 2007. Mercury cont amination in forest and freshwater ecosystems in the Northeastern United States. BioScience 57 :17-28. Driscoll, C. T., G. B. Lawrence, A. J. Bulger, T. J. Butler, C. S. Cronan, C. Eagar, K. F. Lambert, G. E. Likens, J. L. Stoddard, and K. C. Weathers. 2001. Acidic deposition in the

northeastern United States: S ources and inputs, ecosystem effects, and management strategies. BioScience 51 :180-198. Jeremiason, J. D., D. R. Engstrom, E. B. Swain, E. A. Nater, B. M. Johnson, J. E. Almendinger, B. A. Monson, and R. K. Kolka. 2006. Sulfate addition increases methylmercury production in an experimental wetland. Environmental Science and Technology

40 :3800-3806. St. Clair, S. B., J. E. Carls on, and J. P. Lynch. 2005. Evidence for oxidative stress in sugar maple stands growing on acidic, nutrient imbalanced forest soils. Oecologia 145 :258-269. Warby, R. A. F., C. E. Johnson, and C. T. Driscoll. (in press). Continuing aci dification of organic

soils across the northeastern USA: 1984 - 2001. So il Science Society of America Journal.

42

### Dr. Paul J. Hanson

The Risk and Exposure Assessment (REA) ... repres ents a good beginning, but many sections are not yet complete or only partially complete making it difficult to judge the full intent or appropriateness

of the document.

Specific comments and suggested edits:

Front matter :

Page xii: Should the definition of ecological dose be limited to toxicants that inhibit microbe-mediated ecological processes ? I would think that the term should apply to all biological organisms. It may be

that it is a term that dominates microbial studies.

Top of Page xiii: The most common example of an ecosystem benefit would pr obably be an increase in productivity. Why isn’t this an example?

Page xiii: The difference between elasticity and sens itivity (page xv) isn’t clear. Is there a reference for the use of the term elasticity that might be placed here?

Page xv: The precipitation range for semi-arid regions should probably be 250 to 500 mm. It certainly shouldn’t be the same as the definition for arid systems.

Chapter 1

Page 1-3 line 8: I recommend the following wording change “...both ambient air and surface deposited species of NOx and SOx...

Page 1-10 line 23: N 2 O is nitrous oxide not nitrogen dioxide.

Page 1-12 line 9: For parallel structure I would a dd the spelled out version of sulfur dioxide.

Page 1-13 line 5: Remove the semicolon.

Page 1-13 line 13: I would change “direct effects” to ‘direct adverse effects’. There is some evidence for localized N uptake.

Page 1-14 line 11: The text must be changed to “..detail on how acidification affects sensitive ecosystems.....” Don’t leave the r eader with the impression that acidification is having effects on all

ecosystems.

Page 1-14 line 17: I don’t understand “re-acidification” . This concept needs to be further developed.

Page 1-14 line 31: Add ‘productivity’ to the list of changes driven by N deposition.

Page 1-15 line 14: This threshold for N saturation is only relevant for some, but not all eastern forests. Those levels of N deposition would be easily assimilate d by much of the upland oak forests throughout the eastern United States growing on deeps soils with ample base saturation. Page 3-186 of the ISA states

43“there is currently no published national assessment of empirical critical loads for N in the U.S......” Table 3-25 is a nice summary of what is known. The REA needs to reflect the limited amount of data available for developing quantifiable thresholds, and appropriately characterize those ecosystems for which it might appropriately be applied. Avoid inappropriate extra polations. Lines 14 to 19 on page 4-16 of the ISA include good statements that should be used within the REA to qualify the nature of ecosystem sensitivity.

Page 1-15 lines 21 and 22: Similarly, the wording may n eed to be changed here to suggest if these levels represent an appropriate threshold for a ll or just some sensitive grasslands.

Page 1-15 line 30: Add a reference for the sentence ending on this line.

Figure 1.3-3 still doesn’t show the productivity enhanc ement effect of N, which is clearly a dominant process in the N cycle.

Bottom of page 1-17: Should some mention be made at this point to N standards for water pollution? It isn’t necessary, but might be a useful connection. S ection 3.3.6 of the ISA and the associated annex might

be cited.

Figure 1.4-1 doesn’t adequately capture the integrat ed nature of NOx and SOx pollution that is being attempted in this document. Are they truly intert wined all along this process or do they only come together after deposition takes place?

Chapter 2

In Table 2.1-1 ANC should be defined, productivity should be added as an ecosystem service where appropriate, and N leaching might be added as an i ndicator of terrestrial nutrient enrichment. The characteristics of sensitivity for terrestrial nutrient enrichment might be updated.

Sections of Table 2.3-1 still need to be filled in.

Chapter 3

Page 3-4 lines 6 and 7: Check the wording. 30 to 70% of the animal wa stes can’t be emitted as NH 3

. Should it read 30 to 70% of the N losses from animal wastes?

Page 3-5 lines 10 to 15: Are there not any natural sulfur emissions in and around Yellowstone or in other hot springs areas of the country? I realize they may be inconsequential....

Pages 3-10 to 3-11: Question: Have all of the emissions reductions resulting from past clean air legislation been realized? Will new standards for ozone impact the likely deposition rates for N in the

future? Should such a discussion be included someplace in this document?

Chapter 3 doesn’t include much on temporal changes in deference to the maps of recent conditions. Those are fine, but I think some discussion of where we have been and where we are going should be included in the REA. Figures 2-59 or 2-103 from the ISA might be considered.

Page 3-12: Super and subscripts for charge are missing for SO 4 -2 , NO 3 - , and NH 4 +

.

Question: Do the QMAC estimates of deposition to te rrestrial systems include foliar uptake of NO or NO 2 near urban areas or along major roadways where ai r concentrations are high enough to drive this

44pathway?

Table 3.2-2 is not well defined. It needs references.

I was disappointed by how much information was s till not added to the document (especially in this Chapter). We are being asked to provide comment on a document that has a lot missing from it.

Captions to Figure 3.2-12, -13, and -14 need to be reworded to “...nitrogen deposition by source and quarter.... The most interesting data in many cases h as to do with the source of N forms rather than the season of the year.

Figures 3.2-22, -23, -24, and -25 lack units (presumably kg/ha as for N).

Captions to Figure 3.2-27 and -28 need to be reworded to “...sulfur deposition by source and quarter....

Page 3-54: Again...we don’t have much to review yet.

Page 3-54 line 14: Reword as....”Public welfare effect s associated with direct exposure to NOx and SOx

do not occur for current ambient concentrations.”

Page 3-54 line 23: The discussion on pages 1-10 and 1-11 seems to disagree with this statement. The REA has already been defined to deal with total reactive N.

The discussion of Data and Tools (Section 3.2.2.2) should probably be presented earlier within Chapter 3 (perhaps around page 3-17).

Figures 3.2-35 and -36: Adding pixels for actual for est cover within these maps would be useful to better reflect the actual extent of the forest types. The coastal sage map (Figure 3.2-37) appears to be drawn this way.

The text for Figures 3.2-39, -40, -41, -42, -43, and -44 is way too small and the figure captions are inadequate. Please revise.

Page 3-70: At this point of the discussion it occurred to me that a case study for an area dominated by NH3 deposition (i.e., Iowa, Minnesota, Illinois) should probably be added to the REA. It wouldn’t necessarily show adverse effects, but it would complete the picture of total reactive N deposition across the US. Page 3-103 of the ISA provides some rationale for not including such a case study since agricultural areas are overwhelmed by fertilizer add itions. However, limited natural areas (forests, prairies) are embedded within areas dominated by agriculture.

Chapter 4 : Incomplete and not reviewed.

Chapter 5 : Incomplete and not reviewed.

Chapter 6

Figure 6.1-4: SRB should be defined in the figure caption.

Page 6-16 line 13: Remove the word “often”. Fungi should probably also be recognized as an important contributor to decomposition.

45Increased nitrogen does affect the N content of green leaves. Is this pattern well established for litterfall as well? Does the pattern differ by vegetation type (i.e., trees, grasses, crops...)?

Page 6-17: Some of this materi al might be better left to the ISA document. Lines 24 to 28 are not

needed here.

Page 6-19: How the contribution of atmospheric de position to upland watersheds actually finds its way into waterways isn’t clear. The ‘filtering’ effect of upland vegetation w ill vary tremendously from location-to-location. This concept need s to be made clear in the document.

Chapter 6 seems to lack summary conclusions: What terrestrial systems are at risk? What percent of US land area? What aquatic systems are at risk? What percent of US freshwater area?

Chapter 7

Page 7-5 line 4: Replace “ecosystem health” with anothe r term. It isn’t and perhaps can’t be defined.

Page 7-5. Line 7: Change to “this is hypothesized to change....” Or provide the references that show proof.

Page 7-5 line 21: Spell out CSS.

Page 7-7 Table 7.1-1: Replace “tree health” with a more meaningful term or terms such as rate of growth, survival....

Page 7-8: The deposition levels proposed are a ppropriate for ‘sensitive’ ecosystem, but not all ecosystems. A concept of one size does not fit all will n eed to be worked into the conclusions of the REA. While protection of sensitive systems may be a justifi cation for a new standard and level, it shouldn’t be interpreted as having the same effect on all areas of the US. That is, lowering inputs to areas currently unaffected will not help them. Pages 3-78 and 3-79 of the ISA include text that might be useful in clarifying this point.

Chapter 7 ends abruptly and seems incomplete.

Chapter 8

Page 8-1 lines 14 and 15: The concept of achieving a standard based on a “uniform level of ecosystem protection” seems at odds with the REA document. Th e REA clearly states that the impacts of N and S deposition are localized throughout the US and subject to the correct combinations of deposition and susceptibility of the target terrestrial and aquatic ecosystems.

Page 8-4 Figure 8.1-1: An air quality based est imate of total N and S form deposition may not be sufficient information to judge impacts on acid neutra lizing capacity. A data layer on extant edaphic conditions is needed. The deposition metric shoul d probably also be enhanced to allow for the estimation of biological immobilization (i.e., plant an d microbial uptake of some fraction of the total deposition).

Page 8-5 lines 1 to 3: Plant uptake needs to be included in this list.

Page 8-28 lines 2 to 9: I don't agree with the assumpti on that annual accumulation of N inputs into wood

46increment can be ignored in this analysis. Excep t for low or no productivity ecosystems this is a significant sink for atmospheric N deposition that must be included in the calculation of N available for

other soil interactions.

Section 8. 4 is incomplete. More material is needed.

Attachment 3

Page 1 line 16: The phrase “a host of biogeochemical processes” is too vague. Please expand this

concept.

Attachment 4

Pages 2 and 3: Table 1.1-1 is not filled in. The term forest health should be replaced.

Pages 12 and 13: Table 1.2-2 is not complete.

Page 31: The authors conclude that the simple mass balance method would be used in the REA. What caused the authors to exclude the dynamic model met hod? Lack of input data? Lack of validation?

Page 32: All evapotranspiration does not occur at the surface of the soil profile. Did the authors mean to imply evaporation alone?

Page 42 line 17: Is the nitrogen immobilization me ntioned here microbe and plant or just microbe?

Figure 3.1-2 is missing units.

Page 53: The conclusions need work. The imbalances for Ca, Mg, and Al suggested for forest soils are for localized sensitive systems. As worded, the conc lusions would be taken as a broad generalization for all US ecosystems.

Attachment 5: No comment

Attachment 6

Page 6: Table 1.2-2 is missing too much information to be fully evaluated.

The studies cited and discussed for the CSS system shoul d be closely evaluated to determine which were based on manipulative studies capable of determining cause-and-effect relationships versus those that represent correlation studies for which relationships between known variables and measured responses were assumed to be viable explanations for adverse responses.

Studies highlighted in the ISA within Tables 3-15, 3-17, 3-18, and 3-19 might have a larger presence

within the REA.

Figure 5.1-1 and -2: In my opinion th e change in CSS seen in Figure -1 doesn’t correlate very well with the dominant deposition patterns in -2. How well do es N deposition really correlate with change? How much does land use change through time get in the way of the interpretation of N deposition cause and effects in this case study?

Page 46 lines 4 versus line 15: The conclusion of “compelling evidence” on line 4 does not seem to

47agree with the authors conclusion about the research still underway on line 15. A word change seems in

order.

Page 47 line 5: Is a modification of a valued ecosystem an ad

48

### Dr. Rudolf Husar

These comments are addressing primarily the 1st draft REA section: Additional Effects. It also includes both general comments on the approach to the REA as well as comments on sections of the the

first REA draft document.

Comments on REA Chapter 6: Additional Effect

1. Charge: In this chapter, we have presented resu lts from some initial qualitative analyses for additional effects including the impact of sulfur deposition on mercury methylation, the impact of nitrous oxide on climate change, and the impact of nitrogen deposition on carbon sequestration. Are these effects sufficiently addressed in light of the focus of this review on the other targeted effects in terms of available data to analyze them?

Overall, this chapter is a good effort to illustra te additional, non-ecological risks associated with anthropogenic N and S. Indirect sulfur impacts are well captured by the problem of sulfur-induced methylation of mercury, which then causes the effect s in biota. The interaction of nitrogen and carbon cycles is also properly illustrated in the section on nitrogen-induced changes in the carbon sequestration. The utility of the section on N 2 O impact on climate is less obvious.

This chapter is clearly a first draft. In the intr oduction it would be helpful to provide more extensive rationale and criteria on the general approach for sel ecting these Additional Effects. The rationale should also include why some obvious additional effects on materials, visibility and soil are not being considered. See further discussion regarding these ef fects in the general comments on REA below.

6.1 Sulfur and Mercury Methylation

Page 6-2 Line 10: Currently, i.e. since 1995, coal combustion was, indeed, the main cause of anthropogenic mercury deposition. However, prio r to the regulatory action, around 1990, the anthropogenic mercury emissions were dominated by other sources. Since deposited mercury has a long residence time in soil and biota, much of the mercury met hylation occurs on the accumulated mercury from solid waste and other agricultural, medical, residential usages.

Page 6-2 Line 13: Atmospheric mercury particles cannot possibly remain in the atmosphere for more than two years. Even stratospheric particle s, have atmospheric residence time of less than two years. As with the rest of ambient aerosols their atmospheric residence time is less than a week in the planetary boundary layer and le ss than 3-4 weeks in the mid-troposphere.

Page 6-3: Figure 6.1-1 represents the mercury cycl e in the ecosystem. It has many compartments and arrows representing the mercury flow and transport/transformation processes. It is recognized that full quantification of the mercury cycle through air, water, land and biota is not possible at this time. However, it would be helpfu l, at least in the text, to highlight the main flows and processes that domi nate the mercury cycle.

496.2 Nitrous Oxide

Page 6-10: I find little justifica tion for this section on the clim ate impact due to anthropogenic

N 2 O. As stated in the REA, N 2 O contributes only about 6% of GHGs and the man-induced sources of atmospheric N 2 O are only 10% of that, i.e. .6% of the GHGs.

Page 6-12 Line 31: The statement “that nitrogen addition increased N 2 O emission by 215%” could benefit from a reference, compared to what?

6.3 Carbon Sequestration

Page 6-13: This section is an a ppropriate illustration of the interdependence of nitrogen (sulfur?) and carbon cycles through air, land, water and biota. The meta-analysi s of existing literature is an appropriate method for illustrati ng the interdependencies of the earth system components and how changes in one set of e nvironmental chemicals may have intended and unintended consequences throughout the earth system.

General comments on the first draft REA

This REA focuses on ecosystem welfare effects th at result from the deposition of total reactive nitrogen and sulfur.” I concur with D. Johnson that exclusive focus on “negative” effects of N and S deposition is a flawed appr oach. It ignores the broader context and the full dynamics of eco system responses to anthropogenic N and S deposition. The beneficial effects of atmospheric S and N fertilization should also be considered. This would also require definitions

and/or conventions on what’s harmful and what’s beneficial.

The man-induced nitrogen and sulfur depositi on should be compared quantitativel y to the naturally occurring N, S flows. This will allow estimating the significance of the man-induced stress, compared to the naturally occurring values . By avoiding such broader context, the risk assessment will be susceptible to criticisms of incompleteness and possibly irrelevance to actual ecological risk estimation.

Page 1-2 Line 9: “In the Act (Section 109 B 2) the purpose of the secondary NAAQS is to protect the public welfare from any known or anticipated advers e effects...” Clearly, a secondary NAAQS includes all welfare effects, no t only the effects on the ecosystem. This fact is not followed through in the REA and ISA.

Page 1-2 Line 19: “Adverse public welfare effects are based on an assessment of how ecologically adverse impacts transl ate into adverse impacts on public welfare” In this sentence as well as throughout the REA we lfare effects only include eff ects on ecosystem . As stated above welfare effects include damage to ma terials, visibility, soils, climate.

50Specific comments on sections of the first draft REA

Page 1-13: Figure 1.3-2 representi ng the sulfur cycle should be made more quantitative. The schematic Figure on the biogeoche mical cycles of sulfur is good. However, such a general Figure should be fortified by adding magnitudes to the flows represented by the arrows. The transfer rates, say over the US, can be estimate d from the model runs, or based on the empirical evidence. There is ample literature on biogeoche mical cycles that estimates the magnitude and importance of the various flow rates.

Page3-5 Line 4: “ ....combustion of fossil fuels by electric utilities (~66%) “ This percentage is

inconsistent with 71% EGU contributi on shown in the pie diagram, Figure 3.1-5.

Page 3-8: The section layout for 3.1.4 on Depositi on starts with the tota l deposition maps that are obtained by combining the model and measured values. The description of the data and tools is given after that. The customary approach is first to present the input data, tools and methods and then the resulting computed values . Also, as discussed at the October CASAC meeting, a separate section on CMAQ model comp arison with the observations for the key N, S species would be most desirable.

Page 3-8: Section 3.1.4.1 on Nitrogen Depositi on has many useful quantitative numbers. However, the source and estimation methods fo r these estimates are not well documented.

Page 3-10: The useful Figure 3.1-7 on oxidi zed N deposition should be augmented with separate Figures for dry and wet deposition of N. The wet deposition Figure should also compare the model and measured oxidized N deposition.

Page 3-11: Ditto for reduced N deposition.

Page 3-12: Ditto for reduced S deposition.

Page 3-12: Section 3.2. could be subdivided su ch that the procedures for model-observation data fusion has a more extended separate sub-section.

51

### Dr. Dale W. Johnson

As has been noted in previous reviews, I feel th at this document is unbalan ced with respect to the effects of nitrogen deposition. Some very simple facts need to be acknow ledged and considered: 1) most terrestrial ecosystems in the USA are n itrogen-deficient; therefore 2) increased inputs of N are likely to cause growth increases; 3) gr owth increases will almost certainly result in increases in carbon (C ) sequestra tion, which in turn may have inadvertent benefits for the CO 2 / climate problem. This is not to diminish a ny statements about the negative effects of N deposition, it is simply to add balance to this document. As scientific reviewers, we have the responsibility to treat this and all other subjects in a completely objective manner.

Below are some specific comments, some editorial in nature, some technical in nature, and some where I see this lack of object ivity and balance. Following that I will address the specific questions assigned to me.

Specific comments:

p. 1-13, lines 4-7: This is a balan ced statement – the review of effects should really flow from this approach, considering both increased productiv ity (which may be beneficial in some cases, detrimental in others) and increase d soil acidity and eutrophication.

p. 1-15, line 14: 5.6 to 10 kg ha -1 yr -1 ? Can you really narrow this down to one decimal point?

p. 1-15, line 17: should include “and car bon sequestion” after “carbon cycling”.

0. 1-17, line 13: From a soils point of view, th e effects of NOx really cannot be readily distinguished from the effects due to total reactive nitrogen – both are transformed in the soil rather extensively.

p. 2-5, line 25: should add “timber production and car bon sequestration” after “water”. I note that timber production is mentioned page 2-7, lines 19-20, but only in the context of how soil acidification might negatively affect it. Soil acidification may well negatively affect timber production, and the latter statemen t should stay as it is, but incr eased N deposition will probably also increase timber production a nd this needs to be acknowledged.

p. 2-9, line 27: should add “timber production and carbon sequestration” after “water quality”

Attachment 1, p. 3: I see Carbon Sequestration is listed as a potential section 6.3 – this is a good thing. Looking forward to seeing it.

Attachment 3, p. 1, lines 17-26: There needs to be a discussion of the effects of mineral acid anions on soil solution (what Reuss calls intensity effects, which can happen very quickly) in addition to the discussion of how they affect so ils (capacity effects, wh ich take a long time to occur). Reuss points out in his 1983 paper (Reuss, 1983) and in our small book (Reuss and

52Johnson, 1985), both of which are cited later in the Terrestrial Case Study, that Al 3+ increases to the 3/2 power of Ca 2+ , for example, as total mineral ac id anion (e.g., nitr ate and sulfate) concentrations increase, and this happens even if there is NO CHANGE IN THE SOIL AT ALL. Thus, if the soil is already acid, the introduction of mineral acid anions will cause the immediate

mobilization of Al and acidification of soil solutions and probably surface waters long before any change in the soil takes place. C onversely, if the mineral acid an ion concentrations are reduced, one should see a very rapid recovery. In short, the soil solution can change very quickly and almost independently of the soil, and this has major implications for the effects of N and S deposition on aquatic ecosystems.

Attachment 4, p. 1. lines 16-29: Same exact commen t above applies here and in this case, our small book is cited as a source but only part of th e story (the soil part, no t the soil solution part) is reviewed. This is an important point – please include it in the next draft.

Attachment 4, p. 5, lines 10-17: Same comment as above here. It is not necessarily true that “inorganic Al does not become mob ilized until after soil Ca is depl eted” if the soil is already acidic, as many unpolluted soils indeed are.

Question 4 Response: The revisions have improve d the characterization of adverse ecological effects, but I see no real consideration of the potential positive effects of N deposition as yet. Timber production is mentioned, but only in a nega tive context and I see l ittle or nothing on C sequestration. The one pager for section 5 refers to case studies and gives no indication that this approach will be changed.

Question 4b: I see no discussion on effects on carbon budgeting as yet – have I missed something? I do see Carbon Sequestration is lis ted as a potential sec tion 6.3 – this is a good thing. Looking forward to seeing it.

Chapters 7 and 8 (Sent 19 Sept 2008)

Chapter 7: We are asked if the approach is technically sound to consider “ecologically adverse effects”. For the most part, ye s, it is. However, once again, I note that this section focuses entirely on negative effects of N. This documen t should also consider cases where increased production could be a positive effect – such as on timber production and C sequestration.

p. 7-1, lines 21-27: This is a real mouthful. Can it be simplified and broken into at least two

sentences?

p. 7-3, line 12: Why “inorganic and mineral aci ds”? They are basically the same thing.

Section 7.1.4:

Chapter 8: Many questions are posed to the panel here and I will not repeat them. I had problems with the conceptual framework for the calculations, as noted below.

53Section 8.3.3: I had a very difficu lt time following this section and do feel lik e I ought to be able to. It would help a great deal if units could be specified in the various equations and the assumptions were clearly spelled out in the beginning. For example, is it assumed that base

cation concentrations will remain at pre-industrial levels? The equations would suggest so, as would the statement on p. 8-29, lines 13-15. I cannot really agree with the assumption state here that “pre-industrial base cation concentrations effectively se t the long-term capacity of the catchment to neutralize acidic deposition because it represents the only source of base cation input that is sustainable over the long-term”. For one thing, soils in humid regions always naturally acidify and therefore there is no l ong-term steady state base cation flux until soils become extremely acidic– it is always slowly decreasing. I also think that the implicit assumption here that base cation concentrations in streams will not incr eases over the long-term in response to acidic inputs is flawed – some so ils have a very large ex changeable base cation pool and could buffer such inputs for a much longer term than the typi cal attention span of scientists and policy makers, let alone the public.

p. 8-29, lines 18-19: This statement makes no sense. At steady state, the leaching rate of base cations is, by definition, equal to weatheri ng inputs, not “at lesser or greater rates”.

54

### Dr. Donna Kenski

Overarching concerns: EPA staff have clearly ma de a great effort in pulling this document (and its companion ISA) together, and should be commended for the high-quality (and quantity) produced thus far. Nevertheless its current in complete status and the pressing schedule make it hard to see how all the remaining tasks can be completed, and reviewed, in sufficient time to meet the predetermined deadlines. Staff and cont ractors to EPA need to be realistic in judging how much can really be done in th e remaining months. If it is time to set priorities, perhaps that is something that can be disc ussed at this meeting.

The CAA requirement that the secondary standard be in the form of a concentration standard is going to require us to tolerate a much higher level of uncertainty than usual in the standard setting process, because of the need to employ multiple models to characterize the concentration-deposition-ecological effect-ecolo gical indicator linkage. Consequently, the REA in general needs to be much more comprehensiv e and transparent in de scribing the levels of uncertainty encountered at each of these step s and their impacts on overall uncertainty. For example, so much hinges on the CMAQ estimates of deposition, and yet there is little information given in the REA or the ISA on CMAQ performance. It seems from the ISA that CMAQ has really only been evaluate d in terms of its annual estim ates of aerosol deposition, and

those are accurate to within a factor of 2. No CMAQ performance evaluation is given for deposition to specific locations, particularly locati ons that share characteristics of the sensitive areas focused on in this analysis. Likewise, non e is given for measurements with a shorter time frame than annually. A clear-eyed discussion of these uncertainties for CMAQ and for the other models used to support the REA (MAGIC, ASTRAP , Sparrow) is a critical component that needs to be incorporated.

Charge Questions: Scope of the Review

1. Is the review appropriately focu sed in terms of the targeted effect variables and in terms of characterizing the important atmosphe ric and ecologic vari ables that influence deposition and ultimately the ecologic impacts of nitrogen and sulfur? Does the Panel have any further suggested re finements at this time?

Generally, the review seemed to focus on approp riate variables, although as noted above, the complete scope may be too broad to accomplish before the court’s deadline. The policy-relevant questions posed in Sec. 1.4 weren’t actually addressed direct ly (perhaps it’s still too soon, given the incomplete case studies) but I did note th at questions 3 and 4 of that list (i.e., to what extent do receptor surfaces influenc e dry deposition, and can effects of NOx be distinguished from effects due to total reactive nitrogen) did not seem to be discussed or addressed by any of the case studies in Att achments 3-6, although Chap. 3 did present a nice graphical characterization of the areas and their relative proportions of NOx vs total and other forms of N nitrogen. However, most of that was modeled data and little comparison to measured values was presented for comparison. Perhaps more of that is coming in the second draft, since there were lots of missing sections to Chap. 3.

55Similarly, the list of issues on p. 1-20 should include evaluating the impacts of atmospheric deposition relative to other paths (nitrogen runof f from agricultural lands, for example). This might be what is meant by the last bullet, but it wasn’t clear; perhaps it could be made more explicit.

Air Quality Analyses (Chapter 3)

1. To what extent are the air quality characteri zations and analyses presented in Chapter 3 technically sound, clearly communicated, appropri ately characterized and relevant to the review of the NAAQS?

The analyses in Chap. 3 could more accurately be described as modeled estimates of air quality, rather than air quality characterizations, which I think of as based on measured data. While the graphs were useful and logically presented, th ere was very little measured data given for comparison, so it is not possible to judge their ‘soundness’. Combined with the lack of CMAQ validation discussion (mentioned ab ove), it becomes more important to see these in the context of measured data as well. But this may be prem ature if the next draft is meant to include such comparisons.

I would have liked more discussion of the monthl y patterns of deposition shown, for example, in Figs 3.2-14 through 3.2-19. Clearly wet deposition is driven largely by precipitation, but what drives the other components of deposition? Are these emission patterns or meteorological patterns or biological activity patterns? Some discussion of the importance of these various temporal scales for the ecological effects mode led is probably appropriate as well. A minor complaint on the communication of the results: th e color scheme for Figures like 3.2-6 etc. is not intuitive. The scheme used was almost a rainbow-like scale, which is easy to interpret and would have been fine, but instead green was sandwiched between yellow and orange, breaking the natural progression of colors (r ed -> orange -> yellow) that mo st of us have internalized and making it harder to visually establish a continuou s gradient of concentration changes.

2. Section 3.2.1 describes an approach for evaluat ing the spatial and temporal patterns for N and S deposition and associated ambient concentrations in the case study locations. This document includes the analysis for the Adirondacks case study. Does the Panel agree with this approach and should it be appli ed to the other case study areas?

It was a sound approach and a useful exercise th at may give as clear a picture of deposition as we’re likely to get. With the additions/change s noted above, I would welcome this analysis for

the other areas.

3. Section 3.2.2 describes the rela tive contributions of ambien t emissions of nitrogen and ammonia to nitrogen deposition for the case st udy areas. To what extent is the approach taken technically sound, clearly communica ted, and appropriately characterized?

This was an interesting exercise that was very useful in establishing th e relative importance of NOx and NH3 emissions to overall N deposition and the relative responsiveness of deposition to changes in emissions. It was very helpful to es tablish this kind of pers onal internal calibration in a strong visual way. It is also a critical comparison to establ ish in making a strong case for the

56ability of a NOx-concentration based standard to be sufficiently protective, despite our understanding that impacts are rea lly driven by total n itrogen. Given the lack of spatial and temporal variability in the contributions of NOx to oxidized N and NH3 to reduced N, those maps probably don’t need to be shown, just descri bed instead. The results look perfectly logical and convincing, although I resist accepting these results co mpletely until seeing further documentation of CMAQ’s performance. The REA notes that the RSM has been validated for PM and O3, but it’s not clear whet her that validation translates to deposition parameters as well. Presumably the missing section 3.2.2.5 on uncertainty will address some of these issues. Again, as above, the color scale on all th ese plots is counterintuitive. Using the color red to depict no impact and green for 100% impact is contrary to general mapping conventions and at least in my case, caused me to continually misinterpret the plots.

Case Study Analyses (Attachments 2-6)

6. Att. 2: Are the national geos patial datasets chosen adequate to identify sensitive areas?

Are there other data sets that have not been identified by this anal ysis that we should consider? Does the panel agree with this approach or can they suggest alternatives?

I have no knowledge of other datasets that could be useful to this effort. Some of the data were quite old (1971 for the range of red spruce) a nd caused me to wonder whether the range could have changed significantly in the intervening 37 years. Perhaps the authors could comment on the issues that might be affected by such old observations. Similarly, the dataset on acidophytic lichens was clearly not complete, or at least spatially representa tive, and impacts the results. One can’t protect lichens that haven’t been iden tified as sensitive, and the current map, which

shows clusters of lichens within some states but none in neighboring states , strongly implies that some species have not been identif ied in those neighboring states.

7. Att. 3: re MAGIC model to evaluate ANC levels in selected streams and lakes in

Adirondacks and Shenandoahs. To what extent is the approach ta ken technically sound, clearly communicated, and appropriately characterized?

The selection of MAGIC is a ppropriate, but this section was poorly written and extremely confusing, especially the modeling approach an d description of MAGIC and ASTRAP. I think the dates given for scaling the historic data to deposition are wrong in seve ral places, but the text

was too convoluted to tell for sure. Also it would have been nice to see a map or at least a better description of how the ASTRAP sites are connected to the M AGIC sites. The classes and descriptions of ANC limits ke pt changing within the text a nd figures and should be made consistent. The discussions of critical load frequently mixed up the concepts of greater than-less than and above-below, adding to the confusion. It was very difficult to wade through the errors and try to make sense of what was really be ing accomplished here. The approach may be sound, but can’t be assessed on the basis of what was presented. It was certainly not

communicated or characterized in a satisfactory way.

8. Att. 4: use of SMB model to evaluate cu rrent deposition on forest soil ANC for sugar maple in Kane Experimental Forest and red spruce in Hubbard Brook Experimental Forest. To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized?

57The selection of the study area was reasonable and the descripti on of the method was clear. Without results it’s not possible to say too much more. The Table 3.1-2 had some numbers that need to be explained further, however. The rang e of critical N loads vary by a factor of 10 over the 3 study periods shown, and each of the methods gives very different results. Why the big difference? The text mentions biomass changes; is this the sole reason? Is this magnitude of change in biomass typical? How comparable are the methods? The text in Section 1.1.1 was unnecessarily repetitive and coul d be tightened up; no need to quote the ISA at such length.

9. Att. 5: Aquatic nutrient enrichment—eva luate how changes in N deposition affect the eutrophication index in two estuaries: Ch esapeake Bay and Pamlico Sound. To what extent is the approach taken technically sound, clearly co mmunicated, and appropriately
characterized?

10. Att. 6: Terrestrial nutrient enrichment— evaluate effects of N deposition on CSS community in California and mixed conifer forests in San Bernardino and Sierra Nevada Mountains. To what extent is the ap proach taken technically sound, clearly communicated, and appropriately characterized?

Additional Effects (Chap. 6)

1. Impacts of S deposition on Hg methylation, impacts of NO on climate change, and impact of N deposition on C sequestration. Are these effects sufficiently addressed in light of the focus of this review on the other targeted effects and in te rms of the data available to analyze them?

This was an adequate review of these effects. The focus appr opriately belongs on acidification

and enrichment effects.

Synthesis and Integration of Case Study Results into the Standard Set ting Process (Chap 7)

1. Purpose is to summarize the case study results and characterize the relationship between levels of an ecological indica tor and the associated degr ee of ecologically adverse effects. To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized? Does the Panel have suggested refinements?

I’m still uncertain about exactly how the case studies ultimately are used. Are they merely for scientific support and justification, or do the mode l results from them get incorporated eventually into a quantitative relationship th at can be plugged into the framework presented in Chapter 8? I think the confusion stems from the incomplete natu re of this chapter. Wh en it is fleshed out in

the next version with real data , the application of the case study results should be obvious.

Considerations in the Structure of th e NOx/Sox Secondary Standard (Chap 8)

1. Is the suggested overall st ructural framework for a s econdary standard technically sound and logically presented?

58The recently added Chapter 8 was very lucid and well written, presenting a helpful blueprint for

how to move from ambient concen trations to possible secondary standard. I found no technical or logical fault in it.

2. Is the description and development of the de position transformation function (Fig 8.1.1) between air quality indicators and the deposi tion metric clear and technically sound?

3. Is the description and development of the ec ological effect functi on (Fig. 8.1.1) between the deposition metric and the ecologica l indicator clear and technically sound?

4. Does the discussion adequately capture the pote ntial use of categoric al variables versus continuous variables when accounting for the variability of atmos pheric, landscape, and ecological factors?

These were all fine.

5. Are there any key elements missing from the framework?

There needs to be a more complete discussion of how a standard can accommodate geographic variation; i.e., how to equitably control NOx and Sox to adequately protect sensitive areas without overcontrolling in areas th at are far less sensitive to acid deposition. Section 8.3.1 made reference to varying factors w ithin the transformation function by location, and the fact that deposition loads will vary by location, but it was not clear from the text how this translates to

variation in the standard. It seems that the stan dard must account for diff erent concentrations in different regions, but how that is sp ecified is still pretty fuzzy.

Another big piece that is missing is the discussion of CMAQ (or other model) uncertainties. It was interesting that this is the first place in the REA (Sec. 8.3.2.1.2) where CMAQ performance evaluation (or the lack thereof) is mentione d. Given the very heavy reliance of the REA analyses on CMAQ (a necessary re liance, admittedly), it is criti cal to have its performance characterized as thoroughly as possible so that the Administra tor and others can assess a proposed standard’s pote ntial for success.

Section 8.3.2.2.2 leaves aggregation methodology as an open research issue. Does this mean it will be resolved in the next draft by work the sta ff is doing? If not what are the implications of leaving this issue unresolved?

6. Does the framework need to be expanded or revised to accommodate the appropriate consideration of ecological indicators besides ANC when developing a secondary NAAQS for NOx and Sox

Isn’t that the point of the case st udies? It seems premature to answer this question until those results are complete. ANC seems adequate for aci dification effects, but the other case studies weren’t really far enough along to evaluate. The chapter should include some discussion of how the standard might account for multiple indicators.

597. Does the panel have any further sugg ested refinements at this time?

Section 8.3.2.4 needs additional attention. It mentions possible work on MCIP and CMAQ to incorporate measurements, which would be great and I highly encourage. But is it really possible to produce results and incorpor ate them into the next draft?

Section 8.3.3 on the deposition-indicator links coul d benefit from a discussion of how influential the various parameters are on the outcome, at l east in a qualitative sense. It would help the reader (and presumably the Administrator) evaluate which are the critical parameters controlling the relationship. There also needs to be some discussion or graphical analysis of the geographic sphere of influence of NOx/SOx c oncentrations on each sensitive area. For example, if the indicator were set at an ANC of 50 ueq/L in the Adirondacks, how much would

NOx and Sox need to be reduced to reach that ANC, and over what geographic area? Somewhere the document needs to lay out that visual frame of reference for the geography of

influence on the sensitiv e areas. We know that deposition is some function of distance, and that high concentrations close to a sensitive receptor will be more influential than the same concentrations far way; how far away is fa r enough to have negligible impact?

Specific comments, typos, etc.:

p. 3-3, Fig 3.1.2 (also Fig 3.1-5) Avoid use of pi e charts, as they make it difficult to make quantitative comparisons. Bar charts are al most always preferable. The use of 3-D unnecessarily complicates these figures and also makes it more difficult to visually compare the slices of the pies. p. 3-4, lines 12-13: Fig. 3.1-4 actually shows facilities, not annual emissions by state. p. 3-6, lines 14-16: Is the NEI fi re inventory error corrected here ? If not, a statement about the correct magnitude of fire emissions should be added. p. 3-8, line 9: Figure 3.1-6 shows total N de position in Ohio and Pennsylvania of >20 kg/ha/yr, definitely much more than the 9.2-9.6 kg /ha/yr cited here. Which is correct? This and the following figs 3.1-7,8,and 9 are nice but the colors are difficult to distinguish in the printed version. p. 3-50, line 1: ARD -> ADR p. 3-57, line 10: remove question mark p. 6-7 caption to Fig. 6.1-3: watershed should be plural p. 6-18, line 6: Not clear what ‘further stabil izing soil carbon compounds’ actually means. Do they then have longer lifetimes? p. 6-23, line 12: Onondagal ->Onondaga p. 7-1, line 28: area should be plural p. 8-14: Equation numbers don’t follow the text

Attachment 2, p. 2, line 14: remove ‘is’ Attachment 2, p. 3, line 19: is this really 51 inches, or should it be cm, as 4.1.11 says about

this same dataset? Attachment 2, p. 7, line 17: remove ‘Sulfur Containing’ Attachment 2, p. 7, line 26: remove ‘N itrogen Containing Chemical Species’ Attachment 2, p. 8, line 9: remove ‘deposited’

60Attachment 2, p. 11, line 8: remove ‘Nitrogen Containing Chemical Species’ Attachment 2, p. 11, line 18: Containing -> Including Attachment 2, p. 16, line 4: remove meter

Attachment 3: fix the subscripts and supe rscripts throughout. Too many grammar errors and typos to enumerate here – this whol e section needs careful editing. Attachment 3, p. 6, line 24: deposition is more like 17 and 13 kg/ha according to the Figure 3.1-1, not 15 and 10. Attachment 3, p. 8, line 4: deposition is more like 18 and 11 kg/ha according to Fig. 3.2-1.

This makes me distrust the % declines in these species, here and on p. 6, but I didn’t

recalculate them. Attachment 3, p. 12, Fig. caption: 12 streams are shown, not 13. Lots of other typos in this caption. Attachment 3, p. 16, line 26: >50 should be <50 Attachment 3, p. 17, lines 6-8: Fig. 4.1-2 doesn’t imply that biota are not often harmed below and ANC of 100, only that the harm is less severe than for lower ANC Attachment 3, p. 17, line 12: It doesn’t make sens e to say that an ANC of 0 protects surface waters from becoming acidic. waterbody Attachment 3, p. 17, line 17: change ‘deposition – critical load’ to ‘deposition less than

critical load’

Attachment 4, p. 1, line 6: should be ‘sulfur loads to and effects on a chosen...’ Attachment 4, p. 10, line 4: on -> at Attachment 4, p. 11, line 16: not clear, reword Attachment 4, p. 11, lines 21-22: not clear, reword Attachment 4, p. 23, line 22: HBEF Attachment 4, p. 25, line 8: litterfall Attachment 4, p. 33, line 17: put weathering on its own line Attachment 4, p. 38, line 13: Arrhenius Attachment 4, p. 48 and 49: It would be helpfu l for these figures to include the HBEF as well; its very hard to place it accurately given the map on p. 21

61

### Dr. Naresh Kumar

COMMENTS ON SECTION 6.1. SULFUR AND MERCURY METHYLATION

GENERAL COMMENTS

The section begins with a segment on the ch emistry and physics of mercury atmospheric transport, fate, and deposition, followed by a mo re detailed segment di scussing the chemical determinants of mercury methylation.

The two segments of the section differ gr eatly in their accuracy, completeness, and understanding of mercury chemistry and enviro nmental behavior. While the second part, on mercury methylation specifically, is generally complete and accurate , the first, background, segment has a number of factual errors, misinter pretations, and erroneous conclusions in it.

As two examples, the first segment presents an erroneous picture of the behavior of elemental mercury (or Hg 0 ) in the environment, and of “methyl mercury” (dimethylmercuric salts) in organisms. In the first case, Hg 0 is presented as being “reduc ed” in surface ecosystems to become methylmercury; in reality, Hg 0 is the reduced form, and plays no part in methylation, which occurs through bacterial action on the oxidized form, divalent mercury (or Hg +2 in the text). In the second case, methylmercury is openly stated to be “lipophilic,” or preferentially attached to fatty tissues in fauna, when in fact methylmercury is lipopho bic and associated with protein sulfhydryl groups, in muscle tissue.

The entire section need to be thoroughly revi ewed and rewritten from the beginning to more accurately reflect our basic understanding of merc ury chemistry, transport, and fate in the environment. Specific comments on the text follow.



### SPECIFIC COMMENTS

• To date, there has been no unequivocal demonstration of sulfate limitation in US or global waterways such that natural sulfate addition or subtracti on alone has produced a change in methylation rates or mercury in fis h. Such demonstrations have occurred only in experimental manipulations of microc osm ecosystems. Since fish take up only a fraction of the methylmercury in the water co lumn and biota of lower trophic levels, there is always an excess of MeHg in studied wa ter bodies. And downtrends in sulfate addition have always been matched by downtrends in diva lent mercury deposition, so that it is not possible to separate sulfate availabi lity from divalent mercury burden.

• It is mentioned that “Mercury concentrations have in creased approximately 2 to 5 times since the onset of the industr ial revolution and appear in even the most remote locations on the Earth (Munthe et al., 2007; U.S. EPA, 2006).” The accepted global average ratio of atmospheric mercury mass now compared to the period prior to the Industrial Revolution is in the range of 2 to 3, not 2 to 5. Ratios higher than 3 can be found in local,

62single-instance measurements of concentra tions in, e.g., an ice core, but these are

characteristic of individual locations and not the global balance of mercury.

• It is stated in the text that“In the United States, the primary source of mercury to ecosystems is atmospheric deposition due to coal combustion (e.g., coal-fired electric utilities). Other sources include municipal waste combustion, medical waste incineration, chlor-alkali plants, and industrial boilers.” This sentence appears to propagate the common misconception that mercury emissions (anywhere) are proportioned exactly the same as mercury deposition (anywhere else). Th is is obviously incorrec t, since both total and wet deposition of mercury at any location on earth (or in the United States) is made up of contributions from hundreds of sources at widely varying distances upwind, and is not linearly proportional to the fraction of total emissions eac h source, or source type, makes up. Therefore, it should be noted that a significant amount of mercury depositing within the United States originates in ot her countries, primar ily mainland Asia. The sources of mercury depositing to U.S. ecosy stems varies widely, both geographically and by source, depending on the proximity of U.S. sources and the prec ipitation climatology of the setting.

• It is mentioned that, “Depending on the particulate a ssociation and oxidation state, atmospheric mercury particles can remain susp ended in the atmosphere for more than 2 years (Evers et al., 2007; U.S. EPA, 2006) .” This sentence should be rewritten or deleted. There is no relation between “particulate association” (an unexplained term) and oxidation state for mercury; most of the me rcury bound to particles is divalent mercury (or “Hg +2 ” as used in the report). But the statem ent that such partic le-bound mercury has an atmospheric lifetime of more than 2 year s is not true; due to gravitational settling, coagulation, etc., Hg p has an average lifetime in the atmosphere of several days to about two weeks, no more. And no sour ce of mercury emissions to the atmosphere issues more than about 3% of mercury mass in the form of particle-bound mercury, in any case. It is suggested inserting something like this: “There are three primary forms of mercury in atmospheric sources of the substance: elem ental mercury, reactive gaseous mercury, and particle-bound mercury. Once emitted, the thr ee forms behave very differently in the atmosphere and deposit over very different geographic patterns. It generally takes hundreds or thousands of miles for half of th e emitted gaseous elemental mercury to deposit to ground level, while half of the reactive gaseous mercury will deposit within about 150 miles of the source. Pa rticulate-bound mercury, genera lly 3 percent or less of the emitted mercury mass, deposits in intermediate patterns (M. Cohen, 2004).”

• The text states that, “When deposited into terrestrial and aquatic ecosystems, elemental
mercury is oxidized to reactive mercury (Hg +2 ) (Ambrose et al., 2005; U.S. EPA, 2006).”

A number of statements need to be corrected or nuanced in this passage. Any “deposition” of elemental mercury occurs by gas-phase transf er at ground level from regions of higher concentration (that is, the atmosphere) to regi ons of lower concentra tion (to plant stomata, soil pores, interstitial spaces, etc.), basically a down-gradient mass transfer. There is nearly no oxidation of elemental mercury to the diva lent form occurring at the ground surface; more likely is removal of elemental mercury ba ck to the atmosphere by revolatilization, or evasion. There may also be a net output of elemental mercury from the surface by

63insolation (solar radiation) producing photoreduc tion of divalent mercury, or demethylation and photoreduction of mono methylmercuric halides.

• The entire sentence where methylmercury is stated to be “lipophilic” needs to be corrected. First, mercury cannot be “reduced and methylated to methylmercury”; the reduced form of mercury is th e insoluble elemental mercury, Hg 0 ; because of its insolubility in water, it is unavailable to sulfate-reducing bacter ia for the methylation process. Of the “deposited mercury pool,” typically half or more is (wet-deposited) divalent mercury, most of the remainder dry- deposited elemental mercury; of the amount of divalent mercury dissolving in water bodie s, between 1% and 10% may be methylated and dissolved in the water column. Of this 1% to 10% (depending on the particular water chemistry; higher fractions for more anoxic wa terways), perhaps 10% of that (or 0.1% to 1% of the dissolved divalent mercury) may be taken up into the food web. Second, mercury is most certainly NOT lipophilic, but rather lipophobic : it attaches to protein-based sulfhydryl groups and resides primarily in musc le and nerve tissue (“fish flesh”). This distinction is important because it is the root of the finding that cooking fish which may be mercury-laden will in fact not decrease, but increase, the concentration of the mercury in the cooked product. Any fat th at is cooked off is mercury-free, and the lower weight cooked fish remaining has the sa me mass of mercury as prior to cooking, but in a lower-weight portion of fish (with some fat and water mass cooked off), hence higher net mercury concentration.

• There seems to be a faulty reference in the sentence “ The majority of U.S. waters are sulfate-limited (Harmon et al., 2007); theref ore, decreases in sulfate are likely to promote decreases in methylmercury.” Harmon et al., 2007, “Using Sulfate-Amended Sediment Slurry Batch Reactors to Evaluate Mercury Methylation,” Arch. Environ.

Contam. Toxicol. 52 , 326–331 (2007); [DOI: 10.1007/s00244-006-0071-x] does not have a single word to say about sulfate-limited waterways. The term “-limited,” in fact, occurs only once in the document, in the introduction, with no reference to the state of U.S.

waters.

64

### Dr. Myron J. Mitchell

General Comments (For these general comments my responses are in italics .)

The document and associated attachments are extens ive and it is a major challenge to provide a cohesive approach to presenting this information. I recognize the difficulty and complexity of pulling all of this together. The potential for prov iding clearer linkages in this document to the “Integrated Science Assessment for Oxides of Nitrogen and Sulfur – Environmental Criteria” may help maintain focus and reduce the size of the document. More consistency is needed in the use of terms such as oxides of sulfur, oxid es of nitrogen, sulfur oxides, nitrogen oxides, SO

x , NO

x , etc. Also, in the document there are differences in criteria for sensitivity of various parameters such as ANC. Careful editing would help fo cus the document and reduce redundant information. The draft document has many noun trains su ch as “draft revised criteria document”.

Responses to Charge to the CASAC NO

x /SO

x Secondary Review Panel

Scope of the review (Chapters 1 and 2):

1. Chapters 1 and 2 provide the background, hi story, and the framework for this review, including a discussion of our focus on the four key ecological effect areas (aquatic acidification, terrestrial acidification, aquatic nutrient enrichme nt, terrestrial nutrient enrichment). Is this review appropriately focused in te rms of the targeted effect areas and in terms of characterizing the important atmospheric and ecological variable s the influence the deposition and, ultimately, the ecological impacts of nitrogen and sulfur? Does the Panel have any further suggested

refinements at this time?

Chapter 1 needs a more balanced introduction with respect to the impacts of S and N gaseous constituents and deposition with gr eater attention earlier in each chapter on the effects of N on ecosystem structure and function including the alteration of species composition. In Chapter 2 (Section 2.4) the description of errors in the anal yses needs a more rigorous approach that more clearly identifies specific issues related to sour ces and amount of errors. In its current form Chapter 2 provides very broad desc riptions that do not clearly id entify the major sources of error that are important to the current assessmen t. Possibly reference to subsequent chapters that more clearly delineate these errors would be helpful.

Air quality analyses (Chapter 3):

1. To what extent are the air quality characteri zations and analyses presented in Chapter 3 technically sound, clearly communicat ed, appropriately characterized, and relevant to the review of the secondary NAAQS for NO

x and SO

x ?

The terminology and analyses associated with “policy-relevant background concentrations” is confusing. Some consideration is needed of the adequacy of the current monitoring network in

65evaluating air quality especially in relationship to measurements in urban settings.

2. Section 3.2.1 describes an approach for evalua ting the spatial and temporal patterns for nitrogen and sulfur deposition and associated ambient c oncentrations in the case study locations. This draft document includes the analysis for the Adirondacks case study. Does the Panel agree with this approach and should it be a pplied to the other Case Study Areas?

This can be a helpful approach. However, within each of these regions there have been other measurements made of associated paramete rs including precipitation amount, atmospheric deposition, etc. It does not appear that any subst antial attempts are being made in this document to compare these current result s with previously published results ? There is a major emphasis on providing both spatial and temporal patterns using the CMAQ modeling results. Shouldn’t these modeling results be compared with other results of deposition measurements for this region? Having some comparisons with these other measurements would be helpful in evaluating the CMAQ deposition estimates. The issues and pr oblems associated with making measurements of air pollution concentrations and converting them to deposi tion by various inferential procedures needs to be clearly articulated.

3. Section 3.2.2 describes the relative contributions of ambient emissions of nitrogen and ammonia to nitrogen deposition for the case study ar eas. To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized?

Clarification is needed on the relative importance of the emission sources including the accuracy of these emission estimates, atmo spheric chemical conversions and the estimates of deposition velocities in evaluating the result s of these model outputs. Too much of this section describes model output with little supporting evidence of the relationships noted.

Case Study Analyses (Attachments 2-6):

These attachments are extensive and it would be most helpful if they were more targeted to the issues and needs of the “Risk and Exposure Asse ssment to Support the jo int Review of the NO 2 and SO 2 Secondary National Ambient Air Quality Standards”.

1. Attachment 2 presents a GIS analysis to de fine geographical areas th at are sensitive to

acidification and nutrient enrichment. Are the nationa l geospatial datasets chosen adequate to identify sensitive areas? Are there other data sets that have not been identified by this analysis that we should consider? Does the Panel agre e with this approach or can they suggest

alternatives?

In general, the selected regions and associated data sets appear to be appropriate for this analysis.

2. Attachment 3 presents our current progr ess on evaluating the effect of aquatic

acidification in the Adirondacks. It describes the use of the MAGIC model to evaluation ANC

levels in selected lakes and streams in the Adir ondacks and Shenandoahs. To what extent is the approach taken technically sound, clearly comm unicated, and appropriate ly characterized?

66There is some differences in the deposition estimat es being used for estimates using the MAGIC versus other approaches in the document (e.g., ASTRAP versus CMAQ). Will this result in some issues relating to congruity of analyses in the document? These analyses have a specific focus

on the Grimm and MAGIC models. There have b een other efforts to evaluate acid rain/biogeochemical responses in each of thes e sites (especially the Adirondacks) and hence it would be useful to include some of these other resu lts to indicate either differences or support of these current modeling efforts. In these discussi ons different levels of ANC are suggested that differ than for other sections in the document. A more consistent approach is needed on setting the ANC limits of concern with respect to se nsitivity to acidification and recovery from acidification. Possibly a separate section is needed with respect to ANC and its application to evaluating acidity and the various levels that are used. This would need to be included before

the case studies section.

3. Attachment 4 presents our current progre ss on evaluating the eff ect of terrestrial acidification. It outlines a plan to use the Si mple Mass Balance Model to evaluate current deposition levels on forest soil ANC for sugar ma ple in the Kane Experimental Forest and red spruce in the Hubbard Brook Experimental Forest . To what extent is the approach taken technically sound, clearly communicated, and appropriately characterized?

This portion of the document is highly uneven with in some cases substantial detail provided and in other places there are broad generalizations. This makes it difficult for the reader to ascertain the salient points.

4. Attachment 5 presents our current progress on evaluating the effect of aquatic nutrient enrichment. It outlines a plan to evaluate how changes in nitrogen deposition affect the eutrophication index in two estuaries: the Chesapeake Bay and Pamlico Sound. The analysis will model one stream reach (Potomac River and Ne use River) to determine the impact on the eutrophication index for the estuary. To what ex tend is the approach taken technically sound, clearly communicated, and appr opriately characterized?

The Chesapeake Bay has been the focus of considerabl e efforts relating to the effects of nitrogen loading on eutrophication. There have been extensive investigations on this site and there are extensive data sets that can be used in the analys es. A major drawback of this site, however, is that it is not likely that atmos pheric nitrogen loading is a major co mponent of the total nitrogen loading. Hence, the Chesapeake Bay will not be very sensitive to changes in atmospheric nitrogen inputs. Although the inform ation on the Neuse River is less extensive, ther e are similar problems with the overall importance of atmosphe ric N loading. In attachment 5, page 20 it is

indicated that “Previous studi es have estimated that wet at mospheric deposition of nitrogen (WAD-N), as deposition of disso lved inorganic nitrogen (DIN: NO 3 , NH 3 /NH + ) and dissolved organic nitrogen, may contribute at least 15% of the total externa lly supplied or “new” nitrogen flux to the coastal waters of North Carolina”.

5. Attachment 6 presents our current progress on evaluating the effect of terrestrial nutrient enrichment. It describes an appr oach to evaluate the effects of nitrogen deposition on the Coastal Sage Scrub community in California and in mixe d conifer forests in the San Bernardino and

Sierra Nevada Mountains. To what extent is the approach taken technically sound, clearly

67communicated, and appropriately characterized?

The selection of the Coastal Sage Scrub community in California and in mixed conifer forests in

the San Bernardino and Sierra Nevada Mountains n eeds some further justification versus other regions including the alpine and subalpine comm unities of the eastern slope of the Rocky Mountains in Colorado. These sites in California are certainly important and interesting sites, but it may be difficult to separate the effects of nitrogen deposition ve rsus other air pollution components, especially ozone.

Additional Effects (Chapter 6):

1. In this chapter, we have presented results from some initial qualitative analyses for additional effects including the impact of sulfur deposition on mercury methylation, the impact of nitrous oxide on climate change, and the impact of nitrogen deposition on carbon sequestration. Are these effects su fficiently addressed in light of the focus of this review on the other targeted effects and in terms of the available data to analyze them?

These descriptions seem adequate, but certainly the issues go beyond those associated with carbon sequestration. Some additional discussion of the importance of mercury being found in other components of the ecosystems in cluding song birds should be included.

The purpose of Chapter 7 is to summarize the Case Study results a nd characterize the relationships between levels of an ecological indicator and the a ssociated degree of ecologically adverse effects. To what extent is this appr oach technically sound, cl early communicated and appropriately characterized at this point of the review? Does the Panel have any further suggested refinements at this time.

In its current form this Chapter is highly descrip tive. Future revisions will need to include more specific quantitative results that show a clear relationships to the assessment.

Chapter 8 begins to explore how a secondary NAAQS might be structured to address the targeted ecological effects discussed in the risk assessment. The next draft of this document will include one or more examples of how this structure might be used to related specific levels of air quality indicators with a corresponding eco logical indicator for a given lo cation and/or scenario. To

what extent is the described a pproach technically sound, clearly co mmunicated and appropriately characterized at this point of the re view? Specifically, we are asking:

• Is the suggested overall structural framework for a secondary standa rd technically sound and logically presented?

• Is the description and development of the deposition transformation function (Figure 8.11) between air quality indicators and depos ition metic clear and technically sound?

• Is the description and development of the ecological effect function (Figure 8.1-1) between the deposition metric and ecologica l indicator clear and technically sound?

• Does the discussion adequately capture the use of categorical variable s versus continuous variables when accounting for the variability of atmospheric, landscape and ecological

factors?

68• Are any key elements missing from the framework?

• Does the framework need to be expanded or revised to accommodate the appropriate consideration of ecological indicators be sides ANC when developing a secondary NAAQS for NOx and SOx?

• Does the panel have any further suggested refinements at this time?

Providing a clear scientific linkage that is policy relevant between concentrations of SO

x and

NO

x and resultant S and N deposition and subsequent tr anslation to ecosystem level effects is a major challenge. There are good linkages between concentrations of SO

x and NO

x and deposition, but the linkage to ecosystem level e ffects is more complicated due to inherent variability across the United States of the sensitiv ity of these systems. There are major problems with respect to both having con fidence in calculated deposition velocities and how to ascertain “functional forms”. A clear delin eation of which ecosystem type s are most important with respect to specific ecological effects (e.g., acidi fication in the northeast , N deposition affecting biological community structure in the mountain west, etc.) is re quired. Such categorization will be very important in setting secondary standard(s) t hat will be relevant to those effects which are of greatest importance to various regions that ha ve different relative representations of various

ecosystem types.

Specific Comments in which italics indicate specific changes.

Page(s) Lines(s) Comment

xv 3-5 Why should this definition only include terrestrial ecosystems?

1-1 8 Change to “The NAAQS have been established for pollutants”.

1-2 8 Change to “complex interactions among relevant chemical species

of”.

1-3 10 Clarify more specifically who is “we”. Do you mean EPA?

1-3 19 “Chapter 2" should be in bold font.

1-4 1-5 This does not agree with provided definition on nitrogen enrichment (page xv, lines3-5)

1-5 13 Change to “ This draft ”.

1-5 15 Delete “held”.

1-5 24 Change to “identified the critical components to be”.

1-5 25 Specify the title of the “Adm inistrator” here and elsewhere in the

document.

691-6 5 Change “NAAQS for NO2 was set at 0.053 ppm”.

1-6 10 Change to “secondary NAAQS values for SO 2 under”.

1-6 13 Change to “of evidence from vegetation effects ”.

1-6 19 Change to “EPA was aware that SO

x has other”.

1-6 25 Here and elsewhere be consistent in the use of terms SO

x and

sulfur dioxides.

1-7 17 Change “completed by EPA at this time ”.

1-7 20-23 Change to “Administrator’s conclusions that (1) based upon the

then-current scientific understa nding of acid de position, it would be premature and unwise to pres cribe any regulatory control program, and (2) when the scien tific uncertainties had been substantially reduced through ongoing research efforts, EPA would draft and support an appropriate set of control measures”.

1-8 3 Change to “ Due to the complexities and substantial remaining”.

1-8 20-21 Change to “long-term”.

1-9 28 Be more explicit with resp ect to this “Federal Register notice”.

1-10 7 Why “beyond full implementation of Title IV....”?

1-10 7 Change “to presented in the 2005 NAPAP Report”.

1-10 10 Be more specific with respect to which “recent reports”.

1-10-11 It would preferable to start w ith a clearer definition of the different forms of nitrogen oxides and then discuss some of the confusing terminology.

1-11 6 Are another group of indivi duals using different terminology for nitrogen oxides?

1-11 12 Change to “deposition of reactive nitrogen”

1-11 19 Change to “In many regions ”.

1-11 22 Change to “assessing the impacts of nitrogen deposition ”.

1-11 24-26 This is not true most res earch does consider separately the oxidized

70and reduced forms of nitrogen i nputs especially for natural ecosystems. In many cases the total input of reduced nitrogen is

less well known than that of oxidized nitrogen.

1-12 13-14 With reduction in S deposition the relative importance of N deposition in contributing to aci dification has increased. This

should be noted in this introductory information.

1-13 5 The statement “sometimes limiting” with respect to N is misleading. Nitrogen is often a lim iting nutrient with respect to primary production in terrestrial ecosystems. Even though N may be a limiting nutrient does not necessarily imply, however, that there may not be substantial ecosystem damage. Changing N inputs can alter ecosystem structur e including altering the system

from a more desirable state. Such factors are especially important with respect to the evaluation of N deposition in the western U.S. Such secondary effects need to be considered in setting standards.

1-13 6 Change to “acidification, nutrient enrichment, eutrophication, and changes in species composition”.

1-14 7-9 Other effects includi ng changes in species composition and community structure need to be included for both terrestrial and aquatic systems especially associated with N inputs.

1-14 10-24 Clearly there have been substantial studies of acidic deposition effects in the eastern U.S., but so me consideration is needed of effects in the western U.S. where the effects appear to be substantially different especially with respect to N deposition

influences.

1-14 26 Does the reference to “high elevation lakes” refer to the western

U.S.?

1-14 31 In this section the issue of changes in “community composition” is

mentioned and this needs to be included earlier in the document.

1-15 1-4 This statement on alteration of aquatic communities needs to be made congruous with earlier statem ents on overall effects of S and N deposition.

1-15 22 Change to “ a lpine”.

1-16 5 Provide some information on what are these “other factors”. Do you mean periods of relatively high microbial activity?

711-16 8 Be more explicit on the relationship (e.g., posit ive or negative) between “oxygen content, temperat ure, pH, and supply of labile organic carbon”.

1-16 11 Be more explicit on what are these conditions. Do you mean for conditions the amount of wetlands and linkages to drainage

waters?

1-16 Figure 1.3-3 should explicitly have a category for changes in species composition that may differ from altered biodiversity.

2-1 9-12 This listing needs to ex plicitly include effects on community structure and species composition.

2-1 16-18 This statement begins to ra ise the issue associated with different effects depending on region in the U.S.

2-1-2 The absence of case stud ies in the Rocky Mountain west is problematic.

2-4 This introduction can be im proved with a more focused approach. There is considerable repetition in this part of the document.

2-5 4-5 Change to “data were not sufficiently available to perform”.

2-5 18 Clarify in scaling-up clarify how this will be done with respect to sensitive areas (e.g., will this be done for all sensitive areas or will the scaling be a function of other sensitive areas with similar

characteristics?

2-6 27 Change to “ need for them”.

2-6 28 A citation is needed for the “MEA” here. Later it is indicated that MEA (2005).

2-7 3 Care should be made in the us e of the term “regulating” since this term has a different meaning in the context of environmental regulations such as those associat ed with laws formulated by the EPA. Maybe a clarifying phrase is needed to avoid any confusing recognizing that the term regulation has a different meaning in an ecological context.

2-6 14 Are there different references for the MEA? Here it is indicated: MEA, 2005b. Also see Line 17 (MEA, 2005b).

2-7 This section needs some furt her articulation with respect to the

72description of ecosystem services. Is this description based solely on what is provided in (U.S. EPA, 2006)? It would be helpful to provide some further references that link these statements to other

informational sources.

2-7 16 Change to “inter est in the risk assessment described in the current

document ”.

2-7 20-22 A better description is need ed that clarifies the association of NO

x deposition and eutrophication.

2-7 23-25 This statement is poorly worded.

2-7 26-31 The wording of this section needs much better clarification. It is confusing whether a linkage or several linkages are being

evaluated.

2-8 Figure 2.2-2 Ecosystem Services: th e ecological processes or functions having monetary or non-monetary value to individuals or society

.

2-9 1-2 Change to “We have begun identifying the primary ecosystem service(s) affected by either acidification and/or enrichment and for major ecosystem types and components (i.e., terrestrial ecosystems, soils”.

2-9 4 Change to “The impacts affecting various”.

2-9 6-7 Change to “ These impacts on ecosystem services will be”.

2-9 10 Change to “tourism. Effects on fisheries (decreased”.

2-9 21 Change to “tourism. Effects on fisheries”.

2-9 27-28 Change to “hazard mitigation. Methods for evaluating linkages to measurements and ecosystem services may include”.

2-10 5 Clarification is needed on what is meant by “community”.

2-10 7 Change to “changes in stand density, shifts in”. Densification is jargon. Change to “shifts in lichen community species composition”.

2-10 14 Delete “intake”.

2-10 15-16 Why distinguish between “Native Americans and Alaska native Villagers”?

732-13 2-4 Change to “ Our approach in evaluating risk assessment relies upon various analytical tools and te chniques, data sources, and other forms of analyses each of which has inherent uncertainties ”.

2-13 6 Change to “affect the level of its response”.

2-13 10-11 This is not a very succinct or complete descript ion of the errors associated with modeling approaches.

2-13 12 Change to “involved with the transformation and fluxes of nitrogen and sulfur constituents ”.

2-13 14-15 It would be more helpful to be more explicit in describing the sources of uncertainty. For exampl e with respect to deposition, wet deposition of S and N can be relatively well characterized compared to dry deposition. The ma jor issue associated with the errors related to dry deposition are associated mostly with the modeling of deposition velocities. Al so, be more specific in what is being implied with the use of the term “ecological modeling”.

2-13 14-21 This section needs to incl ude more specific information. It would be most helpful to explicitly state the major sources of error in risk

estimates.

2-13 22-30 These statements are very general. At a minium specific examples need to be supplied that show actua l examples of these errors and importance to the assessment.

2-14 2-3 It is anticipated that these discussions will provide sufficient detail

on these sources of error in risk assessment.

2-14-15 References should also include citations to the actu al literature and not rely solely on EPA documents.

3-1 10 Change to “The deposition results ”.

3-1 26 Change to “The total amount of NO

x emitted in the USA in 2002".

3-2 3-4 Change to “primary emitters of NO

x , mainly as NO and NO 2 ".

3-2 5 Change to “utilities, with additional contributions”.

3-2 9 Change to “remainder of anthropogenic emissions”.

3-2 10 Delete “component”.

743-2 15-16 Delete “in the pie charts in”.

3-2 16-17 Change to “ Results are shown on both a national basis (contiguous states only) as well as for the eastern”.

3-2 18 Delete “For this display”.

3-3 1-2 Delete “Note that emissions from Alaska and Hawaii are not included in any of these charts”.

3-3 5-6 (not shown) with the on-road sector being the largest contributor, followed by emissions”.

3-3 8 Change “overall” to “ national ”.

3-3 12 The figure caption needs mo re information (e.g. that Hawaii and Alaska are excluded in these results).

3-3 15 Change to “ contiguous states”.

3-4 3 Change to “emissions from fertilized”.

3-4 5 Clarify what is meant by “30%–70%”. Does up to 70% of the

waste mass be converted to emitted NH 3 ?

3-4 9 Change to “impact from the input of total reactive”.

3-4 10 Explicitly state what is meant by “This”.

3-4 12 Change to “Total USA emissions of”.

3-5 9 Change to “utilities using coal ”.

3-5 12 Change to “up to 10 ppm ”.

3-5 13 This becomes a little conf using since the figure does not provide emission data from Hawaii and Alaska. Why not include values for these states in these figures.

3-5 13-14 Sulfur is found in other forms besides amino acids in vegetation so change to “Sulfur is a macronutrien t (typically being 1 to 2%) and

is released as SO 2 if vegetation is combusted (Levine and Pinto, 1998)”. Also, there can be other fo rms of gaseous releases of sulfur components from vegetati on (as well as soil) including H 2 S, COS, methyl mercaptan, etc. I am not sure where in the document these biogenic sulfur sour ces should be included.

753-6 1-2 Delete since information has been included in my suggested

modification.

3-6 3-6 Change to “The proportion of SO 2 emissions from major sources are shown in Figure 3.1-5 both on a na tional total basis well as for

the eastern and western United States”.

3-6 6 Why not include Alas ka and Hawaii for completeness?

3-6 14-16 The relative importance of th is error needs to be stated explicitly.

3-7 2-5 Not sure the term "policy-rele vant" is a useful term with respect to defining background concentrations. Wh at is the basis of the actual value being used? Is it based on a specific time period or some calculation that attempts to separate out natural versus anthropogenic emissions? How can the general effects of N fertilizers and N atmospheric deposition in affecting NO 2 flux be evaluated? Is this 100 ppt based on some type of area weighted

basis or some other form of calculation?

3-7 4 Delete “policy-relevant”?

3-7 25 Change to “This source di stinction and quantif ication will”.

3-8 13-14 Further information shoul d be provided on the source and methods for estimating these deposition values. This information is provided later on page 3-13. This information should be provided

earlier in the document.

3-8 19 Not sure what “Great Waters” means.

3-8 19-23 References are needed here.

3-9 Figure 3.1-6. Reduce the significant dig its in the figure legend to nearest 1/10th.

3-10 Figure 3.1-7. Reduce the significant dig its in the figure legend to nearest 1/10th.

3-11 Figure 3.1-8. Reduce the significant dig its in the figure legend to nearest 1/10th.

3-11 9-10 Further details on how th ese deposition estimates were derived should be provided. This informati on is provided later on page 313. This information should be provi ded earlier in the document.

3-12 Figure 3.1-9. Reduce the significant dig its in the figure legend to nearest 1/10th.

763-12-13 See previous comments on the placement of this information

within the document.

3-12-16 Isn’t much of this information relevant to the overall predictions of N and S deposition. It was not clear why this more extended

discussion was focused on the case studies. Was there a different type of analyses done for depositi on for the case study regions than

for the overall U.S.?

3-16 Aren’t all these abbreviati ons already provided and hence Table

3.2-1 can be deleted.

3-16 Are these formulas included to show the conversions from formula compound mass to nitrogen or sulfur mass? If this is there only

use then Table 3.2-2 should be deleted.

3-17 11 Has the western case study been identified?

3-20 Within each of these regions there have been other measurements made of associated parameters including precipitation amount, atmospheric deposition. Is there a ny attempt being made in this document to compare these current results with previously published results?

3-23 There are well establishe d geographic patterns in N and S deposition across the Adirondacks. Shouldn’t these be acknowledged? There has also been substantial work on deposition estimates in the Adirondacks using other approaches. For wet only deposition for example see: Ito, M., M.J. Mitchell and C.T. Driscoll. 2002. Spatial patterns of precipitation quantity and chemistry and air temperature in the Adirondack Region of New York. Atmospheric Environment 36:1051-1062. Also other

studies have evaluated the relativ e contribution of wet and dry deposition. See for example: Mitchell, M.J., C.T. Driscoll, J. Owen, D. Schaefer, R. Michener, and D.J. Raynal. 2001 Nitrogen biogeochemistry of three hardwood forest ecosystems in the Adirondack Mountains. Biogeoc hemistry 56: 93-133. Would some comparisons with other investigations be warranted?

3-25 This repeats a previous comm ent with respect to the inclusion of previous analyses of these re gions in these cases studies.

3-26-53 There is considerable detaile d treatment of the results provided by the CMAQ modeling including temporal and spatial results. With so much emphasis on these model re sults it would be useful to provide some other confirmation of these deposition values.

773-54 14-15 This is not entirely true . There can be instances were ambient

concentrations of NO

x and SO

x are directly deleterious. These conditions, however, have not been generally found in the USA during the period of concern associ ated with acidic deposition effects. For Europe conditions in the “black-triangle” and other centers of high pollutant concentra tion there were direct impacts especially associated with SO

x .

3-55-70 The format and output of th e CMAQ modeling runs are provided in some detail. Some further comparison of the CMAQ results, especially, in the areas of test cas es, would be helpful in providing some objective measurements of the model results.

3-70-72 The model results need to be verified with actual data that show these relationships. Clearly the m odel functional relationships and parameterization will effect overall model output. It is important that it be clearly identified when model outputs are producing

results that have been verified elsewhere or whether there are currently no empirical and experimental results that provide data to verify these results. Such arguments can also be made for the other N gaseous constituents.

3-70 16 It is suggested that ther e is “statistical imprecision in the modeling”. There are other important sources of model error that need to be considered including unc ertainty in model formulations.

3-82 7-9 Statements such as “Figure 3.2-55 shows that NO

x emissions account for almost all oxidized nitrogen deposition in the Adirondacks Case Study Area, wh ile Figure 3.2-56 shows that

NH 3 emissions account for almost all reduced nitrogen deposition” have important implications with respect to making

recommendations associated with NO

x emission controls. Are

these results verifiable and can the emissions also be linked to specific geographical areas?

3-87 How are these high emissi on locations ascertained? Is this a function of the location of speci fic monitoring locations (e.g., CASTNET sites).

3-112 This section on uncertainty (3.2.2.5) that has yet to be completed needs to include not only statistical issues, but also uncertainties in the model formulations and associated parameters.

3-113-114 This is a relatively limited re ference list with considerable reliance on EPA documents. This section would be strengthened by inclusion of results from the peer reviewed scientific literature that

78support the suggested findings.

4-1

5-1 The sections on “ACIDIFICATION” and “NUTRIENT ENRICHMENT” include only outlines, but the suggestion of the importance of providing uniform terminology is encouraging.

6-1-10 This section gives a useful review of recent findings linking the cycling of S and Hg. This section also includes more references to the referred literature related to this topic

6-10-13 The section on NITROUS OXI DE provides additional information on this N gas and provides a clear indication of the importance of this gas including its linkage with N deposition and is important role as a “greenhouse” gas.

6-13-18 The synopsis on CARBON SEQUESTRATION provides a useful overview of important interacti ons between N deposition, warming and the carbon cycling in terrestria l ecosystems. This is a very large and important subject area. As suggested a detailed analyses is beyond the scope of this review . The term carbon sequestration does not really capture the tota l content of this section.

6-19-22 More emphasis in the descri ption of aquatic effects should be placed on changes in the phytoplankton community structure that

has been most noted in the western U.S.

7-1

7-15 In its current version this “Synthesis and Integration of Case Study Results” is highly descriptive. This will need to be improved with specific quantitative results that show a clear relationships to the

assessment.

8-1 8-30 Clearly providing a clear scient ific linkage that is policy relevant

between concentrations of SO

x and NO

x and resultant S and N deposition and subsequent translation to ecosystem level effects is a major challenge. Clearly there are good linkages between

concentrations of SO

x and NO

x and deposition, but the linkage to ecosystem level effects is more complicated due to inherent variability across the United States of the sensitivity of these systems to acidification, eutrophica tion and changes in biotic composition. It will be important to formulate an approach that takes into account these geographi cal patterns of sensitivity.

8-4-5 Figure 8.1-1 needs to indicate in some format that these ecological

79indicators may not be constant over the United States (e.g., N deposition levels with respect to changes biotic community structure being more sensitive in the Mountain west than the eastern U.S.). These issues are outline on lines 1-7, page 8-5.

8-5 22 The problem in not including reduced N chemical species in any

formulations associated with N deposition effects is highly problematic. I am not sure it is feasible to focus solely on NO

x .

8-9 There are major difficulties in setting national standards for SO

x and NO

x concentrations without taking into account regional

effects.

8-13 As suggested the development of these “functional forms” will be critical and may have both spatial as well as temporal components.

8-13 Clearly EPA is making heaving reliance on the CMAQ model suggesting the importance of va lidating results using other approaches and the linkages betw een gaseous concentrations and specific deposition levels.

8-14-17 The issues of deposition velo cities are not trivia l. For example look at the differences in depositi on associated with the estimates at the same site for CAPMoN and CASTNET. Although CAPMoN and CASTNET pr ovide similar concentrations of gases the deposition velocities are higher for CAPMoN verus

CASTNET.

8-23 The discussion of uncertainties needs to include the various issues associated with the calculation of deposition velocities.

Attachments

2, pg 2 5 Change “to reflect most recent conditions”.

2, pg 2 14-15 Not sure that there is a relationship between steepness and base cation leaching rates versus the role of slope in affecting the contact of drainage waters to soils and the relative contributions of ground waters to drainage with gr oundwaters generally being more

rich in base cations than waters derived from shallower soil

sources.

2, pg 3 30 Isn’t a threshold of 400 μ eq/L or less considered acid sensitive?

Would a threshold of 100 μ eq/L better? Also, note that the correct symbol for liter is “L” not “l”. Change for entire document.

802, pg. 5 Figure 3.2-1. Give a citati on for the Acid Sensitive Waters (USGS).

2, pg. 7 Why was there no selection of a threshold for sulfate deposition? Is this awaiting the determination of critical load? At a minimum the European critical load could be used.

2, pg 8 Same comment for total N and S deposition and the assignment of a value as that provided by sulfate.

2, pg. 9 The inclusion of high eleva tion could also be justified by other criteria such as the potential contribution of occult (fog) deposition. If occult deposition accounted for in the CMAQ

estimates. This also relates to rationale provided with respect topographic position (Attachment 2, page 17).

2, pg 9 25-28 This is confusing with respect S and N deposition since it was suggested above that no criteria for S and N deposition were defined. If these top quartiles are us ed the actual values need to be supplied that make up these quartiles . Also, the year or years from which these deposition data are derived needs to be given explicitly.

2,pg 10 14 Why “Total nitrogen (Kjeldahl)”. Do you mean total dissolved nitrogen or total dissolved Kjeldahl nitrogen. Why exclude nitrate

in surface waters?

2,pg 11 Although there are weak linkages between N deposition and N

solute concentrations in surface wa ters, it would be preferable to provide the data layer of actual N so lute concentrations in surface

waters.

2, pg12 18-19 Provide these nutrient con centrations available from the National

Nutrient Database. Provide a citatio n for this and the other data

bases.

2, pg 15 These N deposition data layers seem to be redundant from data layers previously described.

2, pg 16 More clearly delineate the difference between “content” and

concentration”. Content should be reserved for the total amount (mass, molar value) of a an element on a per unit area while concentration is the amount (mass, molar value) of an element per unit of mass (sometimes) expressed as %.

2,pg 18 The delineation of the locati on of acidophilic lichens appears to

81have a strong boundary based upon stat e borders especially notable

in Arizona and an absence in New Mexico.

3, pg 10 Here and elsewhere “ μ M” is not a correct abbreviation. The

abbreviation for mole is “mol”.

3, pg 12 Note that these ANC levels are lower than those suggested to be

considered to be of concern in Attachment 2.

3, pg 15 There have been other mode ls (e.g,. PnET-BGC) that have been applied particularly to the Adir ondacks to evaluate especially temporal patterns of acidificati on. Wouldn’t it be helpful to at least do some comparisons using other models besides MAGIC.

3, pg 18 8 Change to “SO 4 2- “.

3, pg 21 Clarify how the ratios of wet to dry deposition were derived.

3, pg 22 15 Are the total deposition valu es used in the MAGIC calculations different from deposition estimates used elsewhere in the entire

document?

3, pg 22 27-29 Some elaboration on how ASTRAP derived deposition would be helpful and how these estimates confirm or differ with the CMAQ

estimates.

3, pg 23-26 There is considerable discussion of the calibrati on of MAGIC in

this section. Some of this could be reduced and inclusion of other ways of comparing model output with other published results including other models (e.g. PnET-BGC) would provide additional perspectives of these results.

3, pg 29 Similar to previous comments, although the discussion and definition of the F-factor provide s background information this is not a novel approach, but rather one that could be cited. More emphasis of the validation and comparisons with actual measurements versus description of the model development would be more helpful.

3, pg 31 Figure 5.1-1. Trends in LTM monitored lakes in the Adirondacks of New York would be improved if specific lake classes were used. It is not clear from these figures how a general trend for the LTM

monitored lakes were obtained.

3, pg 32 Figure 5.1-2. The modeled va lues appear to be substantially

different that those of the measured values. Doesn’t this bring into

82question to validity of the predic tions for 2010? I don’t believe the results of this figure are disc ussed within the document.

3, pg 35 Clearly the document is incomplete at this stage.

4, pg 1-2 This seems repetitious of information provided in the main

document.

4, pg 5 “M” is not the correct SI abbreviation for mole. The correct

abbreviation is “mol”.

4, pg 4-9 Not sure that this much restating of what has previously been found about Al and Ca relationships is needed.

4, pg 11 Would it be more efficient to cross reference th e description of ecosystem services as provided in the main document?

4, pg 18-20 Are the details of the histor y of the Kane Forest needed in this

document?

4, pg 21-25 Similarly to the previous comment, are all these details about

Hubbard Brook needed for this document?

4, pg 26-47 This is difficult to follow due to the level of detail. Perhaps a more generalized format in which could be imbedded specific references

to the literature or the inclusion of appendices so that the major

theme of the discussion is not lost.

4, pg 50 Not sure of the importance of the inclusion of the section on “Implications for other systems” in this document.

4, pg 51-52 The uncertainties issues need to be better integrated into the overall

document.

4, pg 53 The “Conclusions” summarize the important issues and these issues should be the focal points of this entire section with a need

6, p 43 The figure on this page (Fi gures 5.1-1 5.1-2) appears to have an inappropriate numbers. Shouldn’ t they be 6.1-1 and 6.1-2?

83

### Mr. Richard Poirot

These comments pertain primarily to REA Chap ter 3 (Sources, Ambien t Concentrations, and Deposition), for which the following charge questions were provided.

Question 1 : To What Extent are the air quality characterizations and analyses presented in chapter 3 technically s ound, clearly communicated, approp riately characterized, and relevant to the secondary NAAQS for NOx and SOx?

Question 2 : Section 3.2.1 describes an approach fo r evaluating the spatial and temporal patterns for nitrogen and sulfur deposition and associated am bient concentrations in the case study locations. This draft document incl udes the analysis for the Adirondacks Case Study. Does the Panel agree with this approac h and should it be applied to the other Case- Study Areas?

Question 3 : Section 3.2.2 describes the relative c ontributions of ambient emissions of nitrogen and ammonia to nitrogen deposition for the case-study areas. To what extent is the approach taken technically sound, clearly communicated, and appropriately
characterized?

Assuming the many and important missing “placeholde r” sections are filled in, I think the air quality characterizations and analyses presente d in chapter 3 will provide a technically sound, clearly communicated, appropriate ly characterized, and relevant to the secondary NAAQS for NOx and SOx (although it still rema ins unclear to me what kind of 2ndary standards are being contemplated). Many of these placeholders re fer to evaluations of model performance, and since the majority of the chapter consists of pr esentation of intensively graphical model results, filling the placeholders will be ke y to providing confidence in the model results. The technical approach appears to be reasonable, but without a better sense of mode l performance (including both CMAQ and the RSM meta-model), the tec hnical soundness and rele vance to NAAQS can’t really be evaluated.

The presentation of the information is clear (eve n beautiful), but there is minimal discussion or interpretation of the graphical results, which make s it difficult to maintain interest in looking so many pictures. Conversely, it might be informativ e to poll the model results in ways that might provide a better understanding of relationships among the vari ous metrics of air quality, deposition and environmental effects. For exam ple: what would the maps look like that show the ratios of S deposition to S emissions; N (oxidized) deposition to N (oxidized) emissions; N (reduced) deposition to N (reduced) emissions. What would maps look like that show ratios of S (or N) deposition to ambient SO 2 (or NO 2 ) concentrations? What if modeled S emissions were

rolled back to show alternate lower maximum levels of SO 2 (and/or NO 2 ) – what would be the subsequent changes in S (and/or N) deposition in sensitive downwi nd areas? If sections of the Adirondacks were considered to be experienci ng adverse levels of aci difying deposition, how

could the models be used to determine the “s ignificant contributing area” – or perhaps some combination of emission size, and frequency upwind – such that a non-attainment area might be defined to better include the contributing emi ssions? A possible approach for an improved

84secondary SOx or NOx NAAQS might consider (muc h) lower levels but averaged over larger areas or longer averaging times.

With the caveat that the model performance needs to be more clearly examined and documented, I think the more detailed approach applied here for the Adirondack case study is reasonable, and could be applied to other case st udy areas. One possible concern – possibly more relevant to the Adirondacks than to most of the other case study ar eas – is whether the 12 km gridding might be coarse relative to the spatia l variability in deposition, terre strial & aquatic ecosystems and associated effects. Potentially the larger grid cells may fail to adequately capture orographic increases in precip volume & de position and the additional increas es from occult deposition at highest elevations (or in certain coastal areas) – in comparison with variations in sensitive terrestrial and aquatic bi ota within these grid cells . See for example: Miller, E.K. et al. 1993. Atmospheric deposition to forests along an el evational gradient at Whiteface Mountain, NY

USA. Atmos. Environ. 27A:2121-2136.

Possibly this influence of occasionally large terr ain, deposition and species variations within the relatively large grid cells could be evalua ted by conducting a higher resolution sensitivity analyses within selected grid cells in the Ad irondacks case study area. A lternatively, it might at least be possible to disaggregate the coarser modeled dry dep. estimates to combine with the higher resolution wet dep. estimates from the Gr imm & Lynch approach. Arguably the dry dep totals and variability may be le ss important than wet dep at more remote receptor locations. Possibly also a terrain-based cl oud deposition model could be adde d to provide added detail for higher elevations or in coastal areas.

85Regarding the soundness of the technical mode ling approach to estimate the relative

contributions of ambient emissions of oxidized a nd reduced nitrogen to nitrogen deposition for the case-study areas – the approach seems sound but again there is a need to evaluate the performance of the models (CMAQ + RSM). Tr ust but verify. This evaluation could/should extend where possible to subcomponents of the models such as emissions inputs and space/time patterns of modeled estimates of wet oxi dized N and wet reduced N deposition.

That being said, I do like the approach of dir ectly linking the estimates of changes in Nr deposition to changes in specific emission sources. I would think a similar approach could also

be taken to zero out and otherw ise reduce SOx emissions from di fferent source categories. Down the road, this may allow a bundling & compari ng of projected “optional” future emission controls (small, medium, large, etc.) to desired reductions in deposition in sensitive areas, in comparison to the associated concentrations in atmospheric NOx & SOx concentrations (in the event the layers say we have to stick with the traditional indicators). What new NAAQS limits of these indicators (perhaps averaged over larger - or much larger - areas than single monitors) would be necessary to achieve the desired reductions of Nr and/or S deposition in sensitive

areas?

In addition, if you were to add various levels of SOx (and NOx) emission reductions to your modeled scenarios, it would be a snap to calcula te and display the resulting changes in sulfate and nitrate aerosols (and in their visibility effects) that would result from any changes in S & N emissions or deposition or SO 2 & NO 2 concentrations. This woul d allow you to (a) consider a more complete set of welfare benefits that would result from any revised NAAQS based on deposition effects and/or (b) might lead to and he lp justify alternative am bient air indicators – for example the sum of total atmospheric oxidized S and N compounds (sum in ug/m3 of S from SO2 and pSO4 and N from NO, NO2, HNO3, and pNO3 or somesuch) – that might not be considered if only deposition-related effects are considered, but which might, set at the right levels, result in large deposition-related benefits.

Other Minor Comments:

p. 3-1 lines 16-23: This is a good example of what seems like an intentional sense of vagueness regarding which pollutants and secondary transformation products ar e or are not the subject of this review, and/or available as potential indicators for secondary NAAQS. Why are nitric acid and PNO3 considered part of “NOx”, while SOx includes only gaseous SO 2 ?

p. 3-4, Figure 3.1-3: This figure just doesn’t look right – and seems inconsistent with the reduced nitrogen deposition map in Figure 3.1-8 on p. 3-11.

p. 3-4, lines 3-5: Does confined feeding really increase animal wa stes, or does it just increase atmospheric emissions from them?

p. 3-4, line 12: Figure 3.1-4 does not show annual 2002 SO 2 emissions “by state”.

p. 3-5, line 4: I would change “Industrial” to “Anthropogenic”.

86p. 3-5, lines 10-15: Should marine DMS emissions be mentioned here?

p. 3-6, lines 14-16: Can you provi de any quantitative indication of how large these fire SO 2 emission underestimates are?

p. 3-8, lines 5-7: Does this increased depositio n of reduced nitrogen also pertain over the 100-year period of the preceding sentence. Can you say something more precise about trends over the past several decades?

p. 3-12, lines 10-14: This description relates to how NADP interpolates its wet deposition data. However, later you indicate us ing the precip-volume-enhanced estimates from Grimm & Lynch (2004). So which was it? One general concern is that the 12 km gri dding may overly smooth some of the more extreme orographic increases in precip – and you seem to exclude cloud water deposition. Possibly this could be handled by conducting some sensitivity analyses for grid cells containing higher elevation terrain – especially for the Adirondack and Shenandoah case

studies.

p. 3-16, line 11: Why not also describe CASTNet (& AIRMoN dry) data for HNO 3 , NO 3 , NH 4 , SO 4 ?

p. 3-23, lines 4&5 and lines 11&12: sa y roughly the same thing twice.

p. 3-23, line 7: “(25% wet vs . 6% dry)” and 69% what?

p. 3-23, line 12: Change “does” to “do”.

p. 3-54, line 17: You could add “current and hi storical” before “atmospheric deposition”.

p. 3-55, lines 20-21: Can you provide any indica tion of if and how well the RSM technique (and for that matter the underlying CMAQ model) works for all the SOx, NOx and reduced N species you will use it for?

p. 3-57, line 5: Am I missing something or di d you only use a couple (z ero-outs) of these 210

control runs? So what was th e purpose of the other runs?

p. 3-71, line 8: Delete one “deposition” in “great er deposition of oxidized nitrogen deposition”.

p. 3-71, lines 8-15: I would think formation of aerosol NH 4 NO 3 would tend to increase the transport distance, but would not lead to any net decrease or increase in Nr deposition. It all gets deposited eventually. An exception might be if aerosols persist long enough to transport out of the (US or North American) domain.

p. 3-73: I must have blinked somewhere, because I didn’t expect to see this large, international “sugar maple case study” area discussed previously. Its not listed as a “Case Study Location” in

87Table 2.1-1 on page 2-2&3. It reminds me to ask for a clearer “up-front” description (& map) of all the intended case study areas.

88

### Mr. David Shaw

General Comments

Thank you for addressing the outcome of this RE A. I believe that this makes the document

more focused.

I still feel that a specific goal of this assessment should be to identify and report sensitive areas which do not have adequate monitoring. Adopting th is longer view in this analysis will enable the next review process to start from a stronge r point. In identifying areas without adequate monitoring data, we may be able to start the process of getting a stronger data reco rd of results for future analysis. It is my hope that this will lead to better mode ling due to better data.

While there are certainly areas that are deficient in monitoring data , there definitely are areas of strong monitoring data with analysis. I still feel that the areas of certa inty do not receive equal treatment as uncertainty. I feel we must be clear that we do understand causes, effects and variability in our ecosystem response.

On this note, the analyses presented in Chapte r 3 of the REA rely heavily on modeling and don’t always reinforce where the measurements are the strongest. It is important to emphasize where we have the most confidence (e.g. wet deposition, ANC measurements in case study areas) and the least confidence (e.g. air concentrati ons and dry deposition of NOx/SOx, where measurements are lacking). Much of the info rmation on dry deposition will come from CMAQ,

and the measured data from CASTNet and other special studies could be used to assess the

model at selected locations.



### Charge Questions

Scope of the Review Question 1

Chapters 1 and 2 provide the background, hist ory, and the framework for this review, including a discussion of our focus on the four key ecological effect areas (aquatic acidification, terrestrial acidification, aquatic nutrient enrichment, terrestrial nutrient enrichment). Is this review appr opriately focused in terms of th e targeted areas and in terms of characterizing the important atmospheri c and ecologic variables that influence the deposition and, ultimately, the ecologic impacts of nitrogen and sulfur? Does the Panel have any further suggested refi nements at this time?

Pages 1- 1 to 1-10: I feel that this gives good overall information on the Rational, Background and History. It might also be a good place to address other pollutants associated with NO

x and SO

x analyzing the whole set of problems associ ated with these pollutants.

89Page 1-8 lines 3-5: Lines 3-5 state that ‘in spite of the complexiti es and uncertainties....’ it became clear that a program to address acid rain was needed. In actuality, it was the eviden ce of a preponderance of

the scientific data of the NAPAP effort which made it clear that an acid rain program was

needed. This builds on one of my general comments regarding an emphasis on uncertainty rather than giving equal treatment to those areas where certainty exists.

Page 1-16: I would recommend adding a discussion on critical lo ads as the organizing principle of this RAE assessment. Include the current understanding of ecological indicators an d how levels of the proposed standard will be integrated.

Page 1-20: It would be helpful to explain how the existing monitoring data wi ll be used to evaluate the success of the proposed standard? How and when will the existing monitoring networks be evaluated for adequacy of measuring ecosystem response?

Page 2-10: I appreciate the effort in addi ng sulfur and mercury methylatio n. The fact that it will be addressed will make this a stronger analysis.

Page 2-11, Table 2.3-1:

I feel that it would be benefici al to add to Cultural Services “c hemical and biological degradation of Constitutionally (federal and states) protect ed Wilderness areas”. This would apply to several if not all Targeted Effect Areas. The point being that the ADK case study area, for example, represents a 6 million acre region, 43% of which is protected by the NYS Constitution

as ‘forever wild’ Forest Pres erve. Here, tree cutting is not allowed, yet atmospheric deposition damages forests and diminishes a quatic ecosystems within these forests. The remaining 57% is devoted principally to forestry, agriculture, a nd open-space recreation, a portion of which is sensitive to negative effects of atmospheric deposition. This landscape holds an additional cultural value to New Yorkers especially, and to others from the US and around the world.

Pg 2-12: In the box where “provisioning services” and “c ultural services” for Sulfur and Mercury Methylation are provided, fish kills is listed as an ecological impact. From the literature that I am familiar with, fish kills or declines in fi sh populations are not a good indicator of MeHg, however, declines in the success of species highe r in the food web such as loons and humans occur because of MeHg neuron toxic effects and bio accumulation.

Air Quality Analysis Question 1

To what extent are the air quality characteri zations and analyses presented in Chapter 3 technically sound, clearly communicated, appropri ately characterized, and relevant to the review of the secondary NAAQS for NO

x and SO

x ?

90Sections 3.1.4 and 3.2: It seems as if the dataset discussion (Section 3.2) would be more beneficial if it appeared before the composite deposition maps (Section 3.1.4). These composite maps consist of modeled dry and measured/interpolated wet deposition. For these maps, are the units actually kg ha -1 y -1 , or are they kg N ha -1 y -1 and kg S ha -1 y -1 ? Some mention should be made that the dry deposition estimates are generally consistent with whatev er measurements (e.g. CA STNet) are available, that one year of modeling is adequate to capture the seasonal/spatial variability in the predictions (i.e. this is not an atypical year), and that ot her photochemical models are capable of estimating dry deposition and could be used to perform such an analysis.

Section 3.2.1.2: I am interested to know why SO 2 and NO 2 from SLAMS/NAMS monitors are not included in the measured database? While there may not be many NO 2 monitors in rura l areas, there should

still be some measurements of SO 2 in the case study areas.

Page 3-21 ADK case study area: There are several questions regarding the selection of this study that would be of interest to note

in the REA: How were the 44 lakes and ponds selected?

How was the subset of 15 lake sites selected fo r geographic variation in deposition assessment? How representative are these sites of the whole region?

Is there an elevational stratification? Are any of the intensive study sites part of th e current Adirondack m onitoring programs (e.g., ALTM, TIME, AEAP)? Have any or will any of the model results be co mpared with existing long term monitoring data?

Some important facts to point out regarding this region is that 22% of it is above 600 m were the sensitive spruce fir forest community become s dominant. Further up above 900 m are key signature mountain peak ecosyst ems containing over 100,000 acres. Monitors are not measuring any deposition data above 610 m in NYS, with the exception of the top of Whiteface Mountain.

Pages 3-35 through 3-37, and 3-50 through 3-53: It may not be necessary to include the additiona l information on a monthly basis. The form of the annual NAAQS looks to be seasonal or annual , so presenting deposition on a seasonal basis seems to be adequate to capture the variation over the course of a year.

Figures 3.2-29 through 3.2-44: I would recommend that the metrics for these figures are clearly stated. Also, it would be helpful to confirm that the “whiskers” are th e minimum and maximum and that the boxes are

25 th /75 th percentiles.

Figures 3.2-45 onward: It might help the reader to reve rse the color scheme, that is display the smallest impacts in green and the largest impacts in red.

91

### Misc.

In the introduction there are many references to “...noted below in Section 1.x....” I would recommend removing the word “below ” in each of these references.

Page 1-3 line 19, “Chapter 2” should be

92

### Dr. Kathleen C.Weathers

Overarching comments on Chapters 7 and 8 :

First, I think that the case study approach is us eful and appropriate for this analysis. Next, Chapter 8 provides some interesting ideas to ponder. Finally, the incompleteness of this document makes it difficult to provide much in the way of pithy comments. In addition, there’s much editing that will need to be done on these chapters.

Case Studies: As we discussed during the first meeting of the Panel, the choice of case studies is critical. My biggest concern about the case studies identified in this draft is whether they are representative enough. That the th ere is sufficient data and info rmation for a case study is, of course, a major criterion. Further, their use shou ld be supported and justified in regard to the suite of impacts of air pollution they illustrate wi th regard to direct and indirect effects of atmospheric N and S. I question the use of th e Chesapeake Bay/Pamlico Sound in this regard, mainly because atmospheric N deposition to the re gion is not a large proportion of N inputs to the ecosystem. Thus, unless it is used as a c ontrasting example of a system in which the atmospheric deposition of N is not a major compone nt of N loading (I note that this contrast could have utility), the Chesapeake Bay/Pamlico Sound regions may not be the most illustrative case study to use. I do think that, if feasib le, evaluating deposition impacts on a coastal ecosystem(s) would be instructive.

I mentioned in my last review that I thought Da y-Cent-Chem should be cons idered as a potential model to be used for these case study analyses. It has some advantages over Magic, and some parallels with other biogeochemical models (PNET-BGC, for example).

Would it be possible to consid er in some creative way a “cas e study” that summarizes and synthesizes experimental manipulations of N and S inputs (e.g., Harvard Forest, Catskill Mountains, NY, Bear Brook, ME, Mt Ascutney)?

Conceptual pieces: I agree with using a “weight-of-eviden ce” approach, which I interpret to mean that assessing effects using a suite of different tools (modeling, experiments, theory, long-term monitoring) can be used to provide th e most robust syntheses. The IPCC has used this approach successfully.

As the authors of this document are no doubt we ll aware, ecosystems are affected by the amount (and sometimes concentration) of a pollutant or nutrient that is actually makes its way to the ecosystem — i.e., that is deposited. Working backwa rds from that fact sugge sts that what will be necessary is a set of standards that consider ac tual loading — deposition — to ecosystems, rather than atmospheric concentration-ba sed standards that identify the ro le of “modifying factors.” The devil’s in the details of Figure 8.1-1! As research has demonstrat ed, for some chemical species, there may be little connection between emissions and total deposition downwind, much less all of the biologic and geochemical transformations that happen from deposition to terrestrial processing to surface water effects (or not).

93As noted in this REA, lining up th e spatial and temporal scales of analysis and output are critical issues, for example, high temporal resolution (a ir concentrations and deposition on an hourly basis, for example) but low spatial resolution (acr oss the country) may be exactly the opposite of what would be most useful for assessing ecosystem effects.

The likelihood that current ra tes of deposition will show i mmediate effects on downstream ecosystems for nutrients such as N is quite low. Rather, capturing the longer-term average loads and patterns of deposition is likely to be more relevant.

The derivation of deposition metrics and transfor mation functions were at once described in great detail and in not enough detail. Seeing the fore st for the trees will be very important. See comments about a deposition standard, above.

General comments on Chapters 7 and 8:

Note that I have not offered detailed editorial comments for this review.

I’m not sure that I agree (page 7-2, lines 15-16) with the statement that it is the increase in sulfur and nitrogen content of soils that is the sole reason for alteration of major biogeochemical processes. Also, just below, missing from the desc ription of acidic deposi tion’s effects on aquatic system are the properties of th e adjacent terrestrial watershed, including hydrologic pathways. And, at the end of this paragr aph, the reasons why the results from the case studies for the Adirondacks and Blue Ridge Mountains might be app licable to the rest of the Appalachians and

the Northeast should be identified.

There appears to be some confusion about terrestri al acidification, or at least the beginning of the terrestrial acidification should be rewritten for completene ss (i.e., natural and anthropogenic acidification occur in soils), accuracy, and clarity.

I appreciate the importance of the statements on pages 8-12, lines 9-13 in regard to a national

transformation function with local modifying factors within it. This is very important given the importance of landscape (in its broade st sense) in influencing inputs.

I note the absence of cloud or fog deposition in Section 8.3.2.1. I s uggest mentioning in the text that it will not be included directly here. This vector can be critically important, but only in

coastal and mountai nous ecosystems.

Surely the intention in the Catchment parameter section is to use GIS databases (not actual topographic maps)?

Be sure to label figures clearly as well as be clear when discussi ng total (wet + dry? or Nr, or?) deposition. Note annual or s easonal as well in the text.

Organic nitrogen, in regard to both its atmos pheric input (less known) and output (more known)

via surface waters should be at least mentioned as part of the N effects picture. While it is not directly part of NOx/SOx emissi ons, it is nonetheless important and it is becoming especially relevant in regard to climate change.

9495 Such terms as ecosystem services, and ecosystem health, should be explic itly, consistently, and clearly defined among and within these NAAQS review documents.