UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD

December 9, 2010

EPA-CASAC-11-003

The Honorable Lisa P. Jackson

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

Subject: Review of the Policy Assessment for the Review of the Secondary National Ambient Air Quality Standard for NOx and SOx: Second Draft

Dear Administrator Jackson:

The Clean Air Scientific Advisory Co mmittee (CASAC or Committee) Oxides of Nitrogen (NO

x ) and Sulfur Oxides (SO

x ) Secondary National Ambien t Air Quality Standards (NAAQS) Review Panel met on October 6-7, 201 0 and held public teleconferences on November 9, 2010 and November 10, 2010 to review EPA’s Policy Assessment for the Review of the Secondary National Ambient Air Quality Standards for NOx and SOx: Second Draft . This letter provides CASAC’s overall comments and evaluation. The CASAC and Panel membership is listed in Enclosure A. The Panel’s responses to EPA’s charge quest ions are presented in Enclosure B. Finally, Enclosure C is a compilati on of individual panel member comments. This letter provides our views on: 1) the need for retaining the current and developing new secondary standards; 2) limitations in our review of the second draft Policy Assessment and priority needs to be addressed in making revisions; and 3) CASAC recommendations regarding the secondary

standard.

Need for retaining current and for designing new secondary standards

The current public-welfare-based (secondary ) NAAQS standards for oxides of nitrogen (NO

x ) and sulfur oxides (SO

x ) were designed to protect vegeta tion from exposures to injurious concentrations of gaseous NO

x and SO

x . This protection is a desira ble goal and for that reason

the CASAC Panel recommends th at the current secondary NO

x and SO

x NAAQS standards

should be retained. The current standard for NO

x is an annual arithmetic standard of 53 ppb, using NO 2 as the indicator species, identical to the primary annual health-based standard, with no short-term secondary standard. Th e current secondary standard for SO

x is 0.5 ppm 3-hour average, not to be exceeded more than once per year, using SO 2 as the indicator species, and it is separate from the primary standard and there is no long-term secondary standard.EPA staff has demonstrated through the findi ngs of the Integrated Science Assessment (ISA), the Risk and Exposure Assessment (REA), and the draft Policy Assessment that ambient

NO

x and SO

x can have, and are having, adverse e nvironmental impacts on some ecosystems across the United States due to deposition of NO

x and SO

x , even at current concentrations under existing standards. Those imp acts include ecosystem acidificati on and undesirable levels of

nutrient enrichment in some eco systems. For this reason, CASA C has concluded that different and more protective standards are needed for NO

x and SO

x . A NAAQS is needed that would be formulated in a way that would provide requi site protection in sens itive areas, while not providing protection that is mo re stringent than necessary.

We compliment EPA Staff on the progress that has been made since CASAC reviewed

the first draft Policy Assessment and appreciate Staff’s res ponsiveness to CASAC’s initial comments. There are significant scientific cha llenges in developing multipollutant, ecologically relevant secondary standards. These challe nges are made more difficult by the regulatory constraints under which EPA staff operates: th e standard must use ambient air pollutant concentrations as the indicator, rather than pollutant depositiona l flux and only oxidized nitrogen, not chemically-reduced forms (both i norganic and organic) of reactive nitrogen, is currently included as a criteria po llutant. To meet these constraints, EPA has developed a new index, the Atmospheric Acidificat ion Protection Index (AAPI). Th is innovative index integrates the combined effects of atmospherically de posited oxides of nitr ogen and sulfur (NO

x and SO

x ), as well as chemically reduced forms of reactive nitrogen (NH

x ). The AAPI also takes into account a series of ecosystem characteristics that determine sensitivity to total acidifying deposition in various regions of the United States. The AAPI appr oach is responsive to recent recommendations by the National Research Council for multi-pollutant air quality management ( Air Quality Management in the United States , 2004).

Despite the regulatory cons traints described above, the AAPI approach would appropriately integrate the combined effects of NO

x and SO

x deposition on aquatic acidification, and could provide protection for sensitive aquatic ecosystems at an appropriate spatial scale. Use of the AAPI, however, introduces a number of technical complexitie s because it considers depositional effects of multiple pollutants with in diverse and complex ecological systems. Because of these complexities, it is not appare nt how to construct an equally appropriate, and significantly simpler, approach to capture the many important processes that influence the relationship between observable atmospheric con centrations and aquatic acidification.

CASAC notes that EPA did not have suffi cient time in preparing the second draft Policy

Assessment to formulate a complementary approach th at would be the basis for standards to protect against nutrient enrichment effects on a quatic ecosystems and nutrient enrichment and/or

acidification effects on terrestri al ecosystems. Although a sta ndard that focuses on aquatic acidification would provide some co-benefits in addressing these other ad verse effects, in the future, EPA should consider developing approach es for protecting agains t nutrient enrichment effects on aquatic ecosystems and nutrient enrichme nt and/or acidification effects on terrestrial

ecosystems.

2Challenges to the CASAC review of the second draft Policy Assessment and priority needs

to be addressed in final revisions

CASAC’s review of this document has been constrained by the limited time available for review and the incomplete status of the submitted document. Even though the second draft Policy Assessment was novel and complex, the CASAC Pane l received the document only three weeks before the review meeting. As describe d below and in our responses to the Charge Questions, there are criti cal sections of the Policy Assessment that are unclear and/or that require further analyses. In addition, and in contrast to policy assessments for ot her pollutant reviews, EPA did not provide staff recommendations for key elements of the secondary NAAQS for NO

x and SO

x along with supporting rational es. As a result, CASAC is not able to provide specific comments on the EPA Staff recommendations, nor is CASAC able to use Staff recommendations to help frame CASAC discussions or recommendations about th e four key elements of the NAAQS.

The final Policy Assessment needs to more clearly and fu lly set out the basis for the recommended ranges of each of the four elements (indicator, averaging time, level and form) of the proposed NAAQS. The implications of choos ing specific combinations from within the ranges of elements should be thoroughly discussed, with justifications provided for the specific options or range of options that staff recommends. It would also be useful to see a map and/or tabular estimates of the spatial ex tent and degree of severity of NAAQS exceedances expected to

result from the recommended combinati ons of the elements of the standard.

The final Policy Assessment needs to more fully describe the proposed alternative approaches for landscape categorization of inhere nt sensitivities to acidification, and how these alternative approaches relate to the different target fractions of water bodies that would be protected at different acid neut ralizing capacity thresholds. The implications of choosing specific landscape categori zation approaches combined with sp ecific fractions of water bodies to be protected should be thoroughl y discussed, with justification provided for the specific combinations or range of combinations that staff recommends.

The final Policy Assessment needs to provide a more detail ed analysis of the uncertainties associated with the entire AAPI calculation, and of the relative sensitivities of the allowable

ambient concentrations to uncertainties in its individual components, including uncertainties introduced by use of models (e.g., CMAQ and the ecological model, MAGIC). The AAPI formulation is unavoidably complex and de pendent on critical assumptions and model calculations, which are characterized by various le vels of uncertainty. This more complete uncertainty analysis should focus on the overall, cumulative uncertainty estimation including the possible application of Monte Carlo techniques.

CASAC recommendations regarding the secondary standard

While the CASAC Panel is supportive of th e AAPI approach developed, CASAC is not able to provide consensus recommendations on all elements of the standard because of the

constraints to its review identified above. Furt her, each element of the standard should be

considered in the context of the choices for the other elements. The Policy Assessment does not yet provide adequate analyses on all the specifics of a new (and novel) NO

x -SO

x secondary NAAQS. However, CASAC will offer initial comment s on some elements of the standard. We

34 agree that a 3-5 year averaging time appears appropriate. CASAC supports the general structure of the AAPI equation and agrees that acid neut ralizing capacity is an appropriate ecological measure for reflecting the effects of aquatic acidification. Acid neutralizing capacity targets in the range of 20 to 100 μ eq/L appear appropriate to consider at this time.

CASAC recognizes the very tight time lin es associated with revising the NO

x and SO

x secondary NAAQS. However, CASAC should have the opportunity to review a more complete Policy Assessment , one that provides staff recommendations, the basis for the choices made, the direct supporting analyses for t hose choices, and the ramifications of alternative choices within the ranges of the alternatives. To this end, we are working through the SAB Staff Office to plan a meeting to review the completed Policy Assessment in February 2011.Without this information, we are unable to provide the level of advice that you need and to fill our role under the Clean Air Act. EPA staff must provide complete documents with sufficient time to permit an in-depth

review.

Summary

While we have identified various needs fo r additional analyses and enhanced clarity

before the final Policy Assessment is published, CASAC remains supportive of the novel approach described in the Policy Assessment for the Review of the Secondary National Ambient Air Quality Standard for NO

x and SO

x : Second Draft . We support EPA staff’s continuing work on revising the Policy Assessment to establish a foundation for a revised NO

x -SO

x secondary NAAQS. This work is groundbreaking a nd significant for several reasons:

1) The current NAAQS review for welfare-based effects was conducted separately from the

review of the health-based standard and has allowed focus on ecological impacts. 2) The review was designed to cons ider two criteria pollutants at the same time, and set the stage for a "multi-pollutant/multi-media/multi-effect" approach as recommended in the 2004 National Research Council report, and 3) The AAPI takes into account another chemical form of biologically reactive nitrogen,

NH

x that is important to a quatic acidification, but is not a criteria pollutant.

In closing, CASAC trusts that our comments will be useful in revising the Policy

Assessment

.

Sincerely,

/Signed/ /Signed/

Dr. Armistead (Ted) Russell, Chair CASAC Oxides of Nitrogen and Sulfur Oxides Secondary NAAQS Review Panel Dr. Jonathan M. Samet, Chair Clean Air Scientific Advisory CommitteeNOTICE

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 th e 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 b een reviewed for approval by the Agency and, hence, the contents of this report do not necessa rily represent the views and policies of the EPA, nor of other agencies within the Executive Br anch of the federal government. In addition, any mention of trade names or commercial products does not constitute a recommendation for use. CASAC reports are posted on the EPA Web site at: http://www.epa.gov/casac

.

5

### Enclosure A – Rosters U.S. Environmental Protection Agency Clean Air Scientific Advisory Committee Oxides of Nitrogen (NOx) and Sulfur Ox ides (SOx) 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. Naresh Kumar , Senior Program Manager, Environm ent Division, Electric Power Research Institute, Palo Alto, CA

6Dr. Myron Mitchell , Distinguished Professor and Dir ector 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 Dr. Angela Nugent , Designated Federal Officer, U.S. Environmental Protection Agency, Science Advisory Board (1400R), 1200 Pennsyl vania Avenue, NW, Washington, DC, Phone: 202-564-2218, Fax: 202-565-2098, (nugent.angela@epa.gov)

* Provided individual comments only. Did not participate in the Panel’s deliberations.

78 

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

CASAC

CHAIR

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

SAB MEMBERS Mr. George A. Allen , Senior Scientist, Northeast States for Coordinated Air Use Management (NESCAUM), Boston, MA

Dr. Joseph D. Brain , Cecil K. and Philip Drinker Prof essor of Environmental Physiology, Department of Environmental Health, Harvard School of Public Healt h, Harvard University, Boston, MA

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

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

Dr. Helen Suh , Senior Lecturer in Environmental Chemistry and Exposure Assessment, Department of Environmental Health, School of Public Health, Harvard University, Boston, MA

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

SCIENCE ADVISORY BOARD STAFF Dr. Holly Stallworth , Designated Federal Officer, U.S. Environmental Protection Agency, Science Advisory Board (1400R), 1200 Pennsyl vania Avenue, NW, Washington, DC, Phone: 202-564-2073, Fax: 202-565-2098, (s tallworth.holly@epa.gov)

### Enclosure B CASAC Oxides of Nitrogen (NOx) a nd Sulfur Oxides (SOx) Secondary Review Panel Consensus Resp onses to Charge Questions

Chapter 3: Considerations of Adversity to Public Welfare

1. What are the Panel’s views on the definitio ns of adversity that are appropriate to consider in determining what constitutes ad versity to public welfare relative to the NOx and SOx secondary standards?

Ecosystem services provide a framework to characterize and describe how changes in ecosystem structure and function affect public we lfare, even if they cannot be specifically quantified. The link is well-documented between th e selected ecosystem effects indicator, acid neutralizing capacity (ANC), and th e public welfare effects of lost value of recreational fishing, biodiversity, and habitat. Fish populations (and in some cases whole species) become

unsustainable in lakes and streams with decreases in ANC levels caused by elevated inputs of acidic deposition. The text mentions non-use values several times, but it would be helpful to make explicit that this includes values for the preservation of habitat a nd biodiversity that are independent of human use value. These services generally fall into th e category of cultural services. More could be done to explain and ch aracterize the qualitative links between acidic deposition and lost ecosystem services that ar e known and documented but cannot be specifically quantified for a specific amount of acidic deposition. While it is clear that the total value of these services is large; what is im portant to convey is the degree to which they are diminished at current acidic deposition levels.

Evidence of community, local and state actions to decrease acidification is informative regarding adversity even though such evidence do esn’t provide specific estimates of welfare changes. Also including federal actions, such as the Title IV (Clean Air Act Amendments of 1990) program, to address acidifica tion would be appropriate here.



### Chapter 4: Addressing the Ade quacy of the Current Standards

2. What are the Panel’s views on staff’s approach to translatin g the available evidence and risk information and other rele vant information into the bas is for reaching conclusions on the adequacy of the current standards and on alternative standards for consideration? a) In light of the Panel’s views on the appropriate definitions of adversity to public welfare (see Chapter 3), do you agree that th e current levels of NOy and SOx deposition are adverse to public welfare?

Yes, the Panel agrees that current amounts of NO y and SO

x deposition are adverse to public welfare especially with regard to effects on aquatic ecosystems in acid-sensitive regions in various parts of the United States. The Panel also agrees with EPA’s historical interpretation that

9air-pollution-induced effects on ecosystems should be considered “adverse to public welfare” whenever these effects include “disruptions in ecosy stem structure and function” that are considered important to the people of this country.

3. Has staff appropriately applied this approac h in reviewing the ade quacy of the current standards and potential alternative standards?

Yes, the panel finds that EPA staff has a ppropriately reviewed the adequacy of the current standards and potential alte rnative standards. The current NO

x and SO

x standards were designed to protect vegetati on against exposures to SO

x and NO

x. Thus, the current standards address only a fraction of the total nitrogen and sulfur comp ounds that are causing adverse effects on aquatic ecosystems, and these standards are not designed to protect ecosystems from acidic deposition. None of the elements of the current NAAQS standards – indicator, form, averaging time, and level – are suitable for a ddressing the long-term (multi-annual) cumulative

acidification effects of total at mospheric loads of total reactive nitrogen and sulfur on aquatic

ecosystems.

The ISA and REA for the current review (as summarized in Chapters 2 and 3) make it

clear that current ambient con centrations of airborne nitroge n and sulfur compounds (including not only NO y and SO

x , as asked in Charge Question 2 but also ambient NH

x as w ell as organic forms of nitrogen) are now causing significant “disruptions in the structure and function of aquatic ecosystems” in various acid-sensitive regions of the United States.

4. Has staff appropriately acknow ledged the potential beneficial effects of nitrogen inputs into nutrient limited ecosystems, while mainta ining the focus of the review on preventing adverse effects in nitrog en sensitive ecosystems?

While the potential beneficial effects of nitrogen inputs into nutrient-limited ecosystems have been acknowledged, the tone and emphasis gi ven has not been appropriately balanced. As an example, the last few lines of page 4-45 in Ch apter 4 and especially th e first four words, may suggest the potential benefits to be very limited: “In certai n limited situations, additions of nitrogen can (word inserted) increase rate s of growth, and these incr eases can have short-term benefits in certain managed ecosystems....”

A better balanced presentation of these same ideas could read as follows:

“Most ecosystems in the United States ar e nitrogen-limited, so regional decreases in emissions and deposition of airborne nitrogen compounds will lead to some decrease in growth of the vegetation that surrounds the targeted aquatic system. Whether these changes in plant growth are seen as beneficial or adverse will depend on the circumstances. Increased carbon sequestration due to increased growth in N-limited ecosystems may be th e most significant category of potential beneficial effects of N deposition.”

10Carbon sequestration is not addressed in the Policy Assessment . Carbon sequestration is implied, however, by the inclusion of climate-rela ted issues in Table 3- 1 on page 3-11. As indicated above, increased carbon sequestration due to increased growth in nitrogen-limited ecosystems may be the most significant category of potential beneficial effects of nitrogen deposition.

While the Policy Assessment and supporting documents ackn owledge the possibilities of beneficial effects, they tend to minimize them . The panel believes that while such unintended effects by no means justify continuing current le vels of air pollution, a balanced document should discuss these unintended effects more thoroughly.



### Chapter 5: Conceptual Design of an Ecologically Relevant Multi-pollutant

Standard

5. What are the Panel’s views on staff’s revised conceptual fram ework for the structure of a multipollutant, ecologically relevant standard for NOx and SOx? To what extent does the Panel agree that this suggested structure ade quately represents the scientific linkages between ecological responses, water chemis try, atmospheric deposition, and ambient

NOx and SOx?

With some exceptions noted below, the revi sed conceptual framework and structure of the proposed standard(s) ar e well-thought out for addres sing various components and connections between these components (ecological effects, atmospheric wet and dry deposition, atmospheric concentrations of NO y and SO

x , and surface-water chemistry).

For example, the framework and the struct ure “take into account” the reduced ambient

NH

x and its deposition in designing the AAPI (atmo spheric acidification potential index). The

revised treatment of ammonia a nd deposition of reduced nitroge n is an improvement over the

first draft in that AAPI will reflect periodic changes in NH

x concentrations. Emissions of ammonia (which is currently an unregulated air pollutant ) and resulting ammonia and

ammonium concentrations and de position amounts are expected to increase over the next few decades because of increased food production and increased activity in CAFO sources (confined animal feeding operations) in the United States.

The conceptual framework for the proposed mu ltipollutant ecologically relevant standard

for NO

x and SO

x is sound with considerable support from the scientific literature on how the generation of strong mobile acids results in the acidification of soils and water. Some of the information, however, is not correct or is incomp lete. For example, the di scussion of sources of nitrate during snowmelt is incorrect in that it sugg ests that most of the nitrate released is of atmospheric origin. However, most nitrat e mobilized during snowmelt is derived from

nitrification in the soil itself. Also the assumptions associated w ith atmospheric sulfur input being equal to drainage water lo sses are not correct. For ex ample, the soil can serve as a substantial source or sink of sulfur depending upon soil properties and history of atmospheric

sulfur sources.

11Even though the AAPI conceptual framework is sound and useful in principle, further evaluation of robustness is requir ed. One way to evaluate robustness of the AAPI framework is by using sensitivity and/or uncertainty analysis, as discussed in our responses to Charge Questions 14 and 21. The AAPI can also be tested by the use of time series chemistry data. Where data are available, one could use the AAP I to estimate a functional relationship between AAPI and changes in SO

x and NO y concentrations. The values of other components of the AAPI (Q, N

eco , [BC]

o , LNH

x , TNO y and TSO

x ) have already been estimated by EPA or can be

determined from measured values. The recomme nded analysis of historical data should be

carried out at more than one location. The chan ges in predicted AAPI should more or less match the changes in ANC (perhaps with some lag).

Notwithstanding these concer ns, the proposed structure ad equately represents the scientific linkages between ecological effects, surface water chemistry, atmospheric deposition,

and ambient levels of NO y , SO

x , and NH

x .

6. What are the Panel’s view s on the appropriateness of c onsidering a single national population of waterbodies in establishi ng standards to protect against aquatic acidification? What are the Panel’s views on consideration of alternative subdivisions of the U.S. to identify the s patial boundaries of populations of waterbodies and acidsensitivity categories, specifically: a) the use of Ecoregion III areas to aggregate waterbodies ? b) the use of ANC to further aggregate Ecor egion III areas into diffe rent categories of sensitivity? c) the relative appropriateness of the s uggested methods for categorizing spatial boundaries of sensitivity, e.g. one nation, binary sensitive/less -sensitive classes, clusteranalysis based sensitivity cla sses, and individual ecoregions?

The justification, logic, and necessity of the spatial grouping classifications were not clear to the panel. The ecore gions approach has conceptual appeal, but the rationale and limitations for classification and aggregation methods must be better articulated for all options

described in the Policy Assessment before the CASAC Panel can provide meaningful advice.

The first approach (option 1), which consid ers the whole United States as one unit, has the advantage that it provides for a single deposit ion metric and is simple and easy to use. However, the single-region approach also ha s many weaknesses (e.g., over protection for the least sensitive areas and under protection for area s that are most sensitive necessitates having a system with higher spatial resolution) and is prob ably not a desirable approach. Nonetheless, the panel finds it useful to include discussion of this option for th e overall context. On the other hand, the option 2d, which includes 85 ecoregion s, may provide an unnecessary amount of complexity, but future analyses could provide sup port for such a choice. The use of clustering is also conceptually appealing, although the optimal number of sensitivity categories and the degrees of protection that woul d be provided under the different sensitivity categories are not clear. It does appear to strike a more reasonable balance between oversimplification and

12unnecessary complexity. The use of ANC app ears to be a reasonable basis for grouping ecoregions into a relatively small number of cat egories, each containing surface waters with

similar inherent sensitivities to acidification. This approach is c onsistent with the overall goal of developing an ecologically relevant secondary sta ndard to protect sensitive surface waters from

further acidification and decrease acidifying deposition to levels that will allow those water bodies (that have been deleteriously impacted by acidic deposition) to recover as indicated by increasing ANC values.

The Panel recommends that the final Policy Assessment include a more detailed description of the clustering appr oach and other options, along w ith clear illustrations of the advantages and disadvantages of the recommended options.

7. What are the Panel’s views on the appropriateness of the cr itical loads that form the basis for the population assessment to determine deposition metrics?

Using the concept of critical loads is l ogical and appropriate for development of a secondary standard for the biological effects of NO y SO

x and NH

x . This approach links concentrations of the atmospheric oxidized form s of nitrogen and sulfur with N & S deposition and their acidifying effects on aquatic ecosystems and includes consideration of chemically reduced forms of atmospheric N.

a) What are the views of th e Panel on the appropriateness of generalizing the f-factor approach to apply to lakes and streams in th e Western U.S. and other portions of the

Eastern U.S.

The f-factor approach is a r easonable initial approach to evaluate the response of aquatic ecosystems to changes in atmospheric deposition. However the f-factor approach is based on steady-state calculation but ecosyst ems are simply not at steady state. Ultimately, it would be useful to apply dynamic models as management tools to evaluate e ffects of atmospheric deposition on non-steady state ecosystems.

Differences between the use of MAGIC and the SSWC methods to determine background

concentrations of base cations ar e not adequately described in the Policy Assessment. The proposed procedures and differences between the two approaches need to be described more clearly

b) What are the views of th e Panel on the filtering crit eria used to remove lakes and streams that are naturally acidic or not sensitive to atmospheric deposition?

It is justifiable to exclude in advance water bodies impacted by mine drainage. It is not clear, however, why water bodies with low background ANC and high concentrations of naturally occurring organic acid are, likewise, excluded from further consideration since these are often very sensitive water bodi es. The rationale for this appro ach needs to be better explained with examples given, with some discussion of the implications for eliminating these water

13bodies. The panel needs this information before it can fully and meaningfully respond to this charge question.

8. What are the Panel’s views on the suggested methods for de termining appropriate values of reduced nitrogen depo sition in establishing NO

x /SO

x tradeoff curves?

The proposed approach is reasonable and ut ilizes the available knowledge on levels and

distribution of reduced N base d on the CMAQ outputs. Potentially the NADP chemistry and PRISM precipitation results could also be uti lized. Due to the high deposition velocity of NH 3 , steep concentration gradients near the NH 3 source areas can be expected. Therefore averaging

N red concentrations over larger areas may lead to missing smaller areas where NH 3 concentrations may be elevated with potential ly high ecological effects. Consequently, option “2” is preferable since it allows for additional spatial refinement of sensitive areas to reflect the spatial and temporal heterogeneity of NH

x deposition. A better understanding of spatial and temporal distribution of reduced N, especially NH 3 , in the United States is critical. Realizing that estimates of chemically reduced N deposition are viewed as highly uncertain, efforts should be

continued to assure the nationwide monitoring of N red , especially in remote areas.

9. What are the Panel’s views on the revised characterization of the deposition transference ratios (TNOy and TSOx)?

A major concern with T NO y and T SO

x is that although they are the critical links between

NO y and SO

x ambient concentrations and their depositi on, they are derived using a model that has not been thoroughly evaluated for its ability to accurately simulate N and S deposition

because of lack of measurements of the required concentration and deposition components. It is recommended that EPA evaluate the stability of these ratios using different models, emissions and meteorological conditions. It is recommended to calculate these ratios for the following model simulations (in addition to what has already been done): • CMAQ and CAMx models (it is accepta ble, in fact preferable, to use different emissions and meteorological conditions) • Different model grid resolutions (36-km v/s 12-km or even 4-km, if available)

The CMAQ T SOx calculation could also be evaluate d using a combination of measured wet deposition data from NADP and the measured concentrations and estimated dry deposition

of SO 2 and pSO 4 from CASTNET.

The draft Policy Assessment notes the possibility of si gnificant amounts of sulfur and nitrogen deposition in the forest ecosystems in th e coarser particle mode and further notes that CMAQ may not adequately account for coarse particle sulfate deposition. At the same time, most currently available measurement programs do not sp ecifically quantify coarse mode sulfate or nitrate concentrations or deposit ion, so there are only very scant measurement data with which to evaluate related CMAQ estimates. It is not clear how important coar se particle depositoni is and

how it should/would be addressed. The Panel re quests more clarification on this issue.

14On a related topic, the Panel suggests that the Agency consider the feasibility of calculating an alternative depositi on transfer ratio for oxidized n itrogen, using a combination of (or perhaps the sum of) nitric acid and partic ulate nitrate, as an alternative to using NO y . A possible advantage of this approach is that nitric acid is the component of NO y that deposits most efficiently, and correlates best w ith total oxidized N deposition. C onsequently, the resulting total deposition estimate would be less dependent on CMAQ model performance. A second possible advantage is that this calculation (as well as the T

SOx calculation) could be made using currently available and relatively low-cost CASTNET f ilter pack measurements, without a need to establish a large new network of continuous NO y and SO 2 . A disadvantage of this approach is that while CASTNET measurements of total (gas + particle) nitrate are c onsidered reliable, the CASTNET measurements of the separate HNO 3 and p-NO 3 components are subject to large sampling artifacts.

Estimates of total oxidized N deposit ion calculated usi ng the original T NOY method and the suggested alternative approach could be ev aluated against both CMAQ estimates of total deposition as well as wet deposition measurements from the NADP plus dry deposition estimates

from the CASTNETnetwork. It would also be important to consider whether the alternative approach would perform as well as the original T NOY when calculated over broad spatial scales, and over long time periods when NO

x emissions and NO Y species compositions may change.

As an alternative approac h, EPA should attempt to further evaluate the stability of

the T SOx and T SOx ratios over time and space recognizing that these ratios are a function of both air concentrations and deposition velocities. One possi bility would be to use information from other sources (e.g., CASTNET) to make some co mparisons among air concentrations for these chemical species with respect to their modele d deposition velocities and resultant estimated deposition where such data are available. The Pa nel recognizes that the suite of chemical species that can be used in this analysis is less extens ive than that modeled in CMAQ. If these ratios

obtained from other data sources show substantia l variation over time or space, it would be useful to evaluate the relationship between meteorological and/or emissions sources.

10. What are the Panel’s views on staff’s conclusion that an aver aging time of 3 to 5 years is appropriate given the AAPI form of the standard?

The EPA staff makes a good case for using the averaging time of three to five years and the panel agrees with that recommendation.

11. What are the Panel’s views on the preliminary staff conc lusions regarding alternative target ANC levels that are appropriate fo r consideration and the rationale upon which

those conclusions are based?

Based on the available scientif ic data, the range of target ANC values considered in the Policy Assessment is appropriate, i.e., 0, 20, 50 and 100 μeq/ L as target levels. These values encompass the range of sensitive ANC classes for surface waters in the lite rature, and there is a range of biological responses corr esponding to this range of ANC le vels. There will likely be

15biological effects of acidification at higher ANC values within this range, and there are relatively insensitive organisms that are not impacted at ANC values at the low end of this range. Adverse effects of acidification on aquatic biota are fairly certain at the lo w end of this range of ANC and incremental benefits of shifting waters to high er ANC become more un certain at higher ANC

levels. There is substantial confidence that th ere are adverse effects at ANC levels below 20

μ eq/L, and reasonable confidence that there are adverse effects below 50 μ eq/L. Levels of 50

μ eq/L and higher would provide ad ditional protection, but the Pane l has less confidence in the significance of the incremental benef its as the level increases above 50 μ eq/L. As indicated in

the draft Policy Assessment , there are clear and marked biologi cal effects at ANC values near 0 μeq/L, so this is probably not an appropriate targ et value for the AAPI. At a target value of 20 μeq/L, aquatic biota experience acidification effects. Moreov er, at this level of ANC many surface waters experience episodic acidification a nd associated biological effects. As a result, target ANC values of 20 to 100 μeq/L are in th e range of appropriate values, while recognizing that there is additional protect ion at 50 to 100 μeq/L.

a) In light of the Panel’s views on the appr opriate definitions of adversity to public welfare (see Chapter 3), what are the P anel’s views on the appropriateness of the information related to adversi ty considered by staff in evaluating alternative target

ANC levels?

The information on adversity to public welfar e associated with the effects of aquatic organisms and ecosystems at different levels of ANC is appropriate given th e available literature. The reduction in or loss of sensitive species th at would otherwise have been present in that ecosystem is an appropriate point er to adversity to public welfar e. There is relatively little information on the temporal biological response of acid-impacted aquatic ecosystems to marked decreases in acidic depositi on. Most of the information on biol ogical response to acidification is developed from spatial data. It may be useful to emphasize that it is unclear if the biological patterns observed for spatial data of varying ANC will similarly occur temporally in surface waters following increases in ANC due to any futu re decreases in nitrogen and sulfur deposition.

12. What are the Panel’s view s on the approaches considered by staff for assessing alternative target percentages of water bodies for protection at al ternative ANC levels?

This question is difficult to address without specifying the filtering criteria for the watersheds at specific ANC thresholds. As noted in our response to Charge Question 7b, the rationale for the filtering criteria should be be tter explained. It woul d be helpful to see an analysis of the implications of different choices of the filtering criteria for the target percentages. It is difficult to suggest targ et percentages without more in formation on subdivisions of the

United States to be used and the distribution of ANC values in these subdivisions. Since effects at current deposition levels are adverse, the target should be a higher percen tage than is currently adversely affected in sensitive areas.

16The DL factors, which clearly are numeri cal indices of some kind, should either be formally defined in the form of equations or it should be made clear how the numerical values for them presented in Tables 5-12 and 5-13 were derived.



### Chapter 6: Co-protection for Other Eff ects Using Standards to Protect Against Aquatic Acidification

13. What are the Panel’s views on the utility of the additional analyses of co-protection benefits to inform consideration of alternative levels of the standard?

The analyses and conclusions in Chapter 6 are important because the decision to focus on the effects of acidification on aquatic ecosystems means that in the current standard setting process, other important effects on ecosystems (doc umented in the ISA), ar e not being explicitly

taken into account. To the extent that standards set to protect ag ainst effects of acidification on aquatic ecosystems result in decreased amounts of nitrogen and sulfur deposition there may be

additional beneficial and detrimental effects to other ecosystems. It is important to acknowledge these even if they are not quantified.

The analyses reported in Chapter 6 are adequa te for this purpose, but the interpretation of the conclusions could be broadened. One analysis suggests that sensitiv e terrestrial systems

located in the same watersheds with sensit ive aquatic systems would be protected by the deposition levels that would be needed to protect the aquatic systems. A relevant question then is the extent to which sensitive terrestrial ecosystem s are co-located with sensitive aquatic systems throughout the country.

Similarly, even though the standard would not decrease N deposition to the extent required to meet the target share of the TMDL in the Chesapeake watershed, the discussion could say more about what percentage of the target TMDL might be achieved.

The discussion in this chapte r should acknowledge that the level of protection from undesirable effects of N deposition in terrestrial ecosystems is not addressed in this analysis and remains uncertain, especially in the arid and semi-arid ecosystems of the Southwest. Negative effects of N deposition on lichen communities ar e observed in some locations at very low amounts of N deposition.

Introduction of mobile sulfate or nitrate anions into acidic soils (whether naturally acid or acidified by pollution) can result in near in stantaneous acidificati on of waters, whereas acidification of soils is a long-term process occurring over decades or longer. Similarly, recovery of surface waters from acidification could happen relatively quickly if mobile sulfate and nitrate are removed, but recove ry of acidic soils is highly questionable as soils in humid systems naturally acidify but do not spontaneously become less acid. The rate of ac idification of

soils should decrease with decreased atmospheric inputs of sulfur and nitrogen, however.

17

### Chapter 7: Evaluation of Uncertainty a nd Variability in the Context of an AAPI standard, including Model Evaluation, Se nsitivity Analyses, and Assessment of Information Gaps

14. What are the Panel’s views on the following: a. The degree to which the chapter appropria tely characterizes the potential role of information on uncertainty, sensitivity, and variability in informing the standards?

Th e discussion of uncertainty and sensitivity an alysis is much improved compared to the

first draft in consolida ting the uncertainty, sensitivity and variability in th e proposed indices; however, a more complete quantitative analysis of uncertainty is needed for the AAPI. The reason it is particularly impor tant to conduct a comprehensiv e uncertainty and sensitivity analysis for the AAPI form of the standard is that many of the components of the AAPI cannot

be evaluated because of lack of measurements. One way to gain confidence in using the AAPI is to examine quantitatively how sensitive the SO

x and NO y response surfaces are to different components of the AAPI. The Panel’s major comments on this chapter include:

1. Summarize the general framework applied for uncertainty analysis, e.g. the World Health Organization framework used in other NAAQS assessments.

2. Extend the uncertainty analysis beyond the components and examine the propagation of the uncertainties through the entire AAPI, w ith particular focus on how uncertainties impact the levels of NO 2 and SO 2 . Include constraints from available observations.

3. Aggressively pursue the identification and re duction of biases in the CMAQ model that

are relevant to the AAPI.

It is recognized that it is difficult to quantif y the uncertainties associated with the AAPI. Nevertheless, the Panel recommends that EPA pursue more complete uncertainty analysis focusing on the overall, end-to-end, cumulative estim ation, including the po ssible application of Monte Carlo techniques. EPA may want to assess the report presented by the Electrical Power Research Institute at the October 6-7, 2010 meeting.

While there is significant uncertainty associated with model calculations both in CMAQ and the MAGIC/SSWC, there is a considerable amount of empiri cal observations that provide constraints on the magnitude of these uncertainti es. The combined use of uncertainty propagation and the observational constraints should be pursued.

b. The appropriateness and completeness of th e evaluation of CMAQ model performance and sensitivity to critical inputs?

The inclusion of comparisons of CMAQ and CASTNET results and the related discussion on the CMAQ limitations in Chapter 7 is ve ry helpful. It should be useful for future improvements of CMAQ. As indicated, the “sensitivity of CMAQ derived deposition transformation ratios to changes in emissions and treatment of chemistry” is not yet completed. This should be a high priority for EPA.

18Th e performance evaluation of the CMAQ m odel is incomplete. A more complete evaluation with measurements is key to improvi ng confidence in the calculations of the AAPI.

The overestimation of SO 2 is a significant systematic error th at may lead to a bias and may have a major impact on the estimated deposition and th e AAPI overall. A figure si milar to Fig 7-5 for CMAQ-CASTNET comparison for SO 2 could be very revealing because the model cannot be directly evaluated for dry deposition due to th e lack of measurements, and evaluation of the ability of the model to represen t ambient levels can serve as a proxy for its ability to represent dry deposition. It is recommended that following evaluations (usi ng daily or weekly averaged quantities, and showing mean nor malized statistics as well as normalized mean statistics) be performed to assess the model performance:

1. Model performance for simulating nitric oxide , nitrogen dioxide, sulfur dioxide, nitrate, ammonium and aerosol nitrate, ammonium, a nd sulfate for different networks for which the data are routinely available,

2. Model performance for capturing observed levels of wet deposition of sulfate, nitrate, and ammonium using the National Atmospheri c Deposition Program (NADP) network

3. Model evaluation using the continuous meas urements of nitric oxide, nitrogen dioxide,

nitric acid and NO Y from the SEARCH network in th e southeastern United States. EPA should use the results from the model perfor mance evaluation to describe the uncertainties and limitations of CMAQ simulation of total de position of reactive nitrogen and sulfur oxides more completely,

c. The utility of the analyses of tempor al and spatial variability in the deposition transference ratios (TNOy and TSOx)?

The figures in the Policy Assessment showing the spat ial pattern of T NOy and T SOx are insufficient to provide the reader with adequate understanding of the spatial variation of the transfer ratios and how they are linked to acid-sensitive ecosystems. The meaning and implications of the box-and-whisker plots are not obvious. The terms “stiff” and “stiffness” are not explained. The T NOy and T SOx are critically important to th e APPI calculations, are entirely dependent on CMAQ simulations, and are impossible to fully evaluate with currently available measurements. It is therefore important to demonstrate that their spatial patterns appear reasonable, that the resultant deposition calcula tions are consistent with (limited) available measurements, and that these ratios remain stab le as emissions, concentrations and deposition rates are changed over time.

15. What are the Panel’s views on the insights provided by the AAPI sensitivity analysis including: a. The evaluation of elasticities of response? b. The multivariable ANOVA analysis?

Evaluation of elasticity of response is a good way to get an initial estimate of the AAPI sensitivity to its components. However, the Pane l recommends doing this analysis also for the SOx and NOx response surfaces to meet a particul ar standard, as those are the quantities for which compliance with the standard would be determined. The sensi tivity analyses should

19include a larger range of scenarios, such as the sensitivity to the 40% SO2 over-estimation in CMAQ.

A summary is needed for the relative sensitivities of the various parameters that make up the AAPI to show the parameters of the AAPI th at have the most and least impact and their influence on confidence levels. e.g., the role of non-atmospheric inputs , including base cation weathering and runoff rates. Such information should be used in driving research and monitoring efforts by EPA.

. 16. What are the Panel’s views on the discussion of uncertainty in the critical loads models including MAGIC and SSWC?

There is clearly uncertainty associated with model calculations. However, the Policy

Assessment does not acknowledge that ther e is a considerable amount of empirical field data to support application of this secondary standar d. Through monitoring studies there are about 30 years of observations providing a qu antitative understand ing of the nature and extent of soil and surface water responses to decreases in atmos pheric deposition. Through these observations and some field-based experiments, there is also a good understanding of the compensatory response of ANC to changes in concentratio ns of sulfate and nitrate. Thes e empirical data should be used to evaluate the quality of the AAPI calculations and to support the just ification and target parameter values for the AAPI.

There have been limited uncertainty analyses of the ecological models MAGIC and the SSWC. Some uncertainty analysis for MAGIC is presented in the REA. The panel encourages EPA to continue uncertainty analysis of these ecosystem models in the future

B eyond uncertainty analysis, efforts should al so be made evaluate model structure and compare this to the structure of other models available for use. Efforts should be made to

• test models, although it is difficu lt to test steady state models.

• improve and test the N

eco calculation by using observe d data and improved model simulations of N-deposition.

• compare results from steady-state with dynamic models to obtain a sense for the time scale to achieve target ANC values.

• evaluate the effects of variation and ch anges in climate on model calculations.

Some of these evaluations may be feasible within the current NAAQS review cycle, while others will help to refine the standards in future reviews.

17. What are the Panel’s views on the areas for future resear ch and data collection outlined in this chapter, on relative priorities for re search in these areas, and on any other areas that ought to be identified?

The future research areas outlined in Chapter 7 are appropriate However, there are other

areas that should be considered for future research and data collection.

20• Key uncertainties identified in the qualitative uncertainty analysis of Chapter 7 including pre-industrial sulfate, nitrat e, base cation, and ANC levels , dry deposition, and ecological indicators, with particular emphasis on paramete rs that were found to be most influential from the analyses conducted as part of this NAAQS review.

• There is a need to improve understanding of the sources, atmospheric dynamics ambient concentrations, bi-directional transport a nd deposition of both chemically reduced and organic forms of nitrogen.

• Efforts should be made to develop dynami c models to simulate effects of acidic deposition on soil, drainage waters and biota, to test these models and to apply these as tools in determining critical loads. Research should be conducted comparing results from steady-state and dynamic models.

• There is a need for research to improve th e linkages between atmospheric chemistry and transport models with watershed models. At mospheric models typically have relatively large spatial scales and simulate over relativel y short temporal scales. Watershed models simulating acidification of soil and surface waters, in contrast, have small spatial scales and simulate processes over l ong temporal scales. It is impor tant to quantify the subgrid scale variability in atmospheric deposition and how this variability can be addressed in simulations of watershed response to changes in atmospheric deposition.

• It is essential that surface water monitoring programs be maintained and soil and biological monitoring programs be strengthened.

• There needs to be improvements of tools a nd models to predict nitrogen retention in

watersheds.

• There is a need to better unde rstand the compensatory response of naturally occurring organic acids to decreases in acidic deposition.

• Since the current assessment was unable to address endpoints other than aquatic

acidification, there is a need for research regarding endpoints such as terrestrial
acidification and aquatic sy stem nutrient enrichment.

• EPA should organize a future workshop to further enumerate and prioritize research
identified in the Integrated Science Assessm ent, Risk and Exposure Assessment, and the
Policy Assessment for the secondary NAAQS review for NO

x and SO

x .

The CASAC Panel will discuss priorities among these research and data collection needs at
its planned meeting in February 2011.



### Chapter 8: Monitoring

18. What are the Panel’s views on using an open inlet to capture all particulate size fractions for the purpose of analyzing for sulfate? What is your opinion on using existing CASTNET filter packs as a future Federal reference method for sulfate?

21As a prefacing comment on these monitoring ques tions (18-20), this Panel is pleased to learn that the Agency plans to consult with CA SAC to identify the most appropriate monitoring approaches for this NAAQS, and we expect that more informed responses to these and other monitoring questions will be provided in that pro cess. In conducting that monitoring review, we encourage the Agency to emphasize not just compliance determina tion, but the multiple monitoring objectives outlined in chapter 8 of the Policy Assessment , and to consider whether some of those objectives might be most e ffectively addressed by enhancement of and coordination among existing monitoring program s. In addition, we recommend that the membership of the CASAC monitoring and methods subcommittee be enhanced for that review by adding individuals with exper tise in conducting deposition me asurements, as well as in assessing the effects of deposited S and N pollu tants on aquatic and/or terrestrial ecosystems.

The Panel is not opposed to considering the use of open-faced samplers, and possibly the CASTNET sampler in particular, as a possible federal reference method (FRM) for particulate sulfate, as a component of the multiple pollutant measurements needed to determine compliance with this secondary standard. It should be recognized, however , that the inclusion of coarse particle sulfate (excluded in sulfate measurements by more co mmonly deployed fine particle samplers) will not by itself provide any information on how much of the sulfate is present in coarse mode particles and which would contribute proportionately more to deposition than their fine particle counterparts. It shoul d also be noted that inclusion of coarse particles, which tend to be alkaline, could lead to formation of positive sampling artifacts from reactions with acidic S and N gasses.

Since the open-faced CASTNET samplers also measure particulate nitrate, and since coarse particle nitrate can cont ribute to nitrogen deposition, esp ecially in areas influenced by marine aerosols, consideration should be given to evaluating the quality of CASTNET filter pack methods for particulate nitrate as well. CAST NET samplers also measure sulfur dioxide and nitric acid, and so an alternative (to the T NOY ) nitrogen deposition transfer ratio could be developed (see response to question 9) based on combin ed measurements of HNO 3 and pNO 3

. As such, all the measurements needed to determin e compliance with this standard could be made by the existing CASTNET methods, which could be enhanced by adding new sites in acid and nitrogen sensitive regions, and by adding more detailed measurements like continuous NOy,

SO 2 , etc. at a subset of those site s to better address impor tant objectives other than compliance. It would be unprecedented to have a compliance network operated by an EPA contractor (as CASTNET currently is) rather than by state agencies. And as indicated above, there are also

serious concerns with th e quality of CASTNET HNO 3 and particulate nitrate (p-NO 3 ) data. For these reasons, it would be helpful if the pr oposed AAMMS review of monitoring methods for implementing this standard includes consider ation of both continuous and filter pack measurements of all the relevant S and N species, as well as other approaches like passive samplers and diffusion denuders.

2219. What are the Panel’s view s on requiring measurements of ammonia and ammonium to assist implementation of the standard?

Although NH

x deposition estimates could be supplied by CMAQ model output,

additional NH 4 and especially NH 3 measurements would be extr emely valuable for supporting and implementing the standard both directly - to quantify an unregulated but varying element of the compliance metric - and indirectly, to help evaluate and improve emissions inventories and CMAQ model performance. NH 4 measurements are currently available from the CASTNET and (urban) Chemical Speciation (CSN) networks , and could conceivably be added to the Interagency Monitoring of Protect ed Visual Environments. NH 3 measurements are currently much sparser and are more crit ically needed, not only for asse ssing a key parameter in the AAPI used in the proposed secondary standard but also for better understanding sources and trends of

PM 2.5 , regional haze, and sources and effects of N deposition on nutrient enrichment. The passive NH 3 sampling approach currently being deploye d in the AMoN Networ k (at a subset of NADP sites) appears promising and would benef it from more dedicated EPA funding support. Given the current state of development of inst ruments and methods and their costs, the Panel does not believe that comprehensive ammonia monitoring should be required. The panel strongly encourages, however, that monitoring be conducted at a minimum using the passive

NH 3 sampling approach currently being deployed in the AMoN Network.

20. What are the Panel’s views on having a subset (e.g., 3-5 sites) of monitoring stations in different airsheds that measure for the major NO y species; nitric acid, true NO 2 , NO, PAN and p-NO 3 ?

Appropriate design of a networ k required to determine a ttainment with the proposed standard and to inform future reviews will require a major effort. An appropriate design will be impacted by the choices made in formulati ng the standard, includi ng the form, indicator, ecoregion approach and fraction of lakes protected. Insufficient information is available at this time, and we commend EPA staff’s desire to involve the CASAC monitoring and methods subcommittee in addressing the monitoring rela ted issues. Some in itial thoughts are provided

below.

As suggested in the response to question 18, a slight modification to the proposed calculation of the depositi on transfer ratio (currently expressed as T NOY ) for oxidized nitrogen deposition, might allow the use of a modestly expanded version of the existing CASTNET network to determine compliance with the proposed secondary SO

x /NO

x NAAQS. Disadvantages of this approach include the loss of valuable temporal resolution in the weekly aggregated CASTNET filter pack data, uncertainties in the portioning between nitric acid and particulate nitrate, and th e exclusion of important NO y components like NO, NO 2 and PAN,

which better reflect the sources of oxidized nitrogen emissions, wh ich eventually contribute to N deposition downwind, and/or which may represent important components of total deposition at

some locations.

23For these reasons, it is important for implem enting this secondary standard that the existing monitoring network be expanded by adding si tes in different kinds of sensitive areas, and refined by adding more detailed supplemental meas urements at a small subset of these sites. Valuable supplemental measurements would include continuous NO y and trace SO 2 , PAN, true

NO 2 , and possibly nitric acid, as well as p-NO 3 , and NH 3 that would be measured continuously, if practicable, or by integrated methods. Po ssibly there will be oppor tunities to add CASTNET filter packs, passive samplers, denuder analyses , and/or other supplemental measurements to several of the existing or pl anned rural National Core (NCore) Multipollutant Monitoring

Network sites. Such measurements would not onl y help respond to the multiple objectives for this secondary standard outlined on page 8-1 of the PA, they woul d also be of great value for improving data analysis and modeling assessments of sources, atmospheric chemistry, transport

of and the effectiveness of c ontrol strategies for ozone, PM 2.5 and regional haze.



### Chapter 9: Conclusions

21. What are the Panel’s views on the overall characterization of uncertainty as it relates to the determination of an ecologically-relevant multi-pollutant st andard for NOx and SOx?

EPA has done a good job of qualitatively di scussing uncertainties in Chapter 7 and reviewing them in Chapter 9. As noted in res ponse to charge questi ons 14-16, CASAC believes it is important that there is further progress on qu antitative analysis of sensitivity and uncertainty, for key components of the AAPI, for the combined effect of multiple uncertainties on the AAPI, and implications for specification of th e trade-off between NOy and SOx allowable concentrations. In Chapter 9, EPA should provide a concise summary of those key uncertainties that are most likely to lead to bias, imprecisi on, or both, in the AAPI, and the implications of

such uncertainties when translati ng an ANC target into an associated AAPI level. For example, given biases, should the selected AAPI be higher or lower than implied by a specific target ANC? Given imprecision, what range of AAPI might be consistent with a particular target ANC? EPA should conduct a more complete ev aluation of the CMAQ simulations used to calculate the deposition transfer coefficients and consider additional proce sses, such as internal sulfur sources, in the AAPI.

The choice of averaging times needs to inform the variability and un certainty analyses of Chapter 7. This is because the range of variabi lity and uncertainty depend on averaging time. Similarly, the geographic scope needs to be taken in to account in the analys is of variability and uncertainty.

22. What are the Panel’s views on the following: a. The insights that can be gained into potential alternativ e additional secondary standards (using the AAPI form) by considering: i. Information from studies on the re lationship between mortality in aquatic organisms and pH and ANC? ii. Information from studies on the relationship between fish health and/or biodiversity metrics and pH and ANC?

24iii. Information on the relations hip between pH, Al, and ANC? iv. Information on target ANC levels id entified by states and regions, as well

as other nations?

Each of the sources of information mentione d in the charge questi on both separately and taken together provide a compelling case on th e relationships between ANC and other water quality metrics that are associated with biotic health of waters, and provide insight regarding target ANC values. Text should be provided on the validity of sp atial survey data when applied to infer temporal relationships. Different states a nd nations have identif ied different target levels. Some use pH, others use ANC. It will be helpful to explain and compare how these values were developed. Chapte r 9 could clearly and briefly su mmarize possible co-benefits and unintended consequences of various alternatives for the standard. For example, to what extent might a standard focused on aquatic acidification al so be protective of terre strial acidification or aquatic nutrient enrichment? Would higher levels of target ANC provide more protection for these other effects? These points can be made while still placing emphasis on the sufficiency of the scientific evidence supporti ng the need for a revised standa rd to protect from aquatic

acidification.

b. The appropriate role of qualitative and quantitative characterizations of uncertainty in developing standards using the AAPI form?

Conceptually, the AAPI approach is compelling and appropriate. There are uncertainties associated with the practical use of AAPI that should be more fully evaluated. The sensitivity and uncertainty characterization of the AAPI needs to incl ude not only statistical analyses associated with specific model parameters individually, but also consider their joint effect (taking into account covariance and dependencies) and an evaluation of possible omissions (e.g. reduced nitrogen inputs, contribution of sulfate sources and sinks in soil). To the extent possible, biases and imprecision in values of AAPI associated with a target level of ANC should be quantified, and these uncertainties should be used to inform specification of ranges of AAPI associated with a target ANC that may be more or less protective within the range of scientific uncertainty. This would lead to a family of

NO y -SO

x trade-off curves associated with each target ANC for a given geographic location. A specific standard would be set by choosing an AAPI within the range of scientific uncertainty, which would then be associated with just one NO y -SO

x trade-off curve per region. EPA staff is encouraged to offer reasonable judgments about the range of uncertainty in AAPI for a given ANC target based on factors difficult to quantify within the time period of the assessment, such as the preindustrial cation weathering, the deposition transfer ratios, unmodeled factors, ancillary benefits, and unintended consequences.

c. The role of considerations regarding the relationship of the standard to: i. the time trajectory of response, e.g. when specific ANC levels are likely to be realized given a specific level of the AAPI?

Based on recent observations and dynamic model calculations, the time response to recovery in ecosystems from decreases in acidic deposition is very slow. Because of accumulation of sulfur in soils, it is likely that the timescale for recovery of watersheds, especially in the Southeast, would

25likely be even longer. Factors such as changes in climate and carbon dioxide concentration in the atmosphere could affect the time trajectory, and the effects may be substantially different between aquatic and terrestrial ecosystems.

ii. the likelihood of damages to aquatic ecosystems due to episodic acidification events given a specific target for chronic ANC?

Based on surface waters studied in the Northeast, decreases in ANC associated with snowmelt is approximately 50 μeq/L. Thus, based on these studies, a long term ANC target level of 75 μeq/L would generally guard against effects from episodic acidification down to a level of about 25 μeq/L.

iii. the levels of co-protection for terrestri al ecosystems against acidification effects and the for aquatic and terrestrial ecosy stems against effects of excess nutrient

enrichment?

There may be co-benefits for terrestrial and co astal ecosystems with respect to decreases in methylization of mercury associated with decreases in sulfur dioxide emissions and decreases in bioaccumulation of mercury associated with increas es in pH and ANC. Aquatic ecosystems may not be more sensitive to acidic deposition than terrestrial ecosystems. Many soil time series studies suggest ongoing soil acidification while surface waters are recovering from acidic deposition. This may also suggest that soil is more “sensitive” to inputs of acidic deposition than surface waters. Levels of protection provided by the proposed st andard against nutritional nitrogen effects in terrestrial ecosystems are uncertain, especially in arid and semi-arid zones, and should be evaluated

in the future.

23. What are the Panel’s views on Staff’s conclusion that the existing secondary standards for

NO

x and SO

x should be retained to provide protection against direct adverse effects to vegetation due to gas phase exposures?

Based on the information presented in the PA, the scientific understanding of effects from direct foliar exposures to gaseous sulfur and nitrogen oxides has not changed appreciably, and the existing secondary standards for SO 2 and NO 2 should be retained. The indicators, averaging times, levels and forms of the current standards are not appropriate for addressing the (indirect) effects of

SO

x and NO

x deposition to acid-sensitive ecosystems. Therefore, additional secondary standards to protect against adverse effects from acidic depos ition should be added to the existing secondary

standard.

24. In light of the Panel’s views on what cons titutes adverse effects to public welfare (see Chapter 3), what are the Panel’s views on:

a) the degree to which current levels of NO y and SO

x deposition are adverse to public welfare based on evidence and risk information, and information on adversity provided in Chapters 2,3, and 4?

26Current and cumulative levels of NO y and SO

x deposition have been shown to result in environmental damage to an extent that is advers e to public welfare. The effects include acidification of aquatic and terrestrial ecosystems and nutrient enrichment. However, the panel believes that descriptive information about that adversity and its significance could be better and more comprehensively articulated, and that additional discussion of the possible benefits of S and N deposition would be helpful.

b) target values for ANC that protect against adversity to public welfare in light of the information presented in Chapter 5 concerning levels of ANC and the ecosystem effects associated with those target ANC levels?

There is substantial confidence that there are adverse effects at ANC levels below 20 μ eq/L,

and reasonable confidence that there are adverse effects below 50 μ eq/L. Levels of 50 μ eq/L and higher would provide additional protection, but the Panel has less confidence in the significance of

the incremental benefits as the level increases above 50 μ eq/L.

c) factors relevant in selecting target percentages of waterbodies to protect at alternative target ANC levels to protect against adverse effects to public welfare, and weights to place on those factors?

The justification and implications of alternative spatial grouping classifications were not clear to the panel. It is not clear what is gained by the added complexities of going beyond the two groups of sensitive and not sensitive, although there is inherent appeal to taking into account available information about variations across eco-regions. Because there is large variability in

inherent sensitivities of water bodies to acidificatio n effects among different regions and even within regions, protecting a target percentage of lakes from the populations which are potentially susceptible to acidification seems logical, however. It seems that the target should be higher than the current percentages of sensitive water bodies that are below the target ANC.

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking into account

• consideration of target levels of ANC (chapter 5),

The panel concurred that ANC levels from 20 to 100 were appropriate to consider.

• target percentage of water bodies to protect (chapter 5),

T he panel believes that this choice was a value judgment and somewhat arbitrary. Insufficient analysis was provided to adequately support a choice at this time. The panel stresses that the target percentage will also be influenced by whether and how the filters used to exclude lakes (e.g., naturally acidified lakes, for example) are applied.

• consideration of relevant uncertainties in AAPI components (chapter 7),

The Panel spent considerable time discussing how and what is necessary to characterize relevant uncertainties in AAPI components in order to answer this and other questions about the PA.

27The current sensitivity and uncertainty analysis shou ld be strengthened. For suggestions on specific AAPI components see the responses to charge questions 5, 9, 14, 15, 16 and 22. The panel would also particularly like to see some assessment of the cumulative uncertainties associated with the complete AAPI calculation. One approach to this might be to employ available measurement data and model calculations to compare levels and change s in AAPI estimates over the past 20 years with concurrent ANC levels in surface waters. In some cases, individual components of the APPI could also be compared with their measured counterparts over the same recent time period. The goal of these syntheses and analyses would be to lend defensibility to the approach, provide broad bounds on uncertainties, or, in some cases to provide reality checks on the components of the AAPI.

• any other potentially relevant factors, such as levels of co-protection against terrestrial acidification and nutrient enrichment (chapter 6)?

It seems likely that a standard that decreases acidifying deposition to acid-sensitive ecosystems would provide some co-protection benefits to acid-sensitive terrestrial ecosystems. If attaining such a standard results in regional-scale reductions in nitrogen deposition, there may also be reductions in plant growth rates in aquatic or terrestrial ecosystems or components of those ecosystems. These growth rate changes might be view ed as either benefits or dis-benefits, depending on the specific ecosystem and management objective. It is not currently possible to provide quantitative estimates of co-protection benefits or detrimental effects, but it would be useful to qualitatively discuss these associated effects in the final Policy Assessment document.

28

### Enclosure C Compilation of Comments from Individua l Members of the CASAC Oxides of Nitrogen (NOx) and Sulfur Oxides (SOx) Secondary Review Panel

Comments from Dr. Praveen Amar .......................................................................................... 30 Comments from Dr. Andrzej Bytnerowicz ............................................................................... 33

Comments from Ms. Lauraine Chestnut .................................................................................. 36 Comments from Dr. Ellis Cowling ............................................................................................ 41

Comments from Dr. Charles Driscoll ....................................................................................... 53 Comments from Dr. Christopher Frey ..................................................................................... 61

Comments from Dr. Paul Hanson ............................................................................................. 67 Comments from Dr. Rudolph Husar ........................................................................................ 69

Comments from Dr. Dale Johnson ............................................................................................ 71

Comments from Dr. Naresh Kumar ......................................................................................... 76 Comments from Dr. Myron Mitchell ........................................................................................ 81

Comments from Mr. Richard Poirot ........................................................................................ 95

Comments from Dr. Armistead Russell .................................................................................. 104

Comments from Dr. David Shaw ............................................................................................ 106

Comments from Dr. Kathleen Weathers ................................................................................ 108

29Comments from Dr. Praveen Amar

Chapter 3: Considerations of Adversity to Public Welfare

Charge Question 1. What are the Panel’s views on the definitions of adversity that are appropriate to consider in determ ining what constitutes adversity to public welfare relative to the NOy and SOx secondary standards

Chapter Three covers three areas of :a) adversity to public welfare, b) application of ecosystem services framework (provisioni ng, regulating, cultural, and s upporting) as a way to address adversity to public welfare, and , c) usef ulness of economic valuation approaches to “value”/monetize ecosystem services, when possibl e. The second draft of the Policy Assessment is a great improvement over the first draft. The de finition of adversity used in this document is derived from, and based on, recent applications of the concept by EPA in other recent environmental policy contexts and is quite app licable to ecosystem effects from exposure to ambient levels of SOx and NOy.

The Chapter is much improved in describing the current level of ecosystem services as well as

scale of adversity to public welfare driven by cha nges to ecosystem services as a function of changes in atmospheric deposition of SOx, NOy, and potentially no changes (potentially increases) in atmospheric deposition of reduced NHx. The Chapter presents many quantitative

estimates in dollars when economic valuati on/monetizing were possible. Also, monetized benefits of current status of ecosystem se rvices are clearly presented in many Tables.

Specific Comments on Chapter 3:

It would be useful if public we lfare/adversity was mo re clearly discussed for, and separately allocated to, NOy and NHx (both through atmo spheric deposition and through water runoffs) instead of just atmospheric NOy alone. (see page 3-8; TMDL discussion for Chesapeake Bay; this discussion should be more explicit in desc ribing the role of NHx through water discharge and air deposition; please also see Page 3-25, Line 15, nutrient enrichment refers there “only to that due to NOy deposition” ).

For Figure 3-6, the range for high end of N and S deposition (300- 1,337 eq/ha-yr) for the Western U.S. is too large and needs to be sub divided (say, in two or three parts) for finer representation of high-end depos ition levels in the West.

Sections 3.3.2 and 3.3.3 on economics framework and its role in defining adversity are very well

written.

The Section 3.3.4 on “collective action as an indicator of public pref erences” correctly notes the actions and efforts on the part of communities, NGOs, and States to reduce acidity of lakes and

streams. This Section overlooks wh at I believe is the most important action/effort taken so far in the U.S. by the federal government: Title IV of the 1990 CAAA to lower SO 2 emissions by 10

30million tons per year as well as NOx emissions by 2 mm tpy to address ecosystem acidification. The value of the this national “revealed preference” should be valued/monetized at about $5 billion/year, based on $500/ton of SO 2 controlled and should be noted in this section.

Section 3.3.1.1 needs to be written more clearly to make the points it is “trying” to make with

references to table 3-2 and 3- 3. I found it hard to understand.

Finally, Table 3-6 (page 3-33) needs major improve ment in format including column headings.

Chapter 5: Options for El ements of the Standard

Charge question 5: What are the Panel’s views on staff’s revised conceptual framework for the structure of a multipollutant, ecol ogically relevant standard for NOx and SOx? To what extent does the Panel agree that this suggested structur e adequately represents the scientific linkages between ecological responses, wa ter chemistry, atmospheric deposition, and ambient NOx and

SOx?

The revised conceptual framework and structur e of the proposed standa rd (s) is very wellthought out for addressing vari ous components and connections between these components (ecological effects, atmospheri c wet and dry deposition, atmosphe ric concentrations of NOy and SOx, and surface water chemistry), with one major exception noted below. I had made this same point for the first draft of the policy assessment document.

Even though the framework and the structure “t akes into account” the reduced ambient NHx and its deposition in design ing AAPI (atmospheric acidification pot ential index) , it does so in a manner such that future control strategies and policy options most probably will not allow EPA to address and require reductions in U.S. ammonia emissions under proposed standard setting structure. Ammonia emissions are currently at about 4 to 5 million tons per year. Emissions of ammonia (which is an unregulated air pollu tant) and resulting a mmonia and ammonium concentrations and reduced nitrogen deposition leve ls are only expected to increase by as much as ten percent over the next few decades becau se of increased food production and increased activity in CAFO sources (confined anim al feeding operations) in the U.S.

Notwithstanding my concern about not addressing reduced nitrogen/NHx directly, the proposed structure more than adequately represents the scientific linkages betw een ecological effects, surface water chemistry, atmospheric deposition, and ambient levels of NOy and SOx.

Ch arge Question 6: What are the Panel’s views on the appropriateness of considering a single national population of waterbod ies in establishing standard s to protect against aquatic

acidification? What are the Panel’s views on consideration of alternative s ubdivisions of the U.S. to identify the spatial boundaries of populations of waterbodies a nd acid-sensitivity categories, specifically: a) the use of Ecoregion III areas to aggregate watrebodies?

3132 b) the use of ANC to further aggregate Ecoreg ion III areas into di fferent categories of sensitivity? c) The relative appropriateness of the suggested methods for categoriz ing spatial boundaries of sensitivity, e.g., one nation, binary sensitive/less-sensitive classes, cluster-analysis based on sensitivity classes, and individual ecoregions?

The first approach (option 1) that considers th e whole U.S. as one unit and provides for a single deposition metric is simple and easy to calcul ate, but its weaknesses ar e too many to consider this as the preferred approach (e.g., over pr otection for the least sensitive areas and under protection for areas that are most sensitive).

The three sub-options under sec ond option seem to have merits. However, they are based on the concept of “Level 3 Ecoregions,” which is rather poorly described in the document and I was not sure how this approach divides US into 120+ acid-sensitive categories. A reference is made to Omernik’s (1987, 1995) and other works about “the analysis of the patterns and the composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity.....” What is not explained is how “hierarchical levels are developed” at various levels (Level I, II, III, and IV (future)).

Between options 2a, 2b, and 2c, the approach base d on cluster analysis (option 2b) seems to provide the right balance when co mpared to approach that is not detailed enough (option 2a) or detailed too much (option 2c).

Charge Question 9: What are the Panel’s views on the revised characterization of the deposition transference ratios (TNOy and T SOx)?

The policy assessment document proposes to us e the output of CMAQ model to calculate deposition transference ratios for both NOy and SOx. The CMAQ hourly predictions at the scale of 12-km grid will be averaged to provide annual transference ratios so as to be consistent with depositional loads derived from ecosystem models. It is not clear how to account for wet and dry deposition of those nitrogen and sulfur species (w hich ones?) that are not explicitly modeled in the CAMQ. The PAD does note the possibility of large amount of sulfur and nitrogen deposition in the forest ecosystems in the coarser partic le mode and that CMAQ’ s simulations do not account for deposition in the coarse particle mode. It is not clear how big this issue is and how it

should/would be addressed.

Charge Question 10: What are the Panel’s views on staff’s conclusion that an averaging time of 3 to 5 years is appropriate given th e AAPI form of the standard?

The PAD makes a good case for using the averag ing time of three years (Figure 5-22 on the magnitude of coefficient of variation (CV) shows that it is less than 25%, based on CAMQ simulations for the years 2002-2005).Comments from Dr. Andrzej Bytnerowicz

7. What are the Panel’s views on the appropriateness of the critical loads that form the basis for the population assessment to determined deposition metrics?

Using a concept of Critical Loads is logi cal and appropriate for development of a secondary (welfare) standard for biological effects of NO

x and SO

x . This approach links concentrations of the atmospheric oxidized forms of nitrogen and sulfur with N & S deposition and their acidifying effects on aquati c ecosystems. What is important is also a fact that the proposed approach includes reduced forms of at mospheric N as a contributor

to acidification of lakes and streams.

a) What are the views of the Panel on the appropriateness of gene ralizing the f-factor approach to apply to lakes and streams in the Western U.S. and other portions of the

Eastern U.S.

The purpose of the F-factor is to obtain esti mates of the pre-industrial surface water base

cation concentrations needed for calculation of critical loads. These values can be

obtained from the SSWC and MAGIC models.

At this point I am not able to adequately answer the posed ques tion. Explanation of the problem and graphs illustrating differences between the two approach es are not sufficient for understanding the proposed concept.

I believe this question could be modified to: “Is the proposed methodology for obtaining

BC

o values adequately described and what is the Panel’s opinion on extrapolating the knowledge gained for the Adirondacks lakes and the Southern Appalachian streams to the

rest of the US water bodies?”

b) What are the views of the Panel on the filtering criteria used to remove lakes and streams that are naturally acidic or no t sensitive to atmospheric deposition?

It's logical to eliminate in advance wate r bodies impacted by mine drainage, however, advance elimination of water bodies impacted should be considered and the rationale better explained with examples given, preferably in a distri bution form. The panel needs this information before it can fully respond to the question. The panel is concerned about removing lakes and streams with high concen trations of organic acids and with low historical ANC from the analysis since thes e are often highly sens itive water bodies. 8. What are the Panel’s views on the sugge sted methods for determining appropriate values of reduced nitrogen deposition in establishing NO

x /SO

x x tradeoff curves?

The proposed approach makes sense and utiliz es the best available knowledge on levels and distribution of reduced N deposition, howev er, reliance on the CMAQ-derived values provides high level of uncertainty (see my comments below).

33Due to a high NH 3 deposition velocity, steep concen tration gradients near the NH 3 source areas exist. Therefore averaging N red concentrations over larger areas may lead to missing

smaller areas where NH 3 concentrations may be seriously elevated and with potentially high biological and ecological effects. Therefore option 2 “a llow for additional spatial refinement of sensitive areas to reflect the heterogeneity of NH

x deposition” seems to be preferable.

As stated in previous CASAC reviews, a better understand ing of spatial and temporal

distribution of reduced N, especially NH 3 , in the US is critical. Efforts should be

continued to assure the na tion-wide monitoring of NH 3 in remote areas.

Additional remark: It would be good to de velop similar methodologies that account for atmospheric organic N.

11. What are the Panel’s views on the preliminary staff conclusions regarding alternative target ANC levels that are appropriate fo r consideration and the rationale upon which

those conclusions are based?

Focusing on a range of ANC values betw een -50 and 50 eq/L makes sense from a perspective of the expected pH changes, Al toxicity and related bi ological effects. At values <-50 eq/L no further damage should oc cur, while at values > 50 eq/L no more improvement is expected.

Improved biodiversity of fish populations ma y continue up to160 eq/ L and therefore the best protection would be ach ieved at ANC values >100 e q/L. However, considering that such recommendation could be impractic al, the proposed ANC 50 eq/L as a target

value seems to be reasonable and should be supported.

a) In light of the Panel’s views on the appr opriate definitions of adversity to public welfare (see Chapter 3), what are the Pa nel’s views on the appropriateness of the information related to adversity considered by staff in evaluating alternative target ANC

levels?

Appropriate information has been provided fo r the aquatic ecosystems. However, I would

like to see a better discussion of what the main ANC values considered (20, 50 and 100 eq/L) would mean to the surrounding terrestrial ecosystems in various eco-zones. That

could be discussed for such sensitive indica tors and sugar maple and red spruce in the eastern part of the country, and for lichen co mmunities in such areas as Sierra Nevada

Mountains in the West.

12. What are the Panel’s views on the appro aches considered by staff for assessing alternative target percentage s of water bodies for protecti on at alternative ANC levels?

This question comes to an issu e of toxicity (damage to indi vidual species) versus the biodiversity changes. What should be more im portant is where or if there is a common denominator for these two approaches? An appr oach that would provide various levels of

3435 protection against toxic effect s and biodiversity changes would be most desirable for scientists, managers and decision makers.

Additional general comments

In general I support the proposed CL-based ap proach for the newly developed secondary standard. However, at the same time I have to emphasize that such an approach could only work if NOy (NOx plus HNO 3 , HONO, PAN, particulate NO 3 and other oxidized reactive N species) replaces NOx (mainly NO and NO 2 ) as the secondary pollution

standard. Correlation between ambient con centrations of NOx and dry deposition of oxidized N to watersheds is poor. This is not surprising because while NO 2 and NO dominate atmospheric budget of the oxidized N, their contribution to that deposition is low due to their low deposition velocities to vegetation and soils. It is well established that N dry deposition of oxidized N is dominated by HNO 3 (which is a component of NOy, but not of NOx) characterized by very high deposition veloci ty. These problems are well covered on page 4-21 and shown on Fig. 4-21 of the reviewed PA.

Another major problem of the proposed a pproach is its reliance on the modeled concentrations of NOy, NHx and deposition of oxidized & reduced N from the CMAQ model runs. These modeled outputs are char acterized by high level of uncertainty and temporal limitation (model runs are just for certain years). Therefore verification of the model results, both for ambient concentrations and estimates of deposition, is critically needed. Additionally, deriving deposition transference ratios (T values) by dividing modeled deposition of oxidized N by a sum of concentrations of dry and wet N oxidized species will very likely result in highly unreliable values. These values will also differ in time and space considering huge regional and year-to-year differences in ratios of gaseous /particulate/water-dissolved oxidized N and ratios of dry/wet deposition. Better understanding of such issues is need ed while developing this approach.

Another problem, mentioned many times in the CASAC deliberations, is that while concentrations of NOx and NOy slowly diminish, concentrations of NH 3 from agricultural emissions and from 3-way catalyt ic converters are incr easing as well as the importance of N red in N deposition. In my opinion th ere a clear need for regulating all those NHx emissions and development of a new federal air pollution standard for NH 3

.Comments from Ms. Lauraine Chestnut

Charge Question 1:

What are the panel’s views on the definitions of adversity that are appropriate to consider in determining what constitutes adversity to public welfare relative to the NOx and SOx secondary standards?

Overall, the presentation and explanation of available information on losses in ecosystem services and associated economic valuation as a result of NOx/SOx deposition is much improved in clarity and contex t from the first draft PA.

The link is clear and well-documented between the selected ecosystem effects indicator, ANC, and the welfare effects of lost value of recreational fishing as fish populations (and in some cases whole species) are not sust ained in lakes and streams with lower ANC levels. The available quantitative information is well presented and explained (except for a few specific questions noted below). Howe ver, more could be done to explain the qualitative links between deposition and lost ecosystem services that are known and documented, but cannot be specifically quant ified for a specific amount of deposition.

For example, on page 3-13, changes in biodi versity, which are listed as an ecosystem effect of deposition, are associated with change s in cultural ecosystem services related to the preservation of natural ar eas (nonuse values) in addition to productivity, recreational viewing and aesthetics services th at are listed currently in th e text. It is well-established that there is public welfare value to protec tion and preservation of natural ecosystems in condition that supports the flora and fauna speci es that are native to the system, even

when there is no direct use value. This is ev idenced in the state and federal statutes that set aside parks and wilderness areas (noted in the first sections of chapter 3), and in willingness-to-pay study results such as the Banzhaf et al. (2006) study discussed on page 3-29. The text mentions nonuse value several times, but it would be helpful to make explicit that this includes value for the preservation of habitat and biodiversity independent of human use value.

Specific comments/questions in Chapter 3

page 3-9: What is the pollutant referenced in the critical lo ads shown for Europe?

page 3-11: Add nonuse to ecosystem services listed for water.

pages 3-14 and 3-15: Figure 3-5 includes fe deral and state public lands according to the legend, but the text on page 3-14 just refere nces Class I areas, wh ich I think are just federal. Please make clear what areas are included in the maps, and what oher natural areas may not be included that the p ublic may also care about protecting.

36page 3-17, line 20: Ecosystem services provide a framework to characterize and describe how changes in ecosystem function affect public welfare, even if they cannot be specifically quantified.

page 3-18: It is important to recognize and include language that preferences are not just about people’s own use and enjoyment of an ec osystem, but also include preservation and bequest value.

page 3-18, second paragraph: Good discussion and explan ation of how preferences depend on information.

page 3-25: figure 3-7. It woul d be helpful for more general audiences to include words such as biodiversity and habitat preservati on under cultural services. This is part of “nonuse” services, but I’m not sure most people are aware of this.

page 3-26: It might be useful to referen ce the language on page 3-22 about the goal of keeping the Adirondack Forest Preserve as “wild forest lands” and “kept in natural conditions.” This is a significant motivati on behind the public’s wi llingness to pay to prevent the effects of depositi on in these areas and is part of what makes the effects adverse to public welfare.

page 3-28: I’m a little confused by Table 3- 2. Are these threshold categories mutually

exclusive?

page 3-29: Are the results in ta ble 3-3 additive? For example, if a threshold of 100 is met,

is the annual value of additional recreational fishing services for NY residents the amount in the bottom row only, or the sum of the 3 ro ws? If they are all based on a comparison to background, then why are the numbers sma ller for the 100 threshold than for the 50 threshold? These numbers reflect just a portion of benefits, as noted in the text, so it is important to include more information in the ta ble title and headings about what they are: recreational fishing serv ices for NY residents.

page 3:30: Same question for table 3-4.

page 3-34: Is there some descriptive informa tion from the REA or the ISA to give a sense of the overall magnitude of the red spruce a nd maple decline attributable to deposition? The estimates of lost commercial forestry va lue in the second para graph are interesting, but are these forests significant timber reso urces? What can be sa id to describe the implications of the health of these tree species on the natural habitat and health of the natural ecosystems where these species are prominent? It seems like a more comprehensive story could be summed up here ab out the loss in services that is linked to deposition, even though specific quantitative va luation is not possible. Perhaps more

could be said about the Jenkins et al. (2002) results for avoi ding a “significant decline in health” of high elevation spruce in the Sout hern Appalachians. How does the description of decline in this study compare to what ha s been linked to current deposition levels? The

37results indicate substantially greater value than was estimated as commercial forest

losses.

page 3-36: Need to say something about how these services are hurt or impaired by eutrophication. The total value of these services is only releva nt if something can be said about how they are diminished by the effects of deposition. It is okay if this is only descriptive, but the li nk needs to be made.

pages 3-40 and 3-41: There is bett er clarity than in the first dr aft PA when total values of ecosystem services are presented to give context for the potential effects of deposition. The discussion on page 3-41 is helpful in describing why the CSS and MCF ecosystems are important and how the effects of deposition are likely to diminish the services that these systems provide. Anything that could be added about the extent of the current degradation of these ecosystems due to de position would be help ful for understanding whether the effects of current depos ition are adverse to public welfare.

Charge question 4

Has staff appropriately acknowledged the potenti al beneficial effects of nitrogen inputs into nutrient limited ecosystems, while maintaining the focus of the review on preventing

the adverse effects in nitr ogen sensitive ecosystems?

It seems to me that the PA is careful now to acknowledge the potenti al beneficial nutrient effects of N deposition in some systems. Th is will come up again when it is time for regulatory assessment, because there may be so me loss in benefits when N deposition is

reduced.

Charge question 13

What are the panel’s views on the utility of the additional analyses of co-protection

benefits to inform the consideration of alternative levels of the standards?

The analysis and conclusion in Chapter 6 are important because the decision to focus on the effects of acidification on aquatic ecosystems means that in this current standard setting process, other important effects on ecosystems (documented in the ISA), are not being explicitly taken into account. To the ex tent that standards set to protect against effects of acidification on aquatic ecosystems also provide some amount of protection against the other effects of deposition, then this provides support that the proposed standards are justified and beneficial.

The analyses reported in Chapter 6 seem adequa te for this purpose, but the interpretation of the conclusions could perhaps be broadened. It is clear that standards set to protect aquatic resources from adverse effects of aci dification would not fully protect against the effects of deposition on acidifi cation of terrestrial reso urces and nutrient effects on terrestrial and aquatic res ources. However, some partial protection that would be provided could be characterized more fully. For example, the analysis suggests that

38terrestrial systems located in the same watersheds with acid sensitive aquatic systems would be protected by the deposition levels th at would be needed to protect the aquatic resources. So, the question that comes to mi nd is what do we know about where sensitive terrestrial systems are located relative to sensit ive aquatic resour ces throughout the country. Are they mostly located near one another, or do they occur in completely separate locations in significant amounts? Gi ven the regional nature of ambient NOx and SOx concentrations, how close together would sensitive aquatic and terrestrial resources have to be for protections for one to extend to the other?

Related to this is whether there is benefit to reductions in deposition that are short of the targets for full protection. This depends on whether the dose-respons e relationships are continuous or substantially nonlinear. Similar questions come up for the analysis of reductions in N deposit ion relative to the TMDLs for the Chesapeake watershed. Th e discussion on page 6-6 shows that N deposition could be higher unde r an ANC target of 50 than would be allowed given the TMDL target. However, this is the maxi mum that the N deposition could be if SOx deposition were zero. There is a good chance it would be lower than this. Also, how does this N deposition compare to current levels? How much of the reduction to the target

TMDL would be achieved?

Charge question 24

In light of the panel’s views on what constitu tes adverse effects to public welfare, what are the panel’s views on:

a) the degree to which current levels of NOy and SOx deposition are adverse to
public welfare?

The case is well made in the PA, based on the information from the REA and the ISA and information added in the PA, that current levels of NOy and SOx deposition are harming sensitive ecosystems to an extent that is adverse to public welfare. A bit more can be done to carry forward the descriptive information about the significance of the current effects that cannot be fully quantified so that the implications for adversity to pub lic welfare are more comprehensive.

b) target levels of ANC that protect against adversity to public welfare?

The case seems well supported for a target ANC of at least 50. The wording used to describe the benefits of a target hi gher than 50 seems unnecessarily cautious. What I understand is that at 50, most se nsitive species would survive, but not necessarily thrive. It is certainly clear that loss of an entire species of fish that would otherwise be expected to live in such waters is an adverse effect, so a target of 50 to prevent loss of species is justified. To the extent that the size and robustness of the populations matter to public welfare (and I think there is evidence that they do) then it seems ther e would be further benefits of an ANC target higher than 50. It may be difficu lt to quantify the value of this additional

3940 benefit, but is it really all that uncerta in that there would be some additional

benefit?

c) factors relevant in selecting target pe rcentages of waterbodies to protect?

This is a tough question. The choice seem s a bit arbitrary. It is key that those bodies that are naturally acidic and w ould not benefit from reductions in deposition have already been excluded. Protecting only half the sensitive water bodies seems clearly like not enough. What percentage of water bodies in the Adirondacks are currently affected? It is already established that current effects

are adverse?

d) alternative standards for NOx and SOx...tak ing into account target ANC, target
percentages of water bodies pr otected, relevant uncertaint ies, other factors such as
co-protection?

The question of how to group resources seem s an important one that needs to be resolved. At a minimum the split into tw o categories seems necessary. It is not clear that the benefits of going to the eco region level are worth the extra effort. A key question is whether further disaggre gation would put less restriction on locations that are not sensitive—which is the whole reason why something other than a uniform national standard is being developed.Comments from Dr. Ellis Cowling

Charge Question 24. In light of the Panel’s views on what constitutes adverse effects to public welfare (see Chapter 3), what are the Panel’s views on:

a) the degree to which current levels of NOy and SOx deposition are adverse to public

welfare based on evidence and risk informati on, and information on adversity provided in Chapters 2, 3, and 4?

The ISA and REA for the current review of the NAAQS for oxides of nitrogen and sulfur (as summarized in Chapters 2 and 3) make very clear that current levels (ambient concentrations) of air-borne nitrogen and sulfur compounds (that include not only NOy and SOx, as asked about in this Charge Ques tion, but also include NHx and some as yet poorly characterized organic forms of nitroge n -- which I would abbreviate RHx) – see page 7-35) are now causing signi ficant “disruptions in th e structure and function of aquatic ecosystems” in various acid -sensitive regions of the US.

In this connection please note especially the fo llowing paragraphs in Chapter 2 page 2-3:

“The scientific evidence is sufficient to infer a causal relationship between acidifying deposition and effects on biogeochemistry and biota in aquatic

ecosystems (ISA 4.2.2). The strongest evidence comes from studies of surface water chemistry in which acidic deposition is observed to alter sulfate and nitrate concentrations in surface waters, th e sum of base cations, ANC, dissolved inorganic aluminum and pH. (ISA 3.2.3.2). Consistent and coherent documentation from multiple studies on various species from all major trophic levels of aquatic systems shows th at geochemical alteration caused by

acidification can result in the loss of acid sensitive biological species (ISA 3.2.3.3). For example, in the Adirondacks, of the 53 fish species recorded in Adirondack lakes about half (26 species) were absent from lakes with pH below 6.0 (Baker et al., 1990b). Biological eff ects are linked to changes in water chemistry including decreases in ANC a nd pH and increases in inorganic Al

concentration.”

Chapter 3 also makes clear that although the Clean Air Act provides a very broad definition of different kinds of air-pollution- induced “effects” on public welfare, the Act in fact does not define “public welfare” as such, and also does not define “adversity to public welfare.” Nevertheless EPA has hist orically interpreted air-pollution-induced “adversity” to include “disrupti ons in ecosystem structure and function” that are regarded as important to the people of this country. This working definition of “adversity” seems very sensible to me.

Chapter 3 also includes a brie f introduction to the concept of “Ecosystem Services” and describes various economic valuation and “Willingness to Pay” (WTP) studies that show very clearly that many citizens of our count ry are willing to pay the administrative and operational costs of both private- sector and public-sector efforts to decrease the presently

41ongoing acidification of freshwat er lakes and streams in su ch places as the Adirondack

Mountains of New York and New England and the Shenandoah National Park in the eastern US and in acid-sensitive landscapes such as the grasslands of Minnesota and Coastal Sage Scrub (CSS) areas of California.

Chapter 4 makes very clear th at the current NAAQS standard s for oxides of nitrogen and sulfur are not adequate to protect sensitive aquatic and terrestrial ecosystems from

acidification- and nutrient-enrichment effect s induced by atmospheri c deposition of total reactive nitrogen and sulfur compounds. See especially Chapter 4 page 4-2:

“ ... the current standards ar e not directed toward depos itional effects, and none of the elements of the current NAAQS – indicator, form, averaging time, and level – are suited for addressing the effect s of [total reactive] N and S deposition. Thus, by using atmospheric NO2 and SO2 concentrations as indicators, the current standards address only a fraction of total atmospheric NOX and SOX, and

do not take into account the effects fro m deposition of total atmospheric NOX and SOX. By addressing short-term concentra tions, the current SO2 standards, while protective against direct fo liar effects from gaseous SOX, do not take into account the findings of effects in the ISA, whic h notes the relationship between annual deposition of S and acidification effects wh ich are likely to be more severe and widespread than phytotoxic effects unde r current ambient conditions, and include effects from long term deposition as well as short term.”

Thus my response to Charge Question 24a is:

Based on the evidence and risk information as well as the information on adversity provided in Chapters 2, 3, and 4, and in light of my professional views

about what constitutes adverse effects to public welfare, I conclude that current atmospheric deposition loads of total reac tive nitrogen and sulfur (including NOy, SOx, NHx, and probably RHx as well) are causing very substant ial and publicly unacceptable adverse effects on public welf are in various parts of the US.

I also believe that the AAPI approach currently being developed through the currently proposed and well-integrated “t wo criteria-polluta nt” approach (with acidifying NHx emissions and deposition also being taken “as given”) is well grounded in the present state of scient ific understanding a bout acidification effects on aquatic ecosystems.

In addition I believe that the presen t focus on adverse effects in aquatic ecosystems will very likely provide some important co-benefits with regard to

decreased adverse acidification effects a nd decreased nutrient-enrichment effects in sensitive terrestrial and estuarine ecosystems as well as decreased air concentrations of methyl mercury.

42b) target values for ANC that protect agains t adversity to public welfare in light of the information presented in Chapter 5 concerni ng levels of ANC and the ecosystem effects associated with those target ANC levels?

Thus, my response to Charge Question 24b is:

I regard the three suggested target values outlined in Chapter 5 for use of ANC as the ecological indicat or of choice – 20 μ eq/L, 50 μ eq/L, and 100 μ eq/L – to be very reasonable alternative levels for th e Administrator of EPA to use in making her final decisions about the target valu e of ANC that would be appropriate for various acid-sensitive regions of our country.

c) factors relevant in selecti ng target percentages of water bodi es to protect at alternative target ANC levels to protect against adverse effects to pub lic welfare, and weights to place on those factors?

Thus, my response to Charge Question 24c is

The addendum we received on Septembe r23 provided some clarification of “factors relevant in selecting target pe rcentages of water bodies to protect at

alternative ANC levels” and some inform ation about “weights that could be placed on these factors” but after careful and repeated rereading of this addendum and other parts of Chapter 5, I still am not able to figure out how to formulate an appropriate response to Charge Questi on 24c, other than the obvious idea that protecting 90% of the water bodies would be more stringent than protecting 75% of the water bodies, and that protecting only 50% of the water bodies would be even less stringent.

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking into account (i) consideration of target levels of ANC (chapter 5),

C hapter 5 describes the range of ANC values that are necessary to both understand and then make decisions about protection of fres hwater lakes and str eams from acidification caused by atmospheric deposition of total reactive nitrogen and sulfur:

• Water bodies with ANC values near or above 100 μ eq/L have little or no risk of acidification,

• Water bodies with ANC values between 100 and 50 μ eq/L are at progressively increasing risk of acidification,

• Water bodies with ANC values between 50 and 20 μ eq/L are at even greater risk of acidification, and

• Water bodies with ANC values of 20 μ eq/L or lower already are so acidic that most of them will not support viable populations of fish and many other aquatic biota.

43Thus my response to Charge Question 24d(i) is:

The NOx and SOx standards that will be necessary to protect water bodies in an acid-sensitive region of the US will be an inverse function of the ANC values already existing in the populat ion of water bodies that ar e to be protected – i.e., the lower the existing ANC values in the water bodies to be protected, the more stringent must be the NOx and SOx standards that must be met.

In addition, the final SOx standards that are established for each acid-sensitive region that is to be protected will need to be adjusted in part by determinations of the percentage of sensitive water bodies in the region that are to be protected and also by calculations or measurements of the nitrogen-assimilative capacity of the ecosystems that are to be protected.

(ii) target percentage of wate r bodies to protect (chapter 5),

My response to Charge Question 24d(ii) is essentially the same as my response to Charge Question 24b (above)

The addendum we received on Septembe r23 provided some clarification of “factors relevant in selecting target pe rcentages of water bodies to protect at

alternative ANC levels” and some inform ation about “weights that could be placed on these factors” but after careful and repeated rereading of this addendum and other parts of Chapter 5, I still not fi gure out how to formulate an appropriate response to Charge Question 24c, other th an the obvious idea that protecting 90%

of the water bodies would be more stri ngent than protecting 75% of the water bodies, and that protecting only 50% of the water bodi es would be even less stringent.

(iii) consideration of relevant uncertain ties in AAPI components (chapter 7).

Chapter 7 provides a very succinct and thorough introduction to many of the still existing

uncertainties that are inherent in the AAP I approach to setting welfare-based NAAQS standards for NOx and SOx. As Chapter 7 a nd both the earlier ISA and REA documents make clear, however, major advances have b een made in recent years in decreasing many of the scientific uncertainties that were considered in previous NAAQS reviews for NOx and SOx. Thus, a much more robust scie ntific foundation has been developed for establishing NOx and SOx NAAQS standards that will diminish the frequency and intensity of nitrogen and sulf ur induced adverse effects on the structure and function of ecosystems and on ecosystem services importa nt to public welfare in this country.

These important decreases in scientific unc ertainty have resulted from the following developments in recent years:

1) The decision to take a two-criteria polluta nt (nitrogen and sulfu r) integrated approach

rather than to continue to c onsider NOx and SOx separately,

442) Separating the developm ent of public-welfare-based NAAQS standards from the formerly always dominating public-hea lth-based NAAQS review processes,

3) Including in the AAPI approach to mana gement of acidifying nitrogen and sulfur deposition, both chemically oxidized and chemically reduced inorganic forms of nitrogen (and even recognizing that orga nic as well as inorganic form s of nitrogen also must be considered) in the current ecosystem-foc used secondary NAAQS review process,

4) Considering both acidification effects a nd nutrient-enrichmen t effects on whole ecosystems (including interactiv e effects among all types of pl ants, animals, insects, and microorganisms) rather than just direct eff ects on individual species of plants and/or animals,

5) Focusing on nitrogen and sulfur eff ects on naturally occurring and unmanaged terrestrial and aquatic ecosystems (that in clude natural grassla nds; open range lands; unmanaged coniferous, hardwood, and mixed-species forests; a nd riverine, estuarine, and coastal ecosystems -- rather than trying also to consider at the same time, air-borne nitrogen and sulfur effects on commercially important plant and animal agricultural production systems and intensivel y managed commercial forests,

6) Greatly improved mathematical models (e specially CMAQ) of spatial and temporal relationships among air emissions of polluta nts, meteorological transport phenomena, chemical and physical transformations of airborne nitrogen and sulfur compounds, and wet, dry, and occult (cloud and fog) deposition processes at both high and low elevations,

7) Greatly improved concepts and descriptions of the diversity array of eco-regions that exist across this great continent of ours,

8) Much improved understanding of linkage s among bed rock geology, soils, vegetative cover, temperature and moisture-supply gradie nts, episodic phenomena such as droughts, floods, snow melt processes, physical climat e process, and chemical-climate-induced changes in the physical climate,

9) Recognition that our presen t scientific understa nding of nitrogen- and sulfur-induced acidification and nutrient-enrichment proce sses in aquatic ecosystems is much more thoroughly developed than acidifi cation and nutrient-enrichmen t phenomena in terrestrial and estuarine ecosystems.

Thus, my response to Charge Question 24d(iii) is:

Yes, there are still some important uncertainties about how many different categories of sensitivity to aquatic ecosystems should be recognized, how adequately the estimates of chemically reduced forms of nitrogen from the CMAQ air quality model can be trusted, how large the co-benefits for terrestrial ecosystems will be from use of the present AAPI approach with its primary focus

45on protection of aquatic ecosystems, and in the several kinds of Willingness to Pay (WTP) and other kinds of benefit estim ates, but I am confident that these and other sources of uncertainty will continue to decrease during the next few years and that the present scientific foundati on is adequate to implement the AAPI approach as soon as final d ecisions about the indicator, le vel, statistical form, and averaging time of the proposed NAAQS standard can be resolved.

(iv) any other potentially rele vant factors, such as levels of co-protection against

terrestrial acidification and nut rient enrichment (chapter 6)?

Chapter 6 contains a very short but persuasive description of the likelihood of significant co-benefits in protection of terrestrial ecosystems from acidification and nutrient enrichment effects from implementation of an AAPI approach aimed primarily at protection for aquatic ecosystems.

Thus, my response to Charge Question 24d(iv) is:

Although it is difficult to deve lop quantitative estimates of the co-benefits that are likely to accrue in terrestrial ecosy stems from NAAQS standards designed specifically to diminish adverse effect s on aquatic ecosystems in acid-sensitive regions, I believe there is no uncertainty at all that such co-benefits will occur and will not be surprised if these co-benefits turn out to be significant in magnitude.

Chapter 4: Addressing the Adequa cy of the Current Standards

Charge Question 2. What are the Panel’s view s on staff’s approach to translating the

available evidence and risk information and other relevant information into the basis for reaching conclusions on the adequacy of the current standard s and on alternative

standards for consideration?

My response to Charge Question 2 is essent ially the same as my response to Question

24a:

“Chapter 4 makes very clear that the current NAAQS standards for oxides of nitrogen and sulfur are not adequate to protect sensitive aquatic and terrestrial ecosystems against acidification and nutrient enrichment induced by atmospheric deposition of total reactive ni trogen and sulfur compounds.

In this connection, please note es pecially Chapter 4 page 4-2:

“ ... the current standards ar e not directed toward depos itional effects, and none of the elements of the current NAAQS – indicator, form, averaging time, and level – are suited for addressing the effect s of [total reactive] N and S deposition. Thus, by using atmospheric NO2 and SO2 concentrations as indicators, the current standards address only a fraction of total atmospheric NOX and SOX, and

do not take into account the effects fro m deposition of total atmospheric NOX and

46SOX. By addressing short-term concentr ations, the current SO2 standard, while protective against direct fo liar effects from gaseous SOX, does not take into account the findings of effects in the IS A, which notes the relationship between annual deposition of S and acidification effect s which are likely to be more severe and widespread than phytotoxic effect s under current ambient conditions, and include effects from long term de position as well as short term.”

a) In light of the Panel’s views on the appr opriate definitions of adversity to public welfare (see Chapter 3), do you agree that th e current levels of NOy and SOx deposition are adverse to public welfare?

Yes, I do agree that the current levels of NOy and SOx deposition are adverse to public welfare. Once again let me explai n my response by repeating parts of my response to Charge Question 24a:

Chapter 3 makes clear that although the Clean Air Act provides a very broad definition of different kinds of air-pollu tion-induced “effects” on public welfare, the Act in fact does not define “public we lfare” as such, and also does not define “adversity to public welfare.” Neverthele ss EPA has historically interpreted airpollution-induced “adversity” to include “disruptions in ecosystem structure and

function” that are re garded as important to the pe ople of this country. Thus EPA’s working definition of “advers ity” seems very sensible to me.

The ISA and REA for the current review of the NAAQS for oxides of nitrogen and sulfur (as summarized in Chapters 2 and 3) make very clear that current levels (ambient concentrations) of air-borne nitrogen and sulfur compounds (including not only NOy and SOx, as asked about in th is Charge Question (but also include ambient NHx and some as yet poorly char acterized organic forms of nitrogen (see Chapter 7 page 7-35) are now causing signi ficant “disruptions in the structure and function of aquatic ecosystems” in various acid-sensitive regions of the US.

In this regard, please note es pecially Chapter 2 page 2-3:

“The scientific evidence is sufficient to infer a causal relationship between acidifying deposition and effects on biogeochemistry and biota in aquatic

ecosystems (ISA 4.2.2). The strongest evidence comes from studies of surface water chemistry in which acidic deposition is observed to alter sulfate and nitrate concentrations in surface waters, th e sum of base cations, ANC, dissolved inorganic aluminum and pH. (ISA 3.2.3.2). Consistent and coherent documentation from multiple studies on various species from all major trophic levels of aquatic systems shows th at geochemical alteration caused by

acidification can result in the loss of acid sensitive biological species (ISA 3.2.3.3). For example, in the Adirondacks, of the 53 fish species recorded in Adirondack lakes about half (26 species) were absent from lakes with pH below 6.0 (Baker et al., 1990b). Biological eff ects are linked to changes in water

47chemistry including decreases in ANC a nd pH and increases in inorganic Al

concentration.”

3. Has staff appropriately applied this approach in reviewing the adequacy of the current standards and potential alternative standards?

Yes, I believe that EPA staff has very appropriately noted that: 1) the very short-term pr esent secondary NOx and SOx standards (calculated as

the arithmetic mean of 1- hour concentrations of NO 2 and as the arithmetic mean

of 3-hour concentrations of SO 2 ) are wholly inadequate to protect aquatic or terrestrial ecosystems from the long-term cumulative acidifying loads of total reactive nitrogen and sulfur compounds; 2) the “indicators” used in the present NAAQS standards do not include all of the acidifying and nutrient-enriching forms tota l reactive nitrogen and sulfur that are now causing significant adve rse impacts on the structur e and function of aquatic and terrestrial ecosystems in various acid-sensitive regions of the US.

4. Has staff appropriately acknowledged the poten tial beneficial effects of nitrogen inputs into nutrient limited ecosystems, while maintaining the focus of the review on preventing adverse effects in nitrogen sensitive ecosystems?

Yes, in this connection please note the following discussion in Chapter 4 pages 4-

44 and 4-45: “In certain limited situations, additions of nitrogen can increase rates of growth,

and these increases can have short term benefits in certain managed ecosystems. As noted earlier, this review of th e standards is focused on unmanaged ecosystems. As a result, in assessing adequacy of the current standards, we are focusing on the adverse effects of nutrien t enrichment in unmanaged ecosystems. However, the following discussion provide s a brief assessment of effects in managed ecosystems.

Impacts of nutrient enrichment in managed ecosystems may be positive or negative depending on the levels of nutrients from othe r sources in those areas. Positive effects can occur when crops or commercial forests are not receiving enough nitrogen nutrients. Nutrients deposit ed on crops from atmospheric sources are often referred to as passive fertiliza tion. Nitrogen is a fundamental nutrient for primary production in both managed and unmanaged ecosystems. Most productive agricultural systems require external sources of nitrogen in order to satisfy nutrient requirements. Nitrogen uptake by crops varies, but typical requirements for wheat and corn are a pproximately 150 kg/ha-yr and 300 kg/hayr, respectively (NAPAP, 1990). These rates compare to es timated rates of passive nitrogen fertilization in the range of 0 to 5.5 kg/ha-yr (NAPAP, 1991).

48Chapter 6: Co-protection for Other Effects Using Standards to Protect Against Aquatic

Acidification

Charge Question 13. What are the Panel’s view s on the utility of the additional analyses of co-protection benefits to inform consider ation of alternative levels of the standard?

My view is that the additional analyses of co-protection benefits contained in Chapter 6 is a well-reasoned and valuab le addition to this Policy Assessment Document. I was especially well-pleas ed with the following summary paragraph in Chapter 6 page 6-2 and the additional de tailed information contained in Tables 6-1 and 6-2 on page 6-3:

“Results of the comparison between the aquatic critical acid load (ANC = 50

μ eq/L) and

the terrestrial critical aci d loads (Bc:Al 1.2 and 10.0) for the 32 watersheds are presented in Tables 6.1 and 6.2. In the 16 Adirondack watersheds, 13 of the 29 lakes had aquatic critical acid loads that were lower (more protective) than the

terrestrial critical acid loads when a Bc:Al ratio of 10.0 was used. Based on

terrestrial critical acid lo ads determined with a Bc:Al ratio of 1.2, 21 of the 29 lakes in the Adirondacks had aquatic critical acid loads lower than the terrestrial critical acid loads. More importantly, for the terrestrial critical acid loads determined with a Bc:Al ratio of 10.0, 13 of the 16 lakes in the Adirondacks classified as “highly” and “moderately ” sensitive to acidification had aquatic

critical acid loads lower than the terrestrial critical acid loads, and all 16 lakes in these two sensitivity classes had critical ac id loads lower than the terrestrial loads

determined with a Bc:Al of 1.2 The wa tersheds within the Shenandoah region showed similar results (Table 6.1).”

----------------- Let me turn now to a few general remarks de riving from my experien ce as the designated “liaison person” serving as a member of both this NOx/SOx Secondary NAAQS Review Panel and the Integrated Nitrogen Committ ee (INC) developed within EPA’s Science Advisory Board.

The first and perhaps most important linkage between the INC and the NOx/SOx Panel was the following “Resolution” devel oped by the INC and communicated to the NOx/SOx Panel on October 31, 2007:

Resolution: The current air pollution indi cator for oxides of n itrogen, NOx, is an inadequate measure of reactiv e nitrogen in the atmospheric environment. The SAB’s Integrated Nitrogen Committee recommends th at inorganic reduced nitrogen (ammonia plus ammonium) and total oxidized nitrogen, NOy, be monitored as indicators of total chemically reactive nitrogen.

49The NOx/SOx Panel has accepted this resolution and incorporated NOy as the recommended “indicator” of choice for implem entation of the proposed revision of the NOx and SOx Public Welfare based NAAQ S standards using the AAPI approach.

The second important linkage between the INC and the NOx/SOx Panel was a presentation in September 2008 by Chairm an Russell of the then emerging AAPI approach, with its incorporation of chemically reduced forms as well as chemically oxidized forms of reactive nitrogen as an “as gi ven” feature of regions of the US to which the AAPI approach could be applied. This novel approach was useful in developing an integrated way of recognizing that chemi cally reduced inorganic forms of nitrogen (gaseous NH 3 and ammonium ion (NHx + ) as well as chemically oxidized forms of reactive nitrogen and sulfur (NOy+SO 2 + SO 4 ) are all very important parts of the total acidifying deposition that leads to adverse ecosystem impacts in acid-sensitive regions of

the US.

This choice to include NHx “as given” in th e AAPI index for ecosystem effects of oxides of nitrogen and sulfur was is an artful means of avoiding the large administrative and probably nearly prohibitive political challenges of trying to designate ammonia and

ammonium ion as a seventh Criteria Pollutant and thus including three rather than two Criteria Pollutants in this initial step that EPA is now taking in exploring options for multi-pollutant approaches in air quality management in the US as recommended in the National Research Council’s 2004 report on “A ir Quality Management in the United

States.”

The third important linkage between the NOx /SOx Panel and the INC came about during EPA’s renegotiation of the original cour t-ordered deadline for completion of the NOx/SOx NAAQS review process. This cha nge in the court-ordered deadline provided approximately 18 moths of additional time that EPA Staff sorely needed to complete the additional analyses and assessments that we presently have available in this Second External Review Draft Policy Assessment.

The fourth and last importan t linkage between scientific findings and recommendations from the INC and the findings and recommenda tion of the NOx/SOx Panel has to do with the magnitude of air emissions from various US sources of the reactive nitrogen and

sulfur. As indicated in the attached Table 2 from the June 2010 draft report of the INC,

in 2002 the total air emission of reactive nitrogen from industrial and transportation sources totaled about 6.2 Tg of NOx-N compar ed to agricultural sources that totaled about 3.1 Tg/yr of NHx-N – roughly a two-fold difference in air emissions of total reactive nitrogen from these three major sources.

Table 1: Nr fluxes for the Un ited States, Tg N in 2002. a

Nr inputs to the Atmospheric environmental system Tg N/yr %

N 2 O-N emissions 1 0.8 8 Agriculture - liv estock (manure) N 2 O-N 0.03

50Agriculture – soil management N 2 O-N 0.5

Agriculture - field burning agricultural residues 0.001

Fossil fuel combustion - transportation* 0.1

Miscellaneous 0.1

NH

x -N emissions 2 3.1 31

Agriculture: livestock NH 3 -N 1.6

Agriculture: fertilizer NH 3 -N 0.9

Agriculture: other NH 3 -N 0.1

Fossil fuel combustion – transportation * 0.2

Fossil fuel combustion - utility & industry * 0.03

Other combustion 0.2

Miscellaneous 0.1

NO

x -N emissions 2 6.2 61

Biogenic from soils 0.3

Fossil fuel combustion – transportation * 3.5

Fossil fuel combustion - utility & industry * 1.9

Other combustion 0.4

Miscellaneous 0.2

Total Atmospheric inputs 10.0 100

Nr inputs to the Terrestrial environmental system

Atmospheric N deposition b 6.9 19

Organic N 3 2.1

Inorganic NO y -N 4 2.7

Inorganic-NH

x -N 4 2.1

*N fixation in cultivated croplands 5 7.7 21

Soybeans* 3.3

Alfalfa* 2.1

Other leguminous hay * 1.8

Pasture* 0.5

5152 Dry beans, peas, lentils * 0.1

N fixation in non-cultivated vegetation * 6 6.4 15

N import in commodities * 7 0.2 0.3

Synthetic N * 8 15.1 41

Fertilizer use on farms & non-farms 10.9

Non-fertilizer uses 4.2

Manure N production 9 6.0 16

Human waste N 10 1.3 3

Total Terrestrial inputs 43.5 100

Nr inputs to the Aquatic environmental system

Surface water N flux 11 4.8

Also attached please find the following C oncluding Statement from the June 2010 draft report from the INC:

Concluding Statement

Fossil fuel combustion and food production have significantly increased the introduction of Nr (reactive nitrogen) into the US envir onment and, while there have been tremendous benefits, there are also treme ndous damages to the health of both ecosystems and people. Optimizing the benefits of Nr while minimizing its problems will require an integrated nitrogen management strategy that not only invo lves EPA, but also other federal agencies (e.g., USDA, DOE, NOAA), state agency manage rs, the private sector, and a strong public outreach [educationally focused] program.Comments from Dr. Charles Driscoll

Executive Summary

ES-3, paragraph 4 What is meant by balance of base cations? Change to “dissolved inorganic aluminum.”

ES-3, paragraph 5, line 2 Change to “depth of soil and surficial deposits”

ES-4, paragraph 2, line 4 ANC of 50 μeq/L

ES-4, paragraph 4, line 3 Change to “may result in nutrient imbalance”

ES-4, paragraph 6 Change to “as trout are eliminated due to

acidification”

ES-7, paragraph 2 Why would wate rsheds with low base-cation weathering be eliminated from consideration?

These should be the most acid-sensitive watersheds.

ES-10-11, 1 st paragraph ES-11 I don’t believe th is statement on naturally acidic ecosystems is true. There are surface waters that are naturally acidic due to low rates of base cation supply and/or high inputs of naturally occurring organic acids. However, these systems can also be impacted by elevated inputs of acidic deposition. This is a widespread occurrence in the Adirondack region of New York. Thes e naturally acidic surface

waters will exhibit loss of ANC and elevated aluminum concentrations from acidic deposition.

ES-13, last bullet This statement is problematic. Brook trout is not a sensitive species. Maybe the sentence should be changed to state “...protec tion against declines in

fitness of less sensitive species (e.g., brook trout, zooplankton) ...”

Also, what is meant by “the overall health of aquatic communities may not be impacted.” If species are lost, isn’t this an impact on the health of aquatic communities? I thi nk this bullet needs to be re-phrased.

Chapter 1

53P 1-9, line 4-6 Is this sentence co rrect? Aren’t both direct and

indirect effects considered in this PA? Also, total deposition is not just particulate forms. This

sentence should be re-written.

Chapter 2

P 2-2, line 8 This sentence needs to be changed to something like

“in some instances unless strongly retained by soil or biota, leach out ...”

P 2-9 in PnET box Change last line to “The model can be set to operate on any time set, but is generally run on a monthlytime-step. It is applied at the stand to smallwatershed scale.”

P 2-21, line 1 It might be good to re ference Goodale et al. (2010)

here.

P 2-21, paragraph 2 The article by Th omas et al. (2010) on nitrogen deposition on northern tree species should be mentioned in this paragraph.

Chapter 3

P 3-6, line 13-15 This statement about alkalinity is incorrect. For all intents and purposes, alkalinity and ANC are the same. Often alkalinity in volves titration to a fixed pH endpoint (~4.2), while ANC generally involves

Gran Plot determination of the equivalence point.

The difference between the two is subtle at best. For this document, the two should be used interchangeably.

P 3-9, line 11 This sentence on the units conversion does not make sense. Sulfur and nitrogen have different molecular weights. Therefore one cannot have a single mass conversion for a nitrogen map (left) and a sulfur map (right).

P 3-15, Figures 3-5 and 3-6 Does the N deposition include NH 4 + , is the map total N deposition or NO 3 deposition? Please clarify.

Page 3-30, line 8 100 μeq/L

54Chapter 4

P 4-1, line 6 Change to “associated with elevated deposition of

NO

x ...”

P 4-1, line 22 Change to “nutrients and acid neutralizing capacity

...”

P 4-2, line 25 Change to “as the ability of the watershed to counteract acidic inputs is decreased as the supply of acid neutralizing capacity is used more rapidly than can be replaced through geological weathering.”

P 4-20, line 2 The text refers to sulfur fields but the figures referenced (Figure 4-5, 4-6) depict NO

x and NH

x . Is there a mistake here?

P 4-20, line 4 The text refers to concentration patterns, but Figure 4-4 shows deposition.

P 4-20, lines 24, 29 The text refe rs to correlation between NO

x and N deposition. Is this NO

x concentrations? If so, this

should be clarified.

P 4-49, line 27 Change to “and methyl mercury can be taken up...”

P 4-50, line 14-15 Methylation of mercury occurs in watersheds all over the U.S. (and the world) where conditions are appropriate. Please change this sentence, it is

incorrect.

P 4-50 Note there are other li nkages between acidification and fish mercury accumulation. Mercury is accumulated to a greater degree in aquatic biota as pH and ANC decreases. Dittman and Driscoll (2009) noted that as fish condition increased associated with decreases in acidic deposition, fish mercury concentrations decreased.

Chapter 5

P 5-8, line 21-22 Change to “some fraction of the acid neutralizing capacity...”

55P 5-13 (Figure 5-4b) I am not familiar with this paper, but the figure does not make sense, why would the ANC curve have different lines for a wet US average year? This figure should be explained or deleted.

P 5-15, line 6 Change to “t o neutralize the deposition.”

P 5-15, line 16 This definite of stea dy-state models is horrible. A steady state model is one w ith time invariant inputs, outputs and pools. This section should be rewritten.

P 5-17, entire page The authors are using the term equilibrium incorrectly. Equilibrium is a thermodynamic term. Throughout this page, the word equilibrium needs to be replaced with the word “steady-state” (lines 1, 4, 6, 8, 14, 29, 30).

P 5-17, line 16 There is a problem here with the term critical load.

Critical load is a stea dy-state phenomenon. For a

value of critical load that is not at steady-state, the term dynamic critical load or target load should be

used.

P 5-17, line 24 Change to “implying that watersheds with greater inherent supply of acid neutralizing capacity respond ...”

P 5-19, line 7 Change to “in-lake retention of SO 4 2- and N.

P 5-19 (around here) A critical issue n eeds to be addressed if steady-state models are going to be used. Steady-state models will give relative high values of the level of atmosphere deposition need ed to protect ecosystem (critical loads) because they assume steady-state conditions. At any reasonable time frame, thedynamic critical load will be much lower. If steadystate models are going to be used a “safety factor” should be applied to account for this discrepancy.

P 5-19, Figure 5-5 Does the trad e-off figure consider background deposition? In other words, is the zero deposition value really 0? There is background deposition of S and N that will not be changed by controls of

emissions.

56P 5-21, equation 3 This equation does not make sense and needs to be explained better. What is the difference between nitrogen uptake and nitr ogen immobilization?

P 5-23, lines 10, 16 Change to “as the acid neutralizing capacity of the

watersheds increase...”

P 5-26, 5-27, line 18-19, Figure 5-7 The text refers to a map of critical loads, but Figure 5-7 is a map of sites where critical loads have been

calculated.

P 5-27 This approach of eliminating low ANC sites seems

foolish. These are the most sensitive sites. Why would you throw them out? If you don’t want to include these sites, the percentage of the lakes targeted should be relaxed. This would be a more honest, transparent approach rather than throwing

out the most sensitive watersheds. Also I would recommend against throwing out the high DOC lakes. High DOC waters can be impacted by acidic deposition. A better appro ach would be to include

these waters and check the DOC concentrations of the waters that would not be protected. Undoubtedly these would include many high DOC

waters.

P 5-51, Figure 5-18 I would like some additional explanation of this figure. It appears that the NH

x deposition shifts the “dog-leg” to lower values of N deposition for graphs a and c, but not b. Why?

P 5-52, Figure 5-19 This figure is also difficult to follow. I think I have the sense of it, but a mo re detailed explanation would be helpful.

P 5-54, line 14 What is meant by pure nitrogen and sulfur? Do you mean total nitrogen and total sulfur? Please clarify.

P 5-54, line 26 Would better wordi ng be “N and S atoms of NO

x and SO

x removed from the atmosphere, which ...”

P 5-56, line 8 Would better wording be “species that affect the health of ecosystems would...”

P 5-56, line 25 Should you specify which lake in the Adirondacks?

57P 5-58, Figure 5-20 This figure sugge sts that T values are relatively

invariant for the eastern U.S. Is this correct? If so, this would be important information to clarify. It would also be helpful to e xplain why this is the case (also discussed in Chapter 7).

P 5-65, line 6 It is important to define what is meant by uptake and immobilization. It also would be helpful to indicate how uptake, denitrification and

immobilization are calculated.

P 5-66, line 23 Rather than n itrogen buffering capacity, do you mean nitrogen retention capacity?

P 5-66, line 24 Again this is confusing. Do you mean “when reduced nitrogen deposition exceeds the ability of the ecosystem to retain nitrogen?

P 5-66, 2 nd paragraph This paragraph is confusing and needs to be reworded. The term buffering capacity is not being used properly. There is confusion on distinguishing between nitrogen retention and loss of acid neutralizing capacity.

P 5-67, line 3 Clarify units 50 μeq/L.

P 5-70, paragraph ???? This paragraph is horrible. For example, line 7 indicates that below pH 4.5 ANC appears to be uncorrelated with pH. As at pH values below the equivalence point ANC = - [H + ] this shows what an incorrectstatement this is. This paragraph is filled with misstatements and needs to be completely re-written.

P 5-75, Table 5-10 Aren’t these species listed from most sensitive to

least sensitive? See table title.

P 5-81, line 13 How about “as ANC decreases, the probability of very low pH values occurring increases.”

P 5-82, line 24 Brook trout is a relativ ely insensitive fish species.

P 5-82, line 25 How about “When AN C values are <50 μeq/L, the probability of acidic episodes increases substantially.”

58P 5-82, line 30 How about “At these levels during acidic episodes brook trout populations...”

Chapter 5 General Comments (the devil is in the details)

• How will the probability of lakes to be protected be determined?

• How many sites per region/category will be evaluated?

• How will the time-dependence of recovery be addressed? Critical loads vs. target

loads (dynamic critical loads).

Chapter 6

P 6-1 This analysis is nice but I am skeptical. There are limited field observations on this. Many soil time

series studies over the past 15 years show ongoing depletion of soil exch angeable calcium and magnesium which many wate rs, particularly in the Northeast, are showing recovery of ANC. This pattern, if true, suggest s ongoing soil acidification

while surface waters ar e recovering from acidic deposition. This may also suggest that soil is more “sensitive” to inputs of acidic deposition than

surface waters.

P 6-4, line 17 50 μeq/L

P 6-6 How about a short blurb about co-benefits associated with decreases in fish mercury and wildlife mercury concentrations associated with

decreases in sulfate load ing and/or increases in surface water pH?

Chapter 7

P 7-13, 7.4.3.2 It would be helpful a nd important to discuss why T values are relatively homogenous.

P 7-17-7-20, Figures 7-1, 7-4 Indicate wh at the lines on the figures represent.

P 7-32, line 1 Change to “as the supply of acid neutralizing capacity of watersheds increases...”

References:

5960 Dittman, J.A., Driscoll, C.T., 2009. Factors influencing changes in mercury concentrations in yellow perch ( Perca flavescens ) in Adirondack lakes. Biogeochemistry 93 (3), 179-196.

Goodale, C.L., Thomas, R.Q., Dentener, F., Adams, M.B., Baron, J.S., Emmett, B.A., Evans, C.D., Fernandez, I.J., Gundersen, P., Hagedorn, F., Lovett, G.M., Kulmatiski, A., McNulty, S.G., Melvi n, A.M., Moldan, F., Ollinger, S.V., Schleppi, P., Weiss, M.S., In press. Nitrogen deposition and forest carbon sequestration: A quantitative synthesis from plot to global scales. Global Change Biology.

Thomas, R.Q., Canham, C.D., Weathers, K.C., Goodale, C.L., 2010. Increased tree carbon storage in response to nitrogen de position in the US. Nature Geosciences 3, 13-17.Comments from Dr. Christopher Frey

Chapter 7: General Comments

Chapter 7 should have an intr oduction regarding the spatial scope and temporal averaging that is the basis for each of the inputs or f actors discussed in the chapter. Without a context regarding spatial scope and temporal averaging, it is not possible to characterize either variability or uncertainty. It needs to be clear, for example, as to over what geographic domain and for what averag ing time quantities such as deposition

transformation ratios are to be estimated.

Charge Question 16: What are the Panel’s vi ews on the discussion of uncertainty in the critical loads models including MAGIC and SSWC?

The chapter discusses the MAGI C critical load simulations on pages 7-3 to 7-4, page 7-6, and in three paragraphs on pages 7-30 to 7- 31. The discussion is with respect to an uncertainty analysis conducted in the REA. Figures 7-14 and 7-15 illustrate that the

MAGIC model estimates for surface water ch emistry at two locations compared very well with observed values. The simulated values fall very close to the parity line, demonstrating that the model is both precise and accurate in estimating concentrations, ANC, and pH.

On lines 8-9 on page 7-31, the text is “T he estimated confidence bounds on predicted ANC suggest that the 95 percen t upper confidence bound is on average 10 percent higher in lakes, and 5 percent higher in streams.” It is not clear as to what is being compared – higher than what? Is the intended meaning that the 95 percent upper confidence bound is 10 percent higher than the mean value? Or 10 percent higher than the observed value?

For MAGIC, given that there are comparisons of model predictions to observed values that demonstrate the model performance, the discussion appears to be adequate.

T he discussion of uncertainty in the SSWC makes several points:

• The F-factor approach is widely used in Europe and Canada, but not in the U.S.

• Critical loads estimated by steady-state MAGIC and SSWC F-factor approaches

had similar trends and results c onverged for low critical loads

• In the REA, a Monte Carlo-based uncert ainty analysis was conducted by varying runoff rates, water chemistry variables, a nd acid deposition. The coefficients of variations were 5 to 9 percent for critical load limits of 20 to 50 ueq/L.

The statement that the uncertainties introduced by the SSWC F-Factor model are likely to be moderate seems to be supported by the discussion in the text.

Charge Question 17: What are the Panel’s views on the areas for future research and data collection outlined in this chapter, on relative priorities for research in these areas, and on any other areas that oug ht to be identified?

61The chapter does not clearly outline areas for fu ture research or data collection, nor does it offer priorities for research.

Perhaps this charge question refers to th e section on modeling and data gaps. For consistency with the PA’s for other criteria po llutants, consistent header titles should be used. If the purpose of this section is to identify areas for future research and data collection, there should be an introduc tory paragraph that states this.

F rom the current draft, one infers that th e key needs for better models and data are:

• Occult deposition from cloud and fog pro cesses, especially in high elevation

watersheds

• Lightning generated NOx, to be incorporated into CMAQ in 2012

• The role of organic bound nitrogen in we t deposition, and re-entrainment from the

surface

• Increased spatial coverage of ambient measurements, and specific measurement “needs” (better instruments? Could be mo re clear) related to NOy, speciated NOy, ammonia, and ammonium.

• Better emissions estimates for soil and agricultural emissions of [NOy? Or just ammonia and NOx?].

• More data for sensitive ecosystem ar eas, to have more even coverage geographically.

T here is no discussion, based on Table 7-1, of the key sources of uncertainty other than gaps that should be areas for future resear ch or data collection. Examples include:

• Pre-industrial base cation concentration is listed as having a high magniture of uncertainty and a high knowledge base uncer tainty. Should this be a priority for

future research or data collection?

• Dry deposition (generically – N and S species) is listed as having a medium magnitude of uncertainty and a medium-high knowledge base uncertainty.

• Ecological indicator to changes in the value of ecosystem services is listed as having “medium-high” magnitude of uncertain ty, and a “negative” bias. Is there a

need for better information here?

Not mentioned is what research is needed in order to improve the knowledge base for ecosystem effects other than aquatic acidification, such as terrestrial acidification and aquatic system nutrient enrichment.

In the recent CASAC PM Panel review of the PM policy assessment second draft, a fairly

substantial list of research needs was iden tified with a recommendation that EPA hold a follow-up workshop to further refine the resear ch agenda and consider how to implement research in order to improve the state of knowledge before the next review cycle.

Charge Question 21. What are the Panel’s views on the overall characterization of uncertainty as it relates to the determinati on of an ecologically-relevant multi-pollutant

standard for NOx and SOx?

62This charge question is rather broad and it is not clear as to the specific focus. Chapter 7 appears to do a thorough job of listing many sources of uncertainty and providing qualitative characterization of each.

Charge Question 22. What are the Panel’s views on the following:

a. The insights that can be gained into pot ential alternativ e additional secondary standards (using the AAPI form) by considering:

i. Information from studies on the relationship between mortality in aquatic organisms and pH and ANC?

ii. Information from studies on the rela tionship between fish health and/or biodiversity metrics and pH and ANC?

iii. Information on the relationship between pH, Al, and ANC?

iv. Information on target ANC levels identifi ed by states and regions, as well as other

nations?

Chapter 9 could more clearly, and very briefly, summarize what are the key hazards associated with aquatic acidification, and list or briefly describe the key adverse effects, while stating conclusions regard ing the relationship between mortality in aquatic organisms, pH, and ANC. The chapte r presumes that the reader is already familiar with the endpoint effects, and tends to focus only on the indicator.

Likewise, Chapter 9 could more clearly summarize the relationship between fish health and biodiversity metrics with resp ect to pH and ANC. This should be done qualitatively, for a lay reader , leaving the technical details to the earlier chapters.

Although Chapter 9 implies that the use of the indicator for acidic deposition to aquatic systems may afford some protect ion with respect to acidic deposition to terrestrial systems, there could be a para graph that more clearly but succinctly addresses the significance of, and linkages between, pH, Al, and ANC.

There is no discussion in chapter 9 that I could find regarding comparison of target ANC levels among states, regions, or nations . Perhaps a paragraph could be provided that summarizes this, leaving the details to previous chapters.

b. The appropriate role of qualitative and quantit ative characterizations of uncertainty in developing standards using the AAPI form?

EPA has appropriately taken a weight of ev idence approach to h azard identification. EPA has done a reasaonable job in identifyi ng and characterizing individual sources

63of uncertainty, as summarized in Tabl e 7-1. Other committee members may have specific comments on those sources of uncertain ty, or others that might be included. The discussion of model and data gaps in Chapter 7 was useful, but needs to be expanded (see earlier charge question).

A key conclusion from Chapter 7 may be worth repeating in Chapter 9 (page 7-37, lines 19-29):

“there is no apparent directional bias in the uncertainty rega rding the biological, chemical and physical processes incorporated in the AAPI. From the perspective of valuation of ecosystem services, the estimates generally are believed to be biased low, meaning the values of reaching a target level of protection are underestimated. However, quantification of these values is perhaps the most uncertain of all aspects considered. Consequently, the level of th e AAPI should be relatively high in a buffering context to account for the existence of uncertainties in several components. In addition to, but related to these uncertainties discussions , are considerations of time lag to reach a target level ANC due to ecosystem response dynamics, as well the uncertainties in the severity and prevalence of episodic events. Both of these considerations suggest support for an AAPI th at is somewhat higher than the target ANC supported by the specific evid ence and risk information.”

It is not clear, for example, that the conclusion that the AAP I should be somewhat higher than the target ANC (nor is this st atement itself particular ly clear, because it implies that AAPI and ANC are the same quan tity) has been taken into account in the discussion of Target ANC limits in Chapter 9.

c. The role of considerations regardin g the relationship of the standard to:

i. the time trajectory of response, e.g. when specific ANC levels are likely to be realized given a specif ic level of the AAPI?

ii. the likelihood of damages to aquatic ecosystems due to episodic acidification events given a specific target for chronic ANC?

iii. the levels of co-protection for terrestrial ecosystems against acidification effects and the for aquatic and terrestrial ecosys tems against effects of excess nutrient

enrichment?

These questions go beyond my expertise, bu t they imply a question regarding shortterm versus long term responses of ecosystems, and the dynamics of eco-system response, that do not appear to be discusse d in Chapter 9. For example, if a 3 to 5 year averaging time is used, should the level be set so as to also be protective against short term (e.g., seasonal, or shorter episode ) events? A related question is whether the modeling tools, such as steady-state MAGIC simulations, adequately account for

the adverse effects associate with dynamic responses. As another reviewer suggests

64(Dr. Driscoll), perhaps a safe ty factor is needed to acc ount for differences in dynamic versus steady-state response.

There is discussion of the implications of the aquatic system acidification-based standard with regard to its effect on terre strial acidification and nutrient enrichment, which seems adequate but domain experts may have more comment on this issue than

do I.

General comments on Chapter 9

The summary of suggested options given in table form is very useful and should be incorporated into chapter 9.

The choice of averaging times and whether on ly such averages or used, or whether shorter term episodes will be considered, needs to inform the variability and uncertainty analyses of Chapter 7. This is because the ra nge of variability and uncertainty depend on averaging time. Similarly, the geographic scop e needs to be taken into account in the analysis of variability and uncertainty. The spatial options for components of the AAPI equation need to be further discussed or refer the reader to specific text earlier in the

document.

This standard may be challenging to co mmunicate to the public and the regulated community. Finding a way to state the basi c ideas in qua litative language that a lay reader can understand would be very helpful.

Although Chapter 9 alludes to attr ibutes of a standard, it seem s to require referring back to previous chapters in order to have a comp lete picture. In communicating this to the Administrator and other stakeholders, the EP A staff have a significant challenge of how to present the indicator, averag ing time, form, and level in a manner that is relatively easy to explain and complete without overwhe lming the audience with details.

• For example, the summary table is helpful in defining the “indicator” but seems incomplete. Isn’t AAPI actually being used as an indicator? Not just NOy and

SOx?

• The rationale for the 3 year, 5, year, and other averaging times should be explained.

• The form of the standard seems to be e xpressed in a complex manner. The cogent information is that NOy and SOx are rela ted through AAPI. This could be stated more succinctly in the summary table. Explanations of other points can be in

footnotes or the text.

• While the AAPI equation is important, perh aps it can be a fo otnote if it is not actually considered to be an indicator.

• The spatial options should be illustrated graphically in Chapter 9. This chapter should be thought of as the synthesis mate rial that any reader will go to for the bottom line of this policy assessment. T hus, it should be complete in terms of information needed to completely define a standard.

6566 • If the spatial categories are only regard ing non-air quality inputs to the AAPI equation, then perhaps this material is not critical to Chapter 9 as long as it is clearly laid out earlier in the policy assessment. Or, it can be in a different table. On the other hand, there is a need fo r clarity on the geographic scale and averaging time for each of the AAPI inputs. Possibly this material needs to be moved to Chapter 7.

• To be consistent with how NAAQS are structured, the summary table should

include a section on “Level.”Comments from Dr. Paul Hanson

General Comments: I approve of the suggested approach ta ken by EPA staff to retain the existing standards for phytotoxic direct effects of NO

x and SO

x , and the development of an additional standard based on the deposition of combined forms of N and S. The focus on aquatic acidification effects for that additional standard is appropriate to the available data. My expertise lies in the area of terrestrial ecosystems and I will not comment on the specifics of the proposed aquatic- acidification-base d standard. In most instances, the document does an appropriate job of clarifying that

demonstrated effects associated with acidifi cation and nutrient enri chment from N and S deposition are limited to ‘sensitive’ ecosyste ms. Nevertheless, in a number of places the document slips back into language that c ould be interpreted as inferring that all ecosystems will benefit from such a new standa rd. Such language should be corrected to

ensure that the reader unders tands that protection afforded by the proposed new standards would be limited to sensitive ecosystems located in specific regions of the United States. The executive summary and conclusion (Chapt er 9) fail to provide a clear picture about the extent of total US lands subject to the benefits of the proposed standard.

Comments on selected Charge Questions:

What are the Panel’s views on the definitions of adversity that are appropriate to consider in determining what constitutes adversity to public welfare relative to the NOx and SOx secondary standards? Without a defined understanding of how ecosystem changes in species composition would proceed through natural su ccession processes in the absence of anthropogenic N and S inputs, it is difficult to understand when changes in species or biodiversity should be considered adverse. The text tends to suggest that any change from the status quo should be considered advers e. I am not in agreement with such a conclusion. Unfortunately, I am also not providing a definition of the boundary of acceptable vs. unacceptable rates of change. The doc ument should deal with this issue. If species changes in lichens or grassland composition are to be proposed as metrics of adverse effects, an attempt needs to be made to characterize levels of change to be expected in non-polluted ecosystems.

Comments on specific sections of the document:

Ex ecutive Summary:

1. Line numbers should be added to this section to facilitate comments.

2. On Page ES-3 Paragraph 3 the word “often ” might be removed. It is insufficiently quantitative to be informative. Its inclus ion also tends to lead the reader to conclude that deposition of NO X and SO

x routinely leads to leaching from watersheds, which then result in the acidific ation of aquatic systems. This may be the case in some, but not all watersheds throughout the US where deposition of N and S forms are largely retained.

6768 3. Page ES-4 paragraph 3: The claim at the end of this paragraph should be

referenced to the ISA or REA.

4. Page ES-5 fourth paragraph: I don’t agree with the first sentence of this paragraph, but rather think most N-limite d ecosystems would have the capacity to absorb or buffer incoming N and S forms to limit or avoid perturbation. The examples of species change driven by deposition are provided (I guess) as definitive examples of an adverse result w ithout adequate justification of the rates of species change that could or s hould be considered adverse.

5. ES-7 last paragraph: Deposition velocity is not the rate of pollutant deposition. Deposition velocity times the concentration gradient is the rate of deposition.Comments from Dr. Rudolph Husar

Chapter 5: Conceptual Design of the Standard

5.3.1 Conceptual Design of the form.

I like the revised Figure 5.2. Stil l, instead of bidirectional arrows, two rows of arrows, one heading left the other to the right would more clea rly communicate the intent.

9. What are the Panel’s views on the re vised characterization of the deposition transference ratios (TNOyand TSOx)?

In principle, I do agree w ith the approach to derive the ambient concentration – deposition relationship for individual S a nd N species using CMAQ. The aggregation approach also makes sense.

A repeat of my past comment on nomenclatu re: The Deposition/Con centration IS an effective total wet+dry deposition velocit y. So why the addition of the confusing ‘Transference” term? The concepts and form ulae are already messy enough, so why not keep it simple: Effective Total Deposition Velocity. On p 7-3 its ‘transformation ratio’ . On p 7-12 its “Ambient Concentration to Deposition Transformation Ratio”....etc.

Figure 5.23 is the same as Fig 5.4

10. What are the Panel’s views on staff’s conc lusion that an averag ing time of 3 to 5 years is appropriate given th e AAPI form of the standard?

Agree that 3-5 years is adequate for the char acterization of inter-annu al variability of key

measures and indicators.

However, I am not clear as to why and how the episodic events and damage (and the springtime ‘acid shock’) are dismissed as is done in Section 5.2. Wh ere is the evidence that an annual average standard will be more protective than a companion short-term

standard?

Chapter 7 Uncertainty

14. What are the Panel’s views on the following?

a. The degree to which the chapter appropria tely characterizes th e potential role of information on uncertainty, sensitivity, and variability in informing the standards?

This version of the Policy Assessment cam e a long-long way in characterizing the uncertainty, sensitivity and vari ability. My main concern remains to be known systematic errors in CMAQ simulations and their inadequate inclusion in the uncertainty analysis.

6970 b. The appropriateness and completeness of the evaluation of CMAQ model performance and sensitivity to critical inputs?

The overestimation of the SO2 is a significant er ror that is not being ‘corrected for’. Is that correct? High SO2 will probably result in high (unverifiable) dry deposition. So, focusing and showing the propagation of this known error would make the uncertainty analysis more convincing. For instance a figure like Fig 7-5 for CMAQ-CASTNET comparison for SO2 could be very revealing.

c. The utility of the analyses of temporal and spatial variability in the deposition transference ratios (TNOyand TSOx)?

The spatio-temporal variability of the Effec tive Total Deposition Velocity makes sense, since it indeed varies considerably in sp ace and time. However, the CMAQ calculations of the Dep/Conc ratio for S and N compounds in Fig 5-20 do not appear to have the right spatial texture. Near sources where dry de position of gases dominate, Dep/Conc( dep velocity) should be significantly higher th an in the far field where wet deposition

dominates. I don’t see that texture. Inverting T in th e plots FIG. 5.2 makes the interpretation even more difficult.

15. What are the Panel’s views on the insigh ts provided by the AAPI sensitivity analysis including: a. The evaluation of elastic ities of response? b. The multivariable ANOVA analysis?

The value of the sensitivity/elasticity anal ysis heavily depends on what magnitude of perturbations one assumes. Are the assu mptions reasonable?? I don’t know. The CMAQ SO2 concentration bias is a big, known systema tic error. Is it properly incorporated in the uncertainty.Comments from Dr. Dale Johnson

Charge Question 2: What are the Panel’s view s on staff’s approach to translating the

available evidence and risk information and other relevant information into the basis for reaching conclusions on the adequacy of the current standard s and on alternative

standards for consideration?

Response: The Second Review Draft focuses al most entirely on aquatic effects with the

rationale that such effects ar e better known and better documente d than terrestrial effects. This is certainly true. But this raises a que stion in my mind: is it the purpose of this document to provide evidence to support changing standards, more or less in a lawyerly

fashion? Should this be th e purpose? Or should the purpose of the document be to examine all the potential pluses, minuses, a nd potential unintended consequences of changing standards? In short, is this a mission? If so, is the review panel expected to sign on to the mission? These questi ons came to mind as I considered my response to Charge Question 4: many of the points th at I have raised in the past as potential benefits of increased N deposition to forest ecosystems and C sequestration are now moot with the change in focus toward aquatic effects. I re iterate that I am in no way against changing standards to protect aquatic ec osystems, I am only trying to s ee that the approach to it

includes a balanced assessment of the effects of such changes. If EPA does not do it, I am quite sure that someone else will.

Charge Question 2a) In light of the Panel’ s views on the appropriate definitions of adversity to public welfare (see Chapter 3), do you agree that the current levels of NOy and SOx deposition are advers e to public welfare?

Response: This almost becomes a philosophical issu e. It is hard to conceive of an effect of some perturbation that does not have some ad verse as well as some beneficial effect to public welfare, with the proba ble exception of Hg deposition. The example that comes to mind is agricultural fertilization, which is a dverse to public welfar e when it is done in excess and leads to groundwater nitrate pollution, yet on the other hand, it is certainly adverse to public welfare to preclude fertiliz ation with the resultant substantial decline in crop and food production! There is little doubt that current le vels of NOy (combined with NH4) and SOx deposition are having adverse effects on some sensitive ecosystems; how many of such ecosystems can be protected at what cost, and what are the magnitudes and importance of unintended consequences (such as forest ecosystem C balance or crop S fertilization) that might result from such protection, and how does this compare to the benefits of protecting these sensitive ecosystems? The question becomes one of assessing the balance between these two effects, and, while recognizing the considerable uncertainties in some unintended consequences , I do feel that furt her discussions along

such lines will add considerable credibility to this document.

71Charge Question 4: Has staff appropriately acknowledged the potential beneficial effects of nitrogen inputs into nutrient limited ecosy stems, while maintain ing the focus of the review on preventing adverse effects in nitrogen sensitive ecosystems?

Response: The staff acknowledged at various places in the doc ument that some benefits of N deposition might occur in very limited ci rcumstances in commercial forests. They do not mention the C balance issue, whic h could occur in any forest, although the inclusion of Climate in Table 3-1 implies this, and is certainly of more practical relevance

than” Climate Control” or “R egulating Climate” as is now shown in the table. While dismissing the potentially positive effects of N fertilization in non-commercial forests, the staff does, however, spend a considerab le amount of time considering exactly the same phenomenon in non-commercial forests of the southwestern US where increased growth probably provides unwanted fuel fo r the next wildfire. I find this to be unbalanced. In general, however, any benef its of N (or S) deposition to terrestrial ecosystems is far less relevant in this document than in previous ones in that the staff has limited their scope largely to aquatic eff ects, none of which (to my knowledge) are beneficial. The wording in the Executive Summ ary regarding the ISA is correct (p. 1-9, lines 7-9) in that “The ISA highlights the ecological effect s ..... to sensitive ecosystems other than commercially managed forest s and agricultural lands...” Thus, the consideration of any potential benefits to ecosystems whic h by definition are “sensitive” (implying sensitive to negative effects) becomes moot, irrelevant, and dismissable. However, I would note that the first part of the quote from the Clean Air Act in page 2-1, lines 7-9, does not necessarily dismiss any bene fits, but simply addre sses effects. It does indeed mention damage to property, etc in th e middle part of the quote, but the beginning and end do not specify that only negative e ffects be considered (although this may well have been what was intended). In a nutshell, if the scope of this effort is now limited to aquatic effects, then the issu e of potential benefits becomes nearly irrelevant. It is not irrelevant, however, in the larger scheme of things where C balance effects of N deposition are now being hotly debated in the li terature and sure to come up at some later time if new standards are proposed.

Charge Question 11: What are the Panel’s views on the preliminar y staff conclusions regarding alternative target ANC levels that are appropriate for consideration and the rationale upon which those conclusions are based?

The ANC levels at which negative effects on aquatic systems occur appear to be well established and I see no problem with consider ing alternate target ANC levels in this context. The premise of the section on altern ate levels of ANC does not directly assess whether a given AAPI standard will or will not achieve a certain target ANC because of uncertainties, but presumes that the target ANC levels are reached and discusses them in that context (p. 5-69, lines 9-16) . I confess to some degree of confusion as to the logic in some of this section, for example, the disc ussion of alternative ta rget ANC’s and timing on p. 5-85, lines 2-8. Clarification of this logic would help this reader. I would also point out that the capacity (change in soil) and inte nsity (change in soil so lution) considerations raised before should enter into this discussion, as changes in the intensity factor could be very rapid in response to changes in deposit ion whereas changes in the capacity factor

72could be as slow as envisioned here, if indeed they occur at all (for example, it seems very unlikely that soil exchangeable acidity wi ll decline and base saturation will increase in response to a decrease in acid deposition inputs – soils in humid environments would not likely become more basic wi th time, but only continue to acidify at a slower rate). I

also confess to some confusion as to the deri vation of the DL factors discussed on page 5- 88 and 5-89 – if they were expl icitly defined by other than th e general terms used here, I missed it, and these terms are not in the lis t of abbreviations and acronyms up front.

Charge Question 11 a) In light of the Pa nel’s views on appropriate definitions of adversity to public welfare (see Chapte r 3), what are the Panel’s views on the appropriateness of the information related to adversity considered by staff in evaluating alternative target ANC levels?

Here I have nothing further to add in addition to what was stated above.

Charge Question 12: What are the Panel’s vi ews on the approaches considered by staff for assessing alternative target percentages of water bodies for prot ection at alternative

ANC levels?

Again, it is not clear how this was done – th e DL factors, which clearly are numerical indices of some kind, are not defined in pages 5-88 and 5-89, and thus I am unable adequately address this ques tion. If they were defined (p referably in the form of equations) elsewhere, that s hould at least be clearly refe renced here, and preferably formally defined again. It is unclear to me how the DL %eco terms in Tables 5-12 and 5-13 were derived, and yet it seems to be a critical element of the assessment. This needs to be more clearly described.

Other Specific Comments

Table 1-1: It would probably be better to use SI units here, as nearly all journals demand these days.

p. 1-9, lines 7-8: I do not unde rstand why ag systems and commercial forest systems

should be left out.

p. 2-1, line 24: need a space between “9” and “of”

p. 2-2, lines 13-28: Again, the in tensity effects need to be included here – that is, introduction of strong acid anions such as su lfate and nitrate to an already acid soil (and

acid soils do occur in nature , without any air po llution effects), then acidification of waters can occur instantly without any change at all in base saturation.

p. 2-5: Some discussion of na tural acidification processes by natural carbonic and organic acids and by plant uptake should be discu ssed here. The uninitiated may erroneously conclude that acid soils only occur in the presence of air pollution.

73p. 2-19, lines 20-21: This statement seems to fl y in the face of other statements later on which say that there it too much uncertainty in terrestrial effects and therefore the document will concentrate on aquatic effects.

pp. 2-21 through 2-23: As I have said in many previous reviews, I believe some mention

of the C balance issues as related to N deposition deserves a mention here.

p. 3-7: What about DOE? They have funde d a considerable amount of ecological research, including air pollution research.

p. 3-11: Table 3-1 is incomple te. Soils not only provide the service of nutrient cycling, they also provide filters for providing clean water (or, in some cases, provide pollution to clean water). And where are the timber values for forests in here? It is NOT implied only in crops, because there are still forest produc ts removed from Nationa l Forests these days, even though their primary purpose is no l onger for timbering. The vaguest of all is Climate and especially Climate Control? “Re gulating” climate? I di d not realize we had that technology yet. What should really be s hown here is C balance considerations, but I

am aware that the authors ar e very loathe to do this.

p. 3-25, lines 14-19: Again, poten tial beneficial effects, fo r example for C sequestration, are not necessarily limited to managed ecosystems.

p. 3-89 through 3-41: So while potential benefici al effects of N enrichment are summarily dismissed as irrelevant, three full pages are sp ent on the negative, fire related effects of N enrichment. Certainly the fire effects are very valid ones, that is not the point – it is a matter of selective emphas is on only the negative.

p. 4-2, line 25: Again, acidification of waters can take place in minutes as mobile strong

acid anions enter an acidic soil.

p. 4-39, lines 10-16: and D) C sequestration, which can benefit national C balance if permanent and be of benefit, or cause enhanced fire danger in drier systems and thus be extremely negative.

p. 4-45, lines 28-30: This is parsed out very sp ecifically, but is not completely true, as potential benefits can accrue even in unmanaged systems, as stated above.

p. 5-16, lines 4-5 and page 5-7, lines 1-6: Thes e sections clearly poi nt out the problems with steady-state models which assume that base cation flux is equa l to soil weathering rate. This simply cannot be true because if it were, soils w ould never acidify. Acid soils are found all over the world, including in pristine, unpolluted areas.

p. 5-23: CL is not in the list of acronyms

p. 7-7, lines 3-15: This section ha s me lost. I am unclear as to what is being said here.

7475 p. 7-32, lines 8-13: The real source of uncertainty here is in the assumptions and premises upon which these calculations are based. Th is source of uncertainty has not been quantified (and perhaps ca nnot be quantified).

p. A-5, lines 6-11: Nearly all of these assump tions is false. 1. Steady-state conditions never exist, as is well recognized by nearly all ecologists these days. 2. Nutrient cycling effects on soils are profound, often far more important than inputs by deposition and outputs by leaching. 3. N inputs by N-fixation are still greater on a global scale (last time I looked) than those of air pollution (although N fixation is more spotty). 4. I will not contest. 5. Some sesquioxide rich soils can absorb sulfate for a ve ry very long time.

p. A-5, equation 7: This equation and the pr emises upon which it is based clearly point out the problems with steady-state models whic h assume that base cation flux is equal to soil weathering rate. This simply cannot be true because if it were, soils would never acidify. Acid soils are found all over the world, including in pristine, unpolluted areas.

p. A-5, line 26: Where is equation 5?Comments from Dr. Naresh Kumar

Charge question 5: What are the Panel’s view s on staff’s revised conceptual framework for the structure of a multipollutant, ecologica lly relevant standard for NOx and SOx? To what extent does the Panel agree that this s uggested structure adequa tely represents the scientific linkages between ecological responses, water chemistry, atmospheric deposition, and ambient NOx and SOx?

From a theoretical standpoint the conceptual framework l ooks fine, but the practical usefulness of the framework depends on its robustness. One way to determine the robustness is by a comprehensive uncertainty analysis, as discussed in my response to Charge Question 14. Another way the AAPI can be tested is by use of historical data. Where data are available, one could use the AAPI (Equation 18 on Page 5-63) to get a trajectory of changes in AAPI in response to changes in SOx and NOy concentrations (I

don’t know whether concentrations of all form s of SOx and NOy woul d be available, but some assumptions may have to be made for non-measured components of NOy). The values of other components of AAPI (Q, Neco, [BC]o, LNHx, TNOy and TSOx) have already been estimated by EPA or can be dete rmined using models or measurements. It is critical to do this “hindcasting” at mo re than one location. The changes in AAPI predicted using Equation 18 should more or less match the changes in ANC (may be with some lag).

Ch arge Question 6: What are the Panel’s view s on the appropriateness of considering a single national population of waterbodies in establishing standards to protect against aquatic acidification? What are the Panel’ s views on consideration of alternative subdivisions of the U.S. to identify the spat ial boundaries of populations of waterbodies and acid-sensitivity categories, specifically: d) the use of Ecoregion III areas to aggregate watrebodies? e) the use of ANC to further aggregate Ecor egion III areas into different categories of sensitivity? f) The relative appropriateness of the sugge sted methods for categorizing spatial boundaries of sensitivity, e.g., one nation, bina ry sensitive/less-sensitive classes, cluster-analysis based on sensitivity classes, and individual ecoregions?

Using a single national population of water bodies in establishing standards to protect against aquatic acidificati on may seem attractive for its simplicity, but it has many shortcomings as noted in the PAD and by othe r members of the panel. Other approaches discussed by the staff are not too complicat ed either, especially given the overall complexity of the framework, so I see no reas on to settle for a single population of water bodies to represent the whol e nation. I would recommend using Option 2 (d) unless EPA finds it too complicated in which cas e 2 (b) or 2 (c) could be used.

Overall, the whole concept of how ecoregions will be used in esta blishing standards to protect against aquatic acidification was very confusing and EPA needs to do a better job of clarifying this concept.

76Charge Question 9: What are the Panel’s vi ews on the revised characterization of the deposition transference ratios (TNOy and T SOx)?

A major concern with TNOy and TSOx is that although they ar e the critical links between NOy and SOx ambient concentrations and their depositi on, they are derived using a model that can not be evaluated because of lack of measurements of dry deposition. EPA has shown that inter-annual vari ability of these ratios can be large even when using the same model. This is most likely due to variability in wet deposition because of changing rainfall patterns from y ear-to-year. May be EPA should evaluate the stability of the dry and wet deposition ratios se parately. It is also critical to show how these ratios vary when using different m odels and different chemical mechanisms.

I t is recommended that EPA evaluate the st ability of these ratios by examining these ratios for the following model simulations (i n addition to what ha s already been done):

• CMAQ and CAMx models (it is okay, in fact preferable, to use different emissions and meteorological conditions)

• Different chemical mechanisms

• Different model grid resolutions (36-km v/s 12-km or even 4-km, if available)

Charge Question 10: What are the Panel’s vi ews on staff’s conclusion that an averaging time of 3 to 5 years is appropriate given the AAPI form of the standard?

The Agency makes a good case for using the averaging time of three years and I agree

with that recommendation.

Charge Question 14: What are the Panel’s views on the following?

a. The degree to which the chapter appropria tely characterizes th e potential role of information on uncertainty, sensitivity, and variability in informing the standards?

The discussion of uncertainty and sensitivity an alysis is much improved compared to the first draft; however a complete quantitative analysis of uncertainty is needed for the AAPI. Staff has mentioned some good reas ons for conducting this analysis, which includes gaining confidence in the data and th e models used in defining the form of the standard. The reason it is part icularly important to conduct a comprehensive uncertainty and sensitivity analysis for the standard in review is that the many of the components of

the AAPI can not be evaluated because of lack of measurements. So, the only way to gain confidence in using AAPI is to examine how sensitive the SOX and NOY response surfaces are to different components of the AAPI. Although, EPA has evaluated uncertainty of some components – some quantitative, but mostly qualitative – the analysis falls short of what the CASAC panel had requested as part of the review of the

first draft of the PAD.

77T he panel had asked the EPA conduct a sensit ivity study to characterize uncertainty with different components of the conceptual framework and propagate the resulting uncertainty at every step to arrive at an ensemble of SOX and NOY response surfaces to meet a given level of the AAPI. The range of the SOX and NOY response surfaces would have given a confidence level in the use of the AAPI. By not conducting that level of analysis, EPA has failed to really show how robust an AAPI standard is. It is mentioned in the text that a Monte-Carlo analysis was not performed, but no reason is mentioned for that. I believe it is imperative that EPA conduc t a full quantitative anal ysis of uncertainty before moving forward on using the AAPI construct for setting a standard. One way to conduct the quantitative uncertainty analysis is to use the Mont e Carlo approach to arrive

at an ensemble of SO

x and NO y response surfaces to meet a given AAPI standard. As an example, the Monte Carlo analysis for Ad irondacks could be conducted by using the following approach:

• Use a probable range (or a mean value with some assumed or derived standard deviation) of estimates for Neco,

• Use a probable range (or a mean value with some assumed or derived standard deviation) of estimates for [B C ] 0 ,

• Use an estimate of Q based on diffe rent years (dry vs. wet year),

• Calculate L(NH

x ), T NOy and T SOx using different air quality model simulations that may already be available and us e the distributions in Monte Carlo simulations,

o Use CMAQ, CAMx, or other model simu lations for different years (with different meteorological c onditions and different em issions) to get a range of these variables,

o Use different chemical mechanisms, if available

• Use covariant constraints for quantities th at may be correlated when running the

Monte Carlo simulations

b. The appropriateness and completeness of the evaluation of CMAQ model performance and sensitivity to critical inputs?

The performance of the CMAQ model is sti ll incomplete after repeated requests by the CASAC panel. The performance statistics for the major species shown in Table 7- 1 can be misleading. One should use mean normalized bias (and not normalized mean bias) when conducting model performance us ing concentrations that are averaged over long periods (e.g. one week or more). A complete evaluation of CMAQ derived

values with measurements is needed befo re any confidence can be placed on the use of the model to generate the desired parameters. Although th e model cannot be evaluated for dry deposition because of l ack of measurements , evaluation of the ability of the model to repres ent ambient levels can serve as a proxy for its ability to represent dry deposition. It is recommended that following evaluations (using daily or weekly averaged quantities, not annual) be performed to assess the uncertainty in the

model:

784. Model performance for nitric oxide, nitrog en dioxide, sulfur dioxide, nitrate, ammonium and aerosol nitrate, ammonium, and sulfate for different networks for which the data are routinely available,

5. Model performance for wet deposition of sulfate, nitrate, and ammonium using the National Atmospheric Deposition Program (NADP) network,

6. A regional model evaluation using the con tinuous measurements of nitric oxide, nitrogen dioxide, nitric acid and NO Y from the SEARCH network in the

southeastern U.S.

c. The utility of the analyses of temporal and spatial variability in the deposition transference ratios (TNOyand TSOx)?

Showing year-to-year change using the sa me model is not sufficient. A complete analysis should also show how these ratios vary with use of different models and

different chemical mechanisms. EPA has the modeling data from the CAMx model used for the transport rule, so it should be able to compare these ratios easily from

model-to-model.

Charge Question 15: What are the Panel’s views on the insights provided by the AAPI sensitivity analysis including: a. The eval uation of elasticities of response? b. The multivariable ANOVA analysis?

Evaluation of elasticity of response is a good way to get a first hand picture of the sensitivity of the AAPI wrt to different co mponents of the AAPI. However, I would suggest doing this analysis for the SOX and NOX concentrations needed to meet a standard, as those are the quantities fo r which the standard is being set.

Charge Question 24. In light of the Panel’s views on what constitutes adverse effects to public welfare (see Chapter 3), what are the Panel’s views on:

b) target values for ANC that protect agains t adversity to public welfare in light of the information presented in Chapter 5 concerni ng levels of ANC and the ecosystem effects associated with those target ANC levels?

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking into account (i) consideration of target levels of ANC (chapter 5),

Given the lack of complete quantitativ e uncertainty analysis, I don’t think the administrator would have a high degree of c onfidence in whether a particular level of AAPI would indeed provide requisite level of protection or be overly protective for that matter. Qualitative way the uncertainty has b een discussed has the potential to give a

false sense of confidence about the overall uncertainty. On the bottom of Page 7-2 and top of Page 7-3, there is a discussion on what a low level of confidence in the components of the standard mean. It goes on to say that if the confidence is low then

79AAPI could be adjusted upwards or downwar ds depending on whether you want to put more emphasis on providing requisite level of protection or on not making the standard being overly protective. I woul d add one more thing there is that if the level of confidence is too low, then it makes the AAPI form of the standard questionable whether

it is a robust standard or not. The reason it is particularly important to conduct a comprehensive uncertainty and sensitivity analys is for the standard in review is that many of the components of the AAPI can not be ev aluated because of lack of measurements. So, the only way to gain confidence in us ing AAPI is to examine quantitatively how sensitive the SOX and NOY response surfaces are to different components of the AAPI. Given the lack of a quantitativ e sensitivity analysis we have no idea of the confidence interval and in my view it is premature to ta lk of the levels or ra nges of standards unless that shortcoming is overcome.

80Comments from Dr. Myron Mitchell

Three important areas that n eed to be addressed are:

1) Evaluation of AAPI using historical data will be very helpful in developing this combined NOy and SOx standard. There ar e a number of historical data sets including the Adirondacks, Catskills, H ubbard Brook, etc. that have long-term water chemistry data. There may be some difficulties in obtaining all of the needed AAPI inputs including atmospheric de position estimates, but at least some approximation will be very useful. This use of historical data will provide additional confidence in the AAPI approach.

2) The reliance on the CMAQ model with respect to providing estimates of deposition input is important to clearly link this effort by EPA with effects. The importance of the CMAQ output for devel oping this secondary standard clearly suggests that more effort is needed by EPA in the evaluation of the CMAQ output. This should evaluation should be a high priority for EPA in monitoring

and research efforts.

3) Treatment of sulfur in the AAPI. There is no consideration in the AAPI formulation of internal (so il) sulfur sinks (e.g., soil su lfate adsorption) or sulfur sources (organic S mineralization, S mineral weathering, sulfate desorption). It is assumed that watershed sulfur outputs equal sulfur inputs in deposition.

Mitchell 1 et al. (2010, Biogeochemistry) f ound that watersheds that had previously had substantial portions of atmospheric S input that from 1985 through

2002 that internal sour ces contribute 1–6 kg S ha -1 year -1 . This would equal 6 to 37 meq/m 2 /year. This contribution is subs tantial when compared to various analyses provided in the document (e .g., figures 5-15, 5-18, 5-19, etc.). Not including this internal sulfur source w ill result in an underestimate in the amount of reduction for nitrogen and sulfur depositi on needed to meet target loads. Other studies in North America and Europe ha ve also emphasized the importance of

internal sulfur sources.

My other comments are given below.

Executive Summary

1 Mitchell, M.J., G. Lovett, S. Bailey, F. Beall, D. Burns, D. Buso, T. A. Clair, F. Courchesne, L. Duchesne, C. Eimers, D.Jeffries, S. Kahl,, G. Likens, M.D. Moran, C. Rogers, D. Schwede, J. Shanley, K. Weathers and R. Vet. 2010. Comparisons of Watershed Sulfur Budgets in Southeast Canada and Northeast US: New Approaches and Implications. Biogeo chemistry (In Press and Available on Line).

81Page(s)

ES-8 The term Neco used in the figure has not been defined prior to its use.

ES-9 The sentence “Snowmelt can rele ase stored N deposited throughout the winter” is conceptually not correct. The vast majority of N released is nitrate that has been generated microbially within the soil, not atmospherically deposited N in the snowpack.

Chapter 1: Introduction [no questions]

Chapter 2: Known or Antic ipated Ecological Effects [no questions]

Chapter 3: Considerations of Adversity to Public Welfare

3-15 to16 It would be useful to indicate in figure legends 3-5 and 3-6 that it is assumed that all the N and S deposited are converted to nitrate and sulfate respectively for calculation eq/ha/yr.

3-28 Table 3-2 needs further clarification. It is not completely clear why the lake count is 0 for years 2005 for all ANC thresholds.

3-29 For Table 3-3 include within the table legend a replacement of “present”

with “Year 2007".

3-37 In Table 3-7, a delineation of the arro ws used in the value column needs to be provided.

1. What are the Panel’s views on the definitio ns of adversity that are appropriate to consider in determining what constitutes adve rsity to public welfare relative to the NOx and SOx secondary standards?

The Chapter does a good job of desc ribing the various attributes of diversity with particular emphasis on those areas expected to be most

sensitive to NOx and SOx effects in th e USA. The impact of the Chapter could be improved by a summary secti on that clearly indicates which of the adversity components will be the primary focus of the proposed

standards.

Chapter 4: Addressing the Adequa cy of the Current Standards

4-5 line 4 This sentence needs to be changed from “oxidized nitrogen” to

82“reactive nitrogen”–as it currently is written it excludes reduced forms of N including ammonium.

4-15 In describing the issues related to the differences be tween the rural (e.g., CASTNET) and urban deposition monitoring sites, it is clear that there is a

disconnect. Would it be a ppropriate to recommend that a unified network

is needed that includes both rural and urban sites?

4-17 to18 Certainly there is justification for using CMAQ as a predictor of deposition. It is somewhat curious , however, that NADP is used for wet deposition and CMAQ is for dry depos ition. Certainly, there are more problems associated with the estimat es of dry deposition than those for wet deposition. However, to gain more confidence in the CMAQ predictions it would be very important to compare the NADP (measurements) and CMAQ (predictions) for wet deposition. This type of comparison is needed to confirm that “CMAQ promotes analytical consistency and efficiency across analyses of multiple pollutants” and “CMAQ provides a consistent platform incorporating the atmospheric and deposition species of interest ov er the entire United States”.

4-18 The issues related to scaling up in time the CMAQ estimates of hourly

estimates needs to be discussed.

4-21 to 36 It would be very helpful to use the same color ranges for each gases pollutants for comparing estimates from CMAQ, CASTNET and SLAMS. Also, there is very limited discussi on on the differences in the results

associated with these different mon itoring networks. For example, there appear to be major differences in CMAQ (Figure 4-11) and CASTNET (Figure 4-13) sulfate concentrations w ith respect to the absolute values and spatial distribution.

2. What are the Panel’s views on staff’s approach to transl ating the available evidence

and risk information and other relevant information into the basis for reaching conclusions on the adequacy of the current standards and on alternative standards for

consideration?

The general information is certainly cont ained within this document and other supporting information such as within th e ISA and REA, but the actual linkages

of evidence and the translation to the generation of the standards could be improved.

a) In light of the Panel’s views on the appropriate definitions of adversity to public welfare (see Chapter 3), do you agree that the current levels of NOy and SOx deposition are adverse to public welfare?

83b) Yes, the evidence is sufficient that the current levels of NOy and SOx deposition are adverse to public welfare in some sy stems which are particular sensitive to

acidification and or N additi on causing nutrient enrichment.

3. Has staff appropriately applied this approach in reviewing the adequacy of the current standards and potential alternative standards?

Yes, the approach is valid, but more a ttention to the linkages between evidence and the generation of the standards would be helpful.

4. Has staff appropriately acknowledged the poten tial beneficial effects of nitrogen inputs into nutrient limited ecosystems, while maintaining the focus of the review on preventing adverse effects in nitrogen sensitive ecosystems?

The current balance is appropriate in the context of the standard and the protection of sensitive systems.

Chapter 5: Conceptual Design of an Ecologi cally Relevant Multi-pollutant Standard

5-5 lines 5-6 This statement is not co rrect. The vast majority (>95%) of the nitrate released during episodic snowmelt is derived from the forest

floor and mineral soil and not from th e snow. A possible rewording could

be as follows: Snowmelt results in th e mobilization to drainage waters of nitrate most of which has been gene rated within the forest floor and mineral soil. This release of this nitrate can result in episodic

acidification. Literature citations would include (Kendall, 1998, Tracing Nitrogen Sources and Cycling in Catchm ents, Book Chapter; Piatek et al., 2005, WASP; Campbell et al. 2006, J. Geophys. Res.).

5-5 lines 7-8 The statement that “inpu ts of nitrogen and sulfur from snowpack and atmospheric deposition” suggests that snowpack N and S is not derived from atmospheric depositi on. Change to “inputs of nitrogen and sulfur from atmospheric deposition”.

5-12 18 Lien et al. 1992 not in References.

5-28 lines 10-22 This section is difficu lt to follow. Inclusion of a figure illustrating the issue associated with the skewness of the distribution of critical loads would be helpful so thatthe reader does not need to go ahead

to section 5.3.2.7 to understand the issue.

5-33 Figure 5-9 is very difficult to r ead. The numerical designations of ecoregions especially in the dark blue areas are not readable.

845-45 Figure 5-13. In its present form it is difficult to distinguish differences

between the one nation versus binary categorization.

5-55 lines 26-29 The statement “Due to lack of direct measurements, no performance evaluations of CMAQ’s dry deposition calculation can be found; however, the current state of MCIP is the pr oduct of research that has been based on peer-reviewed lite rature from the past two decades (EPA, 1999) and is considered to be EPA’s best estimate of dry deposition values” is rather weak and suggests that effort is needed to further evaluate CMAQ using available information. This issue comes up a number of times in the document (e.g., page 5-64, lines 23-25).

5-56 lines 22-28 The time unit for these depositions and ratios needs to be provided. Is this a yearly interval?

5-57 In showing these coefficient of variation values in Figure 5.22, it is

difficult to see the actual values a nd respective ranges in the Adirondack and Shenandoah case study areas. Inst ead of stating that “values are relatively small”, it would be better to provide the means and standard

error of the means of these ratios.

5-58 In Figure 5-20, for sulfur deposition/concentration, how is marine sulfur

accounted for? For sulfur it seems somewhat curious that there is a change in the isopleths a substantial distance into the Atlantic Ocean. I would expect the difference if it in cludes marine components would be more related to the coastal outline. For this figure, the deposition component needs a time unit as previously stated.

5-61 to 70 I am concerned with the treatmen t of sulfur in the AAPI. There is no

consideration in the formulation of sulfur sinks (e.g., soil sulfate adsorption) or sulfur sources (o rganic S mineralization, S mineral weathering, sulfate desorption). Mi tchell et al. (2010, Biogeochemistry) found that watersheds that had previously had substantial portions of atmospheric S input that from 1985 through 2002 that internal sources contribute 1–6 kg S ha -1 year -1 . This would equal 6 to 37 meq/m 2 /year.

This contribution is substantial wh en compared to various analyses provided in the document (e.g., figures 5-15, 5-18, 5-19, etc.)

5-84 lines 12-23 In considering issues re lated to recovery there is a need to not only consider the issues related to weathering of base cations, but also to internal generation of the mob ile nitrate and sulfate anions. Particularly for sulfate this sulfate will likely result in substantial delays in recovery in those systems with net lo sses of soil sulfur and low levels of base cation weathering.

855. What are the Panel’s views on staff’s revised conceptual fr amework for the structure of a multipollutant, ecologically relevant standa rd for NOx and SOx? To what extent does the Panel agree that th is suggested structure adequately represents the sc ientific linkages between ecological re sponses, water chemistry, atmospheric deposition, and ambient

NOx and SOx?

The conceptual framework for a multipolluta nt, ecologically rele vant standard for

NOx and SOx is sound with considerable s upport from the scientific literature on how the generation of strong mobile acids result in the acidification of soils and water. Some of information, however, is not correct or incomplete. Note for example the discussion of nitrate sources during snow melt as discussed above for page 5-5, lines 5-6. Also the assumptions associated with atmospheric sulfur input being equal to drainage water losse s are also not correct (see page 5-61 to 70).

6. What are the Panel’s views on the appropr iateness of considering a single national population of waterbodies in establishing standards to protect against aquatic

acidification?

Although having a single nationa l population of waterbodies makes is more facile to explain the standard, the problems a ssociated with under protecting sensitive systems and overprotecting insensitive sy stems necessitates having a system with more spatial resolution.

What are the Panel’s views on consideration of alternative subdivisi ons of the U.S. to identify the spatial boundaries of populat ions of waterbodies and acid-sensitivity categories, specifically:

a) the use of Ecoregion III ar eas to aggregate waterbodies ?

This seems to be a reasonable approach that takes advantage of the extensive information on various ecosystem compone nts including both abiotic and biotic

components.

b) the use of ANC to further aggregate Ecor egion III areas into different categories of sensitivity?

The use of ANC is consistent with the overall emphasis on the standard to protect

sensitive surface waters from further aci dification and have deposition that will

allow those water bodies that have been deleterious impacted by acidic deposition to recover as indicated by increasing ANC values.

c) the relative appropriateness of the sugge sted methods for categorizing spatial boundaries of sensitivity, e.g. on nation, bina ry sensitive/less-sensitive classes, cluster analysis based sensitivity classes, and individual ecoregions?

86The analysis is interesting showing the different distributions of sensitivity and that categorization that captures substant ial variation should be used. This will be a compromise between one nation versus using individual ecoregions.

7. What are the Panel’s views on the appropriateness of the critical loads that form the basis for the population assessment to determined deposition metrics?

The use of critical loads has been found to be a useful approach for looking at spatial and temporal aspects of acidificati on. This concept was originally applied to Europe and more recently has been extended to other regions including North

America.

a) What are the views of the Panel on the appropriateness of gene ralizing the f-factor approach to apply to lakes and streams in the Western U.S. and other portions of the

Eastern U.S.

The application of the f-fact or is a useful approach fo r evaluating the potential for mineral weathering to contribute to the generation of base cations and enhance

acid neutralization.

b) What are the views of the Panel on the filtering criteria used to remove lakes and streams that are naturally acidic or not sensitive to atmospheric deposition?

Yes, it is reasonable to exclude lakes in two of these classes: 1) CL < 10 meq/m 2 /yr and for which pre-industrial ANC values could not be calculated; and 2) waters affected by acid mine drainage (>400 eq/L SO 4 2- twice or more than expected by atmospheric deposition. La kes with low ANC values (e.g. < 50 eq/L) and waters with >10 mg C/L DOC those dominated by organic acids

should be included in the an alyses and possibly flagge d with respect to these

characteristics. Alternat ively, the PA should show the consequences related to excluding or including these with respect to the development of the AAPI and

critical loads.

8. What are the Panel’s views on the suggest ed methods for determining appropriate values of reduced nitrogen deposition in establishing NOx/SOx tradeoff curves?

The presentation of the NOx/SOx tradeoff cu rves is difficult to follow since the linkages between the various components in the various figures and tables are not always consistent (e.g. Table 5-7 versus Figure 5-12). Also it would be most helpful to keep the axes lengths the same in plots within the same figures for comparisons (e.g. Figure 5-15). I am so mewhat concerned with respect to the sulfate portion of the curve on how systems are handled in which sulfate losses in drainage waters is not in balance with sulfur deposition. We know that for a

number of sites in the United States that there can either be net retention or net

loss of sulfur. These imbalances can be substantial especially under conditions of decreasing atmospheric sulfur deposition.

879. What are the Panel’s views on the re vised characterization of the deposition transference ratios (TNOy and TSOx)?

Implicit in the use of such an aggregated deposition ratio is that the relative portion of the chemical species in depositi on remain constant both with space and time. This analysis was done for only from 2002 – 2005 and hence may have covered a range of meteorol ogical conditions, but little difference in nitrogen and

sulfur sources. I don’t believe that there is strong evidence sugge sting that this is the case. At a minimum some error analys es associated with this assumption is needed. This analysis should be expa nded beyond the results of CMAQ and to include other estimates of the proportion of gaseous species and their respective deposition velocities. It is recognized th at this other analysis will include fewer chemical species than that provided in CMAQ.

10. What are the Panel’s views on staff’s conc lusion that an averag ing time of 3 to 5 years is appropriate given the AAPI form of the standard?

There should be consideration of not only looking at the averages, but also the minima and maxima for the period of examin ation. Care will need to be taken on issues related to the water regimes and other climatic factors among these years. Droughts or other extreme events such as freezing rain can have a substantial impact on N and S drainage losses and resultant effects on ANC.

11. What are the Panel’s views on the preliminary staff conclusions regarding alternative target ANC levels that are appropriate fo r consideration and the rationale upon which

those conclusions are based?

The use of alternative ANC levels is appropriate and based upon sound science that has shown different levels of sensitivity of various biotic taxa with respect to sensitivity to low ANC.

a) In light of the Panel’s views on the appr opriate definitions of adversity to public welfare (see Chapter 3), what are the Pa nel’s views on the appropriateness of the information related to adversity considered by staff in evaluating alternative target ANC

levels?

The information provided is adequate fo r showing at least some of the major

concerns that are documented with respect to public welfare.

12. What are the Panel’s views on the appro aches considered by staff for assessing alternative target percentage s of water bodies for protecti on at alternative ANC levels?

This approach is useful in providing a ra nge of water bodies to be covered with respect to these alternative ANC levels. This also provides flexibility with

88respect to the administrator regarding choi ces for protection, overall protection of public welfare and costs for implementation of the standard.

Chapter 6: Co-protection for Other Effects Using Standards to Protect Against Aquatic

Acidification

13. What are the Panel’s views on the utility of the additional analyses of co-protection

benefits to inform consideration of alternative levels of the standard?

This discussion is helpful in showing the linkage of protection between terrestrial and aquatic components of watersheds and emphasizes as indicated elsewhere in the document that in general the projection of sensitive aquatic resources results in terrestrial protection with the aqua tic resources being more sensitive to deposition. One issue, however, that need s some consideration is that the time frames for the recovery are substantially different from aquatic and terrestrial components with a greater time lag e xpected for terrestrial systems.

Chapter 7: Evaluation of Uncertainty and Vari ability in the Context of an AAPI standard, including Model Evaluation, Sens itivity Analyses, and Assess ment of Information Gaps

14. What are the Panel’s views on the following:

a. The degree to which the chapter appropria tely characterizes th e potential role of information on uncertainty, sensitivity, and variability in informing the standards?

7-4 lines 13-15 The document stat es that “Confidence regarding the fundamental science supporting causal determination about the effects of acid deposition, and the translation of those efforts into ecosystem services and values is less amenable to quantifi cation”. Even though it is difficult, providing even some approximate evalua tions would be helpful. Some of this uncertainty may be substantial and having uncertainly analysis focus on those components for which the calcu lations are more facile may result in a misunderstanding of the impact of the proposed standard on human

welfare.

7-6 lines 14-17 In addition to the uncerta inties associated with the estimate of catchment supply of base cations via weathering the exclusion of sulfate dynamics (or possibly consider ing a range of internal S supply) will have a major impact on uncertainty especially associated with future

recovery.

7-8 lines 13-23 Some further elaborat ion of the Banzhaf survey would be helpful.

b. The appropriateness and completeness of the evaluation of CMAQ model performance and sensitivity to critical inputs?

897-10 to 24 The inclusion of comparis ons of CMAQ and CASTNET results (i.e., Figures 7-1 to 7-7) is very helpful. The discussion related to the limitations of CMAQ (page 7-10, lines 15-26) are insightful and should be useful in providing future modifications of CMAQ.

7-12 line 1 Is it appropriate to util ize a manuscript in preparation (e.g., Dennis and Foley, 2010) for this document?

7-3 lines 12-27 It is indicated that “sensitivity of CMAQ derived deposition transformation ratios to changes in em issions and treatment of chemistry” is not yet completed. This should be a high priority for EPA.

7-12 lines 1-7 Do these results sugge st that CMAQ needs to be changed such that precipitation estimates are derived from actual measurements

versus modeled estimates. Isn’t th is approach more similar to that employed by the Canadian AURAMS model?

c. The utility of the analyses of temporal and spatial variability in the deposition transference ratios (TNOy and TSOx)?

7-13 The terms “stiff” and “stiffness” are introduced. Is the use of these terms

identical to “invariate”? In indicating that the absolute values remain “stable”, it is difficult to ascertain how these relative large ranges of ratios will affect the overall results in using mean Ts and Tn values.

7-14 This comparison to emission change over time is for only two years (2005 and (2030) and is highly dependent on assumptions of changes in emission

sources. What were th e underlying assumptions of these changes? Do the range in values in Figure 7-12 show the differences based upon these assumptions?

7-16 lines 14-26 With the continual evolution of CMAQ and likely changes in the predictions of AAPI, will there be problems in the standard itself being affected by changes in CMAQ?

7-27 to 28 For Figures 7-11 and 7-12, the fi gure legend needs to in clude a description of the statistical values (mean, ranges, confidence intervals, ??) associated

with these box-and- whisker plots.

15. What are the Panel’s views on the insigh ts provided by the AAPI sensitivity analysis including: a. The evaluation of elasticities of response?

b. The multivariable ANOVA analysis?

7-30 It is challenging to use the resu lts provided in Appendix A and see how

90the various analyses are used in th is evaluation. A summarization is needed on the relative sensitivities of the various parameters that make up the AAPI. An important result is provided by the statement that emphasizes the need to focus on the uncertainties of the non-atmospheric inputs, including base cation weatheri ng and runoff rates. As indicated previously some inclusion of internal generation of sulfate is also needed. An important outcome of this analysis should to show the parameters of

the AAPI have the most and least confidence. Such information should be used in driving research and monitoring efforts by EPA.

16. What are the Panel’s views on the discussi on of uncertainty in the critical loads models including MAGIC and SSWC?

These descriptions of uncertainty for the model calculations for MAGIC and SSWC are adequate. A more quantitative term than “moderate’ should be used in describing the un certainty in SSWC (Page 7-32, line 15). The development of the inform ation in Table 7-2 is helpful in summarizing the uncertainty associated with the AAPI.

7-33 to 34 For Figures 7-14 and 7-15 within the figure legend it needs to be indicated

that these MAGIC model simulations.

17. What are the Panel’s view s on the areas for future re search and data collection outlined in this chapter, on relative priorities for research in these areas, and on any other areas that ought to be identified?

The AAPI needs to include some estimates of the role of internal sulfur sources in contributing to sulfate in drainage waters . The absence of including this factor will result in an underestimate of the deposition required to achieve a desired

level of ANC.

Chapter 8: Monitoring

8-1 to 18 The most critical aspect of monitoring is that there needs to be a more explicit linkage between the monitori ng networks and the evaluation and further refinement of the CMAQ mode l. This interplay between the monitoring and modeling efforts will help ensure that both the monitoring and modeling are most relevant to the environmental issues being

addressed.

18. What are the Panel’s views on using an ope n inlet to capture al l particulate size fractions for the purpose of analyzing for sulfate?

This should be the focus of a resear ch question versus an overall modeling

component.

91What is your opinion on using existing CASTNET filter packs as a future Federal

reference method for sulfate?

This has considerable advantages with re spect to spatial and temporal patterns

since the CASTNET network has been in place for a number of years and includes a generally good represen tation of sites across the US.

19. What are the Panel’s views on requiring measurements of ammonia and ammonium to assist implementati on of the standard?

There is a clear need to expand monitori ng to include measurements of ambient

ammonium and ammonium concentrations. This reduced form of nitrogen is a major component of nitrogen deposition fo r many sites including those within areas with intensive agricultural activities.

20. What are the Panel’s views on having a subs et (e.g., 3-5 sites) of monitoring stations

in different airsheds that measure for the major NOy species; nitric acid, true NO2, NO, PAN and p-NO3?

This could be an important research question.

Chapter 9: Conclusions

21. What are the Panel’s views on the overall characterization of uncertainty as it relates to the determination of an ecologically-rel evant multi-pollutant standard for NOx and

SOx?

The current document does a commendable job in showing were some of the major uncertainly lies with respect to the development of a multi-pollutant standard. Areas that should be targeted for improvement include a more complete evaluation of the CMAQ predictions and the consideration of additional processes, especially internal sulfur sources in the AAPI.

22. What are the Panel’s views on the following:

a. The insights that can be gained into potential alternative additional secondary standards (using the AAPI form) by considering: I. Information from studies on the relationship between mortality in aquatic organisms and pH and ANC?

ii. Information from studies on the rela tionship between fish health and/or biodiversity metrics and pH and ANC? iii. Information on the relationship between pH, Al, and ANC? iv. Information on target ANC levels id entified by states and regions, as

well as other nations?

Each of these sources of informati on both separately and taken together

92provide a compelling case on the re lationships between ANC and other water quality metrics that are associated with biotic health of waters. The findings from these different studies all provide a rather unified picture suggesting appropriate ANC values to be the target for the standard.

b. The appropriate role of qualitative and quantitative characterizations of uncertainty in developing st andards using the AAPI form?

As mentioned previously th e uncertainty of the AAPI needs to include not only statistical analyses associated with speci fic model parameters, but also include an evaluation of possible omissions in th e AAPI (e.g. reduced nitrogen inputs,

contribution of sulfate sources and sinks in soil, etc).

c. The role of considerations regardin g the relationship of the standard to:

i. the time trajectory of response, e .g. when specific ANC levels are likely to be realized given a specific level of the AAPI?

ii. the likelihood of da mages to aquatic ecosy stems due to episodic acidification events given a specific target for chronic ANC? iii. the levels of co-protection for terrestrial ecosystems against acidification effects and the for aquatic and terrestrial ecosystems against

effects of excess nutrient enrichment?

There may be some problems associat ed with the time trajectory of the response due to the understanding a nd ability to model the relative contribution of net N uptake and net S loss from the terrestrial portion of the system. Any factor (e.g. changes in climate, CO 2 concentration in the atmosphere) could have important eff ects on the time trajectory. Also, the effect of factors may be substant ially different between aquatic and terrestrial ecosystems. For example, although for aquatic systems the sum of base cations may be adequate, for te rrestrial systems the availability of specific base cation, calcium, may be a critical factor in affecting tree health. Important tree species such as sugar maple have a high demand

for calcium.

23. What are the Panel’s views on Staff’s conclusion that the existing secondary

standards for NOx and SOx should be retain ed to provide protect ion against direct adverse effects to vegetation due to gas phase exposures?

There is no reason not to retain these ex isting standards since these concentration levels will likely be substantially greater than those associated with join NOx and SOx standards. More importantly the scientific justification is still valid for protecting against deleteri ous impacts to vegetation.

24. In light of the Panel’s views on what consti tutes adverse effects to public welfare (see Chapter 3), what are the Panel’s views on:

9394 a) the degree to which current levels of NOy and SOx deposition are adverse to public welfare based on evidence and ri sk information, and information on adversity provided in Chapters 2,3, and 4?

b) target values for ANC that protect agai nst adversity to public welfare in light of the information presented in Chapter 5 concerning levels of ANC and the ecosystem effects associated w ith those target ANC levels?

c) factors relevant in sele cting target percentages of waterbodies to protect at alternative target ANC levels to protect against adverse effects to public welfare, and weights to place on those factors?

The information provided substantiates th at the current levels of NOy and SOx deposition are producing adverse effects to the public welfar e. The target values selected for ANC are congruent with curre nt scientific unders tanding with respect to which ANC values and any resultant change are most sensitive to biotic components. Selecting a target subs et of waterbodies to be protected by alternative target ANC valu es is a useful approach.

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking into account • consideration of target levels of ANC (chapter 5), • target percentage of water bodies to protect (chapter 5),

• consideration of relevant uncertainti es in AAPI components (chapter 7), and • any other potentially relevant factors, such as levels of co-protection against

terrestrial acidification and nut rient enrichment (chapter 6)?

It may be important to consider alternat e standards especially for protecting those systems where nutrient enrichment (e.g. we stern U.S.) is a substantial effect associated with N deposition.95 Comments from Mr. Richard Poirot

5. What are the Panel’s views on staff’s revised conceptual fr amework for the structure of a multipollutant, ecologically releva nt standard for NOx and SOx?

The revised conceptual framework for the st ructure of the multi-pollutant secondary standard has been substantially improved fr om the first draft policy assessment. The inherently complex framework is more clea rly presented and more carefully justified, with revisions that are directly responsive to previous review comments.

To what extent does the Panel agree that this suggested structure ad equately represents the scientific linkages between ecological responses, water chemistry, atmospheric deposition, and ambient NOx and SOx?

The proposed structure adequately reflects the cu rrent state of scientif ic understanding of the complex linkages between ambient con centrations of SOx and NOx, wet and dry deposition of these and other acidifying pollu tants (i.e. NHx), environmental processing of these deposited S and N compounds, result ant changes in surface water chemistry, and subsequent ecological effects.

6. What are the Panel’s views on the appropr iateness of considering a single national population of waterbodies in establishing standards to protect against aquatic

acidification?

Use of a single national population of water bodies as the basis for selecting (a percent of water bodies to be protected from reaching or maintaining a specific minimal ANC component of) a national standard has th e “advantage” of “simplicity”. But a large

fraction of national surface waters are loca ted in areas where underlying soils, bedrock

and other local environmental factors effec tively preclude adverse acidification effects from past, current, and expected future depos ition rates of S and N, while other water bodies are extremely sensitive to effects from relatively low rates of S and N deposition. Use of a single national population and asso ciated percentage level of protection unnecessarily disregards the large regional variations in inhere nt sensitivity to acidification, and is likely to lead to under-protection in so me areas and over-protection in others (or both).

Since there are various methods and data availa ble to allow refined estimates of inherent sensitivity to be calculated on a regional ba sis, and since many other location-specific

environmental variables are included in the calculation of compliance with the proposed standard, it makes sense (I think – but need more info) to consider protection in the more refined context of the populations of water bodies at risk from aci dification effects.

What are the Panel’s views on consideration of alternative subdivisi ons of the U.S. to identify the spatial boundaries of populat ions of waterbodies and acid-sensitivity categories, specifically:

a) the use of Ecoregion III areas to aggregate waterbodies ?96 Not my area of expertise, but this seems lik e a reasonable approach, and possibly one that could be considered for refining secondary NAAQS for these and ot her criteria pollutants in the future. Off hand, it seems like using 120+ different Ecoregi on III categories for aggregating water bodies is unnecessarily comp lex. However, it also appears that there are reasonably ways to simplify, group or sort these many categories into a much smaller number of Ecoregion subsets which are inhe rently sensitive (or most sensitive) to acidification, and which would make for a more efficient standard better focused on protecting those systems at greatest risk.

b) the use of ANC to further aggregate Ecoreg ion III areas into di fferent categories of sensitivity?

This seems like a logical (almost obvious) metric for sorting/grouping the Ecoregion categories. If only we could ju st use the readily measured di rect ANC indicator of effects as the NAAQS indicator...

c) the relative appropriatene ss of the suggested methods for categorizing spatial boundaries of sensitivity, e.g. on nation, binary sensitive/less-sensitive classes, cluster analysis based sensitivity cla sses, and indivi dual ecoregions?

I don’t have a strong opinion on the relati ve appropriateness of these alternative approaches. None of them seems inappropr iate. Off hand, I think I like the cluster analysis approach, for its inherent scientific merit, its direct focus on sensitivity, and the relative simplicity of a 5-class grouping scheme (especially for the initial roll-out of an extremely complex NAAQS).

However, I also don’t think that the advant ages/disadvantages/ consequences of the various options (2a, b, c, d) are presented here with sufficient clarity to allow an informed choice by the Administrator (o r by me anyway). Hopefully, these options can be presented, discussed and illustrated more clearly in the final PA document, and staff might propose and defend a preferred option. For example, the page 5-50 statement (and associated figures) that “In option I, the Adirondack air quality is slightly out of attainment for a 75%-tile deposition metric based on a CL at ANC=50. In option 2a, the Adirondack air quality is out of attainment for the curve for the sensitive areas, but in attainment for the less sensitive areas.” helps convince me that option 2a is preferable to option 1. But I don’t have a similar feel for the relative strengths or weaknesses of the other options.

8. What are the Panel’s views on the suggest ed methods for determining appropriate values of reduced nitrogen deposition in establishing NOx/SOx tradeoff curves?

Since reduced nitrogen in the air or in (dry) deposition is not curren tly measured, and not currently considered as a regulated component of the NAAQS, but does contribute to the acidifying (and N enrichment) e ffects of SOx and NOx depos ition, I think it’ s reasonable to estimate its location-specific deposition with CMAQ. At the same time, there is also a need to verify and refine the CMAQ estimates with direct measurements, especially for

NH 3

.97 I also strongly support the pr oposed approach to consider NHx as a temporally varying, location-specific component of the AAPI calculation. This is a scientifically preferable approach to the previous proposal which would have considered NHx deposition as a fixed constant. If NHx increases, larger re ductions in SOx and NOx would be required, and conversely, if NHx decreases, SOx and NOx reductions would be lower.

9. What are the Panel’s views on the re vised characterization of the deposition transference ratios (TNOy and TSOx)?

So far as I can tell, the (CMAQ) methods for calculating these de position transference ratios are the same as they were in the la st draft PA, but are de scribed, illustrated and evaluated more clearly in the current documen t. These transfer functions are logically conceived, but seem like such critical elem ents of the proposed standards, which are uncomfortably dependent entirely on CMAQ model performance. The illustrations (Figures 5-20 – 5-22) showing the spatial char acteristics are helpful, and the illustrations (Figures 7-11 and 7-12) showi ng that the transfer functions remain stable over time with large changes in emissions add some confid ence. Although since the model chemistry is fixed, S and N species totals are conser ved, and meteorology held constant, highly variable modeled results would not be exp ected. Some additional confidence might be provided by comparing CMAQ estimates of dr y and total deposition (wet is already shown) at selected CASTNET sites in recent years, and perhaps breaking out the Figure 7-3 performance for TNO 3 into separate figures for part iculate nitrate (which deposits inefficiently) and HNO 3

.

One additional analysis that might be inform ative would be to calculate and evaluate a

modified T NOY function (call it T NOY* ) that would be based on CMAQ modeled total N deposition as a joint function of CMAQ HNO 3 and pNO 3 (separate coefficients could be derived for each species). This empirically derived relationship would be no more of a “black box fudge factor” than the current T NOY calculation (ratio of CMAQ estimate of total N deposition to CMAQ estimate of NOy). Potential benefits of this approach are that it would be less dependent on CMAQ’s ability to accurately pred ict and apportion all the separate NOy components (with their widely different deposition velo cities); it can be applied (as can the sulfur T SOX function) to currently available and relatively low cost CASTNET measurement data; and the measured species would directly represent major components of dry N deposition, compared to NOy, which has no relationship (R = 0.067 in Figure 4-21) without be nefit of the black box CMAQ conversion. In evaluating

whether this alternat ive approach is “close enough” to the original TNOY, both calculations could be compared to both the CMAQ estimates and CASTNET (+ NADP) measurements of total N deposition.

12. What are the Panel’s views on the appro aches considered by staff for assessing alternative target percentage s of water bodies for protecti on at alternative ANC levels?

As indicated previously, I thi nk the alternative approaches se em reasonable, and that the objective should be to focus as tightly as possible on protecting water bodies that are inherently sensitive to ac idification, without adding t oo much complexity to the98 regulatory metric. It might al so be recognized in this case that a metric that provided some “over-protection” in areas less sensit ive to aquatic acidifi cation might provide added protection for terrestrial ecosystems or against nitrification and would unavoidably improve visibility and reduce mortalit y and morbidity associated with PM 2.5 concentrations. 13. What are the Panel’s views on the utility of the additional analyses of co-protection

benefits to inform consideration of alternative levels of the standard?

This seems like a reasonable concept to expl ore in more detail, al though I don’t really see any discussion of this in Chapter 6. It seems clear from the analysis that there are areas –

without surface waters or with relatively insensitive surface waters where adverse affects on terrestrial ecosystems are expected – and for which adding a “co-protection” element to the standard would provide added benefits. If other welfare eff ects of SOx and NOx – such as on materials damage and visibility ha d been considered in this review, the coprotection benefits would have been substantial.

14. What are the Panel’s views on the following: a. The degree to which the chapter appropria tely characterizes th e potential role of information on uncertainty, sensitivity, and variability in informing the standards?

The additional information and discussion unc ertainty, sensitivity, and variability in Chapter 7 is extremely helpful, and represents a major improvement to the previous draft

PA.

b. The appropriateness and completene ss of the evaluation of CMAQ model performance and sensitivity to critical inputs?

While various CMAQ model performance evalua tions have been presented elsewhere, the model performance evaluations and sens itivity analyses presented here are most helpful. Since pNO 3 and HNO 3 have such different de position velocities and are measured separately in CASTNET, it might be informative to show comparisons of the separate modeled species and CASTNET meas urements, and perhaps also for the CMAQ and CASTNET estimates of dry deposition of the separate pNO 3 and HNO 3 species, as well as for the CMAQ and CASTNET estimates of TNO3 dry deposition.

c. The utility of the analyses of temporal and spatial variability in the deposition transference ratios (TNOy and TSOx)?

I have a hard time understanding what the spat ial variability in these transfer ratios actually means, though it is comforting to see th at the patterns seem relatively “smooth” rather than abrupt. Is there is seasonal or diurnal variability in these ratios that might give us a better feeling for what’s rea lly going on inside the model (and in the atmosphere)? I wonder if it would be inform ative to see maps analogous to Figure 5-20 which separately showed the ratios of S conc to S wet dep and S dry dep, and of N conc to N wet dep and N dry dep. Maps showing the ratios of S and N deposition to S and N emissions (perhaps aggregated on a state by state basis) could al so be interesting...99 The illustrations of the relative absence of temp oral variability are comforting, as it is key to have stable regulatory metric which is linearly responsive to emissions changes over time. Some (any) discussion which helped expl ain the causes and implications (if any) of some of the spatial or temporal variations would be helpful.

17. What are the Panel’s view s on the areas for future re search and data collection outlined in this chapter, on relative priorities for research in these areas, and on any other areas that ought to be identified?

I thought this section of Chapter 7 was es pecially well done, and well supported by the preceding discussions. A chapter like this s hould become standard practice in future NAAQS reviews!

18. What are the Panel’s views on using an ope n inlet to capture al l particulate size fractions for the purpose of analyzing for sulf ate? What is your opinion on using existing CASTNET filter packs as a future Fe deral reference method for sulfate?

I don’t oppose these proposal s, although I think the cas e is somewhat overstated, especially in relation to aquatic acidification e ffects. A major concer n is that this would require exclusive use of CASTNET methods or network and preclude use of fine fraction

sulfate measurements which are more abundant , and not demonstrably grossly inferior. Conversely, there’s no reason not to include a similar open inle t approach for pNO 3 , for which coarse particle deposition may be especially important for N deposition

contributions to nutrient enrichment of coasta l estuaries. I also think an argument could

be made to consider CASTNET HNO 3 and pNO 3 as an (interim) alternative to continuous NOy measurements (more detail on this below and in #9 above).

S ome counterpoints to the ope n faced sulfate proposal:

• Away from coastal areas with coarse sea sa lt or arid or agri cultural areas with windblown dust, (and especially in the re mote humid, high elevation areas where acidification occurs) there is relatively little coarse sulfat e (or coarse nitrate) period.

• The particle cut size characteristics of the open faced collectors have not been well characterized, nor is any information provi ded on what (small) fraction of the open faced S or N sample is composed of more rapidly depositing coarse mode particles. You need to add a fudge factor, which you could do just as well using fine fraction

data.

• Open-faced collectors may take in fog or cloud water. In addition, since coarse particles tend to be alkaline, addi tional artifacts may occur as gaseous SO 2 or HNO 3 reacts with the alkaline coarse mate rial collected on the sample filter.

• Sulfate and nitrate in coarse mode particle s which are formed in the air (and are not sampling artifacts) typically result from reactions of acidi c S and N gases and alkaline crustal material or sea salt. Consequentl y, these particles carry their own cations and represent uniquely well buffered forms of S and N deposition.

• Lastly, the total fractions of S and N deposit ions from particulate matter – especially in the higher elevations where acidification is an issue – is not very large. Below are

the 2006-08 estimates of total S and N deposition for the Huntington Forest CASTNET site (relevant to deposition in the Adirond ack case study area). Totalparticulate sulfate and nitrate were estimat ed to account for 2.1% and 0.2% of the total S and N deposition respectively.

As indicated above, I’m not opposed to the proposal to specify an open faced FRM or even the CASTNET filter pack for pSO 4 , but think it could also be specified for pNO 3 (assuming problems with loss of volatile NO 3 during summer sampling can be corrected),

but also think accommodations could be made (FEM) to accommodate use of fine

fraction SO 4 and NO 3 data (with adjustments) to avoid be ing too prescriptive at this early stage of the NAAQS process, to mandate a compliance network (CASTNET) which is not operated by states but by EPA contractor s (funded by $ taken from state monitoring pots), or – in combination with the propos ed continuous NOy indicator – to require deployment of a costly new network which may not be currently feasible, or which might indefinitely delay implementation of the NAAQS.

19. What are the Panel’s views on requiring measurements of ammonia and ammonium to assist implementati on of the standard?

NH 3 and NH 4 measurements would be useful for implementing the sample both directly, to quantify an unregulated but varying elemen t of the compliance metric, and indirectly, to help evaluate and improve emissions inventories and CMAQ model performance.

NH 4 measurements are currently available from CASTNET and (urban) CSN networks, and could conceivably be added to IMPROVE. NH 3 measurements are currently very sparse but would be useful – and have adde d relevance to better understanding sources

and trends of PM 2.5 , regional haze, and sources and effects of N deposition on nutrient enrichment. However, I’m not sure curre nt methods have been sufficiently well developed and evaluated for use in routine network operations.

100101 20. What are the Panel’s views on having a subs et (e.g., 3-5 sites) of monitoring stations

in different airsheds that measure for the major NOy species; nitric acid, true NO2, NO, PAN and p-NO3?

Conceptually this is a good idea and can be (and needs to be) justif ied for reasons beyond just compliance with the proposed NAAQS (for acidification effects). Possibly some of

these measurements could be added to existi ng (or planned) rural NCore sites. NOy, NO and pNO 3 (fine fraction), SO 2 (continuous) and SO 4 (fine fraction) are currently

measured at these sites. Add a CASTNET sampler and you’ve got HNO 3 , Open faced (vs fine) SO 4 and NO 3 (so you will know the coarse fractions), and comparative SO 2 by filter pack and continuous analyzer. Adding true NO 2 would be an excell ent addition at some sites (I understand there’s a photol ytic unit currently applying for FEM status), and this would allow calculating NOy minus (NO, NO 2 , pNO 3 , HNO 3 )...

However, while I support the need for these kinds of more detailed measurements at a few sites in a “clustered network” approac h, I’m not sure they can be or should be justified just to determine compliance with this secondary NOx/SOx standard or for evaluation and improvement of model performance just for this standard alone. Along similar lines, I’m not sure a large new network of conti nuous NOy analyzers (at new, remote rural sites) can be justified (or can be afforded, or could be maintained by shrinking numbers of state personnel). I’m uncomfortable with the relatively vague picture of how these new measurements w ould be conducted. Will this be a stateoperated network (like NCore), an enha nced CASTNET network (operated by EPA contractors), an enhanced IMPROVE networ k – or some combination of the above?

I think a reasonably good argument could be made to specify CASTNET filter pack methods (possibly with some tweaks such as adding NH 3 passive sampler) as the basic monitoring approach, as it does capture the key species – albeit over longer averaging times but which are plenty short enough for the long-term 3-5 year standard. As indicated in the response to question 9 above, I think an alternative T NO3* N deposition transfer function could be developed that would calculate total (CMAQ modeled; or CASTNET + NADP measured) NOx de position as a function of HNO 3 and pNO 3 . If these calculations performed reasonably well, it would allow use of existing and relatively low cost data, use measurements wh ich actually relate to deposition (NOy does not, without a huge assist from the model), and minimize the reliance on complex internal CMAQ calculations. Using this approach, a slightly expanded CASTNET filter pack network might become the initial complian ce network, with new CASTNET samplers at

a limited number of rural NCore or IMPROVE si tes. Continuous NOy could be added to a few of these sites (NCore sites have continuous NOy and SO 2 , as well as fine particle

SO 4 and NO 3 ), but should not be required in a large new network. More exotic measurements such as true NO2, PAN, continuous nitric acid, etc should be considered at only a very few “Level 1” type sites.

23. What are the Panel’s views on Staff’s conclusion that the existing secondary

standards for NOx and SOx should be retain ed to provide protect ion against direct adverse effects to vegetation due to gas phase exposures?102 I agree that existing single-pollu tant secondary standards for NO 2 and SO 2 should be retained to protect against direct effects to vegetation due to gas phase exposures.

24. In light of the Panel’s views on what consti tutes adverse effects to public welfare (see Chapter 3), what are the Panel’s views on:

a) the degree to which current levels of NOy and SOx deposition are adverse to public

welfare based on evidence and risk informati on, and information on adversity provided in Chapters 2,3, and 4?

I believe the evidence and risk information pr ovided in previous chap ters indicates that environmental damage has occurred and contin ues to occur as a result of cumulative and continuing SOx and NOx deposition, and that these effects, including acidification of aquatic and terrestrial ecosystems and nutrien t enrichment, represent adverse effects on public welfare.

b) target values for ANC that protect agains t adversity to public welfare in light of the information presented in Chapter 5 concerni ng levels of ANC and the ecosystem effects associated with those target ANC levels?

ANC is an appropriate environmental indicat or of effects from acidification on aquatic ecosystems, and the target levels of ANC being considered - about 50 μeq/L - would represent an appropriate target level that – if attained – coul d be expected to substantially

reduce the adverse welfare effects due to a quatic acidification. A somewhat higher ANC target of say 75 or 100 μeq/ L would provide a greater de gree of protection for both aquatic and terrestrial ecosystems, although th e degree of protection is co-dependent on the target ANC and the target percentage of water bodies (in what sensitivity class or classes) for which the target ANC is to be attained.

c) factors relevant in selecti ng target percentages of waterbodi es to protect at alternative target ANC levels to protect against adverse effects to pub lic welfare, and weights to place on those factors?

Since there can be large vari ability in the inherent sens itivities of water bodies to acidification effects among di fferent regions and within individual regions, it seems logical to consider protecting a target percentage of lakes from the populations which are potentially susceptible to acidi fication. The proposed use of Ecoregion III classifications clustered into 5 groups on the basis of AN C seems like an appropriate accommodation of

scientific detail without a dding unnecessary complexity. As indicated previously, I had a hard time understanding the implications of the different proposed options for selecting target percentages of water bodies for protec tion. Comparison of the various metrics applied to case study regions where there ar e sensitive and insensitive lakes which are chemically well characterized would be a useful way to judge the appropriate

combinations.

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking into account103 • consideration of target le vels of ANC (chapter 5), • target percentage of water bodies to protect (chapter 5),

• consideration of relevant uncertainti es in AAPI components (chapter 7), and • any other potentially relevant factors, such as levels of co-protection against

terrestrial acidification and nut rient enrichment (chapter 6)?

As indicated above, I suggest considering a modification ( T NOY* ) to the N deposition

transfer function such that it would not require extens ive new measurements of continuous NOy. I’m not sure it would work well enough, but think it could be

considered.

Considering the relatively long time frames a ssociated with acidif ication and recovery, and also considering that there is no pre- specified time frame for attaining secondary standards, some consideration might be give n to standards which require reasonable rates of progress over time toward increasing ANC levels (APPI levels) in water bodies (watersheds) with low ANC levels.104 Comments from Dr. Armistead Russell

EPA staff is to be complemented for this work towards developing a Policy Assessment document (PAd or PA) that can be used to support the promulgation of an ecologicallyrelevant, combined NOx-SOx standard. The PA has evolved considerably since our last review, and the 2 nd draft shows that a significant amount of work and a dditional thought have gone in to its further development. This undertaking demonstrates just how complex it may be to develop multipollutant standards. They are also to be complemented for addressing CASAC’s prior comments. They have gotten very far addressing a very complex issue. However, the current document is noticeably not as informative as desired. It is difficult to ge t the “big picture” of the impacts of choosing different elements of the potenti al standard. There is little doubt in my mind that this is the most difficult PA (or equivalent document) that I have reviewed.

In the current document, having a clear and comprehensive description of the AAPI is key, as well as the associated components of the AAPI, how the AAPI would be applied, and the consequences of various decisions about the AAPI level, ecoregions and percent of lakes protected, and this makes Chapter 5 a key chapter. At pr esent, however, it does not provide the material needed for some one to read the document and get a clear understanding of all of the concepts, a nd the tremendous complexities, without a significant amount of work. In pa rt, more data (or distillation s of the data) are needed to give the reader an idea of just how big and varied are the va rious quantities that are being used (e.g., distributions of ke y variables used to compute the AAPI). Second, sample

calculations could be shown. A particular weakness is a demonstration of how the fraction of lakes protected interacts with the choice of ANC. The skeleton is there, but not enough. For example, a more complete de monstration of what went in to making Table 5-12 would be very useful. (Also, as is true in a number of places, some of the

variables are not defi ned or ambiguous, e.g., DL %ECO : is it for NOy+S (I think) or N+S).

How do the calculated DL %ECO ’s compare with the current estimate of its level? How, specifically, do you find the sites protected from ANC<20 in this case? Further, it would

be of interest to se e a distribution of DL %ECO current vs. distributions of DL %ECO at one of the candidate control levels (e.g., ANC 50, %Pro t.=75), along with a description of the

decrease in DL %ECO (again, potentially a frequency di stribution). (Figs. A11,16 & 20 are informative, but not as so). It might be even more insightful if a spatial distribution of

the control levels were able to be shown (again as % reduction in DL %ECO ). It may be necessary to have a set of assumptions for developing that spatial map, and those should be clearly described. It is difficult to see how the administrator and CASAC can provide their best guidance on th e level of the standard without further understanding of the level of control that would likely be require d to meet various combinations of the level/form/ecosystem choices made to specify the standard. In terms of advising the Administrator, one of the sections that should be strengthened is th e one on the approach to defining/choosing ecosystems. While this section is substantia l, it was difficult to

distill.

I appreciate the chapter on uncer tainties. In this analysis, more than those conducted for other standards, the uncertainties in the modeling have to be put forth in a very transparent fashion because those uncertainties impact directly on the translation of the105 estimated depositional flux to the monitored quantity. They are not small. The magnitude of such uncertaintie s (e.g., in the transfer rati os) should be quantitative or semi-quantitative. Having an “unknown” for th at uncertainty is a w eakness of the current document, and indicates an area needing intense assessmen t. Air quality modeling uncertainty is important to the overall viab ility of the approach, impacting not only the transfer ratio, but also the estimated NH 3 flux.

The Executive Summary does provide a reasonabl e overview of the rest of the PA, and is a valuable component of the PA. However, it does suffer from the same elements from which the rest of the PA suffers (e.g., see above for discussions of what is needed to bolster Chapter 5). It also suffers from trying to overly si mplify the complexities of the proposed approach. In particular, the AAP I equation really should be included, with explanations of the origin and importance (including magnitude) of each term. Symbols should be defined and figures should have explanatory captions. I would add more headings to show the steps in the conceptual design of an ecologica lly-relevant standard.

I would also note that at this time the secondary standard is most strongly supported by the demonstrated relationship between ambien t NOx and SOx and aquatic acidification. Like Chapter Five, there is a n eed to provide more informati on as to the consequences of making various decisions about the choi ce of components of the standard.

It is interesting that this PA does not include staff recomme ndations as to a range of AAPI, % protected or choice of ecosystem appro ach for the standard (i.e., the elements of the standard upon which we are supposed to give guidance). Sim ilar information has been provided in prior reviews, and that info rmation has been very useful to assess the reasoning behind the choices. As part of our review, it would have been very helpful to see similar information, particularly from pe ople who have been intimately immersed in doing the analyses. This is pa rticularly true given the complexity and novelty of the approach. Further, having only had a rather limited time to review the PA magnifies the problem.106 Comments from Dr. David Shaw

This draft demonstrates a marked improveme nt over the first draft and I feel it is responsive to many of the CASAC member co mments. The addition of details with

models and uncertainties has resulted in a more informative document.

While this assessment seems to touch on the n eed for meaningful data from other regions, and it is more specific about what parameters need to be measured to guage the standard,

it does not address the resources needed to expand air monitoring into these other regions. I must emphasize the need for data . While this proposed NAAQS is innovative and I appreciate the efforts being made to identify an appropria te NAAQS, it is also model dependent and because of that, it calls for commitments to get better data for future analysis. I am concerned that the USEPA is taking steps towards ranking model data higher than monitored ambient data, and I wa nt to ensure that this is not the direction which NAAQS will take. I believe that real ambient data should be considered in higher regards than model data.

I feel that the PA is a report that should be more readable and user friendly than the highly technical ISA and REA, and in that vein I suggest that it be clear what each indicator represents. For example, the ANC for lakes is relatively easy to measure and therefore represents a large am ount of available data, but it do esn’t represent streams. In addition, ANC data is typically a summer target which leaves us dependent on models to estimate or adapt for year round use. As a re sult, I suggest that when ANC is discussed in the broad context, it should be prefaced as lake surface water ANC, not to be confused

with stream ANC levels which were not evalua ted. On that same note, I suggest that the base cation to aluminum ratio (Bc/ Al) be specified as soil water.

Flexibility

There is limited data in regions that currently do not have sufficient monitoring data or modeling efforts to characterize their own sensi tive ecosystems at this point. Therefore, I suggest that sufficient flexibility be bu ild into the policy to allow for future monitoring/modeling effort s and characterization.

Models & Data

There are several issues with a heavy reli ance modeling. There are differing levels of

uncertainties associated with each of th e models (thank you for including the updated document on 9/23/2010). One example of these uncertainties is that it is very difficult to assess the dry deposition estimates in CMAQ. As a result, how much confidence do we

have in the NO

x /SO

x transference ratios which are based on modeled deposition?

The PA states that the current monito ring networks (IMPROVE, CASTnet, and NADP/NTN) are not adequate to cover all se nsitive areas while Chapter 5 suggests that CMAQ will be used to help develop the sp atial patterns needed to create the NAAQS.

Without sufficient measurements of ambient NO y and SO 2 in sensitive areas is a serious107 limitation, again leading to the conclusion that a clear commitment be developed to provide adequate data.

Specific Comments

Brook trout is listed as a sens itive species, it is generally not. I suggest using a more general term like fish which is more accurate . This is also comparable to zooplankton which is not specific either.

ES 12 bullet 1. The statement “at least as prot ective” does not seem to be appropriate. The secondary standard should is held separate to be protec tive of human welfare. We most likely will identify different areas of the na tion which have different sensitivities. Perhaps something could be added at the e nd of the sentence to say in the nation, and more protective than the current stan dard in several parts of the US.

ES- 10 figure caption, delete stream sin ce this model is based on lakes only.

ES 12 bullet 2. Specify lake surface water ANC.

ES 12 bullet 3. Specify soil water Bc/Al values

ES-13 bullet 4. Change to “Less protective against species mortality during acidification episodes”

ES-13 bullet 6. Change may to will. Substitute “fish” for brook trout, because brook trout are not generally consid ered a sensitive species.

9-18 line 13 change ‘may’ to ‘would’ ; change ‘brook trout’ to ‘fish’.

A-31-32 Alkalinity section. Text an d table need more explanation.

A-34 Line 8. Simplify the explanation, something to the effect that in glaciated areas, the parent material over the bedrock (e.g. glaci al till) has been deposited miles from its origin. The soils develop from these parent materials and can be very different from the

bedrock.

B-4 Table 1. Suggest identifying the lakes by na me, instead of or in addition to their ID number. This would improve the readability and connect the reader to the landscape feature. Likewise with naming the Shenandoah streams (Table 2). Same for Tables 6, 7, 8

& 9.

B-11. Line 29. Change ‘lakes” to ‘streams’.11/17/10 Draft text for review at the chartered CASAC Public Teleconference 12/06/2 010 Teleconference-- Please Do not Cite or Quote -- This draft is a work in progress, does not reflect consensus advice or recommendations, has not been reviewed or approved by the chartered CASAC and does not represent EPA policy

Comments from Dr. Kathleen Weathers

Clearly EPA staff has put considerable effort in to the conceptual design, analyses, associated uncertainties, and various policy options outlined in this 2nd version of the PA. The stated goal of developing a conceptual design for a standard has been significantly advanced. Many kudos.

It is also true that the time line was tight for generating this (substantial) revision, and the resultant text is rough and unclear in many places , and lacks well-placed, succinct descriptions of, for example, the AAPI and its component part s (the Introduction notwithstanding; Chapter 5 was a challenge in places).

A few general comments:

That the importance of NHx as a source of polluti on/nutrient addition to ecos ystems is explicitly considered is an important improvement, even if it must be taken back out of the calculations because of the current regulatory focus on NOx and SOx only.

Perhaps best summarized by the statement on page 5-69: “A critical issue for the Administrator to address in setting a NAAQS based on the AAPI is to consider and weigh the varying degrees of uncertainty in establishing the elements of the AAPI. These uncertainties impact the likelihood that a specific AAPI sta ndard would in fact achieve a ta rget ANC level for a specified percentage of a population of water bodies.” While the addition of Chapter 7 is most welcome, I still have some concerns with the large and important influence of CMAQ deposition estimates and as [BC]o, in particular, on the AAPI. Some additional analyses, comparisons, and explanatory text would be helpful in at least bounding these concerns. For example, some comparisons and analyses th at would be likely to either increase or bound confidence in, or understanding of-- CMAQ depos ition estimates are still lacking in this document. I do not object to using CMAQ here, in fact, as I said in my comments with the first draft, I think it is appropriate, bu t since this model is so fundament al to the standard setting, it is

critical that the PA is clear about model detail s, caveats and how it compares to other estimates of deposition (e.g., NADP wet, CASTNET modeled deposition, etc). Despite the fact that CASTNET also models (vs measures) dry depos ition, it is instructive to compare the two modeled dry deposition estimates. Similarly CM AQ (or CMAQ/PRISM, as the case may be) vs NADP wet deposition should also be compared. Also, for the case study areas, what are the current deposition estimates and how do th ey compare to NADP + CASTNET for these

locations? I note as well that some of th e discussions about the use of CMAQ and its uncertainties often appear defensive, or unneces sarily offensive. And, please, wherever the CMAQ model appears in the text , include the version used.

In regard to the importance of BC (7-30/31) (“ largest uncertainty and most influence on the CL”), is there any confidence that can be gain ed by doing spatial aggreg ation based on BC? It was dismissed along with bedrock geology by the staff as a way to subdivide or aggregate

waterbodies?

10811/17/10 Draft text for review at the chartered CASAC Public Teleconference 12/06/2 010 Teleconference-- Please Do not Cite or Quote -- This draft is a work in progress, does not reflect consensus advice or recommendations, has not been reviewed or approved by the chartered CASAC and does not represent EPA policy

In regard to spatially aggreg ating or dividing waterbodies, Th e Ecoregions include vegetation and vegetation influences both deposition and th e processes involved in Neco, for example. Therefore, I favor them over the one nation approach. That sa id, 70+ regions seems rather unwieldy. I think that a few more categorie s should be added to the monitoring section if a goal is to be able to evaluate the efficacy of the standar d. Surface water ANC, and soil monitoring should be included along with field deposit ion measurements that can exte nd networks, such as NADP and

CASTNET.

A few more specific items:

I’m confused by the first paragraph on page 5-85 in regard to the timeframe consideration. While it is of course important, I’m not exactly sure wh at, if I were the Admini strator, I would do with

this statement.

5-53: For specified regions (high elevation wa tersheds along the Appalachians, for example), occult precipitation can represent a large fraction of N and S deposit ion, larger than precipitation or dry deposition. I suggest modifying the stat ement and referencing, for example, MADPro results. Perhaps it is the case that occult precipitation is insignificant at the scale of CMAQ model output, which would be important to note.

7-13: Shenandoah and the Adirondacks are regions of reasonably high heterogeneity with respect to variables that are likely to influence not only the deposition of N and S but all the other parameters in the AAPI index, thus while the statem ent may be true for large grid cell sizes, it’s unlikely to be true over the relevant ecological scales. 9-4 and 9-5—here is an exampl e of a Faulkner-like paragraph whose meaning is completely opaque to me (but I think that ther e’s important information there)

Charge Questions:

Chapter 5 (needs work to make it clearer).

7. What are the Panel’s views on th e appropriateness of the critical loads that form the basis for the population assessment to determined deposition metrics?

The critical loads concept has been used by EU countries for quite some time; I think it a good and tested framework for considering ecosystem effects of air pollution and around which to build a secondary standard. I find the aggregation method proposed (ES-7) compelling.

a) What are the views of the Panel on the a ppropriateness of genera lizing the f-factor approach to apply to lakes and st reams in the Western U.S. and othe r portions of the Eastern U.S.

The f-factor did not seem well described to me, despite the fact that there were a few places where it showed up in the text. I wished for a “so what” statement on 5-23 with regard to estimation of [BC]o, and what it might mean within the AAPI. So, I’m not sure exactly what the

10911/17/10 Draft text for review at the chartered CASAC Public Teleconference 12/06/2 010 Teleconference-- Please Do not Cite or Quote -- This draft is a work in progress, does not reflect consensus advice or recommendations, has not been reviewed or approved by the chartered CASAC and does not represent EPA policy

question is here—is the f-factor likely to hold for other locations, or does it matter whether lakes or streams are the target freshwater (given th e divergences in Fig. 5- 6b)? As noted above, the [BC] is a critically important variable.

b) What are the views of the Panel on the filtering criteria used to remove lakes and streams that are naturally acidic or not sensitive to atmospheric deposition?

These are important and appropria te criteria on which to filter freshwater systems from the database. This filtering is responsive to the Panel’s previous recommendation.

8. What are the Panel’s views on the suggested methods for determ ining appropriate values of reduced nitrogen deposition in establishing NOx/SOx tradeoff curves?

As with all of the deposition estimates, CMAQ is the source, and there ar en’t really any other great options. NADP chemistry and PRISM precipita tion might be used to get at wet inputs (or compare them with CMAQ). The inclusion of NHx is important.

CHAPTER 9

23. What are the Panel’s views on Staff’s conclu sion that the existing secondary standards for NOx and SOx should be retained to provide pr otection against direct adverse effects to vegetation due to gas phase exposures?

That there are adverse effects to vegetation as a result of exposures to SOx and NOx has been

established and is reiterated in this document. However, isn’t it likely that the proposed new

standard would result in concentrat ions at, or lower than the curre nt concentrations, and therefore be protective? Or, is the que stion about whether these exis ting secondary standards should remain in place in addition to a deposition stan dard? (I do think that protection against adverse effects to vegetation due to gas pha se exposures should continue.)

24. In light of the Panel’s views on what consti tutes adverse effects to public welfare (see Chapter 3), what are th e Panel’s views on:

a) the degree to which current levels of NOy and SOx deposition are adverse to public

welfare based on evidence and risk informati on, and information on adversity provided in Chapters 2,3, and 4?

Research has shown that acidifying atmospheric deposition at its curren t levels results in ecosystem functional changes, and aquatic acidifi cation, in sensitive ecosystems; the information in Chapters 2-4 reinforces this.

b) target values for ANC that protect against adversity to pub lic welfare in light of the information presented in Chapter 5 concerni ng levels of ANC and the ecosystem effects associated with those target ANC levels? These levels are supported in th e literature; they are defensible and appropriate.

11011/17/10 Draft text for review at the chartered CASAC Public Teleconference 12/06/2 010 Teleconference-- Please Do not Cite or Quote -- This draft is a work in progress, does not reflect consensus advice or recommendations, has not been reviewed or approved by the chartered CASAC and does not represent EPA policy

c) factors relevant in selecting target percentages of waterbodies to protect at al ternative target ANC levels to protect against adverse effects to public welfare, and weights to place on those

factors?

It seems to me that the challenges of creating an d enforcing a spatially explicit standard at fine spatial scales will be large. The graphical repr esentation of percentages of waterbodies that would, or would not be protected is very informative and suggests th at an aim of 50% is too low. But this is clearly a value judgment. What ar e the socio-ecological characteristics of the waterbodies that would not be protected? Ar e they public water supplies? High elevation

waterbodies?

d) alternative standards for NOx and SOx that would protect against adverse effects to public welfare based on the AAPI form, and taking in to account • consideration of target levels of ANC (chapter 5),

These appear to be consistent with what’s in th e literature (see especial ly Driscoll et al. 2001), and what others have used for policy targets.

• target percentage of water bodies to protect (chapter 5), The ranges presented are wide; I cannot come up with rationale to sugge st different targets,

however.

• consideration of relevant uncertainties in AAPI components (chapter 7), and

Thank you for chapter 7. As noted, almost all AAPI components have significant uncertainties, Transference and BC, especially. I continue to wonder whether uncertainties are exacerbated, or could be reduced, by choosing appropriate spatial sc ales for aggregation (see comments from last review). Also, I still find not wholly adequate the discussion a nd analysis of the CMAQ model (see above). While I agree that it is an appropr iate model to be used for examining deposition across the US, the uncertainties that have to do with estimating deposition to heterogeneous terrain were not addressed, for example.

The elasticity analysis was an interesting way to examine uncertainties. It was not clear to me why 1% was chosen for each of the variables, however.

• any other potentially relevant factors, such as levels of co-protection against

terrestrial acidification and nutri ent enrichment (chapter 6)?

I agree that using ANC as a target for chemical protection is a good one, and a defensible place to focus. Further, by definition and as pointed out, there will be some level of protection afforded to the adjacent terrestrial system s that influence downstream freshwater systems. The analysis of protection that would be afforded for terrestrial systems using Bc :Al was very useful. However, since data are limited, and the linked biogeochemical reactions within terrestrial ecosystems as a result of N and S deposition are complex, and may have opposite effects ( nutrient enrichment vs

11111/17/10 Draft text for review at the chartered CASAC Public Teleconference 12/06/2 010 Teleconference-- Please Do not Cite or Quote -- This draft is a work in progress, does not reflect consensus advice or recommendations, has not been reviewed or approved by the chartered CASAC and does not represent EPA policy

112 acidification), I do not think that addressing co-protection further than what has been accomplished in this document is warranted. It w ill be crucial, however, to monitor terrestrial ecosystem responses to changing deposition scenarios so that sufficient data are available for the

next review.