$ mm %
U82)
PRtfl^
Additional Methods, Determinations, and
Analyses to Modify Air Quality Data Beyond
Exceptional Events

-------

-------
EPA-457/B-19-002
April 2019
Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond
Exceptional Events
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Policy Division
Air Quality Assessment Division
Research Triangle Park, NC

-------
Purpose of this Document
The purpose of this memorandum is to clarify the types of regulatory determinations, actions, and
analyses for which the Environmental Protection Agency (EPA) may consider certain modified air
quality monitoring data. These include determinations, actions, and analyses for which certain air
quality data may be excluded, selected, or adjusted. The clarifying information herein is intended
to supplement the 2016 revisions to the Exceptional Events Rule.1 This memorandum is also
consistent with direction contained in the President's April 2018 Memorandum on Promoting
Domestic Manufacturing and Job Creation—Policies and Procedures Relating to Implementation
of Air Quality Standards.2
Specifically, this document first clarifies for which regulatory determinations a request to exclude
monitoring data may be made under the Exceptional Events Rule (provided the request satisfies
the requirements of that rule). Then the document identifies other determinations, actions, and
analyses that are not covered by the scope of the Exceptional Events Rule, but for which the
exclusion, selection, or adjustment of monitoring data may be appropriate and allowable under
other sections of the Clean Air Act (CAA) and EPA rules or guidance. This document does not
create any new regulatory authority and does not supplant or revise any aspects of the Exceptional
Events Rule or other existing CAA authorities identified herein.
The additional determinations, actions, and analyses covered in this memo, and the exclusion of
data via a concurred exceptional events demonstration, are not necessarily mutually exclusive
processes. However, an important distinction between the Exceptional Events Rule mechanism
and the other mechanisms covered in this memo is that, when air quality data is excluded under
the Exceptional Events Rule, design values for the relevant National Ambient Air Quality Standard
(NAAQS) are recalculated in EPA's Air Quality System (AQS). Data exclusion, selection, or
adjustment in accordance with the other mechanisms covered in this memo would not result in a
change to the design value in AQS.
Determinations and actions covered by the Exceptional Events Rule
In September 2016, EPA finalized revisions to the Exceptional Events Rule in accordance with
CAA section 319(b)(2), which requires the Administrator to promulgate regulations "governing
the review and handling of air quality monitoring data influenced by an exceptional event."
Pursuant to CAA section 319(b)(3)(B)(iv), the Exceptional Events Rule provides "criteria and
procedures for the Governor of a state to petition the Administrator to exclude air quality
monitoring data that is directly due to exceptional events from use in determinations by the
Administrator with respect to exceedances or violations of the national ambient air quality
standards [(NAAQS)]."
1	81 FR 68216 (October 3, 2016). This document is intended to fulfill EPA's commitment, as stated in the 2016
Exceptional Events Rule, to develop a supplementary guidance document "to describe the appropriate additional
pathways for data exclusion for some "predicted future" monitoring data applications."
2	83 FR 16761 (April 16, 2018).
1

-------
The 2016 Exceptional Events Rule specified that it applies to the treatment of monitoring data
showing exceedances or violations of any NAAQS for the purpose of the following types of
regulatory determinations by the Administrator:
•	An action to designate an area, pursuant to CAA section 107(d)(1), or redesignate an area,
pursuant to CAA section 107(d)(3), for a particular NAAQS;
•	The assignment or re-assignment of a classification category to a nonattainment area
where such classification is based on a comparison of pollutant design values, calculated
according to the specific data handling procedures in 40 CFR Part 50 for each NAAQS,
to the level of the relevant NAAQS;
•	A determination regarding whether a nonattainment area has attained the level of the
appropriate NAAQS by its specified deadline;
•	A determination that an area has data for the specific NAAQS, which qualify the area for
an attainment date extension under the CAA provisions for the applicable pollutant;
•	A determination under CAA section 110(k)(5), if based on an area violating a national
ambient air quality standard, that the state implementation plan (SIP) is inadequate under
the requirements of CAA section 110; and
•	Other actions on a case-by-case basis as determined by the Administrator.
See 40 CFR §50.14(a)(l)(i). For the actions identified above, air agencies and EPA must satisfy
the requirements in CAA section 319(b) and the Exceptional Events Rule in order to exclude
monitoring data. See, also, 40 CFR §50.14(b). EPA included "other actions on a case-by-case
basis" in the list of actions above to provide a degree of flexibility for addressing other possible
regulatory determinations. However, in accordance with the scope of CAA section 319(b) and the
Exceptional Events Rule, the case-by-case provision is not intended to serve as a data-exclusion
mechanism for determinations by the Administrator not influenced by exceedances or violations
of the NAAQS, nor for non-regulatory purposes.
Independent determinations and analyses covered by other regulatory programs (not
exceptional events)
EPA recognizes there are determinations and analyses not covered by the Exceptional Events Rule
(i.e., not included in the list of covered regulatory actions above) that also rely on ambient air
quality monitoring data that may have been influenced by atypical, extreme, or unrepresentative
events. The data associated with these independent determinations would only be eligible for
exclusion under the Exceptional Events Rule if the relevant data also influenced one or more of
the regulatory determinations explicitly covered by the Exceptional Events Rule (see list above).
This memo identifies the most common determinations and analyses not covered by the
Exceptional Events Rule, and clarifies for each of them whether there is a separate existing
mechanism (apart from the Exceptional Events Rule) under which the exclusion, selection, or
adjustment of air quality monitoring data may be appropriate. Specifically, monitoring data
2

-------
exclusion, selection, or adjustment may be considered for the following types of determinations
and analyses:3
1.	Certain Modeling Analyses under EPA's Guideline on Air Quality Models
("Guideline"; see 40 CFRPart 51, Appendix Wj4
a.	Preparing required air quality analyses for demonstrating compliance under
Prevention of Significant Deterioration (PSD) permitting program.
b.	Estimating base and future year design values for ozone and PM2.5 SIP
attainment demonstrations.
c.	Determining whether a SIP satisfies CAA section 110(a)(2)(D)(i)(I) regarding
interstate transport.
d.	Preparing any required particulate matter (PM) "hot-spot" analysis for a
transportation conformity determination for certain projects under 40 CFR Part
93 and relevant guidance.5
2.	Selecting data for tracking visibility on the 20 percent clearest and 20 percent most
(anthropogenically) impaired days, as required by EPA's Regional Haze Rule.6 In
particular, this pertains to calculations of baseline, current, and natural visibility
conditions; progress to date; the uniform rate of progress; and determination of
reasonable progress goals (RPGs).
3.	Conducting analyses in support of a NAAQS Limited Maintenance Plan (LMP) SIP
submission and implementation.
Table 1 below includes the situations listed above and, where appropriate, identifies mechanisms
for possible monitoring data exclusion, selection, or adjustment. In general, these procedures are
less resource-intensive than those required by the Exceptional Events Rule. Air agencies that are
preparing a determination for which Table 1 indicates monitoring data exclusion, selection, or
adjustment may be possible are encouraged to contact their EPA Regional office to consult
regarding the air agency's specific situation.
The exclusion, selection, or adjustment of data associated with a situation identified in Table 1
does not preclude an air agency from also pursuing exclusion under the provisions of the
Exceptional Events Rule, if the data also affect one of the types of regulatory actions specified by
the 2016 Exceptional Events Rule. For example, an air agency may seek to exclude specific data
influenced by an atypical, extreme, or unrepresentative event in preparing required air quality
analyses in a PSD permit application and then, after completing this exercise, the air agency might
identify that the same data excluded for PSD purposes also affect one of the determinations
specifically addressed in the Exceptional Events Rule. Provided the data have regulatory
significance under the Exceptional Events Rule, the affected air agency could supplement its prior
analyses with the additional analyses and/or processes required for a demonstration under the
3	The treatment of ambient monitoring data influenced by certain types of international emissions may be handled
under section 179B of the CAA, and EPA intends to release separate technical guidance on such demonstrations.
4	40 CFR Part 51, Appendix W is available online at https://www3.epa.gov/ttn/scram/guidance/guide/appw 17.pdf
5	U.S. EPA Office of Transportation and Air Quality, Transportation Conformity Guidance for Quantitative Hot-spot
Analyses U1PM2.5 and PM10 Nonattainment and Maintenance Areas, EPA-420-B-15-084, November 2015.
Available on EPA's web page at: https://www.epa.gav/state-and-local-transportation/proiect-kvel-conformity-and-
hot-spot-analyses#pmguidance.
6	82 FR 3078 (January 10, 2017).
3

-------
Exceptional Events Rule. If EPA were to concur with the air agency's subsequent demonstration
of an exceptional event, then the event-associated data would be also excluded from use in the
relevant regulatory determination(s) under the Exceptional Events Rule.
Determinations and analyses for which there is no mechanism for data exclusion, selection,
or adjustment
In contrast, there are regulatory determinations that are not eligible for monitoring data exclusion,
selection, or adjustment. This memo identifies the following examples, which are listed and further
clarified in Table 2:
1.	Determining monitor siting, sampling frequency, minimum number, or other
monitoring requirements for an area.
2.	Determining monitoring data completeness.
3.	Determining the priority classification of areas and the adequacy of actions for
emergency episode planning (determinations under 40 CFR Part 51, Subpart H).
Additionally, EPA does not exclude ambient monitoring data from AQS for the purpose of non-
regulatory communications or reporting (e.g., see National Air Quality: Status and Trends of Key
Air Pollutants - hitvs://gisjmb.epa.gov/air/trendsrevort/2018/).
Please share this memorandum with appropriate contacts at state, local and tribal air agencies.
For further information
If you have questions concerning this memorandum, please contact Ben Gibson at (919) 541-3277
or gibson.beniamin(a),ena.gov, or George Bridgers at (919) 541-5563 or bridgers.george(d),erxigov.
4

-------
Table 1. Clarification of independent determinations and analyses covered by other regulatory
programs (not exceptional events)
Type of determination
or analysis
Could monitoring data
qualify for exclusion,
selection, or adjustment?
What is the procedure for
monitoring data exclusion,
selection, or adjustment?
1. Certain Modeling
Analyses under EPA's
Guideline on Air
Quality Models
a.	Preparing required
air quality analyses
for demonstrating
compliance under
PSD permitting
program.
b.	Estimating base
and future year design
values for ozone and
PM2.5 SIP
attainment
demonstrations.
c.	Determining
whether a SIP
satisfies CAA
110(a)(2)(D)(i)(I)
d.	Preparing any
required PM "hot-
spot" analysis for a
transportation
conformity
determination for
certain projects under
40 CFR Part 93 and
relevant guidance.
Yes, monitoring data could
qualify for exclusion if:
A.	Data were already excluded
under Exceptional Events Rule;
or
B.	Ambient data are not
representative per other
applicable EPA rules/guidance
(i.e., 40 CFR Part 58
requirements and relevant
guidance); or
C.	Ambient data are not
representative to characterize
background concentrations or
base period concentrations in
accordance with the Guideline,
which may impact a
determinative value in a past or
projected time period.
Situations could include
removal of air quality
monitoring data that apply to
characterizing background
contributions for NAAQS
compliance demonstrations
under PSD and transportation
conformity, and to developing
alternative current and future
year design values for SIP
modeling in attainment
demonstrations and interstate
transport assessments.7
States may follow EPA
recommendations in Section 8.3.2
c.ii. and d., and Section 8.3.3 d. of
the Guideline.
Early discussion in consultation
with EPA or the appropriate
reviewing authority is
recommended, for example, as
part of the modeling protocol
development process (per Section
9 of the Guideline).
EPA or the appropriate reviewing
authority will review whether the
air agency or permit applicant has
appropriately documented and
justified the data exclusion and/or
adjustment when it acts on a
permit action or SIP submission.
7 See "Modeling Guidance for Demonstrating Air Quality Goals for Ozone, PM2.5, and Regional Haze."
5

-------
Table 1. Clarification of independent determinations and analyses covered by other regulatory
programs (not exceptional events)
Type of determination
or analysis
Could monitoring data
qualify for exclusion,
selection, or adjustment?
What is the procedure for
monitoring data exclusion,
selection, or adjustment?
2. Selecting data for
tracking visibility on
the 20 percent clearest
and 20 percent most
(anthropogenically)
impaired days, as
required by EPA's
Regional Haze Rule:
In particular, this
pertains to calculations
of baseline, current,
and natural visibility
conditions; progress to
date; the uniform rate
of progress; and
determination of the
RPGs.
Yes, monitoring data not
affected by natural events could
qualify for selection if they are
among the 20 percent most
anthropogenically impaired or
20 percent clearest days
(Regional Haze Rule, 40 CFR
§51.308(f)(1); 82 FR3078,
January 10, 2017).
States may follow EPA
recommendations in the Technical
Guidance on Tracking Visibility
Progress for the Second
Implementation Period of the
Regional Haze Program
(December 20, 2018,
httm://www.6t}Q.20v/visibititv/t6ch
nical-guidance-tracking-visibilitv-
vrosress-second-imDlementation-
mriod-remonat). or use another
reasonable method to identify the
included days.
EPA reviews whether the state has
appropriately identified the 20%
most impaired days and 20%
clearest days when it acts on a
regional haze SIP submission.
6

-------
Table 1. Clarification of independent determinations and analyses covered by other regulatory
programs (not exceptional events)
Type of determination
or analysis
Could monitoring data
qualify for exclusion,
selection, or adjustment?
What is the procedure for
monitoring data exclusion,
selection, or adjustment?
3. Conducting analyses
in support of a NAAQS
Limited Maintenance
Plan SIP submission.
Yes, monitoring data could
qualify for exclusion for use in
calculating air quality design
values in support of a NAAQS
LMP submission and any
subsequent yearly design value
calculations for areas with
approved LMPs. Air quality
monitoring data above the
NAAQS-specific LMP
threshold will be treated in a
manner analogous8 to the
treatment of exceedance data
under the Exceptional Events
Rule provided the impacted
data otherwise satisfy the
general definition and criteria
for exceptional events.9
A request for data exclusion must
follow the Exceptional Events
Rule demonstration process. See
2016 Exceptional Events Rule, 81
FR 68216 (October 3, 2016):
httm://www. eva. sov/air-qualitv-
analvsis/treatment-air-Qualitv-
data-influenced-excevtional-events
8	"Analogous" for this purpose means to follow the Exceptional Events Rule requirements and demonstration
process to exclude certain monitoring data in LMP submissions even when the data is not an exceedance and does
not contribute to a violation (i.e., does not qualify as an exceptional event under the Exceptional Events Rule).
9	A May 7, 2009, EPA memorandum titled, "Update on Application of the Exceptional Events Rule to the PMio
Limited Maintenance Plan Option" is the original basis for this interpretation regarding PMio. The substantive
content of the memo remains in effect; however, to the extent the memo cites the 2007 Exceptional Events Rule,
EPA has since replaced that rule with the 2016 Exceptional Events Rule. The memo is available at
https://www3.epa.sov/ttn/naaqs/aqm8uide/collection/cp2/20090507 harnett Imp pmlO update exc event.pdf
7

-------
Table 2. Clarification of determinations and analyses for which there is no mechanism for data
exclusion, selection, or adjustment
Type of determination or
analysis
Could monitoring data
qualify for exclusion,
selection, or adjustment?
What is the procedure for
monitoring data exclusion,
selection, or adjustment?
1. Determining monitor
siting, sampling frequency,
minimum number, or other
monitoring requirements
for an area.10
No, monitoring data
generally cannot be
excluded for the purpose of
determining monitoring
requirements.11
Data exclusion is generally not
available, but air agencies may
consult with their EPA Regional
office regarding unique situations.
2. Determining monitoring
data completeness.
No, monitoring data could
not qualify for, nor be
affected by, event-
influenced exclusion. Valid
monitoring data are to be
counted towards data
completeness even if the
data have been affected by
an event and even if the
data have been excluded
from a design value or
other calculation.12
No procedure or mechanism is
available or applicable.
3. Determining the priority
classification of areas and
the adequacy of actions for
emergency episode planning
(determinations under 40
CFR Part 51, Subpart H)
No, monitoring data could
not qualify for event-
influenced exclusion.
No procedure or mechanism is
available or applicable.
10	See, for example, 40 CFR 58.12(d)(l)(iii), which requires a certain frequency of sampling depending on the
monitored design value.
11	Monitoring requirement determinations that rely on a NAAQS design value (e.g., determining monitoring
frequency) generally use the design value that is stored in AQS. To the extent a historical design values in AQS
reflects EPA's concurrence on the exclusion of data influenced by exceptional events for specific regulatory
purposes pursuant to the Exceptional Events Rule, such monitoring requirement determinations would be indirectly
affected by the exclusion of event-influenced data for an unrelated regulatory purpose.
12	For additional information on data completeness, see 40 CFR Part 50, Appendices H, I, K, N, P, R, S, T and U at
https:/Avww.ecfi,.gov/cgi-bm/text-idx?tpl=/ecfrbrawse/Title40/4OcffSO main 02.tpl.
8

-------
United States	Office of Air Quality Planning and Standards	Publication No. EPA-457/B-19-002
Environmental Protection	Air Quality Policy Division/Air Quality Assessment Division April 2019
Agency	Research Triangle Park, NC

-------