SEPA
United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangie Park NC 27711
EPA-450/4-86-007
July 1986
Air
Guideline on the
Identification and
Use of Air Quality
Data Affected by
Exceptional Events
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EPA-450/4-86-007
Guideline on the Identification
and Use of Air Quality Data
Affected by Exceptional Events
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Monitoring and Data Analysis Division
Research Triangle Park, NC 27711
July 1986
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DISCLAIMER
This report has been reviewed by the Office of Air Quality Planning and
Standards, Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products is not intended to constitute
endorsement or recommendation for use.
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CONTENTS
1. INTRODUCTION .....' 1
2. PURPOSE AND MANAGEMENT OF FLAGGING SYSTEM, 5
2.1 Pre-Airs 5
2.2 Post-Airs 6
3. USES OF FLAGGED DATA 8
3,1 General Guidelines on the Use of Flagged Data 3
3.2 NAAQS Status 9
3.3 Trends Analysis ...... 10
3.4 SIP Regulatory Activities 11
4. DEFINITION AND APPLICATION OF EXCEPTIONAL EVENTS 12
. " 4.1 Definitions of Exceptional Events 12
4.1.1 General Exceptional Event Criteria ....... 13"
4.1.2 Specific Definitions . . ._ 14
4.2 Demonstration of Causal Relation ,...,.. 24
4.3 Application of Definitions and/or Criteria . 25
4.4 Documentation 26
APPENDIX '. . , . . . 28
Development of Criteria for Possible Exceptional Events
I. Identification of Events ..... . 28
II. Events Not Considered Exceptional for Data Flagging
Purposes 31
REFERENCES , .' 34
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SECTION 1
INTRODUCTION
Federal, State, and local air pollution control officials have expressed
a great deal of concern regarding the handling of air quality data that are
influenced by both natural and man-made events that are considered exceptional.
These events are considered exceptional for two reasons; they are not expected
to recur routinely at a given location, or they are possibly uncontrollable
or unrealistic to control through the State Implementation Plan (SIP) process.
In some cases in the past, air quality data collected during these "exceptional"
events have not been submitted to the National Air Data Bank (NADB) because
State or local agencies were concerned about the potential misuse of such
data. This guideline document was prepared as a response to this concern and
is intended to provide national guidance for Identifying ("flagging") and using
ambient air quality data influenced by exceptional events.
The guidance includes definitions of 18 acceptable exceptional events
and describes the procedures for submitting flagged data influenced by these
events to EPA's Aerometric Information Retrieval System (AIRS), The Appendix-
provides information on other events which were also initially proposed for
consideration as "exceptional" but are not included in the final flagging
system.
The need for a flagging (or "identification") system was implied in
previous Agency guidelines and regulations. The first example is Office of
Air Quality Planning and Standards' Guideline No. 1.2-008 (revised February
1977) entitled, "Guidelines for the Interpretation of Air Quality Standards."!
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This guideline addressed the submission and use of all valid air quality data
for determining an area's overall compliance status with respect to National
Ambient Air Quality Standards (NAAQS). Issue 9 in the guideline posed the
following question: "How should participate matter (PM), carbon monoxide
(CO), and other pollutant concentrations resulting from severe recurring dust
storms, forest fires, volcanic activity, and other natural sources be taken
into account in determining compliance with NAAQS?" The guideline recommended,
"Regardless of the source, ambient pollutant concentrations exceeding a NAAQS
constitute a violation." The guideline, however, implied a need for data
'flagging by further stating, "Detailed information establishing that viola-
tions are due to uncontrollable natural sources may be used in determining
the feasibility of modifying control strategies."
The second example is in 40 CFR 51.12 (d), the regulations for the
development, adoption, and submittal of SIP's.2 The regulations stated: "For
purposes of developing a control strategy, data derived from measurements of
existing ambient levels of a pollutant may be adjusted to reflect the extent
•to which occasional natural or- accidental phenomena, e.g., dust storms,
forest fires, industrial accidents, demonstrably affected such ambient levels
during the measurement period."
A third example is provided in the March 20, 1984, 40 CFR Part 50
Feder_a| Regi_ste_r proposed revisions to the national ambient air quality stan-
dards for particulate matter.3 Appendix K of Part 50 would allow consideration
of the influence of rare or unusual events on PMjQ data by various techniques.
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All three examples, OAQPS 1.2-008, 40 CFR 51.12(d), and the proposed
40 CFR 50 Appendix K reflect concern that some air quality data associated
with the occurrence of certain types of events may require special
consideration in order to avoid misuse.
The guideline's general policy is to allow consideration of excluding
flagged data from use in regulatory actions. The actual exclusion of the use
of flagged data would only be allowed if, as a result of a public review
process, the responsible government agency e.g., the State Air Agency during
the State regulatory process, and the U. S. EPA during the Federal review/
• approval process, determines that the data are inappropriate for use in a
specific regulatory activity. This consideration for-exclusion of flagged
data carries with it no prior presumption towards use or non-use of flagged
data.
By establishing uniform procedures and criteria for flagging and
determining the use of data associated with exceptional events, EPA expects
data collectors to submit to the NADB all valid ambient air quality data,
i.e., data collected in accordance with 40 CFR 58. Having a complete national
air quality data file will provide a data base adequate to evaluate and
substantiate the impact of exceptional events on air quality and to assist
users in interpreting the data.
The guideline provides criteria and procedures by which potential users
of air quality data can be informed of "exceptional events" which may have
influenced the data. The guideline has no regulatory or legal significance
regarding use of any air quality data. Use or non-use of air quality data,
whether flagged or not, must be subjected to full public disclosure and
rulemaking procedures.
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The criteria for identification of "exceptional events" are designed to
be expansive enough to encompass most good faith claims by State and local
agencies of when data should be considered for.special treatment. It is not
intended to reflect EPA's views on the validity of these claims. The flagging
of data is merely a way for a State or local agency to state that it regards
the data as influenced by exceptional events, and may later claim that the
data should be discounted for certain purposes.
As experience with this guideline is gained, periodic revisions may be
made. The guideline is to be implemented on a trial basis for approximately
2 years, after which the Standing Air Monitoring Work Group (SAMWG) will
assess its effectiveness and make any appropriate recommendations for revision.
The SAMWG is composed of Federal, State, and local air pollution control
officials who constitute a forum for discussion and resolution of ambient air
quality monitoring issues.
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SECTION 2
PURPOSE AND MANAGEMENT OF THE'FLAGGING SYSTEM
The basic purpose of the flagging system is to identify those air quality
measurements that are influenced by exceptional events. These are events
which, if unidentified, could lead to possible misinterpretation or misuse of
the data. Because the flagging system relies heavily on the identification
and understanding of events that may have influenced a particular air quality
measurement, its major thrust is information exchange. If a particular air
quality measurement is influenced by an exceptional event, it is important
for all those who may review and ultimately use the data to be aware of this
influence and to take care that such data are not misinterpreted or misused.
Knowledge and understanding of what the data represent are critical in the
overall air quality planning process.
Under the flagging system, State and local air pollution control agencies
will be responsible for initially identifying and documenting data influenced
by exceptional events. These agencies also must develop the appropriate back-
ground information used to support the decision to flag an individual piece
of data; they must submit the information to EPA for concurrence and make it
available for the public's review upon request. Because of the potential
implications on the use of flagged data, the agency flagging the data must
(as discussed in Section 4.2) clearly demonstrate a causality between the
exceptional event and the flagged air quality data.
2.1 PRE-AIRS 'PROCEDURES
Until the Aerometric Information Retrieval System (AIRS) is operational,
the flagged data should be specifically identified and discussed in the "
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annual State and Local Air Monitoring System (SLAMS) Report. The EPA Regional
Offices will be responsible for review and concurrence or non-concurrence with
the flag, except for data related to stratospheric ozone intrusions which
will be reviewed and concurred or non-concurred with by OAQPS. States should
initiate discussions with EPA Regional Offices regarding data that may be
flagged as soon as possible after data collection, and should not wait until
the annual SLAMS Report is submitted.
2.2 POST-AIRS PROCEDURES
After AIRS is operational, all flagged data will be entered and stored
in the AIRS; and as-data are retrieved, a user will be able to identify those
data that have been flagged. Each exceptional event will be assigned a
unique flag code by the AIRS for the exceptional events included in this
guideline. The procedure for submitting, reviewing, and assigning appropriate
flags for data identified by State or local agencies to be associated with an
exceptional event are as follows:
(1) The State or local agency should submit their flagged data with the
proper unique flag code to AIRS as part of their routine data submissions to
EPA's data bank.
(2) The State or local agency should provide to the Regional Office,
within 30 days, appropriate documentation and demonstration of causality as
discussed in Section 4.4.
(3) The Regional Office should concur or non-concur with the data flag
and notify the State or local agency within 30 days of receipt of documenta-
tion from the agency. If the Regional Office concurs with the flagging of
the data, they will change the unique flag code associated with the data to
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designate EPA Regional Office concurrence with the flag. If the Region non-
concurs with the data flag, the State or local agency flag will remain in
AIRS with the particular data point. The non-concurrence by the Regional
Office could be revised upon subsequent submission of adequate justification
by the State and local agency. The exception to the procedure is stratospheric
ozone intrusion, which is to be reviewed and acted upon by OAQPS rather than
the Regional Office.
(4) Those States electing to submit to NADB only an annual SLAMS report
rather than raw data should include a section in their annual report which
lists all flagged data, SARQAD I.D.., date of occurrence, and type of acceptable
exceptional event.
Notification must be sent to AIRS and the Regional Office by the
responsible State or local agency when flagged data are to be changed to a
nonflagged status for any reason.
Two data records will be maintained in AIRS. One record will contain
all the data including the flagged data, and the other will contain only
data that have not- been flagged. All users of the data will have access to
both records, including the rationale for the flag and .the EPA Regional
Office concurrence or non-concurrence with the flag.
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SECTION 3
USES OF FLAGGED DATA
3.1 GENERAL GUIDELINES ON THE USE OF FLAGSED DATA
Concern over-the potential for misuse has made some State and local
agencies reluctant to submit air quality data that were influenced by what
they consider to be an exceptional event, i.e., an event that 1s not expected
to recur routinely at a given location, or that is possibly uncontrollable
or unrealistic to control through the State Implementation Plan (SIP) process.
The views of Federal, State, and local agency officials have varied concerning
the use of air quality data collected during an exceptional event. Some
believed that air quality data collected during an exceptional event should
not be used under any circumstances; some" believed that all valid (i.e., col-~
lected in accordance with 40 CFR 58) data should be used (without exception);
some believed that the data should be used only to determine the status of
the area with respect to the NAAQS; and still others believed that the data
not only should be used to determine the compliance-status of the area, but
also to develop trends analyses and control strategies (with some qualifica-
tions). This document addresses these differences by requiring the States
(and EPA) to identify and explain the use or non-use of data influenced by
exceptional events during a public review process. Furthermore, nhe guidance
provided does not dictate any prior presumption toward use or non-use for any
specific purpose.
In general, decisions on the use or non-use of flagged data will be made
on a case-by-case basis for specific purposes (attainment designations, control
strategies, etc.), and the public must be informed tnat the data exist, whether
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the data are used or not. The main,concern lies with-understanding what the
flagged data represent.- Three steps usually should be taken in order to
decide whether questionable data should be flagged, and to assist potential
users In determining how the data should be used. The first step is to deter-
mine the portion of the measured air quality level attributable to the single
-event, as well as the cumulative effect of several similar exceptional events,
that create substantial impacts at a monitoring site. In some cases, modeling
(either source apportionment or dispersion) or other procedures may be used to
determine the relative contribution of the event. The relative contribution of
the event provides a better understanding of' what the air quality level for the
day or days in question actually represents.
The second step is to determine the area influenced by the event. In
most cases, the impact will be limited. Therefore, if the data are .being con-
sidered for use in or exclusion from regulatory purposes, the agency should
determine the area which would be influenced by the determination.
The third step is to demonstrate how the flagged data relate to data
previously collected at the monitoring site. This step is extremely critical
for trends analyses and for preparing reports to the public on air quality
levels for a given area. Obviously, if flagged data are used or excluded in
preparing summaries of air quality data, the reader should be made aware of how
the. data were used.
3-.2 NMQS Status
NAAQS compliance status involves the use of data to determine whether the
area represented by the data is meeting or exceeding the NAAQS for the pollutant
being monitored. It is EPA's policy and a regulatory requirement to have valid
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NAMS and SLAHS data (i.e., data collected in accordance with 40 CFR 58)
submitted to the NADB or included in the annual SLAMS report. All data,
flagged or unflagged, should be available to the public for comparison to the
NAAQS to determine if exceedances have occurred. All relevant flagged data
along with the reasons for flagging, and a demonstration of causality between
the exceptional event and the flagged data, shall be submitted for considera-
tion of use/non-use during any public hearing or comment period called under
Sections 107, 110-113, 119, 120, 122, 123, 126, Part C or Part D of the Clean
Air Act.^ Consideration of ambient air quality data during public reviews
called under the authority of other sections or titles of the Clean Air Act,
although not prohibited, does not appear to be relevant to the purpose of those
reviews. For example, consideration of ambient data at a hearing held regarding
automotive emissions standards may or may not be appropriate. Such consideration
is neither mandatory nor prohibited.
3.3 Trends Analysis
Trends analysis involves the evaluation of the long-term trends associated
with the measured levels of a given pollutant for a given area. These analyses
are useful in evaluating the overall progress of the air pollution control pro-
gram for the given pollutant and in understanding why the concentration levels
of a pollutant are increasing or decreasing.
In some cases the data collected during an exceptional event can be
used for trends analysis (as long as the analyst understands the limitations
associated with the data). The trends analyses should clearly state how the
flagged data were treated and to what extent the flagged data were or were
not included in the analyses and why. The trends analyses also should consider
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(to the extent possible) what effect the. flagged data have on the overall
trend line for the area in light of other confounding variables that may also
affect the trend Tine,
3.4 SIP ReguUto_ry_ Activities
The use of flagged a'ir quality data for SIP regulatory activities
(areawide or local control strategy development, SIP design values, attain-
ment/non-attainment status, enforcement actions, etc.) shall be considered on
a case-by-case basis and discussed during the public review process. Exclu-
sion of the flagged data would only be allowed if the responsible control
agency determines in conjunction with a public review that the flagged
data are inappropriate for use.
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SECTION 4
DEFINITION AND APPLICATION OF EXCEPTIONAL EVENTS
4.1 DEFINITIONS OF EXCEPTIONAL EVENTS
This guideline provides general definitions for these events and general'
criteria for their use in flagging air quality data. The application of a
definition may vary from area to area because of differing air quality and
control situations. For example, salting and sanding of streets for snow and
ice control may be an exceptional event in the southern sections of the country,
whereas they may be routine, controllable events in the northern sections.
Therefore, the following definitions are only a national guide and are not
meant to replace reasonable judgment on the part of the Regional, State, and
local air pollution control agency officials in defining and identifying
exceptional events for the purpose of flagging data.
In situations where it can be shown that the national criteria are
generally inappropriate, a State Agency may propose alternate criteria to their
EPA Regional office. These proposals would have to be subjected to puolic
review within the State. The Regional office would be responsible for review
and preliminary approval of the alternative criteria. The OAQPS will have
final approval authority and if approved, will include the alternative criteria
as a supplement to this national guideline.
With the above limitations in mind, the following general definitions-have
been developed to promote consistency with respect to flagging data that have
been collected during an exceptional event. Whenever possible, specific cri-
teria or terms have been used to define the event to minimize inconsistent
interpretations. Of course, no term can be absolutely defined so that there is
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no room for interpretation. Thus, these definitions and associated criteria
provide for some flexibility in their application to an individual event.
What may be unusual or exceptional for one part of the country may be typical
for another and this variability requires flexibility in national definitions
and criteria.
The definitions that follow have in some cases specific numbers included
within the definition. Although they are not fully supported by technical
studies, they are included as a practical alternative to deleting weakly sup-
ported values and, to the extent possible, reflect the comments received during
development of this guideline. These numbers may require adjustments as
experience is obtained with the guideline.
4.1.1 General Exceptional Event Criteria
Before one can define an individual exceptional event, one must have a
general definition of "exceptional." In a sense, this definition also serves
as an overriding criterion with regard to the specific definitions presented
in 4.1.2..
Webster defines "exceptional" as forming an exception, rare, uncommon,
extraordinary, deviating from the norm. With respect to air quality consider-
ations in this guideline, an exceptional event is defined as an event that is
not expected to recur routinely at a given location, or that is possibly uncon-
trollable or unrealistic to control through the SIP process. As noted previously,
what is exceptional in one area of the country may not be exceptional in another.
Therefore, some judgment is needed in identifying whether an event is exceptional
in the area of the country where it has occurred.
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4.1.2 Specific Definitions
The following definitions are provided for the purpose of identifying
an exceptional event. Some additional discussion is provided in each case
to aid 1n the application of these definitions.
HIGH HINDS (PH)
Definition:
An hourly windspeed of greater than or equal to 30 mph or gusts
equal to or greater than 40 mph, with no precipitation^ or only
a trace of precipitation (observed as scattered drops that do not
completely wet or cover an exposed area up to a rate of 0.01
inch/hrj).
The high wind condition with no precipitation or only light precipitation
and dry soil must be associated with a significant contribution (estimated to '
be >_ 8S% by weight) of crustal material on the PM sampling medium. High winds
without unusually high PM levels due to the suspension or resuspension of
crustal materi-al should not be considered an exceptional event. Additionally,
fugitive emissions or dust from any part of an industrial source should not be
flagged.
STRATOSPHERIC OZONE INTRUSION (0-j)
Definition:
A stratospheric ozone intrusion occurs when a parcel of air
originating in the stratosphere, average height 20 km (12.4 mi),3
is entrained directly to the surface of the earth.
Although this event is exceptional, the circumstances or the criteria
under which it occurs are difficult to measure or document given current
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measured meteorological parameters. Stratospheric ozone intrusions are
infrequent and very localized events of short duration, which makes it dif-
ficult to use currently available airport data to determine whether a strato-
spheric ozone intrusion has occurred. Stratospheric ozone intrusions are
typically associated with strong frontal passages or severe thunderstorms and,
thus, may occur primarily during the spring of the year. The above definition
is provided only as a general guide for differentiating between stratospheric
ozone intrusion, which is an exceptional event for the purpose of flagging
data, and other nonexceptional meteorological events. Although data have been
identified in the past as being the result of stratospheric ozone intrusion, no
standard definition or criteria have been established for concrete identifica-
tion. Therefore, determining whether a stratospheric ozone intrusion has
occurred should be a case-by-case decision based on reasonable judgment regarding
the Reason of the year, time of day, and accompanying meteorological conditions
associated with the ozone measurement in question. The EPA concurrence or
non-concurrence authority for flagging of ozone data for stratospheric intrusion
is the responsibility of OAQPS upon review of the documentation submitted by
the State or local agency flagging the ozone data,
VOLCANIC ERUPTIONS (CO, SO?, NO?, PM)
Definition:
The emission or ejection of volcanic materials at the Earth's
surface from a crater or fissure.9
Emissions from volcanic eruptions have a large-scale areawide impact on
air quality. Excessive air quality concentrations resulting from volcanic
eruptions should be flagged regardless of the frequency of eruptions. In most
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cases, however, the eruptions and resulting impact on air quality would be
very infrequent.
SANDBLASTING (PM)
Definition:
Sandblasting or gritblasting refers to the temporary use of
abrasive blasting with pressurized air for surface preparation
purposes at a given location.
Methods currently available are used to control these operations to
minimize their impact on air quality at fixed point sources where routine
applications are part of the facilities' operations. Ambient air quality
levels influenced by these activities should not be flagged. However,
completely effective control techniques are not necessarily available or
possible for portable sandblasting operations. Therefore, data collected at
a site within a micro or middle scale distance from a temporary (generally 3
weeks or less) sandblasting operation may be flagged if all reasonable control
measures have been employed to minimize adverse impacts on air quality.
FORESTFIRES (CO, PH)
Definition:
An uncontrolled fire in vegetation or associated flammable material
that requires suppressive action to protect natural resources or
"values associated with natural resources or that is destructive to
natural resources.10
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Class
A
B
C
Size, acres
£0.25
0.26 - 9
10 - 99
Cl ass
D
E
F
G
Size, acres
100 - 299
300 - 999
1000 - 4999
>5000
Some forest fires are unpreventable and because uncontrollable emissions
from forest fire can adversely affect air quality concentrations over a large
area, forest fires should be considered an exceptional event for the purpose of
flagging air quality data. In. general, Class A and B fires tend to have a more
localized impact; therefore, only data collected at downwind monitors within 3
miles of these type fires should be flagged. For Classes C through 6, the
impact of the fire is more widespread and the location with respect to the
monitor should be supported by receptorll«12,13,14 or dispersion modeling.15,16
STRUCTURAL FIRES (CO. PM)
- Definition:
Any accidental fire involving- some kind of structure. In
general, a structural fire involves a building having at
least 500 square faet.
The structural fire should be within a micro- or middle-scale distance (up
to 500 meters as defined by 40 CFR 58, Appendix D) of a monitor in most instances
for the data from that monitor to be flagged. However, a much greater distance
may be appropriate for large fires such as a refinery, industrial, or commercial
business area fire provided the causal relation is supported by receptor or
dispersion modeling.
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HIGH POLLEN COUNT (PH)
Definition:
A pollen count index above 25 grains/cm2 or 1000 grains per
cubic meter.17
The pollen count index is usually obtained by use of a coated slide
mounted on a circular plate that is generally mounted on the top of a seven
or eight-story building with, an unobstructed air flow. The index is in units
of grains of pollen per cm,2 Another method of measuring the concentration
of pollen is volumetric, i.e., counting the number of grains per cubic meter.
Other recognized methods for measuring pollen levels-may be used. For a
high-pollen count to be flagged as an exceptional event, the pollen count
index should be greater than 25, or 1000 grains per cubic meter and the high-
volume filters on which the samples were collected should be analyzed micro-
scopically to ensure that significant amounts of pollen (i.e., 50% or greater
than the normal pollen count for a typical sample) were collected on the day
or days being considered for flagging. Where high pollen is considered to be
a problem, State or local agencies should develop procedures for ascribing
the effects of high pollen count on filters and should submit them to the
respective Regional Office for approval.
CHEMICAL SPILLS AND INDUSTRIAL ACCIDENTS (CO, SO?. NOg, PH)
Definition:
Emissions that result from accidents such as fire,
explosions, power outages, train derailment, vehicular
accidents, or combinations of these'.18
The spill or accident must, of course, not be a routine occurrence. Any
of these situations that do occur routinely should be critically evaluated and
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stopped. Data from sites that can be unequivocally related to a non-routine
accident or spill riiay be flagged,
UNUSUAL TRAFFIC CONGESTION (CO)
Definition:
A condition resulting from a major accident (rather than
frequent minor accidents,) or short-duration obstruction,
such as demolition or construction. During these conditions
the level of traffic may increase until it exceeds the
maximum capacity of a given street or highway. Speeds are
reduced substantially and stoppages may occur for short or
long periods of time because of downstream congestion. In
extreme cases, both speed and volume can drop to zero.19
As a general rule of thumb, congestion must occur within five hundred
meters of a monitoring site (i.e., micro- to middle-scale) and not be a regular
occurrence for the data from that site to be flagged.
CONSTRUCTION/DEMOLITION (PM)
Definition:
The building/destroying/renovation of any residential,
institutional, commercial, or industrial building (including
apartment buildings with more than four dwelling units),
structure, facility, or installation that-lasts for only a
short period of time and is reasonably controlled.
The construction or demolition activity must take place within a reasonable
distance of the monitoring site and all reasonable control measures must be
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in use before the data from the site can be flagged. Flagged data should be
limited to sites classified as micro- or middle-scale (up to 500m) and downwind
with respect to the construction activity.
AGRICULTURAL TILLING (PM)
Definition:
The act of preparing dry soil for cultivation or for
controlling the growth of weeds by the use of mechanical
"devices during periods with an hourly average windspeed
of greater than 20 mph.
Generally, agricultural tilling operations must occur within a reasonable
distance (500 meters) of the monitoring site and tilling must have occurred at
the same relative location while the hourly average windspeed is greater than
20 rnph for the monitoring data to be flagged. Flagged data must have been
collected during or immediately after the day tilling occurred and should be
limited to sites which would be classified as micro- or middle-scale with
respect to the tilling operations,
HIGHHAY CONSTRUCTION (PM)
Definition:
The act of building a new, or repairing an existing,
highway, road or street.
Particulate matter resulting from reasonably controlled highway
construction for short time periods may be flagged provided that a microscopic
analysis of the filter indicates that 85 percent of material on the filter is
related to construction activities and all reasonable control measures have
been utilized. ,
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REROUTING OF TRAFFIC (CO)
Definition:
A temporary deviation or detour of vehicular traffic
because of an accident, construction, or demolition. The
detour must be for no more than.l week.
The rerouting of traffic should be within a reasonable distance of a
monitoring site and last for no more than 1 week for the monitoring data to
be flagged. Flagged data should be limited to sites classified as micro- or
* middle-scale (within 500 meters) with respect to the detour.
SALTING/SANDING OF STREETS (PH)
Definition:
The application of salt and/or sand to the road surface to
increase traction and/or prevent the surface water from
refreezing after it has melted.
The salting and sanding must occur within a reasonable distance (up to
500 meters) of the monitoring site if the data from the site are to be flagged,
Flagged data should be limited to sites classified as micro- or middle-scale
with respect to the salting/sanding operations and microscopic examination
shows that 85 percent of the material on the filter is salt and/or sand. Data
collection is not limited to the date of salting or sanding of the street.
All reasonable control measures must be taken to minimize the adverse air
quality impact of the salting or sanding operations in order for the data to
be flagged. In general this type of data should not be flagged in areas
which experience a significant use of salt and/or sand.
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INFREQUENT LARGE GATHERINGS (CO, _PH)
Definition:
A gathering of more than 10,000 people (5000 cars) at any
one time and at a -single location. Unusual traffic congestion
must be associated with the event.
A large gathering in and of itself without the associated traffic
congestion would not qualify as an unusual event for the purpose of flagging.
(See discussion of unusual traffic congestion for more details on the cri-
teria for flagging data because of unusual traffic congestion). The event
would also be expected to occur less than once per year, and the event should
be at a location not regularly used for such purposes. Flagged data should be
limited to sHes classified as micro- or middle-scale with respect to the
gathering.
ROOFING OPERATIONS (PH. SO?)
Definition:
The process of building, repairing, or recoating the external
upper covering of .a house or building that involves the
application of a petroleum-based material (usually haavy
residuals from a refining operation) to a roof. The material
is heated and then sprayed or rolled onto the surface.
Generally, a roof so covered would be resurfaced or treated
no more than once every 3 to 5 years. Unless major damage
has occurred, some surfaces would require treatment only every
5 to 10 years.
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Roofing operations must occur within a micro-scale distance and upwind
of the monitoring site, and all reasonable control measures must be applied
for the data to be flagged.
PRESCRIBED BURNING (PH, CO)
Definition:
A controlled fire of vegetative material that is used
to improve range lands, agricultural or forestry resources,
or associated values,
Prescribed burning is generally a controlled activity that is limited .to
those days or periods when the meteorological conditions' are conducive to good
dispersion. Thus, the emissions which affect air quality are dispersed to the
extent possible. However, the resulting emissions occasionally adversely affect
air quality concentrations over- a large area. In areas of the country where
prescribed burning is used regularly and extensively for agricultural and/or
forestry land management, prescribed burning-may not be considered an excep-
tional event for the purposes of flagging air quality data. Prescribed
burning in these areas is usually subject to rules and regulations, including
smoke management plans, under which a regulatory agency permits burning after
deciding where, and to what extent, the smoke will be allowed to impact air -
quality.
However, in many areas of the country, prescribed burning for agricultural,
forestry land management, or other purposes is an infrequent but necessary
activity and may be impractical to fully control. These practices may.be con-
sidered an exceptional event for the purposes of flagging air quality data.
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However, it must be demonstrated through receptor or dispersion modeling,
that the burning operations have a substantial impact on the monitored air
quality data.
CLEAN UP ACTIVITIES AFTER A MAJOR DISASTER (PH. CO, SO?)
Definition;
For the purposes of flagging, major disasters are serious
public misfortunes for which State or Federal relief has
been granted.
PM, CO, S02 or other pollutant data affected by and collected during, or
for a reasonable period after, the clean up activities following a major
disaster may be flagged.
4.2 DEMONSTRATION OF CAUSAL RELATION
Excluding the use of valid air quality data from regulatory purposes
is a serious action. Accordingly, a clear demonstration of the relationship-
between the exceptional event and the measured air quality must be provided.
. As a minimum, this demonstration should: (a) include all relevant raw data
(e.g., air quality data, meteorological data, traffic counts, etc.); (b) show
that the monitor did not record high concentrations before and after the
period of the exceptional event; (c) show that the local wind direction was
such that the monitored pollutant was transported from the exceptional event
source to the monitor during the period in question; (d) include as appro-
priate receptarll>12,13,14 or dispersion modeling!5,16 connecting the monitored
concentrations with the exceptional source emissions; (e) include, as appro-
priate, microscopic filter analyses (for particulate emissions); and (f)
include documentation supporting the existence of the exceptional event.
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4,3 APPLICATION OF DEFINITIONS AND/OR CRITERIA
As noted earlier, the purpose of this guideline is to provide guidance
and direction for flagging air quality data associated with exceptional
events and thus promote national consistency in the flagging of such data.
Having established general definitions for the exceptional events and
the criteria for applying flags to the data, the State or local agency should
consider flagging of any data meeting the criteria of this guideline and
prepare adequate evidence to clearly demonstrate the causal relationship
between the exceptional event and the flagged data. The flagged data with
adeq-uate documentation of the causal relationship should be submitted to the
appropriate Regional Office following the procedures outlined in Sections 2.1
and 2,2. The Regional Office, after review, should notify the State or local
agency of any disagreements, their reasons for disagreeing, and seek to resolve
the conflict. Following their determination (concurrence or non-concurrence),
the Regional Offices should notify AIRS and the State or local agency of their
action so that the. appropriate notation may be made to the AIRS data base
and/or the Annual SLAMS Report.
The only exception to this policy is the flagging of stratospheric ozone
intrusion. Because of the technical complexity of determining stratospheric
ozone intrusion, OAQPS will, upon request by the State or local agency through
the Regional Office, either concur or non-concur based on documentation
submitted by the requestor.
The criteria (definitions) presented in this guideline will serve as the
basis for reviewing determinations associated with exceptional events. If a
State or local agency chooses to apply criteria that are less stringent than
those contained in the guideline, such recommendation should be subjected
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to public review. The recommendation, along with the summary of comments,
should then be submitted to the respective Regional Office for review and
approval. OAQPS will have final approval authority and, if approval is granted,
will include the alternative criteria in a supplement to this national guideline.
4.4 DOCUMENTATION
All decisions regarding the flagging of data because of exceptional
events must be documented so that the EPA and the public can review these
decisions. The documentation may take several forms. It may include reports
from the National Weather Service; a copy of a newspaper clipping or news
report indicating that a chemical spill or industrial accident has occurred; a
report from the local health department on the pollen count for a given day,
supported by filter analyses; special reports prepared by the State or a con-
sultant; or special statistical- analyses of the air quality data and other
key parameters associated with the event. The actual form of the documentation
depends on the event and the extent of publicly available reports or documents
that would support the determination of its occurrence. As appropriate, the
State or local agency is encouraged to rely on available reports and documen-
tation. When such documentation is not available, the State or local agency
must prepare the necessary material sufficient (see Section 4.2) to support
its decision regarding the flagged data.
The State or local agency should retain copies ,of the necessary supporting
material or documentation in its offices for review upon request. Copies of
this material will have to be available in the record during the public
review process and must be provided to EPA for concurrence. It is not intended
that a public review process (comment period or public hearing) be conducted
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solely for the purpose of determining whether data should or should not be
flagged. Instead, the public review process referred to in this guideline
refers to the public review process which is otherwise required for regulatory
actions taken in accordance with the Clean Air Act. Although the main purpose
of the documentation is to support the decision to flag a given piece of data,
it also provides air quality analysts with background and supporting information
regarding the events associated with the data on which the analyst can rely if
and when the data are needed to make a particular air quality decision. The
air quality analyst will also be awara of any limitations that should be con-
sidered in the use of such data.
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APPENDIX
DEVELOPMENT Of CRITERIA FOR EXCEPTIONAL EVENTS
The purpose of this appendix is to summarize the development history of
this guideline and to assist users in understanding the information contained
herein,
The Standing Air Monitoring Work Group (SAMWG) first addressed the issue
of exceptional values and data flagging in December 1981. Subsequent to that
time, SAMWG solicited input from EPA Regional Offices and State and local
agencies to identify those exceptional events that could have any adverse
effect on air quality values measured during.their occurrence. The SAMWG also
solicited input on how air quality measured during the exceptional event should
be flagged. An initial list of possible exceptional events was compiled based
on comments by selected Regional Offices and State and local agencies for
further consideration.
I. IDENTIFICATION OF EVENTS
In general, the events given further consideration were grouped into three
major - categories: (1) natural events (meteorological and other natural events),
(2) unintentional anthropogenic events, and (3) intentional anthropogenic events.
The events within each major category were as follows;
1, Natural Events
(a) Meteorological Events
o Sustained high windspeeds (PM)
o Stagnations/inversions (all pollutants)
o Unusual lack of precipitation (PM)
o Stratospheric ozone intrusion (03)
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(b) Other Natural Events
o Volcanic eruption (CO, S02, PM)
o Forest fires (CO, PM)
o High pollen count (PM)
2. Unintentional Anthropogenic Events
o Large accidental structural fires (CO, PM)
o Major traffic congestion due to accident or nonrecurring
obstruction (CO)
o Chemical spills (SC>2, NOZ, PM, CO)
o Industrial accidents ($02, N02, PM, CO)
3. Intentional Anthropogenic Events
o Short-term construction/demolition (PM)
o Sandblasting (PM)
o High-sulfur oil refining (SOg)
o Roofing operations (PM, $03)
o Salting or sanding of streets (PM)
o Infrequent large gatherings (PM, CO)
o Soot blowing from ships (PM)
o Agricultural tilling (PM)
o Prescribed burning (CO, PM}
o floncompl iance—point source (CO, $02» NOg , PM)
Those whose comments and suggestions were solicited generally agreed that
natural events, other than meteorological events, and unintentional anthropo-
genic events are, by their very nature, exceptional events. The control of
emissions from such events is usually not Included in the general control
strategy for a given pollutant, although it is sometimes handled as part of an
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emergency response action immediately after the event has occurred to minimize
possible adverse health impacts on local residents. Reasonable precautions
would not guarantee against recurrence or that the air quality would not be
affected by these events in the future.
Some disagreement was expressed with regard to intentional anthropogenic
events. Some argued that these events occur routinely and the data therefore
should not be flagged. Others argued that, although intentional anthropogenic
events occur routinely, they are exceptional with respect to normal activities
around a particular monitoring site. Still others argued that intentional
anthropogenic events can and should be controlled; they further argued that,
unless these events or activities occur within the immediate vicinity of a
monitoring site, they should not be considered as exceptional and the data
collected during their occurrence should not be flagged.
Finally, some strong disagreement was expressed with respect to two
meteorological events—stagnations and inversions. Many argue that these two
events routinely occur. They further argue, that because these events are
climatological factors rather than exceptional events, pollutant levels
measured during their occurrence should not be flagged.
The list of suggested exceptional events was reviewed and evaluated to
determine whether each of the events listed should be considered exceptional and
whether other events should be added. The review indicated that this list was
comprehensive and that no additional events should be considered at this time.
After considerable discussion over an extended period of tim'e, a general
consensus was reached that 15 of the events initially considered for designation
did generally satisfy the criteria for defining an exceptional event. Six of
the events initially considered (implementing transportation controls,
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stagnation/inversions, high-sulfur oil refining, sootblowing from ships,
noncompliance—local sources, and unusual lack of precipitation) however, were
finally rejected. The rationale for rejecting these events is summarized
below.
II. EVENTS NOT CONSIDERED EXCEPTIONAL FOR DATA FLAGGING PURPOSES
1. Implementing Transportation Controls
Transportation control measures are not considered exceptional, and data
collected during the implementation of transportation controls should not be
flagged. If, however, traffic must be temporarily rerouted during the imple-
mentation of the transportation control measures or some congestion occurs
.due to initial startup of the transportation plan, the data collected at
monitors near the rerouted traffic or congestion may be flagged.
2. Stagnati ons/1nversi ons
Stagnations and inversions are frequent climatological occurrences that
must be considered in evaluating whether a control program is adequate to
attain and maintain the NAAQS. An inversion is said to occur at a point, or
through a layer, where temperature increases with increasing height,20»21
Surface-based inversions are those that extend vertically from the surface to
some altitude aloft. One study found that surface-based inversions generally
occur about 32 percent of the time.22 They are usually short-lived and disperse
shortly after sunrise. Because inversions are expected to occur frequently and
are part of weather patterns, they are not considered exceptional events for
the purpose of flagging data.
Stagnation episodes are periods of 4 or more days with surface wind speeds
of generally 4 ra/sec or less and no precipitation or frontal passage. In some
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parts of the United States stagnations usually persist for an extended period
of time, and they can affect an entire air basin; therefore, they are not
generally considered exceptional' for the purpose of flagging-data.
3, High-Sulfur Oil Refining
High-sulfur oil refining refers to the process of refining crude oil
with a sulfur content that is 20 percent or greater than the design capacity
of the refining operation. Because this is a common practice at many
refineries, and procedures and control methods are used to minimize 502
emissions, it is not considered to be an exceptional event for the purpose
of flagging data.
4. Sootblowing from Ships
Sootblowing from ships is a method in which air is used to remove
deposits that may build up on the walls of the vessel's boiler tubes. This is
a common practice that is either controlled or limited (in many areas of the
country) by establishing opacity limits. Because these activities are common
and steps can be taken to minimize associated emissions, sootblowing from
ships (like general sootblowing from utility and industrial boilers) is not
considered-an exceptional event for the purpose of flagging data.
5. Noncompli ance—Local Sources
Limited noncompliance of local sources can be expected from time to time
as a result of process upsets or malfunctioning control equipment. These
events are usually classified as "upsets" or "malfunctions" as defined by
the applicable State or local agency regulations, or they may be considered
a violation of applicable enission or opacity limits. If these events are
caused by upsets or malfunctions, they should be so noted and reported to the
appropriate control agency. If they constitute a violation, the appropriate
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legal remedies will be taken. If legal action is taken, the air quality data
collected 1n the vicinity of the source will in all likelihood be used in the
legal proceedings, and any appropriate limitations associated with the data
would be reviewed and evaluated as part of the legal process. Because, data
collected during noncompliance conditions have special uses and the source
is required to notify the .State of the upset or malfunction, noncompliance of
local sources is not considered an exceptional event for the purpose of
flagging data.
5. Unusual Lack of Precipitation
Lack of precipitation in and of itself would not be considered an
exceptional event because it has very little impact on PM air quality levels.
Lack of precipitation or drought conditions combined with high winds, however,
would be considered an exceptional event. Therefore, unusual lack of precipi-
tation is not considered an exceptional event for the purpose of flagging
data.
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REFERENCES
1. "Guideline for Interpretation of Air Quality Standards," U. S. Environmental
Protection Agency, Office of Air Quality Planning and Standards, Research
Triangle Park, N.C. OAQPS No. 1.2-008 (revised February 1977).
2. 40 CFR 51.12d, Code of Federal Regulations, July 1, 1984.
3. Federal Register, Vol. 49, March 20, 1984 pp. 10433-10435.
4. Clean Air Act as amended August 1977.
5. ByerSj H. R. General Meteorology. McGraw Hill, New York, New York, 1974,
6. Anthes, R. A., et al. The Atmosphere. Charles E. Merril Publishing
Co., Columbus, Ohio, 1975.
7. Federal Meteorological Handbook No. 1, Surface Observations. Washington,
O.C. 1976.
8. Dorn, W. I. Meteorology. Third edition. McGraw Hill, New York,
New York, 1965.
9. Bates, R. L., and J. A. Jackson. Glossary of Geology. Second edition.
American Geological Institute, Falls Church, Virginia, 1980.
10. Personal Communication with Linda Farnsworth of the USDA Forest Service,
Aviation and Fire Management Division, Fire Department, November 1983.
11. Receptor Model Technical Series, Volume I, Overview of Receptor Model
Application to Particulate Source Apportionment, U.S. Environmental
Protection Agency, Office of Air Quality Planning and Standards, Research
Triangle Park, N C. EPA Publication No. EPA-450/4-81-Q16a. July 1981.
12. Receptor Model Technical Series, Volume II, Chemical Mass Balance, U.S.
Environmental Protection Agency, Office of Air Quality Planning and Stand-
ards, Research Triangle Park, N C. EPA Publication No. EPA-45Q/4-81-Q16b.
July 1981.
13. Receptor Model Technical Series, Volume III, User's Manual for Chemical
Mass Balance Model, U.S. Environmental Protection Agency, Office of Air
'Quality Planning and Standards, Research Triangle Park, N C. EPA Publica-
tion No. EPA-450/4-83-014. July 1983.
14. Receptor Model Technical Series, Volume IV, Summary of Particle Identifi-
cation Techniques, U.S. Environmental Protection Agency, Office of Air
Quality Planning and Standards, Research Triangle Park, N C. EPA Publica-
tion No. EPA-450/4-83-018. June 1983.
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15, Guideline on Air Quality Models, OAQPS, U.S. Environmental Protection
Agency, Research Triangle Park, N C. EPA Publication No. EPA-45Q/2-78-
027 (NTIS PB 288-783). April 1978, or subsequent revisions.
16. Regional Workshops on Air Quality Modeling: A Summary Report, U.S.
- Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, N C. EPA Publication No. EPA-450/4-
82-015, (NTIS PB 83-150573), April 1981. (NTIS documents include 1982
and 1983 addendums)
17. Air Pollution Aspects of Aeroallergens (Pollens). National Air Pollution
Control Administration Consumer Protection and Environmental Health
Services, Department of Health, Education, and Welfare, September 1969.
18. Sonti, R. S. Practical Design and Operation of Vapor-Depressuring
Systems. Chemical Engineering, 91(2);66, January 23, 1984.
19. An Introduction to Highway Transportation Engineering. Institute of
Traffic Engineering, 1978,
20. .Mclntosh, 0. H. Meteorological Glossary. Chemical Publishing, New York,
1972.
21. Huschke, R. E. Glossary of Meteorology. - American Meteorological
Society, 1959.
22. Seiger, R. The Climate Near the Ground. Harvard University Press.
1966.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA 450/4-86-007
3. RECIPIENT'S ACCESSION NO.
d. TITLE AND SUBTITLE
Guideline on the Identification and Use of Air Quality
Data Affected by Exceptional Events
5. REPORT DATE
July 1986
6. PERFORMING ORGANIZATION CODE
. AUTHOH(S)
B. PERFORMING ORGANIZATION REPORT NO.
EPA 450/4-86-007
. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Monitoring and Data Analysis Division
Monitoring and Reports Branch
Monitoring Section, RTP, NC 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as 9.
13. TYPE OF REPORT AND PERIOD COVERED
Technical guideline
14, SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This guideline is intended to provide information to State and local air
pollution control agencies concerning the flagging of air quality data affected
by exceptional events. The guidance defines exceptional events, establishes
uniform criteria and procedures for flagging air quality data, and provides a
mechanism for allowing consideration of excluding flagged data.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b..lDENTlF!ERS/OPEN ENDED TERMS
COSATI Field/Group
Exceptional events
Data flag
Air quality data
Excluding flagged data
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS /Tin's Report)
Unclassified
21. NO. OF PAG£S
20. SECURITY CLASS (Tills page)
Unclassified
22. PRICE
EPA Farm 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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