Document ID: EPA-HQ-OAR-2007-1145-0074
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-09-28T04:00Z

September 15, 2010

MEMORANDUM

SUBJECT: CASAC Review of Policy Assessment for the Review of the
Secondary National Ambient Air Quality Standards for NOx and SOx: 
Second External Review Draft

FROM: Lydia N. Wegman, Director /s/

Health and Environmental Impacts Division (C504-02)

Office of Air Quality Planning and Standards

United States Environmental Protection Agency

TO: Angela Nugent

Designated Federal Officer

Clean Air Scientific Advisory Committee

EPA Science Advisory Board Staff Office

Attached is the draft document, Policy Assessment for the Review of the
Secondary National Ambient Air Quality Standards for NOx and SOx: 
Second External Review Draft (September 2010), prepared by the
Environmental Protection Agency’s (EPA) Office of Air Quality Planning
and Standards (OAQPS) staff as part of EPA’s ongoing review of the
secondary (welfare-based) national ambient air quality standards (NAAQS)
for oxides of nitrogen (NOx) and sulfur (SOx). This document will be the
focus of a review by the Clean Air Scientific Advisory Committee (CASAC)
Oxides of Nitrogen (NOx) and Sulfur Oxides (SOx) Secondary Review Panel
(the CASAC NOx SOx Secondary Panel) at a public meeting to be held in
Durham NC on October 6-7, 2010.  I am requesting that you forward these
draft documents to the CASAC NOx SOx Secondary Panel to prepare for the
October meeting.  

As part of the review of the current secondary (welfare-based) NAAQS for
NOx and SOx, EPA’s OAQPS staff has prepared a second draft Policy
Assessment.  This draft Policy Assessment evaluates the policy
implications of the key scientific information contained in the document
Integrated Science Assessment for Oxides of Nitrogen and
Sulfur-Ecological Criteria, prepared by EPA’s National Center for
Environmental Assessment (NCEA) and the results from the analyses
contained in the Risk and Exposure Assessment for Review of the
Secondary National Ambient Air Quality Standards for Oxides of Nitrogen
and Oxides of Sulfur.  These documents, along with EPA’s Integrated
Review Plan, can be found at   HYPERLINK
"http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html" 
http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html .

The second draft Policy Assessment reflects consideration of comments
from the Panel, as well as public comments, on the first draft Policy
Assessment, which was reviewed by the Panel on April 1-2 and May 3,
2010. The main comments from the Panel on the first draft Policy
Assessment were provided to us in a June 22, 2010 letter (Russell and
Samet, 2010). These comments, and the changes made in the second draft
Policy Assessment in response to them, are summarized in Attachment 1. 
Note that the structure of the Policy Assessment has changed somewhat
from the first draft.  While there are still 9 chapters, Chapters 5 and
6 in the first draft have been combined into Chapter 5 in the current
draft; Chapter 7 in the first draft is now Chapter 6 in the current
draft, Chapter 7 in the current draft is a new chapter on uncertainty,
variability and sensitivity analyses, and Chapter 8 in the current draft
is a new chapter on monitoring issues.

The current draft contains several placeholders indicating missing
tables or discussions.  We expect to provide the Panel with these tables
and discussions in a separate submission two weeks prior to the October
6-7 Panel meeting.  These will include a table in Chapter 9 summarizing
the options for elements of the standards, a table in Chapter 7
summarizing key uncertainties, and a discussion in Chapter 5 of the
implications of a range of choices of the target percent of lakes and
streams to protect for alternative target ANC levels.  This discussion
will also cover the various spatial aggregation choices and resulting
implications on the target percentages.  We recognize that there are
some formatting issues in several chapters, and these will be addressed
in the final PA.  

The CASAC and public comments on the draft Policy Assessment will be
taken into consideration in making revisions to the draft document.  A
final Policy Assessment will be released in December of 2010.  Following
completion of the final Policy Assessment, EPA will conduct a rulemaking
with regard to its review of the secondary NOx and SOx NAAQS. 
Consistent with the terms of a consent decree, the EPA Administrator
will sign a notice of proposed rulemaking by July 12, 2011 and a final
rulemaking notice by March 20, 2012.  Draft documents are being made
available to the CASAC NOx SOx Secondary Panel in the form of attached
electronic files. The documents are also available from the EPA website
at   HYPERLINK
"http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html" 
http://www.epa.gov/ttn/naaqs/standards/no2so2sec/index.html .  Printed
copies of these documents will be sent to CASAC NOx SOx Secondary Panel
members via UPS. A set of charge questions related to the draft Policy
Assessment will be submitted separately.

We look forward to discussing the second draft Policy Assessment with
the CASAC NOx SOx Secondary Panel at our upcoming meeting. Should you
have any questions regarding the first draft NOx SOx Secondary NAAQS
Policy Assessment, please contact me (919-541-5505; email
wegman.lydia@epa.gov) or Dr. Bryan Hubbell (919-541-0621; email  
HYPERLINK "mailto:hubbell.bryan@epa.gov"  hubbell.bryan@epa.gov ).

Attachments

cc: 	Vanessa Vu, SAB, OA 

John Vandenberg, ORD/NCEA-RTP 

Mary Ross, ORD/NCEA-RTP

Ron Evans, OAQPS/HEID

Dale Evarts, OAQPS/HEID

Richard Haeuber,  OAP/CAMD

Karen Martin, OAQPS/HEID

Christine Davis, OAQPS/HEID

Tara Greaver, ORD/NCEA-RTP

Bryan Hubbell, OAQPS/HEID

Meredith Lassiter, OAQPS/HEID

Jason Lynch, OAP/CAMD

Norm Possiel, OAQPS/AQAD

Adam Reff, OAQPS/AQAD

Rich Scheffe, OAQPS/AQAD 

Travis Smith, OAQPS/HEID

Ginger Tennant, OAQPS/HEID

Randy Waite, OAQPS/HEID

Nealson Watkins, OAQPS/AQAD

Attachment 1

CASAC comments on first draft PM Policy Assessment and responses to
those comments

The CASAC Panel’s comments and recommendations on the first draft of
the NOx and SOx Secondary NAAQS Policy Assessment, as well as changes
made in the second draft in response to those comments, are summarized
below. Overarching comments and recommendations are summarized below,
followed by comments and recommendations on chapters 2 through 9.

Overarching comments and recommendations

The Panel made several overarching comments and recommendations,
including:

The second draft should include in a separate chapter a more
comprehensive sensitivity and uncertainty analyses of the proposed
approach.  This chapter should provide more reasoning to support EPA’s
assessment of the relative values of the uncertainties.  The sensitivity
analyses should include the sensitivity of the AAPI to component terms. 
The chapter should provide a more thorough evaluation of the ability of
CMAQ to simulate the ambient concentrations and wet and dry deposition
fluxes of the SOx, NOx and NHx species used in determining the AAPI.

The second draft should include a succinct discussion of other potential
impacts of NOx deposition to N-limited ecosystems, including potential
production increases that may be either beneficial or adverse depending
on the system and management goals.

The second draft should ensure the use of a consistent set of units in
its presentation of data, results and equations.

In response to these comments, we have made extensive edits throughout
the second draft Policy Assessment to ensure consistent units are used,
and have included a table in Chapter 1 which clearly identifies units
and conversions used in the document (Table 1-1, Section 1.1).   We have
added a new chapter (Chapter 7) which provides a more extensive
discussion of uncertainties and variability in the science, data, and
models which inform our considerations of the standards.  This chapter
also provides assessments of the sensitivity of models and the AAPI to
inputs.   We have added additional discussions of the broader set of
potential impacts of NOx deposition, while continuing to focus the
overall review on the effects of NOx and SOx deposition on sensitive
aquatic ecosystems, and protection against adverse effects of NOx
additions (ES-4, Section 1.6, Section 4.5.2, Section 2.2.2, and Section
3.4).

Chapter 2 (Known or Anticipated Ecological Effects)

The panel was generally supportive of the review of effects provided in
the chapter.  The panel asked primarily for clarifications of the text
and additional references.  The panel asked for a summary of the
assumptions and limitations of the steady-state models used in the
ecological effects studies.  The panel requested that we clarify that
ecological effects due to deposition of N and S occur in a relatively
small set of sensitive ecosystems, rather than throughout all
ecosystems.  The panel also asked for a more thorough discussion of
uncertainties, with justifications for rankings of uncertainties, and
sensitivity analyses for the different models used for aquatic
acidification.

Changes made in chapter 2 in the second draft Policy Assessment were
primarily focused on streamlining the chapter as well as on improving
and clarifying the approach for characterizing uncertainty.  In
addition, we included a new table (Table 2-2) that summarizes the
assumptions and limitations of the ecological effects models.

Chapter 3 (Considerations of Adversity to Public Welfare)

The panel asked for a more focused discussion on how and why the current
effects of SOx/NOy deposition on sensitive ecosystems matter in terms of
services and functions of ecosystems that are important to people,
emphasizing that effects occur only in a limited set of sensitive areas.
The panel asked for more explanation of the policy implications of the
monetary values of ecosystem services discussed in the chapter. The
panel also asked for a table summarizing the monetary valuation
associated with various ecosystem services estimates.  The panel asked
for more focus on the effects that are likely occurring due to NOx and
SOx deposition and less on those that potentially could be affected. 
The panel also asked for greater acknowledgement of the potential
beneficial effects of nitrogen inputs to nutrient limited ecosystems.

Change made in chapter 3 in the second draft Policy Assessment were
focused on describing those ecosystem services that were likely impacted
by current NOx and SOx deposition.  In addition, we have expanded the
discussion of insights that can be gained by evaluating public
decisionmaking regarding protection of aquatic resources (Section
3.1.2.4.3), and through evaluation of programs in Europe that have
established targets for ecosystem protection as part of critical loads
policies (Section 3.1.2.4.4).  We have modified Figures 3.4 and 3.5 to
include deposition levels in a wider range of public lands, including
Federal Class I Areas, as well as state and local parks and wilderness
areas.  We have added an additional assessment of the value of decreases
in acidification in the Adirondacks based on the Banzhaf et al (2006)
valuation survey of NY residents (Section 3.4.2).  We have added a
number of additional tables, including a summary of values of ecosystem
services affected by current N deposition (Table 3-7 and 3-8).  We have
included a discussion of the potential beneficial effects of N
deposition in nitrogen-limited areas in Chapter 4, and have added a
clarification to this chapter acknowledging these effects and
reiterating our focus on adverse effects (Section 3.4.5).

Chapter 4 (Addressing the Adequacy of the Current Standards)

The panel was generally supportive of the information provided
demonstrating that current NOx and SOx secondary standards are not
adequate to protect against effects of deposition of NOx and SOx to
sensitive ecosystems.  While the panel agreed that steady state models
are appropriate to evaluate the adequacy of the standards, they note
that approach could be enhanced by also applying dynamic acidification
modeling techniques to “hindcast”changes in ANC.  The panel
recommended that the evaluation of adequacy should consider the extent
to which and rates at which some less sensitive systems may continue to
recover at current S + N deposition, while other more sensitive systems
will not recover or may experience further deterioration.  The panel
also asked for additional plots showing the relationship of NOy to NOx,
compared with NO2 to NOx.  The panel also asked that a summary of the
performance assessment of CMAQ be included.

The performance assessment of CMAQ has been incorporated in the new
Chapter 7 addressing uncertainty, variability, and sensitivity.  Much of
the monitoring discussion has been moved to a separate Chapter 8 on
monitoring issues, and that chapter also provides more discussion on the
ambient concentration to deposition relationship of individual sulfur
and nitrogen species.   New plots of NOy to NOx and NO2 to NOx have been
added to chapter 4.  

While the panel recognized that the current review was focused on
sensitive, non-managed ecosystems, the panel requested more discussion
of fertilization effects.  In response to these comments an additional
discussion has been added to Chapter 4 (Section 4.5.2) regarding
nutrient enrichment effects in both managed and non-managed systems.  In
addition, language has been added in several other chapters highlighting
the range of potential responses to nitrogen nutrient enrichment in
different types of ecosystems, especially in N-limited ecosystems.

Chapters 5 (Conceptual Design of an Ecologically Relevant
Multi-pollutant Standard) and 6 (Options for Elements of a Standard to
Protect Against Effects from Aquatic Acidification)

Note:  We have combined Chapters 5 and 6 from the first draft Policy
Assessment into a single Chapter 5 in the second draft Policy Assessment
to reduce redundancy and improve the flow of the document.  

The panel was generally supportive of both the conceptual framework
developed to address effects associated with deposition of NOx and SOx,
and the Atmospheric Acidification Protection Index introduced as a new
form of the standards.  The panel agreed with selection of NOy and SOx
as atmospheric indicators, and with the selection of ANC as the
ecological indicator.  The panel agreed that a multi-year averaging time
from 3 to 5 years was appropriate.  The panel also agreed that a
multipollutant standard is appropriate to protect aquatic ecosystems
from acid deposition. 

The panel asked that reduced nitrogen be treated as a variable component
of the AAPI standard that can be updated.  The panel asked that the
underlying assumption of steady state behavior should be evaluated with
a parallel effort using sensitivity analysis and dynamic modeling.  The
panel asked that the AAPI equation for the proposed standard should
include the geographical extent and numerical range of its
applicability.  The panel recommended that the mass balance approach to
determining Neco be used over the dynamic modeling approach.  The panel
recommended that in evaluating methods for aggregating catchment scale
critical loads, consideration be given to approaches by which the water
bodies within any specified area could be first stratified to include
only those which were considered potentially susceptible to
acidification, based on estimates of preindustrial ANC, or acid
sensitivity class.  The panel advised EPA to focus on an AAPI standard
driven by aquatic effects concerns, given both the availability of data,
and the likelihood that such a standard would decrease N and S inputs to
ecosystems, which would provide protection against additional effects. 
The panel recommended that EPA conduct a sensitivity study to
characterize uncertainty associated with different components of the
conceptual framework and propagate the resulting uncertainty at every
step to arrive at an ensemble of SOx and NOy response surfaces to meet a
given standard.  The panel asked for inclusion of a separate conceptual
diagram which shows the important contributing factors for each term in
the AAPI equation.

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

Uncertainty in pre-industrial levels of ANC

Uncertainty in the use of steady state models

Uncertainty in the atmospheric deposition transformation ratios

Uncertainty in modeled estimates of reduced nitrogen deposition

In addition, the panel recommended that close attention be given to the
issue of matching temporal and spatial scales in various components of
the AAPI.

The panel recommended disaggregating the g(·) term in the AAPI
equation, and include a term to account for naturally occurring organic
acids.  The panel recommends that consideration of chronically acidic or
highly acid sensitive surface waters that would not be recoverable at a
given ANC limit should be given.

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

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

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

A regional model evaluation using the continuous measurements of nitric
oxide, nitrogen dioxide, nitric acid and NOY from the SEARCH network in
the southeastern U.S.

The panel expressed support for the use of NOx/SOx tradeoff curves, but
recommended that these curves include the impact of reduced nitrogen.

In response to the comments from the panel, Chapter 5 has been revised
in the following ways:

We have added a section comparing critical loads calculated using
steady-state versus dynamic modeling has been added (5.3.2.3).

The mass balance approach to determining Neco has been used (5.3.2).

The tradeoff curves now show the impact of NHx, based on a range of NHx
deposition values which are modeled to occur across the U.S. (5.3.9).

Criteria have been identified to only consider critical loads from
catchments that are susceptible to acidification from atmospheric
deposition, while excluding those catchments in which acidification
results from high organic acid content, acid mine drainage or naturally
low base cation weathering (5.3.2.6).

The focus of the conceptual design is on aquatic acidification (5.3.1)
with co-protection to other effects presented in Chapter 6.

A new conceptual diagram has been added that outlines each step to
develop the tradeoff curves and the AAPI (5.3.1)

The g(·) term from the first draft PA has been disaggregated so that
each component is represented in the AAPI equation (5.3.4).  As stated
above, the critical load dataset is screened to exclude those catchments
which would not be able to recover based on pre-industrial ANC values
(5.3.2.6).

Chapter 7 (Co-protection)

Note:  The chapter on co-protection is now Chapter 6.

The panel supported evaluation of co-protection provided by an aquatic
acidification based standard for terrestrial acidification endpoints and
terrestrial and aquatic nutrient enrichment endpoints.  The panel
recommended that the chapter be expanded to better explain the potential
interrelationships between aquatic and related terrestrial responses to
acidification.  The panel recommended that further consideration not be
given to developing a single standard addressing both acidification and
nutrient enrichment.

Chapter 9 (Conclusions)

The panel generally supported the preliminary staff conclusions
regarding the adequacy of existing standards, and options for the
indicators, averaging times, and form of additional standards to protect
against the effects of NOx and SOx deposition to sensitive aquatic
ecosystems.  The panel reiterated the request for a separate uncertainty
chapter.  They also asked that discussions of future research needs be
linked to the identification of critical uncertainties.

Chapter 9 has been expanded to include a discussion of staff conclusions
regarding the options for elements of the standard.  We have included
discussions of how critical uncertainties might influence the AAPI, with
references to the broader uncertainty discussions in Chapter 7. 
Research needs are discussed briefly in the new Chapter 7, but will need
to be more fully developed in the final PA.

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