September 15 , 2010

MEMORANDUM SUBJECT: CASAC Review of Policy Assessment for the Review of the Secondary National Ambient Air Quality Standards for NOx and SOx : Second External Review Draft FROM: Lyd ia N. Wegman, Director /s/ Health and Envi ronmental Impacts Division (C504

- 02) Office of Air Quality

Planning and Standards United States Environmental Protection Agency TO: Angela Nugent Designated Federal Officer Clean Air Scientific Advisory Committee EPA Science Advisory

Board Staff Office Attached is the draft document, Policy Assessment for the Review of the Secondary National Ambient Air Quality Standards for NOx and SOx : Second External Review Draft ( September 2010) , prepared b y the Environmental Protection Agency’s (EPA) Office of Air Q ualit y Planning and Standards (OAQPS) staff as part of EPA’s ongoing review of the secondary (welfare

- based) national ambient air quality standards (NAAQS) for oxides of nitr ogen (NOx) and sulfur (SOx). This document will be the focus of a review b y the Cl ean Air Scientific Advisory Committee (CASAC) Oxides of Nitrogen (NOx) and Sulfur Oxides (SOx) Secondary Review Panel (the CASAC NOx SOx Secondary Panel) at a public meeting to be held in Durham NC on October 6

- 7 , 2010. I am requesting that you forward th e s e draft document s to the CASAC NOx SOx Secondary Panel to prepare for the October meeting. As part of the review of the current secondary (welfare

- based) NAAQS for NOx and SOx, EPA’s OAQPS staff has prepared a second draft Policy Assessment. This dra ft Policy Assessment evaluates the policy implications of the key

scientific information contained in the document Integrated Science Assessment for Oxides of Nitrogen and Sulfur

- Ecological Criteria, prepared b y EPA’s National Center for Environmental Asse ssment (NCEA) and the results from the anal ys es contained in the Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur

. These documents, along with EPA’s Integrated Revi ew Plan, can be found at http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html

. The second draft Policy

Assessment reflects considerat ion of comments from the Panel, as wel l as public comments, on the first draft Policy Assessment, which was reviewed by the Panel on April 1

- 2 and May

3 , 2010. The main comments from the Panel on the first draft PolicyAssessment were provided to us in a June 22, 2010 letter (Russell and Samet , 2010) 1

. These

comments, and the changes made in the second draft Policy Assessment in response to them, are summarized in Attachment 1. Note that the structure of the Policy Assessment has changed somewhat from the first draft. While there are still 9 chapters, Chapters 5 and 6 in the first draft have been combined into Chapter 5 in the current draft; Chapter 7 in the first draft is now Chapter 6 in the current draft, Chapter 7 in the current draft is a new chapter on uncertainty, variability

and sensit ivity anal ys es, and Chapter 8 in the current draft is a new chapter on monitoring issues. The current draft contains several placeholders indicating missing tables or discussions. We expect to provide the Panel with these tables and discussions in a sepa rate submission two weeks prior to the October 6

- 7 Panel meeting. These will include a table in Chapter 9 summarizing the options for elements of the standards, a table in Chapter 7 summarizing key uncertainties, and a discussion in Chapter 5 of the impli cations of a range of choices of the target percent of lakes and streams to protect for alternative target ANC levels. This discussion will also cover the various spatial aggregation choices and resulting implications on the target percentages. We recogn ize that there are some formatting issues in several chapters, and these will be addressed in the final PA. The CASAC and public comments on the draft Policy Assessment will be taken into consideration in making revisions to the draft document

. A final Policy Ass essment will be released in December of 2010. Following completion of the final Policy Assessment, EPA will conduct a rulemaking with regard to its review of the secondary NOx and SOx NAAQS. Consistent with the terms of a consent decree, the E PA Administrator will sign a notice of proposed rulemaking b y July 12, 2011 and a final rulemaking notice by March 20, 2012. Draft documents are being made available to the CASAC NOx SOx Secondary Panel in the form of attached electronic files. The documents are also available from the EPA website at http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html

. Printed copies of these documents will be sent to CASAC NOx SOx Second ary Panel members via UPS

. A set of charge questions related to the draft Policy Assessment will be submitted separately

. We look forward to discussing the second draft Policy Assessment with the CASAC NOx SOx Secondary

Panel at our upcoming meeting. Shou ld you have an y questions regarding the first draft NOx SOx Secondary NAAQS Policy

Assessment , please contact me (919

- 541

- 5505; email wegman.l ydia @epa.gov) or Dr. Bryan Hubbell (919

- 541

- 0621; email hubbell.bryan @epa.gov ). Attachments

cc: Vanessa Vu, SAB, OA John Vandenberg , ORD/NCEA

- RTP Mary Ross, ORD/NCEA

- RTP Ron Evans, OAQPS/HEID Dale Evarts, OAQPS/HEID

1 Russell, A. and Samet, J. (2010). Letter from Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, Administrator, US EPA. Review of the Policy Assessment for the Revie w of the Secondary National Ambient Air Quality Standards for NOx and SOx: First Draft (March 2010) . June 22, 2010.Richard Haeuber, OAP/CAMD

Karen Martin , OAQPS/HEID Christine Davis, OAQPS/HEID Tara Greaver, ORD/NCEA

- RTP Bryan Hubbell, OAQPS/HEID Meredith Lassiter, OAQPS/HEID Jason Ly nch, OAP/CAMD Norm Possiel, OAQPS/AQAD Adam Reff, OAQPS/AQAD Rich Scheffe, OAQPS/AQAD Travis Smith, OAQPS/HEID Ginger Tennant, OAQPS/HEID Randy Waite, OAQPS/HEID Nealson Watkins, OAQPS/AQ ADAttachment 1

CASAC comments on first draft PM Policy Assessment and responses to those comments The CASAC Panel’s comments and recommendations on the first draft of the NOx and SOx Secondary

NAAQS Policy Assessment, as well as changes made in the seco nd draft in r esponse to those comments, are summarized below. Overarching comments and recommendations are summarized below, followed by comments and recommendations on chapters 2 through 9

. Overarching comments and recommendations The Panel made several overarching comments and recommendations, including:

 The second draft should include in a separate chapter a more comprehensive sensitivity and uncertainty

anal ys es of the proposed approach . This chapter should provide more reasoning to support EPA’s as sessment of the relative values of the uncertainties. The sensitivity

anal ys es should include the sensitivity of the AAPI to component terms. The chapter should provide a more thorough evaluation of the ability of CMAQ to simulate the ambient concentrati ons and wet and dry deposition fluxes of the SOx, NOx and NHx species used in determining the AAPI

.

 The second draft should include a succinct discussion of other potential impacts of NOx deposition to N

- limited ecosy stems , including potential production increases that may be either beneficial or adverse depending on the s ys tem and management goals.

 The second draft should ensure the use of a consistent set of units in its presentation of data, results and equation s. In response to these comments, we hav e made extensive edits throughout the second draft Policy Assessment to ensure consistent units are used, and have included a table in Chapter 1 which clearl y identifies units and conversions used in the document ( Table 1

- 1, Section 1.1 ). We have added a new chapter (Chapter 7) which provides a more extensive discussion of uncertainties and variability

in the science, data, and models which inform our considerations of the standards. This chapter also provides assessments of the sensitivity of models and the AAPIto inputs. We have added additional discussions of the broader set of potential impacts of NOx deposition, while continuing to focus the overall review on the effects of NOx and SOx deposition on sensitive aquatic ecosy stems , and protection against adverse effects of NOx additions ( ES

- 4, Section 1.6, S ection 4.5.2, Section 2.2.2, and Section 3.4 ). Chapter 2 (Known or Anticipated Ecological Effects) The panel was generall y supportive of the review of effects provided in the chapter. The panel asked primaril y for clarifications of the text and additional references. The panel asked for a summary of the assumptions and limitations of the steady

- state models used in the ecological effects studies . The panel requested that we clarify that ecologi cal effects due to deposition of N and S occur in a relatively small set of sensitive ecosy stems, rather than throughout allecos ys tems. The panel also asked for a more thorough discussion of uncertainties, with

justifications for rankings of uncertaintie s, and sensitivity analy ses for the different models used for aquatic acidification

. Changes made in chapter 2 in the second draft Policy Assessment were primarily focused on streamlining the chapter as well as on improving and clarifying the approach for characterizing uncertainty. In addition, we included a new table (Table 2

- 2 ) that summarizes the assumptions and limitations of the ecological effects models. Chapter 3 (Considerations of Adversity to Public Welfare) The panel asked for a more focused discussion on how and wh y the current effects of SOx/NOy deposition on sensitive ecosy stems matter in terms of services and functions of ecos ys tems that are important to people , emphasizing that effects occur onl y in a limited set of sensitive areas. The p anel asked for more explanation of the policy implications of the monetary values of ecos ys tem services discussed in the chapter. The panel also asked for a table summarizing the monetary valuation associated with vario us ecos ys tem services estimates. The panel asked for more focus on the effects that are likel y occurring due to NOx and SOx deposition and less on those that potentially

could be affected. The panel also asked for greater acknowledgement of the potential beneficial effects of nitrogen input s to nutrient limited ecosy stems
. Change made in chapter 3 in the second draft Policy Assessment were focused on describing those ecos ys tem services that were likel y impacted by current NOx and SOx deposition. In addition, we have expanded the discussion of insights that can be gained b y evaluating public decisionmaking regarding protection of aquatic resources (Section 3.1.2.4.3 ), and through evaluation of programs in Europe that have established targets for ecos ys tem protection as part of critical loads policies (Section 3.1.2.4.4) . We have modified Figures 3.4 and 3.5 to include deposition levels in a wider range of public lands, including Federal Class I Areas, as well as state and local parks and wilderness areas. We have added an additional assessm ent of the value of decreases in acidification in the Adirondacks based on the Banzhaf et al (2006) valuation survey of NY residents (Section 3.4.2). We have added a number of additional tables, including a summary

of values of ecosy stem services affected by current N deposition (Table 3

- 7 and 3

- 8 ). We have included a discussion of the potential beneficial effects of N deposition in nitrogen

limited areas in Chapter 4, and have added a clarification to this chapter acknowledging these effects and reiterat ing our focus on adverse effects (Section 3.4.5). Chapter 4 (Addressing the Adequacy of the Current Standards) The panel was generall y supportive of the information provided demonstrating that current NOx and SOx secondary

standards are not adequate to p rotect against effects of deposition of NOx and SOx to sensitive ecosy stems. While the panel agreed that steady state models are appropriate to evaluate the adequacy of the standards, they

note that approach could be enhanced by also applying dy

namic acid ification modeling techniques to “hindcast”changes in ANC. The panel recommended that the evaluation of adequacy should consider the extent to which and rates at which some less sensitive sy stems may continue to recover at current S + N deposition, while other more sensitive sy stems will not recover or may experience further deterioration

. Thepanel also asked for additional plots showing the relationship of NOy to NOx, compared with NO2 to NOx. The panel also asked that a summary o f the performance asse ssment of CMAQ be included. The performance assessment of CMAQ has been incorporated in the new Chapter 7 addressing uncertainty, variability, and sensitivity

. Much of the monitoring discussion has been moved to a separate Chapter 8 on m onitoring issues, and that chapter also provides more discussion on the ambient concentration to deposition relationship of individual sulfur and nitrogen species. New plots of NOy

to NOx and NO 2 to NOx have been added to chapter 4. While the panel recognized that the current review was focused on sensitive, non

- managed ecos ys tems, the panel requested more discussion of fertilization effects. In response to these comments an additional discussion has been added to Chapter 4 (Section 4.5.2) regarding nutrient enrichment effects in both managed and non

- managed s ys tems. In addition, language has been added in several other chapters highlighting the range of potential responses to nitrogen nutrient enrichment in different ty pes of ecos ys tems, especiall y in N

- limited ecos y stems. Chapters 5 (Conceptual Design of an Ecologically Relevant Multi

- pollutant Standard) and 6 (Options for Elements of a Standard to Protect Against Effects from Aquatic Acidification) Note: We have combined Chapters 5 and 6 from the first draft Pol icy Assessment into a single Chapter 5 in the second draft Policy Assessment to reduce redundancy and improve the flow of the document. The panel was generall y supportive of both the conceptual framework developed to address effects associated with depo sition of NOx and SOx, and the Atmospheric Acidification Protection Index introduced as a new form of the standards. The panel agreed with selection of NOy and SOx as atmospheric indicators, and with the selection of ANC as the ecological indicator. The panel agreed that a multi

- year averaging time from 3 to 5 years was appropriate. The panel also agreed that a multipollutant standard is appropriate to protect aquatic ecos ys tems from acid deposition. The panel asked that reduced nitrogen be treat ed as a variable component of the AAPI standard that can be updated . The panel asked that the underlying assumption of steady state behavior should be evaluated with a parallel effort using sensitivity analy sis and dy

namic modeling . The panel asked that the AA PI equation for the proposed standard should include the geographical extent and numerical range of its applicability

. The panel recommended that the mass balance approach to determining Neco be used over the dynamic modeling approach. The panel recommen ded that in evaluating methods for aggregating catchment scale critical loads, consider ation be given to approaches b y which the water bodies within an y specified area could be first stratified to include only those which were considered potentiall y s uscep tible to acidification, based on estimates of preindustrial ANC, or acid sensitivity class . The panel advised EPA to focus on an AAPI standard dri ven by aquatic effects concerns, given both the availability

of data, and the likelihood that such a standard would decrease N and S inputs to ecos ys tems, which would provide protection against additional effects. The panel recommendedthat EPA conduct a sensitivity study to characterize uncertainty associated with different components of the conceptual framewor k and propagate the resulting uncertainty at every step to arrive at an ensemble of SOx and NOy response surfaces to meet a given standard. The panel asked for inclusion of a separate conceptual diagram which shows the important contributing factors for e ach term in the AAPI equation

. The panel noted a number of challenges in specifying the AAPI form. The panel highlighted a number of areas of uncertainty , including

 Uncertainty in pre

- industrial levels of ANC
 Uncertainty in the use of steady state models
 Uncertainty in the atmospheric deposition transformation ratios
 Uncertainty in modeled estimates of reduced nitrogen deposition In addition, the panel recommended that close attention be given to the issue of matching temporal and spatial scales in vario us components of the AAPI

. The panel recommended disaggregating the g(·) term in the AAPIequation, and include a term to account for naturall y occurring organic acids. The panel recommends that consideration of chronicall y acidic or highly acid sensitiv e surface waters that would not be recoverable at a given ANC limit should be given

. The panel recommended that the CMAQ modeling that is used to develop the atmospheric deposition transformation ratios be evaluated for sensitivity to emissions and chemis try , and that characterization of the uncertainties in precipitation and wet deposition be included. The panel recommended several specific evaluations of CMAQ, including:

 Model performance for nitric oxide, nitrogen dioxide, sulfur dioxide, nitrate, ammo nium and aerosol nitrate, ammonium, and sulfate for different networks for which the data are routinely available
 Model performance for wet deposition of sulfate, nitrate, and ammonium using the National Atmospheric Deposition Program (NADP) network
 A regi onal model evaluation using the continuous measurements of nitric oxide, nitrogen dioxide, nitric acid and NOY from the SEARCH network in the southeastern U.S. The panel expressed support for the use of NOx/SOx tradeoff curves, but recommended that these curves include the impact of reduced nitrogen. In response to the comments from the panel, Chapter 5 has been revised in the following way s:

 We have added a section comparing critical loads calculated using steady - state versus dy namic modeling has been a dded (5.3.2.3).
 The mass balance approach to determining Neco has been used (5.3.2).
 The tradeoff curves now show the impact of NHx, based on a range of NHx deposition values which are modeled to occur across the U.S. (5.3.9).
 Criteria have been identified to only consider critical loads from catchments that are susceptible to acidification from atmospheric deposition, while excluding thosecatchments in which acidification results from high organic acid content, acid mine

drainage or naturall y low base cat ion weathering (5.3.2.6).
 The focus of the conceptual design is on aquatic acidification (5.3.1) with co

- protection to other effects presented in Chapter 6.
 A new conceptual diagram has been added that outlines each step to develop the tradeoff curves and the AAPI (5.3.1)
 The g(·) term from the first draft PA has been disaggregated so that each component is represented in the AAPI equation (5.3.4). As stated above, the critical load dataset is screened to exclude those catchments which would not be able to recover based on pre

industrial ANC values (5.3.2.6). Chapter 7 (Co

- protection) Note: The chapter on co

- protection is now Chapter 6. The panel supported evaluation of co

- protection provided by an aquatic acidification based standard for terrestrial a cidification endpoints and terrestrial and aquatic nutrient enrichment endpoints. The panel recommended that the chapter be expanded to better explain the potential interrelationships between aquatic and related terrestrial responses to acidification . Th e panel recommended that further consideration not be given to developing a single standard addressing both acidification and nutrient enrichment. Chapter 9 (Conclusions) The panel generally

supported the preliminary staff conclusions regarding the adeq uacy of existing standards, and options for the indicators, averaging times, and form of additional standards to protect against the effects of NOx and SOx deposition to sensitive aquatic ecos ys tems. The panel reiterated the request for a separate uncertainty chapter. They

also asked that discussions of future research needs be linked to the identification of critical uncertainties. Chapter 9 has been expanded to include a discussion of staff conclusions regarding the options for elements of the standard . We have included discussions of how critical uncertainties might influence the AAPI , with references to the broader uncertainty discussions in Chapter 7. Research needs are discussed briefl y in the new Chapter 7, but will need to be more full y develope d in the final PA.