UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD August 28, 2009

EPA-CASAC-09-013

The Honorable Lisa P. Jackson

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

Subject: Peer Review of EPA’s Risk and Exposure Assessment to Support the Review of the Secondary National Ambient Ai r Quality Standard (NAAQS) for Oxides of Nitrogen and Sulfur: Second Draft

Dear Administrator Jackson:

The Clean Air Scientific Advisory Committee (CASAC) NO

x & SO

x Secondary NAAQS Review Panel met on July 22-23, 2009 to review EPA’s Risk and Exposure Assessment (REA) to Support the Review of the Secondary National Am bient Air Quality Standard for Oxides of Nitrogen and Sulfur: Second Draft . This letter has been review ed and approved by the chartered CASAC at a public conference call on August 20, 2009. In this letter, CASAC offers general comments and recommendations for finalizing the REA. We also address the Agency’s framework for developing the forthcoming Po licy Assessment. During the meeting, EPA’s Office of Air Quality Planning and Standards (OAQ PS) informed the Panel of the final schedule for the current primary and secondary NO

x and SO

x NAAQS reviews and rulemaking. CASAC is very concerned about the sc hedule’s implications on the po licy options under consideration by the Agency for the secondary standards.

EPA staff informed the Panel that there is insufficient time to meet its court-ordered deadlines and complete the level of analysis needed to sufficiently formulate and justify recommendations for a secondary NAAQS for NO

x and SO

x . EPA will likely propose one of three alternatives for rule-making:

1. Retain the current secondary standards;

2. Revise the current NO 2 secondary standard to make it identical to the primary and retain the current secondary standard for SO 2 ; or 3. Revoke the current secondary standards for NO 2 and SO 2

. None of these options represen t a NAAQS(s) with the appropriat e indicators, ambient levels, forms, and averaging times to address secondar y, welfare effects. Th e Integrated Science Assessment (ISA) and the REA both provide ampl e evidence that deposition of oxidized forms

1of sulfur (SO

x ) and nitrogen (NO

x ), along with chemically reduced (NH

x ) and volatile organic forms (RH

x ) of reactive nitrogen (Nr) adversely impact sensitive ecosystems at current ambient atmospheric concentrations. All three of the pro posed options leave at ri sk sensitive aquatic and terrestrial ecosystems in ma ny parts of the United States.

Previous CASAC panels and National Rese arch Council Reports have called upon EPA to do exactly what is being attempted in the current NO

x and SO

x reviews: develop standards that appropriately integrate across pol lutants and outcomes. The Pane l recognizes the complexities involved in developing the information needed to support an ecologi cally relevant, multipollutant standard(s). Given that CASAC has no purview to grant the Agency more time, we recommend the Agency complete the current reviews for NO

x and SO

x to fulfill its statutory and legal obligations, and simultaneously expedite th e analyses to support ec ologically appropriate welfare standards. The Panel supports a fast -track development of an alternative Policy Assessment (and the associated rulemaking). Bu ilding upon the ISA and REA completed in the current review, EPA should complete the expedited analyses in less than two years.

With regard to the review of the second draft REA, the Panel found it greatly improved over the prior version and res ponsive to CASAC’s advice. EPA staff is commended for providing the information essential in developmen t of a set of secondary standards to address multiple ecosystem outcomes resulting from the e xposure to multiple pollutants, some of which are not criteria pollutants. Th e Panel considers the following issues critical to finalizing the

REA:

• The Executive Summary (ES) is still not a comprehensive summary of the REA. The Panel maintains that the ES is a very important part of the REA. In its current form, however, it does not fully capture the conclusi ons and findings presented in the REA.

• The synthesis of case studies in Chapter 7 is inadequate. The chapter provides a summary of the case studies, but does not fully synthesize th eir results. Nor does Chapter 7 provide the type of contextu al information that is needed to extend these results to

broader national scales.

• The treatment of uncertainty in the current draft REA should be improved to strengthen the analysis in this review. The applicati on of the various steady state, dynamic, and statistical air quality and ecosystem process models is the foundation of the REA. The

Panel recommends the addition of a model performance evaluation to describe the strengths and limitations of the various models used, especially with respect to spatial and temporal predictions, and how the models can be effectively used to inform the decisionmakers about the time needed for ecosystem recovery. A table summarizing model characteristics and capabilities would be especially useful in the ES.

• The Panel would also like the REA to acknow ledge the potential be nefits of reactive nitrogen deposition on nitrogen deficient ecosystems.

2The CASAC and Panel membership is listed in Enclosure A. The Panel’s consensus responses to the Agency’s charge questions are presented in Encl osure B. Individual review comments from the Panel are compiled in Enclos ure C. We look forward to the Agency’s response and the opportunity to provide a dvice on EPA’s Policy Assessment document.

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

Enclosures

3Enclosure A

Rosters of the NO

x & SO

x Secondary Review Panel and CASAC



### U.S. Environmental Protection Agency

CASAC NO

x 

### & SO

x 

### Secondary Review Panel

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

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. 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. Charles T. Driscoll, Jr. , Professor, Department of Civ il and Environmental Engineering, College of Engineering and Computer Scie nce, Syracuse University, Syracuse, NY

Dr. H. Christopher Frey , Professor, Department of Civ il, Construction and Environmental Engineering, College of Engineering, No rth Carolina State University, Raleigh, NC

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

Dr. Rudolf Husar , Professor, Mechanical Engineeri ng, Engineering and Applied Science, Washington University, St. Louis, MO

Dr Dale Johnson , Professor, Nat. Res. Env. Sci., Co llege of Agriculture, Biotechnology, and Natural Resources, University of Nevada, Reno, 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

4Dr. Myron Mitchell , Distinguished Professor and Direct or of Council on Hydrologic Systems Science, College of Environmental Science a nd Forestry, State University of New York, Syracuse, NY

Mr. 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 Resour ces, Department of Environmental Conservation - New York State, New York State, Albany, NY, United States of America

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

SCIENCE ADVISORY BOARD STAFF Ms. Kyndall Barry , Designated Federal Officer

5

### U.S. Environmental Protection Agency

Clean Air Scientific Advi sory Committee (CASAC)

CHAIR

Dr. Jonathan M. Samet , Professor and Flora L. Thornton 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, No rth Carolina State University, Raleigh, NC

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

6NOTICE

This report has been written as part of the activ ities of the EPA’s Clean Air Scientific Advisory Committee (CASAC), a federal advisory committee independently chartered to provide extramural

scientific information and advice to the Administrator and other officials of the EPA. CASAC provides balanced, expert assessment of scientific matters related to issues and problems facing the Agency. This report has not been reviewed for approval by the Agency and, hence, the contents of this report do not necessarily represent the views and policies of the EPA, nor of other agencies within the Executive Branch of the federal government. In addition, any mention of trade names of commercial products does not constitute a recommendation for use. CASAC reports are posted on the EPA website at http://www.epa.gov/CASAC.

7Enclosure B

CASAC Panel’s Consensus Response s to EPA’s Charge Questions

Executive Summary:

1. In response to the Panel’s review of the first draft Risk and Exposure Assessment, we have included an executive summary of this document. Does the Executive Summary adequately summarize and characterize the key i ssues driving this review as well as the important findings of the analyses? Does the Panel have any suggestions for clarification or refinement of the Executive Summary?

The Panel is pleased to see an Executive Summar y (ES) in this draft of the REA, which was

recommended in the Panel’s review of the firs t draft. However, the ES is still not a comprehensive summary of the REA because it fails to capture the major findings and conclusions presented in Chapters 3 – 7. One way to highlight th e important results of the REA would be to replace the current “Conclusions” section with one entitled “Key Findings”, similarto the format of the ES in the ISA. In both the ES and Chapter 1 a number of important policyrelevant questions are listed. It should be expl ained in the ES that these questions are not answered in the REA; rather they set the stag e for their discussion in the forthcoming policy assessment document. Also, the list of policy-releva nt questions in the ES is not consistent with the list in Chapter 1. It would be helpful if the sequence of que stions followed the logical layout of Fig. ES-2.

The introduction to the ES should explain why th e review focuses on the ecological effects of

NO

x /SO

x deposition, but takes a limited view of other potential welfare effects such as foliar injury from gaseous phases of NO

x /SO

x and other effects of deposition such as injury to materials. An explanation of th e selection of the case studies is also missing from the ES. The reader is left to ponder if the justification is based on data availability, representativeness, sensitivity, or some combination of these crite ria. The ES should provide a sense of what percentage of the US exhibit similar problems as represented in each of the four categories of the ecological effects. The treatment of reduced forms of nitrogen (NH

x ) is much improved in this second draft. However, the regi onal nature of ammonia and NH

x needs to be clearly acknowledged in the ES and throughout the REA. One way to illustrate the regional nature of nitrogen deposition would be to supplement Fig. ES-7 with two new figures, one for NH

x and the

other for oxidized N.

The key data gaps should be identified in th e ES, along with EPA’s intention/recommendations to fill those data gaps. The Panel was pleased with the inclusion of an explanation of the concept of ecosystem services and how this concept may ultimately help to quantify adverse effects on public welfare. However, if specific examples su ch as recreation usage are included in the ES, these must be tied, at least qual itatively, to the effects of depos ition on the quality and abundance of these ecosystem services. The Panel maintains th at the ES is a very im portant part of the REA and, in its current form, does not fully capture the conclusions and findi ngs presented in the

REA.

8Air Quality Analyses (Chapter 3):

1. This chapter describes an approach for characterizing the spatial and temporal patterns of nitrogen and sulfur deposition in the case study locations including both oxidized and reduced nitrogen, and both wet and dry deposition of oxidized nitrogen, reduced nitrogen, and sulfur. Ar e the uncertainties associat ed with these analyses appropriately identified and described?

The Panel was encouraged to see that the Chapte r 3 characterization of emissions, air quality and deposition information was a substantial improveme nt over the previous draft, especially in combination with the Appendix 1 performan ce evaluation of the CMAQ model that is prominently employed in the air quality and deposition estimates. The detailed map presentations of the various emissions, air qual ity and deposition patterns are informative and directly responsive to prior CASAC requests.

A relatively complete “listing” of uncertainties associated with the air quality-related characteristics is provided in section 3.5. Howeve r, the discussion is minimal and the absence of any quantitative estimates of uncertainty substant ially limits the usefulness of this section. The Panel recommends that some quantitative estimates of uncertainty be provided here, even if these are not intended to be comprehensive. For example, the (informative, but graphic-only) comparison of various model and measurement-based sulfur deposition estimates for the Adirondack case study area could be enhanced by scatter plots which show quantitative differences among the estimates. Some of the CMAQ model performance metrics from Appendix 1 might also be summarized in Chapter 3, along with a comparison of results from CMAQv4.6 vs. CMAQv4.7. At a mini mum, some indication should be provided of the relative uncertainties of the different air quality and de position estimates, which are presumably greater for dry than for wet deposition and greater for NH

x than for SO

x . For example, EPA has done some work on quantifying uncerta inties in ammonia emissions th at could be included here.

2. In response to CASAC’s recommendation, th e RSM analysis presented in the first draft Risk and Exposure Assessment was repl aced by an analysis of results from a new series of CMAQ simulations designed to explore the relative contributions of

NO

x and NH 3 emissions to total, reduced and oxidized nitrogen deposition and the relative contribution of SO 2 emissions to sulfur deposition. Does this approach enable us to adequately examine the contribution of NO

x to total nitrogen deposition?

It would also be informative to see a number of “ratio” or “difference” maps. For example, maps showing the ratios of wet, dry and total sulfur deposition to SO 2 concentration and to SO 2 emissions, and ratios of wet, dry and total N, and oxidized N deposition to NO 2 concentrations

and to NO

x emissions would be informative. Ratio or difference maps would also be an informative way to present additional details on CMAQ model performance. For example, what

is the ratio of or differen ce between CMAQ modeled wet S (or N) deposition and measured (interpolated NADP) wet S (or N) deposition?

Some explanation should also be given for why potentially important contributions to NO

x emissions from lightning and soils and from increased S and N deposition from cloud water at

9higher elevations were excluded fr om the analyses. The Panel feels there is merit to include some discussion of the potential importan ce of the effects from these sources.

3. The CMAQ application and model performan ce evaluation is presented in Appendix 3-1, as recommended by the Panel. Is this ana lysis sufficient to support the use of the

model in this review?

The evaluation of CMAQ model performance in Appendix 1 is a substantial improvement over the previous draft, and provides added confiden ce in some of the deposition estimates, their inter-annual variability a nd their uncertainties. However, th e Panel recommends that additional model performance metrics be shown to fully as sess the model performance to gain confidence in applicability of CMAQ for this assessment. These metrics should include model performance statistics (and plots) for daily or weekly averaged quantities (based on available data), mean normalized bias (and error) instead of normalized mean bias, and model performance for specific regions rather than the whole c ountry. It would also be useful if model performance for NO

x is

also included whatever such data are available. There should also be mo re discussion of what level of model performance is c onsidered "acceptable", as there were many results for which the model performance were not particularly compelling.

Case Study Analyses (Chapters 4 & 5):

Questions related to the indi vidual case study analyses are presented below. Overarching questions across all the case studies include:

1. Are uncertainties appropriately characte rized across the case studies? Is there adequate information to allow us to weigh the relative strengths of each case study to inform the standard setting process?

The discussion of uncertainty was generally well pres ented in a qualitative sense, but needs to be made more quantitative wherever po ssible. In particular, it would be useful to convey a sense of the relative importance of the vari ous sources of uncertainty and ar ticulate which are critical for policy assessment. This should include a disc ussion across the various links in the proposed structure of the standard (Fig. ES -2 and throughout); i.e., consider the impacts of uncertainty in CMAQ inputs and outputs on deposition, and the subsequent impacts of deposition estimates on ANC, and then the impact on critical loads. It is difficult to assess the importance of this uncertainty due to inherent prob lems in extrapolation from the case studies to other ecosystems or across larger regions. Some of this uncertain ty is related to the case studies because they do not represent the full spectrum of effects associ ated with the depositi on of sulfur and total reactive nitrogen.

2. In using the Risk and Exposure Assessment to inform the policy a ssessment, we plan to focus on aquatic acidification as the basis for an alternative multi-pollutant secondary

standard as this is the area where we have the most confidence in our ability to characterize adverse effects. Does the Panel agree with this approach?

10The Panel agrees with the focus on aquatic acidi fication, based on the quantity and quality of data available, but strongly recommends that EPA continue to consider multiple indicators and find a way to truly integrate multiple indicators into a standard. Multiple indicators will expand the geographic relevance and scope of the standard and afford protection to a maximum number of sensitive ecosystems. Moreover

, recent findings suggest that th e recovery of soils from acidification may take an extended period, which ove r the long-term will also affect the rate of recovery of aquatic ecosystem s.

Chapters 4 and 5 should also include an overvie w of the tools and models used in the case studies and present a justificati on of EPA’s choices, in particul ar with respect to the use of

SPARROW and the choice of BC/Al ratios rather than the more commonly used Ca/Al ratios. An additional case study or at least a discussion of a nitrogen-deficient site is needed in order to avoid potential bias in extrapolating from only sensitive sites. Additional discussion on aquaticterrestrial linkages would be help ful, as well as explicit information on the relationship between deposition and ANC.

Acidification:

The CASAC is generally pleased with the effort to evaluate the effects of acidification on aquatic and terrestrial ecosystems. However, this chapter needs considerable editorial work including the use of proper terminology, reduc tion of duplication and improvement in the clarity of the text and figures. A more accurate use of concep ts is needed and terminology should include descriptions related to ANC and buffering. The “cri tical loads” concept is important, but the text needs to clarify its utilization both in published literature and its adaptation in the REA. Averages and steady-state calculations are used in various ways including the application of critical loads and determining the effects of ANC. The advantages and limitations of using averages and steady state calculations need to be provided. In the REA, the effects of sulfur and nitrogen deposition needs furthe r description to delineate the relative importance of natural acidification and internal ecosystem processes in affecting the temporal and spatial patterns of

acidification.

1. Section 4.2 and Appendix 4 describe the analyses used to evaluate th e effect of aquatic acidification. The analysis eva luates the ANC in selected lakes and streams in the Adirondacks and Shenandoah relative to three potential ANC cutoff levels (20, 50, and 100 μeq/L) to determine the impact of current l evels of deposition in these area s as well as a larger assessment area. Are these data adequate to establish critic al loads of deposition for the case study area?

The use of ANC to evaluate the impacts of curr ent levels of deposition is appropriate. The emphasis on using the results from aquatic ecosy stems for analysis and model predictions on acidification is appropriate ba sed upon available historical and temporal data sets. The implementation and uses of models (e.g., CMAQ, MAGIC, SSWC) are integral to this chapter and the focus of the REA in ascertaining the effect s of acidification. The analysis of uncertainty within models focuses mostly on variation in pa rameter estimates and how this variation affects model output. Further discu ssion on why specific models were selected and the implicit limitations (e.g., processes not covered, repres entation of internal elemental cycling, appropriateness of spatial and temporal scales, et c.), as well as the strengths of the various

11models would help the reader ev aluate the appropriateness of m odel results and applicability for predicting acidification temporal a nd spatial patterns of acidification.

2. The ecological effect func tion for aquatic acidification (section 4.2.7) attempts to characterize the relationship between deposition and ANC. In order to estimate the amount of NOx and SOx deposition that will maintain an ANC level above a given limit requires the knowledge of the average catchment flux of bas e cation from weathering of soils and bedrock (i.e., preindustrial cation flux (B C0)). How might we generalize fr om location specific inputs (Ffactor approach) to using this approach on a broader scale - watershed, regionally, or some other way - to generalize bey ond individual locations? What ot her methods should be examined for estimating catchment weathering ra tes nationwide for surface acidity?

This is a challenging question a nd a difficult but critical problem. More attention is needed on the contribution of weathering rates – especially the release of base cations from soil primary minerals in affecting the recovery of terrestria l and aquatic ecosystems from acidification. The determination of base cation supply rates is critical to predict the effects of sulfur and nitrogen deposition on rates of acidifica tion and possible recovery from aci dification. Unfortunately there are no effective ways to estimate base cation weat hering rates over large regions. Clarification is

also needed on the utilization of the Bc (sum of base cations)/Al versus the more commonly used Ca/Al ratio in evaluating effects of soil acidity. Al so, discussion is needed as to how the F-factor is applied in predicting the spat ial and temporal patterns of ba se cation supplies and resultant effects on acidity.

It is vital to separate the capacity effects from in tensity effects in assessing sensitivity to aquatic and terrestrial ecosystems to aci dification and the potential rec overy from acidification. An acidic soil is a necessary but not sufficient condi tion for the acidification of waters – a second requirement for acidification of wa ters is the introduction of mob ile strong acid anions, such as sulfate and nitrate. Soils that are already na turally acidic will produce acidic waters nearly instantaneously with the introdu ction of mobile strong acid ani ons, and conversely, acidic waters

in these cases will recover almost instantaneous ly when such mobile strong acid anions are removed. On the other hand, acidification of a so il that was not historically acidic is not so easily reversed.

In the consideration of impacts on ecosystem se rvices, acidification effects are placed in a broader context. The section on ecosystem serv ices is a good summary of helpful information related to ecosystem services and acidification issues . It is useful that the REA explicitly states some of the issues in estimating directly how eco system services are affected by terrestrial and aquatic acidification.

3. Section 4.3 and Appendix Y describe the analyses used to evaluate the effect of terrestrial acidification. This analysis uses the Simple Mass Balance Model to de termine the impact of current deposition levels on Bc/Al levels relati ve to three potential Bc /Al cutoff levels (0.6, 1.2, and 10.0) for sugar maple in the Kane Expe rimental Forest and red spruce in the Hubbard Brook Experimental Forest and a la rger assessment area based on the FIA database for 17 states. Is this approach adequate to develop critical l oads of deposition for the broader terrestrial acidific ation case study area? Is th e regression analysis between

12Bc/Al ratios and tree health sufficiently described and are unc ertainties adequately
characterized?

The extrapolation of the critical load calculations for sugar maple and red spruce to other regions (e.g., different states) beyond those of the case st udies helps place these results in a broader geographical context. It is not clear, however, whether the approach will be adequate for predicting effects in all sensitive areas. It is a surprising result that su ch a high percentage of sites have been compromised by acidifying total nitrogen and sulfur de position in 2002 (page 4- 62). The limitations of the USA FIA data in analyzing critical load s to high and medium

elevation forests in the northeaste rn US needs further evaluation.

In this section there is some use of the use of average critical loads rela ted to three levels of protection. It is not cl ear if this “average” is meaningful in the context of critical load determinations due to critical loads being depe ndent on the specific edaphic features of each area. Does the average critical load take into account the spatial distri bution of specific edaphic features? Does this “average” ap ply to specific case study areas or to larger regions? The discussion and analyses that show how specific factors, includ ing parent material and soil properties, affect critical load calculations need to be devel oped further due to the importance of these factors in affecting acidi fication of both terrestrial a nd aquatic ecosystems. How does variation in these edaphic fact ors both within and among regions affect the uncertainties in

critical load calculations?

Nutrient Enrichment:

The title of the chapter was a point of disc ussion amongst the Panel. Some found “Nutrient Excess” to be a more accurate because nutrient enrichment commonly occurs but does not necessarily result in an envir onmental problem unless the ecosystem is not able to fully assimilate nitrogen inputs. Further background in formation should be provided on nitrogen as a limiting nutrient in terrestrial, freshwater aqua tic and coastal ecosystems. Most temperate terrestrial ecosystems are nitrogen deficien t and increased depositi on may cause increased growth, which can be viewed as positive or ne gative. Recent evidence suggests that nitrogen

limitation is more common than onc e thought for freshwater ecosys tems. A major challenge in developing protocols for returning ecosystems to a level of lower nutrient enrichment is defining what attributes and their specific values are neces sary for the restoration of ecosystem structure

and function. The attributes that control sensi tivity of different ecosyst em types to nitrogen loading needs further clarificati on. It would be helpful to indi cate the spatial extent of those areas in the West (e.g., Rocky Mountains of Colora do) that are impacted by relatively low levels of atmospheric nitrogen inputs.

1. Section 5.2 and Appendix 6 describe th e analyses used to evalu ate the effect of aquatic nutrient enrichment. The analysis uses the SPARROW model on one stream reach (Potomac River and Neuse River) to determine the impact of atmospheric total nitrogen deposition on the eutrophication index for the estuary. Does the Panel th ink that the model is adequately described and appropriately applied?

13The SPARROW model and its links to the CMAQ m odel’s deposition data and to the ASSETS

EI’s estimates of current or future occurrences of eutrophication are well described in the Appendices. However, better description of the SPARROW model is needed in the main document. EPA should bring forward some of the model’s description in the Appendix 6 to improve readability of this chapter. Also, it wo uld be helpful to clearl y indicate that SPARROW is a statistically-based, steady-state model. The limitations of using this model for extrapolation to conditions of lower atmospheric nitrogen deposition should be given.

The Panel found the broader extrapolation of the SPARROW results helpful in discussion of the Potomac River/Potomac Estuary and Neuse Rive r/Neuse River Estuary case studies. The discussion of the uncertainty estimates provides important information on the application of the model simulations. A summary should be provided to help the reader identify which component of uncertainty is most important with respect to policy recommendations

2. Section 5.3 and Appendix 7 describe the a nalyses used to evaluate th e effect of terrestrial nutrient enrichment. This qualitative analysis de scribes the impacts due to nitrogen deposition on the Coastal Sage Scrub community in Califo rnia and in mixed conifer forests in the San Bernardino and Sierra Nevada Mountains and larger areas where possible. In addition, the effects of nitrogen deposition in the Rocky Moun tain National Park supplemental case study location are summarized. How would the Panel apply the threshold values pr esented in this case study to allow for a broader geographic applicati on that accounts for regional variability? Have the associated uncertainties been adequately characterized?

Considering the general scarcity of ecological effects data due to excessive atmospheric N deposition, the use of a “patchwork quilt” of sp ecies and ecosystem types from across the United States is a reasonably acceptable option. The Pa nel finds it will be difficult to translate the results from these case studies to other ecosy stems because the selected ecosystems represent regions that are ecologically sensitive to total reactive N deposition. Recognizing that a secondary standard must protect the most sens itive ecosystems, the Panel recommends that Nlimited ecosystems (which are far more common than suggested by these cases) should be duly

considered.

The emphasis on the California coastal sage scrub (CSS) and San Bernardino Mountains mixed conifer forest (MCF) systems seems appropriate due to their importa nce with respect to population centers. Also linkages wi th other environmental issues, such as fire susceptibility and the potential effects on biodiversit y and threatened species, are important for these case study areas. The alpine ecosystems of the Rocky Mount ains were also consid ered and the suggestion that these systems have “the ecological benchm arks ....comparable to the benchmarks from CSS and MCF ecosystems” (p. 5-57) needs to be reco nsidered since these systems are especially

sensitive to low levels of n itrogen deposition. The section on “Uncertainty and Variability” (5.3.8) is a good summary of the major issues wi th a particular focus on the CSS and MCF case

studies. On the other hand th e “Conclusions” (5.4) section should be expanded, linking the chapter with the entire document.

The main question remains – how to translate eco logical changes caused by the total deposition of reactive nitrogen into ambient concentr ations of a single criteria pollutant, NO

x ? The critical

14loads approach based on deposition of total reac tive N should be considered for setting a new secondary standard.

Additional Effects (Chapter 6):

1. In this chapter, we have presented resu lts from some qualitative analyses for additional effects including visibility, climate and materials, the in teractions between sulfur and methylmercury production, nitrous oxide effect s on climate, nitrogen addition effects on primary productivity and biogenic greenhous e gas fluxes, and phytotoxic effects on plants. Are these effects suffici ently addressed in light of the focus of this review on the other targeted effects and in terms of the availabl e data to analyze them?

The Panel appreciated improvement s to the chapter on additional e ffects of N and S deposition. Notwithstanding specific editorial comments and que stions, the Panel concl uded that the sections on visibility and materials, su lfur and mercury methylation, N 2 O production, methane emissions, phytotoxic effects of gaseous NO

x and SO

x and productivity changes from N deposition had appropriate content and context for the REA. However, the discussion of N deposition effects on carbon cycle processes and carbon se questration was found to be inc onsistent with the available literature and EPA is requested to look at the specific comments provided by panel members to correct the existing text.

Synthesis of Case Studies (Chapter 7):

The synthesis chapter provides a summary of th e disparate case studies, but does not fully synthesize their results. The chapter also does not provide the type of contextual information needed to extend these results to broader, nati onal scales. Rather th an reiterating the case studies’ summaries, the Panel suggests revising the chapter to better reflec t the sum of the parts and possible linkages among them. Potential fo ci include developing common category labels (comparable levels of concern for the different environmental effects), exploring how ecosystem services might be used as a way to focus and contrast the different ca se studies, developing illustrative figures that integrate across case studies, and adding an uncertainty section that synthesizes the net sum of and implications of th e multiple uncertainties rather than just listing the individual components. In regard to th e latter, the Panel sugge sts addressing the key uncertainties that have the most important polic y implications, for example. The chapter should also include a section that identifies the major re search and data gaps, in cluding those that would allow spatial scaling of welfare e ffects and relationships between SO

x , NO

x and ecological

structure and function.

1. Here, the case study analyses are integrat ed and synthesized within the conceptual framework of ecosystem services as show n in Figure 7-2. Where possible, we have quantified select ecosystem servic es associated with the ecologi cal effects targ eted in this review. This chapter discusses adversity by characterizing the degr ee to which ecological effects are occurring under given levels of deposition to inform the discussion of adversity in the policy assessm ent and standard setting process. To what extent do you think the description of ecosystem services pr ovides a useful framework in the case study

15analyses for informing standard setting? Does the Panel have suggestions for additional considerations or characterizations for ecosyst em services relative to the case studies?

The concepts of ecosystem services are useful to help explain the implications of the effects of N/S deposition on ecosystems for public welfar e, and support the policy assessment of what standards are needed to preven t adverse welfare effects. Th e Panel suggests EPA include a comprehensive description of ecosystem services expected to be aff ected by N/S deposition, and

not limit the discussion to those services that can be quantified, such as recreation fishing or commercial timber production. What is most impor tant is a description of how the abundance and quality of ecosystem services are affect ed by the currently observed effects of N/S deposition on ecosystems. Total services at cu rrent deposition levels do not reflect what has been lost due to current depositi on effects, and only a portion of cu rrent services are at risk if deposition continues or increases.

2. Based on the information pres ented in the current Risk and Exposure Assessment, given adequate time and resources, is there enough in formation to inform setting separate standards based on the other targeted ecologi cal effects, specif ically, terrestrial acidification, aquatic nutrient enrichment, and terrestrial nu trient enrichment? If not, how can our understanding of these ecological eff ects be enhanced in time to inform the next 5-yr review?

Based on the Panel’s understandi ng of the Agency’s court-ordered deadlines for completing this review, we have recommended a hybridized appr oach whereby the EPA can fulfill its statutory obligations and move forward with an expedited review to set an ecologically relevant secondary NAAQS. With adequate time and resources to further develop the appro aches being considered and identify the needed foundational analyses, th e Panel finds the information in the current REA sufficient to set separate standards for terrestrial acidification, eutrophication of western alpine lakes and terrestrial nut rient enrichment. However, the Panel believes that setting a

standard for coastal nutrient enrichment would be difficult because of th e substantial inputs of non-atmospheric sources of N to these system s. Further research on cause and effect relationships driven by acidification and excess nutrient enrichment will facilitate future rulemaking.

16Enclosure C

Compilation of Individual Pa nel Member Comments on EPA’s Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfu r: Second Draft (EPA-452/P-09-004a)

Dr. Praveen Amar....................................................................................................................... 18 Dr. Andrzej Bytnerowicz ............................................................................................................ 23

Ms. Lauraine Chestnut............................................................................................................... 27 Dr. Ellis B. Cowling .................................................................................................................... 30

Dr. Charles T. Driscoll ................................................................................................................ 35 Dr. H. Christopher Frey ............................................................................................................. 46

Dr. Paul J. Hanson ...................................................................................................................... 55

Dr. Rudolf B. Husar .................................................................................................................... 61

Dr. Dale W. Johnson ................................................................................................................... 63

Dr. Donna Kenski ........................................................................................................................ 73

Dr. Naresh Kumar ...................................................................................................................... 78 Dr. Myron J. Mitchell ................................................................................................................. 83

Mr. Rich Poirot ......................................................................................................................... 111

Mr. Dave Shaw .......................................................................................................................... 120

Dr. Kathleen Weathers ............................................................................................................. 126

17

### Dr. Praveen Amar

First of all, this second draft of the REA “R isk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standard s for Oxides of Nitrogen and Oxides of Sulfur” is a substantial improveme nt over the first REA draft. It is very well-written, is more complete, emphasizes important issues of risk a nd exposure at the right le vel, and is organized

and structured in a manner that makes it much more readable.

In addition to general comments on the section of REA dealing with air quality analysis (Chapter 3, “Sources, Ambient Concentrations, a nd Deposition”), detailed comments are also provided on the Executive Summary.

Comments on Executive Summary

The charge question relating to the Executive Summary notes:

“In response to the Panel’s review of the firs t draft REA, we have included an executive summary of this document. Does the Execu tive Summary adequately summarize and characterize the key issues driving this revie w as well as the important findings of the analysis? Does the Panel have any suggestions for clarification or refinement of the Executive Summary? "

I think it is very important to include an Executive Summary for this REA. At 24-page length, it is really more of a “synthesis report/document ” than an “Executive” summary and that is good. My general impression is that, as written, it presents a good s ynthesis of all the issues raised in the REA. However, I believe that it need s a better focus on the summary of the findings described in various Chap ters (Chapters 3,4,5,6, and 7).

The eight policy-relevant questions (page ES-3) do provide a focu s on what needs to be done in the next phase of this CASAC review process. What, however, is not clear to me, is how these questions actually will be answered in the next “policy phase” of this process. Should EPA have made the first attempt to answer these questions here in this REA? What is missing in the Executive Summary and in the rest of the REA is a clear roadmap (or, a serious attempt) of how REA will get to the next “policy assessment” phase.

The articulation of the “right questions to ask” right at the beginning of the REA process is an excellent idea, even though it is difficult to formulat e and write them out clea rly. It is not clear to me why the List of policy-relevant questions in Chapter 1 (Section 1.4) is expanded to fifteen questions from original eight que stions in the Executive Summary. Some of the questions in Chapter 1(Section 1.4) are included in the Executi ve Summary, but new ones are also added. I

recommend that both Lists include the same set of policy-relevant que stions. If the two Lists which follow each other need to be different, pl ease do provide a rationa le. Otherwise, it is confusing to observe that the List of questions is almost doubled ri ght in the beginning of REA. If one assumes that the List of eight questions in the Executive Summary is more “focused” and more ‘Executive” in nature, then the sequence of ques tions in Chapter 1 is not at all “parallel” to

18what is in the Executive Summary. For exampl e, Questions 1, 2, 3, 4, 5, 6, 7, and 8 in the Executive Summary are Questions 6, 7, 2, 4, 8, 12, 14, and 15. This also means that Questions 1, 3, 5, 9, 10, 11, and 13 in Section 1.4 are not menti oned at all in the Executive Summary.

Also, the sequence of policy-rele vant questions should follow the layout of the REA itself. For example, the structure shown in Figure ES-2 (air quality indicators to deposition metric to ecological indicators to establishing standards to determination of whether these standards are met) is a good way to re-arrange the se quence of policy-relevant questions.

The first and second questions in Executive Summary need to clearly say “to what extent do the current SECONDARY standards pr ovide protection...” and “to what extent does the current SECONDARY NOx standard provide protection....” The fifth policy-relevant question (ES-4)

should be modified to also include the coroll ary and related and impor tant policy-relevant question “Does the available informa tion provide support for considering joint air quality indicators for NOx and SOx?” The third policy qu estion needs to address uncertainty in addition to variability “associated with those responses.” Also, fifth bullet on Page 1-17 is awkward (“... trying to be protected against?”).

A general comment about reduced nitrogen/NH 3 /NH 4 , etc.: This REA is a substantial improvement over the ISA and previous REA (fir st draft) in how it a ddresses the role of ammonia and reduced forms of nitrogen in total nitrogen deposition (how ever, it still does not address organic forms of nitrogen). The EPA staff deserves to be commended for this major shift in their treatment of total reactive nitrogen. However, there are references in the Executive Summary and in the body of the document (Chapter 3 and other places, s ee below) that ammonia is a “local” pollutant or that th e ammonia sources are located in “rural” areas or that at four million tons per year, U.S. emissions are “small,” compared to emissions of NOx and SO 2 . These statements seem to imply that ammonia is not as important as the other two pollutants.

Recent work by EPA (Dr. Robin Dennis and others ), however, indicates that even local “hot spot” emission sources (such as a CAFO or conf ined animal feeding operations) have a large regional total deposition footprint in addition to a more than minor total deposition local footprint. For example, they state that “the ra nge of influence of a concentrated source of NH 3 (high-emission cell) is 200-400 km; 300 + km may be a good estimate.” Si nce there is a large regional component associated w ith emissions, atmospheric chemistry, and transport of the NOxSO 2 -NH 3 system in addition to important “local” component, it is important that this REA, including the Executive Summary, be revised appropriately to better re flect the regional nature of ammonia emissions, and the regional role of re duced nitrogen in deposition and in ecological effects. The results presented in Chapter 3 clea rly show reduced nitrogen deposition is from 20 percent to as high as 50 percen t (above 30 percent on average) of total nitrogen deposition at locations of various case studies. Therefore, a mmonia/reduced nitrogen n eeds to be treated the same way in the REA as SOx and NOx.

The Atmospheric Deposition Transformation Func tion (ADTF) and Ecologi cal Effect Function (EEF) as shown in Figure ES-2 and as describe d in the Text are good conceptual framework to

address “source to welfare effect”. What is mi ssing here, however, is an acknowledgement that these functions are simply not some “magic tran slators” but are very difficult to “derive,” once

19EPA takes into account geographical and season al variability of the relationship between concentrations and deposition, as well as uncertainty associated with measurements and model predictions. This needs to be clea rly addressed in the context of Figure ES-2 and at other places where this Figure appears as the organizing principal of this REA.

Page ES-6: The Executive Summary and the docum ent use “nitrogen enrichment,” (please see Page ES-6), “nutrient enrichment,” (see Table on Page ES-7) and “nitr ogen nutrient enrichment” to mean the same thing. Please choose one (I sugg est “nitrogen nutrient enrichment”) and use it throughout the document for clar ity and for ease in reading.

Page ES-8 (line 6): “broad look” needs to be replaced with someth ing more rigorous. For example, “broad evaluation/investigation” etc. The description on Page ES-9 (top) of monetized

and non-monetized benefits is excellent.

Page ES-11: Figure ES-5, Title should say, NOx, and not, NOy.

Page ES-13: As an extension of my comment about reduced nitrogen/NH 3 above, it would be very helpful that the Executive Summary include two additional Figures in addition to the Figure ES-7, one on spatial distribution of oxidized nitr ogen and the other of reduced nitrogen, with accompanying Text that highlights the important ro le that reduced nitrogen plays in conjunction

with the role of oxidized nitrogen.

Page ES-15: It is important that this Executiv e Summary describe how the case studies will be “extrapolated” from “smaller scale to other sensitive areas in the country.” This important concept has been described in pr evious EPA efforts and needs to be addressed here before the four main ecosystem effects are presented

Page ES-19: Aquatic Nutrient Enrichment: The Text states “human activity has likely

contributed to a six-fold increase in nitrogen flux ....” Note that RE A (Chapter 3) notes that this has happened over the last 100 years. I would speculate that this large increase has occurred over a much shorter time horizon, of say, last 30 to 40 years, over which emissions of NOx from some industrial sources, and esp ecially, ammonia from animal operat ions have substantially increased at an accelerated pace. If this could be c onfirmed by EPA, it should be noted in the REA, because this finding may be policy -relevant if it implies a larger and more recent role of reduced nitrogen in total n itrogen deposition.

Page ES-20: The ASSETS index needs to be spel led out and clearly explained here as well under “Key Terms,” especially under “Key Terms” in its proper context. I f ound it hard to understand. For example, it should be clear under “Key Terms” that it applies to nitr ogen enrichment. Please also explain the use of the term “pressure” in its proper context. Same for “Determined Future Outlook” for the ASSETS index. The term, ASSETS itself, needs to be spelled out.

In “Key Terms” and in other sections in cluding Executive Summary, the definition of “Uncertainty” needs to recognize that there is more to uncertainty than simply “parameter uncertainty.” Please note that in addition to para meter uncertainty, there is equally important, if not more important, the concept of model uncer tainty (that sometimes is addressed through

20expert solicitation or other methods). It would also be very helpful to explain here that uncertainty is different than ot her terms with which it gets conf used (for example, variability, precision, sensitivity, and risk). It would be also useful to explain all th ese other concepts under “Key Terms.”

Page ES-22; The various ecological thresholds for CSS community need to be summarized. This is too much detail for the Ex. Summary.

Page ES-24, Conclusions: This section needs to be redone and rewritten. It does not do justice to

an otherwise well-written Execu tive Summary. The words “confid ence,” “most confidence,” “fair amount of confidence” may be following the recent IPCC format, but they just do not fit here. One suggestion is to write this Conclusi on section in the excellent format of “Key Findings,” prepared by EPA staff during the earlier phase of the REA process.

Comments on Chapter 3

The first key charge question relating to air quality anal yses deals with treatme nt of uncertainties associated with air quality analyses in Chapter 3 and whether uncertainties have been identified and described appropriately. Chap ter 3 describes EPA’s chosen a pproach that characterizes the spatial and temporal patterns of deposition at locations of chosen case studies. The deposition is characterized for both wet and dry forms and for total reactive nitrogen (and its two components of oxidized and reduced forms) as well as for total sulfur.

The discussion of “uncertainties” in Section 3-5 is descriptive in nature. It is, however, not helpful in providing a quantitati ve and relative sens e of uncertainties in various components (emissions, wet and dry deposition, sulfur versus nitrogen deposition). For example, it would be

useful to state that NH 3 emissions are much more uncertain th an NOx emissions that in turn are

less certain than SO 2 emissions. It may also be useful to state that dry deposition is simply not

measured but inferred from model calculati ons and has therefore uncertainties of unknown magnitude. For such cases, sensitivity studies could be useful to put bounds on the results. “Uncertainty” in “Key Terms” also needs to re cognize that there is more to uncertainty than simply “parameter uncertainty” (see above).

The s econd charge question on air quality analyses is related to the replacement of Response Surface Modeling (RSM) in the first draft of REA with a new series of full-blown CMAQ

simulations. The REA now contains CMAQ simulations to estimate th e relative contributions of emissions of NOx and ammonia to nitrogen depo sition (total N, and its oxidized and reduced forms) and a similar analysis for contribution of SO 2 emissions to total sulfate deposition. The second charge question asks, “Does this approa ch enable us to adequately examine the

contribution of NOx to tota l nitrogen deposition?”

The replacement of RSM model with CMAQ and a ssociated sensitivity runs (impact of 50% reduction in NOx, NH 3 , and SO 2 emissions on deposition of nitrogen and sulfur) is step in the right direction. Evaluating the inter-annual variab ility in emissions and meteorology and their impact on deposition fluxes is an important and useful addition to this REA. The results in Chapter 3 and Appendix 1 are described in great deta il in various figures, tables, and charts. My

21major comment, however, is that a much better a nd more realistic approa ch to investigate the impact of emission reductions on deposition fluxes is through the appl ication of “ Direct decoupled Method”( DDM) than the “brute forc e” approach of reducing emissions of one of three pollutants by a set percentage (in this case, 50%). Realistically, emission strategies are not based on “one pollutant at a tim e” reduction, but are a combination of different reductions in the

emissions of SO 2 , NOx, and NH 3 . The relative sensitivity of various components of deposition fluxes (wet, dry, total, oxidized and reduced nitrogen, sulfur, etc. ) should be investigated more meaningfully through the application of DDM or similar approach. It is not clear if EPA would

be able to undertake such an effort in the shor t time available to develop secondary standards for

SOx and NOx.

My second major comment (also noted above in the Executive Summary a nd repeated here) is that this Chapter needs to more clearly a ddress ammonia and its emissions and impacts on deposition. Statements such as ammonia emissi ons are “local” or “rural” or are not as widespread as NOx and SO 2 miss the important point that a mmonia is an extremely important chemical in the context of establishing sec ondary standards for SOx and NOx. Even though I do recognize that under the current re gulatory constraints, REA ca n only develop a secondary NOx standard with ammonia “embedded” in it, the task is going to get only more difficult if we do not

address the issue of ammonia a nd reduced nitrogen clearly.

The third charge question on air quality analyses relates to the CMAQ model performance evaluation undertaken by EPA afte r the first draft of REA in response to recommendations made by our Panel. This charge question asks, “Is this (new) analysis sufficient to support the use of

the model in this review?”

Appendix 1 does provide useful and clearly presented informa tion on the evaluation of CMAQ for annual average concentrations and annual wet deposition fluxes for components of nitrogen (nitrate, ammonium, sulfate, etc. ) for the year 2002. It also pr ovides data on model performance by comparing predictions of monthly concen trations and wet deposition fluxes with measurements for the four-year period of 2002-2005. Though model-measurement comparisons are useful for annual and monthly time scales, it may be useful to evaluate model at finer temporal scale (for example, hourly and weekly data where available) for a more “stressed” performance evaluation of CMAQ’s results.

22

### Dr. Andrzej Bytnerowicz

Executive Summary

Does the Executive Summary adequately summarize and characterize the key issues driving this review as well as the importa nt findings of the analyses?

Generally, it does. The section is well wr itten and provides a good overview of the entire document. Graphics, maps and tables are informa tive and useful. However, some corrections are needed (see my replies to the next question).

Does the Panel have any suggestions for clarific ation or refinement of the Executive Summary?

a. the second paragraph in the box of page ES-1 should be corrected to : “Substances known as oxides of sulfur, or SOx, include multiple gaseous substances (e.g., sulfur dioxide [SO 2 ], ....”

b. page ES-2 – in the end of the last paragraph a statement that biodiversity changes have also been observed in other ecosystems, such as coastal sage scrub, mixed conifer forests in California or alpine ecosystems of the Rocky Mountains, should be added.

c. page ES-11, text and Figure ES 5 – while the text described NOx, the figure shows NOy. Consistency is needed here. On the same page, line 3, change “Peak SO 2 concentrations” to “Highest annual SO 2 average concentrations”.

d. page ES-18, lines 13-16 - this paragraph seems to be out of place. Consider deleting.

e. pages ES-21 through ES-23, section “Terrestrial Nutrient Enrichment” – references should be

added to this section.

f. page ES-23, Table ES-4 – zeros for N depos ition > 17 kg N/ha/yr do not make sense. Please change to some meaningful values.

Case Study Analyses

1. Are uncertainties appropriately characterized across the case studies? Is there adequate information to allow us to weigh the relativ e strengths of each case study to inform the standard setting process?

Yes. For all described cases (acidification of aquatic and terrestrial ecosystems; nutrient enrichment of aquatic and terrestrial ecosystems) uncertainties have been well described and examples of potential problems have been gi ven. A good example is a statement on page 5-41 describing uncertainties related to the SPARROW model: estimates of N loading based on the CMAQ/NADP overall N loading in the model ca librated against the wet nitrate deposition

23values. Similarly, for the nutrient enrichment case studies for the terrestrial ecosystems, problems and uncertainties related to air pollution monitoring techniques (such as for ammonia), those due to limitations in the spatial extent and density of monitoring networks, or uncertainties due to the design and performance of the CMAQ model are listed.

2. In using the risk and Exposure Assessment to inform the policy assessment, we plan to focus on aquatic acidification as the basis fo r an alternative multi-pollutant secondary

standard as this is the area where we ha ve the most confidence in our ability to

characterize adverse effects. Does th e Panel agree with this approach?

Yes. This research is most advanced and we ll documented and therefore I agree with such a

selection.

Nutrient Enrichment

1. Section 5.2 and Appendix 6 describe the analys es to evaluate the effect of aquatic nutrient enrichment. The analysis uses the SPARROW model on the stream Reach to determine the impact of atmospheric total nitrogen deposition on the eutrophication index for the estuary. Does the Panel think that the model is adequately described and appropriately applied?

The SPARROW model and its links to the CMAQ mode l that provides deposition data and to the

ASSETS EI that estimates a like lihood of the current or future occurrence of eutrophication are well described in the Appendices. A better description of the SPARROW model is needed in the main document. Therefore I suggest that mostof the information contained on pages 6-31 through 6-33 and Figure 2.2-3 of the Appendices is copied into Chapter 5 of the main document.

Otherwise a reader has to read both volumes to understand the SPARROW model and the entire methodological approach.

2. Section 5.3 and Appendix 7 describe the analyses used to evaluate the effect of terrestrial nutrient enrichment. This qualitative analys is describes the impacts due to nitrogen deposition on the coastal sage scrub community in California and in mixed conifer forests

in the San Bernardino and Sierra Nevada Mount ains and larger areas where possible. In addition, the effects of nitrogen depositi on in the Rocky Mountain National Park supplemental case study location are summa rized. How would the Panel apply the threshold values presented in this case study to allow for a broader geographic application that accounts for re gional variability? Ha ve the associated uncertainties been adequately characterized?

The proposed approach of an assemblage of a “p atchwork quilt” of species and ecosystem types

from across the United States is a reasonable a nd probably the best opti on considering a general scarcity of data on the ecological effects of atmospheric N depos ition. Research results from the ecosystems selected for the case study (coastal sage and mixed conifer forest s), as well as from alpine ecosystems in the Rocky Mountains, north-eastern forests, and mid-western grasslands, provide a reasonable representa tion of the continental US eco logical zones, and a high probability that comparable responses would take place in other zones. A range of benchmarks

24is based on the well characterized sensitive ecolo gical indicators such as changes in lichen communities, especially decrease of nitrophytes at the low e nd of the sensitivity spectrum; changes in mycorrhizal associations in the mid- range of the spectrum; and nitrate leaching to streams at high levels of atmospheric N deposition. Changes in lichen communities seem to be the most promising N deposition indicators of N deposition effects which could be used nationwide - comparable changes of epiphytic lichens in various ecological zones can be expected at the similar levels of N deposition si nce such lichens get thei r nutritional N from the atmosphere. However, when considering response s of lichens to N deposition, also other factors such as phytotoxic ozone or climatic differences have to be taken into account. Changes in higher plants used as sensitive indicators of N deposition would be characterized by much larger margins of uncertainty because of the edaphi c, climatic and many other differences in ecosystems or ecological zones in the US.

The main question still remains – how to tr anslate changes caused by the total nitrogen deposition just into the ambient concentrations of the criteria pollu tant (i.e., NOx). Since ecological indicators included in th is analysis, as well as the biol ogical systems in general, react to the total reactive N (including its reduced inorganic and organic forms), this seems to be the most important problem to solve.

Additional problem is related to the N deposition data produced by the CMAQ model. Improvements of the model are needed in orde r to include N organic species in total N deposition estimates as well as the more recent, finer resolution data.

Other Comments

Page 5-30, Figure 5.2-12 – please check the lege nd. Number of a group should be assigned to

each color. Number of estuaries is already listed in Table 5.2-2 and should not be duplicated in

the table.

Page 5-32, line 6 – change “reductions” to “decrease”.

Page 5-34, Figure 5.2-15 – drawi ng a line through these data po ints is highly problematic.

Page 5-55, lines 3-8 – there is also a need for improving th e dry deposition methodologies through more robust models aided by empirical, ground level estimates based on well developed monitoring networks.

Page 5-66, line 11 – in contrast to fire s uppression policy and in creased atmospheric N deposition, ozone does not contribu te to increasing stand density.

Page 5-72, line 3 – add “of exo tic species” after “invasion”.

Page 5-79, line 11 – check the units.

Page 5-81, line 20 – add “especially in remote areas” after “networks”.

25Page 5-85, lines 10-12 – reference has already been cited above.

Pages 6-29 through 6-42 – check references, ma ny cited in the text are missing.

26

### Ms. Lauraine Chestnut

Final comments on Risk and Exposure Assessmen t for NOx/SOx secondary standard review, August 5, 2009

Executive Summary

Introduction: Setting the stage for this asse ssment would benefit from a short paragraph explaining why this secondary standard review is focusing on the eco logical effects of NO

x &

SO

x deposition, and not covering othe r potential welfare e ffects such as foliar injury from gaseous phases of NO

x & SO

x or other effects of deposition su ch as injury to materials.

Page ES-2: The end of this section gives a descrip tion of the extent of the problem (a description of the effect and its geographic extent) for th e effects of N deposition through excess nutrient enrichment in terrestrial ecosystems. Similar de scriptions should be added for acidification and eutrophication. For example, the discussion on page 4-9, lines 18-28, does this well for acidification of aquatic ecosystems in the US.

Policy-relevant questions: The document does not a ppear to attempt to directly answer these question. Is this something that is going to be done in the policy document? It would help the reader to understand where to expect to see these answered. The first question seems very important, although perhaps a bit too broad. This review is looking at only ecosystem-related

welfare effects associated with NO

x & SO

x deposition. When will the case be made that current

standards for SO 2 , NO 2 , PM 2.5 and ozone (of which the latter two are currently exceeded in many locations) are not sufficient to remedy or prev ent ecosystem-related welfare effects from NO

x &

SO

x deposition?

Page ES-5, lines 18-20: The relationship betwee n the standard and the “maximum deposition load” still seems a little vague. The standard wo uld be the maximum ambient concentration (in the air) that would keep the deposition level at or below th e maximum deposition load? The maximum deposition load is determined based on maintaining the ecological indicator at or below the level determined to be acceptable in the policy assessment? Plea se clarify the use of

this term in this document versus the term “cr itical load,” which seems to have a somewhat different usage in the scientific literature.

Figure ES-2: The logical flow of this figure is good, but I still have quest ions about the spatial dimension. Seems like this type of standard woul d allow ambient concentra tions to be higher in locations where it does not lead to unacceptable le vels of ecosystem indicators, which may make sense but is an unusual approach for a NAAQS. The geographic scal e on which the standard will

be assessed as met or not will have to be addressed somehow.

Page ES-6, line 10: Insert “sel ected” in front of “ecosystems”, and add some explanation of why these ecosystems were selected as case studies . They aren’t the only sensitive ecosystems—do they have the best data, are they most representative, are they the most sensitive? Any way to

27give a sense of what share of th e problem in the US that these case studies represent for each of the four categories of effects?

Page ES-8: It is good to be working in the concepts of ecosystem services and how that relates to

the CAA definition of welfare e ffect. Be careful to include no nuse values such as habitat preservation in the descriptions of ecosyste m services because there are many aspects of ecosystem services that are important to the publ ic even though they do not involve direct human use. For example, I benefit from knowing that lakes in the Adirondack s support aquatic life without significant loss of quality due to manmade emissions even though I never intend to go fishing there. This type of ecosystem service is mentioned several places in the assessment, but is

not mentioned in the sections on aquatic acidification. Even though the only service intended for quantification is recrea tional fishing, nonuse types of serv ices should also be listed and

described.

Page ES-12: Add some sentences on the key conc lusions from chapter 3 about the analysis of

oxidized and reduced N.

Page ES-13: In what locations are acidification effects a problem in the US? It is not the whole

country.

Page ES-18, lines 13-16: Some data are presented on forest recreation usag e. It would be good to

make a connection between these activities and the effects of acidification. Presumably there is some degradation in the quality of experience, and perhaps even loss of area suitable for some types of recreation, due to declin ing forest health. Similar inform ation for aquatic acidification could also be mentioned, as it is included in Chap ter 4. It is important to note both here and in Chapters 4 and 5 that total ecosystem services at current deposition levels do not reflect what has been lost due to current depositi on effects, and only a portion of cu rrent services are at risk if deposition continues or increases. Some connecti ons between the quantity and quality of these ecosystem services and the effects of NO

x & SO

x deposition need to be made, even if the connections are only descriptive.

Page ES-19: How significant and extensive is the problem of eutrophi cation in US coastal

estuaries?

Page ES-20: It is a very significant finding that more than 100% reduction in NO

x deposition would be needed to move the case study areas from bad to poor on the indicator scale. How generalizable is this conclusion? Does NO

x cause a comparable share of total N deposition in other sensitive locations? Is this because total N deposition is a small share of the total nitrogen entering the estuaries? Be careful with the word ing here. In Chapter 7 there is mention of a “weak” relationship between aquatic nitrogen and the indicator. Th e weakness is in terms of the effect of changes in NO

x deposition on the indicator, I think, not necessarily when all sources of N are considered. Also, be caref ul to avoid implying that ther e is no benefit of reducing NO

x deposition—it may not alone be enough to solve the pr oblem, but it might be useful if part of a broader policy to re duce all N emissions.

28Page ES-22: Some explanation of the relationship between lichen and forest health would be helpful here.

Page ES-24, line 14: Restrict this statement to say there is less confid ence in the relationship

with NO

x deposition, not with N enrichment as a whol e. Are there any specific circumstances

with these case studies that contribute to this result, or would all coastal estuaries be similar?

Detailed comments:

Page ES-2, line 11: Sounds like sulfur can lead to nutrient enrichment and eutrophication. May

need to make two sentences here.

Page ES-2, line 16: repla ce “alters” with “can alter”

Page ES-6, line 10: Insert “selected” before “ecosystems”

Page ES-9, line 6: Line be gins “remain unidentified”, s hould say “remain unquantified”

Page ES-16, line 20: Connect these effects categories to the ANC leve ls, as is done in Chapter 4.

Page ES-16, line 35: Insert a sentence on the resu lts for lakes at various ANC thresholds as line

37 does for the streams.

Page ES-17, lines 14-15: What does reduction in fine root growth mean for tree mortality, growth, or susceptibility? It says more in Chapter 4.

Chapter 4, page 4-8

The current value of recreational fishing has pres umably been lowered because of current effect of aquatic acidification, by lo wering the number of lake with fish and lowering the number of

fish in other lakes. In the absence of these eff ects there would presumably be more days spent in this activity and many days would have better qu ality (with more location s available and better fishing experience at locations now being used). The total value today does not say much about what the change in value would be (although it give s a sense of scale) if the effects of deposition were eliminated. Are there plans to make a quantit ative link? Perhaps this is part of the policy

assessment?

29

### Dr. Ellis B. Cowling

In preparation for the July 22-23, 2009 CASA C meeting, my individu al comments on the

Second External Review Draft of the Risk a nd Exposure Assessment (REA) for the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur are organized below in part in re sponse to Charge Questions pose d in Lydia Wegman’s memoranda to Kyndall Barry dated June 5, 2009. As you will se e, greater attention has been given to the Executive Summary and the several Case Study An alyses which were the specific assignments given to me by Chairman Ted Russell.

With regard to the Executive Summary, the principal Charge Questions were in

essence: 1) Does the Executive Summary adequately summarize and characterize the key issues as well as the important findings of this REA analysis? 2) Does the Panel have any suggestions for improvement of the Executive Summary?

My general response is that it is highly desirable to have an Executive Summary in this Second Draft REA. My specific respons e to question 1, however, is that the Key Issues are presented very well but that the Important Findings are not so adequately presented. Thus, my suggestion for improvement of the Executive Summary is to give much more attention to the Important Findings (such as those that are presented in the “Summary of Case Study Analysis Findings” on pages 3-79 through 3-81 in Chapter 3, “Results for the Case Study Areas on pages 4-56 through 4-71 in Chapter 4, “Current Conditions in th e Case Study Areas” on pages 5-18 through 5-43 and on pages 5-58 through 5-81 in Chapter 5, “Nitrogen Addition Effects on Primary Productivity and Biogenic Greenhous e Gas Fluxes on pages 6-13 through 6-28 in Chapter 6, and in the “Synthesis and Integration of Ca se Study Results” on pages 7-1 through 7-24 and especially the “Conclusions” section on pages 7-24 and 7-25 of Chapter 7.

In my opinion, the Important Findings in this Second Draft REA should be presented in the Executive Summary in the form of as direct an swers as possible to ea ch of the eight PolicyRelevant Questions presented for the first time on pages ES-3 and ES-4. It also would be desirable for these Important Findings to be pres ented in close physical proximity within the text of the Executive Summary to the presentation of Policy Relevant Questions to which these Findings/Answers to Policy Relevant Questions apply.

General Comments on the Chemical Forms of Total Reactive Nitrogen

It was a pleasure to see that both the Executive Summary and all of the main chapters (1 though 7) of this Second Draft REA give more appropriately balanced at tention than was given in the

First Draft REA to the chemically reduced as well as the chemically oxidized forms of the inorganic parts of total reactive nitrogen (Nr). But both the Executive Summary and each of the main chapters of this Second Draft RE A do not give appropriate attention to the organic as well as the inorganic forms of total reactive nitrogen

.

30I was pleased to see that the te rm “Total Reactive Nitrogen” is listed among the “Key Terms” listed on pages xxi-xxviii of this Second Draft RE A. But I was disappointed to see that the definition given for “total reactive n itrogen” in the “Key Terms” list is: 1) Not consistent with the way this same term is used in Chapters 3, 4, and 5, and also 2) Not consistent with the generally accepted scientific definition of this very important

term.

In this connection, please note th e perhaps subtle but very impo rtant differences between the definition of “total reactive nitrogen” as presente d in the “Key Terms” list on page xxvii of this

REA: “Total Reactive Nitrogen: A ll biologically, chemically, and radiatively active nitrogen compounds in the atmosphere and the biosphere, such as ammonia gas (NH 3 ), ammonium ion (NH 4 + ), nitric oxide (NO), reduced nitrite (NO 2 ), nitric acid (HNO 3 ), N 2 O, reduced nitrate (NO 3 - , and organic compounds (e.g., urea, amines, nucleic acids);” and the definition of the term “reactive nitrogen” in the now publically available Executive Summary of the report of EPA’s Science Advisory Board’s Integrated Nitrogen Committee:

“The term reactive nitrogen (Nr) is used in this report to include all biologically active, chemically reactive, and radiatively active nitrogen (N) compounds in the atmosphere and biosphere of Earth. Thus, Nr includes inorganic chemically reduced forms of N (NH

x ) [e.g., ammonia (NH 3 ) and ammonium ion (NH 4 + )], inorganic chemically oxidized forms of N [e.g., nitrogen oxides (NO

x ), nitric acid (HNO 3 ), nitrous oxide (N 2 O), N 2 O 5 , HONO, peroxy acetyl compounds such as PAN, and nitrate ion (NO 3  ̄ ), as well as organic compounds (e.g., urea, amines, amino aci ds, and proteins), in contrast to nonreactive gaseous N 2 .”

In Chapters 3, 4, and 5, the terms “reactive nitrog en” and “total reactive nitrogen” are used to refer the sum of wet plus dry deposition of ch emically reduced and chemically oxidized inorganic forms of air-borne biologically active nitrogen compounds and do not include the additional organic forms of airborne reactive ni trogen compounds (urea, amines, amino acids, and proteins).

In truth, at present, much more is known about the chemically reduced and chemically oxidized inorganic forms of reactive n itrogen deposited across the Unite d States than about the amounts of organic forms of Nr deposited across the Unite d States. But, at least in the Neuse River Estuary (which is one of the eight important “Cas e Study Areas” used in this REA report!), Hans Pearl has presented reliable evidence that as much as one third of the total atmospheric deposition of Nr compounds delivered to this estuary is deposited in the form of organic compounds -- in addition to the chemically redu ced and chemically oxidized inorganic forms of Nr. Although it is not know n how much organic nitrogen is pres ent in the air sh eds of the other Case Study Areas used in this REA, it would be appropriate to admit this uncertainty in the estimates of “total reactive nitrogen” and to use the term “total inorgani c reactive nitrogen” or “total inorganic Nr” (for shor t) rather than the misleadi ng “total reactive nitrogen.”

It also would be desirable to include some disc ussion (or at least an ac knowledgement) about the current uncertainty about the amounts of organic forms of Nr in the air-sheds of all of the Case Study Areas. This would be especi ally desirable in the various specific sections of this Second

31Draft REA that deal with “Uncertainty” -- for ex ample, on page 2-18 in Chapter 2, on pages 3-90 through 3-96 in Chapter 3, on pages 4-68 and 4-69 in Chapter 4, on pages 5-40 through 5-43 in Chapter 5, on pages 6-23 and 6-24 in Chapter 6, and on pages 7-21 through 7-24 in Chapter 7).

General Comments on the Major Ecological E ffects of Reactive Nitrogen and Sulfur

It was a great pleasure to see very clear divisions and scie ntifically sound desc riptions of the phenomena of excess Nr- and S- induced Acidif ication, Nutrient Enrichment, and Additional Effects in both terrestrial and aquatic ecosystems that are the object of the reviews of the ISA

and REA documents we have reviewed so fa r in this integrated NOx and SOx NAAQS Secondary Standards Review process.

It is even more satisfying to see the very t horoughly thoughtout general a pproach to management of the ecological effects of excess Nr and S that is presented for the first time in Chapter 2 and is used as a “reminder symbol” before the title of all the main Chapters of this Second Draft REA document. I presume that the frequent use of this symbol is an indication of the pride that NCEA and OAQPS who collaborated in the creation of th is general approach. Your pride in this accomplishment is well-deserved in both my personal and professional opinions.

The effort both organizations have made to develop this general approach – which is necessitated in part by the fact that chemically reduced forms of reactive nitrogen are not (yet?) recognized as Criteria Pollutants, and by the huge variety and complexity of the ecological phenomema that are of concern in the widely scattered geographical areas in which these phenomena are manifested – is especially commendable in light of the rather substantial departure from the dominating past

concerns of the USEPA with la rgely urban- and suburban-based public-health rather than also public-welfare effects of ai r pollution in our country.

Permit me also to congratulate the authors of this Second Draft REA for their abundant and effective use of color illustrations that display many of the special features and unique challenges of management that will be necessary if the eco system protection approach that is necessary for success in establishing improved secondary stan dards for NOx and SOx as proposed in this

REA.

It was particularly satisfying to see that the c oncept of Ecosystem Services has been so clearly explained and used in the development of this RE A document. It also was very satisfying to see that the concept of Critical Loads is not only expl ained very properly but also used in presenting some of the recommendations in Chapters 4 and 7 in this Second Draft REA document.

Specific Continuing Concerns about Some of the Specific Words and Phrases Used in the Chapters of this REA

During the now nearly six years in which I have se rved as a statutory member of CASAC, I have offered persistent suggestions a nd recommendations to decrease th e confusion that often results from the use of terms that have multiple meanings and thus frequently lead to lack of clarity in many of the ideas that are presented in the ISA, REA, and Staff Paper documents used in the NAAQS review processes.

32The words and phrases that I once again call attention to in the context of this REA document include the following:

“ Level ” which most importantly is used in NAAQS review documents to mean “EPA designated allowable air concentration of a criteria pollutant.” But the word “level” also is used to mean many other things such as: 1) “amount” of anything -- such as the amount of biomass lost, or amount of some chemical constituent in a water body, 2) “extent” of some physical or chemical phe nomenon or even the number of people in a population that are concerned a bout some public health or public welfare impact of pollution, 3) “elevation” when altitude or dist ance above sea level is intended, 4) “degree” or “intensity” of some biol ogical phenomenon or social concern, 5) “distance above zero” for example in a graph, 6) “Type of interest” such as at the “biologi cal species level” as opposed to “physiological level” or “biochemical level,” etc, etc. In all NAAQS review documents, I recommend th at the word “level” be reserved almost exclusively to discussions about the “EPA designated allowable ai r concentration of a criteria pollutant” and that the great variet y of alternative words be used wh enever they are in fact what

is intended.

“Reduce, Reducing, and Reduction” – These three terms all have both chemical and numerical meanings. Fortunately we have the unambiguous terms “decrease” and ”decreasing” which have only a single (always numerical) meaning.

Thus I recommend that the unambiguous term “decrea se” be used instead of the word “reduce” when our intended meaning is numerical -- and th us reserve the term “reduce” exclusive for its chemical meaning? I further recommend that th e couplet “chemically reduced” and “chemically oxidized” be used when referring to the two major chemical forms of inorganic reactive nitrogen.

A particularly interesting (and at the same time very frustrating!) example of an effort to follow

this recommendation in this Second Draft REA document is provided by the wording for the captions of Figure 3.4-1, Figure 3.42-2, Figur e 3.4-3, Figure 3.4-5, Fi gure 3.4-6, and Figure 3.4- 7 on pages 3-82 through 3-85 in Chapter 3. Please note that the unambiguous word “decrease” was used in the captions of all six of these figures. For example, the caption for Figure 3.4-1

reads as follows:

“Figure 3.4-1. The percentage impacts of a 50% decrease in NOx emissions on total reactive nitrogen deposition in the East.” [The Bolding was added by me, for emphasis].

What a great disappointment it was to then read the description of th is very same figure as it was written on lines 13 through 15 of the text on page 3-82 within Chapter 3!. The text reads as

follows:

33“Figure 3.4-1shows the impacts of the 50% NOx s cenario on total reactiv e nitrogen in the East. In general, a 50% reduction in NOx had a 30% to 40% impact (i.e., reduction ) on total reactive nitrogen deposition. [Once again this Bolding was also added by me for emphasis.]

Please also note that text description of this figure refers (i ncorrectly) to the impacts of a “50%

reduction in NOx” – which is not th e same as a 50% reduction in NOx emissions -- as is stated (correctly) in the caption itself !!!

Nitrogen, NOx, NHx, Reactive Nitrogen, Tota l Reactive Nitrogen, and Total Inorganic Nitrogen . There are many examples in all seven chapte rs of this REA document where it is not

clear whether the intende d meaning of the sentence is best conveyed by the word “nitrogen,” “NOx,” “NHx,”“ reactive nitrogen,” “total reactive nitrogen,” or “tot al inorganic nitrogen. I list below a few examples where the meaning of th e sentence was were particularly puzzling: 1) Lines 13-20 on page 1-10 and lines 5-6 on page 1-19 in Chapter 1. 2) Lines 4-10 on page 2-6 in Chapter 2. 3) Lines 14-20 on page 3-3 in Chapter 3. 4) Line 6 on page 3-6 and line 13 on page 3-7 in Chapter 3. 5) Lines 5 and 6 on page 4-15 in Chapter 4. 6) Lines 5 and 6 on page 5-21 in Chapter 5. 7) Lines 27-31 on page 6-17 in Chapter 6.
8) Lines 7-9 on page 7-8 in Chapter 7.

34

### Dr. Charles T. Driscoll

For each chapter general comments are given followed by specific comments.

Overall

The EPA is to be commended for this effort at compiling and completing the REA on ecosystem effects of sulfur and nitrogen oxides. This was a major undertaking and an important new initiative for future air quality management in the U.S. This report lays of a framework for a critical loads approach to guide mitigation of ecosystem effects from air pollution. The REA document is much improved over the previous draf t. There are less typos and wording problems. Some of the redundancy has been eliminated. Mo st importantly the document is more focused than the previous draft

While I am enthusiastic about the initiative and report, there are a few considerations that should

be addressed before the REA is finalized. Firs t, there needs to be a more comprehensive and systematic discussion on the front end of the document on the concepts of maximum deposition load, critical load and target load. I have no idea what maximum deposition load is or how it is

different from critical load. The term is introduc ed at the beginning of the report and then not really addressed again, while th e term critical load is used throughout the report. Also the

distinction needs to be made betw een critical loads and targets loads. This distinction is ignored in the report, but it has critically important polic y considerations. Critica l load is a steady-state concept. Unfortunately ecosystems are rarely, if ever at steady st ate. Steady-state models can be used to determine critical loads and/or empirical models. Target loads are a time –dependent phenomenon, and calculated with dynamic models. An important management consideration in this analysis is the time for ecosystems to reach critical chemical limits or achieve conditions of critical biological indicators following emission controls. Al so the time to reach steady-state is important to understand for management consider ations. The REA does not consider these time dependent process. The document really needs a cl ear treatment of these concepts and how they are used in the REA and for ecosystems management of air pollution effects.

Another important consideration is the spatial and temporal compatibility of the atmospheric transport models (i.e., CMAQ) and the watershed effects models. CMAQ is designed to address large spatial scales over short temporal scales . Many of the ecosystem effects and associated models are manifested over smaller spatial scales and over long time frames (e.g., decades to centuries). In the air quality chapter the authors provides some discussion of these

considerations. If a critical load /target load is to be used to a ssess and guide ecosystem effects of air quality a rigorous analysis of the compatibility using transfers between atmospheric transport and watershed/ecosystem models this disconnect needs to be rigorously evaluated. While such an analysis is beyond the scope of the REA some te xt needs to be dedicate d to this issue to set the stage for a future research initiative.

I have some pet peeves with the writing style that I have mentioned in previous reviews. Throughout the document the text is written as inanimate objects are doing something. For example, Figure xxx shows... This chapter discu ssed... An inanimate object cannot do anything.

35A better approach would be: such and such is shown in Figure xx or In this chapter current

emission sources are discussed...

I also urge that the word reduced only be used when referring to chemical reduction or a reduced

chemical form such as ammonium. In the doc ument the term reduced is used to refer to

decreases as well as reduced chemical forms. Th is makes for some confusing text. Please make this change.

Executive Summary

General Comments

The quality of the Executive Summary is good. It provides a good overview of the report.

ES-2, line 10 - The text indicates that sulfur can limit productivity. I don’t think this is a likely

situation. The text should be cl arified and probably corrected.

ES-5, line 18 – the REA uses a term maximum depos ition load. How does this compare with the terms critical or target loads which are used later in the document (Cha pter 4). Introducing a

new term that is similar to other terms used in the report will confuse the reader. This term

should be clarified relative to critical/target loads.

ES-16, text box – In this text box cr itical load is defined. I would like to see the actual definition of critical load, “the le vel of atmospheric deposition of a s ubstance below which there is no harm to the ecosystem” or something like that. How does critical load compare with maximum deposition load? Also no effort is made to clar ify the time-dependent nature of the problem. Critical load is a steady- state phenomenon; target load is a ti me dependent value. The text box should be expanded to address these issues.

Specific Comments

ES-2, line 7 – I do not like the term occult depositi on. I do not believe it is a very accurate or descriptive term. W hy not refer to it as cloud and fog deposition?

ES-2, line 13 – Change to ... localized loss and extinction of fish.

ES-16, line 13- MAGIC should be defined or clarified.

ES-18, paragraph 2 – Some mention should be made of the value of sugar maple in fall foliage with respect to tourism.

Chapter 1.

General Comments

None

36Specific Comments

1-13, line 4 – I do not like the term occult deposition. It is not a very acc urate or descriptive term. Why not just refer to cloud and fog deposition?

1-13, line 6 - The text indicates that sulfur can sometimes limit plant growth and productivity. I don’t think this is a likely s ituation. The text should be clarified and corrected.

1-15, line 21 – Methylati on of mercury can occur in virtua lly all watersheds, not just the

northeastern U.S and southeastern Canada. This sentence needs to be deleted or corrected.

Chapter 2.

General Comments

2-10, line 9 - As discussed above I do not like the term “maximum deposition load” it seems redundant with the concept of crit ical/target load. Why introduce a new term? This term should be clarified with respect to how it is different/ related to critical lo ad. Also the second half of the phrase is not correct. It is not the amount that solves a mass balance equation for an ecological

indicator. This sentence n eeds to be corrected.

Specific Comments

2-12. line 15 – The sentence “Valua tion may be an important step...” is very similar to 2-11, line 18 “In addition valuation may be an important step...”. You may want to delete one of

these.

2-15, line 24- data are...

Chapter 3

General Comments

My hat is off to the authors of the chapter it is greatly improved ove r the last version. It is much

more focused and easier to read. The authors did a great job re-orienting to focus on the ecosystem case studies. I also appreciate the effo rt made at the end of th e chapter to discuss the sub-grid scale issues.

This section could be shortened further by eliminating the text on sulfur deposition for the nutrient case study areas; Potom ac, Neuse, and western sites.

The authors should examine the text with respect the writing style. In some sentences the text is written as the present tense, in ot hers it is written as the past tens e. The text should be consistent, I would suggest in the past tense.

37Specific Comments

3-1, line 21- Change to: we re used as modeling...

3-2, line 8 – Change to: emissions, transformations and deposition...

3-2, line 9, 18- A typo? additional x? Should this be NHx?

3-2, line 28- Change to: The emissions to atmospheric concentrations-to-deposition...

3-3, line 17- Change to: are important components...

3-14, line 12- Change to: United States were also used.

3-15, line 16 – Aren’t there about 200 NADP sites?

3-22, line 8 – The term non-ambient loadings is horrible. It doesn’t mean anything. Please change it. I would suggest non-atmospheric N sources.

3-27, line 16- Should be Whiteface.

3-27, line 17- Change to: show a downward pattern to 2006.

3-48, line 8- Change to: is fairly uniform...

3-48 line 9- Change to: are generally consistent with...

3-59, line 10- Change to : Whiteface

3-80, line 10- Change to: and t hus, decreasing atmospheric...

3-80, line 23- Change to: simulations were run.

3-81, line 23- space between to and 50%

3-82, line 5- Change to: for the pattern is th at decreasing NOx decreases HNO3 which limits NO3.. There is a 4 before NO3, should this be HNO3?

3-82, line 5- Change to: This change... also NH4+ superscript on the charge.

3-82, line 8- Should this be dry deposition of NHx?

3-82, line 29- Should th is be limits HNO3? Also a space between (NO3) and increases.

Chapter 4

38General Comments

The acidification chapter is in n eed of some editing. Several sect ions are difficult to follow and the wording needs to be cleaned up. The term inorganic aluminum should be changed to dissolved inorganic aluminum, to clarify that the aluminum is in the aqueous phase not particulate phase. Throughout the chapter the authors re fer to ANC concentrations. ANC is not really a concentration. It is a measure of acid base chemistry and represents the composite of many solute concentrations. It is possible to have negative ANC values ; concentrations cannot be negative. The authors should refer to it as simply ANC or ANC value

4-14 In the section on critic al loads, it is not at all clear what calculations are being done. This

needs to be clarified. How are critical loads determined? Also critical load is a steady-state phenomenon, but model calculations were done fo r 2020 and 2050. Aren’t these values really target loads? Finally critical loads are discus sed here, but in the Executive summary the term maximum deposition load is introduced. How are th ese concepts different? In addition to the MAGIC calculations, the steady state water chemis try model (SSWC) is introduced on p 4-36.

Both models should be introduced in this met hods section. It should be made clear how the models are used and how they complement each other. On 4-36 and 37 the description of the SSWC model is very confusing. This seems to come from left field. This section needs to be rewritten to clarify what is being done, and why.

Throughout the chapter the term buf fering is used incorrectly. Bu ffering more specifically pH buffering is the resistance to change in pH. pH buffering can be high due to dissolution of aluminum minerals while contributing to acidificati on. A better term is th e ability to neutralize

acid.

4-53, paragraph- I strongly disagree with the statements on steady-state vs dynamic models. Agreed critical loads are a steady-state phenomenon, but ecosystems are not at steady state. A more balanced treatment should be given in the text. There are advantages and disadvantages associated with steady-state and dynamic models, wh ich should be stated. Earlier in the text a dynamic model MAGIC is used for “critical load ” calculations. (Although I might argue that these are not critical load calculations, rather ta rget loads.) Applicati on of steady-state models are problematic for ecosystems that are not at steady state. As many sensitive forest ecosystems are exhibiting soil exchangeable cation depletion, one might argue that it is not appropriate to use a steady-state model.

Specific Comments

4-1, line 15- Occult deposition is a poor term. I would just refer to cloud and fog deposition.

4-1, line 21- Change to: depleting soil exchangeable base cations...

4-2, line 2 and throughout the document- Ch ange to: dissolved inorganic aluminum...

4-2, line 27- Need to de fine nitrogen saturation.

394-3, line 14- Change to: ecosyst ems and biological species...

4-4, line 1- Change to: availa ble base cation pools of...

4-4, line 14- Change to: chronic or base flow chemistry....occasional acidic episodes, with..

4-4, line 41- Need to define base cation surplus.

4-5, line 21- The statement made concerning PnET is not entirely true. ANC can be calculated as base cations less strong acid anions in PnET- BGC, but PnET also simulates ANC by depicting the protonation of bicarbonate, organic anions and aluminum to repr esent measured ANC.

4-5, line 24- The statement made is incorrect and contradicts the statement made on line 13. Change to: Low ANC coincides with effects on...

4-13 on Figure 4.2-4 and several of the other fi gures in the chapter (e.g., 4.2-12, 13, 14) it is a challenge to read the labels and scale on the fi gures. The font size needs to be increased. The quality of these figures should be improved.

4-13, line 17 and throughout the chapter- Change to: trends in sulfate and nitrate concentrations

and ANC...

4-14, line 3- Change to: were used...

4-14, line 6- Change to: because historic al measurements are not available.

4-14, line 12- Change to: and low concern (Table 4.2-1).

4-16, line 14- Change to: 0 ueq/L (acidic), 20 ueq/L...

4-16, Table 4.2-1, first row Change to : Near complete loss of fish...

4-17, line 8- Change to have decreased (Figure 4.2-3)...

4-18, Figure 4.2-6- If these are mean values for all lakes this should be made clear.

4-18, line 11- Change to: base cati on supply neutralizes the inputs...

4-18, line 17- It is not clear which monitored lakes is bei ng referred to here; the LTM lakes?

4-21, line 9- Change to: le ss neutralizing ability...

4-21, line 15- Change to: the lake could neutralize and still...

4-29, line 2- Change to: have less ability to neutralize acid in puts than sites......

404-31, line 7- Change to: may degrade by 2050...

4-24, line 22- In addition to input s of organic acids, some watersheds simply have low rates of base cation supply.

4-36, line 19- What is meant by ac counting for effects of chloride?

4-37, paragraphs 2 and 3- This section is c onfusing. For example on line 21 it states maximum deposition load for sulfur is equal to the amount of sulfur the catchment can remove. On line 14 an assumption is that long-term sinks of sulfate in the catchment is negligible. This section

needs to be re-written. I thought I understood the SSWC mo del until I read this section.

4-38, line 14- Change to: all possible combinations of...

4-38, line 17- Change to: each combination of depositions...

4-40, line 24- Change to: ANC = 50 ueq/L.

4-44, paragraph 1- You also may want to mention that regeneration of sugar maple is restricted

under low calcium conditions. See Juice et al. 2006.

4-50, line 17- the abil ity of a system to neutralize acid...

4-50, line 18- Change to: successfully neutralize acidifying...

4-50, line 20- Change to: to neutralize acidifying...

4-50, line 23- Change to: bedrock with lo w ability to neutralize acid inputs..

4-55, line 16- This statement is not true. Wate rshed 6 has been cut and the forest biomass has been impacted by climatic disturbance events. See Aber et al. 2002.

Chapter 5

General comments

The nutrient enrichment chapter is well done. It is good to see a balan ced description of the

effects of fertilization in the beginning of the chapter. The Potomac and Neuse case studies illustrate the difficulty is quantifying the effects of atmospheric nitrate deposition in complex and

diverse watersheds.

The chapter would benefit from a brief descri ption of SPARROW, including the limitations of the model. Using a model like SPARROW will not allow for a determination of the time of recovery in response to decreases in nitr ogen loading.

Specific Comments

415-9, line 14- Should the sentence say “at which the system is not nitrogen-limited”?

5-19, last paragraph- I don’t understand incremen tal yield and delivered yield. Can these terms

be clarified?

5-20, line 27- Define TNs.

Figures 5.2-7 and 5.2-11. There appears to be a mistake in the figure legend. Shouldn’t the units be kg/ha-yr? Also more desc riptive figure titles defining incremental nitrogen yield and delivered nitrogen yield would be helpful.

5-33, line11- Change to: leve ls by decreasing the oxidized...

Figure 5.2-16. Note that the con centration scale here is very small, not very meaningful

differences in terms of measured concentrations.

5-45, line 18- Space between section 3.3). and Changes..

5-45, line 25- Typo: waters, reduced...

5-45, line 28- Typo: uptake (Figure 5.3-1).

5-48, line 27- Change to: from decreasing nitrogen...

5-58, line 18- Typo: analytical

Chapter 6

General comments

The material on the linkages betw een mercury and sulfur is gene rally a good overview. There

are some inconsistencies in the text that need to be revised. For example on p -2, line 26 it is stated that inconsequential amounts of methyl mercury can be produced in the absence of sulfate. But on p 6-4, line 12 the text corre ctly indicates that methyl mercury can be produced by iron reducing bacteria. The first statement should be deleted. On p 6-3, line 5 the statement is made

“Watersheds with conditions known to be c onducive to mercury methylation have been

identified in the northeastern U.S. and southeaste rn Canada..” but is followed by the statement “ whereas watersheds with elevated methylmercury levels... are seen in most of the U.S. The first phrase should be deleted. It is inconsistent with the second part of the sentence and with figure

6.2-5.

Specific comments

6-1, line 24- Change to: stated that decreases in visibility...

426-3, line 17- Should be Driscoll et al. 2007

6-7, line 34- I believe now all 50 states have some sort on mercury consumption advisory.

6-20, line 16- There seems to be part of a sentence missing.

6-21, line 15- What other types of ecosystems we re data available besi des conifer and deciduous

forests?

6-23, line 5- Standard deviation is given for N2O and CH4, can the variability for CO2 uptake response factor be given.

6-23, line 26- Should this be section 6.4.4?

6-25, line 17- Change to: Because of decreases in ambient SO2...

Chapter 7

General comments

Some of the overall suggestions th at I made at the beginning of th is report could be incorporated

in this section.

7-23, line 22- The information presented in Tabl e 7.1-3 is not quantitativ e and no information on Bc/Al is presented. This sentence needs to be changed.

Specific comments

7-2, Figure 7-1- I find the font difficult to read on the purpl e background in this figure.

7-5, Line 10- Change to (i.e., ra in, snow), cloud and fog, and dry...

7-5, line 12- Change to: Both are essential. Nitr ogen often limits the growth or productivity, and species diversity of ecosystems.

7-5, line 14- Change to: acidification and w ith excess nitrogen to nutrient enrichment.

7-5, line 16- Change to: lo calized loss or extinction...

7-7, line 22- Change to: n early complete loss of...

7-8, paragraph 2- Again maximu m depositional load. How is th is related to critical load?

7-9, line 2- Change to: lake could ne utralize inputs of acids and still...

7-10, line 1- Do you mean: 30 ueq/L in summer than in spring...

437-10, lines 2 and 3- Change drops to decrease.

7-10, line 3- Change to: Severe impacts can occur to fish...

7-10, line 5- Do you mean low or high pulses?

7-10, line 14- Change to: mobilization of dissolved inorganic Al...

7-10, line 25- typo on superscript.

7-10, line 26- Change to: concentrations of ava ilable Al, as measured by exchangeable base...

7-11, line 5- Need a period at the end of the table title.

7-11, line 12- Sverdrup a nd Warfvinge 1993 is not in the references.

7-14, line 21- Do you need the word magnesium?

7-17, line 19- red spruce

7-19, line 29- Is ocon ic a word? Iconic?

7-21, line 8- Change to: Tahoe drain through...

7-22, line 4- Are continuous monitoring units used for NOx?

7-22, line 16- Change to: data are...

7-23, line 7- Change to ANC and aquatic acidification.

7-23, line 8- Change to: between soil exchangeab le Bc/Al ratio and terrestrial acidification.

7-23, line 21- Change to: between ANC and fish species...

7-23, line 22- The information presented in Tabl e 7.1-3 is not quantitativ e and no information on Bc/Al is presented.

7-24, line 13- Change to: sustain te rrestrial and aquatic food chains.

44References

Aber, J.D., S.V. Ollinger, C.T. Driscoll, G.E. Likens, R.T. Holmes, R.J. Freuder and C.L. Goodale. 2002. Inorganic N losses from a forested ecosystem in response to physical, chemical, biotic and climatic perturbances. Ecosystems 5:648-658.

Juice, S.M., T.J. Fahey, T.G. Siccama, C.T. Driscoll, E.G. Denny, C. Eager, N.L. Cleavitt, R. Minocha, and A.D. Richardson. 2006. Response of sugar maple to calcium addition to northern hardwood forest. Ecology 87(5):1267-1280.

45

### Dr. H. Christopher Frey

Comments on “Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitroge n and Oxides of Sulfur, Second Draft”

GLOSSARY:

The definition of variability in the glossary is weak and misleading. The explanation of variability given on page 2-18 is much better. The glossary should be updated to better reflect accepted definitions of risk assessment terminology.

EXECUTIVE SUMMARY

Please define NO y in the text box.

Figure ES-2: The term “atmospheric landscape” is confusing. One does not associate a landscape with the atmosphere. Use a more descriptive term.

Page ES-4: It is helpful to list what was analyz ed. However, some explanation of what was not analyzed and why would also be helpful. For exam ple, earlier it is indi cated that sulfur is a nutrient, and a reader may wonder therefore why sulfur “enrichment” is not considered.

Figure ES-3. Remove the brown background color, because it is not useful.

Page ES-8. The “concept of ecosystem services” is mentioned but not defined. It should be explained to the reader.

Page ES-9 . The allusion to monetization in th e first paragraph seems entirely inappropriate for this document. By law, the costs associated w ith a potential standard cannot be considered in setting the standard. Why should any of the endpoints be monetized in the context of this

document? The issue of monetizat ion related to benefits assessmen t, which may be relevant to a regulatory impact analysis or to information requested by OMB, but is not relevant to the process of developing NAAQS. Hence, either delete th is material throughout the document, or provide a context that clearly differentiates that it is not related to standard setting and is mentioned for other reasons, and enumerate what those reasons are.

Page ES-10. Since CMAQ is a framework, it is non-specific to say that “CMAQ” was used to

simulate concentrations. The reader would need to know more about what versions of components within CMAQ were used – i.e. what chemical mechanism, what advection algorithms, what treatment of planetary boundary layer, what “light” model, etc.

Figure ES-5. What layer of the atmosphere is repr esented here? Is it the lowest layer? Similar comment for Figure ES-6.

46Figure ES-7. In lower right, it appears that ther e is a minus sign but some explanation should be given as to why “Total N – CMAQ dry + NADP Wet”

Page ES-14. For policy relevant background con centrations, please indicate how these were estimated: where they estimated based on monitore d values at remote measurement stations, or are they based on model estimates?

Page ES-15. What was the finding regarding whet her “area-based risk and exposure assessments

are ... suitable”?

Page ES-16. The level of detail on this page and a few others that follow seems to ramp up significantly. Who is your audience? If the ES is intended to be read by lay policy people, they will either stop reading here or eyes will glaze over. Try to write in shorter sentences and paragraphs. For example, the pa ragraph that starts on page ES -15 and goes onto page ES-16 is nearly a page long. The text box contains a run- on sentence and awkward and unclear definition

of critical load. Ther e is much repetition in the second paragraph on page ES-16. The phrase “ANC values” or “ANC limits” or similar is repeated three times.

Page ES-17. Top of page: “It was not possible t o... a larger dataset” Wh at larger dataset was desired? Larger in what way? This sentence is unclear.

“may aid” does this mean that the writer is not sure if the “connection” helps determine “adverse impacts”? Why so tentative?

The section non Terrestrial Acidific ation is likewise not likely to be read by a lay policy reader. Is the audience intended to be peer experts in terrestrial acidifica tion? If so, they can probably read this. Doubtful that others can, however. May want to start out di fferently, explaining and introducing concepts step by step. i.e. soil acidi fication is bad, and explain why. Then explain

that acidification of soil cha nges the concentrations of Ca++ and Al, and why. Then introduce that Ca++ is part of a “base cati on” (explain what that is) that includes a few other ions. Then introduce the ratio of Bc to Al, and explain that it gets smaller or la rger as acidifica tion gets more

severe. Etc.

Last paragraph on the page. Do the numbers 0.6, 1.2, and 10 have units? The way the sentence is written, it is not clear that these are Bc/Al ratios, since the sentence says that Bc/Al was calculated from the number given. Ve ry unclear to the reader.

Page ES-18. What is a Al/Ca++ imbalance? In what way are Al and Ca++ supposed to be in “balance”? And why is the ratio now inverted ? These kinds of inconsistencies are a good way

to lose the reader.

Middle of page, the monetization seems entir ely inappropriate. See earlier comment.

Page ES-20. Please clarify if “atmospheric depos ition” includes only direct deposition or if indirect pathways are included – e.g., does deposition to land a nd then run-off into estuaries constitute “atmospheric deposition” to the estuary? It is a bit odd and conf using to the reader to

47say that more than 100% or greater reduction in atmospheric deposition was necessary. How can

one have more than 100% reduction in deposition?

Bottom of page... e.g., 1.5 kg N/ha – should there be a time dimension to this number? i.e. over what time period did this amount of deposition take place?

Page ES-22: The term “mycorrhizal community” is mentioned before it is defined. This will confuse lay readers who are not experts in the topic area.

Table ES-3. Is the area really known to 6 significant figures?

Bottom of page ES-22. “The pressures exerted” seems to be a metaphor. In technical writing, avoid technically-based metaphors, as they can be confused for a literal interpretation, depending on the background of the reader. Since my b ackground is mechanical engineering, I tend to think of pressure in terms of force per area. I don’t think this is the intended meaning.

Page ES-24. It is not clear to the reader as to why the critically important role of N2O as a greenhouse gas is beyond the scope of this assess ment. If they are beyond the scope of this “review,” then why were they a ddressed qualitatively. It is c ontradictory to say they were beyond the scope but that they were included in the assessment, even if qualitatively. Why is an

assessment of the effect of N2O on climate of necessity qualitative? Why can’t it be quantitative? What are the key findings of th e qualitative assessments of these endpoints?

There needs to be a section that addresses the key findings, conclusi ons, and implications associated with assessment of uncertainty and variability. What are the largest sources of uncertainty and variability? Given the uncertain ty and variability, what findings can be made with a high degree of conf idence? Which can’t?

CHAPTER 7. My review focused on the section regarding uncertainty.

The section on uncertainty, starting on page 7-22, reads like the t ypical qualitative “laundry list” approach of acknowledging uncerta inties but not characterizing them. This is, frankly, unacceptable.

The National Research Council (NRC, 1994) stated the need to describe uncertainty and to capture variability in risk estimates. Risk ch aracterization became EPA policy in 1995, and the principles of transparency, clarity, consistenc y, and reasonableness are explicated in the 2000 Risk Characterization Handbook (EPA, 2000). Transparency, clarity, consistency, and reasonableness criteria require analysts to descri be and explain the uncertainties, variability, and known data gaps in the risk analysis and impl y that decision makes should explain how they affect resulting decision-making processes (USEPA, 2000, 1992, 1995).

On numerous occasions, the NRC has explicit ly called for the use of probabilistic risk assessment (NRC, 2007a,b). NRC (1992) recomme nded that EPA should thoroughly discuss uncertainty and variability in the context of ecological risk asse ssment (NRC, 1993). NRC (1994), in a major review of risk assessment met hodology, stated that “uncerta inty analysis is the

48only way to combat the ‘false sense of certaint y,’ which is caused by a refusal to acknowledge and [attempt to] quantify the uncertainty in risk pr edictions.” NRC (2002) suggested that EPA’s estimation of health benefits were not wholly credible because EPA failed to deal formally with uncertainties in its analyses.

EPA’s Science Advisory Board has made recommenda tions similar to those of the NRC. Parkin and Morgan (2007) urged the Agency to character ize variability and uncertainty more fully and more systematically and to replace single-point un certainty factors with a set of distributions using probabilistic methods (Parkin and Morgan , 2007). EPA has developed numerous internal handbooks on how to conduct quantitative analysis of uncertainties in various contexts (e.g., EPA, 1995; 1997; 1998; 2000; 2001) EPA (2009) provides a detailed overview of the current use of probabilistic risk analysis within EPA (including 16 detailed case study examples), an

enumeration of the relevance of PRA to d ecision-making, common challenges faced by decision makers, an overview of PRA methodology, a nd recommendations regarding how PRA can support regulatory decision ma king. EPA’s National Exposur e Research Laboratory has recently explored methodological issues for d ealing with uncertainty quantitatively when coupling models for air quality, exposur e, and dose (Ozkaynak et al., 2008).

There are numerous texts on how to conduct anal ysis of uncertainty (e .g., Morgan and Henrion, 1990; Cullen and Frey, 1999; Vose, 2008). The World Health Organization has recently released guidance on qualitative and quantit ative methods for uncertainty analysis in the context of exposure assessment (WHO, 2008). These guidelines have been used by EPA to support uncertainty assessments of exposure and health effects for criteria pol lutants under the National Ambient Air Quality Standards (NAAQS). Hence, th e framework is a general one. In particular, WHO proposed guiding principles that are adapted here:

• Uncertainty analysis should be an integral part of the assessment.

• The objective and level of deta il of the uncertainty analysis should be based on a tiered approach and be consistent with the overall scope and pur pose of the assessment.

• Sources of uncertainty a nd variability should be sy stematically identified

• The presence or absence of moderate to st rong dependencies between inputs is to be discussed and appropriately accounted for.

• Data, expert judgment, or both should be used to inform the specifica tion of uncertainties for scenarios, models, and inputs.

• Sensitivity analysis should be an inte gral component of the assessment.

• Uncertainty analyses should be fully and systematically documented in a transparent manner, including: quantitative aspects pertai ning to data, methods, inputs, models, outputs; sensitivity analysis; qualitative aspects; and interpretation of results

• The results of the assessment including the unc ertainty should be subject to an evaluation process that may include peer review, model comparison, quality assurance, or comparison to relevant data or independent observations.

• Where appropriate to an assessment objective, assessments should be iteratively refined over time to incorporate new data, info rmation and methods in order to reduce uncertainty and improve the ch aracterization of variability.

• Communication of assessment uncertainties to the stakeholders should reflect the

different needs of the audiences in a transparent and understandable manner.

49The decision context of risk assessment includes: (a) how to prioritize the activities of the assessment, and development of data for the a ssessment, in order to characterize and, where possible, reduce uncertainty; (b) how best to mana ge risk. Decision makers often want to know: who is at risk; the magnitude of risk; and tr adeoffs between risk management alternatives. Examples of specific questions that decision-makers may ask include (Bloom et al., 1993; Krupnick et al., 2006):

• How representative is the estimate, (e.g., what is the variability around an estimate)?

• What are the major gaps in knowledge, and wh at are the major assumptions used in the assessment? How reasonable are the assumptions?

• Would additional data collecti on and research likely lead to a different decision? How long will it take to collect the informati on, how much would it cost, and would the resulting decision be significantly different?

Generally, from a scientific perspective, it is preferred to quantify uncertainties wherever possible. As WHO (200 8) explains (p. 31):

Determination of an appropriate level of sophistication required from a particular uncertainty analysis depends on the intended purpose and scope of a given assessment. Most often tiered assessm ents are explicitly incorporated within regulatory and environmental risk manageme nt decision strategies. The level of detail in the quantificatio n of assessment uncertainties, however, should match the degree of refinement in the underl ying exposure or risk analysis. Where appropriate to an assessment objecti ve, exposure assessments should be iteratively refined over time to incor porate new data, information and methods to reduce uncertainty and improve the charac terization of variability. Lowest-tier analyses are often performed in screen ing-level regulatory and preliminary research applications. Intermediate tie r analyses are often considered during regulatory evaluations when screening-leve l analysis either indicates a level of potential concern or is not suited for th e case at hand. The highest tier analyses are often performed in response to regul atory compliance need s or for informing risk management decisions on suitable alternatives or trade-offs.

Hence, the Tier 1 (Qualitative) a pproach is not a default. It should be a justified choice that is consistent with the purpose and scope of the assessment.

WHO specifies a structured approach to qualita tive assessment of uncertainty that includes 1) qualitatively evaluate the level of un certainty of each specified source; 2) define the major sources of uncertainty; 3) qualitatively evaluate the appraisal of the knowledge base of each major source; 4) determine the controversial sources of uncertainty; 5) qualitatively evaluate the subj ectivity of choices of each controversial source; and 6) reiterate this methodology until th e output satisfies stakeholders

Somewhat amazingly, the document seems to ignor e an effort undertaken in the mid 1990s to create a quantitative framework for characterizing variability a nd uncertainty associated with acid deposition, which is the Tracking and Analysis Framework (TAF) . The details of this

50framework, and the associated software, are available at http://www.lumina.com/taf/ . TAF represents a systematic effort sponsored by th e National Acid Precipita tion Assessment Program (NAPAP) to develop an “integrated assessment” model that represents emissions, transport and fate, deposition, and adverse effects to terrestrial and aquatic systems, and for which variability and uncertainty were quantified. The philosophy of TAF was to develop a reduced form model

that was tractable and that c ould be used for repetitive anal ysis, such as “what-if” policy scenarios, sensitivity analysis, and assessment of the effect of variability and uncertainty on estimated end points. This approach is a prac tical one, and should serve as an illustrative example of how variability and uncertainty can be quantified in an assessme nt such as needed in

the REA. EPA should review TAF and either use this framework, or update it and use it.

A laundry list of uncertainties, as given in Sectio n 7.2 is not useful in in terpreting the assessment results unless it is conducted in a systematic mann er that puts priority on quantification and that leads to comparative assessments of which source s of uncertainty are important with respect to well defined endpoints. At a mini mum, there should be summary ta bles that categorize sources of uncertainty with respect to a well defined end point. What are the implications of uncertainty for interpretation of the assessment results?

Why is there a benefits assessment component to Chapter 7? As noted in comments regarding the executive summary, costs cannot be consider ed when setting the NAAQS. What is the purpose of providing monetized assessment of be nefits in the context of this REA?

References Cited and Bibliography (not all references listed below are cited):

Bloom, D.L., D.M. Byrne, and J.M. Andr eson. 1993. Communicating Ri sk to Senior EPA Policy-Makers: A Focus Group Study. Prepared by Bloom Research and the Office of Air Quality Planning and Standards. U.S. Environmental Protection Agency, Research Triangle Park, NC.

Bogen, K., A. Cullen, H.C. Frey, and P. Price, “Probabilistic Exposure Analysis for Chemical Risk Characterization,” Toxicological Sc iences, submitted August 20, 2008, revised and resubmitted Jan 2009, accepted February 8, 2009. Available on-line at http://toxsci.oxfordjournals .org/cgi/reprint/kfp036?ijkey=s IBW9Sm3pvbPQnm&keytype=ref

Cullen, A.C., and H.C. Frey. 1999. Probabilistic Exposure Assessment: A Handbook for Dealing with Variability and Uncerta inty in Models and Inputs. Plenum Press, New York.

EPA. 1997a. Guiding Principles for Monte Ca rlo Analysis. EPA/630/R- 97/001, Risk Assessment

Forum. U.S. Environmental Pr otection Agency, Washington.

EPA. 1998. Guidance for Submission of Probabilis tic Human Health Exposure Assessments to the Office of Pesticide Programs. Office of Pes ticide Programs. U.S. Environmental Protection Agency, Draft, 11/4/98, http://www.epa .gov/fedrgstr/EPA-PEST/1998/November/Day05/6021.pdf (accessed August 8, 2007).

EPA. 2000. EPA Science Policy Council Handbook, Risk Characterization. EPA 100-B-00-002.

51EPA. 2001. Risk Assessment Guidance for Superfund: Volume III - Part A, Process for Conducting Probabilistic Risk Assessment. EPA 540-R-02-002, Office of Emergency and Remedial Response, U.S. Environmen tal Protection Agency, Washington, http://www.epa.gov/oswer/riskassessme nt/rags3adt/ (accessed August 8, 2007).

EPA. 2007. Letter from M.G. Morgan and R.T. Park in (SAB) to S. Johnson (EPA), February 28,

2007. EPA-SAB-07-003.

EPA, 2009, Using Probabilistic Methods to Enhan ce the Role of Risk Analysis in DecisionMaking, External Review Draft, Prepared by Risk Assessment Forum PRA Technical Panel Working Groups, U.S. Environmental protection Agency, Washington, DC.

Evans, J.S., J.D. Graham, G.M. Gray, and R. L. Sielken. 1994. A Distributional Approach to Characterizing Low-Dose Cancer Risk. Risk Analysis, 14(1):25-34.

Frey, H.C., and S.R. Patil. 2002. Identification and Review of Sensitivity Analysis Methods. Risk Analysis, 22(3):553-578.

Hattis, D.B., and D.E. Burmaster. 1994. “Asse ssment of Variability and Uncertainty

Distributions for Practical Risk Anal yses,” Risk Analysis, 14(5):713-730.

Hoeting, J.A.; D. Madigan, A.E. Raftery, and C.T. Volinsky. 1999. Bayesian Model Averaging:

A Tutorial. Statistical Science, 14(4):382-417.

IEC. 2006. Expanded Expert Judgment Assessment of the Concentration-Response Relationship Between PM2.5 Exposure and Mortality, Final Re port. Prepared by Industrial Economics, Incorporated for Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, http://www.epa.gov/ttn/ecas/regdata /Uncertainty/pm_ee_report.pdf.

Krupnick, A., R. Morgenstern, M. Batz, P. Nelson, D. Burtraw, J. Shih, and M. McWilliams. 2006. Not a Sure Thing: Making Regulatory C hoices Under Uncertainty. Resources for the Future, Washington.

Mokhtari, A., H.C. Frey, and J. Zheng. 2006. Evaluation and Recommendation of Sensitivity Analysis Methods for Application to Stochast ic Human Exposure and Dose Simulation (SHEDS) Models. Journal of Exposure Science and Environmental Epidemiology, 16(6):491-506.

Morgan, M.G., and M. Henrion. 1990. Uncertainty : A Guide to Dealing with Uncertainty in Quantitative Risk and Policy Analysis. Cambridge University Press, New York.

NRC. 1983. Risk Assessment in the Federal Government: Managing the Process. Committee on

the Institutional Means for Assessment of Risks to Public Health, National Academy Press, Washington.

52NRC. 1994. Science and Judgment in Risk Asse ssment. National Research Council, National Academy Press, Washington.

NRC. 2002. Estimating the Public Health Bene fits of Proposed Air Pollution Regulations. National Research Council, Nati onal Academy Press, Washington.

NRC. 2007b. Models in Environmental Regul atory Decision Making. National Research Council, National Academy Press, Washington.

OSTP/OMB. 2007. Memorandum (M-07-24) for the Heads of Executive Departments and Agencies; from Susan E. Dudley, Administrator, Office of Information and Regulatory Affairs, Office of Management and Budget, to Sharon L. Hays, Associate Director and Deputy Director for Science, Office of Science and Technology Po licy: Updated Principles for Risk Analysis, September 19, 2007.

Ozkaynak, H., H.C. Frey, J. Burke, and R.W. Pi nder, “Analysis of coupled model uncertainties in source to dose modeling of human exposures to ambient air pollution: a PM2.5 case-study,” Atmospheric Environment (accepted December 4, 2008).

Parkin, R.T., and M.G. Morgan. 2007. Consulta tion on Enhancing Risk Assessment Practices and Updating EPA’s Exposure Guidelines. EP A-SAB-07-003, Science Advisory Board, U.S. Environmental Protection Agency, Washington.

PCRARM. 1997. Framework for Environmental Health Risk Management Final Report, Volume 1. Presidential/Congressional Commission on Risk Assessment and Risk Management, http://www.riskworld.com/nreports/1997/risk-rpt/pdf /EPAJAN.PDF.

Pearl, J. 2000. Causality: models, Reasoning, and Inference. Cambridge University Press, New

York.

RFF (2007), “Uncertainty Modeling in Dose Respons e: Dealing with Simple Bioassay Data, and Where Do We Go from Here?,” Workshop, Res ources for the Future, Washington, DC, October 22 - 23, 2007. ( http://www.rff.org/Events/Pages /Cooke-Uncertainty-Workshop.aspx , accessed 6/27/09).

Royall, R.M. 1997. Statistical Evidence: A Likelihood Paradigm. Chapman & Hall, London.

Saltelli A, S. Tarantola, F. Campolongo, et al. 2 004. Sensitivity Analysis in Practice. John Wiley & Sons, New York.

Small, M.J. (2008) Methods for Assessing Un certainty in Fundamental Assumptions and

Associated Models for Cancer Risk Asse ssment Risk Analysis, Vol. 28, No. 5, 2008 DOI: 10.1111/j.1539-6924.2008.01134.x

53Stahl, C.H., and A.J. Cimorelli. 2005. How Much Uncertainty Is Too Much and How Do We Know? A Case Example of the Assessment of Oz one Monitor Network Options. Risk Analysis, Vol. 25, No. 5, pp. 1109-1120, October 2005.

Vose, D. (2008), Risk Analysis: A Quantitati ve Guide, Third Edition, John Wiley and Sons, West Sussex, England.

World Health Organisation (2008) , Harmonization Project Document No. 6, Part 1: Guidance Document on Characterizing and Communicatin g Uncertainty in Exposure Assessment, International Program on Chemical Safety, World Health Organization, and Co-sponsored by International Labour Organization, and the Un ited Nations Environmental Programme, WHO Geneva, Switzerland, 2008. (http://www.who.int/ipcs/publications/methods/harmonization/exposure_assessment.pdf)

54

### Dr. Paul J. Hanson

Final Comments on the Second Draft

Risk and Exposure Assessment (REA) for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur

Submitted 29 June 2009

General Comments:

I found the second draft REA to be improved over the first draft. The document is largely successful in defining air quality indicators and ec ological indicators that might be used in the context of evaluating exposure metrics for both aqua tic and terrestrial ecosystems in the context of acidification and nutrient enrichment for exposures to SO

x and both oxidizes and reduces forms of nitrogen.

In some cases data and justifica tion are provided for the levels of the ecological indicators that might be considered in evaluating ecological res ponses, but for the most part levels, averaging times, and forms are not discussed.

While the document makes clear statements about the nature of exposures to US land surfaces and target case study ecosystems, it provides very little (if any) useful characterization of the welfare risks involved in allowing current pollutant levels to con tinue. Case studies for nitrogen deficient ecosystems were not included in the analysis.

The following specific comments and minor editor ial suggestions are provided for discussion and consideration by EPA staff.

Front Matter – Key Terms

Page xxi: Add a definition for ASSETS

Page xxii: The definition listed for Determined Future Outlook doesn’t stand on its own. You might also reference page numbers in the body of the text for all of the definitions related to

ASSETS.

Page xxiii: Prior comments on the definition of ecological dose were not addressed. Why is this

definition limited to microbes?

Page xxvi: The definition of a semi-arid region was not changed from the first draft. The rainfall amounts overlap with those for Arid Regions, which seems inappropriate.

Executive Summary:

55Page ES-2 Line 12: Change “These effects include” to ‘When fully developed acidification

effects include...’

Page ES-2 Line 22: Change to “ a well-documented phenomenon indicating...”

Page ES-3 Line 6: Change “the” to ‘that’.

Table ES-7 under Terrestrial acidif ication: “Tree Health” is used as an undefined and unclear term. Use other words or phrases to describe wh at is really intended (e.g., changes in growth).

Figure ES-3 and elsewhere throughout the REA: Although some process was conducted to limit

the number of case studies for inclusion within the REA that process is not well described. Why

were these case studies chosen from an original longer list of possibilities? Should these be

characterized as worst-case scenarios? Should th e reader assume that these are the only areas of the US for concern with respect to aci dification or nutrient enrichment?

Figure ES-4 and elsewhere throughout the REA: “Change in ecosyst em structure and process” is used to describe an ecological benefit/Welfare effect. How do (or can) we distinguish changes occurring through natural processes from changes from the effects of acidification and nutrient

enrichment? The document should include some discussion about ecological changes in the context of ‘background temporal changes” vs . those driven by pollutant exposure.

Pages ES-11 to ES-14 are quite good, but I noted one issue. The term NOy is used in the caption for figure ES-5, but it hasn’t been used much in the text. Is it intended to be a placeholder for

total reactive forms of N?

Page ES-17 Line 18: In this paragraph sugar ma ple and red spruce are characterized as being the “most sensitive” to acidification with the implication that all other tree species are less sensitive. Is this really true? Perhaps ot her tree species simply haven’t been evaluated in enough detail to appropriately characterize their sensitivity. Please reword the beginning of the paragraph to indicate that these species are being highlighted because sufficient data are available to evaluate their response to acidification.

Table ES-2: Does the concept of a policy relevant backgrou nd Bc/Al ratio belong in this

discussion?

Page ES-18 Lines 4 through 16: These paragraphs provide a description of valued characteristics of northeastern forests, but they do not provide an indication of th e fraction of these welfare

metrics that are at risk under acidification

.

General comment: The previous statement is a recurri ng theme throughout the REA (especially in Chapters 4, 5, and 6). Ecologi cal benefits or measurable welf are metrics are listed for key ecosystems or case study areas with the presumpti on that all are subject to loss or failure with

acidification or nutrient enrichme nt. In most cases the text (a nd presumably the available data) do not provide sufficient information to fully characterize what fraction of a measurable

56ecological endpoint is likely to be subject to loss under pollutant e xposure. I don’t believe that it is appropriate for the reader to conclude that 100 percent of a given welfare metric is likely to be

lost.

Page ES-21 Line 7: Don’t use the term ecologi cal health without an adequate definition.

Page ES-21 Line 12: Can you provide the depositi on rate needed to drive mortality? Is it a higher level of deposition or might it alternatively be simply l ong term cumulative exposure to a lower deposition level?

Page ES-21 Lines 20 and 21: Pl ease provide a range to clarify what is meant by a low C: N

ratio.

Page ES-22 Lines 19 to 21: Su rface area increases of root syst ems driven by mycorrhizae are most often associated with the morphologica l changes driven by ectomycorrhizae, but the authors are using AM as the example. Are th ey referring to fungal f ilament exploitation beyond the root systems of plants?

ES-23 Line 13: Are fishing a nd hunting really a big land use ac tivity for the California Coastal Sage area?

Chapter 1:

Page 1-12 Line 19: Remove the word “not”. It appears to generate a double negative that changes the sentence meaning.

Page 1-13: I suggest modifying the sentence by adding the underlined text as follows: “Both are

essential elements for vegetation growth and development , and..

Page 1-14: Should “main source” be ch anged to ‘main anthropogenic source’?

Page 1-17: These are all good po licy relevant questions. Unfo rtunately, a number are not

addressed within the REA.

Chapter 2:

Page 2-1: This section starts out with a great point – “response to pollutant exposures can vary greatly between ecosystems”. Unfortunately, th e REA doesn’t fully address how to handle extrapolation of responses in case st udy areas to the balance of the US.

Page 2-1 Line 19: I would remove the word “and” in this line.

Figure 2.4-1: Please add more e xplanations to the figure caption. What do the arrow widths imply?

57General Comment: How do we distinguish ecological e ffects of acidification and nutrient enrichment from other co-occurring and likely highly correlated pollutant exposures (e.g., ozone)? This issue should be fully vetted in the document.

Chapter 3:

Page 3-2 Line 18: Add the phrase ‘o ther forms of reactive N’ after NOx.

Figure 3.2-1: Increase the font size.

Figure 3.2-4: Increase the font size.

Figure 3.2-6: The figure caption uses NOy, but th e related text on the previous page (3-11) exclusively discusses NOx. The authors shoul d be consistent and define and use NOy appropriately or not at all.

Figure 3.2-10: The color scale in this figure was in appropriately changed from the scales used in the two prior figures. This isn’t a big deal, but by changing the color scale a direct visual comparison isn’t really possible.

Section 3.2.5: Should the concept of policy rele vant background loadings or deposition levels be

introduced and used?

Temporal trend data for atmospheric deposition of N and S forms through time is presented in Appendix 2. I would like to see this material pr esented visually in Chapter 3 to emphasize the history of control successes on SO

x and NO

x .

Chapter 4:

Section 4.3.1.2 This section is a good example of how an eco logical indicator can be developed for the characterization of a response to acidification. Unfortunately, the other metrics described in the

REA are not this clear.

Page 4-43: Is this a true general statement or should it apply only to sugar maple on susceptible

sites?

Page 4-47 Lines 9 to 12: This sentence underscores a continuing theme. It is difficult to isolate and estimate the proportion of a given measure of welfare benefit attributable to acidification and nutrient enrichment. See also Page 4-48 lines 4 to 6. Given this reality, how do we proceed in the development of standards to protect welfare issues without a capacity to judge success or failure in the context of the target pollutants (or combined pollutants)?

Chapter 5:

Page 5-1 Lines 6 to 12: This sentence s hould also appear in the executive summary.

58Page 5-6 line 6: Spell out and define NEEA.

Page 5-44 and Section 5.3.1.1: This section is very useful and help ful to the reader. I would add

sentences to further describe w hy this discussion is limited to a couple of southern California case studies. Are other ecosystems in the US not impacted? Is there insufficient data to evaluate impacts in other ecosystems? For those that don’t live in the region disc ussed, tell them why or how these results have meaning to broa der pollutant exposures across the US.

Page 5-46 Lines 1 to 10: Staff should remind the reader that one size doesn’t fit all at this point in the discussion. These data are quite good for li chens, but they may not have quantitative value for evaluating the response for other species or species in other regions of the US.

Section 5.3.1.3: How is the reader supposed to interpret this information? Wh at fraction of these services is at risk? Much of this information seems tangential.

Page 5-55 line 1: This bullet statement was discu ssing Eastern United States ecosystems. Do we

have semi-arid lands in the eastern US?

Page 5-55 Lines 9 to 19: These statements seem to undermine the discussion. If we don’t have the data, why are we having the extended discussion?

Figure 5.3-5: A solid connection of this graphic to N deposition isn’t made. What fraction of fuel loadings leading to fire danger and frequency can be attributed to pollutant exposure as apposed to natural secondary succession?

Page 5-66 lines 21 and 22: This is a key point.

Page 5-66 line 24: Replace “tree health” with te rms that describe what you really mean.

Chapter 6:

Page 6-13 Lines 28 and 29: This statement is written as though it would apply equally to all ecosystems. I’m not convinced that this would be true for all systems at similar time frames.

Page 6-23 Lines 20 to 22: This is an important statement. I’m glad to see it included here.

Chapter 7:

Page 7-10 Line 17: Change “most” to ‘known to be’.

Page 7-14 line 27: Add the level of de position needed to drive mortality.

Page 7-15 lines 17 to 26: Why the focus on these specific metrics for CSS and MCF? Are we to

conclude that these are the metrics that are the best fit for all US ecosystems? Where is the discussion about the metrics needed for the development of a US national standard? Is a

59standard likely to be based on most sensitive systems in the west and then applied to all ecosystems?

Page 7-18 Lines 9 to 30: What is the point of this information? How is it be used? What

fraction of each of welfare metric is at risk unde r terrestrial acidificatio n? I would remove the bullets on this page and also on page 7-17.

Page 7-19 lines 1 to 3: Add some specifics.

Page 7-19 line 29: Should oconic be iconic?

Page 7-22 lines 28 to 30: Again. This is a very key conclusion. How do we use this conclusion in the extrapolati on of case study data?

60

### Dr. Rudolf B. Husar

SOx and NOx Risk and Exposure Assessment (REA) Second Draft

EPA is to be commended for the significant improvements of REA, Second Draft. EPA has responded effectively to many of the comments from CASAC. In particular , the inclusion of a section on the CMAQ model descri ption and evaluation is a signi ficant addition (Appendix 1-1), since so many of the key exposure estimates and conclusions depend on CMAQ.



### Appendix 1: Description of CMAQ Applications and Model Performance

Evaluation

Appendix 1-4, line 5.

‘The purpose of these evaluations is to provi de information on how well model predictions match the observed data on the regional basis’. Evidently, ‘regional’ in the context of the REA means the entire Eastern US and the entire Western US. Since the SOx-NOx pattern varies considerably within each model domain, this larg e scale aggregation makes it difficult to assess the regional model performance, ie. NE, SE, NW, etc.

The criteria for ‘acceptability’ of model performance based on comparability with photochemical model performances is somewhat dubious. It is my understa nding that CMAQ ozone simulations have not improved significantly for the past decade. Hence, photochemical model performance is a rather poor metric for this REA. A more defendabl e criterion for the CMAQ model evaluation may be the performance on de position estimates, particularly of nitrogen compounds. The CMAQ model performa nce for simulating nitrogen (NO 3 +NH 4 ) deposition is modest. Nevertheless, the REA (A ppendix 1-5, Line 2) states that ‘The model performance results give us confidence that our applications provide a scientifically credible approach for the purposes of this assessment’. EPA’s confidence in the nitrogen deposition pattern is not shared by this reviewer.



### Chapter 6 Additional Effects

6.1 Visibility, Climate and Materials

According to the charge sheet, this chapter cont ains results from ‘some qualitative analyses for the additional effects, including visibility, climate and materials...’ Evidently, the section on visibility, climate, and materials was include d at the recommendation of several committee members. However, this Section 6.1 does not reflect the result of any analys es, but merely points to PM Criteria Document as the source where aerosol effects on visibility, climate and materials

are treated in detail.

Since EPA has not presented a concise summary of the welfare effects on visibility, climate and materials, I would recommend eliminating this section 6.1 and replacing it with a simple

disclaimer such as the sent ence in Page 6-2, Line 2.

61Certainly, the current phrasing does not give justi ce to the role of sulfates and nitrates in visibility and climate. For example, (Page 6.1, Line 16) the REA states that impairment of visibility ‘can result from atmospheric particul ate matter (PM), which is composed in part of sulfate and nitrate..’. In reality, even sub-microgram concentration of ambient SO 4 /NO 3 does result in impaired visibility.

Also, the statement that ‘theoretical and empirical findings suggest that su lfates often dominate the fine particle mass and hence the impairment of visibility’ is a dubious formulation of the role of sulfates. The findings on the optic al effects of sulfates is not ju st suggestive, but it is based on firm, direct measurements of both sulf ate concentration a nd light scattering.

6.2 Sulfur and Mercury Methylation. This section is relevant to the REA. It also prope rly illustrates the interaction of sulfates with the chemistry of other compounds.

6.3 Nitrous Oxide

The discussion of nitrous oxide is re levant to the climate effects of NO

x . This section appropriately describes the role of nitrous oxide. Unfortunately, the climate effects of sulfate/nitrate aerosols has fallen through the cracks. At a minimum, the recognition of those effects as part of the welfare effects of SO

x /NO

x should be stated along w ith the pointer to the

Climate Section of the PM Criteria Document.

62

### Dr. Dale W. Johnson

Review of “The Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitr ogen and Oxides of Sulfur, Second Draft”

Amended 28 July 2009

Case Study Questions to the panel:

1. Are the uncertainties appropriately charac terized across the case studies? Is there adequate information to allow us to weigh the relative strengths of each case study to inform the standard setting procedure?

2. In using the Risk and Exposure Assessment to inform the pol icy assessment, we plan to focus on aquatic acidification as the basis for an alternative multi-pollutant secondary

standard as this is the area where we have the most confidence in our ability to characterize adverse effects. Does the panel agree with this approach?

My answers to these two questions are as fo llows, with more detailed reviews below:

1. No, the uncertainties are not appropriately characterized a nd there it not, in my opinion, adequate information to inform standard se tting procedures. For the aquatic case studies,

there is confusion about how anions and cations interact and considerable uncertainty as to how reduced (or increased) mineral acid anions like SO 4 and NO3 affect base cation concentrations directly and immediately through the necessity for charge balance as opposed to much longer term change cha nges in soils. The document appears to implicitly assume the latter, but without soil data to verify it, we cannot know whether soils have in fact changed at all. For the terrestrial case st udies, I believe that there are significant and erroneous assumptions in the si mple model used that at least should be acknowledged and discussed before any conc lusions are drawn. Also, the case for red spruce decline due to acidification is not as clear as the document would lead us to

believe.

2. I think this approach is OK as a focus , but I do not believe that it should occur to the

exclusion of all other effects. I assume that this will not be the case.

There are three chapters that deal with case stud ies: 3, 4, and 5. These cas e studies all appear to focus on sites either with high levels of deposition of very high sensitivity to increased deposition. This is logical, given that the focus of this report is on poten tially negative effects, but care must be taken not to extrapolate the results from these case studies to regional or national scales without first accounting for th e many other sites that are not sensitive.

Chapter 3 deals with deposition rates and characteristics of the cas e study areas, and I really have no comment or issue with anything there.

Aquatic Acidification Case Studies

63Chapter 4 deals acidificati on, 4.2 deals with aquatic sens itivity and 4.2.3 focuses on the

Adirondack and Shenandoah sites for case studi es. Here, I would comment on the section on page 4-18 that it should include a more detailed discussion of the two possible reasons for the

observed decline in streamwater base cati on concentrations: 1) the reduction in the

concentrations of mineral acid an ions (mainly sulfate), which n ecessitate a reduction in cations, including base cations, in order to maintain charge balance, and 2) soil acidification. This relates to my earlier review comments as to the critic al importance of considering capacity effects (change in the soil, which take a long time and ar e not easily reversed) a nd intensity (change in solution, which can take place almost instantly an d are very easily reversed). The statement on lines 1-13, page 4-18 implicitly assumes that the changes are of the capacity nature, and ignore the intensity component, which in fact must play a role. Indeed, without so il data, it is impossible to know if capacity changes played any role at all or whether “”b ase cations buffer the inputs of NO3- and SO42-, which will likely limit future r ecovery of ANC concentrations.” This is a somewhat confused (cations do not buffer anions) and very incomplete statement, because if the

base cation decline is due to changes in SO4 and NO3 only, complete ANC recovery can be expected if the levels of t hose anions are brought back to pre-industrial levels somehow.

I have significant problems with the premises upon which the equations and associated text on page 4-37 are based. First of all, the assumpti on that the preindustria l rates of base cation leaching are sustainable is completely without foundation; were this the case, we would never find acidized soils in nature (without pollution) , and we certainly do find them. The natural genesis of soils with more rainfa ll than evapotrans piration is to acidify; th e question here is to what extent this process has been sped up by pollutant inputs. Sec ondly, I think that the assumption that nutrient cycling effects by plants can be ignore d is deeply flawed, as the literature is full of examples where tree uptake of base cations well exceed s the removal of base cations by leaching. Furthermore, it appears that N cycling is NOT ignore d, so this is only a partially imposed and inconsistent assumption.

Specific Comments:

p. 4-25: The legend on Figure 4.2-14 is way too small p. 4-36, lines 10-12: This is true only in acid soil s. In basic soils, inputs of SO4 and NO3 will

have little or no effect on the “acid balance of headwater lake s”. Anions affect total cation concentration by simple charge balance requirements, but they do not prescribe the type of

cation.

Terrestrial Acidification Case Studies

Before specifically going into my assignme nt, I must comment on Section 4.3.1.1, Ecological

Indicators. Here for the first time I see Bc/Al ra tios, where Bc includes Ca, Mg, and K. This is only logical if the units are in mole s or micromoles of charge (μmol

c ), yet no units are given. What are the units? This appears to be based on a report by Sverdrup and Warfvinge published in 1993, but I was unable to get the reference and do not know what it is based on. The more commonly used indicator is that Ca/Al mo lar ratio of Cronan and Grigal (Cronan

, C.S. and D.F. Grigal

. 1995. Use of Ca/ Al ratios as indicators of stress in forest ecosystems. Journal of Environmental Quality 24: 209-226.

64Also, on page 4-44, it is clearly st ated that acidification negatively affects red spruce – I admit to not being up to speed on the latest developm ents, but I do recall that Art Johnson found that climate change, not acid rain, was responsible fo r the red spruce decline in New England. I think

this treatment is a bit one side d and the situation is not that clear. (Johnson, A.H., E.R. Cook, and T.G. Siccama. 1988. Climate and red spruce growth and decline in the northern Appalachians.

Proc. NatI. Acad. Sci. USA, Vol. 85, pp. 5369-5373.)

The actual case studies for HBEF, which assumes that net forest increment is zero (I doubt that very much, even if the site has not been recently harv ested and would ask for some documentation of that) and the KEF sites, and builds the analysis on the SMB model which has numerous assumptions and the unitle ss Bc/Al ratio to conclude that “These results suggest that the health of red spruce at HBEF and sugar maple at KEF may have been compromised by the acidifying nitrogen and sulfur deposition receiv ed in 2002.” I realize that all models are imperfect and yet there may be good reasons to run them anyway, but this seem grossly overstated and I would add many many caveats to this section.

Nutrient Enrichment Questions for the Panel:

1. Section 5.2 and Appendix 6 describe the analyses used to evaluate th e effect of aquatic nutrient enrichment. The analysis uses the SPARROW model on one stream reach (Potomac River and Neuse River) to determine the impact of atmosphe ric total nitrogen deposition on the eutrophication index for th e estuary. Does the Panel think that the model is adequately describe d and appropriately applied?

2. Section 5.3 and Appendix 7 describe the analyses used to evaluate the ef fect of terrestrial nutrient enrichment. This qualitative analysis describes the impacts due to nitrogen deposition on the Coastal Sage Scrub commun ity of California and mixed conifer forests in the San Bernardino and Sierra Nevada Mountains and larger areas where possible. In addition, the effects on nitrogen deposition in the Rocky Mountain National Park supplemental case study location are summari zed. How would the Panel apply threshold values presented in this case study to allow for broader geographic application that accounts for regional variabili ty? Have the associated un certainties been adequately
characterized?

My answers to these two questions are as fo llows, with more detailed reviews below:

1. I cannot intelligently answer th is question. I am not familiar with the SPARROW model and would not be confident in commenting on it without considerably more information as to its structure and premises – more than could or should be included in a document such as this. I will pass on this one to othe r panelists who probably have more knowledge

on the matter than I do.

2. I would not apply the threshold values pr esented in this case study to a broader geographic region because these case studies, while appropriate for negative effects of pollutant inputs either at hi gh levels or on sensitive sites, do not in any way address the larger majority of ecosystems which are either resistant to negative effects or in fact might benefit from the additional nitrogen inputs. This is in essence a philosophical issue: should standards be set on the basis of the most sensitive or highly impacted systems or

65should they be based on regional effects? Since the question asked about regional application, I am assuming the la tter and thus my answer is th at these case studies are in no way regionally applicable. The uncertainties with this are considerable and not well

characterized.

First of all, this section is really mislabeled: it really focuses on nutrient excess, not enrichment and I suggest Nutrient Excess as the title. Nutrient enrichment to terrestrial people often implies something good, and that certainly is not the focus of this section.

Aquatic Nutrient Enrichment

I am not familiar enough with either the SPARROW model or the sites to intelligently comment

on that section.

Terrestrial Nutrient Enrichment

The case studies for nutrient excess are good ones, with excellent research programs documenting negative effects of high levels of N deposition. As in my previous reviews, however, I must again go to the mantra of taking a balanced approach to this issue and if this

section is still to be entitled Nutrient Enrich ment, some mention of the possible benefit to

commercial forests in the Pacific Northwest and Southeast should be mentioned. I fully recognize by now how loathe the authors are to do this, but I will continue to make this comment as long as I am on this panel as I think it is import ant and the omission of it will be greatly regretted later. (for example, see Chappell, H.N., D. W. Cole, S. P. Gessel and R. B. Walker.

1991. Forest fertilization research and practice in the Pacific Northwest. Nutrient Cycling in Agroecosystems . 27: 1385-1314; see also this link for a lay article on fer tilization in southeastern pine forests: http://www.ipni.net/ppiweb/bcrops.nsf /$webindex/2476B56D4FDD9EB0852571B1006A6F2E/$ file/06-3p12.pdf )

66Additional Effects Ques tions for the Panel

1. In this chapter, we have presented results from some qualitative analyses for additional effects
including visibility, climate and materials, the interactions between sulfur and methylmercury
production, nitrous oxide effects on climate, nitrogen addition effects on primary productivity

and biogenic greenhouse gas fluxes, and phytotoxic effects on plants. Are these effects
sufficiently addressed in light of the focus of this review on the other targeted effects in terms

of the available data to analyze them?

My answers to this questions are as follo ws, with more detailed reviews below:

1. The segments on visibility, climate and materials, the interactions between sulfur and
methylmercury production, nitrous oxide effects on climate seem to be adequately addressed,
but, for the reasons given in detail below, the segment on nitrogen effects on primary productivity still has some serious problems and issues, as detailed below.

I have serious problems with the assessment of nitrogen effects on primar y productivity in this section. First of all, the authors appear to go through significant intellect ual gymnastics in order to either ignore or disprove the concept th at greater primary production leads to more C sequestration. There may be cases where prim ary production does not lead to increased C sequestration, and the best example of this is th e forest floor, which decreases in mass as mean annual temperature increases desp ite the increases in primary pr oductivity. However, given that organic C for sequestration is produced during prim ary production, to cling to the notion that the two are not related defies logic.

Furthermore, the statements regard ing nitrogen in this section ar e largely untrue and often given without citation, and fly in the f ace of published literature. Examples of this is are on page 6-13, lines 15-17 which states that gr owth increases due to N inputs are offset by increases in soil respiration and on page 6-14, lines 27-29 where it states that “increased leaf N concentration under conditions of elevated nitrogen depositi on may result in higher carbon loss by increasing both autotrophic and hetero trophic respiration”. This is simply not true: most studies show that N

fertilization causes decreases in soil respiration (see for exam ple Tyree, Michael C.; Seiler, John R.; Fox, Thomas R. The Effects of Fertili zation on Soil Respiration in 2-Year-Old Pinus taeda L.

Clones Forest Science , Volume 54, Number 1, February 2008 , pp. 21-30; see also Olsson, P., S. Linder, R. Giesler, and P. Högberg. 2005. Fertiliz ation of boreal forest reduces both autotrophic and heterotrophic soil respir ation. Global Change Biology 11 1745 – 1753; and Google “Fertilization effects on soil respir ation” for many other references )

On page 6-14, lines 23-31, the authors state that higher nitrogen concentration in organic matter stimulates decomposition; while this is sometimes true in the early stag es of decomposition, the literature is clear on the long-term effects: greater N concentration increases the long-term storage of stable organic matter.

See:

B. Berg and C. Mcclaugherty (2003). Plant Litter–Decomposition, Humus Formation, Carbon Sequestration. Springer Verlag, 286 pp., 76 figs.

67Sarah E. Hobbie (2008) NI TROGEN EFFECTS ON DECOMPOSITION: A FIVE-YEAR

EXPERIMENT IN EIGHT TEMPERATE SITE S. Ecology: Vol. 89, No. 9, pp. 2633-2644

Berg, B., Ekbohm, G., Johansson, M.-B., McCla ugherty, C., Rutigliano, F., and Virzo De Santo, A. 1996. Maximum decomposition limits of forest litter types: a synthesis. Can. J. Bot. 74 : 659–

672.

Berg, B., McClaugherty, C., Virzo De Santo, A., and Johnson, D. 2001. Humus buildup in boreal

forests: effects of litterfall and its N concentration. Can. J. For. Res. 31 : 988–998.

For the reasons given above, I beli eve this section to be seriousl y biased and flawed. I believe

that the authors need to better research the literature and present a more balance and accurate assessment of the effects of N on ecosystem C sequestration. Amendments, 28 July 2009

Executive Summary

p. ES-15, lines 5-7 (only odd line numbers are shown?): The firs t sentence on this page is incomplete and misleading – if the mere deposi tion of Sox, NOx and NHx leads to exposure to acidification, then is the goal to have no deposition at all? If s o, many ecosystems would have no N or S in them at all, as atmospheric deposition is the only source (there are no primary soil minerals containing N and few c ontaining S). You should add the word “excessive” in front of “Deposition”.

p. ES-15, lines 7-12: The next sentence may well be true, but I am unsure if the ISA documented the fact that N and S deposition has increased soil N and S contents. And if so, there is nothing really harmful about this (as I think the authors would imply) . All those follow on statements about leaching etc. refer only to specific cases where N and S deposition are excessive; they are NOT the general rule.

p. ES-17, lines10-11: Again, it makes no sense to us e Bc/Al ratio to repres ent Ca/Al, when in

fact Bc includes Ca.

p. ES-18, line 4: Now we are using Al/Ca? Be consistent.

p. ES-18, lines 19-20: The term “nutrient enrichme nt” does not imply nutrien t imbalance at all, it implies exactly the opposite and will certainly confuse people. I suggest that you use the term

“nutrient excess”

p. ES-19, lines 19-20: I thought that the coastal eutrophication problem was driven primarily by

animal waste?

p. ES-21, lines 4-6: Now this is a good way to st ate the issue! It clearl y states that excess nitrogen causes these problems and it certainly do es! The rest of the ES and the entire document

should reflect this – it is not a matter of n itrogen being “bad” , it is a matter of how much nitrogen is being applied.

68p. ES-21, line 19: Again, good wording: ove renrichment is exactly the issue!

p. ES-24, lines 9-11: I do not sh are this confidence aside from the case study areas where N deposition is very high and ecosystems are sensitive. The Pregitzer paper that I asked to be

reviewed in earlier comments s hows the opposite effect. Again, I se ek balance here. Not all areas

are sensitive to current levels of N deposition – in fact, very few are. This summary and the document do not acknowledge this fact and it will be regretted later.

69General Comments

At the suggestion of Ellis Cowling and Charlie Driscoll, I am inserting the following background material taken from my class presentation (N RES 497/697, Forest and Range Soils, Department

of Natural Resources and Environmental Sc ience, University of Nevada, Reno).

707172

### Dr. Donna Kenski

Revised comments, NOx/SOx Secondary REA (2 nd Draft)

General Comments: Overall, the 2 nd draft REA provides, through its case studies, a comprehensive summary of acidification and nutrien t enrichment effects of sulfur and nitrogen deposition in sensitive ecosystems. I am gene rally satisfied that the data presented here sufficiently demonstrate the environmental damage done at current atmospheric concentrations of NOx, SOx and NHx and that it constitutes eno ugh evidence on which to base a standard. What’s still lacking is a clear discussion of the specific route to formulating a standard. The Executive Summary lays out a very general outline, which is repeated in various fashions in Chapters 1, 2, and 7, but there is still no concrete , detailed example of ho w a standard might be structured, despite having all th e necessary information collected here. The committee raised a number of questions related to this in the last review, and it would have been good to see those addressed here, rather than waiting for a separate policy assessment. For example, how will varying degrees of geographic susceptibility and va riability be incorporat ed (i.e., ANC might be the most logical indicator for the eastern US , but would it protect CSS and MCF communities?) Is EPA contemplating a standard based on just one of the ecological in dicators (ANC seems like the logical choice) or will it be combined with other indicators? What kind of overlap might there be if multiple indicators are selected and how do we determine which is controlling? Is there any accommodation for uncertainty in th e estimation of concentrations, deposition, ecological effects, and indicators? Because linking all of these modeled values will incorporate so many different estimates of variability and unc ertainty, it is very difficult to imagine their

cumulative effect on a standard. Given that EPA is proposing a brand new approach to an ambient air quality standard, the sooner these issues are dealt with and reviewed the better.

I like the stylized graphic of Fi g. ES-2 that is used on the intr oduction pages to each chapter. The use of boldface for figure and table references in the text was a big help to readers hunting for those. Also I thought the use of the call- out boxes was very effective. Throughout the document, but especially in Chapter 3, the figur es were well done – no extraneous information, thoughtful and consistent use of color. Very nice.

One point that needs to be made more strong ly throughout the document, whenever the various ecosystem services are being described, quantified, or otherwise valued, is that they are only a

small subset of the sum total of services we derive from these resources.

Exec. Summary: The last statement of the c onclusions to the ES was disappointingly weak (“...effects due to aquatic a nd terrestrial acidification may be the most useful...”). The REA was quite convincing that the aquatic nitrogen enrichment effect was not going to be a suitable basis for a standard, and also that aqua tic and terrestrial acidification we re the effects we have the best science for and the most developed quantitative re lationships on which to ba se a standard. The

ES could be a bit more fort hright about its findings.

Chapter 1: I like the list of po licy relevant questions at the end of Chapter 1, but I expected to see answers to the questions when we got to the final synthesis and integration in Chapter 7. A

73conclusions section framed in such a way would be ultimately more useful than the current structure of Chapter 7.

Chapter 2: Good overview.

Chapter 3 (and Appendix 1): Great graphics , except for the unnecessa ry 3d pie charts. Conclusion 6 on p. 3-79 that the se ason (in the East) with the most TN deposition corresponds to the season with the most S deposition is difficu lt to confirm because the N and S data aren’t shown together. Could a plot or two be added to demonstrate that this is indeed the case? The CMAQ comparison with measurements was well done and did provide some reassurance that CMAQ was adequate for this assessment, a lthough the model performance assessment in Appendix 1 wasn’t exactly what I was expect ing. Making the assessments on an annual or monthly domain-wide basis isn’t the typical way of evaluating CMAQ, and looking at those long term averages tends to make performance look much better than on a shorter term basis. If the logic was to look at long term averages because the case studies are only looking at long term averages, the text should be clear about it, alt hough I’m not sure that’s a sufficient reason. EPA has plenty of model performance guidelines, so it’s surprising that th e validation results presented here did not follow those guidelines. Also, I’m not convinced that because these results fell within the range of other studies, that constitu tes acceptable performance (as discussed much too briefly on pp. 1-4 and 1-5). The performance is not particularly good for many of the components and it deserves a more thoughtful discussion of what is really acceptable for this particular application. That sa id, I think this is a much better approach than the previous draft’s RSM approach.

Chapter 4: This chapter’s finding that aquatic acidification in both cas e study areas was driven primarily by sulfate was not brought out in a ny of the conclusions or summary statements, although it seems like it could potenti ally be significant informa tion in the standard setting process. I was confused by the contradicti on between these statements (on pp. 4-18 and 4-25) and Figure 4.2-23, which implies that the two Adirondack lakes shown are sensitive to both sulfate and nitrate. These contradictory results would lead policy makers to very different conclusions, depending on which one is given the most weight. The text must do a better job explaining the reasons for the different conclusions (different models used, with very different assumptions), or otherwise reconcile these finding s. The section (4.2) th at looked at recovery potential should have examined at least one or two scenarios with reduced emissions, since maintaining emissions at current levels for the ne xt 10 or 40 years is not realistic and expected emissions reductions might well make a significant di fference in the estimated recovery times. It

could have been tied in with the emissions reduc tions analysis in Chapte r 3. Also, the chapter could use a brief discussion of the averaging time for ANC. It uses mostly annual average values, although frequent mention of episodic pulses of acidity are made. Do seasonal patterns in deposition have any impact on ANC? This is n’t my area of expertise, coming from the ambient air world of hourly measurements, but it was a little startling to see that much of the lake data is based on one measurement a year. So a brief explanation of AN C behavior over time might be helpful. With respect to uncertainty, the specific discussions ab out uncertainty in the various models employed was generally adequa te (note comments above about CMAQ though). The discussion on uncertainty in the aquatic nutri ent enrichment was especially well done (Sec. 5.2.8). However, a broader discu ssion that pulls together uncerta inty from MAGIC, along with

74uncertainty from CMAQ, and uncertainty in the ef fects of ANC on sensitive biota, etc., needs to take place somewhere. Chapter 7 takes a broade r look but still doesn’t discuss the cumulative, quantitative impact of these vari ous sources of uncertainty on a st andard. Perhaps this is more appropriately left for the policy analysis, but it needs to take place at some point.

The 2 nd charge question for this chapter asks if we agree with focusing on aquatic acidification

for a basis of the standard. I do agree; the quantity and quality of data available for aquatic acidification really make it the only logical choice, relative to th e other effects examined in the REA. The nutrient enrichment studies were just too qualitative to thi nk about basing a standard on them. However, it is important for EPA to con tinue to consider terrestrial acidification as well as the nutrient enrichment cases, and find a wa y to truly integrate multiple indicators into a standard. Multiple indicators will expand the geographic relevance and scope of the standard and afford protection to a maximum number of sensitive ecosystems.

Specific comments (page, line number)

ES-10, 10-11: MM is not an SI unit, nor is it a standard abbreviati on in the air quality community. Scientific notation would be better . Or at least include it in the table of

abbreviations.

ES-10, 18: fix subject-verb agreement

ES-15, 11: missing a closing parentheses for the phrase that star ts “(especially...”

ES-16, 27, 36, and others throughout document: should be “sensitive to or at risk from acidifying deposition” . The phrase “at ri sk to acidifying deposition” is jarring.

ES-16, 31; ANC level of above

ES-18, 1: Bc/Al level of above

1-12, 17-19 : Is this sentence correc t? Or do you mean there is li ttle new evidence that S and N oxides are high enough to be phytotoxic (delete not ?)

1-17, bullet 2: this bullet is awkwardly phrased – reword

2-2, 5: It is not clear what the role of these supplemental study areas is. Little Rock Lake, for example, is not summarized in Table 2.1-1 or Fig. 2.1-1, and it’s not even mentioned again except a passing reference to it in Chapter 6. It hardly seems to mer it mention here. Rocky Mountain alpine lakes are discussed in Chap 5.

2-7, 17: public

3-2, 9 and 18: the subscript x should be NHx

753-4, 1-4: MM is not an SI unit, nor is it a standard abbreviati on in the air quality community.

Scientific notation would be bett er. Or at least include it in the table of abbreviations.

3-11, 27: Figure 3.2-6 says it shows NOy, not NOx – which is correct?

3-28: Table 3.3-1 says the Neuse River has 14 kg N/ha/yr in 2002, but the figure 3.3-1a says it has 15; shouldn’t these be the same?

3-30, 1: contains should be contain

3-82, 5 and 8: seems to be missing NH before the orphaned subscripts

3-90, 14: ...are based on the application of

3-91,24: ...the formation of sulfate and nitrate...

3-93, 5: similarities and differences

4-6, 11-14: edit this final sentence

4-11, 15: delete sulfate

4-23, Fig. 4.2-13 misspells exceedan ces in each of the 4 titles

4.34, 10-13: This first sentence is too long and convoluted.

4-37, 10: Shouldn’t Q be in m3/yr?

4-39, 6: SSWC is not defined in the text or list of abbreviations – I had to dig in the Appendix

for it.

4-40, 23: levels -> level

4-41, 3-12: This explanation of the MAGIC calibration procedure is pretty fuzzy. At least refer

the reader to Attachment A of A ppendix 4 for additional information.

4-45, 6-8: Delete these lines

5-16, Fig. 5.2-3: this figure was pretty confusin g – too much information is presented, and it’s

hard to read besides.

5-47, Fig 5.3-2: the 7 th bullet on Minnesota grassl ands doesn’t list any ec ological effect. Farther down the list, Bytnerowicz is misspelled

7-12, 4: res -> red

767-16, Fig. 7.1-3: the 7 th bullet on Minnesota grasslands doesn’t list any ecological effect. Farther down the list, Bytnerowicz is misspelled

7-17, 19: res -> red

7-19, 29: oconic -> iconic

7-21, 12-16: fix run on sentence

77

### Dr. Naresh Kumar

The second draft of the Risk and Exposure Assessment (REA) document is much improved from the first draft. However, there are still some ar eas that need improvement and further analyses that need to be performed. My major comments, with a main focus on the air quality analysis,

are:

1. Figure 1.4-1 (reproduced below) appears as the key figure in the REA document. As noted, the Atmospheric Deposition Transf ormation Function depicted in Box 3 “quantifies the relationship between atmosphe ric concentrations and deposition of NOx

and SOx”.

It appears that the CMAQ model used in th e analysis is the “Atm ospheric Transformation Deposition Function.” However, the CM AQ model transforms emissions, not concentrations. Moreover, it predicts both concentrations and deposition fluxes. As a result, there must be some other form for th e atmospheric function depicted in Box 3 that

EPA has not shown in the document. The relationship between concentrations and deposition fluxes of NOx and SOx is expect ed to be proportional, i.e. changes in concentrations would be reflected as proporti onal changes in deposition fluxes. However, it is likely that the relationship will vary seasonally and spatially depending on regional chemical regime, precipitation and other meteor ological variables, as well as land use and

78terrain features. Because of limited measurem ents of NOx, it would be difficult to show the relationships between obser ved concentrations and deposition, but (at a minimum) the CMAQ model results could have been used instead (as they are being used for dry deposition).

It is essential that EPA should show the relationships between concentrations of SO 2 and NOx and the corresponding deposit ion measures for different regions of the country and

for different seasons. These should include:

a. The relationship between measured SO 2 and measured wet sulfur deposition

b. The relationship between modeled SO 2 and total sulfur de position (measured wet deposition and modeled dry deposition)

c. The relationship between measured NO 2 and measured wet nitrate deposition

d. The relationship between modeled NOx and total nitrate deposition (measured wet deposition and modeled dry deposition).

The EPA should also explore the impacts of combined reductions in SOx and NOx on total N deposition fluxes and their spatial distribution.

2. Since the approach used by EPA relies on model predicted data due to lack of measurements of dry deposition, it is essentia l to show that the CMAQ model used in the analysis perform adequately when compared against measurement data. The model evaluation presented in Appendix 1 is inadequate for a variety of reasons:

a. Evaluation is shown for annual averag ed quantities that can mask model performance issues, as the compensating effects can cancel out biases and errors in the model. It is a general practi ce in regulatory applications to choose averaging period commensurate with the measured quantities (e.g., see Morris et al., 2006; Tesche et al., 2006) when eval uating model performance. Therefore, EPA should base model performance statis tics using daily or weekly averaged quantities, as appropriate, instead of the annual average quantities. In addition, the statistics should be aggregated for each season, as appropriate.

b. There is no reason to use normalized mean bias statistics when using annual average quantities. It is recommended to use mean normalized bias for longer averaging periods and fractional normalized bias when using averaging periods of

one week or less.

c. The report does not include a model ev aluation performed for NOx purportedly due to lack of available data. However, NO 2 data are available for a model performance evaluation of NO 2 . Notwithstanding the issues with the current FRM

method for NO 2 , it is appropriate to show th ese model performance results.

In addition, there are continuous, highly sensitive and highly precise measurements of nitric oxide, nitrogen dioxide, total oxidized nitrogen (NOy),

and nitric acid available for the SEARCH network in the southeastern U.S.

79(Hansen et al, 2003; Edgerton et al. 2006) that could have been relied on to conduct a regional evaluati on. Although limited in scope to the Southeast, conducting an evaluation using SEARCH da ta is better than not conducting any

evaluation for NOx at all.

Because of the limited model evaluation show n in the document, the statement on Page 1-5 (Lines 2 to 4) of Appendix 1 that “the model performance results give us confidence that our applications provide a scientifically credible appr oach for the purposes of this assessment” cannot be supported. Since th ere is no way to measure the model performance for dry deposition, the estimates of total deposition that rely on predicted dry deposition are highly uncertain.

3. Figure 3.2-1 does not mention or include light ning NOx (LNOx) and soil NOx emissions,

so it can be assumed that either those emi ssions were ignored or were assumed to be negligible (<1% of total). Hudman et al. (2007) show that these emissions can be significant (9% and 27% of total U.S. NOx emissions from soil and lightning, respectively for July 1 to August 2004 peri od). The magnitude of the lightning source

relative to the anth ropogenic source in summer 2004 was constrained by the extensive

aircraft observations of NOx as part of the ICARTT campaign, so there is high degree of confidence in those estimates. Although th ese emissions estimates may still have uncertainty associated with them, one cannot ignore a combined source that could be as

much as 1/3 of the total NOx emissions over a significant period, especially when estimating regional deposition loads. Additiona l analysis (Lee Murra y and Daniel Jacob, Personal Communications) shows than on an annual basis, lightning and soil NOx may contribute up to 20% of total NOx emissions in the U.S. The exclusion of these emissions used in the CMAQ model simulation further reduces confidence in the modeling results

shown in the REA.

Harvard has conducted preliminary work (Lee Murray and Daniel Jacob, Personal Communications) on estimating c ontribution of LNOx to nitrogen deposition over several years using the GEOS-Chem model. The result s show that LNOx alone (not including the contribution from soil NOx) can contribute ~15% of total annual oxidized nitrogen deposition over the U.S. Anothe r interesting result of their work is that dry deposition accounts for 2/3 of total nitrogen deposition, a result that is different from the results shown in the REA. This indicates that using a single model for a single year to estimate dry deposition could give unreliable estimat es. A better approach would be to use multiple models for multiple years.

4. Chapter 3 discusses various uncertainties asso ciated with the anal ysis, but there is no attempt made to quantify any of those uncerta inties. It may not be possible to quantify every source of uncertainty, but there are cases for which this is possible. For example, it is known that ammonia emissions are highly uncertain and studies have been done by

EPA to “correct” biases in ammonia emissions using inverse modeling (Gilliland et al., 2003). It is recommended that EPA rerun the CMAQ model with the revised ammonia emissions to quantify the e ffect of that uncertainty.

805. The REA is not consistent in its use of de finitions for NOx and NOy. The first paragraph of Page 1-10 states that “oxides of nitrogen” and “nitrogen oxides” used in this document refers to all forms of oxidized nitrogen com pounds, similar to the term NOy used in the scientific community. It is not clear from the document whether the term NOx used in the document refers to (NO + NO 2 ) or to NOy and it seems to be used interchangeable throughout the document (e.g., in Line 1 of Pa ge 1-14, “NOx” seems to be referring to NOy, but on page 3-3 when discussing emissions, “NOx” seems to referring to sum of

NO and NO 2 ). A better clarification needs to be made in Chapter 1 and followed throughout the document. The following instan ces of inconsistencies are noted as examples:

a. Page ES-11: Line 1 refers to annual av erage NOx concentrations shown in Figure ES-5, but the caption for Figure ES-5 refers to annual average NOy.

b. Similarly, Page 3-11, Line 27 refers to annual average NOx concentrations, but the caption for Figure 3.2-6 re fers to annual average NO y. It is not clear what quantity is shown in the figure.

c. Page 3-21: The policy-relevant back ground concentrations are shown for NO 2 . If the indicator is NOx, shouldn’t those concentrations be shown for NOx?

Minor Comments:

1. Page 3-29, Line 19: “These findings show th at NOx emissions are much higher than NH 3 emissions in most areas of the country”. Th ere is a logical flaw here. The finding that oxidized nitrogen deposition is higher than the reduced nitrogen deposition is a result of emissions that are input into th e model, not the other way around.

References:

• Edgerton, E.S., Hartsell, B.E., Saylor, R.D., Jansen, J.J., Hansen, D.A., and Hidy, G.M. (2006). The Southeastern Aerosol Research and Characterizati on Study: Part III.

Continuous Measurements of PM 2.5 Mass and Composition. J. Air Waste Mange. Assoc.

56 , 1325-1341.

• Gilliland, A. B., Dennis, R. L., Roselle, S. J., and Pierce, T.E. (2003). Seasonal NH3

emission estimates for the eastern United States based on ammonium wet concentrations and an inverse modeling method. Journal Of Geophysical Research

, 108 , D15, 4477,

doi:10.1029/2002JD003063

• Hudman .... Hudman, R. C., Jacob, D. J., Tu rquety, S., Leibensperger, E. M., Murray, L. T., Wu, S., Gilliland, A. B., Avery, M., Bertram, T. H., Brune , W., Cohen, R. C., Dibb, J. E., Flocke, F. M., Fried, A., Holloway, J., Neuman,9, J. A., Orville, R., Perring, A., Ren, X., Sachse, G. W., Singh, H. B., Swanson, A. and Wooldridge, P. J., 2007. Surface and lightning sources of nitrogen oxi des over the United States: Magnitudes, chemical evolution, and outflow. Journal Of Geophysical Research

, 112 , D12S05,

doi:10.1029/2006JD007912

• Hansen, D.A., Edgerton, E.S., Hartsell, B.E ., Jansen, J.J., Kandasamy, N., Hidy, G.M., and Blanchard, C.L. (2003). The Southeastern Aerosol Research and Characterization Study: Part 1 – Overview. J. Air Waste Mange. Assoc. 53 1460-1471.

• Morris, R. E. , Koo, B., Guenther, A., Yarwood, G., McNally, D., Tesche, T. W., Tonnesen, G., Boylan, J., and Brewer, P. (2006) . Model sensitivity ev aluation for organic

81carbon using two multi-pollutant air quality mode ls that simulate regional haze in the

southeastern United States. Atmos. Environ. 40 (26) 4960-4972

• Tesche, T. W., Morris, R. E., Tonnesen, G ., McNally, D., Boylan, J., and Brewer, P. (2006). CMAQ/CAMx annual 2002 performa nce evaluation over the eastern US. Atmos.

Environ. 40 (26) 4906-4919

.

82

### Dr. Myron J. Mitchell

General Comments and Responses to the Charge to the CASAC NO

x /SO

x Secondary

Review Panel Final: July 28, 2009

Comments are provided in italics

Charge to the CASAC NOx/Sox Secondary Review Panel

Within each of the main sections of th e second daft Risk and Exposure Assessment document, we ask the panel to address the foll owing questions, taking in to consideration the changes and additions since the firs t draft Risk and Exposure Assessment:

Executive Summary:

1. In response to the Panel's review of the first draft Risk and Exposure Assessment, we have included an executive summary of this document. Does the Executive Summary adequately summarize and characterize the key issues driving this review as well as the important findings of the analyses? Does the Pa nel have any suggestions for clarification or refinement of the Executive Summary?

The Executive Summary does a good job of providing a summarization of the document. The summary, however, needs attention to detail, clar ity and consistency. The figures and tables

need to have clear and accurate labels. There is some redundancy in the document such as the mentioning at various locations of the importance of looking at the effects of total reactive nitrogen versus NO

x . I know that there has been consid erable discussion of the importance of using total reactive nitrogen in these analyses , but some of this usage and other areas of duplication should be reduced. A succ inct statement indicating why total reactive nitrogen is the most appropriate metric for nitrogen atmospheri c deposition should be included. There needs to be more consistency in the use of the past and pres ent tense. If the focus is on the summary of findings, the past tense is appropriate. However, if emphasis is on the current conditions, the present tense should be used. A clearer transition and better linkage between Section 2.0 (OVERVIEW OF RISK AND EXPOSU RE ASSESSMENT) and previous text need to be provided.

In my detailed comments, I have provided a number of editorial corrections and suggestions. There should be consistency of whether or not to use direct references in the executive summary. I would suggest, unless there is a very compelling reason, that direct lite rature references should not be part of the Executive Summary.

There were no specific questions directed at Chapter 2, but the comments provided for the Executive Summary are relevant to this chapter. Mu ch of the contents of this chapter is based upon further elaboration and justifica tion of the use of ecosystem se rvices in this assessment.

83The entire document could be improved by at tention to repetition both within and between chapters. A more succinct narra tive would provide a more focuse d presentation of the important

issues.

Air Quality Analyses (Chapter 3):

1. This chapter describes an approach for char acterizing the spatial a nd temporal patterns of nitrogen and sulfur deposition in the case study locations incl uding both oxidized and reduced nitrogen, and both wet and dry deposition of oxidized nitrogen, re duced nitrogen, and sulfur.

Are the uncertainties associated with these anal yses appropriately identified and described?

The Chapter does a good job of describing the sp atial and temporal patterns of nitrogen and sulfur deposition incl uding the areas of the case studies. The report needs to further emphasize

the inherent limitations associated with estimates of dry deposition. In the Chapter it is sometimes indicated that “measured deposition” is provided. Although good measurements of wet deposition can be provided, there is c onsiderable uncertainty in the dry deposition estimates and the importance of this uncertainty s hould be emphasized in this chapter.

2. In response to CASAC's recommendation, the RSM analysis presented in the first draft Risk and Exposure Assessment was replaced by an analysis of results from a new series of CMAQ simulations designed to explore the relative contributions of NOx and NH3 emissions to total, reduced and oxidized nitr ogen deposition and the relative c ontribution of SO2 emissions to sulfur deposition. Does this approach enable us to adequately examine the contribution of NOx to total nitrogen deposition?

The relative role of NO

x and NH 3 simulations is better develo ped in the current document.

3. The CMAQ application and model performance evaluation is presented in Appendix 1, as recommended by the Panel. Is th is analysis sufficient to support the use of the model in this

review?

There is more information provided on the CMAQ application and model performance. The comparisons of the model with other independent measures (e.g., CMAQ wet deposition versus NADP/NTN wet deposition estimat es) provide important inform ation with respect to the estimates of deposition. Some fu rther comparisons with other deposition measurements would strengthen the report. These results need to be used in showing potential uses and limitations of the model predictions both w ith respect to regional cover age and temporal changes. These comparisons could include more quantitative analyses of model versus measured performances including comparisons among regions. A clear r ecognition should be provided that indicates limitations (absence of long-term historical simulations) as well as opportunities (direct linkages between emissions and deposition) in CMAQ modeling. It would be helpful to include some type of critique on the model applic ation results in Appendices 1 a nd 2 and how these results affect the setting of standards.

84Case Study Analyses (Chapters 4 & 5)

Questions related to the indivi dual case study analyses are presented below. Overarching questions across all the case studies include:

1. Are uncertainties appropriately characterized across the case studies? Is there adequate information to allow us to weigh the relative stre ngths of each case study to inform the standard setting process?

There is sufficient information related to understanding some of the variation associated with each case study. However, it is di fficult to translate this uncertain ty to developing standards that can be used that include larger re gions. Some of this uncertainty is related to the case studies not representing the full spectrum of effects associated with the de position of nitrogen and sulfur. The tradeoffs in using case studies that focus on sensitive areas versus ar eas that are spatially representative needs to be stated explicitly. This selection has a major impact on how the results can be extrapolated to other areas.

2. In using the Risk and Exposure Assessment to inform the policy assessment, we plan to focus on aquatic acidification as the basis for an alternative multi-pollutant secondary standard as

this is the area where we have the most confidence in our ability to characterize adverse effects. Does the Panel agree with this approach?

The focus on aquatic acidificati on is reasonable based upon the curre nt information related to both acidification and nutrient enrichment. How ever, recent findings are suggesting that the recovery of soils from acidific ation may take an extended period and over the long-term this will also affect the rate of re covery of aquatic ecosystems.

Acidification:

1. Section 4.2 and Appendix 4 describe the analyses used to evaluate the effect of aquatic acidification. The analysis eval uates the ANC in selected lakes and streams in the Adirondacks

and Shenandoah relative to th ree potential ANC cutoff levels (20, 50, and 100 ueq/L) to determine the impact of current levels of depositi on in these areas as well as a larger assessment area. Is this data adequate to establish critical loads of deposition for the case study area?

2. The ecological effect function for aquatic acidification (section 4.2.7) attempts to characterize the relationship betw een deposition and ANC. In or der to estimate the amount of NOx and Sox deposition that will maintain an ANC level above a gi ven limit requires the knowledge of the average catchment flux of base cation from weathering of soils and bedrock (i.e., preindustrial cation flux (BC0)). How might we generali ze from location specific inputs (Ffactor approach) to using this approach on a broader scale - wate rshed, regionally, or some other way - to generalize beyond individual locations? What other methods should be examined for estimating catchment weathering ra tes nationwide for surface acidity?

85This section now does a better job of describing th e importance of mobile anions with respect to soil acidification and result ant effects on the depletion of nutrien t cations. Many of the figures in this section need to be redone so that lege nds, axis values, etc. are easier to read.

This section relies substantially on MAGIC m odel simulations to show various spatial and temporal trends. It needs to be made clear which version of MAGIC is being used in these calculations since there are major differences with respect to the ability of the model to predict nitrogen watershed chemistry.

In this chapter the term “acidify ing deposition” is used. I assume this is done to account for the role of ammonium inputs that can be nitrified resulting in acidification. However, this is not common terminology in the public policy and scienti fic literature and it ma y be preferable to use the more standard term “acidic deposition” th roughout the document to avoid confusion. On the other hand, if this term is considered to be of importance than it must be clearly defined and justified early in the document.

Within the chapter the term “natural acidity” is used (e.g., pages 4-34 through 4-35). In some of the discussion related to ecological effects of acidification, it is not clear what are the consequences associated with some of the assu mptions such as the soils not being a sink for sulfur. We know that some soils are strong sulfur sinks and also there is considerable information that there is a net loss of sulfur from soils (e.g., soils as sulfur sources) (e.g., page 4- 37). Such internal elemental cycling can have major effects on the consumption and/or generation of acidity.

In the section on uncertainty and variability (4.2.8) a variety of approaches are provided and these appear mostly to be associated with vari ation in parameter estimates and how this affects model output. Some discussion on the implicit lim itations of the model us ed (e.g., processes not covered, appropriateness of scale both spatiall y and temporally, etc.) would help place this section in a broader context of the validity of the model results and any possible major

limitations.

The section on ecosystem services is a good summary of helpful informati on related to ecosystem services and acidific ation issues (4.3.1.3). It is useful that the report expl icitly states the problems of estimating directly how ecosystem services are affe cted by terrestrial and aquatic acidification.

3. Section 4.3 and Appendix 5 describe the analyses used to evaluate the effect of terrestrial acidification. This analysis us es the Simple Mass Balance Model to determine the impact of current deposition levels on Bc/A l levels relation to three pote ntial Bc/Al cutoff levels (0.6, 1.2, and 10.0) for sugar maple in the Kane Experiment al Forest and red spruce in the Hubbard Brook Experimental Forest and a larger assessment area ba sed on the FIA database for 17 states. Is this approach adequate to develop cr itical loads of deposition for the broader terrestrial acidification case study area? Is the regressi on analysis between Bc/Al rations and tree health sufficiently described and are uncertainties adequately characterized?

86In the sections looking at critical load calc ulations, there is cons iderable emphasis on the CMAQ model and its application and other issues related to depositi on. I am not sure that there is sufficient balance between th ese issues and the other issues related to the within system elemental cycles includ ing those processes affecting acidification.

The extrapolation of the critical load calculations for sugar maple and red spruce to other regions (e.g., different states) beyond those of the case studies helped place these results in a broader geographical context. There are some poten tial issues in looking at these results on state by state basis since these boundaries do not reflect the important characteristics that affect critical loads, but having this information on a state by state basis might be of more interest to policy makers. It is a surprising result that such a high percentage of sites have been compromised with the acidifying total nitr ogen and sulfur deposition in 2002 (page 4-62).

In this section there is some use of average critic al loads related to three levels of projection. It is not clear if this “average” is meaningful in the context of how critical loads may be applied since the critical load is depende nt on specific edaphic features of an area. Does the average take into account how the spatial distribution of edaphic features? Does this “average” apply to specific case study areas or to larger regions? The discus sion and analyses that show how specific factors such as parent soil properties aff ect critical loads calcul ation is most important.

Nutrient Enrichment:

1. Section 5.2 and Appendix 6 describe the analyses used to evaluate the effect of aquatic nutrient enrichment. The analysis uses th e SPARROW model on one stream reach (Potomac River and Neuse River) to determine the impact of atmospheric total ni trogen deposition on the eutrophication index for the estuar y. Does the Panel think that th e model is adequately described and appropriately applied?

In discussing nutrient enrichme nt it would be helpful to provide some background on nitrogen being a limiting nutrient in freshw ater aquatic systems. Recent evidence suggests that nitrogen

limitation is more common than once thought for freshwater sy stems. Historically, the importance of phosphorus limitation has been emphas ized, but more recent work has suggested that nitrogen limitation was less noted due to it being at relatively high levels in many freshwater systems. A major challenge in developing prot ocols for returning systems to a level of lower nutrient enrichment is defining what attributes an d their specific values that are the goals in the restoration of ecosystem type and function. The presentation of ar eas related to sensitivity to nitrogen loading needs some further clarificatio n on the importance of those areas in the west (e.g., Rocky Mountains of Colorado) that are impac ted by relatively low levels of atmospheric nitrogen inputs. Such areas have very different at tributes and issues comp ared to the estuaries that are affected by relatively high levels of anthropogenic nitrogen. There are different issues associated with nitrogen deposition in areas w ith recent histories of relatively low nitrogen deposition versus areas that are being subjected to very high loadi ngs. How these issues vary among the regions needs to be clearly identified.

The discussion of the case studies related to the Potomac River/Potomac Estuary Case Study Area and Neuse River/Neuse River Estuary Case Study Area including the application of the

87SPARROW model is adequate. The br oader extrapolation of these resu lts is also helpful. Some of the details provided in this chapter should possibly put into the appendices. The discussion of the uncertainty estimates provides important information on the appl ication of the model simulations. A summary of which of these compone nts is most important with respect to policy recommendations would help clarify what are the most important issues that could affect the interpretation of these results.

2. Section 5.3 and Appendix 7 describe the analyses used to evaluate the effect of terrestrial nutrient enrichment. This qualita tive analysis describes the imp acts due to nitrogen deposition on the Coastal Sage Scrub community in Califor nia and in mixed conifer forests in the San Bernardino and Sierra Nevada Mountains and larger areas where possible. In addition, the effects of nitrogen deposition in the Rocky Mountain National Park supplemental case study

location are summarized. How would the Panel apply the threshold values presented in this case study to allow for a broader geogr aphic application that accounts for regional variability? Have the associated uncertainties been adequately characterized?

The emphasis on the California coastal sage scrub (CSS) and San Bernar dino Mountains mixed conifer forest (MCF) systems seems appropriate due to their importance with respect to population centers and interactions with nitrogen deposition with other environmental issues including fire susceptibility. Also, other enviro nmental issues such as the potential effects on biodiversity and threatened species is important for these case study areas. The document clearly indicates that although qualitative inte ractions among these various environmental

concerns are well documented there is not good information on th e actual quantitative relationships including direct and indirect effects of sulfur and nitrogen deposition. It is noteworthy that the alpine ecosystems of the Ro cky Mountains was considered as a case study
area, but was not selected. It is suggested that “the ecological benchmarks suggested for alpine ecosystems were comparable to the benchmarks from CSS and MCF ecosystems”(p. 5-57). I am

not sure this is true since the alpine systems seem to be especi ally sensitive to low levels of nitrogen deposition. These is some extensive di scussion of the specific issues related to the Eastern Slope of the Rocky Mountains (including Rocky Mountain National Park) in Section

5.3.6.2.

The section on “Uncertainty and Variability” (5 .3.8) does a good job of summarizing some of the major issues with a particular focus on th e CSS and MCF case studies. On the other hand the “Conclusions” (5.4) section is too short to be very helpful in linking this Chapter with the entire focus of the document.

Additional Effect s (Chapter 6):

1. In this chapter, we have presented results from some qualitative analyses for additional effects including visibility, climate and mate rials, the interactions between sulfur and methylmercury production, nitrous oxide effects on climate, nitrogen addition effects on primary productivity and biogenic greenhouse gas fluxes, and phytotoxic effects on plants. Are these effects sufficiently addressed in light of the focus of this review on the ot her targeted effects and

in terms of the availabl e data to analyze them?

88The section on methyl mercury formation and relationships to sulfur are generally adequate and well done. Some of the wording needs to be change d so that it is clear that this process can occur in areas beyond just surface waters.

The other sections including 6.3 NITROUS OX IDE, 6.4 NITROGEN A DDITION EFFECTS ON

PRIMARY PRODUCTIVITY AND BIOGENIC GREENHOUSE GAS FLUXES (including subsections: 6.4.1 Effects on Primary Productivity and Carbon Budgeting; 6.4.2 Biogenic Emissions of Nitrous Oxide; 6.4.3 Methane Em issions and Uptake; 6.4.4 Emission Factors; 6.4.5 Uncertainty), 6.5 DIRECT PHYTOT OXIC EFFECTS OF GASEOUS SO X AND NO X [including

subsections: 6.5.1 SO 2 ; 6.5.2 NO, NO 2 and Peroxyacetyl Nitrate (PAN),6.5.3 Nitric Acid (HNO 3 )] are adequate in the context of the needs of the current report.

Synthesis of Case Studies (Chapter 7):

1. Here, the case study analyses are integrated and synthesized with in the conceptual framework of ecosystem services as shown in Figure 7-2. Where possible, we have quantified select ecosystem services associated with the ec ological effects targeted in this review. This chapter discusses adversity by ch aracterizing the degree to which ecological effects are occurring under given levels of deposition to inform the di scussion of adversity in the policy assessment and standard setting process. To what extent do you think the descripti on of ecosystem services provides a useful framework in the case study analys es for informing standard setting? Does the Panel have suggestions for additional considerati on or characterizations for ecosystem services

related to the case studies?

The information in Chapter 7 pr ovides a summary of previous information incl uding emphasis on ecosystem services. Much of this information has been previously stated in earlier chapters, but having this summarized informat ion in a single chapter is help ful. It should be emphasized that the results from these case studies can only be regionally extrapolated to those areas of similar characteristics with respect to sensitive to sulfur and nitrogen deposition.

2. Based on the information presented in the current Risk and Exposure Assessment, given adequate time and resources, is there enough info rmation to inform setting separate standards based on the other targeted ecological effects, specifically, terrestrial acidification, aquatic nutrient enrichment, and terrestrial nutrient en richment? If not, how can our understanding of these ecological effects be enhanced in time to inform the next 5-year review?

There appears to be sufficient information provided in the current “Risk and Exposure Assessment” given additional time an d resources to form standards with respect to effects of acidification and nutrient enrichment on terrest rial and aquatic systems. Clearly, however,

there is considerable uncer tainty on these effects especially with respect to both the current and future deposition of sulfur and nitrogen. Simila rly there are complexities associated with interactions with a broad range of factors including land use, climat e, effects of invasive species, etc. that result in uncertainties for predicting the effects of sulfur and n itrogen deposition. It may be helpful to show the range of ecosystem services and w hat is known about how they are affected by acidification and nutri ent alteration due to sulfur and nitrogen deposition. It would be helpful to show what is known and unknown about the linkages over a range of ecosystem

89services. Inclusion of what is needed to prov ide information in the fu ture about the effects of nitrogen and sulfur deposition on various ecosyst em services would be helpful for both the current REA and also setting the stage fo r other efforts to evaluate multiple pollutant/environmental effects on these ecosystem services.

90Detailed Comments and Responses to the Charge to the CASAC NO

x /SO

x Secondary Review Panel Final: July 28, 2009

Page Line(s) Comment

xxiv 4-5 This statement makes no sense: “Ecosystem Structure: Refers to the species composition, distribution, and interactions with some abiotic attributes of the environment s they vary through space and time”.

xxiv 21 Change “ This indicator may either be the actu al criteria air pollutant” to

“

An indicator may either be the ac tual criteria air pollutant”.

xxv 2 Delete “As a result”.

xxvii 3 Delete “reduced” twice in th is line. Why use the term reduced?

xxvii 3 Give the charge for “NO 2 " (nitrite) as “-“.

xxviii 7 Change to “other forms of precipitation”.

ES-2 12-13 Change “slower biomass gr owth” to “lower rates of production”.

ES-2 14 Change “In addition to acidification, NO

x acts” to “In addition to contributing to acidification, NO

x acts”.

ES-2 22-23 Change “the ecosystem is receiv ing more nitrogen than it uses” to “an ecosystem is receiving nitrogen in excess of biotic nutritional needs”.

ES-2 23 Delete “also”.

ES-2 24 Clarify what “This” refers to. Does this mean nitrogen deposition, primary productivity and/or te rrestrial carbon cycling?

ES-2 26 Change to “Lichens”.

ES-2 27-28 This statement seems out of place. Does this statement have any relevance to lichens? Clarify what aspects of biodiversity have been reduced in grasslands.

ES-3 Figure ES-1. Within the figure ch ange “Soil Process” to Soil solute generation”.

ES-4 9 Change “to determining when the” to “to determining when and where

the”

91ES-5 8 Replace “enrich” with “impact”.

ES-5 8 Clarify what “this” refers to.

ES-5 12 Change “while the Ecological Effect Function (box 6) relates the deposition metric into the” to “while the Ecological Effect Function (box 6) links the deposition me tric to the relevant”.

ES-5 19 Change “the degradation of” to “deleterious affecting”.

ES-6 2 Change “Because ecosystems are diverse” to “Because ecosystems differ”.

ES-7 In Table ES-1 the Adirondack M ountains should be referred to as the

“Adirondacks” and not the Adirondack”.

ES-8 9 Change “ecosystem services is bein g used as an umbrella term” to “the term ecosystem services is being used as a broad concept”.

ES-8 10 Change “It is a way to help e xplain” to “The evaluation of ecosystem services helps to explain”.

ES-9 3-4 Change “some of the ecosystem se rvices likely to be affected are readily identified, while others will remain unidentified” to “ only some of the ecosystem services that are likely to be affected can be readily identified”.

ES-9 4-6 Change “Of those ecosystem se rvices that are identified, some changes can be quantified, whereas others will remain unidentified” to “Of those ecosystem services that are identified, only subset of changes will likely be quantifiable”.

ES-9 6-7 Change “Within those services whose changes are quantified, only a few will likely be monetized, and many will remain unmonetized” to “For those quantifiable services only a few will be subject to monetization”.

ES-9 8 Change “A conceptual model integr ating” to “An example of a conceptual model of effects on aquatic ecosystems is used to integrate”.

ES-9 12 Change “can be used to inform a policy judgment” to “can be used to in developing policy”

ES-9 16 Change “inform” to “provide”.

ES-9 18-21 Figure caption needs to be changed to indicate that this is an example focusing on aquatic ecosystems.

92ES-11 3 The term “magnitude” can be misleading. The correspondence between the actual amount and relative spatial patterns of measured versus modeled

concentrations needs clarification.

ES-12 7 Change “information about meteorol ogy and land use in each grid cell of

the domain” to “information abou t meteorology and land use both of which are critical components in affecting dry deposition”.

ES-13 5-7 Change “In the East, high levels of deposition exceeding 18 kg S/ha/yr occur in the immediate vicinity of isol ated major sources, as well as in and near areas having a high concentration of SO 2 sources” to “In the East, the highest levels of deposition that exceeding 18 kg S/ ha/yr occur in proximity to sources of high SO 2 emission” .

ES-15 13 Change “Acidification can degrade the health of terres trial and aquatic ecosystems” to “Acidification can have deleterious impacts on terrestrial and aquatic ecosystems”.

ES-15 19 Delete “method”.

ES-15 28 Delete “the additional”.

ES-16 12-13 Change “direct relationship be tween ANC and fish and phyto-zooplankton diversity and abundance” to “direc t relationship between ANC and the diversity and abundance of fish and phyto-zooplankton”.

ES-16 13 Change “MAGIC” to “The MAGIC model”.

ES-16 Within this page direct citations are provided. This does not seem to be consistent with other portions of the Executive Summary. I would suggest that these should be deleted for consistency. This problem is also found in other parts of the Executive Summary.

ES-17 9 Change “Calcium and Al are strong ly” to “Calcium and Al concentrations are strongly”.

ES-17 13 See previous comments on the us e of citations in the Executive Summary.

ES-17 18 Change “The tree species most sensitive” to “Tree species sensitive”

ES-17 19 Delete “a deciduous tree species”.

ES-17 20 Delete “a coniferous tree species”.

ES-17 22 Change “to” to “on”.

93ES-17 23 Delete “both”.

ES-18 6 Change “total rem oval” to “total harvest”.

ES-18 6 Remove “from timberland”.

ES-18 9 Change “roughly” to “approximately”.

ES-18 10 Remove “from timberland”.

ES-18 11-12 Change “spruce forests are home t o the spruce-fir moss spider (endangered), the rock gnome lichen 12 (endangered), and the Virginia northern flying squirrel (delisted, but considered importa nt).” to “spruce forests are important habitats for en dangered species including the sprucefir moss spider, the rock gnome liche n, and the Virginia northern flying squirrel (delisted, but sti ll considered important).

ES-19 1-4 Change “Some organisms may at first respond positively to an initial increase in nutrients, exhibiting an in crease in growth due to fertilization effects. However, as the nutrient load continues to rise, the imbalance can have negative effects either in the organism’s response or in the invasion of new organisms that benefit from increased nutrients” to “ Some organisms may at first respond to an increase in nutrients with increased growth. However, as nutrient load continues to ri se, the resulting imbalance can have negative effects e ither directly on the organism or indirectly by the invasion of other species that are better competitors under high nutrient conditions”.

ES-19 12-14 Change “Nitrogen is an essentia l nutrient for aquatic ecosystem fertility, including lake, marine, and estuarine ecosystems, and is often the limiting nutrient for growth and reproduction in many of these ecosystems” to “Nitrogen is often a lim iting nutrient for lake, marine, and estuarine ecosystems”.

ES-19 15 Delete “of a system”.

ES-19 21 Change to “nitrogen enrichment now represents”.

ES-19 26 Change “Due to the cascading imp acts and effects of nitrogen enrichment” to “Due to the cascading imp acts of nitrogen pollutants”.

ES-20 2 Change “estimation” to “estimate”.

ES-20 5 Change “In this assessment” to “In the current assessment”.

ES-20 14 Change “reductions in additional” to “reductions from additional”.

94ES-20 15 Change “resident commercial species” to “resident commercial species important for various fisheries”.

ES-20 24-25 See previous statements a bout citations in the Executive Summary.

ES-20 29 See previous statements a bout citations in the Executive Summary.

ES-20 29 Change “that was only about” to “of only ~”.

ES-20 31 See previous statements a bout citations in the Executive Summary.

ES-21 2 Change “only source of nitrogen to these systems” to “the dominant source of nitrogen to these systems”.

ES-21 5-6 Change “; creating increased grow th rates in some species over others, which changes competitive interactions among species; and nutrient imbalances” to “. This higher N availability affects the relative interspecific competitive of plant species resulting in changes in species composition and vegetation structure”.

ES-21 13-14 Change “to cause increased li tter accumulation in the soils and carbon storage in aboveground biomass” to increased carbon storage in aboveground biomass and litter”.

ES-21 16 Change “can” to “may”.

ES-21 17 Change “by nitrogen limitation can now better compete and alter species dominance” to “by nitrogen limitation are more competitive”.

ES-21 19-20 Change “the leaching of NO 3 - in soil drainage waters” to “soil NO 3 - leaching”.

ES-21 20 Change “in stream water” to “in surface waters”.

ES-21 22-23 Delete “; however, these measur ements are not always widely available”.

ES-21 26 Change “that nitrogen” to “that increased nitrogen inputs”.

ES-21 28- Is the description on the “extent of ecosystems” or the extent of the ecosystems impacted by nitrogen deposition?

ES-22 3-6 Delete these lines.

ES-22 19-23 This seems like a rather detailed finding and could be deleted from the Executive Summary.

95ES-23 8 Change “could be qui te high” to “is quite high”.

ES-23 11-13 Change “enrichment potentially incl ude decline in CSS habitat, decline in protection of native specie s, increase in abundanc e of nonnative grasses,

and increase in wildfires” to “enrichme nt potentially include declines in CSS habitat the protection of nativ e species, and increases in nonnative grasses and wildfires”.

ES-23 16 Change “helps regulate” to helps control”.

ES-23 17 Change “upset” to “disrupted”.

ES-23 19 Change “could” to “may”.

ES-24 1 Change “SO

x deposition on methylmerc ury production” to “SO

x deposition and resultant cha nge in soil and wetland SO 4 2- concentrations in affecting methylmercury production”.

ES-24 3 Change “scope of this review ” to “scope of the current review”.

ES-24 9-10 Change “While there are many uncertainties associated with these analyses, from a scientific perspective there is confidence that known or anticipated adverse ecological eff ects are occurring” to “Although uncertainties exist, there is strong evidence that known or anticipated adverse ecological eff ects are occurring”.

ES-24 12-13 Change “Of all the case study anal yses, there is most confidence in the ecological responses, effects, and be nefits associated with aquatic acidification” to “Within the case study analyses, there is most confidence in the ecological responses, effects, and the deleterious impacts associated with acidic deposition”.

ES-24 13-14 Change “and there is a fair am ount of confidence about those associated

with terrestrial acidification” to “S imilarly, the importance associated with the impacts of acidic deposition on terrestrial systems is clearly

documented”.

ES-24 15 Change “benefits” to “deleterious impacts”.

ES-24 18 Delete “However”.

ES-24 20 Change “only” to “dominant”.

ES-24 22 Change “benefits” to “deleterious impacts”.

96ES-24 25-26 Change “terrestrial acidification may be the most useful in terms of developing a secondary” to “terrestrial acidification should be most useful in developing a secondary”.

ES-25 These specific citations shoul d be removed f rom the Executive Summary.

1-2 2 Change “The species of nitrogen an d sulfur” to “The chemical species of nitrogen and sulfur’.

1-2 5-7 Change “because NO

x , SO

x , and their associated transformation products are linked from an atmospheric chemistr y perspective, as well as from an environmental effects perspective” to “because the atmospheric chemistry

and environmental effects of NO

x , SO

x , and their associated transformation products are linked”.

1-2 10 Change “of these two pollutants has been conducted” to “of SO

x and NO

x as well as total reactive N has been conducted”.

1-2 11 Delete “at this time”.

1-2 16-17 Change “in an ecologically mean ingful way” to “tha t is ecologically meaningful”.

1-3 1 Change “see” to “go to:”.

1-4 13 Why “identical”?

1-4 22 Change “This draft document” to This latter draft document”.

1-5 29 Change “At that time, EPA was aware that SO

x have” to “At that time,

EPA was aware that SO

x has”.

1-6 1 Change “specific SO

x concentrations” to “specific atmospheric SO

x concentrations”.

1-8 8 Change “at that time” at the time of the report (1995).

1-8 14 Change “particular relevance to this review” to “particula r relevance to the

current review”.

1-10 13-20 Should some mention be made of organic forms of N in the atmosphere including DON? It is noteworthy that in Figure 1.3-1 (page 1-11) that organic forms of N are shown

1-11 9-15 Although the figure shows some of the organic atmospheric S forms.

There is no mention of these chem ical species in the text.

971-12 19 Change “not high enough” to “not sufficiently high”.

1-13 6-7 Change “Both are essential and sometimes limiting, nutrients needed for growth and productivity” to “Both N and S are essential macronutrients”.

1-13 7 Change “Excess” to However, excess”.

1-13 10 Change from “These effects include slower growth” to “These effects include slower biotic growth”.

1-13 23 Change “Models suggest that” to “Models for the latter study area suggest

that”.

1-13 28 Change “acidification effects from acidifying deposition” to “acidification effects from atmospheric deposition”.

1-14 9 Change “that leads” to “that may lead”.

1-14 21 Change “quality in the western United States (U.S. EPA, 2008, Section 3.3" to “quality in the western United States, a region especially sensitive to increased nitrogen atmospheric inputs (U.S. EPA, 2008, Section 3.3"

1-14 23 Change “which leads to eutroph ication” to “which may lead to eutrophication”.

1-14 27 Change “in highly eutrophic estuar ies” to “in some eutrophic estuaries”.

1-14 30-31 Change “In terrestrial ecosystems, there are multiple chemical indicators for the alteration of the biogeochemical cycling of nitrogen that is caused by total reactive nitrogen deposition” to “In terrestrial ecosystems, there are multiple chemical indicators that the biogeochemical cycling of nitrogen has been altered by the de position of total reactive nitrogen”.

1-14-15 Change “Nitrate leaching” to “Nitrate leaching from terrestrial ecosystems”.

1-15 2 Change “the onset of leaching” to “the atmospheric de position threshold for nitrate leaching”.

1-15 7 Change “occurring at 3 kg” to “occu rring at atmospheric inputs as low as 3 kg”.

1-15 13 Change “this” to “the current”.

981-15 19 Change “In watersheds where ch anges in sulfate deposition did not produced an effect” to “In watersheds where changes in sulfate deposition did not result in changes in methylmercury generation”.

1-15 20 Change “meaningful” to “substantial”.

1-16 Figure 1.3-3 See previous comments on Figure ES-1 (Is this figure the same as Figure 1.3-3?)

1-17 18-20 This sentence needs to be reworded.

1-18 15-17 This sentence is confusing. Wh at is meant by “the uncertainties in the

estimated reductions”? Is the uncer tainty on the amount of atmospheric

reduction that will occur or uncerta inty on the effects of reductions?

1-19 21 Change “Identifying important ch emical species in the atmosphere” to “Identifying important N and S chem ical species in the atmosphere”.

1-21 6 Change “All of Figure 1.4-1" to “All of the components of Figure 1.4-1".

2-6 14-15 Change “to total loadings of in the environment” to “to the combined atmospheric loadings of both elements”.

2-7 7 Change “a broad look into the” to “an overview of”.

2-7 8 Change “services that is one tool that can help lin k” to “services. The analysis of the effects on ecosystem services will help link “.

2-7 10-11 Change “In this Risk and Expos ure Assessment, ecosystem services is

used as an umbrella term to aid in describing the impacts of ecological effects on public welfare and to help explain how” to “In this Risk and Exposure Assessment, ecosystem services is used to show the impacts of ecological effects on public welf are and help explain how” .

2-8 3 Change “data were not abundant enough” to “data were not sufficient”

2-8 19-20 This sentence seems out of place.

2-15 2-3 Does the statement “The analysis of ecosystem services for the aquatic

acidification focused on r ecreational fishing” indicating that focus for the current assessment of the general analys is of ecosystem services in aquatic ecosystems. I believe the sentence should be changed to: “The current assessment the analysis of effects on ecosystem services from aquatic

acidification focused on recreational fishing”.

2-15 24 Change “little data is” to “little data are”.

992-16 2 Change “ecosystems are addressed” to “ecosystems were addressed”.

3-2 25 Change “species-specific” to chemical species-specific”.

3-16 13-24 The term “measured deposition” is used and this needs to be changed to “estimated deposition” since dry deposition are inferred by model

calculations and not measured rates. Such nomenclature needs to be changed throughout the document.

3-22 8-16 The title should be changed to “Non-Atmospheric Loadings of Nitrogen and Sulfur”. The inclusion of exampl es associated with the contribution

of other sources such as the weathe ring of sulfur minerals should be

considered.

3-27 16 Change “White Face” to “Whiteface”.

3-93 23-28 The statement that “Although there are uncertainties in the data, models, and techniques used for this assessment, this analysis relies upon the most applicable measurements and state- of-the-science models. In addition,

these data and models are used in a manner that considers their relative strengths and limitations. Th e inherent uncertainties are not expected to measurably affect the robustness of these conclusions and findings on the

characterization of concentrations an d deposition” places a very “positive spin” on these model applications, I am not sure that this is entirely justified based upon the level of uncerta inties especially with respect to dry deposition estimates of the available models.

4-1 26-27 Change “Under natural conditions (i.e., low atmospheric deposition of nitrogen and sulfur), the limited mobility of anions in the soil controls the rate of base cation leaching” to “Under conditions of low atmospheric deposition of nitrogen and sulfur, the naturally produced bicarbonate anion

is often the dominant mobile anion with SO 4 2- and NO 3 - playing a limited role with respect to cation leaching”.

4-1 27-30 Change “However, acidifying depos ition of nitrogen and sulfur species can significantly increase the concentrat ion of anions in th e soil, leading to

an accelerated rate of base cation l eaching, particularly the leaching of

Ca 2+ and Mg 2+ cations” to “Increased atmospheric deposition of sulfur and nitrogen can result in marked increases in SO 4 2- and NO 3 - soil fluxes resulting in the concomitant leaching of nutrient (Ca 2+ , Mg 2+ ) and toxic (Al n+ and H + ) cations”.

4-2 8 Change to “Criteria for case study selection”.

4-2 11 Change “Current conditions for ot her areas” to “Current conditions for

these other areas”.

1004-2 26-28 Change “sum of soil and water processes that occur upstream within a watershed, it also reflects the results of watershed-scale terrestrial effects, including nitrogen saturation, forest decline, and so il acidification (Stoddard et al., 2003).” to “sum of te rrestrial and aquatic processes that occur upstream within a watershed. Im portant terrestrial processes include nitrogen saturation, forest decline, a nd soil acidification (Stoddard et al., 2003)”.

4-3 8 Change “certain” to “some”.

4-3 10 Change “where strong acids are depo sited into the soil” to “where strong mineral acids (e.g., H 2 SO 4 and HNO 3 ) are deposited or generated within

the soil.

4-2 13-14 Change “inorganic Al can become mobilized, leading to the leaching of Al into soil waters and surface waters” to “inorganic Al can be mobilized, leading to the leaching of Al fr om soils to surface waters”.

4-2 15 Change “differently” to “differently to acidic deposition”.

4-2 15-16 Change “on sensitive species” to “on different ecosystems and species”.

4-2 20 Change “migrates” to “leaches”.

4-3 23 Change “maintains the balance of electric charge” to “maintains electroneutrality”.

4-4 1 Delete “further”.

4–4 8 I would disagree that ep isodic acidification is more important than chronic

acidification.

4-4 7-8 Change to “Short-term (i.e., hour s or days) episodic changes in water chemistry have perhaps the most signi ficant biological effects” to “Shortterm (i.e., hours or days) episodic changes in water chemistry have important biological effects”.

4-4 9 Change “rainstorms or snowmelt” to “precipitation or snowmelt events”

4-4 10 Change “which tends to provide le ss neutralizing of atmo spheric acidity as compared with” to “than tends to provide less acid neutralizing than water passing through”.

4-4 12 Change “storm runoff or snowmelt” to “events”.

1014-5 9-10 Change “receptors” to “parameters”.

4-5 13-14 Delete “Although ANC does not relate directly to the hea lth of biota” and start sentence with “The utility”.

4-5 22 Delete “the”.

4-5 24 Change “Low ANC concentrations have” Low ANC has”.

4-5 30 Change “(Figure 4.2-1, a), whic h” to “(Figure 4.2-1, a) that”.

4-6 3 Change “has been found in studi es” to “has been found in various

studies”.

4-6 8-9 Change “Below 100 μ eq/L, it has been shown that fish fitness and community diversity begin to decline” to “Below 100 μ eq/L ANC fish fitness and community diversity begin to decline” .

4-6 11 Delete “decline; however, the overall health of the community remains good”.

4-6 13 Change “that are sensitive to negativ e effects on biota that are sensitive to

acidification” to “that are sensitive to acidification”.

4-7 2 Change “had to have” to “need to have”.

4-7 9 Delete “primarily”.

4-7 17 Change “fishers” to “fisherman”–this may not be a “sex neutral” term, but fishers refers to a type of animal.

4-8 2 Delete “in these states”.

4-8 13-14 Change “services, such as hydr ological regime regulation and climate regulation” to “services associat ed with hydrology and climate”.

4-8 15 Delete “specific”.

4-8 16-17 Change “delicate aquatic food chains” to “aquatic food webs” .

4-8 19 Delete “it is worth noting that”.

4-8 20-22 Delete “For example, these biol ogical control services may serve as “intermediate” inputs that support th e production of “fin al” recreational fishing and other cu ltural services”.

1024-9 4-5 Change “The regions of the United States with low surface water ANC values are the areas that are sensitive to acidifying deposition” to “The regions of the United States with low surface water ANC values are sensitive to acidifying deposition’.

4-9 6-7 Delete “at their existi ng ambient concentration levels”.

4-9 14 Change “surface water data” to “analyses of sulfur waters”.

4-9 19 Delete “are estimated to”.

4-9 21-24 Change “In 2002, Stoddard et al. (2 003) took another comprehensive look

at the level of acidifi cation within all of these regions. Although improvement in ANC occurred, about 8% of lakes in the Adirondack

Mountains and 6% to 8% of streams in the northern Appalachian Plateau and Ridge/Blue Ridge region were still acidic at base-flow conditions” to “Stoddard et al. (2003) suggested th at although improvement in ANC had

occurred ~8% of lakes in the Adiron dack Mountains and from 6% to 8% of streams in the northern Appalachian Plateau and Ridge/Blue Ridge region were acidic at base-flow conditions”.

4-10 9-12 Change “After considering this information, the Adirondack Mountains and the Shenandoah Mountains (referred to in this chapter as Adirondack and Shenandoah case study areas, resp ectively) were selected. The rationale for choosing these two cas e study areas is described in the following subsections” to “Using the ra tionale described in the following

subsections the Adirondack Mountains and Shenandoah Mountains were selected for case study areas”.

4-10 16 Change “The case study area” to This area”.

4-10-11 Delete “, which all dr aw water from the preserve”.

4-12 For Figure 4.2-3, the axes le gends and numbers are too small.

4-13 For Figure 4.2-4, the axes le gends and numbers are too small.

4-14 6-7 Delete “because it can no longer be measured”.

4-14 7 Change “Likewise, it is also difficu lt to determine” to “Likewise, it is also difficult to empirically determine”.

4-14 9 Change “hydrological” to “bioge ochemical”–MAGIC is not a hydrologic

model.

4-14 10 Change “quality levels” to “chemistry”.

1034-16 The insert on critical lo ads includes the value of 50 meq/m 2 . yr. This value may be confusing in using a load based upon charge versus mass since much of the proceeding discussion including inputs used mass values.

4-17 19 Change “the condition” to “the modeled condition”.

4-18 5-8 It is important to mention that although SO 4 2- still dominates the relative importance of NO 3 - is increasing substantially. Also, comparing

concentrations of SO 4 2- and NO 3 - in surface waters can be misleading since there may be s ubstantial losses of NO 3 - due to biotic processes in

watersheds.

4-18 13 Were these declines in Al statistica lly significant?

4-18 14 Change “significant” to “substantial”.

4-20 1-5 Reword this sentence it makes not sense.

4-20 7 Change “is” to “was”.

4-20 10 Change “are” to “were”.

4-21 2-5 Change “Percentage of Adirond ack Case Study Area lakes in the five

classes of acidification (i.e., Acute, Severe, Elevated, Moderate, Low) for years 2006 and 1860 (preacidification) for 44 lakes modeled using

MAGIC. Error bar indicates the 95% confidence interval” to “Percentage of Adirondack Case Study Area lakes in the five classes of acidification (i.e., Acute, Severe, Elevated, Moderate, Low) for years 1860 (preacidification) and 2006 for 44 la kes modeled using MAGIC. Error bar

indicates the 95% confidence interval ”. (Make similar changes in other figure captions including 4.2-19)

4-21 8-11 Change “Sites labeled by red or orange dots have less buffering ability than sites labeled with yellow and gr een dots, and hence, indicate those

lakes that are most sensitive to aci difying deposition, due to a host of

environmental factors” to “Sites indi cated by red or orange circles have less buffering ability than sites labele d with yellow and green circles, and hence, indicate those lakes that are most sensitive to acidifying deposition”.

4-22 2-7 In figure caption chan ge “dots” to “circles”. Make similar changes in all figure captions and text.

1044-23 7-9 Change “In considering the future responses of lakes to current emissions and given the current cond ition of the lakes, the question becomes whether lakes can recover to healthy systems (i.e., ANC > 50 μ eq/L)” to “In considering the future responses of lakes, the question becomes whether lakes can recover to healthy systems (i.e., ANC > 50 μ eq/L) under current levels of deposition”.

4-24 4-11 Change “Based on a deposition s cenario that maintains current emission levels to years 2020and 2050, the s imulation forecast indicates no improvement in water quality” to “B ased on a deposition scenario that

maintains current emission levels to up to years 2020 and 2050, the simulation forecast indicates no improve ment in water quality over either of these periods”.

4-24 15 Change from “will likely not improve the acidification of lakes” to “will not likely improve the recove ry from acidification”.

4-24 15-17 Delete this sentence.

4-24 24-25 Change “At this time, it is uncle ar why ANC initially improved and is now declining” to “It is not known what has caused this temporal pattern of ANC in this case study”.

4-25 Table 4.2-4 Indicate wh at “+/-“ columns signify.

4-26 3 Change “changed statistically” to “did not significantly differ”.

4-26 19 Change “industrially generate d acidifying deposition” to “acidic deposition”.

4-26 21 Change “is” to “was”.

4-31 3 Change “Based on a deposition scen ario that maintains current emission

levels to 2020 and 2050" to Based on a deposition scenario that maintains current emission levels to years 2020 and 2050".

4-31 12 Change “country” to ”U.S.”.

4-31 13 Change “across populations” to “across various populations”.

4-31 14 Change “picked” to “selected”.

4-31 15 Change “to make estimates of region al extent of condition (e.g., number of lakes, length of stream)” to “to make regional estimates of surface water

conditions”.

1054-31 21 Change “to be susceptible” to “to be especially susceptible”.

4-32 24 Change “area” to “areas”.

4-32 32 I don’t believe the term “ecoregi on” been defined in the document.

4-26 19 Change “industrially generate d acidifying deposition” to “acidic deposition”.

4-34 10 Change “SO 2 " to “SO

x ”.

4-34 13-14 Change “One hundred 17 lakes of the 169 lakes modeled fo r critical loads are part of a subset of 1,842 lakes in the Adirondack Case Study Area” to

“ Of the 169 lakes modeled for critic al loads, 117 of these lakes were within 1,842 lakes in entire the Adirondack Case Study Area”.

4-34 14-15 Delete “which include all lakes from 0.5 to 2,000 ha in size and at least 1 m in depth”.

4-34 21 Change to “13% of the total population ”.

4-34 22 Change “some lakes would have never had ANC” to “some lakes would

have never had ANC”.

4-34 24-25 Change “estimate based on the cr itical load alone” to “estimate based solely using the critical load criterion”.

4-34 26 What is meant by “natural”? Do es this refer to current conditions or preindustrial concentrations? The term natural with respect to surface water acidity needs to be defined. It mi ght be clearer to di scuss the role of

DOC in these waterbodies that have historically low ANC.

4-35 20 Change “the same” to “similar”.

4-36 12-14 Change “a host of catchment pr ocesses and environmental factors that affect the level of base cations (e.g., Ca + , Mg + ) concentrations and the sinks of nitrogen and sulfur in the la ke and terrestrial catchment” to “a series of biogeochemical processes that produce and c onsume acidity in

watersheds”.

4-36 19-21 Change “Although ANC does not dir ectly affect the health of biotic communities, it ameliorates acidity-related biotic stress that provides an “ecological indicator” of overall inte grity of the ecosystem” to “Although ANC has not generally been used as a parameter for predicting the health of biotic communities, it provides useful information of the potential acidity-related biotic stress and hence is a useful “ecol ogical indicator”.

1064-36 22 Delete “then”.

4-37 9-10 Change “To convert surface water concentrations into surface water fluxes, multiply by runoff (Q) (in m/yr) from the site” to Surface water concentrations are converted to fluxes by multiplying concentrations by runoff (Q) (in m/yr)”.

4-37 12 Change “between plants and soil is ignored” to “between plants and soil is negligible”.

4-37 19-21 This sentence is confusing. Certainly the nitrogen and sulfur biogeochemical fluxes and transformations affect acidity.

4-40 1-3 This is not just a problem fo r the United States. The estimate of weathering rates (including the genera tion of base cations) is a major limitation for many biogeochemical an alyses and interpretations

4-42 22 Delete “a coniferous tree sp ecies” and “ a deciduous tree species”.

4-48 6 Delete “and forest”.

4-62 14-18 The following statement “Collectivel y, these results suggest that the health of at least a portion of the sugar maple and red spruce growing in the United States may have been comp romised with the acidifying total nitrogen and sulfur deposition in 200 2; even with the lowest level of protection, half the states contained s ugar maple and red spruce stands that were negatively impacted by acidi fying deposition” will receive

considerable attention. It is important that any caveats be provided on these results so that the interpretatio n is placed in the most complete picture of the state of the science.

4-65 10 Change “was” to “is”.

4-66 17 Does the “average critical loads” have any real meaning in the context of setting critical loads. I would suggest that the ra nge is the most important and demonstrates and clearly shows ho w edaphic factors can have a major

influence on critical loads.

4-67 Figure 4.3.9 See previous comment w ith respect of providing the values for average critical loads.

4-68 Figure 4.3.10 See comment above on th e use of average critical loads in this figure.

1074-69 The discussion of uncertainty is important and highlights some of the

issues related to the actual calculatio n of critical loads. It may be over stretching the uncertainty analyses to suggest that “If all or a large majority of estimates indicate that the critical load of a system is exceeded with current total nitrogen and sulfur deposition rates, the probability is high that deposition is greater than the critical load and that the trees and vegetation in that system are being ne gatively impacted by acidification”. The use of the term “probability” seems out of place and suggests that this approach has a stronger statistical un derpinning than is the actual case. The key factor is what are the range of values that affect these calculations and how confident are you in usi ng these values in making these calculations. Similarly the term “certainty” would suggest more confidence in these estimates than may actually be the case.

4-71 3-5 This type of calculation in which it is clearly shown how different values

can be obtained for critical loads ba sed upon specific edaphic factors (e.g., parent material acidity) is a useful approach and show how this factor can have a dramatic impact on these calculations.

5-2 24 Change “resulting in increased pr oductivity (e.g., of algae or aquatic plants)” to “resulting in in creased primary productivity”.

5-2 25 Change “increases, dissolved” to “i ncreases with concomitant increases in organic matter production, dissolved”.

5-4 24 Change “for a portion of the nitr ogen input” to “for a portion of this nitrogen input”.

5-8 21-22 Delete “Therefore, if the suscepti bility is known and held constant, a curve

can be created”.

5-9 10 The determination of on the nitroge n inputs in “pristine” conditions is a difficult task. I agree that providi ng some upper and lower bounds is a useful approach.

5-10 19 Change “fish” to “seafood”. Th roughout this section ch ange wording so

that is clear that the entire “seafood” resources, not only fish are being

considered.

5-11 5 Change “fish” to “seafood”.

5-12 10 Change “and reduce” to “and reduced”.

5-14 7 Change “are” to “were”.

5-14 14 Change “175 million days” to “175 million participant days”.

1085-14 15 Change “more than 35 million days per year” to “more than 35 million participant days per year”.

5-14 19-20 Change “including climate, biol ogical, and water regulation; pollution detoxification; erosion prevention; an d protection agains t natural hazards” to “including those important for th e quality and quantity of water and effects on climate including impacts from storms”.

5-15 13 Change “defining” to “determining”

5-29 3 Change “under suspicion of eutrophication”likely to be subject to eutrophication”.

5-29 31 Not sure if “in prep” information should be cited.

5-47 2 There is a mixture of aquatic a nd terrestrial ecosystem benchmarks in “Figure 5.3-2. Benchmarks of atmosphe ric nitrogen deposition for several ecosystem indicators” with the inclusion of the diatom changes in the Rocky Mountain lakes.

5-57 7-8 I am not sure that the follow ing statement is valid: “However, the ecological benchmarks suggested for alpine ecosystems were comparable

to the benchmarks from CSS and MC F ecosystems”. At a minimum some supportive statements are needed.

5-64 10-15 The discussion on amounts of nitrog en in throughfall appears to suggest

that these differences are due to di fferences in atmospheric deposition. Although some of this difference may be due to the amounts of atmospheric deposition, the impor tance of canopy exchange in contributing to nitrogen in throughfall ma y also be important. See also on page 5-68 with respect to the esta blishment of critical loads based upon throughfall nitrogen flux.

5-67 1-3 The statement that “increased litter deposition may facilitate faster rates of microbial decomposition initially but may reduce decomposition over the long term because of changes in the C:N ratio and increasing lignin

content over time” needs clarification.

5-72 1 Change “classic” to “documented”.

5-75 17 Delete “from nitrogen-saturated forest soils”.

5-75 17 Change “into streams” to “int o streams of the northeastern U.S.”.

6-2 31-32 Change “aquatic environments” to “aquatic and terrestri al environments, including wetlands,”

1096-2 33 Delete “surface water”.

6-11 1 Change “emissions” to “deposition”.

6-12 24 Change “its global warming potential” to “its global warming potential per

molecule”.

6-14 14-15 Change “Nitrogen deposition can a ffect the patterns of carbon allocation because most growth occurs above ground” to “Nitrogen deposition can affect the patterns of carbon alloca tion between above and below ground production”.

6-14 15 Change “This increases the shoot-to-root ratio” to “Inc reased nitrogen availability increases th e shoot-to-root ratio”.

6-11 20 Change “Reducing SO

x ” to “Reducing SO

x emissions”.

110

### Mr. Rich Poirot

General Comments on Chapter 3 This chapter summarizes the technical approach fo r characterizing spatial and temporal patterns in the atmospheric deposition of S and N co mpounds – originating from anthropogenic SO

x , NO

x and NH

x emissions - in the various case study areas. As a practical matter, these estimates are made with relatively high spatial and tempor al resolution covering the entire US, and with flexible modeling methods that will allow scaling of estimated deposition patterns and effects to other sensitive areas, and would also support evaluating potential responses to changes in deposition, air quality and/or precursor emissions.

Generally, I think the chapter is clearly written, conveys useful information, and presents convincing support for the approaches taken to pr ovide the best possible estimates of air quality and deposition in the case study areas and else where within th e US measurement and modeling domains. One general criticism is that on seve ral occasions the discus sion seems unnecessarily qualitative in places where it would take no more space and provide more useful information if quantitative information was provided. Rather th an saying “much greater” or a “vast majority” you could say “5 times greater” or “90%”, etc.

The various maps showing emissions concentrations , depositions, etc. are very helpful. Even though effects of aerosol-phase S and N compounds are intentiona lly (and unfortunately in my opinion) excluded from these s econdary NAAQS discussions, I th ink it would be useful to include maps of sulfate, nitrat e and ammonium aerosol concentra tions. These should be readily available as CMAQ model output, as well as from the relatively dense IMPROVE + CSN aerosol speciation networks. It woul d also be useful to show some “ratio” or “difference” maps – for example the ratio of S (or N) deposition to SO 2 (or NO 2 ) concentration and S (or N) deposition to S (or N) emissions, and the ratio of total reduced nitrogen deposition to total nitrogen deposition. Ratio or difference maps could also be a useful way of communicating differences between measured and modeled gaseous or aerosol concentra tions or deposition. In making these maps, it may be necessary to employ some spatial aggregation or smoothing to “show” the information clearly.

1. The first charge question asks if the chapter appropria tely identifies and describes

uncertainties associated with th ese air quality-related analyses . The Section 3.5 “discussion of uncertainties” includes a fairly complete listing of the various types of uncertainties associated with the characterization of air quality and de position in the case study areas. However, the descriptions and discussions of th ese various causes of uncertainty are so minimally detailed and (intentionally) non-quantitative that I’m not sure much useful information is conveyed.

One exception is a detailed (but graphical on ly) comparison of the wet N and S deposition estimates derived from simple interpolation of NADP data (the method used in this assessment) compared to similar estimates based on a highe r-resolution enhanced deposition model (Grimm and Lynch, 2004), as well as to CMAQ wet depos ition estimates for the Adirondack case study area and surrounding region. This is an informa tive comparison (and responsive to previous CASAC suggestions), but the resu lts could be more useful if somewhat more quantitative

111comparisons could be included. For example, th e maps showing the “similar” spatial patterns might be accompanied by scatter plots providing a more quantitative comparison of the gridded data, perhaps with different colored symbols to indicate grid points (a) within the Adirondack case study area and (b) within or including the watersheds of the case study lakes. A minor point here is that I don’t think the Grimm/Lynch m odel really accounts for cloud water deposition,

which can make substantial additional cont ributions above elevations of about 600m.

Section 3.3.2 indicates that the discussion of uncertainties in s ection 3.5 will include a comparison of (2002) results from CMAQv4.6 a nd v4.7, but no such comparison is actually included there. A brief mention of these compara tive results is given in Appendix 1, but this is quite minimal (TNO 3 over-prediction in CMAQv4.7 is about twice that of CMAQv4.6), includes no discussion of possible causes of the differenc es, and is not especially useful. I recommend adding some quantitative summary (perhaps a table) of the model/measure and model/model comparisons presented in Appendix 1 to Section 3.5. This could be accompanied by a caveat that such quantitative comparisons ar e not intended to be comprehensive...

To the extent possible, it would be useful if so me indications of relative uncertainties could be provided. For example, I would guess that uncerta inties in estimated dry deposition are greater than for wet deposition, and that uncertainties in the total depo sition of deposition of reduced N are greater than for oxidized N, which are greater than for sulfur depositio n. In addition, I would imagine that uncertainties in the characterizati ons of emissions, air qua lity and deposition are relatively small compared to uncertainties in th e resultant chemical and biological responses in the affected ecosystems.

2. The second charge question asks whether replacing the prev iously presented RSM analysis with a new set of CMAQ simulations provides an ability to adequately examine the contributions

of NO

x emissions to total (reduced and oxidized) N deposition. I’m not sure that the previous RSM approach was inadequate; rather I think th e RSM and its uncertainti es were not very well explained and documented in the last draft REA. However, I do think the current approach including additional CMAQ runs, which separately explore effects of 50% reductions in NO

x , NH

x and SO 2 emissions and also explore inter-annua l variability through use of different meteorological years, provides a clearer and more transparent view of the relative contributions

from oxidized and reduced N emissions. This is further supported by the model/measurement and model/model comparisons summarized in Appendix 1.

3. The 3 rd charge question asks if the evaluation of CMAQ model performance presented in Appendix 1 is sufficient to support the use of the model in this review. In my opinion, Appendix 1 is presented very clearly and concisely, and doe s provide sufficient support for the use of the model in this review. One suggestion that might help strengthen this support would be to include some additional references documenting the fairly extensive past perfor mance evaluations to which the model has been subject (i.e. by Appel, Napelenok, Pinder, Gillia nd, Dennis, etc.). A second suggestion is to add – either in the append ix or in the Chapter 3 section on uncertainties, a brief summary of the possible implications of the model performance evaluation to the risk assessments being conducted in the selected case study areas.

112Specific comments on Chapter 3 p. 3-2, line 18: “

x ” should be “NH

x ”. Also you could add “, and their atmospheric transformation products” after “SO

x ” and add “the earth’s” before “surface properties”.

p. 3-2, line 19: You could change “parameters” to “variables”.

p. 3-2, line 22: absence of routin e occult deposition measurements is not much of an excuse for ignoring what we know very well is an important input at higher elev ations and in coastal areas. You could have at least modeled it, as you have done for dry deposition.

p. 3-3, lines 3-4: This is only a half truth. NO and NO 2 are also relatively reactive and may be removed by chemical transformation (to so luble species and/or to compounds like HNO 3 with high deposition velocities) and more rapidly th an less reactive more soluble gases like SO 2 under a range of conditions. Al so, a high proportion of NO

x emissions are from automotive sources at ground level, and so the potential for long range transport is less th an for elevated stack releases.

p. 3-4, line 11: Could you add a parenthetical (XX%) to indicate more clearly what you mean by “the vast majority”.

p. 3-5, line 4: Same comment as previous one. It would cost you no space to indicate quantitatively by how much are the NO

x emissions “far greater” in the East than in the West. One easy way to do this would be to add “(tota l 2002 emissions = XXXX tons/yr)” to the labels of the Eastern , Western and National US NOx emi ssion pie charts in Figure 3.2-1. Also in line 5, instead of telling us that the most of the Western NO

x emissions are from California but are “not shown”, why not just add a (XX%) and show us what you mean.

p. 3-5, lines 7-8: So what’s th e implication (if any) for depos ition-related effects of highly episodic NO

x emissions from forest fires? Do we expect episodic acidification or eutrophication? I doubt it.

p. 3-6: I don’t understand how confined animal feeding operations greatly increase the volumes

of animal wastes. I can see c onfined feeding increasing emissions densities and the emissions of volatile components of these wastes to the atmosphe re (or in runoff to surf ace waters), but would think the volume of waste produced by 100 cows is about the same weather they are confined or

disbursed.

p. 3-8, line 5: You could add “stationary com bustion” between “non-EGU” and “sources”, as everything is either an EGU or a non-EGU.

p. 3-8, line 10: How much is “much greater in the East”? Again, why not just add the East, West & National totals to the pie chart labels in Figure 3.2-4.

p. 3-10, line 13: add “.” after “area”.

p. 3-11, lines 27, 28, 32 and p-3-12, lines 1, 4, 7, 10: Text describing fi gure refers to “NO

x ” but Figure 3.2-6 refers to “NO y ”.

113p. 3-15, lines 21-22: I assume you mean “reduced nitrogen wet deposition was calculated from measurements of wet ammonium (NH 4 + ) deposition”.

p. 3-16, line 13: You could add “”N” after “measured”.

p. 3-24, lines 9-10: Refers to a comparison of CMAQ v4.6 and v4.7 results included in Section 3.5 discussion of uncertainties, but no such comparat ive results are presente d there, and these are only minimally described in Appendix 1 (which includes a footnote on p 1-1 noting that the differences in v4.6 and v.4.7 are small, “as described in Chapter 3”. It would be useful to actually see this description in chapter 3, along with a more detailed comparison in the Appendix.

p. 3-27 and elsewhere “Whiteface” is one word.

p. 3-27, lines 17-18: The recently available 2008 data show a decrease, and you could add a

comment to this effect.

p. 3-31, Figure 3.3-3a: I think it would be clearer a nd shorter to present this data and that from the following 8 pie charts in tabular form and to show both the amounts in kg/ha/yr as well as in %, or you could at least add the totals (X kg/ha/y r) in the figure titles.

pp. 3-49 through 3-57: I would prefer that figures 3.3-6a through 3.3-6i were stacked bar charts showing the absolute (rather th an %) amounts of the various com ponents (Wet Re N, dry Ox N, etc.) in each season. We don’t need the units to be “% of annual total by season” to see which seasons are most and least important and by how much. Similarly, the charts in figures 3.3-7a through 3.3-7i don’t seem to convey very useful in formation. I think deposition of some species may have different environmental consequences in different seasons, and so it would be more important to no how much of spring N deposition co mes from oxidized N than it is to know what

fraction of total annual oxidized N is deposited in spring. Also, if absolute amounts were shown rather than percentages of total, it would give a good sense of differences in the various kinds of deposition by site and by season.

p. 3-59, line 10: Whiteface is one word.

p. 3-62: Use consistent terms for the case study ar eas in the 2 figures (Transverse Range vs. Los Angeles Range).

pp. 3-70 through 3-78: As for the seasonal N de position charts, I think stacked bar charts showing absolute amounts from wet & dry S dep. by season would convey more useful information, and would also convey the differences in total & seasonal dep. rates in the different study areas. Also, what’s the purpose of the la rge gap between dry & wet dep. bars in figures 3.3-15a through i?

p. 3-81, line 15: It isn’t clear what “This” refers to.

114p. 3-82, line 5: “ 4 NO 3” should be “NH 4 NO 3 ”.

p. 3-82, line 8: “

x ” should be “NH

x ”.

p. 3-82, lines 14 & 15: Figure 3.4-4 doesn’t really show “contributions of total reactive nitrogen approaching 50%”. It shows a nearly 50% reduction in to tal nitrogen deposition if NH 3 emissions were reduced by 50%. If contributio ns of 50% were reduced by 50%, total N dep would have been reduced by 25%.

p. 3-82, line 29: “ 4 NO 3 ” should be “NH 4 NO 3 ”.

p. 3-93, line 5: I think “similarities in differences” should be “similarities and differences”.

pp. 3-94 – 3-96: The figure captions refer to “tot al” oxidized N, reduced N or sulfur deposition, but I think they are (and text indica tes they are) for “wet” deposition only.

Specific comments on Chapter 4 p. 4-5, line 17: I think you m ean “...models do a better job pr ojecting ANC than they do for projecting pH and inorganic Al ...”

p. 4-1, Figure 4.2-4: The font labeling the fi gure axes and legend is too small to read.

p. 4-14, Table 4.2-2: Give units in table ( μ eq/l, I presume).

p. 4-18, line 7: Table 4.2-2 does se em to indicate that current SO 4 2- is “19 fold” greater than

NO 3 - but this seems inconsistent with Fi gure 4.2-6 – which shows current (2006) SO 4 2- is about 4 times greater than NO 3 - . Why the difference?

p. 4-24, line 1: Should be “reduc tions ... are” or “reduction ...is”.

p. 4-25, lines 24 & 25: Table 4.2-4 needs units, and again the observation that SO 4 2-
concentration is 11 fold greater than NO 3 - (from table) is inconsiste nt with figure 4.2-14 which shows current (2005) sulfat e being about 6x nitrate.

p. 4-40: It would be more effective to show some quantitative results from the sensitivity analysis in tabular or graphical form – possibly in an appendix – rather than just claiming that you did it and that it looked good to you. Without better context and detail, its impossible to know the implications of some of your summary statements – for example what does it mean that “similar results were given for the number of lakes with all realizations a bove the critical load” or that “changes in critical load valu es could range from 3 to 24 meq/m2/yr...”

p. 4-41, lines 13-18: Its not clear what’s being described “which is on average a 15 μ eq/l

difference in ANC concentrations or 10%” or what’s “on average [an] 8 μ eq/l difference in ANC

concentrations or 5%”.

115General comments on Chapter 7 Synthesis and integration of these disparate cas e study results is an in herently challenging undertaking, and given the difficult task, I think chapter 7 is reasonably well done. I especially

like the discussion of uncertainties in Section 7.2 which is organized along the lines of a conceptual model which ultimately relates ecological benefits or welfare effects back to ambient air quality indicators. This conveys the logical progression fro m air quality to environmental

effects and also illuminates the weakest links in this chain. Since the case studies are both diverse and also represent rath er extreme conditions, its difficu lt to envision how the case study results might be scaled to cover a range of e nvironmental effects exte nding over broader spatial areas. For aquatic acidification, ex amples are provided for how th e case study results might be extended to larger populations of lakes and streams, but its much less clear how this could be done – in ways that would either support selec tion of specific air quality indicators, or support implementation of secondary NAAQS based on those indicators – for terrestri al acidification or aquatic or terrestrial nutrient enrichment. Some added discussion of the spatial extent of the

kinds of environmental effects cons idered in the case studies woul d be useful in this chapter.

Another possible missing piece in this synthesi s and integration is a discussion of how the different environmental indicators might relate to each other. Using the example conceptual model diagram in Figure 7-2, it seem s like there might be (at least) four different diagrams and secondary standards - one each for aquatic and terre strial acidification and aquatic and terrestrial

nutrient enrichment. And each of these would be further modulated by various mixes of S and N deposition and the inherent sensitiv ities of the effected ecosystems . However, it also seems likely

that there would be substantial overlap in areas with surface waters exceeding an ANC threshold

and areas where forest soils have Bc/Al ratio s below a specific threshold. Possibly the two indicators are sufficiently closely related that a single indicator c ould be selected that would be “controlling”. I wonder if it would be possible to identify a Bc/Al ratio that’s the approximate “equivalent” (i.e. would cover about the same spatial area) of an ANC of 50? Or in terms of the severity of environmental effects or the sustai nability of some current or improved level of environmental quality, what level of ANC is the approximate equivalent of a Bc/Al ratio of 10, and what kinds of ecological effects from a quatic or terrestrial N enrichment would be

considered to be of similar severity? For a given “acid sens itive” area with poor buffering capacity, it would be useful to know whether the aquatic acidification thres hold or the terrestrial threshold is more limiting (and whether the answer to this question is based on the inherent

environmental sensitivities or on the relative sever ity of the selected thre sholds of adversity).

1. The first charge question asks about the extent to whic h the description of ecosystem services provides a useful framework in the case study analysis for informing standard setting. While I think the quantitative estimates of (sel ected) ecosystem servi ces can be one useful

consideration to inform standa rd setting, I think it should be clearly recognized that each presented example of ecosystem services is it self a limited case study. I think the example of considering (only) sport fishing (dis-) benefits from aquatic acidification helps illustrate this point – as it seems only a few degrees rem oved from David Stockman’s infamous 1983 calculation that acid rain controls would cost $6,000 per pound of Adirondack brook trout. I think the presentation of example ecosystem servi ces is useful in chapter 7, but it should be emphasized that only a few examples – with re latively easily monetized benefits - are provided here. An alternative approach to considering “ad versity” of effects might be to consider the

116concept of “sustainability”. Given geo-specific rates of soil & bedrock weathering for example, what rates of acidic deposition can be sustained indefinitely without eventually leading to degradation of environmental resources. I think this concept of sustainability is especially important in considering effects which result from long-term, cumulative deposition processes.

Another relevant concept which is not really addressed in this chapter or in previous sections

relates to the nature and/or rate s of “recovery” of adversely affect ed ecosystems. A current level of damage that has resulted from past a nd continuing deposition of acidifying or nutrient enriching S and N compounds may not be fully re versible to pre-deposi tion conditions and/or may require a substantial lag period between re duction in emissions (and concentrations and deposition) and improvements in environmental conditions. Possibly the “time to” and “degree of” recovery might be va riables considered in judging the re lative adversity of effects. Since secondary standards have no fixed time requireme nt for attainment, another possible approach here might be to consider sta ndards requiring a certain rate of progress towards long-term goals which may not be feasible to a ttain quickly in all areas.

2. The second charge question asks if sufficient information is provided to inform standard setting based on effects other th an aquatic acidification (terrest rial acidification, terrestrial nutrient enrichment and/or aquatic nutrient enrich ment). As indicated above, I think its possible to identify some deposition thresholds estimates of terrestrial acidifi cation effects, using something like the Bc/Al ratio, that might be ex tended over relatively large spatial areas (as has been recently done for New England and Eastern Canada and as is currently being extended to NY). I also think its likely that there will be co nsiderable overlap in regions of, and extent of severity of effects on, aquatic a nd terrestrial acidification, and/ or that there may be a common level of S+N deposition that provides an approxim ately equivalent level of protection against both kinds of effects. If a specific ANC threshold is considered for aquati c effects, it should also be relatively easy to calculate necessary S+N deposition reductions to attain such thresholds and then to calculate improvements in Bc/Al ratios and terrestrial effect s that would result.

Another possibility that should be considered is that if the ambient air quality indicators are required to be in units of the nomin al gaseous criteria pollutants – SO 2 and NO 2 – such measures are more related (spatially and temporally) to th e emissions that need to be controlled, while the

effects of those emissions are more related to the long-term deposit ion of the chemical transformation products – SO 4 = and NO 3 - – in combination with inherently sensitive bedrock and soils. These areas of greatest effects are therefore inevitably displaced, sometimes at considerable distance, downwind of the areas of highest emissions and gaseous precursor

concentrations. An exceedance of an environmen tal indicator should ther efore logically trigger exceedances of the air quality indicator in rela tively large upwind regions. If for example an

ANC or Bc/Al threshold is exceeded in the so uthern Green Mountains of VT – as can be expected given recent TMDL calculations for acid sensitive lakes there, and recent Bc/Al calculations by the NEGECP for th at area – a zero-out of all SO

x and NO

x emissions in VT would have little or no effect on reducing the S + N related exceedances of the ANC or Bc/AL thresholds in that region (which is much mo re dependent on emissions from NY PA and OH). The secondary SO 2 and NO 2 standards should be considered to be exceeded until they are reduced to such levels throughout the eastern US that the deposition-related indicators are not exceeded in (VT and other) acid se nsitive areas within that region.

117Regarding possible NAAQS based on nutrient enri chment indicators, th e various terrestrial effects at different and widely varying N depositi on rates as summarized in Figure 7.1-3 provides some basis for considering secondary NAAQS based on several different (low, medium and high) degrees of protection base d on total N deposition rates, and calculations could be made of the necessary reductions in NO 2 concentrations and NO

x emissions over broad spatial scales needed to attain those levels of protection. As with acidification-based standards, I don’t think its necessary – and may be count er-productive – to try to link environmental indicators and air quality indicators on a point-specifi c basis, but rather we might c onsider what levels of total N deposition and effects protection would be achieved in areas with the most sensitive ecosystems

if ambient NO 2 concentrations (and NO

x emissions) were reduced by various amounts or percentages throughout the surrounding region.

Considering a secondary NO

x standard based on aquatic nut rient enrichment is further complicated by the large and often dominant contributions from non-air sources. However, calculations could still be made of improvements in aquatic effects that would be expected if oxidized N deposition (and/or NO 2 concentrations) were reduced to certain absolute levels or by certain percentages, with contributions from NH

x and non-air sources taken as a given. This process along with similar assessments for terres trial nutrient effects and acidifying effects of N deposition might lead to considering a range of secondary standards that would yield a range of

beneficial environmental effects.

I think the discussion of uncertainties in secti on 7.2, organized as a conceptual model linking air quality indicators to ecological e ffects, can also be used as a guide to areas that would benefit

most from future research and/or environmenta l assessment for future NAAQS revisions. I also

think continuation of the work conducted for th is assessment has good poten tial applications in areas outside the specific SO

x and NO

x NAAQS revision process. Hi storically, major reductions

in SO

x and NO

x revisions have resulted largely through national and regional programs justified by benefits in a wide range of health and environm ental effects. This will likely hold true in the future as future revisions to national automotive emissions standards, (whatever replaces) the Clean Air Interstate Rule, future checkpoint s for the Regional Haze Rule, and likely lower NAAQS for PM and ozone will all result in, or be strengthened by advance assessments of, the

environmental benefits of lower SO

x and NO

x emissions.

Specific comments on Chapter 7 p. 7-1, lines 21-22 : I don’t think you really mean that a welfare effect is what “society views as beneficial”. Society vi ews good visibility or a healthy envi ronment as beneficial. A welfare

effect occurs when these bene ficial welfare or environmenta l goods are adversely affected.

p. 7-10, lines 1-7: Its not really clear if or how you intend a singl e ANC indicator threshold to be protective against seasonal or episodic variat ions. Nor does it seem likely that a given ANC limit, measured at summer low flow for example, would protect all lakes and streams equally against episodic acidification effects from spring snowmelts.

p. 7-11, lines 16-19: For the Bc /Al ratios of 0.6 and 1.2, quantit ative estimates of reduced growth are provided (and seem rather “non-protec tive” if they would allo w 75% or 50% of North American tree species to experien ce growth reductions). By cont rast, not much justification is

118provided for the selection of the more protective Bc/Al ratio of 10 – othe r than the observation

that it’s the most conservative value used in so me analyses. There isn’t really any better justification for the 10 ratio provid ed in Chapter 4 or in Appendix 5, and I think there needs to be a clearer explanation for why a nu mber of prominent studies have used this ratio. This seems especially important given the large range between 1.2 and 10, and the large spatial areas that will presumably fall within those extremes.

p. 7-12, line 4 “res” should be “red”.

p. 7-13, Figure 7.1-2: This figure is not described very well in th e text. For example, what are the OEC and OHI scores, or how does the chart show that a greater than 100% reduction in atmospheric N deposition was needed to move from bad to poor.

p. 7-14, line 22: What’s a “compar ed forest health decline”?

p. 7-14, line 26: Its not clear wh at “(generally at deposition ra tes of < 10 kg N/ha/yr)” means here. I assume this is a general description of the N additions applied in a particular set of experiments – that have shown transient growth increases followed by increased mortality at deposition rates below 10 kg N/ha/yr, but don’t mean to imply that experimental treatments at 10 kg N/ha/yr or greater showed no transient growth increases or increased mortality.

p. 7-19, line 12: I assume that non -use (existence) servic es would also be affected by aquatic or

terrestrial acidification or terrestrial nutrient enrichment.

119

### Mr. Dave Shaw

Executive Summary

1. In response to the Panel’s review of the first draft Risk and Exposure Assessment, we have included an executive summary of this document. Does the Executive Summary adequately summarize and characte rize the key issues driving this review as well as the important findings of the analyses? Do es the Panel have any suggestions for clarification or refinement of the Executive Summary?

I feel that the REA Executive Summary provides a clear summary of each of the chapters with conclusions allowing the reader to extract highlights of the report without reading the entire

report.

I would like to see some clarification on critical loads and how it is used in this assessment. I appreciate that the area s of confidence are expre ssed in the conclusions.

General Comment

I am still committed to the idea that one of the key issues driving this review should be to also identify where data is missing with the intention of filling those gaps. I feel that this should be clearly stated in the Executive Summary, perhaps al so listed in the Policy Relevant Questions on Page ES-3. While this may be so mewhat addressed in the last two bullets, I feel that it deserves a little more emphasis.

Some other items that would help to emphasize this key issue:

• Improve the link/reduce uncertainties be tween ambient air quality indicator and deposition.

• Improve/reduce uncertainty in response m odels (e.g. MAGIC and SMB) or create new ones, to be better predictors (e.g. of pH, Al) and to be better at scaling up to the broader regions. Consider developing Base Cati on Surplus as a substitute for ANC.

• The above bullets would require improved input data.

The natural course of action in addressing the above bulleted i ssues would be to ask EPA to make a separate exercise of identifying future da ta refining needs. Now that we have the ISA and

REA documents to substantiate the needs. Th e goal should be to increase the confidence in ecological exposure, responses, effects and benefits to all other areas beyond aquatic acidification

.

I propose that EPA sponsor or provide for a fo cus group on monitoring and research information that would reduce uncertainty (by improving the input data and improving the models themselves) from these case study areas for national assessments of CL. Un certainty analysis of those results should be ongoing in the CL process.

Chapter 3: Sources, Ambient Concentrations, and Deposition

1201. This chapter describes an approach for ch aracterizing the spatial and temporal patterns of nitrogen and sulfur deposition in the case study locations including both oxidized and reduced nitrogen, and both wet and dry deposition of oxidized nitrogen and sulfur. Are the uncertainties associ ated with these analyses appropriately identified and described?

The uncertainties associated with these analyses are appropriately identif ied and described, with a few possible exceptions. In terms of air conc entrations, was there an attempt to compare

modeled NOx and SOx where measurements are available? Even though there are few NO 2 monitors, and most are in urban ar eas, it would help to see that at least in urban locations, the model predictions of NO 2 were reasonable. There are still numerous SO 2 monitors at

SLAMS/NAMS sites as well.

Section 3.5 does mention some of the issues rela ted to combining measured wet deposition with modeled dry deposition, but leaves out at least one limitation. Th e spatial analysis using NADP wet deposition data does not captu re urban influences well (if at all), whereas the modeled dry deposition will include urban sources and influe nces (that, of course, are not measured routinely). This methodology may overemphasize dr y deposition in the vicinity of large point sources or urban/suburban areas, and we don’t ha ve adequate data to assess how important this

is.

2. In response to CASAC’s recommendation, the RSM analysis presented in the first draft Risk and Exposure Assessment was replaced by an analysis of results from a new series of CMAQ simulations designed to explore the relative contributions of NO

x

and

NH 3 emissions to total, reduced and oxi dized nitrogen deposition and the relative contribution of SO 2 emissions to sulfur deposition. Does this approach enable us to adequately examine the contribution of NO

x

to total nitrogen deposition?

Yes, the 50% NOx and 50% NH 3 reduction scenarios are generall y adequate to quantify the contributions of NOx to total N deposition acros s the modeling domain. However, Section 3.4

has a disconnect with the rest of this chapter of the draft REA. In this section the wet deposition is taken directly from the model, whereas in previous sections the wet deposition is derived from the NADP data. This is necessary in this se ction since you are trying to estimate changes in modeled wet and dry deposition resulting from changes in modeled emissions.

3. The CMAQ application and model performance evaluation is presented in Appendix 1, as recommended by the Panel. Is this an alysis sufficient to support the use of the

model in this review?

The analysis presented in Appendix 1 is generall y sufficient to support th e use of CMAQ in the draft REA, especially with regard to wet de position. The seasonal, year-to-year, and broad geographic variations are clearl y displayed. On the “dry” side, the model evaluation suggests that ambient concentrations are reasonably we ll characterized. However, dry deposition is a significant contributor to the total loading of S or N, and it is not clear that the CMAQ dry deposition estimates are valid or even reas onable. While the CA STNet program does not

121measure dry deposition directly, it still might be useful to compare model predictions of dry deposition at CASTNet sites.

Chapter 4: Acidification

1. Section 4.2 and Appendix 4 describe the analyses used to evaluate the effect of aquatic acidification. The analysis evaluates the ANC in selected lakes and streams in the

Adirondacks and Shenandoahs relative to three potential ANC cu toff levels (20, 50,

and 100 μ eq/L) to determine the impact of current levels of deposition in these areas as well as a larger assessment area. Is this data adequate to establish critical loads of deposition for the case study area?

ANC is a good indicator and these are good cut off levels for selected lakes in the Adirondacks and selected streams in the Shenandoahs. However, these lake standard s may not be protective of streams in the Adirondacks. For instance, we know from ongoing research that Adirondack streams do not respond the same as lakes and are not experiencing the recovery that has been

detected in lake trends. We are also learning that Base Cation Su rplus is a better indicator than ANC to characterize biological impa cts in streams. This was mentioned in the ISA (Lawrence et al) and should be reported in the REA.

There are aspects of the Adirondack Case St udy Area assessment that need clarification including:

1. Respresentativeness of the modeled waters

2. The treatment of natural acidity

3. Review of the paleolimnological da ta on preacidification conditions

Representativeness of the modeled waters The modeling discussion is not clear about the vari ous Adirondack data sets used. There is not enough explanation as to which lakes were used from what survey program and why. For instance (pg 4-14) MAGIC was r un on 44 lakes in the Adirondack Case Study, said to be taken from the EPA TIME (n =43 lakes) and LTM (n= 52 lakes). It would be helpful to explain why

some lakes were chosen and not others.

It appears that average yearly ANC values were calculated from single measurements, because Adirondack TIME waters are collected only once per year. This should be explained more clearly.

Page 4-16, shows 169 lakes were modeled in th e Adirondack Case Study Area. Figure 4.2-9 (pg 4-20) shows ANC values from 94 TIME/LTM lake s, however there are only a maximum of 89

TIME and LTM lakes due to the 6 ov erlap waters between the two.

The treatment of natural sources of acidity in lakes Natural acidity is a common phenomenon for the Adirondack Lakes region, this, combined with the observation that DOC is increasing in some ar eas, demonstrates that more consideration is required than what is provided here. I am unclear as to how a ‘natural’ ANC concentration of less than 50 determined (pg 4-34 line 26), perhaps more e xplanation is in order.

122Review of the paleolimnological da ta on preacidification conditions Were any of the selected MAGIC lakes, part of PIRLA (Paleolimnologi cal Investigation of Recent Lake Acidification) lakes where diatom sediments provide for reconstructed histories of lake chemistry to prior to the onset of recent acidification?

2. The ecological effect function for aquatic acidification (sectio n 4.2.7) attempts to characterize the relationship between depositi on and ANC. In order to estimate the amount of NO

x

and SO

x

deposition that will maintain an ANC level above a given limit requires the knowledge of the average catchm ent flux of base cation from weathering of soils and bedrock (i.e. preindustrial cation flux (BC 0 )). How might we generalize from location specific inputs (F-factor approach) to using this approach on a broader scale – watershed, regionally, or some othe r way – to generalize beyond individual

locations? What other methods should be examined for estimating catchment weathering rates nationwide for surface acidity?

The link between deposition and an ANC in surface water is crucial and di fficult not only at each specific location but also in order to generalize findings on a broader scale. Determining catchment weathering rates is critical because ‘t he catchment supply of base cations from the weathering of bedrock and soils is the factor that has the most influence on the critical load calculation and has the largest unc ertainty” (pg 4-40 lines 3-5) c ontributing almost half of the total variability in critical lo ad estimates (pg 4-69 line 16).

As far as methods to examine this and the genera lization from specific i nputs/sites to apply to a broader scale, I note that curre nt research is underway through the New York State Energy Research and Development Authority by Miller , Lawrence, Weathers an d others to examine weathering rates and these region alization questions. These resu lts and other related work e.g. sponsored by the National Park Service should be incorporated as they are made available

Aquatic acidification is the best place to start because of the weight of the evidence across many sensitive areas. However, while ANC is cu rrently the indicator of choice, other more biologically direct indicators (pH and Alumin um) should be considered along with the newly developed Base Cation Surplus. These will likely be more useful further down the road in the critical loads process. For example, inorgani c monomeric aluminum at detectable levels (2 umol/L) is toxic to biota in any environment, a quatic or terrestrial. Its presence is directly associated with anthropo genic acidic deposition.

3. Section 4.3 and Appendix 5 describe the anal yses used to evaluate the effect of terrestrial acidification. This analysis uses the Simple Mass Balance Model to determine the impact of current deposition levels on Bc/Al levels relative to three potential Bc/Al cutoff level s (0.6, 1.2, and 10.0) for sugar maple in the Kane Experimental Forest and red spruce in the Hubbard Brook Experimental Forst and a larger assessment area based on the FIA database for 17 states. Is this approach adequate to develop critical loads of depositio n for the broader terrestrial acidification case study area? Is the regression analys is between Bc/Al ratios and tree health sufficiently described and are uncer tainties adequately characterized?

123The approach is adequate to develop critical loads for these case study areas, but I feel that

further discussion is needed to determine whether the a ssessment is adequate to inform about the terrestrial responses of all sens itive areas like the Adirondacks a nd other US regions (Fig 4.3-3) with potential red spruce and suga r maple sensitivities. It woul d be helpful to explain how the

indicator soil solution ratios at the Kane Experimental Forest (PA) and/or the Hubbard Brook Experimental Forest (HBEF) in NH are going to be translated to protection of sensitive sugar maple and red spruce ecosystems in other regions? Specifically, how will the uncertainties with misclassification of soil parent material (pg 4-69) be resolved?

While HBEF is a pre-eminent long term forest ecosystem study site, it has limitations representing high elevation northeas tern forests. For example, the high elevation forests (greater than 900 m above mean sea level) of the Adir ondacks cover over 100,000 ac res and according to

Miller et al 1993 have accumulated 80% more sulfur than the lower elevation forest at HBEF. A significant portion of the sulfur as measured at Whiteface Mountain in the Adirondacks comes from dry deposition and cl oudwater contributions.

A question that may be in order for discussi on is: Are the number, location and routine parameters collected by the USFA FIA perman ent sampling plots adequate to support the analysis for acidity critical loads to high and me dium elevation forests in the northeastern US?

Chapter 5: Nutrient Enrichment

1. Section 5.2 and Appendix 6, describe the analyses used to evaluate the effect of aquatic nutrient enrichment. The analysis uses the SPARROW model on one stream reach (Potomac River and Neuse River) to determin e the impact of atmospheric total nitrogen deposition on the eutrophication index for the estuary. Does the Panel think that the model is adequately describe d and appropriately applied?

I feel as if SPARROW is ade quately described within the REA and appreciate the detail in Appendix 6. I especially appreciate the use of the New England waters paper by Moore et al.

I believe it would be helpful if in either the REA or Appendix 6 a table with the data type and sources were printed. For example, where was the loads data derived from, or the stream

network? The use of the other tabl es in this section are especially helpful, so this additional table would contribute to the ease of understanding. Case Study Analyses (Chapters 4 & 5)

2. In using the Risk and Exposure Assessment to inform the policy assessment, we plan to focus on aquatic acidification as the basis for an alterna tive multi-pollutant secondary standard as this is the area where we have the most confidence in our ability to characterize adverse effects. Do es the Panel agree with this approach?

I feel that aquatic acidification is the best place to start because of the weight of the evidence across many sensitive areas. However, while ANC is currently the indicator of choice, I believe that other more biologically di rect indicators (pH and Aluminum) should be considered along with the newly developed Base Cation Surplus. These will likely be more useful further down

124the road in the critical load s process. For example, i norganic monomeric aluminum at detectable levels (2 umol/L) is toxic to biota in any environment, aquatic or terrestrial. Its presence is directly associated with anthropogenic acidic deposition.

Specific comments/questions

Chapter 3: There are several in stances in which “NH” is left out – Page 3-2 lines 9 and 19, and Page 3-82 line 5.

page 4-10 Figure 4.2-2 New England is not an ecosystem

Pg 4-15 Figure (a) How were the critical lo ad (green dot) mode ling sites selected?

Pg 4-14 line 14. What is the present condition? Here it is defined as ‘present (2002 and 2008)’ whereas the discussion starting on pg 4-18, calls 2006 the current condition. Wh ich are actual

measured and which are modele d current condition values?

Pg 4-39 Uncertainty and variability. How well do the MAGIC model simulations for current ANC concentrations measure ag ainst measured median ANC?

Pg 7-1 lines 21 to 27. By transitioning to the “ecosystem services” concept, (we must also preserve) there is a danger of lo sing the broader definition of eff ects that are important to people or that society views as benefici al. Specifically it should be rec ognized that the majority of the sensitive areas identified in these documents are either national or state parks or scientific experimental forests that they have a collectiv e intrinsic value that have been previously identified as exemplary. They deserve the bar of level of protection to be raised. (Protecting biota in a park or a scie ntific reserve is ‘more important’ than anywhere else because we have as a society identified these are part of the public good.)

Pg 7-10 lines 5 to 7. Crucial point but sentences are awkward. Not exposure to an annual mean, but on average with an annual mean of 50, the proba bility is low that the lake will go down to 0 during springmelt. The length of time sentence s hould be deleted as it does not summarize that section, but a point to be made as part of the back ground to this discussion.

Appendix 1, Footnote 8: Why is NOy listed as the sum of NO, NO 2 , HNO 3 , and PAN? It should include also HONO, N 2 O 5 , ANO 3 , and NTR as is listed in the Table 1.1-2 for deposition.

Appendix 1, Section 2.1 and Figures 2.1-1 through 2.2-7: Don’t these additional lines indicate a

factor of 1.5 around the 1:1 lin e (not a factor of 2)?

Discuss further the consequences of MAGIC usi ng a calculated ANC rather than measured Gran ANC. How well does MAGIC scale up beyond the wate rsheds of the modeled lakes themselves?

125

### Dr. Kathleen Weathers

I appreciate the enormous work involved in putting this REA together. It was (and is) a

Herculean effort.

I have included brief comments—some overarchi ng, some specific—on many of the chapters in the REA, and on the charge questions.

Executive Summary

While I like the idea of Figure ES-1, I thi nk some of the pieces are a bit misplaced and mislabeled. For example, mobile anions might be depicted in associa tion with cation leaching, and to what are “soil processes” meant to refer (e.g., NO3—meaning nitrification?).

Figure ES-2. I am a fan of using multiple colors in Figures only when th eir purpose(s) are clear, or clearly identified. At first glan ce, I’m not sure what the different colors are meant to depict (if anything) in this, and other figures in this documen t. Ditto for shapes. I suggest either identifying the significance of both in the Figure legend, or (re)considering car efully their use.

Figure ES-4: The recreational fishing example here, and throughout the document, in fact, would benefit from a footnote, or a few lines in the text that give a cl ear explanation about why and/or how the effect of fish stocking or invasions, an important driver in species distributions and abundance, can be separated from the e ffects of acidification via deposition.

Pages ES-12, 13—it would be a good place to note some brief caveats about where this spatial estimation is likely to underestimate (or perh aps overestimate) deposition (e.g., high elevation ecosystems, heterogeneous terrain, and regions with significant snowfall). It would also be useful to note in the figure legends what the spatial resolution is for these maps.

Page ES-16 (line 14): I think that MAGIC and othe r models are used to estimate (vs determine).

Note how the “critical load appr oach” boxed here either parallel s, or does not, that used by Europeans and others.

I think it very important to note, and put in context, when, where, and how natural (vs anthropogenic, or strong mineral) acidification occurs (terrestrial and aquatic). (The language exists in chapter 4.) Nothing more than a brie f mention is necessary in this Executive Summary.

What determines when references are incl uded, or not included, throughout the REA and especially appendices? Mostly th e text is not referenced (be yond the ISA), except when it is!

Chapter 1:

There is reference to “the late st scientific knowledge,” yet many of the references I noticed in this document are from quite some time ago.

1261-10, line 26: the term “tot al nitrogen” should be qua lified here. Sometimes to tal is referred to as having captured all the vectors of N, i.e., having estimated dry, wet and cloud or fog deposition.

1-12, lines 18-19??

1-14, lines 4-6 and a few other places in this document: In these systems, atmospheric N deposition is the main source of new N to the system, but it may also travel through vegetation and soil before getting to headwater streams a nd lakes, depending upon where they sit in the landscape and by what they are surrounded. Perh aps what was meant here was headwater streams and high elevation lakes th at are above treeline? This stat ement should be clarified here

and elsewhere in the document.

1-19: I agree with the paragraph starting on line 7 (and th e bulleted list preceding it), and thus Figure ES-4 (depicting relationships) challenges my sensibilities. I’ll be interested to be reminded of its heuristic utility.

Chapter 3: I suggest adding the spatia l scale/resolution to the figure legends of all of the figures that show spatial data.

3-2: While it is reasonable that cloud or fog deposition could not be considered for lack of monitoring data, there are places throughout the document where th e qualitative resu lt of this (necessary) omission could be pointed out (e.g., for example, eastern high elevation sites where cloud/fog has been shown to contribute significantly to N and S loads).

3-24. It would be useful to repor t under “spatial allocation of gri dded data to case study areas” how many (roughly) grid cells were used/study ar ea. Given the coarse resolution of the CMAQ data, it seems possible that the Hubbard Brook E xperimental Forest, for example, could contain few grid cells.

3-26: For the data that span a 4-year time period, “trend” analysis is dub ious. Analysis of the long-term record at Hubbard Brook suggests that detection of statistical trends took more than 3X that time period.

3-90s: I expected to read more about the uncertainties associated with complex terrain in this section. It is one of the importa nt drivers in uncertainties fo r estimating dry deposition and a major challenge to estimating deposition.

Chapter 4:

Overall, I found most sections of this chapter to be confusing, and in need of significant editing-- for clarity, for completeness, for accuracy, especial ly in the aquatic sectio n. As a result, I have not made detailed comments, rather I have iden tified some general (and a few specific) issues.

It might be helpful to discuss charge balance early on.

127As I’ve suggested before, defining what is meant by such terms as “health” of terrestrial and aquatic ecosystems is important if the word is going to be used.

I suggest adding a section on te rrestrial-aquatic linkages.

There are many figures in this section (and in the Appendix) that are identified as showing declines (by x%, for example) over time, yet no re gression, or trend analysis seems to have been performed, rather a line graph ha s been generated and trends/dec lines suggested. In the case of the associated appendix, lines may have been fit to the data, but there is not information about what kind of a polynomial fit may have been used, why, and what its significance is, for example. It is important to support the assertion of trends or declines over time with appropriate trend analyses and documentation.

I like the idea of using boxes. However, many of the boxes need editing as well. The box on page 4-16 was particularly convoluted.

4-15: critical load approach –there seem to be a few different definiti ons and interpretations throughout the REA. It would be helpful to standardize.

4-17: I assume signs of improvement mean that NO3 and SO4 have decreased in surface waters of the ADK case study. See my comments, above , about the lack of trend analyses.

4-24: what are “slight” signs of improvement, or wh at does it mean to have “not resulted in much improvement?”

Figure 4.2-21. Fix spelling on title.

Terrestrial Effects

4-36: what’s it mean to account “for the effects input of Cl-?

The connections between tree “healt h,” direct and indirect tree responses, and growth responses should be made clear. And again, it is necessary to define what is meant by health (box on 4-44).

4-45. Many things affect the prov isioning of services, of course . Some contextual statistics would be useful in this section, especially about some of the othe r factors that might affect these two species’ productivity.

4-51: What percentage of the area used for the HBEF is covered by red spruce?

4-61: what area (ballpark) do the FIA plots cover for each of the species?

Chapter 7, Synthesis:

128Much of the first part of the synthesis chapter is a reiteration of other chapters in the REA. I

think that the focus should be more actual synthesis among these chapters.

I prefer the use of ecosystem st ructure or function (vs processe s, as used throughout the REA).

Is change the right opera tive word/focus here? 7-2, line 13 changes can be or are quantified? tense?

Figure 7-1: see comments above about the use of colo r, or not. In this fi gure, color obscures the

text.

7-3, line 19, Knowledge about the relations hips, whether direct or indirect,... Foliar injury is not really a process. Perhaps it’s the change in structure that affects a process (photosynthesis) that is th e point of this example? The examples at the bottom of this page could

be clarified.

7-5, first para: I like the idea of this—clarifying which data are best suited to informing a policy on welfare effects, but it wasn’t clear to me the current answers, i.e., I was looking for a clear path to answering the question.

7-5: Nitrogen is known to limit growth and produc tivity. S is necessary, but not identified as limiting, usually. The text should be changed. Reproduction of ecosystems? Anthropogenic

acidification can cause...This paragraph could use some editing.

See earlier comment on the statement that atmosphe ric nitrogen deposition is the main source of new N. It’s the main source of new N to ecosy stems, and subsequently to most headwater

streams...

7-6, line 1: Nitrogen deposition can alter ecosystem processes, such as primary production and nutrient cycles...

Figure 7.1.3 needs a little more description in the legend. Are the deposition ranges from the modeling and estimates in this REA, or are they estimates provided in the studies cited for the

effects noted? I like the idea of this kind of figure that can be used to synthesize across systems and depositional loads.

7-17, line 6, will remain unmonetized because?

In regard to some of the speci fic charge questions asked:

Case studies:

Uncertainties: I am inclined to ask what kinds of uncertainty analysis are necessary from the policy making perspective, as well as how best the myriad scientific uncertainties that exist can be communicated in such a way that it is obvious which are the most “important” (e.g. have the biggest effects). Finally, I would ask how uncertainties can be communicated in such a way that

129130 they do not undermine what is known. Currently, I do not think that uncertainties are as well characterized as they might be.

I agree that it is in aquatic systems where the most direct and clearest effects of acidifying deposition have been shown. However, Chapter 4 should be significantly improved to make it useful to that process.

Acidification:

The first question is tied to the definition of critical loads, and critical loads approach. Isn’t the question really are these the critical loads?

Synthesis:

The idea of ecosystem services focuses on the wo rk that ecosystems do in service of humans. A focus on ecosystem services can limit understa nding of ecosystem st ructure and function. However, it has purchase in the sc ientific community. And, in the REA the definition of welfare effects given on page 7-1 underscore s the fact that discussing ecosy stem services may be a useful way for scientists to translate ecologi cal function into welfare effects.

Understanding will be enhanced significantly through generating better estimates of (all important chemical forms of N and S, especia lly NHx and organic N) deposition (including wet, dry and fog) to complex ecosystems, through long term experimental manipulations, and process

studies that included link ed biogeochemical studies.