The Federal Land Managers’ Air Quality Related Values 

Work Group (FLAG) formed to develop a more consistent 

approach for the Federal Land Managers (FLMs) to 

evaluate air pollution effects on resources. As discussed 

in the Preface, the FLAG Phase I Report (FLAG 2000) is 

being revised in part at this time. The primary—but not 

sole—focus of FLAG is the New Source Review (NSR) 

program, especially in the review of Prevention of Significant 

Deterioration (PSD) of air quality permit applications. The 

goals of FLAG have been to provide consistent policies 

and processes both for identifying air quality related values 

(AQRVs) and for evaluating the effects of air pollution on 

AQRVs, primarily in Federal Class I air quality areas, but also 

in some instances, in other national parks, national forests, 

national wildlife refuges, wilderness areas, and national 

monuments. Federal Class I areas are defined in the Clean 

Air Act as national parks over 6,000 acres and wilderness 

areas and memorial parks over 5,000 acres, established as of 

1977. All other FLM areas are designated Class II. Maps of 

the Agencies’ Federal Class I areas are provided in 

Appendix E. 

FLMs have an “affirmative responsibility” to protect AQRVs. 

In this respect, the FLM role consists of considering 

whether emissions from a new or modified source may 

have an adverse impact on AQRVs and providing comments 

to permitting authorities (States or EPA). FLMs have no 

permitting authority under the Clean Air Act, and they have 

no authority under the Clean Air Act to establish air qualityrelated rules or standards. It is important to emphasize that 

the FLAG report only explains factors and information the 

FLMs expect to use when carrying out their consultative 

role. It is separate from Federal regulatory programs. 

FLAG members include representatives from the three 

primary agencies that administer the nation’s Federal Class 

I areas: the U.S. Forest Service (USFS), the National Park 

Service (NPS), and the U.S. Fish and Wildlife Service (FWS). 

(Subsequently in this report, these three agencies collectively 

will be referred to as “the Agencies” or the “FLMs.” Class 

I and Class II air quality areas are called “FLM areas” in 

this report.) Appendix F contains a list of participants that 

worked on the original FLAG 2000 report.

This report describes the work accomplished in Phase I of 

the FLAG effort as revised to reflect current developments. 

That work includes identifying policies and processes 

common to the FLMs (herein called “commonalities”) 

and developing new policies and processes using readily 

available information. This report provides State permitting 

authorities and potential permit applicants a consistent and 

predictable process for assessing the impacts of new and 

existing sources on AQRVs, including a process to identify 

those AQRVs and potential adverse impacts. The report also 

discusses considerations unrelated to new source review 

and managing emissions in Federal areas. If and when the 

Agencies embark on Phase II, FLAG will address unresolved 

issues including those that will require research and the 

collection of new data.

This revised FLAG Phase I Report consolidates the results 

of the FLAG Visibility, Ozone, and Deposition subgroups. 

The chapters prepared by these subgroups contain issuespecific technical and policy analyses, recommendations 

for evaluating AQRVs, and information for completing and 

evaluating NSR permit applications. This information and 

the associated recommendations are intended for use by the 

FLMs, permitting authorities, NSR permit applicants, and 

other interested parties. The report includes background 

information on the roles and responsibilities of the FLMs 

under the NSR program.

This document includes recommendations for completing 

and evaluating NSR applications that may affect Class I FLM 

areas. This information can also be used to evaluate impacts 

on Class II parks and wilderness areas. It does not provide a 

universal formula that would, in all situations, allow one to 

determine whether or not a source of air pollution causes 

or contributes to an adverse impact. That determination 

remains a project-specific management decision, the 

responsibility for which remains with the FLM, as delegated 

by Congress. The FLM’s assessment of whether or not an 

adverse impact would occur is based on the sensitivity of the 

AQRVs at the particular FLM area under consideration, as 

well as the consideration of several other factors, including 

the magnitude, frequency, duration, timing, and geographic 

extent of the new source’s impacts.

To provide information for the FLM’s assessment of adverse 

impacts on AQRVs, the permit applicant should identify the 

potential impacts of the source on all applicable AQRVs of 

that area. An FLM may ask that an applicant address any or 

all of the areas of concern. The primary areas of concern 

to the FLMs with respect to air pollution emissions are 

Executive Summary (Revised)

Marble Mountain Wilderness, California. 

Credit: Steve Boutcher

xii FLAG Phase I Report—Revised (2010)
visibility impairment, ozone effects on vegetation, and effects 

of pollutant deposition on soils and surface waters. 

The FLAG Phase I Report also describes the FLAG effort, 

including the FLAG approach, organization, and plans for 

future FLAG work. Appendix A of the report contains a 

glossary of technical terms, abbreviations, and acronyms 

used in the report along with associated definitions. 

Appendix G provides a list of all references cited in the 

FLAG report.

The key recommendations developed by the Visibility, 

Ozone, and Deposition subgroups are summarized below, 

and updated in part in this FLAG 2010 revision. However, 

for all three subject matter areas, FLAG recommends that 

the permit applicant consult with the appropriate permitting 

authority and with the FLM for the affected area(s) for 

confirmation of preferred procedures. This consultation 

should take place in the early stages of the permit application 

process.

Recommendations for Evaluating Visibility 

Impacts (Revised)

FLAG provides recommendations, specific procedures, and 

interpretation of results for assessing visibility impacts of 

new or modified sources on Class I area resources.2

FLAG addresses assessments for sources proposed for 

locations near (generally within 50 km) and at large distances 

(greater than 50 km) from these areas. The key components 

of the recommendations are highlighted below.

In general, FLAG recommends that an applicant:

•	 Apply the Q/D test (see “INITIAL SCREENING TEST” 

below) for proposed sources greater than 50 km from 

a Class I area to determine whether or not any further 

visibility analysis is necessary. 

•	 Consult with the appropriate regulatory agency and with 

the FLM for the affected Class I area(s) or other affected 

area for confirmation of preferred visibility analysis 

procedures.

•	 Obtain FLM recommendation for the specified reference 

levels (estimate of natural conditions) and, if applicable, 

FLM recommended plume/observer geometries and 

model receptor locations.

2. Nevertheless, the FLMs are also concerned about resources in 

Class II parks and wilderness areas because they have other mandates 

to protect those areas as well. The information and procedures outlined 

in this document are generally applicable to evaluating the effect of new 

or modified sources on the AQRVs in both Class I and Class II areas, 

including the evaluation of effects as part of Environmental Assessments 

and/or Environmental Impact Statements under the National 

Environmental Policy Act (NEPA). However, FLAG does not preclude 

more refined or regional analyses being performed under NEPA or 

other programs.

•	 Apply the applicable EPA Guideline, steady-state models 

for regions within the Class I area that are affected by 

plumes or layers that are viewed against a background 

(generally within 50 km of the source).

- Calculate hourly estimates of changes in visibility, as 

characterized by the change in the color difference 

index (∆E) and plume contrast (C), with respect to 

natural conditions, and compare these estimates with 

the thresholds given in section 3.3.3.

•	 For regions of the Class I area where visibility impairment 

from the source would cause a general alteration of the 

appearance of the scene (generally 50 km or more away 

from the source or from the interaction of the emissions 

from multiple sources), apply a non-steady-state air 

quality model with chemical transformation capabilities 

(refer to EPA’s Guideline on Air Quality Models), which 

yields ambient concentrations of visibility-impairing 

pollutants. At each Class I receptor:

- Calculate the change in extinction due to the source 

being analyzed, compare these changes with the 

reference conditions, and then compare these results 

with the thresholds given in section 3.3.3.

- Utilize estimates of annual average natural visibility 

conditions for each Class I area as presented in 

Table 6, unless otherwise recommended by the 

FLM or permitting authority. Alternative estimates 

of visibility conditions are provided in Table 5 

for consistency with State agencies that elected to 

use 20% best visibility for regional haze or BART 

implementations, or when FLMs recommend using 

the 20% best visibility as natural background. 

•	 If first-level modeling results are above levels of concern, 

continue to consult with the Agencies to discuss other 

considerations (e.g., possible impact mitigation, more 

refined analyses). 

This review process for distant/multi-source applications is 

portrayed schematically in Figure 1.

Recommendations for Evaluating Ozone 

Impacts (Revised)

•	 FLM actions or specific requests on a permit application 

will be based on the existing air pollution situation at the 

area they manage. These conditions include (1) whether 

or not actual ozone damage has occurred in the area, and 

(2) whether or not ozone exposure levels occurring in 

the area are high enough to cause damage to vegetation 

(i.e., phytotoxic O3

 exposures). Figure 2 shows the FLM 

review process to assess ozone impacts for a project that 

exceeds the initial annual emissions over distance (Q/D) 

screening criteria. As noted in Figure 2, ambient ozone 

concentrations are considered along with data from 

exposure response studies (EPA 2007b) to determine 

whether a source will cause or contribute to phytotoxic 

 USFS–NPS–USFWS xiii
ozone levels (i.e., levels toxic to plants) at the affected site. 

The FLM may ask the applicant to calculate the ozone 

exposure values if these data are not already available. 

Ozone damage to vegetation is determined from field 

observations at the impacted site.

•	 Oxidant stipple necrosis on plant foliage and ozoneinduced senescence infer adverse physiological or 

ecological effects, and are considered to be damage if they 

are determined to have a negative impact on aesthetic 

value.

•	 Established ozone metrics to describe ozone exposure are 

referenced.

•	 NOx

 and VOC emissions are of concern because they are 

precursors of ozone. Current information indicates most 

FLM areas are NOx

 limited. Until we determine the VOC 

or NOx

 status of each area, we will focus on NOx emission 

sources. 

Recommendations for Evaluating Deposition 

Impacts (Revised) 

For a project that exceeds the initial annual emissions over 

distance (Q/D) screening criteria, the permit applicant 

should consult with the appropriate regulatory agency and 

FLM for the affected area(s) to determine if a deposition 

impact analysis should be done (i.e., expected sulfur and/

Figure 1. Procedure for Visibility Assessment for Distant/Multi-Source Applications (Revised) 

*Q/D test only applies to sources located greater that 50 km from a Class I area.

**Difference Change in the 98th percentile with respect to (wrt) the annual average Natural Condition (NC). Applicant should use the 20th percentile best natural condition background if recommended by the FLM or permitting authority.

xiv FLAG Phase I Report—Revised (2010)
or nitrogen deposition impacts are above the Deposition 

Analysis Threshold (DAT) or concern threshold (see 

section 3.5.6). Please note that although mercury and other 

toxic emissions are of interest to the FLM, the deposition 

impact analyses discussed here applies only to nitrogen 

and sulfur emissions. If an analysis is advised, the permit 

applicant should obtain available information on Class I 

AQRVs, critical loads, and concern thresholds from the 

FLM. In addition, the applicant should refer to section 3.5.6 

‘Recommendations for Evaluating Potential Effects from 

Proposed Increases in Deposition to an FLM Area’ section 

of the Deposition Chapter. The following steps summarize 

that process.

•	 From the respective Agency web sites, identify available 

on-site or representative wet and dry deposition data for 

the FLM area. 

•	 Estimate the future deposition rate by adding the existing 

rate, the new emissions’ contribution to deposition, 

and the contribution of sources permitted but not yet 

operating, while subtracting emission reductions that 

will occur before the proposed source begins operation. 

Modeling of new, reduced, and permitted but not yet 

operating emissions’ contribution to deposition should be 

conducted following EPA recommendations.

•	 Compare the future deposition rate with the 

recommended screening criteria (e.g., critical load, 

Figure 2. FLM Assessment of Potential Ozone Effects from New Emissions Source (Revised)

*Q/D test only applies to sources located greater that 50 km from a Class I area.

**Note: Ambient ozone concentrations are considered along with data from exposure response studies (EPA 2007b) to determine whether a source 

will cause or contribute to phytotoxic ozone levels (i.e., levels toxic to plants) at the affected site. 

 USFS–NPS–USFWS xv
concern threshold, or screening level value) for the 

affected FLM area. A list of documents summarizing 

these screening criteria, where available, can be found in 

Appendix G. 

- Information for USFS Class I areas is also available at:

http://www.fs.fed.us/air

- NPS and FWS Class I area information is available at:

http://www.nature.nps.gov/air

•	 Figure 3 shows the FLM review process to assess 

deposition impacts from new emission sources.

Figure 3. FLM Assessment of Potential Deposition Effects from New Emissions Sources (Revised)

*Q/D test only applies to sources located greater that 50 km from a Class I area.

xvi FLAG Phase I Report—Revised (2010)