Regulatory Citation

40 CFR 51.308 (up to date as of 10/15/2024)
Regional haze program requirements.

40 CFR 51.308 (Oct. 15, 2024)

This content is from the eCFR and is authoritative but unofficial.

Title 40 —Protection of Environment
Chapter I —Environmental Protection Agency
Subchapter C —Air Programs
Part 51 —Requirements for Preparation, Adoption, and Submittal of Implementation Plans
Subpart P —Protection of Visibility
Authority: Secs. 110, 114, 121, 160-169, 169A, and 301 of the Clean Air Act, (42 U.S.C. 7410, 7414, 7421, 7470-7479, and 7601).
Source: 45 FR 80089, Dec. 2, 1980, unless otherwise noted.
Authority: 23 U.S.C. 101; 42 U.S.C. 7401-7671q.
Source: 36 FR 22398, Nov. 25, 1971, unless otherwise noted.

§ 51.308 Regional haze program requirements.
(a) What is the purpose of this section? This section establishes requirements for implementation plans, plan
revisions, and periodic progress reviews to address regional haze.
(b) When are the first implementation plans due under the regional haze program? Except as provided in §
51.309(c), each State identified in § 51.300(b) must submit, for the entire State, an implementation plan
for regional haze meeting the requirements of paragraphs (d) and (e) of this section no later than
December 17, 2007.
(c) [Reserved]
(d) What are the core requirements for the implementation plan for regional haze? The State must address
regional haze in each mandatory Class I Federal area located within the State and in each mandatory
Class I Federal area located outside the State which may be affected by emissions from within the State.
To meet the core requirements for regional haze for these areas, the State must submit an
implementation plan containing the following plan elements and supporting documentation for all
required analyses:
(1) Reasonable progress goals. For each mandatory Class I Federal area located within the State, the
State must establish goals (expressed in deciviews) that provide for reasonable progress towards
achieving natural visibility conditions. The reasonable progress goals must provide for an
improvement in visibility for the most impaired days over the period of the implementation plan and
ensure no degradation in visibility for the least impaired days over the same period.
(i)

In establishing a reasonable progress goal for any mandatory Class I Federal area within the
State, the State must:
(A) Consider the costs of compliance, the time necessary for compliance, the energy and nonair quality environmental impacts of compliance, and the remaining useful life of any
potentially affected sources, and include a demonstration showing how these factors
were taken into consideration in selecting the goal.
(B) Analyze and determine the rate of progress needed to attain natural visibility conditions by
the year 2064. To calculate this rate of progress, the State must compare baseline
visibility conditions to natural visibility conditions in the mandatory Federal Class I area
and determine the uniform rate of visibility improvement (measured in deciviews) that
would need to be maintained during each implementation period in order to attain natural

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40 CFR 51.308(d)(1)(ii)

visibility conditions by 2064. In establishing the reasonable progress goal, the State must
consider the uniform rate of improvement in visibility and the emission reduction
measures needed to achieve it for the period covered by the implementation plan.
(ii) For the period of the implementation plan, if the State establishes a reasonable progress goal
that provides for a slower rate of improvement in visibility than the rate that would be needed to
attain natural conditions by 2064, the State must demonstrate, based on the factors in
paragraph (d)(1)(i)(A) of this section, that the rate of progress for the implementation plan to
attain natural conditions by 2064 is not reasonable; and that the progress goal adopted by the
State is reasonable. The State must provide to the public for review as part of its
implementation plan an assessment of the number of years it would take to attain natural
conditions if visibility improvement continues at the rate of progress selected by the State as
reasonable.
(iii) In determining whether the State's goal for visibility improvement provides for reasonable
progress towards natural visibility conditions, the Administrator will evaluate the
demonstrations developed by the State pursuant to paragraphs (d)(1)(i) and (d)(1)(ii) of this
section.
(iv) In developing each reasonable progress goal, the State must consult with those States which
may reasonably be anticipated to cause or contribute to visibility impairment in the mandatory
Class I Federal area. In any situation in which the State cannot agree with another such State or
group of States that a goal provides for reasonable progress, the State must describe in its
submittal the actions taken to resolve the disagreement. In reviewing the State's
implementation plan submittal, the Administrator will take this information into account in
determining whether the State's goal for visibility improvement provides for reasonable
progress towards natural visibility conditions.
(v) The reasonable progress goals established by the State are not directly enforceable but will be
considered by the Administrator in evaluating the adequacy of the measures in the
implementation plan to achieve the progress goal adopted by the State.
(vi) The State may not adopt a reasonable progress goal that represents less visibility improvement
than is expected to result from implementation of other requirements of the CAA during the
applicable planning period.
(2) Calculations of baseline and natural visibility conditions. For each mandatory Class I Federal area
located within the State, the State must determine the following visibility conditions (expressed in
deciviews):
(i)

Baseline visibility conditions for the most impaired and least impaired days. The period for
establishing baseline visibility conditions is 2000 to 2004. Baseline visibility conditions must be
calculated, using available monitoring data, by establishing the average degree of visibility
impairment for the most and least impaired days for each calendar year from 2000 to 2004.
The baseline visibility conditions are the average of these annual values. For mandatory Class I
Federal areas without onsite monitoring data for 2000-2004, the State must establish baseline
values using the most representative available monitoring data for 2000-2004, in consultation
with the Administrator or his or her designee;

(ii) For an implementation plan that is submitted by 2003, the period for establishing baseline
visibility conditions for the period of the first long-term strategy is the most recent 5-year period
for which visibility monitoring data are available for the mandatory Class I Federal areas
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40 CFR 51.308(d)(2)(iii)

addressed by the plan. For mandatory Class I Federal areas without onsite monitoring data, the
State must establish baseline values using the most representative available monitoring data,
in consultation with the Administrator or his or her designee;
(iii) Natural visibility conditions for the most impaired and least impaired days. Natural visibility
conditions must be calculated by estimating the degree of visibility impairment existing under
natural conditions for the most impaired and least impaired days, based on available
monitoring information and appropriate data analysis techniques; and
(iv) For the first implementation plan addressing the requirements of paragraphs (d) and (e) of this
section, the number of deciviews by which baseline conditions exceed natural visibility
conditions for the most impaired and least impaired days.
(3) Long-term strategy for regional haze. Each State listed in § 51.300(b) must submit a long-term
strategy that addresses regional haze visibility impairment for each mandatory Class I Federal area
within the State and for each mandatory Class I Federal area located outside the State that may be
affected by emissions from the State. The long-term strategy must include enforceable emissions
limitations, compliance schedules, and other measures as necessary to achieve the reasonable
progress goals established by States having mandatory Class I Federal areas. In establishing its
long-term strategy for regional haze, the State must meet the following requirements:
(i)

Where the State has emissions that are reasonably anticipated to contribute to visibility
impairment in any mandatory Class I Federal area located in another State or States, the State
must consult with the other State(s) in order to develop coordinated emission management
strategies. The State must consult with any other State having emissions that are reasonably
anticipated to contribute to visibility impairment in any mandatory Class I Federal area within
the State.

(ii) Where other States cause or contribute to impairment in a mandatory Class I Federal area, the
State must demonstrate that it has included in its implementation plan all measures necessary
to obtain its share of the emission reductions needed to meet the progress goal for the area. If
the State has participated in a regional planning process, the State must ensure it has included
all measures needed to achieve its apportionment of emission reduction obligations agreed
upon through that process.
(iii) The State must document the technical basis, including modeling, monitoring and emissions
information, on which the State is relying to determine its apportionment of emission reduction
obligations necessary for achieving reasonable progress in each mandatory Class I Federal
area it affects. The State may meet this requirement by relying on technical analyses developed
by the regional planning organization and approved by all State participants. The State must
identify the baseline emissions inventory on which its strategies are based. The baseline
emissions inventory year is presumed to be the most recent year of the consolidate periodic
emissions inventory.
(iv) The State must identify all anthropogenic sources of visibility impairment considered by the
State in developing its long-term strategy. The State should consider major and minor
stationary sources, mobile sources, and area sources.
(v) The State must consider, at a minimum, the following factors in developing its long-term
strategy:

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40 CFR 51.308(d)(3)(v)(A)

(A) Emission reductions due to ongoing air pollution control programs, including measures to
address reasonably attributable visibility impairment;
(B) Measures to mitigate the impacts of construction activities;
(C) Emissions limitations and schedules for compliance to achieve the reasonable progress
goal;
(D) Source retirement and replacement schedules;
(E) Smoke management techniques for agricultural and forestry management purposes
including plans as currently exist within the State for these purposes;
(F) Enforceability of emissions limitations and control measures; and
(G) The anticipated net effect on visibility due to projected changes in point, area, and mobile
source emissions over the period addressed by the long-term strategy.
(4) Monitoring strategy and other implementation plan requirements. The State must submit with the
implementation plan a monitoring strategy for measuring, characterizing, and reporting of regional
haze visibility impairment that is representative of all mandatory Class I Federal areas within the
State. This monitoring strategy must be coordinated with the monitoring strategy required in §
51.305 for reasonably attributable visibility impairment. Compliance with this requirement may be
met through participation in the Interagency Monitoring of Protected Visual Environments network.
The implementation plan must also provide for the following:
(i)

The establishment of any additional monitoring sites or equipment needed to assess whether
reasonable progress goals to address regional haze for all mandatory Class I Federal areas
within the State are being achieved.

(ii) Procedures by which monitoring data and other information are used in determining the
contribution of emissions from within the State to regional haze visibility impairment at
mandatory Class I Federal areas both within and outside the State.
(iii) For a State with no mandatory Class I Federal areas, procedures by which monitoring data and
other information are used in determining the contribution of emissions from within the State to
regional haze visibility impairment at mandatory Class I Federal areas in other States.
(iv) The implementation plan must provide for the reporting of all visibility monitoring data to the
Administrator at least annually for each mandatory Class I Federal area in the State. To the
extent possible, the State should report visibility monitoring data electronically.
(v) A statewide inventory of emissions of pollutants that are reasonably anticipated to cause or
contribute to visibility impairment in any mandatory Class I Federal area. The inventory must
include emissions for a baseline year, emissions for the most recent year for which data are
available, and estimates of future projected emissions. The State must also include a
commitment to update the inventory periodically.
(vi) Other elements, including reporting, recordkeeping, and other measures, necessary to assess
and report on visibility.
(e) Best Available Retrofit Technology (BART) requirements for regional haze visibility impairment. The State
must submit an implementation plan containing emission limitations representing BART and schedules
for compliance with BART for each BART-eligible source that may reasonably be anticipated to cause or
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40 CFR 51.308(e)(1)

contribute to any impairment of visibility in any mandatory Class I Federal area, unless the State
demonstrates that an emissions trading program or other alternative will achieve greater reasonable
progress toward natural visibility conditions.
(1) To address the requirements for BART, the State must submit an implementation plan containing the
following plan elements and include documentation for all required analyses:
(i)

A list of all BART-eligible sources within the State.

(ii) A determination of BART for each BART-eligible source in the State that emits any air pollutant
which may reasonably be anticipated to cause or contribute to any impairment of visibility in
any mandatory Class I Federal area. All such sources are subject to BART.
(A) The determination of BART must be based on an analysis of the best system of
continuous emission control technology available and associated emission reductions
achievable for each BART-eligible source that is subject to BART within the State. In this
analysis, the State must take into consideration the technology available, the costs of
compliance, the energy and nonair quality environmental impacts of compliance, any
pollution control equipment in use at the source, the remaining useful life of the source,
and the degree of improvement in visibility which may reasonably be anticipated to result
from the use of such technology.
(B) The determination of BART for fossil-fuel fired power plants having a total generating
capacity greater than 750 megawatts must be made pursuant to the guidelines in
appendix Y of this part (Guidelines for BART Determinations Under the Regional Haze
Rule).
(C) Exception. A State is not required to make a determination of BART for SO2 or for NOX if a
BART-eligible source has the potential to emit less than 40 tons per year of such
pollutant(s), or for PM10 if a BART-eligible source has the potential to emit less than 15
tons per year of such pollutant.
(iii) If the State determines in establishing BART that technological or economic limitations on the
applicability of measurement methodology to a particular source would make the imposition of
an emission standard infeasible, it may instead prescribe a design, equipment, work practice, or
other operational standard, or combination thereof, to require the application of BART. Such
standard, to the degree possible, is to set forth the emission reduction to be achieved by
implementation of such design, equipment, work practice or operation, and must provide for
compliance by means which achieve equivalent results.
(iv) A requirement that each source subject to BART be required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after approval of the
implementation plan revision.
(v) A requirement that each source subject to BART maintain the control equipment required by
this subpart and establish procedures to ensure such equipment is properly operated and
maintained.
(2) A State may opt to implement or require participation in an emissions trading program or other
alternative measure rather than to require sources subject to BART to install, operate, and maintain
BART. Such an emissions trading program or other alternative measure must achieve greater

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40 CFR 51.308(e)(2)(i)

reasonable progress than would be achieved through the installation and operation of BART. For all
such emission trading programs or other alternative measures, the State must submit an
implementation plan containing the following plan elements and include documentation for all
required analyses:
(i)

A demonstration that the emissions trading program or other alternative measure will achieve
greater reasonable progress than would have resulted from the installation and operation of
BART at all sources subject to BART in the State and covered by the alternative program. This
demonstration must be based on the following:
(A) A list of all BART-eligible sources within the State.
(B) A list of all BART-eligible sources and all BART source categories covered by the
alternative program. The State is not required to include every BART source category or
every BART-eligible source within a BART source category in an alternative program, but
each BART-eligible source in the State must be subject to the requirements of the
alternative program, have a federally enforceable emission limitation determined by the
State and approved by EPA as meeting BART in accordance with section 302(c) or
paragraph (e)(1) of this section, or otherwise addressed under paragraphs (e)(1) or
(e)(4)of this section.
(C) An analysis of the best system of continuous emission control technology available and
associated emission reductions achievable for each source within the State subject to
BART and covered by the alternative program. This analysis must be conducted by making
a determination of BART for each source subject to BART and covered by the alternative
program as provided for in paragraph (e)(1) of this section, unless the emissions trading
program or other alternative measure has been designed to meet a requirement other than
BART (such as the core requirement to have a long-term strategy to achieve the
reasonable progress goals established by States). In this case, the State may determine
the best system of continuous emission control technology and associated emission
reductions for similar types of sources within a source category based on both sourcespecific and category-wide information, as appropriate.
(D) An analysis of the projected emissions reductions achievable through the trading program
or other alternative measure.
(E) A determination under paragraph (e)(3) of this section or otherwise based on the clear
weight of evidence that the trading program or other alternative measure achieves greater
reasonable progress than would be achieved through the installation and operation of
BART at the covered sources.

(ii) [Reserved]
(iii) A requirement that all necessary emission reductions take place during the period of the first
long-term strategy for regional haze. To meet this requirement, the State must provide a
detailed description of the emissions trading program or other alternative measure, including
schedules for implementation, the emission reductions required by the program, all necessary
administrative and technical procedures for implementing the program, rules for accounting
and monitoring emissions, and procedures for enforcement.

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40 CFR 51.308(e)(2)(iv)

(iv) A demonstration that the emission reductions resulting from the emissions trading program or
other alternative measure will be surplus to those reductions resulting from measures adopted
to meet requirements of the CAA as of the baseline date of the SIP.
(v) At the State's option, a provision that the emissions trading program or other alternative
measure may include a geographic enhancement to the program to address the requirement
under § 51.302(b) or (c) related to reasonably attributable impairment from the pollutants
covered under the emissions trading program or other alternative measure.
(vi) For plans that include an emissions trading program that establishes a cap on total annual
emissions of SO2 or NOX from sources subject to the program, requires the owners and
operators of sources to hold allowances or authorizations to emit equal to emissions, and
allows the owners and operators of sources and other entities to purchase, sell, and transfer
allowances, the following elements are required concerning the emissions covered by the cap:
(A) Applicability provisions defining the sources subject to the program. The State must
demonstrate that the applicability provisions (including the size criteria for including
sources in the program) are designed to prevent any significant potential shifting within
the State of production and emissions from sources in the program to sources outside the
program. In the case of a program covering sources in multiple States, the States must
demonstrate that the applicability provisions in each State cover essentially the same size
facilities and, if source categories are specified, cover the same source categories and
prevent any significant, potential shifting within such States of production and emissions
to sources outside the program.
(B) Allowance provisions ensuring that the total value of allowances (in tons) issued each year
under the program will not exceed the emissions cap (in tons) on total annual emissions
from the sources in the program.
(C) Monitoring provisions providing for consistent and accurate measurements of emissions
from sources in the program to ensure that each allowance actually represents the same
specified tonnage of emissions and that emissions are measured with similar accuracy at
all sources in the program. The monitoring provisions must require that boilers,
combustion turbines, and cement kilns in the program allowed to sell or transfer
allowances must comply with the requirements of part 75 of this chapter. The monitoring
provisions must require that other sources in the program allowed to sell or transfer
allowances must provide emissions information with the same precision, reliability,
accessibility, and timeliness as information provided under part 75 of this chapter.
(D) Recordkeeping provisions that ensure the enforceability of the emissions monitoring
provisions and other program requirements. The recordkeeping provisions must require
that boilers, combustion turbines, and cement kilns in the program allowed to sell or
transfer allowances must comply with the recordkeeping provisions of part 75 of this
chapter. The recordkeeping provisions must require that other sources in the program
allowed to sell or transfer allowances must comply with recordkeeping requirements that,
as compared with the recordkeeping provisions under part 75 of this chapter, are of
comparable stringency and require recording of comparable types of information and
retention of the records for comparable periods of time.

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40 CFR 51.308(e)(2)(vi)(E)

(E) Reporting provisions requiring timely reporting of monitoring data with sufficient frequency
to ensure the enforceability of the emissions monitoring provisions and other program
requirements and the ability to audit the program. The reporting provisions must require
that boilers, combustion turbines, and cement kilns in the program allowed to sell or
transfer allowances must comply with the reporting provisions of part 75 of this chapter,
except that, if the Administrator is not the tracking system administrator for the program,
emissions may be reported to the tracking system administrator, rather than to the
Administrator. The reporting provisions must require that other sources in the program
allowed to sell or transfer allowances must comply with reporting requirements that, as
compared with the reporting provisions under part 75 of this chapter, are of comparable
stringency and require reporting of comparable types of information and require
comparable timeliness and frequency of reporting.
(F) Tracking system provisions which provide for a tracking system that is publicly available in
a secure, centralized database to track in a consistent manner all allowances and
emissions in the program.
(G) Authorized account representative provisions ensuring that the owners and operators of a
source designate one individual who is authorized to represent the owners and operators
in all matters pertaining to the trading program.
(H) Allowance transfer provisions providing procedures that allow timely transfer and
recording of allowances, minimize administrative barriers to the operation of the
allowance market, and ensure that such procedures apply uniformly to all sources and
other potential participants in the allowance market.
(I)

Compliance provisions prohibiting a source from emitting a total tonnage of a pollutant
that exceeds the tonnage value of its allowance holdings, including the methods and
procedures for determining whether emissions exceed allowance holdings. Such method
and procedures shall apply consistently from source to source.

(J) Penalty provisions providing for mandatory allowance deductions for excess emissions
that apply consistently from source to source. The tonnage value of the allowances
deducted shall equal at least three times the tonnage of the excess emissions.
(K) For a trading program that allows banking of allowances, provisions clarifying any
restrictions on the use of these banked allowances.
(L) Program assessment provisions providing for periodic program evaluation to assess
whether the program is accomplishing its goals and whether modifications to the program
are needed to enhance performance of the program.
(3) A State which opts under 40 CFR 51.308(e)(2) to implement an emissions trading program or other
alternative measure rather than to require sources subject to BART to install, operate, and maintain
BART may satisfy the final step of the demonstration required by that section as follows: If the
distribution of emissions is not substantially different than under BART, and the alternative measure
results in greater emission reductions, then the alternative measure may be deemed to achieve
greater reasonable progress. If the distribution of emissions is significantly different, the State must
conduct dispersion modeling to determine differences in visibility between BART and the trading
program for each impacted Class I area, for the worst and best 20 percent of days. The modeling
would demonstrate “greater reasonable progress” if both of the following two criteria are met:
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(i)

40 CFR 51.308(e)(3)(i)

Visibility does not decline in any Class I area, and

(ii) There is an overall improvement in visibility, determined by comparing the average differences
between BART and the alternative over all affected Class I areas.
(4) A State whose sources are subject to a trading program established under part 97 of this chapter in
accordance with a federal implementation plan set forth in § 52.38 or § 52.39 of this chapter or a
trading program established under a SIP revision approved by the Administrator as meeting the
requirements of § 52.38 or § 52.39 of this chapter need not require BART-eligible fossil fuel-fired
steam electric plants in the State to install, operate, and maintain BART for the pollutant covered by
such trading program in the State. A State may adopt provisions, consistent with the requirements
applicable to the State's sources for such trading program, for a geographic enhancement to the
trading program to address any requirement under § 51.302(b) or (c) related to reasonably
attributable impairment from the pollutant covered by such trading program in that State.
(5) After a State has met the requirements for BART or implemented an emissions trading program or
other alternative measure that achieves more reasonable progress than the installation and
operation of BART, BART-eligible sources will be subject to the requirements of paragraphs (d) and (f)
of this section, as applicable, in the same manner as other sources.
(6) Any BART-eligible facility subject to the requirement under paragraph (e) of this section to install,
operate, and maintain BART may apply to the Administrator for an exemption from that requirement.
An application for an exemption will be subject to the requirements of § 51.303(a)(2)-(h).
(f) Requirements for periodic comprehensive revisions of implementation plans for regional haze. Each State
identified in § 51.300(b) must revise and submit its regional haze implementation plan revision to EPA by
July 31, 2021, July 31, 2028, and every 10 years thereafter. The plan revision due on or before July 31,
2021, must include a commitment by the State to meet the requirements of paragraph (g) of this section.
In each plan revision, the State must address regional haze in each mandatory Class I Federal area
located within the State and in each mandatory Class I Federal area located outside the State that may be
affected by emissions from within the State. To meet the core requirements for regional haze for these
areas, the State must submit an implementation plan containing the following plan elements and
supporting documentation for all required analyses:
(1) Calculations of baseline, current, and natural visibility conditions; progress to date; and the uniform
rate of progress. For each mandatory Class I Federal area located within the State, the State must
determine the following:
(i)

Baseline visibility conditions for the most impaired and clearest days. The period for
establishing baseline visibility conditions is 2000 to 2004. The State must calculate the
baseline visibility conditions for the most impaired days and the clearest days using available
monitoring data. To determine the baseline visibility condition, the State must calculate the
average of the annual deciview index values for the most impaired days and for the clearest
days for the calendar years from 2000 to 2004. The baseline visibility condition for the most
impaired days or the clearest days is the average of the respective annual values. For purposes
of calculating the uniform rate of progress, the baseline visibility condition for the most
impaired days must be associated with the last day of 2004. For mandatory Class I Federal
areas without onsite monitoring data for 2000-2004, the State must establish baseline values
using the most representative available monitoring data for 2000-2004, in consultation with the

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40 CFR 51.308(f)(1)(ii)

Administrator or his or her designee. For mandatory Class I Federal areas with incomplete
monitoring data for 2000-2004, the State must establish baseline values using the 5 complete
years of monitoring data closest in time to 2000-2004.
(ii) Natural visibility conditions for the most impaired and clearest days. A State must calculate
natural visibility condition by estimating the average deciview index existing under natural
conditions for the most impaired days or the clearest days based on available monitoring
information and appropriate data analysis techniques; and
(iii) Current visibility conditions for the most impaired and clearest days. The period for calculating
current visibility conditions is the most recent 5-year period for which data are available. The
State must calculate the current visibility conditions for the most impaired days and the
clearest days using available monitoring data. To calculate each current visibility condition, the
State must calculate the average of the annual deciview index values for the years in the most
recent 5-year period. The current visibility condition for the most impaired or the clearest days
is the average of the respective annual values.
(iv) Progress to date for the most impaired and clearest days. Actual progress made towards the
natural visibility condition since the baseline period, and actual progress made during the
previous implementation period up to and including the period for calculating current visibility
conditions, for the most impaired and for the clearest days.
(v) Differences between current visibility condition and natural visibility condition. The number of
deciviews by which the current visibility condition exceeds the natural visibility condition, for the
most impaired and for the clearest days.
(vi) Uniform rate of progress.
(A) The uniform rate of progress for each mandatory Class I Federal area in the State. To
calculate the uniform rate of progress, the State must compare the baseline visibility
condition for the most impaired days to the natural visibility condition for the most
impaired days in the mandatory Class I Federal area and determine the uniform rate of
visibility improvement (measured in deciviews of improvement per year) that would need
to be maintained during each implementation period in order to attain natural visibility
conditions by the end of 2064.
(B) As part of its implementation plan submission, the State may propose (1) an adjustment
to the uniform rate of progress for a mandatory Class I Federal area to account for
impacts from anthropogenic sources outside the United States and/or (2) an adjustment
to the uniform rate of progress for the mandatory Class I Federal area to account for
impacts from wildland prescribed fires that were conducted with the objective to establish,
restore, and/or maintain sustainable and resilient wildland ecosystems, to reduce the risk
of catastrophic wildfires, and/or to preserve endangered or threatened species during
which appropriate basic smoke management practices were applied. To calculate the
proposed adjustment(s), the State must add the estimated impact(s) to the natural
visibility condition and compare the baseline visibility condition for the most impaired
days to the resulting sum. If the Administrator determines that the State has estimated the
impact(s) from anthropogenic sources outside the United States and/or wildland
prescribed fires using scientifically valid data and methods, the Administrator may
approve the proposed adjustment(s) to the uniform rate of progress.

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40 CFR 51.308(f)(2)

(2) Long-term strategy for regional haze. Each State must submit a long-term strategy that addresses
regional haze visibility impairment for each mandatory Class I Federal area within the State and for
each mandatory Class I Federal area located outside the State that may be affected by emissions
from the State. The long-term strategy must include the enforceable emissions limitations,
compliance schedules, and other measures that are necessary to make reasonable progress, as
determined pursuant to (f)(2)(i) through (iv). In establishing its long-term strategy for regional haze,
the State must meet the following requirements:
(i)

The State must evaluate and determine the emission reduction measures that are necessary to
make reasonable progress by considering the costs of compliance, the time necessary for
compliance, the energy and non-air quality environmental impacts of compliance, and the
remaining useful life of any potentially affected anthropogenic source of visibility impairment.
The State should consider evaluating major and minor stationary sources or groups of sources,
mobile sources, and area sources. The State must include in its implementation plan a
description of the criteria it used to determine which sources or groups of sources it evaluated
and how the four factors were taken into consideration in selecting the measures for inclusion
in its long-term strategy. In considering the time necessary for compliance, if the State
concludes that a control measure cannot reasonably be installed and become operational until
after the end of the implementation period, the State may not consider this fact in determining
whether the measure is necessary to make reasonable progress.

(ii) The State must consult with those States that have emissions that are reasonably anticipated
to contribute to visibility impairment in the mandatory Class I Federal area to develop
coordinated emission management strategies containing the emission reductions necessary to
make reasonable progress.
(A) The State must demonstrate that it has included in its implementation plan all measures
agreed to during state-to-state consultations or a regional planning process, or measures
that will provide equivalent visibility improvement.
(B) The State must consider the emission reduction measures identified by other States for
their sources as being necessary to make reasonable progress in the mandatory Class I
Federal area.
(C) In any situation in which a State cannot agree with another State on the emission
reduction measures necessary to make reasonable progress in a mandatory Class I
Federal area, the State must describe the actions taken to resolve the disagreement. In
reviewing the State's implementation plan, the Administrator will take this information into
account in determining whether the plan provides for reasonable progress at each
mandatory Class I Federal area that is located in the State or that may be affected by
emissions from the State. All substantive interstate consultations must be documented.
(iii) The State must document the technical basis, including modeling, monitoring, cost,
engineering, and emissions information, on which the State is relying to determine the emission
reduction measures that are necessary to make reasonable progress in each mandatory Class I
Federal area it affects. The State may meet this requirement by relying on technical analyses
developed by a regional planning process and approved by all State participants. The emissions
information must include, but need not be limited to, information on emissions in a year at least
as recent as the most recent year for which the State has submitted emission inventory
information to the Administrator in compliance with the triennial reporting requirements of
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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(f)(2)(iv)

subpart A of this part. However, if a State has made a submission for a new inventory year to
meet the requirements of subpart A in the period 12 months prior to submission of the SIP, the
State may use the inventory year of its prior submission.
(iv) The State must consider the following additional factors in developing its long-term strategy:
(A) Emission reductions due to ongoing air pollution control programs, including measures to
address reasonably attributable visibility impairment;
(B) Measures to mitigate the impacts of construction activities;
(C) Source retirement and replacement schedules;
(D) Basic smoke management practices for prescribed fire used for agricultural and wildland
vegetation management purposes and smoke management programs; and
(E) The anticipated net effect on visibility due to projected changes in point, area, and mobile
source emissions over the period addressed by the long-term strategy.
(3) Reasonable progress goals.
(i)

A state in which a mandatory Class I Federal area is located must establish reasonable
progress goals (expressed in deciviews) that reflect the visibility conditions that are projected
to be achieved by the end of the applicable implementation period as a result of those
enforceable emissions limitations, compliance schedules, and other measures required under
paragraph (f)(2) of this section that can be fully implemented by the end of the applicable
implementation period, as well as the implementation of other requirements of the CAA. The
long-term strategy and the reasonable progress goals must provide for an improvement in
visibility for the most impaired days since the baseline period and ensure no degradation in
visibility for the clearest days since the baseline period.

(ii)
(A) If a State in which a mandatory Class I Federal area is located establishes a reasonable
progress goal for the most impaired days that provides for a slower rate of improvement
in visibility than the uniform rate of progress calculated under paragraph (f)(1)(vi) of this
section, the State must demonstrate, based on the analysis required by paragraph (f)(2)(i)
of this section, that there are no additional emission reduction measures for
anthropogenic sources or groups of sources in the State that may reasonably be
anticipated to contribute to visibility impairment in the Class I area that would be
reasonable to include in the long-term strategy. The State must provide a robust
demonstration, including documenting the criteria used to determine which sources or
groups or sources were evaluated and how the four factors required by paragraph (f)(2)(i)
were taken into consideration in selecting the measures for inclusion in its long-term
strategy. The State must provide to the public for review as part of its implementation plan
an assessment of the number of years it would take to attain natural visibility conditions if
visibility improvement were to continue at the rate of progress selected by the State as
reasonable for the implementation period.
(B) If a State contains sources which are reasonably anticipated to contribute to visibility
impairment in a mandatory Class I Federal area in another State for which a
demonstration by the other State is required under (f)(3)(ii)(A), the State must
demonstrate that there are no additional emission reduction measures for anthropogenic
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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(f)(3)(iii)

sources or groups of sources in the State that may reasonably be anticipated to contribute
to visibility impairment in the Class I area that would be reasonable to include in its own
long-term strategy. The State must provide a robust demonstration, including
documenting the criteria used to determine which sources or groups or sources were
evaluated and how the four factors required by paragraph (f)(2)(i) were taken into
consideration in selecting the measures for inclusion in its long-term strategy.
(iii) The reasonable progress goals established by the State are not directly enforceable but will be
considered by the Administrator in evaluating the adequacy of the measures in the
implementation plan in providing for reasonable progress towards achieving natural visibility
conditions at that area.
(iv) In determining whether the State's goal for visibility improvement provides for reasonable
progress towards natural visibility conditions, the Administrator will also evaluate the
demonstrations developed by the State pursuant to paragraphs (f)(2) and (f)(3)(ii)(A) of this
section and the demonstrations provided by other States pursuant to paragraphs (f)(2) and
(f)(3)(ii)(B) of this section.
(4) If the Administrator, Regional Administrator, or the affected Federal Land Manager has advised a
State of a need for additional monitoring to assess reasonably attributable visibility impairment at
the mandatory Class I Federal area in addition to the monitoring currently being conducted, the State
must include in the plan revision an appropriate strategy for evaluating reasonably attributable
visibility impairment in the mandatory Class I Federal area by visual observation or other appropriate
monitoring techniques.
(5) So that the plan revision will serve also as a progress report, the State must address in the plan
revision the requirements of paragraphs (g)(1) through (5) of this section. However, the period to be
addressed for these elements shall be the period since the most recent progress report.
(6) Monitoring strategy and other implementation plan requirements. The State must submit with the
implementation plan a monitoring strategy for measuring, characterizing, and reporting of regional
haze visibility impairment that is representative of all mandatory Class I Federal areas within the
State. Compliance with this requirement may be met through participation in the Interagency
Monitoring of Protected Visual Environments network. The implementation plan must also provide
for the following:
(i)

The establishment of any additional monitoring sites or equipment needed to assess whether
reasonable progress goals to address regional haze for all mandatory Class I Federal areas
within the State are being achieved.

(ii) Procedures by which monitoring data and other information are used in determining the
contribution of emissions from within the State to regional haze visibility impairment at
mandatory Class I Federal areas both within and outside the State.
(iii) For a State with no mandatory Class I Federal areas, procedures by which monitoring data and
other information are used in determining the contribution of emissions from within the State to
regional haze visibility impairment at mandatory Class I Federal areas in other States.
(iv) The implementation plan must provide for the reporting of all visibility monitoring data to the
Administrator at least annually for each mandatory Class I Federal area in the State. To the
extent possible, the State should report visibility monitoring data electronically.

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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(f)(6)(v)

(v) A statewide inventory of emissions of pollutants that are reasonably anticipated to cause or
contribute to visibility impairment in any mandatory Class I Federal area. The inventory must
include emissions for the most recent year for which data are available, and estimates of future
projected emissions. The State must also include a commitment to update the inventory
periodically.
(vi) Other elements, including reporting, recordkeeping, and other measures, necessary to assess
and report on visibility.
(g) Requirements for periodic reports describing progress towards the reasonable progress goals. Each State
identified in § 51.300(b) must periodically submit a report to the Administrator evaluating progress
towards the reasonable progress goal for each mandatory Class I Federal area located within the State
and in each mandatory Class I Federal area located outside the State that may be affected by emissions
from within the State. The first progress report is due 5 years from submittal of the initial implementation
plan addressing paragraphs (d) and (e) of this section. The first progress reports must be in the form of
implementation plan revisions that comply with the procedural requirements of § 51.102 and § 51.103.
Subsequent progress reports are due by January 31, 2025, July 31, 2033, and every 10 years thereafter.
Subsequent progress reports must be made available for public inspection and comment for at least 30
days prior to submission to EPA and all comments received from the public must be submitted to EPA
along with the subsequent progress report, along with an explanation of any changes to the progress
report made in response to these comments. Periodic progress reports must contain at a minimum the
following elements:
(1) A description of the status of implementation of all measures included in the implementation plan
for achieving reasonable progress goals for mandatory Class I Federal areas both within and outside
the State.
(2) A summary of the emissions reductions achieved throughout the State through implementation of
the measures described in paragraph (g)(1) of this section.
(3) For each mandatory Class I Federal area within the State, the State must assess the following
visibility conditions and changes, with values for most impaired, least impaired and/or clearest days
as applicable expressed in terms of 5-year averages of these annual values. The period for
calculating current visibility conditions is the most recent 5-year period preceding the required date
of the progress report for which data are available as of a date 6 months preceding the required date
of the progress report.
(i)
(A) Progress reports due before January 31, 2025. The current visibility conditions for the
most impaired and least impaired days.
(B) Progress reports due on and after January 31, 2025. The current visibility conditions for
the most impaired and clearest days;
(ii)
(A) Progress reports due before January 31, 2025. The difference between current visibility
conditions for the most impaired and least impaired days and baseline visibility
conditions.

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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(g)(3)(ii)(B)

(B) Progress reports due on and after January 31, 2025. The difference between current
visibility conditions for the most impaired and clearest days and baseline visibility
conditions.
(iii)
(A) Progress reports due before January 31, 2025. The change in visibility impairment for the
most impaired and least impaired days over the period since the period addressed in the
most recent plan required under paragraph (f) of this section.
(B) Progress reports due on and after January 31, 2025. The change in visibility impairment
for the most impaired and clearest days over the period since the period addressed in the
most recent plan required under paragraph (f) of this section.
(4) An analysis tracking the change over the period since the period addressed in the most recent plan
required under paragraph (f) of this section in emissions of pollutants contributing to visibility
impairment from all sources and activities within the State. Emissions changes should be identified
by type of source or activity. With respect to all sources and activities, the analysis must extend at
least through the most recent year for which the state has submitted emission inventory information
to the Administrator in compliance with the triennial reporting requirements of subpart A of this part
as of a date 6 months preceding the required date of the progress report. With respect to sources
that report directly to a centralized emissions data system operated by the Administrator, the
analysis must extend through the most recent year for which the Administrator has provided a Statelevel summary of such reported data or an internet-based tool by which the State may obtain such a
summary as of a date 6 months preceding the required date of the progress report. The State is not
required to backcast previously reported emissions to be consistent with more recent emissions
estimation procedures, and may draw attention to actual or possible inconsistencies created by
changes in estimation procedures.
(5) An assessment of any significant changes in anthropogenic emissions within or outside the State
that have occurred since the period addressed in the most recent plan required under paragraph (f)
of this section including whether or not these changes in anthropogenic emissions were anticipated
in that most recent plan and whether they have limited or impeded progress in reducing pollutant
emissions and improving visibility.
(6) An assessment of whether the current implementation plan elements and strategies are sufficient to
enable the State, or other States with mandatory Class I Federal areas affected by emissions from
the State, to meet all established reasonable progress goals for the period covered by the most
recent plan required under paragraph (f) of this section.
(7) For progress reports for the first implementation period only, a review of the State's visibility
monitoring strategy and any modifications to the strategy as necessary.
(8) For a state with a long-term strategy that includes a smoke management program for prescribed
fires on wildland that conducts a periodic program assessment, a summary of the most recent
periodic assessment of the smoke management program including conclusions if any that were
reached in the assessment as to whether the program is meeting its goals regarding improving
ecosystem health and reducing the damaging effects of catastrophic wildfires.
(h) Determination of the adequacy of existing implementation plan. At the same time the State is required to
submit any progress report to EPA in accordance with paragraph (g) of this section, the State must also
take one of the following actions based upon the information presented in the progress report:
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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(h)(1)

(1) If the State determines that the existing implementation plan requires no further substantive revision
at this time in order to achieve established goals for visibility improvement and emissions
reductions, the State must provide to the Administrator a declaration that revision of the existing
implementation plan is not needed at this time.
(2) If the State determines that the implementation plan is or may be inadequate to ensure reasonable
progress due to emissions from sources in another State(s) which participated in a regional planning
process, the State must provide notification to the Administrator and to the other State(s) which
participated in the regional planning process with the States. The State must also collaborate with
the other State(s) through the regional planning process for the purpose of developing additional
strategies to address the plan's deficiencies.
(3) Where the State determines that the implementation plan is or may be inadequate to ensure
reasonable progress due to emissions from sources in another country, the State shall provide
notification, along with available information, to the Administrator.
(4) Where the State determines that the implementation plan is or may be inadequate to ensure
reasonable progress due to emissions from sources within the State, the State shall revise its
implementation plan to address the plan's deficiencies within one year.
(i)

What are the requirements for State and Federal Land Manager coordination?
(1) By November 29, 1999, the State must identify in writing to the Federal Land Managers the title of the
official to which the Federal Land Manager of any mandatory Class I Federal area can submit any
recommendations on the implementation of this subpart including, but not limited to:
(i)

Identification of impairment of visibility in any mandatory Class I Federal area(s); and

(ii) Identification of elements for inclusion in the visibility monitoring strategy required by § 51.305
and this section.
(2) The State must provide the Federal Land Manager with an opportunity for consultation, in person at a
point early enough in the State's policy analyses of its long-term strategy emission reduction
obligation so that information and recommendations provided by the Federal Land Manager can
meaningfully inform the State's decisions on the long-term strategy. The opportunity for consultation
will be deemed to have been early enough if the consultation has taken place at least 120 days prior
to holding any public hearing or other public comment opportunity on an implementation plan (or
plan revision) for regional haze required by this subpart. The opportunity for consultation on an
implementation plan (or plan revision) or on a progress report must be provided no less than 60 days
prior to said public hearing or public comment opportunity. This consultation must include the
opportunity for the affected Federal Land Managers to discuss their:
(i)

Assessment of impairment of visibility in any mandatory Class I Federal area; and

(ii) Recommendations on the development and implementation of strategies to address visibility
impairment.
(3) In developing any implementation plan (or plan revision) or progress report, the State must include a
description of how it addressed any comments provided by the Federal Land Managers.

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40 CFR 51.308 (up to date as of 10/15/2024)
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40 CFR 51.308(i)(4)

(4) The plan (or plan revision) must provide procedures for continuing consultation between the State
and Federal Land Manager on the implementation of the visibility protection program required by this
subpart, including development and review of implementation plan revisions and progress reports,
and on the implementation of other programs having the potential to contribute to impairment of
visibility in mandatory Class I Federal areas.
[64 FR 35765, July 1, 1999, as amended at 70 FR 39156, July 6, 2005; 71 FR 60631, Oct. 13, 2006; 77 FR 33656, June 7, 2012; 82
FR 3124, Jan. 10, 2017]

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