# Integrated Review Plan for the Secondary National Ambient Air Quality Standards for Nitrogen Dioxide and Sulfur Dioxide[This page intentionally left blank.]EPA-452/R-08-006 December 2007



## Integrated Review Plan for the Secondary Nation al Ambient Air Quality Standards for Nitrogen Dioxide and Sulfur Dioxide

U. S. Environmental Protection Agency National Center for Environment Assessment Office of Research and Development and Office of Air Quality Planning and Standards Office of Air and Radiation Research Triangle Park, North Carolina 27711December 2007 

### DISCLAIMER

This integrated review plan serves as a manage ment tool for the U.S. Environmental Protection Agency's National Center for Environmental As sessment and the Office of Air Quality Planning and Standards. The approach described in this plan may be modified to reflect information developed during this review and to address ad vice and comments received from the Clean Air Scientific Advisory Committee and the public thr oughout this review. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.December 2007 

### TABLE OF CONTENTS

KEY TERMS..........................................................................................................................i

1. INTRODUCTION ........................................................................................................... ............................... 1-1
1.1 LEGISLATIVE REQUIREMENTS....................................................................................................... 1-2 1.2 REGULATORY HISTORY OF THE S ECONDARY NAAQS FOR NO 2 AND SO 2 ................................... 1-3 1.2.1 NO 2 NAAQS ......................................................................................................................... ................... 1-3 1.2.2 SO 2 NAAQS......................................................................................................................... .................... 1-4 1.3 OVERVIEW OF THE NAAQS REVIEW PROCESS............................................................................ 1-8 1.4 S CIENCE P RIMER : NO X /SO X EFFECTS ON ECOSYSTEMS .......................................................................... 1-10 1.4.1 Acidification Effects on Freshwater and Terrestria l Ecosystems from Sulfur and Nitrogen Deposition ...................................................................................................................................1-12 1.4.2 Excess Nitrogen in Terrestrial and Estuarine Ec osystems .............................................................. 1-13 1.4.3 Reduced N itrogen ............................................................................................................... ............. 1-13
2. REVIEW SCHEDULE ................................................................................................................ .................. 2-1

3. KEY POLICY-RELEV ANT IS SUES ..................................................................................................... ..... 3-1

4. SCIENCE ASSESSMENT............................................................................................................. ................ 4-1
4.1 SCOPE AND ORGANIZATION ........................................................................................................... 4-1 4.2 A SSESSMENT A PPROACH ......................................................................................................................... 4-2 4.2.1 Literature Search .............................................................................................................. ................. 4-2 4.2.2 Criteria for Study Selection ................................................................................................... ............ 4-3 4.2.3 Content and Organiza tion of the ISA............................................................................................ ..... 4-4 4.3 Public and Scie ntific R eview................................................................................................... ........... 4-6 4.3.1 Informal Peer Consultation Work shop of the IS A Annexes ............................................................... 4-6 4.3.2 Public Review of Exte rnal Review Drafts........................................................................................ .. 4-6 4.3.3 Review by Clean Air Scien tific Advisory Committee ......................................................................... 4-6
5. RISK/EXPOSURE ASSESSMENT....................................................................................................... ....... 5-1
5.1 ASSESSMENT APPROACH .......................................................................................................................... 5-2 5.2 T OOLS FOR R ISK A SSESSMENT ................................................................................................................ 5-4 5.3 K NOWLEDGE G APS

............................................................................................................................... ... 5-4 5.3 PUBLIC AND SCIENTIFIC REVIEW.................................................................................................. 5-6
6. POLICY ASSESSMENT.............................................................................................................. ................. 6-1

7. REFERENCES..................................................................................................................... .......................... 7-1

APPENDIX A: CASAC PANEL ........................................................................................................ ................... A-1

APPENDIX B: ASSESSMENT TOOLS................................................................................................... .............B-1
B.1 M ODELS

............................................................................................................................... ...................B-1 B.1.1 Community Multi-Scale Ai r Quality (CMA Q) Model ........................................................................... ..B-1 B.1.2 Response Surf ace Models (RSM)............................................................................................ ................B-4 B.1.3 Air Quest................................................................................................................ .................................B-5 B.1.4 Total Risk Integrat ed Methodology (TRIM)................................................................................. ...........B-5 B.1.5 Regional Vulnerab ility Assessmen t (Re VA) ................................................................................. ...........B-6 B.2 C ASE S TUDY M ODELING

............................................................................................................................... ..B-7 B.3 E COSYSTEM S ERVICES : I MPACT AND V ALUATION ..........................................................................................B-9 B.3.1 Ecosystem services overview and why their consideratio n is needed................................................B-9 B.3.2 Ecosystem services relating to NOx/ SOx secondary stan dard issues ..............................................B-10 B.3.3 Valua tion ...................................................................................................................... ...................B-13December 2007 i 

## KEY TERMS

Acidification : The process of increasing the acidity of a system (lake, stream, forest soil). Atmospheric deposition of acidic or aci difying compounds can acidify lakes, streams and forest soils. 

### Air Quality Indicator : The substance or set of substances (e.g., PM 2.5 , NO 2 , SO 2 ) occurring in the ambient air for which a level is set for a NAAQS standard and monitoring

occurs.


### ANC (Acid Neutralizing Capacity): A key indicator of the ability of water to neutralize the acid or acidifying inputs it receives. This ability depends largely on associated biogeophysical characteristics. 

### Biologically Relevant Indicator: A measure that sufficientl y characterizes the exposureresponse relationship between a biological r eceptor and a pollutant stressor so as to be useful as a predictor of expected receptor response over a range of pollutant exposure levels.


### Dry Deposition : The removal of gases and particles fr om the atmosphere to surfaces in the absence of precipitation (rain, snow) or occult deposition. 

### Ecosystem : A dynamic complex of interacting plan ts, animals, and microorganisms and the non-living environment. 

### Ecosystem Benefit : The value, expressed either qua litatively, quantitatively and/or in economic terms where possible, associated with changes in ecosystem services that result, either directly or indirectly in improved human health and/or welfare. Some examples of ecosystem benefits that derive from improved air quality include improvements in habitat for sport fish species, drinking water quality, visual quality of scenic views, and quality of recreational areas. 

### Ecosystem Services: Conditions and processes through which natural ecosystems, and the species that are part of them, currently he lp sustain and fulfill human life or have the potential to do so in the future. Exampl es include, clean air, clean water, food and fiber production, flood protection, wate r purification, poll ination, and pest control. Improvements in these services may be valued as an ecosystem benefit. 

### Eutrophication : The process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of a quatic plant life usually resulting in the depletion of dissolved oxyge 

### n 

### Occult Deposition : The removal of gases and particles from the atmosphere to surfaces by fog or mist.December 2007 ii 

### Welfare Effects : Effects on soils, water, crops, vege tation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transporta tion, as well as effects on economic values and on personal comfort and well-being, whethe r caused by transformation, conversion, or combination with othe r air pollutants (CAA 302(h)) 

### Wet Deposition : The removal of gases and particles fr om the atmosphere to surfaces by rain or other precipitation



### Valuation : The economic or non-economic process of determining either the value of maintaining a given ecosystem type, state or condition, or the value of a change in, an ecosystem, its components, or the services it provides.December 2007 1-1 

## 1. INTRODUCTION

The U.S. Environmental Protection Agency (E PA) is conducting a revi ew of the existing primary (health-based) and seconda ry (welfare-based) National Ambient Air Quality Standards (NAAQS) for nitr ogen dioxide (NO 2 ) and sulfur dioxide (SO 2 ). The reviews of the primary NAAQS for NO 2 and for SO 2 are addressed in separate plan s released during the winter of 2006/2007. The purpose of this document is to co mmunicate the integrated plan for the joint review of the secondary NAAQS for these pollutants. In this document, the terms NO 2 and NO x and SO 2 and SO x are not interchangeable. The
terms NO x (oxides of nitrogen) and SO x (sulfur oxides) refer to the listed Criteria Air Pollutants for which EPA has regulatory authority under S ections 108 and 109 of the Clean Air Act (CAA), and for which criteria must be developed and review ed every 5 years. In this review, NOx refers to all oxides of nitrogen (convent ionally referred to as NOy in the scientific community), not simply the sum of NO and NO 2 (conventionally referred to as NOx in the scientific community). The oxides of nitrogen compounds in the ambient air are nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O), nitrogen trioxide (NO 3 ), dinitrogen trioxide (N 2 O 3 ), dinitrogen tetroxide (N 2 O 4 ), dinitrogen pentoxide (N 2 O 5 ); other ambient oxides of nitrogen include nitric acid (HNO 3 ), peroxyacetylnitrate (PAN), and other orga nic compounds such as nitrites, nitrates, nitrogen acids, and N-nitroso compounds (EPA, 1993). The terms NO 2 and SO 2 refer to the specific air quality indicators (pollutant species) specified by the current standards whose
concentrations are monitored to determine whet her the NAAQS is being met in a given location. The ecological importance of both oxidized and reduced forms of nitrogen has been widely recognized by the scientific community. The science assessment and the risk/exposure
assessment will also evaluate total reactive nitr ogen (which includes both oxidized and reduced forms), and its impacts on public welfare. Additionally, we will attempt to evaluate, and quantify where possible, the separate contributions of ambient versus other so urces of total reactive nitrogen in various ecosystems nationwide, as well as the contributions of NOx to ambient reactive nitrogen relative to other contributo rs to ambient reactive nitrogen. Section 1.1 below includes additional explana tion on the use of these terms within the context of the various phases of the new NAAQS re view process. This review will evaluate newDecember 2007 1-2 information published in the peer-reviewed literature since the completion of the last NO 2 (1995)
and SO 2 (1996) reviews, including assessments of the adequacy of the current secondary NAAQS, and consider the possible need for a new si ngle indicator or suite of indicators, as well as changed or retained level(s) and/or averaging times for the standards, which may include nitrogen and sulfur compounds other than NO 2 and SO 2 . This review plan is organized into si x chapters. Chapter 1 presents background information on the recently-revised NAAQS revi ew process; on the nature of the NOx/SOx problem; on the legislative requirements for th e review of the NAAQS; and on the regulatory history of past reviews of the NAAQS for NO 2 and SO 2 . Chapter 2 presents the proposed review schedule. Chapter 3 presents a set of key policy-relevant questions that will serve to focus the NAAQS review process on the critic al scientific and policy issues. Chapters 4 through 6 discuss the science, risk/exposure, and policy assessment portions of the review.
We consulted with the Clean Air Scien tific Advisory Committee (CASAC, panel members are listed in Appendix A), an independ ent scientific advisory committee established under the Clean Air Act, on an earlie r draft of this document. As this review proceeds, the plan described here may be modified to reflect inform ation received during the review process and to address advice and comments received from the CASAC and from the public throughout this
review.



### 1.1 LEGISLATIVE REQUIREMENTS Two sections of the Clean Air Act (CAA) gove rn the establishment and revision of the NAAQS. Section 108 (42 U.S.C. 7408) directs the Administrato r to identify and list “air pollutants” that “in his judgment , may reasonably be anticipated to endanger public health and welfare” and their “presence . . . in the ambient ai r results from numerous or diverse mobile or stationary sources” and to issue ai r quality criteria for those that ar e listed. Air quality criteria are intended to “accurately reflect the latest sc ientific knowledge useful in indicating the kind and extent of identifiable effects on public health or welfare which may be expected from the presence of [a] pollutant in ambient air . . . .” Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate “primary” and “secondary” NAAQS for pollutants listed under section 108. A secondary standard, as defined in Section 109 (b)(2), must “specify a level of air quality the attainment and maintenance of which, in the judgment of the Admini strator, based on such cr iteria, is required toDecember 2007 1-3 protect the public welfare from any known or anticipated advers e effects associated with the presence of [the] pollutant in the ambient air.” 1 In setting standards that are “requisite” to pr otect public health and we lfare, as provided in section 109(b), EPA’s task is to establish standard s that are neither more nor less stringent than necessary for these purposes. In so doing, EPA may not consider the costs of implementing the
standards. Whitman v. American Trucking Associations , 531 U.S. 457, 465-472, 475-76 (2001). Section 109(d)(1) requires that “not later than December 31, 1980, and at 5-year intervals thereafter, the Administrator sh all complete a thorough review of the criteria published under
section 108 and the national ambient air quality standards . . . and shall make such revisions in
such criteria and standards and promulgate such new standards as may be appropriate . . . .” Section 109(d)(2) requires that an independent sc ientific review committee “shall complete a
review of the criteria . . . and the national primary and secondary ambient air quality standards . . . and shall recommend to the Administrator any new . . . standards and revisions of existing criteria and standards as may be appropriate . . . .” Since the early 1980's, this independent review function has been performed by the Clean Air Scientific Advisory Committee (CASAC) of EPA’s Science Advisory Board.



### 1.2 REGULATORY HISTORY OF THE SECONDARY NAAQS FOR NO 2 

### AND SO 2 

### 1.2.1 NO 2 

### NAAQS

In 1971, the first air quality criteria docume nt for NOx was issued by the National Air Pollution Control Association (NAPCA), one of EPA’s predecessor agencies. After reviewing the relevant science on the public health and welf are effects associated with oxides of nitrogen, EPA promulgated identical primary and secondary NAAQS for NO 2 on April 30, 1971. Under section 109 of the Act, these standards were set at 0.053 parts per million (ppm) as an annual average (36 FR 8186). In 1982, EPA published Air Quality Criteria for Oxides of Nitrogen (EPA, 1982), which updated the scientific criteria upon which the initial standards were based.

1 Welfare effects as defined in section 302(h) [42 U.S. C. 7602(h)] include, but are not limited to, “effects on soils, water, crops, vegetation, man-made materials, anim als, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as ef fects on economic values and on personal comfort and well-being.”December 2007 1-4 On February 23, 1984, EPA proposed to retain thes e standards (49 FR 6866). After taking into account public comments, EPA published the final d ecision to retain these standards on June 19, 1985 (50 FR 25532). In November 1991, EPA released an update d draft Air Quality Criteria Document (AQCD) for CASAC and public review a nd comment (56 FR 59285). The draft AQCD provided a comprehensive assessment of the ava ilable scientific and technical information on
heath and welfare effect s associated with NO 2 and other NO x compounds. The CASAC reviewed the document at a meeting held on July 1, 1993 and concluded in a closure letter to the Administrator that the document “provides a scie ntifically balanced and defensible summary of current knowledge of the effects of this pollutant and provides an adequate basis for EPA to make a decision as to the appropriate NAAQS for NO 2 ” (Wolff, 1993). The EPA also prepared a draft Staff Paper that summarized and integrated the key studies
and scientific evidence contained in the revised AQCD and identified the critical elements to be
considered in the review of the NO 2 NAAQS. The Staff Paper recei ved external review at a December 12, 1994 CASAC meeting. The CASA C comments and recommendations were reviewed by EPA staff and incorporated into the final draft of the Staff Paper, as appropriate.
The CASAC reviewed the final draft of the St aff Paper in June, 1995 and responded by written closure letter (Wolff, 1995). In September, 1995, EPA finalized th e Staff Paper, “Review of the National Ambient Air Quality Standards for Ni trogen Dioxide: Assessment of Scientific and Technical Information,” (EPA, 1995). On October 2, 1995, the Administrator announced her proposed decision not to revise either the primary or secondary NAAQS for NO 2 based on the information available to her in this review (60 FR 52874; October 11, 1995). Afte r careful evaluation of the comments received on the October 1995 proposal, the Ad ministrator made a final dete rmination that revisions to neither the primary nor the secondary NAAQS for NO 2 were appropriate at that time (61 FR 52852, October 8, 1996). The level for both the existing primary and secondary NAAQS for
NO 2 remains 0.053 ppm (equivalent to 100 micr ograms per cubic meter of air [ug/m 3 ]) in annual arithmetic average, calculated as the arithmetic mean of the 1-hour NO 2 concentrations.



### 1.2.2 SO 2 

### NAAQS

Based on the 1970 sulfur oxides criteria document (DHEW, 1970), EPA promulgated primary and secondary NAAQS for SO 2 , under section 109 of the Ac t on April 30, 1971 (36 FRDecember 2007 1-5 8186). The secondary standards included a standard at 0.02 ppm in an annual arithmetic mean and a 3-hr average of 0.5 ppm, not to be exceed ed more than once per year. These secondary standards were established solely on the basis of vegetation effect s evidence. In 1973, revisions made to Chapter 5 “Effects of Sulfur Oxide in the Atmosphere on Vegetation” of Air Quality Criteria for Sulfur Oxides (EPA 1973), indicated that it could not properly be concluded that the vegetation injury reported resulted from the average SO 2 exposure over the growing season, rather than the short-term peak concentrati ons. EPA, therefore, proposed (38 FR 11355) and
then finalized a revocation of the annual mean secondary standard (38 FR 25678). At that time,
EPA was aware that sulfur oxides have other public welfare effects, including effects on materials, visibility, soils and wa ter. However, the available data were considered insufficient to establish a quantitative relationship between spec ific sulfur dioxide concentrations and effects needed for standard setting (38 FR 25679). In 1979, EPA announced that it was revising th e AQCD for sulfur oxides concurrently with that for particulate matter and would produce a combined particulate matter (PM) and sulfur oxides criteria document. Following its review of a draft revised criteria document in August, 1980, the CASAC concluded that acid deposition was a topic of extreme sc ientific complexity because of the difficulty in establishing firm qua ntitative relationships among: (1) emissions of relevant pollutants (e.g., SO 2 and oxides of nitrogen), (2) formation of acidic wet and dry deposition products, and (3) effects on terrestr ial and aquatic ecosystems. CASAC also noted that acid deposition involves, at a minimum, se veral different criteria pollutants - oxides of sulfur, oxides of nitrogen, and the fine partic ulate fraction of suspended particles. The Committee felt that any document on this subj ect should address both wet and dry deposition, since dry deposition was believed to account for at least one half of the total acid deposition problem. For these reasons, the CASAC recommended th at a separate, comprehensive document on acid deposition be prepared prior to any cons ideration of using the NAAQS as a regulatory mechanism for the control of acid deposition. CASA C also suggested that a discussion of acid deposition be included in the AQCDs for both ni trogen oxides and PM and SOx. In response to these recommendations, EPA subsequently prepared the following documents: The Acidic Deposition Phenomenon and Its Effects: Critical Assessment Review Papers, Volumes I and II (EPA, 1984), and The Acidic Deposition Phenome non and Its Effects: Critical Assessment Document (EPA, 1985) (53 FR 14935 -14936). Th ese documents, though they were notDecember 2007 1-6 considered criteria documents and did not undergo CASAC review, re presented the most comprehensive summary of relevant scientific information completed by the EPA at that point. Following CASAC closure on th e criteria document for SO 2 in December 1981, EPA OAQPS published a Staff Paper in November, 1982. The issue of acid deposition was not, however, assessed directly in this Staff Paper because EPA followed the guidance given by
CASAC. On April 26, 1988 (53 FR 14926), EPA proposed not to revise the existing primary and secondary standards. This pr oposal regarding the secondary SO 2 NAAQS was due to the
Administrators conclusions that (1) based upon the then-current scientific understanding of the acid deposition problem, it would be premature and unwise to pr escribe any regulatory control program at that time, and (2) when the fundament al scientific uncertain ties had been reduced through ongoing research efforts, EPA would draf t and support an appropriate set of control

measures. In spite of the complexities and significan t remaining uncertainties associated with the acid deposition problem, it soon became clear th at a program to address acid deposition was needed. On November 15, 1990, Amendments to the CAA were passed by Congress and signed into law by the President. In Title IV of th ese Amendments, Congress included a statement of findings that had led them to take this acti on, including that: (1) the presence of acid compounds and their precursors in the atmosphere and in de position from the atmosphere represents a threat to natural resources, ecosystems, materials, visibility, and public health; (2) the problem of acid deposition is of national and inte rnational significance; and (3) current and future generations of Americans will be adversely affected by delaying measures to remedy the problem. The goal of
Title IV was to reduce emissions of SO 2 by 10 million tons and NOx emissions by 2 million tons
from 1980 emission levels in order to achieve redu ctions over broad geographic regions/areas. Congress, however, clearly envisioned that further action might be necessary in the long term and reserved judgment on the form it could take, as evidenced by the inclusion of section 404 of the 1990 Amendments (Clean Air Act Amendments of 1990, Pub. L. 101-549, § 404). This section required EPA to conduct a study on th e feasibility and effectiveness of an acid deposition standard or standards to protect “s ensitive and critically sensitive aquatic and
terrestrial resources” and at the conclusion of the study, submit a report to Congress. Five years later EPA submitted to Congress its report titled Acid Deposition Standard Feasibility Study: Report to Congress (EPA, 1995) in fulfillment of this requirement. The Acid DepositionDecember 2007 1-7 Standard Feasibility Study Report to Congre ss concluded that establishing acid deposition standards for sulfur and nitrogen deposition may at some point in the future be technically feasible although appropriate depos ition loads for these acidifying chemicals could not defined with reasonable certainty at that time. The 1990 Amendments also added new language to sections of the C AA pertaining to the scope or application of the s econdary NAAQS designed to protect the public welfare. Section 108 (g) specified that “the Administrator may a ssess the risks to ecosystems from exposure to Criteria Air Pollutants (as identified by the Administrator in the Administrator’s sole discretion).” The definition of public welfare in section 302 (h) was expanded to state that the
welfare effects identified should be protected from adverse effect s associated with criteria air pollutants “...whether caused by transformation, conversion, or combination with other air pollutants.” In 1999, seven Northeastern States cited this amended language in section 302(h) in a petition to EPA to use its authority under the NAAQS program to promulgate secondary NAAQS for the criteria pollutants as sociated with the formation of acid rain. The petition stated that this language “clearly references the transf ormation of pollutants resulting in the inevitable formation of sulfate and nitrate aerosols and/or their ultimate environmental impacts as wet and dry deposition, clearly signaling Congressional intent that th e welfare damage occasioned by sulfur and nitrogen oxides be addressed through the secondary standard provisions of Section 109 of the Act. The petition further stated that “recent federal studies, including the NAPAP Biennial Report to Congress: An Integrated Assessment, documen t the continued-and increasingdamage being inflicted by acid deposition to th e lakes and forests of New York, New England and other parts of our nation, dem onstrating that the Title IV pr ogram had proven insufficient.” The petition also listed other a dverse welfare effects associated with the transformation of these criteria pollutants, including vi sibility impairment, eutrophicati on of coastal estuaries, global warming, tropospheric ozone and st ratospheric ozone depletion. In a related matter, the Office of the Secretary of the U.S. Department of Interior (DOI) requested in 2000 that the EPA initiate a rulemaking proceeding to enhance the air quality in national parks and wilderness areas in order to protect resources and values that are being adversely affected by air pollution. Included am ong the effects of concern identified in the request were acidification of streams, surface waters and/or soils, eutrophication of coastal waters, visibility impairment , and foliar injury from ozone.December 2007 1-8 In a Federal Register notice in 2001, EPA announ ced receipt of these items and requested comment on the issues raised by th ese requests. EPA stated that it would consider any relevant comments and information submitted, along with the information provided by the petitioners and DOI, before making any decision concerning a response to these requests for rulemaking. In this review, EPA will again revisit th e appropriateness and feasibility of setting a secondary NAAQS to address the welfare effects re sulting from the deposition of these criteria pollutants and their transformati on products. This plan describe s potential elements of that
review.



### 1.3 OVERVIEW OF THE NAAQS REVIEW PROCESS U.S. EPA has recently decided to make a numbe r of changes to the process for reviewing the NAAQS (described at www.http://epa.gov/ttn/naaqs/). The revised NAAQS review process contains four major components: an integrated review plan, a sc ience assessment, a risk/exposure assessment, and a policy assessment/rulemaking. In addition to these procedural modifications, for this secondary NAAQS review we have decided to examine two of the six criteria pollutants, oxides of nitrogen and sulfur oxide s, together, rather than indivi dually, as has been done in the past. This decision derives from the fact th at NOx, SOx, and their associated transformation products are linked from an atmospheric chemistry perspective, as well as from an environmental effects perspective (most notably in the case of secondary aerosol formation and acidification in ecosystems). These interactions have been re cognized historically by both CASAC and EPA;
the science related to these interactions c ontinues to evolve and grow, emphasizing the importance of considering them together. The first phase of the revised NAAQS review pr ocess is the development of the integrated review plan. This document represents the current plan and specifies the schedule of the review, the process for conducting the review, and the key policy-relevant science issues that will guide the review. This plan will be submitted fo r review and comment to CASAC, other non-EPA scientists, and the public. The final integrated review plan will take in to account comments from
these entities. The second phase of the proce ss is the development of th e science assessment, which consists of the Integrated Science Assessment (ISA) for NOx and SOx and supporting details in
its annexes. The U.S. EPA’s National Center for Environmental Assessment (NCEA) along with contractor support is currently de veloping the annexes to the ISA. These annexes will contain aDecember 2007 1-9 comprehensive description and evaluation/assessment of the full breadth of the recent scientific literature pertaining to known and anticipated effects on public welfare associated with the presence of the NOx and SOx criteria polluta nt(s) in the ambient air, emphasizing the
information that has become available since the last review in order to refl ect the current state of knowledge. NCEA will then critically evaluate, integrate, and synthesize the most policyrelevant science from the annexes into an ISA. The ISA is intended to provide information useful in forming judgments about air quality indicator( s), form(s), averaging time(s) and level(s) for the secondary NAAQS. Hence, the ISA and its associated annexes function in the new NAAQS review in part as the Air Quality Criteria Do cument (AQCD) did in previous reviews. The schedule includes production of a first and seco nd draft ISA, both of which will undergo CASAC and public review prior to completion of the fi nal ISA. Section 4 provides a more detailed description of the planned scope , organization and assessment appr oach for the annexes and ISA, as well as EPA’s rationale for conducting a joint review of thes e criteria pollutants. In the third phase of the re vised review process, the ri sk/exposure assessment, OAQPS plans to draw upon the ISA to develop quantita tive and qualitative estimates of the risks of adverse welfare effects occurring as a result of current ambient levels of nitrogen oxides and sulfur oxides, levels that m eet the current standards for NO 2 and SO 2 , or levels that meet possible
alternative standards. Section 5 of this Plan co ntains more detail about possible approaches EPA could take in conducting the risk/exposure Asse ssment. Once the draft ISA is complete, EPA will release a Scope and Methods Plan/document for CASAC and public review that describes the actual scope of the analyses to be performe d and the tools/methods th at will be employed. Once the risk/exposure assessment is complete, a report will be developed that focuses on key results, observations, and uncertainties and may in clude results from specific analyses designed to inform the review. This risk/exposure asse ssment report will also undergo review by CASAC and the public. The fourth component of the revised pro cess will be a policy assessment/rulemaking. Under the revised NAAQS process, a policy a ssessment reflecting Agency views will be published in the Federal Register as an advan ce notice of proposed rulemaking (ANPR). The ANPR will be accompanied by supporting documents, such as air quality analyses and technical support documents, as appropriate. The ANPR take s the place of the Staff Paper prepared for previous NAAQS reviews. Issuance of a pr oposed and final rule will then complete the rulemaking process.December 2007 1-10 

### 1.4 SCIENCE PRIMER: NO X 

### /SO X 

### EFFECTS ON ECOSYSTEMS The following section is intended to provide a brief summary of the generally-accepted effects of NOx and SOx pollution on ecosystems. The information presented here is drawn from the last NOx (1995) and SOx (1996) NAAQS reviews as well as from more recent peer-reviewed scientific literature. Nitrogen and sulfur interactions in the envi ronment are highly complex. Both are essential, and sometimes limiting, nutrients needed for growth and productivity. Excesses of nitrogen or sulfur can lead to acidification, nu trient enrichment, and eutrophication. Nitrogen effects occur along a continuum, from growth-enhancing fertil ization to growth-depressing conditions associated with varying levels of nitrogen inputs. The excess nitrogen deposition
described here results when av ailable nitrogen cannot be assi milated by the existing vegetation or immobilized by the soil buffering capacity.
Emissions of NOx and SOx compounds into the air reac t through a complex series of gasphase and heterogeneous reactions to produce additional intermediate compounds and final products. These reactions with NOx and SOx often occur and under the same meteorological influences as those acting on formation of ozone (O 3 ) and secondary aeroso ls. These nitrogenand sulfur-containing compounds are removed from the air by deposition – wet (rain, snow), cloud and fog, and dry (gases and particles) -- onto surfaces. Prevailing winds can transport these compounds hundreds of miles and acr oss state and national borders. Deposition of other chemical species deri ved from NOx and SOx emissions to the environment can initiate changes in ecosystem biogeochemistry, structur e, and function. Since
both NOx and SOx emissions can react in the a tmosphere to form strong acids, one of the possible environmental endpoints is acidification. Acidification results in a cascade of effects that alter biogeochemical cycles and harm te rrestrial and aquatic ecosystems. These effects include slower growth, the injury or death of forest vegetation, and localized extinction of fish and other aquatic species. Ac id deposition can also cause ac celerated erosion of exposed materials and structures, such as buildings and statues. In addition to acidification, NOx acts with ot her sources of reactiv e nitrogen, including ammonia-based nitrogen, to increase the total amount of nitrogen available to the organisms in terrestrial and aquatic ecosystems. Depending on the ecosystem and the endpoints that are of concern, this extra nitrogen can be considered to have both positive and negative effects. For example, low-level chronic nitroge n deposition can act as a fertilizer and increase productivity inDecember 2007 1-11 terrestrial forests, but this extra nitrogen may change the species composition of the understory plants and lichens. At high levels of nitrogen deposition there may be negative effects on forest productivity. In general, ecosystems adapted to low nitrogen availability are most vulnerable to the effects of nitrogen deposition. Excess nitroge n to vulnerable ecosystems can cause “Nitrogen pollution,” resulting in a suite of terrestr ial and aquatic ecologi cal problems including biodiversity losses, community shifts, eu trophication, and harmful algal blooms. L astly, SOx interacts with mercury (Hg) in ecosystems to increase the production of methylmercury, a powerful toxin that bioaccumulates, often to the point of causing toxic doses to top members of food chains (e.g., river otters and panthers). A summary illustration of NOx and SOx effects on the environment is presented in Figure 1.1.December 2007 1-12 Figure 1.1 Nitrogen and Sulfur cy cling and interactions in the environment.



### 1.4.1 Acidification Effects on Freshw ater and Terrestrial Ecosystems from Sulfur and Nitrogen Deposition

The process of acidification a ffects both freshwater aquatic and terrestrial ecosystems. Acid deposition causes acidification of sensitive surface waters. The effects of acid deposition on aquatic systems depend largely upon the ability of the ecosystem to ne utralize the additional acid. As acidity increases, aluminum leached fr om soils and sediments, flows into lakes and
streams and can be toxic to both terrestrial and aquatic biota. The lower pH concentrations and higher aluminum levels resulting from acidifica tion make it difficult for some fish and other aquatic organisms to surviv e, grow, and reproduce.
Research on effects of acid deposition on forest ecosystems has come to focus increasingly on the biogeochemical processes th at affect uptake, rete ntion, and cycling of nutrients within these ecosystems. Decreases in available base cations from soils are at leastDecember 2007 1-13 partly attributable to acid depos ition. Base cation depletion is a cause for concern because of the role these ions play in acid neutralization and, because calciu m, magnesium and potassium are essential nutrients for plant growth and physiolog y. Changes in the rela tive proportions of these nutrients, especially in comparison with aluminum concentrations, have been associated with declining forest health.



### 1.4.2 Excess Nitrogen in Terrestr ial and Estuarine Ecosystems

In addition to acidification effects, NOx c ontributes to total nitrogen loading of ecosystems. In terrestrial systems, too much n itrogen can affect species diversity by favoring plant species with high nitrog en requirements over other species which may have evolved specialized capabilities to thrive under more nitrogen-limited c onditions. Elevated soil nitrogen tends to cause changes in the abil ity of invasive species to col onize, biodiversity, and community structure. Animals that depend on specific plants for habitat and food may also be threatened by changes in vegetation resulting from increased nitrogen inputs. Atmospheric deposition of nitrogen is a si gnificant source of to tal nitrogen to many
estuaries in the United States. The amount of nitr ogen entering estuarie s that is ultimately attributable to atmospheric deposition is not well-defined. On an annual basis, atmospheric nitrogen deposition may contribute significantly to the total nitrogen loa d, depending on the size and location of the watershed. In addition, episod ic nitrogen inputs, which may be ecologically important, may play a more important role than indicated by the annual average concentrations.
Estuaries in the U.S. that suffe r from nitrogen enrichment ofte n experience a condition known as eutrophication. Symptoms of eutrophication in clude changes in the dominant species of phytoplankton, low levels of oxygen in the water co lumn, fish and shellfish kills, outbreaks of toxic alga, and other population changes wh ich can cascade throughout the food web. In addition, increased phytoplankton growth in the water column and on surfaces can attenuate light causing declines in submerged aqua tic vegetation, which serves as an important habitat for many estuarine fish and shellfish species. 

### 1.4.3 Reduced Nitrogen

Although this review must initially address NOx, it appears evident that total reactive nitrogen (i.e., both oxidized and reduced forms of nitrogen) is important from an ecosystem effects perspective. As such, the interactions between reduced forms of nitrogen (namelyDecember 2007 1-14 ammonia, NH 3 , and ammonium, NH 4 + ) and NOx and SOx in the atmosphere and associated deposition processes will be considered. Ammoni a is an additional source of nitrogen to the environment that contributes to the problems caused by excess nitrogen deposition — nutrient enrichment and eutrophication. Ammonia can al so contribute to increasing soil acidity via nitrification, the microbially-mediated transforma tion of ammonium to nitrate. The atmospheric lifetime of gas-phase ammonia is on the order of a day; however, in the presence of sulfuric or nitric acids, ammonia can form aerosols, pr edominantly ammonium sulfate and ammonium nitrate, with lifetimes on the or der of 7-10 days. This longer life time increases th e potential for long-range transport of nitrogen and sulfur, and contri butes to fine partic ulate matter pollution and regional haze. Ammonium sulfates and nitr ates also participate in climate modification effects, directly through radiativ e cooling by light sca ttering and indirectly through modifications of cloud cover and precipitation by acting as clou d condensation nuclei. A detailed discuss of these processes is included in the PM review.December 2007 2-1 

## 2. REVIEW SCHEDULE

EPA’s National Center for Environmental Asse ssment in Research Triangle Park, NC (NCEA-RTP) announced the official initiation of the current periodic re view of air quality criteria for NOx on December 9, 2005 and for SOx on May 15, 2006. For each of these reviews, the Agency began by announcing in the Federa l Register (70 FR 73236 and 71 FR 28023) the
formal commencement of the review and a call for information. With these reviews underway, a workshop addressing the separate, joint review of just the sec ondary standards for these two pollutants was announced in the Federal Regi ster on June 20, 2007 (72 FR 11960). The proposed schedule for this joint review pr ocess is shown in Table 2-1; unde rlined dates indicate the courtordered schedule. Table 2-1. Proposed Schedule for Joint NOx and SOx Secondary Standard Review 1 Stage of Review Major Milestone Target Dates Literature Search Ongoing Federal Register Call for Information December 2005 Prepare Draft NO 2 /SO 2 NAAQS Work Plan December 2005-August 2007 Workshop on science/policy issues July 2007 CASAC consultation October 2007 Planning

Prepare final integrated NO 2 /SO 2 NAAQS Work Plan December 2007

Prepare first draft of ISA December 2007 CASAC/public review first draft ISA April 2008 Prepare second draft of ISA July/August 2008 CASAC/public review second draft ISA October 2008 Integrated Science Assessment (ISA)

Prepare final ISA December 12, 2008 REA methodology released to CASAC and the public January 2008

CASAC/public consultation on REA methodology April 2008 First draft REA released to CASAC and the public August 2008 CASAC/public review of the first draft of the REA October 2008 Second draft of REA released to CASAC and the public March 2009

CASAC/public review of second draft of REA May 2009 Risk/Exposure Assessment (R/EA)

Final REA released July 2009 Publish ANPR August 2009 CASAC review/public comment on ANPR October 2009 Proposed rulemaking February 12, 2010 Policy Assessment/ Rulemaking

Final rulemaking October 19, 2010

1 Schedule may be modified from time to time, as necessary, to reflect actual project requirements and progress.December 2007 3-1 

## 3. KEY POLICY-RELEVANT ISSUES

In this review of the ecosystem-related e ffects on public welfare related to NOx and SOx, a series of policy-relevant questions will frame our approach and will be addressed in detail in the science assessment, risk/expos ure assessment, and policy assessm ent sections of the review. For this first time in the NAAQS review proce ss, the secondary standards for NOx and SOx will be reviewed together due to the pollutants’ combined effects on atmospheric chemistry, deposition processes, and ecosystem-related public welfare effects. As a result, the issue of appropriate indicators becomes central to the review of the standards. This review will evaluate what appropriate indicators are for NOx and SOx, if these indicators should be combined into one standard, if separate standards should be issued, or if a su ite of standards should be issued. In evaluating environmental responses to these pollu tants, the variability present in ecosystems
across the nation should also be considered. Issues of ecosystem susceptibility should be addressed, as should the issue of whether individual effects or combined effects are more important to a given ecosystem (i.e., is it NOx or SOx alone or the combination that is important). As noted in the introduction, both EPA a nd CASAC have acknowledged the importance of NOx, SOx, and their associated transformation products with re spect to acidification effects on ecosystems. This review will focus on the ecos ystem-related welfare effects that result from the deposition of these pollutants and their transformation products, rather than on the effects of aerosol NOx and SOx that remain in the atmosphe re. The issues associated with NOx and SOx particles; including visibility im pairment and climate associated with ambient concentrations of particulates and aerosols are bei ng addressed in the secondary PM NAAQS review, which is also currently underway. The review of the adequacy of the current standard for each effects category involves addressing questions such as:

• To what extent does the available inform ation demonstrate or suggest that NOx/SOxrelated effects are occurring at current ambien t conditions or at levels that would meet the current standards? • To what extent does the available inform ation inform judgment s as to whether any observed or anticipated effects are adverse to public welfare? • To what extent are the current secondary st andards likely to be e ffective in achieving protection against any identified adverse effects?December 2007 3-2 To the extent that the evidence suggests that revision of the current secondary NO 2 /SO 2 NAAQS is appropriate, ranges of st andards will be identified (i ncluding different or alternate indicators, terms of exposure indi ces, averaging times, levels, and forms) that reflect a range of alternative policy judgments as to the degree of protec tion that is requisite to protect public
welfare from known or an ticipated adverse effects. To acco unt for variability in ecosystem responses across the nation, ecosystem characteris tics may be an important consideration in evaluating the form(s) of the standard(s). The form(s) of the standard(s) may be based on a complex formula that incorporates ecosystem characteristics, atmospheric transformations, climatic conditions, environmental effects and ot her interactions. In so doing, the following questions should be addressed:
• Does the available information provide support for considering different NOx/SOx chemical indicators or exposure indices? • Does the available information provide support for considering some joint standard(s) or are separate st andards appropriate? • What range of levels a nd forms of alternative sta ndards are supported by the information, and what are the uncertainties and limitations in that information? • To what extent do specific levels and fo rms of alternative standards reduce adverse impacts attributable to NOx/SOx, and what are the uncertainties in the estimated reductions?

In order to be able to answer these questions, we believe that the relevant scientific issues that need to be addressed in the science, risk /exposure, and policy assessment portions of this
review include:
• identifying important chemical species in the atmosphere • identifying the atmospheric pathways that govern chemical transformation, transport, and deposition of NOx and SOx to the environment • identifying the attributes of ecosystem r eceptors that govern their susceptibility to effects from deposition of nitrogen and sulfur compounds • identifying the relevant time scales of eco system impacts and matching those time scales to relevant time s cales for ambient indicators • describing the relationships between ambi ent indicators and bi ologically relevant indices of effects, including ecosystem servi ces associated with th e indicator (but not excluding other non-economic evaluations) • evaluating alternative measures to assess th e adversity of effects on ecosystem services, including, for example, economic valuationDecember 2007 3-3 • evaluating if current levels may have a l ong-term impact due to cumulative loadings, and if this is releva nt to a NAAQS review • evaluating environmental impacts and sensitiv ities to varying mete orological scenarios and climate conditionsDecember 2007 4-1 

## 4. SCIENCE ASSESSMENT

4.1 SCOPE AND ORGANIZATION The scope of the joint NO X and SO X ISA is limited to welfare topics that do not duplicate those addressed by the part iculate matter (PM) science a ssessment. The welfare effects of visibility impairment and climate inte ractions associated with particulate NO X and SO X will be addressed within the secondary PM NAAQS review, as these pr ocesses occur via NO X and
SO X residing in the particulate or aerosol phase and interact with other chemical components of PM. The issue of NOx as a tropospheric precurs or to ozone is discus sed in detail in the photochemical oxidant NAAQS re view (EPA 2006 and 2007). The effects of acidification and nitrogen-nutrient deposition on ecosy stems are the main focus of this assessment; however, other
welfare effects are discussed. The science assessment will be organized in to the integrated science assessment (ISA) and its supporting annexes. The ISA will critic ally evaluate and integrate the scientific information on the exposure and environmental eff ects associated with atmospheric deposition of
NO x and SO x to provide a policy-relevant revi ew as discussed in Chapter 3 2 . The annexes, which
evaluate and summarize relevant st udies, will provide a detailed basis for developing the ISA. The annexes will evaluate over a thousand publis hed papers. Key findings will be summarized and integrated by discipline, pollutant impact or assessment endpoint pe rtinent to decisions on possible revision of the NO 2 and SO 2 secondary NAAQSs. Although emphasis will be placed on the presentation of environmental effects data, other scientific data will also be presented and evaluated in order to provide a better understa nding of the nature, s ources, distribution, measurement, transformations , and concentrations of NO x and SO x in ambient air and in various environmental compartments
The focus of the ISA and its annexes will be literature published since the previous reviews of air quality criteria for NO x and SO x . Key findings and conclusions from the previous Air Quality Criteria Documents (AQCDs) will be briefly summarized at the beginning of the ISA. The results of recent studies will be integr ated with previous findi ngs. Important older studies will be more specifically discussed if they are open to reinterpreta tion in light of newer

2 Note that evidence related to human health effects of NO x and SO x will be considered in two separate science assessment documents that will prepared as part of the review of the primary NAAQS.December 2007 4-2 data. Generally, only information that has under gone scientific peer review and that has been published (or accepted for publication) in the ope n literature will be considered. However, exceptions may be made depending on the impor tance of the subject information and its
relevance to the review of the NO 2 and SO 2 secondary NAAQS, as determined in consultation
with CASAC. Emphasis will be placed on studi es conducted at or near NO x and SO x concentrations
found in ambient air. Other stud ies may be included if they cont ain unique data, such as the documentation of a previously unreported effect or of a mechanism for an observed effect; or if they were studies that included both higher a nd lower concentrations designed to determine exposure-response relationships.



### 4.2 ASSESSMENT APPROACH The NCEA-RTP is responsible for preparing the ISA and its annexes for NOx and SOx. Expert authors include EPA st aff with extensive knowledge in their respective fields and
extramural scientists contracted to the EPA.



### 4.2.1 Literature Search

The NCEA-RTP uses a systematic approach to identify relevant studies for consideration. A Federal Register Notice (FRN) was published on December 9, 2005 for NOx and on May 15,
2006 for SOx to announce the initiati on of this review and request information from the public. An initial publication base has been establishe d by searching various databases using as key words the terms nitrogen oxides (NO x ), nitrogen dioxide (NO 2 ), nitric acid (HNO 3 ), peroxyacytyl nitrate (PAN), ammonia (NH 3 ), total reactive nitrogen, atmos pheric deposition of nitrogen and sulfur, terrestrial ecosystems, aquatic ecosystems, wetlands, etc. This search strategy will periodically be reexamined and modified to enha nce identification of pert inent published papers. Additional papers are identified for inclusion in th e publication base in several ways. First, EPA staff reviews pre-publication tabl es of contents for journals in which relevant papers are published. Second, expert chapter authors are char ged with independently identifying relevant literature. Finally, additional publications ar e identified by both the public and CASAC during the external review process. The studies iden tified will include research published or accepted for publication by a date determined to be as incl usive as possible given th e relevant target dates in the NAAQS review schedule. Some additional st udies, published after th at date, may also beDecember 2007 4-3 included if they provide new info rmation that impacts one or more key scientific issues. The combination of these approaches should produce a comprehensive collecti on of pertinent studies
needed to form the basis of the ISA.


### 4.2.2 Criteria for Study Selection

Emphasis shall be placed on studies that evalua te effects at realistic ambient levels and
studies that consider NO X and SO X as components of a complex mixture of air pollutants. Studies conducted in any country that contribute signi ficantly to the knowledge base shall be included in the assessment, but emphasis may be placed on findings from studies conducted in
the United States and Canada where differences in emissions and the air pollutant mixture are important. In assessing the relative scientific qua lity of studies reviewed here and to assist in interpreting their findings, the following considerations will be taken into account: (1) to what extent are the aerometric data/exposure metr ics of adequate quality and sufficiently representative to serve as cr edible exposure indicators; (2 ) were the study populations well defined and adequately selected so as to al low for meaningful comparisons between study groups; (3) were the ecological assessment endpoint s reliable and policy re levant; (4) were the statistical analyses used appropr iate and properly performed and interpreted; (5) were likely important covariates (e.g., potenti al confounders or effect modifi ers) adequately controlled or taken into account in the study de sign and statistical an alyses; and (6) were the reported findings internally consistent, biologically plausible, and coherent in te rms of consistency with other
known facts. These guidelines provide benchmarks for ev aluating various studies and for focusing on the highest quality studies in assessing the body of environmental effects evidence. Detailed critical analysis of all NO X and SO X environmental effects studies, especially in relation to the above considerations, is beyond the scope of the ISA and its Annexes. Of most relevance for
evaluation of studies is whethe r they provide useful qualitativ e or quantitative information on exposure effect or exposure res ponse relationships for environm ental effects associated with
current ambient air concentrations of NO X and SO X or deposition levels likely to be encountered
in the United States.December 2007 4-4 

### 4.2.3 Content and Organization of the ISA

The content of the ISA will be organized and developed to address the overarching policy-relevant questions listed in Chapter 3.
The scientific information in the ISA will be drawn from a series of more comprehensive
ISA annexes. The annexes will be focused on accom plishing two goals. The first goal will be to identify scientific research that is relevant to informing key policy issues . The second goal will be to produce a base of evidence containing all of the publications relevant to the review of the NOx and SOx secondary standards. Sections of the ISA annexes will include the following, not necessarily in this order: (1) Atmospheric chemistry of NO x and SO x ; emissions, transport, and transformations in the atmosphere
(2) Deposition processes of atmospherically derived NO x and SO x , ambient concentrations and the relationship between ambient concentrations and deposition
(3) Environmental response networks , monitoring networks and models; (4) Acidification effects of NO x and SO x on terrestrial and aquatic ecosystems (5) Non-acidification effects of NO x on terrestrial and aquatic ecosystems; (6) Non-acidification effects of SO x on terrestrial and aquatic ecosystems; (7) Impacts of NOx/SOx on ecosystems modified by climate change factors (8) Assessing the available information for pot entially determining critical loads to ecosystems (9) Effects of NO x and SO x deposition on acid-driven er osion of man-made materials and structures; and (10) Valuation of NOx and SOx effects on the environment.

The ISA will convey the reasoning used to selectwhich scientific studies are most policyrelevant. Detailed discussions of studies consid ered for the ISA, but not deemed most relevant, will be limited to the annexes. The ISA will integr ate scientific information from the 10 subject areas identified by the annexes into main topic ar eas. At this point we anticipate these sections to be Atmospheric Concentration and Depos ition, and Ecosystems. However upon further
evaluation of the literature Materials and Structur es Damage may be a third area of the ISA.

1. Atmospheric Concentration and Deposition : The ISA will evaluate what we know about the factors that influence deposition, the unc ertainties associated with extrapolation fromDecember 2007 4-5 ambient air concentrations to ecosystem expos ures to NOx and SOx, and spatial patterns of NOx and SOx deposition. Specific ques tions include, but are not limited to:

a. How are uncertainties described when extrapolating between stationary monitoring instruments and ecosystem exposure?

b. What is the spatial distribution of NOx a nd SOx on a national scale? What are the most effective means of using our observ ations and predictive models to address spatial, temporal and compositional dist ribution of nitrogen and sulfur? What additional information (observations, pr ocess formulations) would enhance our ability to quantify current exposur es and track changes over time?

c. How does reduced nitrogen (NHx) alter th e atmospheric chemistry, transport and deposition of NOx or SOx?

2. Integration of ecological evidence: The integration secti on will begin with an overview of three ecologic concepts that are important to cl arify at the onset of the discussion: scale, function and structure (organism to region) a nd ecosystem services. The integration of ecologic evidence will be organized according to impacts. These impacts are acidification (combined effects of NOx and SOx), nitrogen nutrient effects (NOx) and sulfur nutrient effects (SOx). With regard to nitrogen nutrient effects, it is important to note that ecosystems are typically sensitiv e to total reactive nitrogen (Nr) input. Therefore NOx is evaluated as a component of total nitrogen input from various anthropogenic sources. The following questi ons will be addressed for each ecological impact:

a. Is the biogeochemistry of ecosystems impacted and what are the chemical indicators of impact?

b. How are organisms impacted? Which biologi cal species are most sensitive? How is sensitivity defined?

c. What ecosystems are most sensitive to NOx and SOx pollution?

d. How does NOx and SOx pollution impact ecosystem services?

e. What new information is available on the le vels of deposition that can cause harm in ecosystems?

f. What are the most appropriate spatial and temporal scales to evaluate impacts on ecosystems?

g. What is the relationship between ecol ogical vulnerability and NOx and SOx pollution variations in current mete orology or gradients in climate?

h. Are there time lags to ecosystem “recove ry”? What are the physical, chemical and ecological characteristics of “recovery”?December 2007 4-6 

### 4.3 Public and Scientific Review
4.3.1 Informal Peer Consultation Workshop of the ISA Annexes

A combined peer review/polic y kickoff workshop was held in Chapel Hill, NC on July 17-19, 2007. This peer consultation workshop provi ded a forum for the authors of the ISA and
its annexes to receive comments from their scien tific peers on the first draft of their findings. Peer reviewers were given a copy of the chapte r they were assigned pr ior to the workshop and were asked to conduct an informal review by providing written comments on its scientific content. Each peer consultant was also as ked to participate in the workshop. Reviewers provided critical comments on the adequacy of the coverage of the literature, the presentation of
the evidence in both text and fi gures or tables, the appropriatene ss of the conclusions from the evidence and any new issues or lite rature that should be consider ed. At this workshop, expert reviewers were also asked to par ticipate in a discussion of the inte grative aspects of the evidence, to assist the EPA in subseque nt preparation of the ISA.



### 4.3.2 Public Review of External Review Drafts

Since the conclusion of the workshop review pr ocess, the authors, contributing reviewers, and NCEA-RTP Project Team have met to reso lve how to address comments received and will revise the draft annexes and complete preparatio n of the First External Review Draft (ERD) NO x and SO x ISA. After clearance by the U.S. EPA, th e draft document will be released for public comment as announced in a Federal Register No tice. The ERD will be made available for review during a specified time pe riod, usually of 60 to 90 days ; written comments are solicited during this time. A similar procedure will be followed for public and CASAC review of a Second External Review Draft that EPA expects to be necessary before completion of the Final
NO x and SO x ISA.



### 4.3.3 Review by Clean Air Scientific Advisory Committee

At the time the First External Review Draft is released to the public, that draft document
will also be sent to the Clean Air Scien tific Advisory Committee (CASAC) of EPA = s ScienceDecember 2007 4-7 Advisory Board (SAB). CASAC members and consultants (see Appendix A) will review the
draft document and discuss th eir comments in a public meeting announced in the Federal Register. At the meeting, the NCEA-RTP Project Team plans to present an overview of the main features of the document, a summary of key issues raised by public comments received on the document, and the charge to the committee, as well as being prepared to discuss proposed revisions, if indicated. Based on CASAC = s past practice, EPA expects that key CASAC advice and recommendations for revision of the document will be summarized by the CASAC Chair in
a letter to the EPA Administrator. EPA will take into account any such recommendations, as well as CASAC and public comments at the meeting and any written comments received, in revising the draft NO x and SO x ISA. As noted earlier, EPA exp ects that it will be necessary to prepare a Second External Review Draft for furt her CASAC review and public comment. After appropriate revision, the final document will be made available on an EPA website and subsequently printed, with its public availability being announced in th e Federal Register.December 2007 5-1 

## 5. RISK/EXPOSURE ASSESSMENT

The risk/exposure assessment for the NOx and SOx secondary NAAQS review will build upon the scientific information presented in the Integrated Science Assessment. As discussed earlier in this document, the risk/exposure assess ment will not focus on other welfare effects that might be associated with secondary pollutants associated with NOx and SOx. Depending on the results of the science assessment, air quality indi cators for these criteria pollutants that differ from the current indicators may be cons idered in the risk/exposure assessment. The risk/exposure assessment will evaluate potential alternative indices, in an attempt to quantify the relationship between ambient concentrations of NOx and SOx and potential welfare effects. To create these indices, we will evaluate exposures and impacts in various ecosystems with differing responses related to nitrogen and sulfur inputs. One possible approach, recommended by both CASAC and the NRC (2004) is considering the use of critical loads when evaluating secondary standards. Further, the risk/exposure assessment will use a variety of methods to assess the potential a dversity of impacts including th e effects of the pollutants on ecosystem goods and services, the degree to whic h ecosystem functions are impaired, long-term trends in specific ecosystems (where availa ble), and both economic and non-economic valuation of ecosystem services. Our ability to address thes e issues will enable us to determine the extent to which the current standards provide requisi te protection from a ny known or anticipated
adverse effects associated with ambient leve ls of NOx and SOx. Given that it is the
Administrator’s final decision as to whether an effect is signifi cantly adverse to warrant revising and/or replacing the current standa rds, or if the body of scientif ic evidence and assessment tools provide an adequate basis for supporting revised standards, the risk/exposure assessment will be designed to provide quantitative results which will best inform that decision. To evaluate the nature and magnitude of eco system responses associated with adverse effects, the risk/exposure assessment will examin e various ways to quantify the relationship between air quality indicators, de position of biological ly-accessible forms of nitrogen and sulfur, biologically-relevant indices relating deposition, exposure and effects on sensitive receptors and related impacts to ecosystem service(s). The ri sk/exposure assessment will evaluate the overall load to the system for nitrogen and sulfur as we ll as the variability in ecosystem responses to these pollutants and determining the exposure metric(s) that incor porates the temporal considerations (i.e. biologically-relevant ti meframes), pathways, and biologically-relevantDecember 2007 5-2 indices in order to maintain the functioning of these ecosystems. In addition, the risk/exposure assessment will attempt to address how sensitive ecosystems and their services affected by nitrogen and sulfur deposition may respond to variations in climatic elements such as temperature and rainfall. The scope of the risk/exposure assessment will depend in part on the answers to the following questions:

• What are the appropriate ge ographic scale(s) and/or time frame(s) for the risk assessment? Information that will be considered in addressing this question includes: national-scale mapping, case studies of sensitive ecosystems, identification of representative ecosystem types, air pollution gradient studies, a weight-ofevidence approach incorpor ating both qualitative and quantitative information on risk, and, perhaps, some combination of the above.

• How can regional variation of effects be taken into account? How should the risk/exposure assessment address acidificat ion and nutrient enri chment effects in different areas and ecosystem types (e.g., me sic, arid, mountain forests, alpine, and sub-alpine) at varying ambient concentra tions of nitrogen and sulfur compounds? Can differences in regional sensitivity to deposition be comple tely characterized by underlying physical or biological attributes?

• To what degree are assumptions suppor ted by the available science regarding linkages between pollutants in ambient ai r, deposition, and measurable ecosystem effects? What are the most useful metric s of both ambient pollution and the resulting effect?

• To what degree should the risk/exposure asse ssment take the potential for recovery into account in selecting data for qua litative and quantitative assessments?

• How can uncertainties be minimized and appropriately characterized?



### 5.1 ASSESSMENT APPROACH There are a variety of ways to address the risk/exposure assessment for the review of the secondary NAAQS for NOx and SOx. One of the pur poses of this document is to solicit ideas and evaluate the most appropriate way to approach this review. In order to assess risks to public welfare due to ambient nitrog en and sulfur deposition, the re lationships (and associated uncertainties) between ambient concentrations, de position, environmental effects, environmental receptors, and ecosystem services and ecosystem valuation should be established. Some of our preliminary ideas for the risk/exposure assessment ar e outlined below. A de tailed description of
the tools mentioned here and others that are currently available are described in detail in Appendix B.December 2007 5-3 Understanding the atmospheric chemistry and de position of nitrogen a nd sulfur is central to this review. Most likely, we will use the Co mmunity Multi-Scale Air Quality (CMAQ) model (and derivative models such as the response-surf ace model) described in Appendix B to estimate ambient concentrations and deposition areas. Any assessment of atmospheric chemistry and deposition is highly-dependent on the variability associated with baselin e inputs. Consideration will be given to analyzing five consecutive years of CMAQ outputs (2001-2005) delivered as part of EPA’s Interagency Agreement with CDC to improve understanding of baseline deposition and the relationships between nitrog en and sulfur concentration and deposition in terms of magnitude and spatial relationships. Initially we plan to conduct regression a nd related statistical an alyses to generate statistical correlations between grid-level ambient concentrations of NOx and SO 2 and grid-level or appropriately spatially averag ed (e.g., at the watershed level) deposition rates of sulfur and nitrogen. The regression analysis will use the results from the 2001-2005 CMAQ simulations conducted for the joint EPA/CDC project. The analysis will use linear and non-linear regression modeling, as well as spatial regre ssion techniques, to develop re duced form equations. To the extent that data are available, the statis tical modeling may also incorporate relevant meteorological and physical attr ibutes, e.g. precipitation, rela tive humidity, wind speed and direction. These statistical relationships are not expected to provide predictive models. Rather, the goal is to develop appropriate estimates of the relationship between deposition metrics and
ambient levels of NOx and SOx.
Another central issue in this review is de termining which ecosystems are more or less sensitive to nitrogen and sulfur deposition. It may be useful to rank ecosystems (where data is available) based on a small subset of dete rminative underlying characteristics. These characteristics may include (but are not limited to ): (1) potential nitroge n and sulfur retention rates, (2) potential nitrogen and sulfur uptake rates, which might include vegetative uptake, potential denitrification, and pot ential mobilization of nitrogen a nd sulfur, (3) potential residence time based on local hydrology (precipitation rate s, conductivity) and geology (bedrock type, pervious surfaces, soil properties), and (4) total supply of nitrogen and sulfur including current and historical atmospheric deposition, and other non-atmospheric sources (such as fertilization, sewer leaks, point sources, etc.). Other ecosystem -specific characteristics, which may help assess sensitivities, include threatened and endangered species data wh ere available, land-use type (including Class I, National Parks and Fish and Wildlife Refuges and National WildernessDecember 2007 5-4 areas), and baseline nitrogen and sulfur lo ading estimates. Where ca se-study or ecosystemspecific data are available, a subset of maps for the case-study region may be created. Complementary to these efforts, we may use sta tistical cluster analysis to group ecosystem units into similar sets. By clustering ecosystems togeth er, we may reduce the number of locations that need to be modeled to adequately characterize the variability in ecosystem response to changes in nitrogen and sulfur deposition. These types of analyses may aid in determin ing if case studies might be appropriate for looking at nitrogen and sulfur effects on various ecosystems and geographic regions as a means of extrapolating these impacts to the entire country. For those ar eas where data are available, watershed models (e.g., MAGIC, PnET-BGC, and DayCent-Chem) ma y be useful for evaluating the emission-deposition-ecosystem response linkage. (These models are desc ribed in more detail in Appendix B.) As the integrated science asse ssment and risk/exposure assessment progress, we anticipate identifying additional ways to evaluate biologically-relevant indicators and ecosystem valuation techniques that will ultimately help to direct and focus the final Risk Assessment.



### 5.2 TOOLS FOR RISK ASSESSMENT In order to develop a risk analysis for a meaningful nationwide or ecosystem-specific metric, some of the available analytical tools for conducting a risk assessment are described/summarized in Appendix B. The more detailed model evaluation discussion included in the annexes and ISA will aid in selecting the a ppropriate modeling tools. With these tools, the risk/exposure assessment should be able to dete rmine the appropriate en dpoint(s)/indi cator(s), geographic level/scale of prot ection, national or case-study modeling, and which ecosystem services are important.



### 5.3 KNOWLEDGE GAPS
As discussed above and in detail in Appendix B, the risk /exposure assessment will use simulation models of atmospheri c emissions, transformation, fate , transport, and deposition to follow emissions from a source to a receptor, either aquatic or terrestrial. We plan to overlay
available data sets related to de position and adverse impacts with GIS-based approaches to aid in the evaluation of their spatial correlations. We also have published a nd evaluated regional or area-specific models that will aid in evaluating ecosystem effects in specific watersheds (i.e., for the Chesapeake Bay or the Adirondack mountains ). Additionally, we are beginning to quantifyDecember 2007 5-5 ecosystem services and the benefits they provide . However, there are knowledge gaps in the linkages between these areas. Some of the main questions the risk/exposure assessment will try to answer are, “If we can identify appropriate biological ly relevant indices, can we es tablish a link between deposition of NOx and SOx and ecosystem response? Additiona lly, what ecosystem services are associated with changes in emissions?” Answering these qu estions raises other issu es regarding the links between atmospheric deposition and an ecosyst em response, and ecosystem services and emissions changes. Some of th ese questions ar e listed below.

Atmospheric Deposition, Fate, and Transport Modeling
• What are typical uncertainties for observed and regional model estimates of wet and dry NOx, NHx, and SOx deposition rates? • Can deposition models be used to estimate deposition (wet, dry, cl oud, fog) to a landuse specific surface, such as mountainous te rrain, coniferous/deci duous forests, etc? • If not, are there models that can take th is output and estimate deposition to specific ecosystems?

Ecological Response Modeling
• Do we have sufficient data to develop dose-response functions linking changes in nitrogen and sulfur deposition to changes in ecosystem functions? • Can we adequately characterize the uncer tainties in these do se-response functions? • Can ecosystem-specific models be used to represent similar ecosystems nationwide? What are the uncertainties associated with the transferability between a specific watershed model to multiple watersheds?

Ecosystem Services
• Can the current known ecological responses be translated into an ecosystem service or services? • Can we value the changes in ecosystem serv ices associated with changes in ecological indicators? • Can a process-based model serve to link multiple ecosystem services in order to assess the ‘true’ impact of air quality on th e ‘bundles of services’ provided by that ecosystem? • How can we show that reducing emissions of NOx/SOx results in a specific ecosystem benefit?December 2007 5-6 Valuation

• What does the current valuation literature indicate about the values of change in ecosystems and the services they provide? • Are there other methods for developing non-monetized value estimates? • How do we link ecosystem responses and eco system services and how do we value the changes in those services?



### 5.3 PUBLIC AND SCIENTIFIC REVIEW Drafts of the risk/exposure assessment will be reviewed by CASAC of EPA’s Science Advisory Board (SAB). CASAC members and consultants (see Appendix A) will review the
draft document and discuss th eir comments in a public meeting announced in the Federal Register. Based on CASAC’s past practice, EPA expects that key CASAC advice and
recommendations for revision of the document will be summarized by the CASAC Chair in a
letter to the EPA Administrator. In revi sing the draft risk/expos ure assessment for NO x and SO x , EPA will take into account any such recommendations. EPA will also consider comments received, from CASAC or from the public, at the meeting itself and any written comments received. EPA anticipates preparing a second draft of the risk/exposur e assessment for CASAC review and public comment. After appropriate revision, the final doc ument will be made available on an EPA website and subsequently printed, with its pub lic availability being announced in the Federal Register.December 2007 6-1 

## 6. POLICY ASSESSMENT

Based on the information in the ISA and the risk/exposure assessment, the Agency will develop an advance notice of proposed rulemaking (ANPR) that reflects EPA’s views regarding the need to retain or revise the secondary NAAQS for NO 2 and SO 2 . The ANPR will identify conceptual evidence-based and risk/exposure- based approaches for reaching public welfare policy judgments. It will discuss the implicatio ns of the science and risk/exposure assessments for the adequacy of the current standard, and it will present risk/exposure information associated
with alternative standards. The ANPR will also describe a range of policy options for standard setting including a description of the underlying interpretations of the scientific evidence and risk/exposure information that might support such alternative standards and that could be considered by the Administrator in making NAAQS decisions. The use of an ANPR will provide an opportun ity for CASAC and the public to evaluate the policy options under consideration and to offer comments and recommendations to inform the development of a proposed rule. Taking into account CASAC advice and recommendations as well as public comment on the ANPR, the Agency will pub lish a proposed rule. This proposal will be followed by a public comment period. Taking into account comments received on the proposed rule, the Agency will then issue a final rule to complete the rulemaking process. A final decision must draw upon scientific ev idence and analyses about effects on public welfare and the nature and magn itude of ecosystem responses that are understood to have adverse effects, as well as judgments about how to deal with the range of uncertainties that are
inherent in the scientific evidence and analyses. The Agency’s approach to informing these judgments is based on the recognition that the available public welfare effects evidence generally reflects a continuum consisting of ambient levels at which scientists generally agree that public welfare effects are likely to occur, and that at lower ambient levels the likelihood and magnitude of the ecosystem responses become increasingly uncertain. This evaluation should recognize that the e ffects of NOx/SOx compounds on aquatic and terrestrial ecosystems are di verse and occur over time as a result of de position, include
acidification and fertilization e ffects, are regionally specific, and occur through the atmospheric reactions, transport, and depos ition of NOx/SOx compounds emitte d from varied and ubiquitous sources. The links in the fate, transport, a nd deposition apply to both acidification andDecember 2007 6-2 fertilization (which is unde rstood to capture both eutrophi cation in aquatic systems and fertilization in terrestrial systems).
Other considerations in devel oping an indicator include usin g total reactive nitrogen as a biologically-relevant index for nutrient enrich ment. Total reactive nitrogen deposited (and transported) should be viewed in context of ba seline nitrogen availabil ity. Ecosystem impacts may differ due to form of nitrogen deposited (e.g. , oxidized vs reduced nitrogen), and the various forms of nitrogen deposited may be important in determining the form of the standard. Nitrogen deposition impacts also depend on soil characterist ics, species composition and competition, and soil composition. In aquatic ecosystems, the range of biologically-relevant indices for nitrogen sensitivity may include dissolved oxygen concentra tions, and the ratio of algae to diatoms. Acid neutralizing capacity (ANC) may be an appropriate biologically-rele vant index for acidification depending on the time scale being considered. Acidification measured by sulfate and nitrate concentrations can change relatively rapidly (ove r several years), while ANC can take decades to change and reach a new equilibrium depending on releases of sulfate and other acidifying components due to current emissions/deposition or release of soil constituen ts including sulfate. The short-term effects from acid pulses may point to the need for a seasonal form of the standards. Nitrogen impacts th rough fertilization also have a seasonal component that may display a different pattern than that for acidifi cation. The need for seasonal standards will be evaluated, noting that impacts may differ by the water type and land use in different areas. Ecosystem recovery time may also play an importa nt role in determining the appropriate form and averaging time of standards. The policy determination of what is an adverse impact may vary, depending on the method chosen to assess adversity. The NAAQS provi sions in the Act require the Administrator to establish secondary standards that are requisite to protect p ublic welfare from any known or anticipated adverse effects associated with the pres ence of the pollutant in the ambient air. In so doing, the Administrator seeks to establish standards that are neither more nor less stringent than necessary for this purpose. The provisions do not require that secondary standards be set to eliminate all welfare effects, but rather at a leve l that protects public welfare from those effects that are judged to be adverse. In the evalua tion of ecosystem services and valuation as one potential measure of adversity, the assessment s hould consider the ecosystem benefits that are projected to occur as a result of reductions in the current standards.December 2007 7-1 

## 7. REFERENCES

Aber, J.D., S.V. Ollinger, and C.T. Drisco ll, Modeling nitrogen saturation in forest ecosystems in response to land use and atmospheric deposition, Ecol. Modell., 101 , 61- 78, 1997. Amar, P., R. Bornstein, H. Fe ldman, H. Jeffries, D. Steyn, R. Yamartino, and Y. Zhang. 2004. Final Report Summary: December 2003 P eer Review of the CMAQ Model. pp. 7. Balmford, A., A. Bruner, P.Cooper, R. Co stanza, and others. 2002. Economic reasons for conserving wild nature. Science 297 (5583): 950-953. Banzhaf, S. and J. Boyd. 2005. The architecture and measurement of an ecosystem services index. Decision Paper, RFF DP 05-22. Res ources for the Future, Washington, D.C. Boyd, J. and S. Banzhaf. 2006. What are ecosyst em services? The need for standardized environmental accounting units. Decision Pa per, RFF DP 06-02. Resources for the Future, Washington, D.C. Byun, D.W., and K.L. Schere. 2006. “Review of the Governing Equations, Computational Algorithms, and Other Components of the Mode ls-3 Community Multiscale Air Quality (CMAQ) Modeling System.” J. Applied Mechanics Reviews 59(2):51-77. The Acidic Deposition Phenomenon and Its Effect s: Critical Assessment Document (EPA, 1985) (53 FR 14935 -14936) The Acidic Deposition Phenomenon and Its Eff ects: Critical Assessment Review Papers, Volumes I and II (EPA, 1984) Cosby, B.J., Wright, R.F., Hornberger, G.M., and Galloway, J.N. 1985a. Modelling the Effects of Acid Deposition: Assessment of a Lumped Parameter Model of Soil Waterand Streamwater Chemistry.” Water Resour. Res. 21:51-63. Cosby, B.J., Wright, R.F., Hornberger, G.M. and Galloway, J.N.. 1985b. “Modelling theEffects of Acid Deposition: Estimation of Long-Te rm Water Quality Responses in a Small Forested Catchment.” Water Resour. Res. 21:1591-1601. Cosby, B.J., Hornberger, G.M., Galloway, J.N ., and Wright, R.F. 1985c. Time scales of catchment acidification: a quantitative model for estimating freshwater acidification. Environ. Sci. and Technol

. 19, 1145-1149. Daily, G.C., S. Alexander; P. R. Ehrlich, L. Goulder, L J. Lubchenco, P.A. Matson, H.A. Mooney, S. Postel, S.H. Schneider, D. Tilman, and G.M. Woodwell. 1997. Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems. Issues in Ecology 1:1-18. Dennis, R.L., D.W. Byun, J.H. Novak, K.J. Galluppi, C.J. Coats, and M.A. Vouk. 1996. “The next generation of integrated air quality modeling: EPA’s Models-3.” Atmospheric Environment 30:1925-1938. Department of Health, Education an d Welfare (DHEW). 1970. Air Quality Criteria For Sulfur Oxides. U.S. Governme nt Printing Office, Washington, D.C., AP-50. Galloway, J.N., Aber, J.D., Erisman, J.W., Seitz inger, S.P., Howarth, R.W., Cowling, E.B., and Cosby, B.J. 2003. The Nitrogen Cascade. BioScience. Vol.53.No.4. Gbondo-Tugbawa, S.S., C.T. Driscoll, J.D. Aber, and G.E. Likens, Evaluation of an integrated biogeochemical model (PnET-BGC) at a northern hardwood forest ecosystem, Water Resour. Res., 37 , 1057-1070, 2001.December 2007 7-2 Grell, G., J. Dudhia, and D. Stauffer, 1994: A Description of the Fifth-Generation Penn State/NCAR Mesoscale Model (MM5), NCAR/TN-398+STR ., 138 pp, National Center for Atmospheric Research, Boulder CO. Millennium Ecosystem Assessment. 2005. Ecosys tems and Human Well-being: Synthesis. Island Press, Washington, DC. NRC (National Research Council). 2004. Valui ng Ecosystem Services: Towards better environmental decision-making. Washingt on, DC: National Academies Press. 277 p EPA, 1973. “Effects of Sulfur Oxide in the Atmosphere on Vegetation”. Revised Chapter 5 of Air Quality Criteria For Sulfur Oxides. U.S. Environmental Protection Agency. Research Triangle Park, N.C. EPA-R3-73-030. U.S. EPA. Air Quality Criteria for Oxides of Nitrogen (1982). U.S. Environmental Protection Agency, Washington, D.C., EPA/ 600/8-82/026 (NTI S PB83131011), 1982. EPA, 1984. The Acidic Deposition Phenomenon and Its Effects: Critical Assessment Review Papers. Volume I Atmospheri c Sciences. EPA-600/8-83-016AF. Volume II Effects Sciences. EPA-600/ 8-83-016BF. Office of Research and Development, Washington, D.C. EPA, 1985. The Acidic Deposition Phenomenon and Its Effects: Critical Assessment Document. EPA-600/8-85/001. Office of Research and Development, Washington, D.C. EPA, 1993. Air Quality Criteria for Oxides of Nitrogen. Vol. I of III. EPA/600/8-91/048aF. Office of Research and Deve lopment, Washington, D.C. EPA, 1995. Acid Deposition Standard Feas ibility Study: Report to Congress. U.S. Environmental Protection Agency (1995) Review of the National Ambient Air Quality Standards for Nitrogen Dioxide: Assessment of Scientific and Technical Information. Office of Air Quality Planning and Standards, Research Triangle Park, N.C., EPA-452/R95-005. U.S. Environmental Protection Agency (EPA ). 1999. “Science Algorithms of EPA Models-3 Community Multiscale Air Quality.” (CMAQ Modeling System D.W. Byun and J.K.S. Ching, Eds. EPA/600/R-99/030, Office of Research and Development). U.S. Environmental Protection Agency. 2006a . Regulatory Impact Analysis for the 2006 National Ambient Air Quality Standards for Pa rticle Pollution. Office of Air Quality Planning and Standards. U.S. EPA. 2006b. Ecological Benefits Asse ssment Strategic Plan. EPA-240-R-06-001. U.S. Environmental Protection Agency, Washington D.C. U.S. Environmental Protection Agency. 2007. Re gulatory Impact Analysis of the Proposed Revisions to the National Ambient Air Qu ality Standards for Ground-Level Ozone. Office of Air Quality Planning and Standards. EPA-452/R-07-008, July. Wolff, G. T. (1993) CASAC closure letter fo r the 1993 Criteria Document for Oxides of Nitrogen addressed to U.S. EPA Administra tor Carol M. Browner dated September 30, 1993. Wolff, G. T. (1995) CASAC closure letter fo r the 1995 OAQPS Staff Paper addressed to U.S. EPA Administrator Carol M. Browner dated August 22, 1995. Yantosca, B. 2004. GEOS-CHEMv7-01-02 User’s Guide, Atmospheric Chemistry Modeling Group, Harvard University, Cambridge, MA, October 15, 2004.December 2007 A-1 

## APPENDIX A: CASAC PANEL

U.S. Environmental Protection Agency Science Advisory Board (SAB) Staff Office Clean Air Scientific Advi sory Committee (CASAC)

NO X and SO X Secondary NAAQS Review Panel
The Clean Air Scientific Advisory Comm ittee (CASAC) was esta blished under section 109(d)(2) of the Clean Air Act (CAA or Act) ( 42 U.S.C.7409) as an independent scientific advisory committee. CASAC provides advice , information and recommendations on the scientific and technical aspects of air quality criteri a and national ambient air quality standards (NAAQS) under sections 108 and 109 of the Act. The CASAC is a Federal advisory committee chartered under the Federal A dvisory Committee Act (FACA), as amended, 5 U.S.C., App. The Panel will comply with the provisions of FACA and all appropriate SAB Staff Office procedural policies. Section 109(d)(1) of the CAA requires that the Agency periodically review and revise, as appropriate, the air quality criteria and the NAAQS for the si x “criteria”' ai r pollutants, including NO X and SO X .

CHAIR Dr. Armistead (Ted) Russell , Georgia Power Distinguished Professor of Environmental Engineering, Environmental Engineering Group, School of Civil 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 C onsulting Inc., Boulder, CO
Dr. Douglas Crawford-Brown , Professor and Director, Departme nt of Environmental Sciences and Engineering, Carolina Environm ental Program, University of North Carolina at Chapel Hill, Chapel Hill, NC
Dr. Ellis B. Cowling , Emeritus Professor, Colleges of Natural Resources and Agriculture and Life Sciences, North Carolina St ate University, Raleigh, NC
Dr. Charles T. Driscoll, Jr. , Professor, Environmental Systems Engineering, College of Engineering and Computer Science, Syracuse University, Syracuse, NY

Dr. Paul J. Hanson , Distinguished R&D Sta ff Member, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TNDecember 2007 A-2 Dr. Rudolf Husar , Professor and Director, Mechanical Engineering, Engineering and Applied Science, Center for Air Pollution Impact & Tr end Analysis (CAPITA), Washington University, St. Louis, MO

Dr. Dale Johnson , Professor, Department of Environmen tal and Resource Sciences, College of Agriculture, University of Nevada, Reno, NV
Dr. Donna Kenski, Director, Lake Michigan Air Dire ctors Consortium, Rosemont, IL

Dr. Naresh Kumar , Senior Program Manager, Environm ent Division, Electric Power Research Institute, Palo Alto, CA
Dr. Myron Mitchell , Distinguished Professor and Direct or, College of Environmental and Forestry, Council on Hydrologic Systems Science, State University of New York, Syracuse, NY

Mr. Richard L. Poirot , Environmental Analyst, Air Polluti on Control Division, Department of Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT

Mr. David J. Shaw , Director, Division of Air Resources , New York State Department of Environmental Conservation, Albany, NY

Dr. Kathleen Weathers , Senior Scientist, Institute of Ecosystem Studies, Millbrook, NYDecember 2007 B-1 

## APPENDIX B: ASSESSMENT TOOLS

B.1 MODELS B.1.1 Community Multi-Scale Air Quality (CMAQ) Model

The CMAQ model is a three-dimensional grid-b ased Eulerian air quality model designed
to estimate the formation and fate of ozone and other oxidants and their precursors; primary PM and secondary particulate matter precursors and atmospheric concentrations; toxics; and deposition of chemical species over scales rang ing from continental to regional and urban to neighborhood (EPA, 1999; Byun and Schere, 2006; Dennis et al., 1996). The CMAQ model was peer-reviewed in 2003 for EPA as reported in “P eer Review of CMAQ Model” (Amar et al., 2004). CMAQ is most often configured to output sp atial fields of gridde d concentrations and deposition on an hourly basis for the entire modeling domain. Pollutant concentrations are output for each vertical layer included the m odel simulation. Additional information on the
horizontal and vertical c onfiguration of the model is provided below. The current version of CMAQ (v4.6) is capable of one atmosphere m odeling in which NOx, SOx, ozone, particulates, mercury, and selected toxic pollutants are incl uded in a model simulation. A list of the key nitrogen and sulfur containing deposition spec ies output by CMAQ is provided in Table B.1. This table also identifies the deposition speci es derived from CMAQ’s nitrogen and sulfur deposition outputs. The standard hourly CMAQ model predictions ar e post-processed to cr eate gridded fields of daily average, monthly average, and annual av erage concentrations for layer 1, which is the layer nearest to the ground. The hourly depositio n outputs are post-processed to produce gridded fields of daily, monthly, and annual total wet, dry and wet plus dry deposition.

Table B.1. Key Predicted and Derived Nitroge n and Sulfur Deposition Species from CMAQ 1

Predicted Deposition Species Derived Deposition Species Nitrogen Oxide (NO) Oxidized Nitrogen Nitrogen Dioxide (NO 2 ) Reduced NitrogenDecember 2007 B-2 Nitric Acid (HNO 3 ) Total Nitrogen Dinitrogen Pentoxide (N 2 O 5 ) Total Sulfur Peroxyacetyl Nitrate (PAN) Ammonia (NH 3 ) Sulfur Dioxide (SO 2 ) Particulate Sulfate (SO 4 ) Particulate Nitrate (NO 3 ) Particulate Ammonium (NH 4 )

1 Model predictions include both wet and dry deposition in units of kg/ha.

2002-Based Platform CMAQ Modeling EPA/AQAD is developing an air quality modeling platform that includes meteorology
and emissions 3 for 2002 along with projected emissions for 2009, 2014, 2020, and 2030. The future year projections reflect the combined effects of emissions growth and reductions associated with “national rules” up through the CAIR/CAMR/CAVR. CMAQ will be run for each of these five years for a 36 km nationw ide domain and for separate 12 km modeling domains covering the eastern and western U.S. The area covered by each of these domains is shown in Figure B.1. The domain specifications ar e provided in Table B.2. All three modeling domains contain 14 vertical layers with a top at about 16,200 meters, or 100 mb. Note that the
horizontal and vertical resolution selected for these simulations are not limited by the model. Rather, they were selected to ba lance (1) the desire to have a nnual nationwide simulations with fine scale resolution versus (2) the computational requirements of the simulations which increase
with horizontal and vertical resolution 4

. The CMAQ meteorological input files were de rived from simulations of the Pennsylvania State University / National Center for Atmosphe ric Research Mesoscale Model (Grell, Dudhia, and Stauffer, 1994). This model, commonl y referred to as MM5, is a limited-area, nonhydrostatic, terrain-following system that solves for the full set of physical and thermodynamic equations which govern atmospheric motions. The outputs from MM5 were processed to create model-rea dy inputs for CMAQ using the Me teorology-Chemistry Interface

3 Emissions inputs for to CMAQ include anthropogenic and biogenic emissions from areas of the U.S., Canada, and Mexico that are within the modeling domain. Anthropogenic emissions for the U.S. were derived from the 2002 National Emissions Inventory.December 2007 B-3 Processor (MCIP) version 3.2: horizontal wind components (i .e., speed and direction), temperature, moisture, vertical diffusion rates, and rainfall rates for each grid cell in each vertical layer (EPA, 1999). The lateral boundary and in itial species concentrations for the CMAQ 36 km domain were obtained from a three-dimensional global atmospheric chemistry model, the GEOS-CHEM model (Yantosca, 2004). The global GEOS-CHEM model simulates atmospheric chemical and physical processes driven by assimilated meteor ological observations from the NASA’s Goddard Earth Observing System (GEOS). This model was r un for 2002 with a grid resolution of 2 degree x 2.5 degree (latitude-longitude) and 20 vertical layers. The predictions were used to provide one-way dynamic boundary conditions at 3-hour inte rvals and the initial concentration field for the CMAQ simulations. The outputs from the 36 km domain are utilized to provide the initial and boundary condition concentrations fo r each of the two 12 km domains.

36km Domain Boundary

12km East Domain Boundary 12km West Domain Boundary

Figure B.1. Map of the CMAQ 36 km and 12 km Modeling Domains.

Table B.2. Geographic Specificat ions of Modeling Domains.

4 For various special studies, CMAQ has been run at 4 km and 1 km horizontal resolution for urban-scale domains and with a vertical resolution of over 30 layers.December 2007 B-4 36 km Domain (148 x 112 Grid Cells) 12 km Eastern Domain (279 x 240 Grid Cells) 12 km Western Domain (213 x 192 Grid Cells) Lon lat lon lat lon lat SW -121.77 18.17 SW -106.79 24.99 SW -121.65 28.29 NE -58.54 52.41 NE -65.32 47.63 NE -94.94 51.91



### B.1.2 Response Surface Models (RSM)

Air quality models can be a powerful regula tory tool for comparing the efficacy of
various emissions control strate gies, regulatory impacts and policy decisions. However, due to the often large computational costs and the co mplication of the required emission inputs and processing, using individual simula tions from photochemical air qua lity models to meet policy deadlines can be inefficient. A promising to ol for addressing this issue, Response Surface Modeling (RSM), has been developed by using advanced spatial stat istical techniques to characterize the relationship betw een model outputs and input para meters in a highly economical manner. The RSM aggregates numerous pre- specified individual air quality modeling simulations into a multi-dimensional air quality "response surface." Simply, this metamodeling technique is a “model of the model” and can be shown to reproduce the results from an individual modeling simulation with little bias or error. The RSM provides a wide breadth of model outputs that can be used to rapidly assess air quality impacts of different control measures and assist in the development of multi-pollutant c ontrol strategies. Spec ifically, the RSM can be used in a variety of ways: (1) strategy design and assessment (e.g. comparison of urban vs. regional controls; comparison across sectors; comparison across pollutants); (2) optimization (develop optimal combinations of controls to attain standard s at minimum cost); (3) model sensitivity (systematically evaluate the relativ e sensitivity of modeled air quality levels to changes in emissions inputs. Response surface models have been successfully applied in the context of the ozone and particulate matter regulatory impact analyses. In those contexts, the RSMs were used to explore the sensitivity of ambient ozone and PM concentr ations to changes in precursor emissions, for the purpose of designing strategi es to reduce ambient concentrations. Documentation of these applications can be found in the regulatory impact analyses (U.S. EPA, 2006a, 2007). Response surface models for nitrogen and su lfur deposition are in development and should be available to inform the Risk/Exposure Assessment. These models will allow us to explore the sensitivity of nitrogen and sulfur deposition for a number of different depositionDecember 2007 B-5 species (reduced and oxidized nitrogen, wet and dry sulf ur) to emissions of NOx, SO 2 , and NH 3 . The RSMs will also allow us to explore the chained relationships between emissions of NOx,
SO 2 , and NH 3 and ambient concentrations of NOx, NH x, and SOx, and the resulting changes in deposition. This will help to identify correlations or differences in the sp atial patterns of the response of ambient concentrations versus the response of deposition.



### B.1.3 Air Quest

AirQuest is a data management system. It st ores air data in a singl e location and delivers it to various tools and applications. The data in AirQuest can be accessed via SAS, Excel, MS Access, Google Earth, ArcGIS, and a cust omized web-based interactive map. AIRQuest was designed to serv e as a single source for inte grated, high quality, readily available air quality data, summaries, and statis tics from regulatory monitoring networks. In addition, AIRQuest represents an opportunity to leverage data pr ocessing and storage resources, since a fully functional AIRQuest will remove th e need for analysts to store large amounts of data on their desktops. In addition, by carefu lly defining and coming to agreement on business rules that define “the right way” to calculate air quality metrics, AIRQuest can ensure that every analyst has a consistent approach and consistent answers.


### B.1.4 Total Risk Integrated Methodology (TRIM)
The TRIM design includes thre e individual modules which have been the subject of peer review and publication. Two of th ese modules are applicable to ecological risk assessments. The Environmental Fate, Transport, and Ecological Exposure module, TRIM.FaTE, accounts for movement of a chemical through a comprehensive system of discrete compartments (e.g., media and biota) that represent possi ble locations of the chemical in the physical and biological environments of the modeled ecosystem and prov ides an inventory, over time, of a chemical throughout the entire system. TRIM.FaTE is a spatially explicit, compartmental mass balance model that describes the movement and transformation of pollutants ove r time, through a user-defined, bounded system
that includes both biotic and abio tic compartments. Outputs include pollutant concentrations in multiple environmental media and biota, and also biota and pollutant intakes (e.g., mg/kg-day), all of which provide exposure estimates for eco logical receptors (i.e., plants and animals).December 2007 B-6 Significant features of TRIM.FaTE include: (1 ) a fully coupled multimedia model; (2) user flexibility in defining scenarios, in terms of the links among compartments, and number and types of compartments, as appropriate for the application spatial and temporal scale; (3) transparent, user-accessible algorithm and input libra ry that allows the user to review and modify how environmental transfer and transformation pr ocesses are modeled; (4 ) a full accounting of all of the pollutant as it m oves among environmental compartments during simulation; (5) an embedded procedure to characterize uncertainty and variability; and (6) the capability to provide exposure estimates for ecological receptors.

In the Risk Characterization module, TRIM.Risk, estimates of human exposures or doses are characterized with regard to potential risk using the corresponding exposure- or doseresponse relationships. The TRIM.Risk module is also designed to charact erize ecological risks from multimedia exposures. The output from TRIM .Risk is intended to include documentation of the input data, assumptions in the analysis, and m easures of uncertainty, as well as the results of risk calculations and exposure analysis. The uncertainty and variability features (e.g., sensitivity & Monte Carlo analysis) augment TRIM's capability for performing iterative analyses. For example, the user may perform assessments varying from simple deterministic screening analyses usi ng conservative default parameters to refined and complex risk assessmen ts where the impacts of parameter uncertainty and variability are assessed for critical parameters.



### B.1.5 Regional Vulnerab ility Assessment (ReVA)

The Regional Vulnerability Assessment (ReVA) program conducts research on innovative approaches to the evaluation and inte rpretation of large and complex datasets and
models to assess the current conditions and likely outcomes of environmental decisions, including alternative futures. ReVA works with select client groups to develop research and demonstration pilots on how current data a nd appropriate models can be combined and interpreted across a geographic regi on to set management and ecosystem protection priorities and to proactively assess the outcomes of decisions that may impact multiple outcomes or involve tradeoffs in a transparent, defensible fashion. To date, ReVA has completed the developm ent of an environmental toolkit for EPA Region 3 and is actively engaged in developing tools for decision making that support urban andDecember 2007 B-7 interstate issues (SEQL), regional multipollutant i ssues that affect human health and ecosystems (Region 4), and multistate partnerships that aff ect the health of international environmental resources (Region 5/ Great Lakes).



### B.2 CASE STUDY MODELING Integrated assessment case studies provi de results for numerous environmental parameters, including emissions, atmospheric con centrations of pollutants, pollutant deposition to land and water surfaces, and changes in ecological parameters such as surface water chemistry, forest soil chemistry, or fish populations . In some cases, it may also be possible to link changes in ecological parameters to change s in ecosystem services, and ultimately to the economic value of the changes in ecosystem se rvices (which is one potential measure of adversity of effect). By comparing the e nvironmental impacts of existing programs with alternative policy scenarios, integrated assessments of this type provide estimates of the incremental ecological effects of potential policy changes. Th e process for assessing the ecological outcomes of different potential standards frequently focuses on relationships between pollutant emissions, pollutant deposition (the mean s of exposure for many aquatic and terrestrial ecosystems) and ecosystem response. Currently, analytical tools exist to analyze the emissiondeposition-ecosystem response linkage with part icular focus on two ecological parameters – surface water chemistry and forest soil ch emistry – in three case study areas:

• Northern New England lakes;

• Adirondack Mountain region lakes;

• Southern Blue Ridge region streams. The assessment approach involves several steps and employs various analytical and modeling tools that, once integrated, provide a m eans to assess ecological impacts. The National Emissions Inventory is used to develop emissions inventories for area, mobile, and point sources other than electricity generating utilities (EGU). The Integrated Planning Model (IPM) is used to develop emissions inventories for EGUs. The inventories specify profiles of emissions by pollutant, place, time, and source type for each policy scenario. Atmospheric models (e.g., CMAQ) employ the emissions inventory inputs to project changes in atmospheric concentrations and deposition of pollutants to land and water su rfaces. Ecological impacts, such as lake and stream water chemistry, or changes in forest so ils, are assessed by using watershed models (e.g., MAGIC, PnET-BGC). These models employ atmos pheric modeling output (deposition changes)December 2007 B-8 to project changes in the surface water chemistry of lakes and streams, or changes in forest soil chemistry, in regions that are se nsitive to atmospheric deposition of sulfur and nitrogen species. Ecological impacts of policy scenario implementa tion are then assessed using algorithms based on observed relationships between ecosystem ch emical parameters (e.g., acid neutralizing capacity, soil base saturation) a nd biological indicators of ecosystem health (e.g., fish species richness). Briefly, MAGIC is a lumped-parameter model of intermediate complexity, developed to predict the long-term effects of acidic deposition on surface wa ter chemistry (Cosby et al. 1985a,b,c, 2001). The model simulates soil solution and surface water chemistry to predict average concentrations of the major ions. MAGIC calculates for each time step (in this case year) the concentrations of major ions under the assumption of simultaneous reactions involving sulphate adsorption, cation exchange, dissolution- precipitation-speciation of aluminium and dissolution-speciation of inorganic and organi c carbon. MAGIC accounts for the mass balance of major ions in the soil by accounting for the fluxe s from atmospheric inputs, chemical weathering, net uptake in biomass and loss to runoff. At the heart of MAGIC is the size of the pool of exchangeable base ca tions in the soil. As the fluxes to and from this pool change over time owing to changes in atmospheric deposition, the chemical equilibria between soil and soil so lution shift to give changes in surface water chemistry. The degree and rate of change of surface water acidity thus depend both on flux
factors and the inherent characte ristics of the affected soils. Da ta inputs required for calibration of MAGIC comprise lake and catchment ch aracteristics, soil chemical and physical characteristics, input an d output fluxes for water and major ions , and net uptake of base cations by vegetation. PnET-BGC is a comprehensive forest-soil- water model developed by linking a monthly carbon, nitrogen, and water balance model PnET (A ber et al., 1997) with a soil model BGC to allow for comprehensive simulations of element cycling within forest and the interconnected aquatic ecosystems (Gbondo-Tugbawa et al., 2001). The model is able to simulate both abiotic processes and biotic processes. Especially th e representation of biomass accumulation and the associated element cycling enable the evaluation of land disturbance and climatic events on soil and water chemistry (Gbondo-Tugbawa et al., 2001). The model uses relatively simple formulations and requires a moderate number of inputs to quantify the acid-base status of soilDecember 2007 B-9 and surface waters under various levels of atmos pheric deposition; therefore it can serve both as a research and a management tool. Its simplic ity also makes it a good candidate for regional applications.



### B.3 ECOSYSTEM SERVICES: IMPACT AND VALUATION The final step of an integrated assessme nt of risks to the public welfare involves determining what level of ecosystem response transl ates into an effect that could reasonably be considered adverse to the public welfare. Ther e are a number of ways to do this, including



# · direct measures of quantities that are of known value to the public, e.g. numbers of endangered species,



# · direct economic valuation of ecosystem functions, including use and nonuse values (values that do not require an individual’s direct use of an ecosystem – for example, the value of preserving an endangered species habitat, even though that individual will ever see that species in the wild),



# · translation of ecosystem attributes into m easures of ecosystem services which can then be valued using economic valuation methods, and



# · direct non-economic valuation of ecosyst em functions based on enumeration of preferences using non-monetized indices of preferences.

Similar to other elements of the Risk/Expos ure Assessment, we are seeking input on the range of valuation methods that should be cons idered in helping to inform the discussion of adversity of ecosystem impacts.



### B.3.1 Ecosystem services overview and why their consideration is needed

One way to assess adverse effects on welfare is through valuation of ecosystem services.
The adverse effect would be the loss or reduction of t hose services through the effects of NOx and SOx on the underlying ecological processes and functions that constitute the service. The EPA defines ecosystem services as the outputs of healthy, intact ecosy stems and the underlying ecosystem processes and functions that contri bute to human well-bei ng (USEPA 2006b). As articulated by the Millenium Ecosystem Asse ssment (2005) from the United Nations, these include provisioning services (e .g., clean water, food, wood, fiber, fuel), regulating services (e.g., water purification, climate regula tion, etc.), supporting services (e.g. nutrient cycling, soilDecember 2007 B-10 formation), and cultural services (e.g. recreation, spiritua l) (Figure B.2). Regulating services are of key importance to the EPA because they direct ly impact air and water quality, and they have strong links to human heath and well-being. As such, valuation of ecosystem services may be one means of assessing whether an effect is a dverse. Valuation provides a means for evaluating different services. The valuation may be mone tized or non-monetized. Non-monetized measures of valuation include such things as quality of critical habitat, biodiversit y, species composition, control/limiting invasive species and pest outbreaks. Determin ing the exposure response relationships of NOx and SOx on the ecosystem service and the underlying ecological process and function will provide a broader focus in determination of adverse impacts. Figure B.2. Ecosystem services as defined by th e Millennium Assessment and their linkage to human well being (From Millennium Assessment, 2005).



### B.3.2 Ecosystem services relating to NOx/SOx secondary standard issues

Ecosystems provide services through a comple x web of ecosystem processes that create and sustain the services. For example, if we are interested in how terrestrial and riparianDecember 2007 B-11 ecosystems can help regulate nitrogen inputs to aquatic systems, we s hould consider all the nitrogen transformations and flow paths with in these ecosystems (Figure B.3). Ecosystem processes can help mitigate adverse effects from environmental stressors, but processes can also be negatively affected by environmental stressors , decreasing the amount of ecosystem services they provide. For example, plant nutrien t uptake and microbial denitrification and
immobilization decrease the nutri ent content in soil water, decreasing the potential for leaching into aquatic systems. Environmental stressors that decrease plant grow th can increase nutrient flows to aquatic systems. The web of ecosystem processes that influe nce the regulation of nitrogen transport to aquatic systems will also affect other ecosystem services such as carbon sequestration, so that management activities that alter these processes will affect a bundle of services, not just one. The impact of a land-use change will not have th e same impact on all of the ecosystem services; while one ecosystem service may be improved by a land-use change, it may come at a cost of decreasing another ecosystem service. Food production is a classic example of tradeoffs between ecosystem services. A dding fertilizer to crops will increase food production but may decrease water quality as some fertilizer ends up in the waterways. Thus, when ecosystems services are quantified, it is impe rative that the entire bundl e of services is evaluated, and that the tradeoffs between ecosystem services be included in the quantification.December 2007 B-12 Figure B.3. The Nitrogen Cascade illustrates th e complexity of pools and processes at the watershed scale that are interconne cted with the addition of nitrog en to the system, and with the output of the system in terms of ecological serv ices to benefit man. Adapted from, Galloway et al. 2003 (Ecological Research Program Strate gic Directions, ORD, April 2007, Preliminary Draft)

Energy production NO x

People (food; fiber) Ozone effects

NH x

Terrestrial Ecosystems

N or g anic

Groundwate r effects Particulate Matter effects Stratospheri c effects N 2 O Atmosphere

Food production

Surface wate r effects

Ocean effects NH 3

A quatic Ecosystem s NO 3 Soil Agroecosyste m effects

Soil Crop A nimal Forests & Grasslands

effects

Indicates denitrification potentia l Coastal effects NH x NO y NO x Greenhouse effects N 2 O

N 2 O (terrestrial)

Galloway et al., 2003December 2007 B-13 

### B.3.3 Valuation

While not the sole means of assessing adve rsity of effect, ecological improvements can benefit people indirectly by increasing the deli very of “ecosystem services,” which are the end products of ecological functions important to humans (Daile y 1997, Balmford et al. 2002, NRC 2004, Banzhaf and Boyd 2005, Boyd and Banzhaf 2006) . Such valuable ecological functions
include the maintenance of stable climate cond itions, the regulation of water availability and quality, and nutrient retention (Dailey 1997). Through their e ffect on ecosystem services, ecological improvements may lead to improved agricultural yields, re creational opportunities, human health or other types of benefits. For ex ample, protecting wetlands and the natural flow regulation and water purification se rvices they provide may lead to enhanced recreational fishing or swimming opportunities in connected wa ter bodies, reduced flooding in downstream residential areas, or reduced incidences of illne ss from contaminated drinking water. Ecological improvements may also benefit people direct ly through aesthetic im provements or through increases in “nonuse” values (e.g., NRC 2004), whic h can arise from a variety of motivations including an intrinsic concern for the existen ce of species populations or ecosystems in a relatively undisturbed state or a desire to preser ve healthy ecosystems for future generations. Valuation is a tool for integrating inform ation on the effects of NOx and SOx on the multiple ecosystem processes that form the basis for the ecosystem service. It provides a common currency to compare impacts. The Nati onal Research Council ( 2004) noted that the translation from ecosystem structure and functio n to ecosystem goods and services is described by an ecological production function (goods and serv ices that can be produced from inputs of natural and human capital, labor, and other resources). Many ecological relationships can be quantified using existing data and models, at le ast for particular settings where data are quantified and models have been calibrated. A very simple example of some ecological processes or functions that would need to be qua ntified in order to determined the impact of nitrogen deposition on an ecological service is shown in Figure B.4.December 2007 B-14 Figure B.4. Ecological Relationshi ps Potentially disrupted by nitrogen deposition and the Ecosystem Service potentially affected (prepared by Dr. Bob McKane, ORD)

A number of different approaches have been suggested for valuing ecosystem services: 1) Provisioning services commodity values. There are methods and data for obtaining monetary values for commodities under scenario s of change. These break down into ‘natural resource values’ for extracted goods (e.g. cut and sell the tree in the market) and ‘environmental quality values’ to leave the tree in the forest and obtain the benefits of it in its role in the ecosystem. 2) Other kinds of monetization. Economic methods that have been used to value ecological improvements include production or cost function appr oaches, travel cost models, hedonic property models, and stated preference surveys. Bioeconomic modeling, which involves combining models of species population or ecosystem dynamics with economic models of human behavior, is another a pproach that can potentially be used to value ecological improvements. Most bioeconomic models ha ve been applied to fishery and forestry management problems, but in many cases these m odels could be adapted to estimate willingness

N Deposition to Watershed

Ecological Process/Function

Alter microbial communities – biomass, fungal:bacterial, ectomycorrhizal Alter soil chemistry, organic matter dynamics Changing C:N Ratios Altering Plant available Nutrients (e.g. N, Ca)

Alteration of Production
Altered Plant Communities Ecos y stem Service

Habitat Changes in timing and amount of N leaching, acidity

Food and Fiber Carbon sequestration

Habitat Water Quality

Alteration of lake and stream biota Water Quality Habitat Surface wate r effects

Ocean effects Surface wate r effects

Ocean effects

Surface wate r effects

Ocean effectsDecember 2007 B-15 to pay for environmental improvements that may a ffect the growth rates or carrying capacities of the focal species. 3) When direct valuation is infeasible, benefits or va lue transfer methods may be employed. This method takes direct values for ecosystem services from a primary study for a particular location and transfers t hose values to a different locati on using either a point estimate
or value transfer function. Dir ect transfer of point value estimat es has the potential to lead to large uncertainties and in some cases biases in estimated values for ecosystem services, because of the high dependency of most ecosystem values on the specific characteris tics of the location in which they were collected. Value transfer func tions which allow the values to vary with ecosystem characteristics can provide for mo re accurate estimation, but still have large
uncertainties. 4) Non-monetary values for individual and bundled services. These are developed from experimental field studies, lit erature and modeling activities. There are two types of nonmonetary valuation methods, one based on direct physical or biological tr adeoffs, and the other based on tradeoffs defined by human preferen ces for the ecosystem functions defined by different bundles of physical and biological at tributes. Figure B.5 illustrates a conceptual approach for developing non-monetary values using physical and/or biological tradeoff functions. Ecological response functions (ERFs) and ecological tradeoff functions (ETFs) can be developed to quantify the response of a service to changes in NOx/SOx concentrations and the tradeoffs between different services given these ambient air quality drivers. ERFs and ETFs will have to be, for the most part, defined by data mining from existing published literature. In the future, however, these quantifying f unctions will be the focus of res earch to broaden the scope of the science assessment and risk/exposure assessment . Process-based models will be used to (1) synthesize/link the suite of ERFs and ETFs and (2) generate maps and summaries of ecosystem services and tradeoffs in response to current a nd future ambient air indicators for NOx and SOx. Ecological response functions are de veloped to show the response of a service to changes in an ecosystem driver and ecological tradeoff functions combining re sponse functions to show the tradeoffs between different services given a driver. By describing the differing bundles of ecosystem services under varying levels of NOx and SOx and offering choices between those bundles, tradeoff or indifference curves can al so be generated refl ecting individual and population level preferences for di fferent ecosystem functions. Th ese tradeoffs can be presented to survey respondents using methods such as conjoint analysis, to provide measures ofDecember 2007 B-16 preferences for different levels of ecosystem f unctions as expressed through ecosystem service levels. Figure B.6 shows an example of how eco system services information might be presented to a survey respondent in a conjoint analysis framework. Figure B.5. Conceptual approach for quantif ying Ecological Response Functions (ERF) and Ecological Tradeoff Functi ons (ETF) for ecosystem services in relation to different levels of NOx or SOx (forcing variables)

N FertilizationCrop Yield ERF 1

N FertilizationN Export ERF 2

Socioeconomics

Valuation & Trading of

Ecosystem Services ERF X-axis: Forcing Variables • N Fertilization (rate, timing, form) • Harvest (interval, intensity, residues) • Climate (Temp, Precip, Light, CO 2 ) • Cover type (% landscape coverage) • Riparian buffers (width, age, species) ERF Y-axis: Ecosystem Services

• Food/fiber yield • Water quality • Water quantity • C sequestration • N 2 O, NO x , CH 4 Ecosystem Service vs. Forcing Variable = ERF

N Export ETF Another way to show this ETF

(ES vs. ES)Crop Yield ERF 1 + ERF 2

N FertilizationN Export Y

i e l d

N E x

p ETFCrop YieldDecember 2007 B-17Figure B.6. Example Survey Design forPreference Based Ecosystem TradeoffsWater Quality HabitatFood and FiberProductionCarbonSequestrationScenario 1 Drinkable Low diversity High HighScenario 2 Drinkable High diversity Low LowScenario 3 Swimmable Medium diversity Medium MediumScenario 4 Boatable Low diversity High MediumScenario 5 Swimmable Low diversity Low LowHighlyDesirable Quite Desirable DesirableSlightlyDesirableNeitherDesirablenorUndesirableSlightlyUndesirable UndesirableQuiteUndesirableHighlyUndesirableScenario 1 1 2 3 4 5 6 7 8 9Scenario 2 1 2 3 4 5 6 7 8 9Scenario 3 1 2 3 4 5 6 7 8 9Scenario 4 1 2 3 4 5 6 7 8 9Scenario 5 1 2 3 4 5 6 7 8 9Ecosystem Services Scenario DescriptionsScenario RatingPlease rate how desirable each scenario is overall by circling one of the numbers in each row of the following table:Example Conjoint Scenario Rating FormUnited StatesEnvironmental ProtectionAgencyOffice of Air Quality Planning and StandardsHealth and Environmental Impacts DivisionResearch Triangle Park, NCPublication No. EPA-452/R-08-006December 2007