6560­
50­
P
ENVIRONMENTAL
PROTECTION
AGENCY
40
CFR
Parts
50
and
51
[
EPA­
HQ­
OAR­
2005­
0159;
FRL
]

RIN
2060­
AN40
The
Treatment
of
Data
Influenced
by
Exceptional
Events
AGENCY:
Environmental
Protection
Agency
(
EPA).

ACTION:
Proposed
Rule.

SUMMARY:
Today,
EPA
is
proposing
a
rule
to
govern
the
review
and
handling
of
air
quality
monitoring
data
influenced
by
exceptional
events.
Exceptional
events
are
events
for
which
the
normal
planning
and
regulatory
process
established
by
the
Clean
Air
Act
(
CAA)
is
not
appropriate.

In
this
rulemaking
action,
EPA
is
proposing
to:
implement
section
319(
b)(
3)(
B)
and
section
107(
d)(
3)
authority
to
exclude
air
quality
monitoring
data
from
regulatory
determinations
related
to
exceedances
or
violations
of
the
National
Ambient
Air
Quality
Standards
(
NAAQS)
and
avoid
designating
an
area
as
nonattainment,
redesignating
an
area
as
nonattainment,
or
reclassifying
an
existing
nonattainment
area
to
a
higher
classification
if
a
State
2
adequately
demonstrates
that
an
exceptional
event
has
caused
an
exceedance
or
violation
of
a
NAAQS.
Also,
EPA
is
proposing
four
options
with
respect
to
whether,
and
to
what
extent,
States
should
be
required
to
take
additional
actions
to
address
public
health
impacts
related
to
the
event.

DATES:
Comments
must
be
received
on
or
before
[
Insert
date
60
days
after
publication
in
the
Federal
Register].

Comments
must
be
postmarked
by
the
last
day
of
the
comment
period.

ADDRESSES:
Submit
your
comments,
identified
by
Docket
ID
No.
EPA­
HQ­
OAR­
2005­
0159,
by
one
of
the
following
methods:

$
www.
regulations.
gov.
Follow
the
on­
line
instructions
for
submitting
comments.

$
E­
mail:
Comments
may
be
sent
by
electronic
mail
(

email
to
A­
and­
R­
Docket@
epa.
gov,
Attention
Docket
ID
No.
EPA­
HQ­
OAR­
2005­
0159.

$
Fax:
Fax
your
comments
to:
202­
566­
1741,
Attention
Docket
ID
no.
EPA­
HQ­
OAR­
2005­
0159.

$
Mail:
Send
your
comments
to:
Air
and
Radiation
Docket
and
Information
Center,
U.
S.
Environmental
Protection
Agency,
Mail
Code:
6102T,
1200
Pennsylvania
Ave.,
NW,

Washington,
DC,
20460,
Attention
Docket
ID
No.
EPA­

HQOAR
2005­
0159.
3
$
Hand
Delivery:
Air
and
Radiation
Docket
and
Information
Center,
U.
S.
Environmental
Protection
Agency,
1301
Constitution
Avenue,
NW,
Room
B102,

Washington,
DC,
Attention
Docket
ID
No.
EPA­
HQ­
OAR­

2005­
0159.
Such
deliveries
are
only
accepted
during
the
Docket's
normal
hours
of
operation,
and
special
arrangements
should
be
made
for
deliveries
of
boxed
information.

Instructions:
Direct
your
comments
to
Docket
ID
No.
EPA­

HQOAR
2005­
0159.
The
EPA's
policy
is
that
all
comments
received
will
be
included
in
the
public
docket
without
change
and
may
be
made
available
online
at
www.
regulations.
gov,
including
any
personal
information
provided,
unless
the
comment
includes
information
claimed
to
be
Confidential
Business
Information
(
CBI)
or
other
information
whose
disclosure
is
restricted
by
statute.
Do
not
submit
information
that
you
consider
to
be
CBI
or
otherwise
protected
information
through
www.
regulations.
gov,
or
e­
mail.
The
www.
regulations.
gov
website
is
an
"
anonymous
access"
system,
which
means
that
EPA
will
not
know
your
identity
or
contact
information
unless
you
provide
it
in
the
body
of
your
comment.
If
you
send
an
e­
mail
comment
directly
to
EPA
without
going
through
wwww.
regulations.
gov,
your
e­
mail
address
will
be
4
automatically
captured
and
included
as
part
of
the
comment
that
is
placed
in
the
public
docket
and
made
available
on
the
Internet.
If
you
submit
an
electronic
comment,
EPA
recommends
that
you
include
your
name
and
other
contact
information
in
the
body
of
your
comment
and
with
any
disk
or
CD­
ROM
you
submit.
If
EPA
cannot
read
your
comment
due
to
technical
difficulties
and
cannot
contact
you
for
clarification,
EPA
may
not
be
able
to
consider
your
comment.
Electronic
files
should
avoid
the
use
of
special
characters,
any
form
of
encryption,
and
be
free
of
any
defects
or
viruses.
For
additional
instructions
on
submitting
comments,
go
to
Supplementary
Information.

Docket:
All
documents
in
the
docket
are
listed
in
the
www.
regulations.
gov
index.
Although
listed
in
the
index,

some
information
is
not
publicly
available,
e.
g.,
CBI
or
other
information
whose
disclosure
is
restricted
by
statute.
Certain
other
material,
such
as
copyrighted
material,
will
be
publicly
available
only
in
hard
copy.

Publicly
available
docket
materials
are
available
either
electronically
in
www.
regulations.
gov
or
in
hard
copy
at
the
Office
of
Air
and
Radiation
Docket
and
Information
Center,
EPA
West,
Room
B102,
1301
Constitution
Ave,
NW,

Washington,
DC.
The
Public
Reading
Room
is
open
from
8:
30
a.
m.
to
4:
30
p.
m.,
Monday
through
Friday,
excluding
legal
5
holidays.
The
telephone
number
for
the
Public
Reading
Room
is
(
202)
566­
1744,
and
the
telephone
number
for
the
Office
of
Air
and
Radiation
Docket
and
information
Center
is
(
202)

566­
1742.

FOR
FURTHER
INFORMATION
CONTACT:
General
questions
concerning
this
proposed
rule
should
be
addressed
to
Mr.

Larry
D.
Wallace,
Ph.
D.,
Office
of
Air
Quality
Planning
and
Standards,
Air
Quality
Policy
Division,
Mail
Code
C539­
01,

Research
Triangle
Park,
N.
C.
27711;
telephone
(
919)
541­

0906,
and
e­
mail
address
wallace.
larry@
epa.
gov.

Questions
concerning
technical
and
analytical
issues
related
to
this
proposed
rule
should
be
addressed
to
Mr.

Neil
Frank,
Office
of
Air
Quality
Planning
and
Standards,

Air
Quality
Assessment
Division,
Mail
Code
C304­
04,

Research
Triangle
Park,
N.
C.
27711;
telephone
(
919)
541­

5560,
and
e­
mail
address
frank.
neil@
epa.
gov.

SUPPLEMENTARY
INFORMATION:

Public
Hearing
The
EPA
will
hold
two
public
hearings
on
today's
proposal
during
the
comment
period.
The
details
of
the
public
hearings,
including
the
times,
dates,
and
locations
will
be
provided
in
a
future
Federal
Register
notice.
The
public
hearings
will
provide
interested
parties
the
opportunity
to
present
data,
views,
or
arguments
concerning
6
the
proposed
rule.
The
EPA
may
ask
clarifying
questions
during
the
oral
presentations,
but
will
not
respond
to
the
presentations
or
comments
at
that
time.
Written
statements
and
supporting
information
submitted
during
the
comment
period
will
be
considered
with
the
same
weight
as
any
oral
comments
and
supporting
information
presented
at
the
public
hearings.
Under
CAA
section
307(
d)(
1)(
A),
the
procedural
requirements
of
section
307(
d)
apply
to
this
proposal.
In
addition,
under
section
307(
d)(
1)(
U),
the
Administrator
determines
that
this
action
is
subject
to
the
provisions
of
section
307(
d).
Section
307(
d)(
1)(
U)
provides
that
the
provisions
of
section
307(
d)
apply
to
"
such
other
actions
as
the
Administrator
may
determine."
The
EPA
is
including
the
proposals
in
today's
proposed
rulemaking
under
sections
307(
d)(
1)(
A)
and
(
U).

Comments
1.
Submitting
CBI.
Do
not
submit
this
information
to
EPA
through
www.
regulations.
gov
or
e­
mail.
Clearly
mark
the
part
or
all
of
the
information
that
you
claim
to
be
CBI.

For
CBI
information
in
a
disk
or
CD
ROM
that
you
mail
to
EPA,
mark
the
outside
of
the
disk
or
CD
ROM
as
CBI
and
then
identify
electronically
within
the
disk
or
CD
ROM
the
specific
information
that
is
claimed
as
CBI.
In
addition
to
one
complete
version
of
the
comment
that
includes
7
information
claimed
as
CBI,
a
copy
of
the
comment
that
does
not
contain
the
information
claimed
as
CBI
must
be
submitted
for
inclusion
in
the
public
docket.
Information
so
marked
will
not
be
disclosed
except
in
accordance
with
procedures
set
forth
in
40
CFR
part
2.

2.
Tips
for
Preparing
Your
Comments.
When
submitting
comments,
remember
to:

$
Identify
the
rulemaking
by
docket
number
and
other
identifying
information
(
subject
heading,

Federal
Register
date
and
page
number).

$
Follow
directions­
The
agency
may
ask
you
to
respond
to
specific
questions
or
organize
comments
by
referencing
a
Code
of
Federal
Regulations
(
CFR)
part
or
section
number.

$
Explain
why
you
agree
or
disagree;
suggest
alternatives
and
substitute
language
for
your
requested
changes.

$
Describe
any
assumptions
and
provide
any
technical
information
and/
or
data
that
you
used.

$
If
you
estimate
potential
costs
or
burdens,

explain
how
you
arrived
at
your
cost
estimate
in
sufficient
detail
to
allow
for
it
to
be
reproduced.
8
$
Provide
specific
examples
to
illustrate
your
concerns,
and
suggest
alternatives.

$
Explain
your
views
as
clearly
as
possible,

avoiding
the
use
of
profanity
or
personal
threats.

$
Make
sure
to
submit
your
comments
by
the
comment
period
deadline
identified.

In
addition,
please
send
a
copy
of
your
comments
to:

Mr.
Larry
D.
Wallace,
Ph.
D.,
U.
S.
Environmental
Protection
Agency,
by
one
of
the
means
listed
below:

1.
E­
Mail:
wallace.
larry@
epa.
gov.

2.
Fax:
(
919)
541­
5489,
Attention:
Mr.
Larry
D.
Wallace,

Ph.
D.

3.
Mail:
Mr.
Larry
D.
Wallace,
Ph.
D.,
U.
S.
Environmental
Protection
Agency,
Office
of
Air
Quality
Planning
and
Standards,
Mail
Code:
C539­
01,
Research
Triangle
Park,

NC
27711.

4.
Hand
Delivery:
Mr.
Larry
D.
Wallace,
Ph.
D.,
U.
S.

Environmental
Protection
Agency,
Office
of
Air
Quality
Planning
and
Standards,
109
T.
W.
Alexander
Drive,

Research
Triangle
Park,
NC
27709.

Table
of
Contents:

The
following
is
an
outline
of
the
preamble.

I.
Preamble
Glossary
of
Terms
and
Acronyms
9
II.
Background
and
Purpose
of
Today's
Rulemaking
A.
Legislative
Requirements
B.
Historical
Experience
Concerning
Exceptional
and
Natural
Events
III.
Today's
Proposed
Action
A.
To
Whom
and
to
What
Pollutants
Does
Today's
Proposed
Rule
Apply?
B.
How
Does
This
Rule
Relate
to
Indian
Tribes?
C.
What
is
an
Exceptional
Event?
D.
Examples
of
Exceptional
Events
1.
Chemical
Spills
and
Industrial
Accidents
2.
Structural
Fires
3.
Exceedances
Due
to
Transported
Pollution
4.
Exceedances
Due
to
a
Terrorist
Attack
5.
Natural
Events
a.
Volcanic
and
Seismic
Activities
b.
Natural
Disasters
and
Associated
Clean­
up
Activities
c.
High
Wind
Events
d.
Unwanted
Fires
e.
Stratospheric
Ozone
Intrusions
IV.
The
Management
of
Air
Quality
Data
Affected
by
Exceptional
Events
A.
Flagging
of
Data
in
the
AQS
Data
base
B.
What
Does
it
Mean
for
an
Event
to
"
Affect
Air
Quality"?
1.
Option
1:
95th
Percentile
Criterion
2.
Option
2:
75th
Percentile/
95th
Percentile
Tiered
Approach
3.
Option
3:
Case­
by­
Case
Approach
Based
On
Weight
of
Evidence
C.
Use
of
a
"
But
For"
Test
D.
Schedules
and
Procedures
for
Flagging
and
Requesting
Exclusion
of
Data
1.
Option
1:
Early
Data
Flagging
and
Demonstration
Submission
2.
Option
2:
Early
Data
Flagging
and
Delayed
Demonstration
Submission
3.
Option
3:
Delayed
Data
Flagging
and
Demonstration
Submission
E.
Exclusion
of
Entire
24­
Hour
Value
as
Opposed
to
a
Partial
Adjustment
of
the
24­
Hour
Value
F.
What
Should
States
be
Required
to
Submit
in
Their
Exceptional
Events
Demonstrations?
10
G.
Special
Considerations
Relevant
to
Proposed
Standards
for
PM10­
2.5
H.
Public
Availability
of
Air
Quality
Data
and
Demonstrations
Related
to
Exceptional
Events
V.
Additional
Requirements.
A.
Option
1:
Proposed
Option:
Require
Public
Notification,
Education
and
Appropriate
and
Reasonable
Measures
B.
Option
2:
The
Development
of
a
Mitigation
Plan
by
States
under
Section
110
of
the
CAA
C.
Option
3:
The
Development
of
a
Mitigation
Plan
for
Episodic
Events
D.
Option
4:
Do
Not
Require
States
to
Adopt
and
Implement
Specific
Mitigation
Plans
or
Measures
Under
this
Rule
VI.
Special
Treatment
of
Certain
Events
Under
this
Rule
A.
Volcanic
and
Seismic
Activities
B.
High
Wind
Events
C.
Stratospheric
Ozone
Intrusion
VII.
Treatment
of
Fireworks
Displays
VIII.
Statutory
and
Executive
Order
Reviews
A.
Executive
Order
12866:
Regulatory
Planning
and
Review
B.
Paperwork
Reduction
Act
C.
Regulatory
Flexibility
Act
D.
Unfunded
Mandates
Reform
Act
E.
Executive
Order
13132:
Federalism
F.
Executive
Order
13175:
Consultation
and
Coordination
with
Indian
Tribal
Governments
G.
Executive
Order
13045:
Protection
of
Children
from
Environmental
Health
and
Safety
Risks
H.
Executive
Order
13211:
Actions
that
Significantly
Affect
Energy
Supply,
Distribution,
or
Use
I.
National
Technology
Transfer
Advancement
Act
I.
Preamble
Glossary
of
Terms
and
Acronyms
The
following
are
abbreviations
of
terms
used
in
the
preamble.
11
AQS
Air
Quality
System
BACM
Best
Available
Control
Measures
CAA
Clean
Air
Act
CAAA
Clean
Air
Act
Amendments
EPA
Environmental
Protection
Agency
FIP
Federal
Implementation
Plan
FMP
Fire
Mitigation
Plan
NAAQS
National
Ambient
Air
Quality
Standards
NEAP
Natural
Event
Action
Plan
OAQPS
Office
of
Air
Quality
Planning
and
Standards
PM10
Particles
with
a
nominal
mean
aerodynamic
diameter
less
than
or
equal
to
10
micrometers
PM10­
2.5
Particles
with
a
nominal
mean
aerodynamic
diameter
greater
than
2.5
micrometers
and
less
than
or
equal
to
10
micrometers
PM2.5
Particles
with
a
nominal
mean
aerodynamic
diameter
less
than
or
equal
to
2.5
micrometers
RACM
Reasonably
Available
Control
Measures
SIP
State
Implementation
Plan
SAFE­
TEA­
LU
Safe
Accountable
Flexible
Efficient­

Transportation
Equity
Act­
A
Legacy
for
Users
12
SMP
Smoke
Management
Plan
TAR
Tribal
Authority
Rule
TIP
Tribal
Implementation
Plan
II.
Background
and
Purpose
of
Today's
Rulemaking
A.
Legislative
Requirements
Today,
EPA
is
proposing
a
rule
to
govern
the
review
and
handling
of
air
quality
monitoring
data
influenced
by
exceptional
events.
As
discussed
below,
these
are
events
for
which
the
normal
planning
and
regulatory
process
established
by
the
CAA
is
not
appropriate.
Section
319
of
the
CAA,
as
amended
by
section
6013
of
the
Safe
Accountable
Flexible
Efficient­
Transportation
Equity
Act:
A
Legacy
for
Users
(
SAFE­
TEA­
LU)
of
2005,
requires
EPA
to
publish
this
rule
in
the
Federal
Register
no
later
than
March
1,
2006.1
Further,
EPA
is
required
to
issue
the
final
rule
no
later
than
1
year
from
the
date
of
proposal.

The
EPA
is
proposing
to
establish
procedures
and
criteria
related
to
the
identification,
evaluation,

interpretation,
and
use
of
air
quality
monitoring
data
related
to
any
NAAQS
where
States
petition
EPA
to
exclude
data
that
are
affected
by
exceptional
events.
Section
319
1
All
subsequent
references
to
section
319
of
the
CAA
in
this
proposal
are
to
section
319
as
amended
by
SAFE­
TEALU
unless
otherwise
noted.
13
defines
an
event
as
an
exceptional
event
if
the
event
affects
air
quality;
is
a
natural
event
or
an
event
caused
by
human
activity
that
is
unlikely
to
recur
at
a
particular
location;
and
is
determined
by
the
Administrator
to
be
an
exceptional
event.
The
statutory
definition
of
exceptional
event
specifically
excludes
stagnation
of
air
masses
or
meteorological
inversions;
a
meteorological
event
involving
high
temperature
or
lack
of
precipitation;
or
air
pollution
relating
to
source
noncompliance.

Section
319(
b)(
3)(
B)(
i)
requires
a
State
air
quality
agency
to
demonstrate
through
"
reliable,
accurate
data
that
is
promptly
produced"
that
an
exceptional
event
occurred.
2
Section
319(
b)(
3)(
B)(
ii)
requires
that
"
a
clear
causal
relationship"
be
established
between
a
measured
exceedance
of
a
NAAQS
and
the
exceptional
event
demonstrating
"
that
the
exceptional
event
caused
a
specific
air
pollution
concentration
at
a
particular
location."
In
addition,

section
319(
b)(
3)(
B)(
iii)
requires
a
public
process
to
determine
whether
an
event
is
an
exceptional
event.

2
While
this
document
refers
primarily
to
States
as
the
entity
responsible
for
flagging
data
impacted
by
exceptional
events,
other
agencies,
such
as
local
or
Tribal
government
agencies,
may
also
have
standing
to
flag
data
as
being
affected
by
these
types
of
events,
and
the
criteria
and
procedures
that
are
discussed
in
this
rulemaking
also
apply
to
these
entities.
14
Finally,
section
319(
b)(
3)(
B)(
iv)
requires
criteria
and
procedures
for
a
Governor
to
petition
the
Administrator
to
exclude
air
quality
monitoring
data
that
is
directly
due
to
exceptional
events
from
use
in
determinations
with
respect
to
exceedences
or
violations
of
the
NAAQS.

Section
319
also
contains
a
set
of
five
principles
for
EPA
to
follow
in
developing
regulations
to
implement
section
319:

(
i)
protection
of
public
health
is
the
highest
priority;

(
ii)
timely
information
should
be
provided
to
the
public
in
any
case
in
which
the
air
quality
is
unhealthy;

(
iii)
all
ambient
air
quality
data
should
be
included
in
a
timely
manner
in
an
appropriate
Federal
air
quality
data
base
that
is
accessible
to
the
public;

(
iv)
each
State
must
take
necessary
measures
to
safeguard
public
health
regardless
of
the
source
of
the
air
pollution;
and
(
v)
air
quality
data
should
be
carefully
screened
to
ensure
that
events
not
likely
to
recur
are
represented
accurately
in
all
monitoring
data
and
analyses
(
42
U.
S.
C.
7619(
b)(
3)(
A)).
15
In
adopting
revisions
to
section
319,
EPA
believes
that
Congress
sought
to
provide
statutory
relief
to
States
to
allow
them
to
avoid
being
designated
as
nonattainment
or
to
avoid
continuing
to
be
designated
nonattainment
as
a
result
of
exceptional
events
in
appropriate
circumstances.

In
addition,
Congress
indicated
that
States
should
not
have
to
prepare
and
implement
regulatory
strategies
when
their
air
quality
is
affected
by
events
beyond
their
reasonable
control.
To
accomplish
this
goal,
Congress
enumerated
certain
minimum
requirements
for
this
rulemaking.
In
addition,
Congress
provided
certain
statutory
principles
for
EPA
to
follow
in
promulgating
regulations
to
exclude
data
affected
by
exceptional
events.

Section
319
also
includes
an
interim
provision,

section
319(
b)(
4),
that
addresses
the
transition
period
between
the
present
and
the
date
that
a
final
regulation
governing
the
treatment
of
data
related
to
exceptional
events
is
promulgated.
The
provision
indicates
that
following
EPA
guidance
documents
continues
to
apply
until
the
effective
date
of
a
final
regulation
promulgated
under
section
319(
b)(
2):
"
Guidance
on
the
Identification
and
Use
of
Air
Quality
Data
Affected
by
Exceptional
Events"
(
July
1986);
"
Areas
Affected
by
PM10
Natural
Events,"
May
30,

1996;
and
appendices
I,
K,
and
N
to
40
CFR
part
50,
which
16
describe
how
air
quality
monitoring
data
are
to
be
used
and
interpreted
to
determine
compliance
with
the
applicable
NAAQS.
The
statute
requires
the
promulgation
of
the
final
rule
no
later
than
1
year
following
the
publication
of
this
proposed
rule.

B.
Historical
Experience
Concerning
Exceptional
and
Natural
Events
Since
1977,
EPA
guidance
and
regulations
have
either
implied
or
documented
the
need
for
a
flagging
system
for
data
affected
by
an
exceptional
event.
The
first
EPA
guidance
related
to
the
exclusion
or
discounting
of
data
affected
by
an
exceptional
event
was
an
Office
of
Air
Quality
Planning
and
Standards
(
OAQPS)
guidance
document
entitled,
"
Guidelines
for
the
Interpretation
of
Air
Quality
Standards,"
Guideline
No.
1.2­
008
(
revised
February
1977).
3
In
July
1986,
EPA
issued
the
guidance
entitled,

"
Guideline
On
the
Identification
and
Use
of
Air
Quality
Data
Affected
By
Exceptional
Events"
(
the
Exceptional
3
"
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).
The
guidance
indicated
the
need
for
a
data
flagging
system
which
would
require
the
submittal
of
detailed
information
establishing
that
a
violation
was
due
to
uncontrollable
natural
sources
and
that
the
information
could
be
used
in
decision­
making
related
to
the
feasibility
of
modifying
control
strategies.
17
Events
Policy).
The
Exceptional
Events
Policy
provided
criteria
for
States
to
use
in
making
decisions
related
to
identifying
data
that
have
been
influenced
by
an
exceptional
event.

In
addition
to
the
Exceptional
Events
Policy,
on
July
1,
1987,
EPA
promulgated
the
NAAQS
for
PM10
(
particulate
matter
with
an
aerodynamic
diameter
of
10
micrometers
or
less)
which
also
addressed
the
issue
of
excluding
or
discounting
data
affected
by
exceptional
events.
4
Appendix
K
of
that
rule
allows
for
special
consideration
of
data
determined
to
be
affected
by
an
exceptional
event.
Section
2.4
of
appendix
K
authorizes
EPA
to
discount
from
consideration
in
making
attainment
or
nonattainment
determinations
for
air
quality
data
that
are
attributable
to
"
an
uncontrollable
event
caused
by
natural
sources"
of
PM10,
or
"
an
event
that
is
not
expected
to
recur
at
a
given
location."
Section
2.4
of
appendix
K,
together
with
EPA
guidance
contained
in
the
Exceptional
Events
Policy,

describes
the
steps
that
should
be
taken
for
flagging
PM10
data
that
a
State
believes
are
affected
by
an
exceptional
or
natural
event.

4
Federal
Register
(
52
FR
24667),
July
1,
1987.
18
In
1990,
section
188(
f)
was
added
to
the
CAA.
This
section
of
the
CAA
provided
EPA
authority
to
waive
either
a
specific
attainment
date
or
certain
planning
requirements
for
serious
PM10
nonattainment
areas
that
were
affected
by
nonanthropogenic
sources.
In
response
to
section
188(
f),

and
in
consideration
of
the
CAA
consequences
for
areas
affected
by
elevated
concentrations
caused
by
natural
events,
in
1996
EPA
issued
a
policy
to
address
data
affected
by
natural
events
entitled,
"
Areas
Affected
by
PM10
Natural
Events,"
(
the
PM10
Natural
Events
Policy).
5
On
July
18,
1997,
EPA
issued
revised
NAAQS
for
ozone
and
a
new
NAAQS
addressing
PM2.5.
For
ozone,
the
revised
NAAQS
provided
for
an
8­
hour
averaging
period
(
versus
1
hour
for
the
previous
NAAQS),
and
the
level
of
the
standard
was
changed
from
0.12
ppm
to
0.08
ppm
(
62
FR
38856).
For
the
PM2.5
NAAQS,
EPA
established
both
a
new
24­
hour
standard
and
a
new
annual
standard.
In
that
Federal
Register,
EPA
also
promulgated
appendices
I
and
N
to
40
CFR
part
50.

Appendices
I
and
N
provided
the
methodologies
for
determining
whether
an
area
is
in
attainment
of
the
8­
hour
5
Memorandum
from
Mary
D.
Nichols,
Assistant
Administrator
for
Air
and
Radiation,
to
EPA
Regional
Offices
entitled,
"
Areas
Affected
by
PM10
Natural
Events,"

May
30,
1996.
19
ozone
and
PM2.5
NAAQS
respectively,
using
ambient
air
quality
data.
Section
1.0
of
appendix
I,
and
section
1.0(
b)
of
appendix
N
provide
the
authority
for
EPA
to
give
special
consideration
to
data
determined
to
be
affected
by
an
exceptional
or
natural
event.

Appendices
K,
I,
and
N,
which
are
a
part
of
the
NAAQS
for
the
affected
pollutants
as
described
above,
provide
that,
while
States
must
submit
all
valid
ambient
air
quality
data
to
EPA's
Air
Quality
System
(
AQS)
data
base
for
use
in
making
regulatory
decisions,
in
some
cases
it
may
be
appropriate
for
the
Regional
Administrator
to
exclude,
discount,
weight,
or
make
adjustments
to
data
that
have
been
appropriately
flagged
from
calculations
in
determining
whether
or
not
an
area
has
attained
the
standard.
These
decisions
are
to
be
made
on
a
case­
by­
case
basis
using
all
available
information
related
to
the
event
in
question,
and
are
required
to
be
made
available
to
the
public
for
review.
It
should
also
be
noted
that,
while
it
would
be
desirable
to
be
able
to
adjust
the
daily
value
to
exclude
only
those
portions
of
the
data
that
are
attributable
to
the
exceptional
event,
due
to
technical
limitations,
such
subtraction
has
not
been
possible,
and
EPA's
historical
practice
has
been
to
exclude
a
daily
measured
value
in
its
entirety
when
that
value
is
found
to
20
be
largely
caused
by
an
exceptional
event.

Following
the
promulgation
of
the
8­
hour
ozone
and
the
PM2.5
NAAQS,
EPA
provided
additional
guidance
to
States
on
how
to
address
data
affected
by
exceptional
and
natural
events.
6
That
guidance
directed
the
States
to
follow
three
specific
EPA
guidance
documents
in
making
determinations
related
to
data
influenced
by
exceptional
and
natural
events:
(
1)
The
Exceptional
Events
Policy;
(
2)
The
PM10
Natural
Events
Policy;
and
(
3)
The
Interim
Air
Quality
Policy
on
Wildland
and
Prescribed
Fires,
Memorandum
from
Richard
D.
Wilson,
Acting
Assistant
Administrator
for
Air
and
Radiation,
to
EPA
Regional
Administrators,
May
15,

1998.
The
Interim
Air
Quality
Policy
on
Wildland
and
Prescribed
Fires
addressed
the
treatment
of
air
quality
monitoring
data
that
are
affected
by
wildland
and
6
"
Guideline
on
Data
Handling
Conventions
for
the
PM
NAAQS,"
United
States
Environmental
Protection
Agency,
Office
of
Air
Quality
Planning
and
Standards,
Research
Triangle
Park,
N.
C.
27711,
EPA­
454/
R­
99­
008,
April
1999.

"
Guideline
on
Data
Handling
Conventions
for
the
8­
hour
Ozone
NAAQS,"
United
States
Environmental
Protection
Agency,
Office
of
Air
Quality
Planning
and
Standards,
Research
Triangle
Park,
N.
C.
27711,
EPA­
454/
R­
99­
008,
April
1999.
21
prescribed
fires
that
are
managed
for
resource
benefits.
7
The
EPA
will
continue
to
use
these
policies
to
address
issues
related
to
the
existing
and/
or
revised
PM2.5
NAAQS
pending
EPA's
final
action
on
today's
proposed
rulemaking.

Similarly,
issues
related
to
exceptional
and
natural
events
affecting
the
ozone
standard
will
continue
to
be
addressed
under
the
1986
Exceptional
Events
Policy
until
EPA
issues
a
final
exceptional
events
rule.

III.
Today's
Proposed
Action
A.
To
Whom
and
to
What
Pollutants
Does
Today's
Proposed
Rule
Apply?

Under
the
statutory
scheme
established
by
the
CAA,

States
are
primarily
responsible
for
the
administration
of
air
quality
management
programs
within
their
borders.
This
includes
the
monitoring
and
analysis
of
ambient
air
quality
and
submission
of
monitoring
data
to
EPA,
which
are
then
stored
in
EPA's
AQS
data
base.
The
EPA
retains
an
important
oversight
responsibility
for
ensuring
compliance
with
CAA
requirements.
With
respect
to
the
treatment
of
air
quality
monitoring
data,
States
are
responsible
for
7
Following
the
promulgation
of
this
rule,
EPA
will
revise
the
"
Interim
Air
Quality
Policy
on
Wildland
and
Prescribed
Fires"
to
be
consistent
with
current
policies
related
to
wildland
and
prescribed
fires
as
well
as
the
final
rulemaking
on
exceptional
events.
22
ensuring
data
quality
and
validity
and
for
identifying
measurements
that
they
believe
warrant
special
consideration,
while
EPA
is
responsible
for
reviewing
and
approving
or
disapproving
any
requests
for
such
consideration.
Therefore,
if
adopted,
today's
proposed
rule
would
apply
to
all
States;
to
local
air
quality
agencies
to
whom
a
State
has
delegated
relevant
responsibilities
for
air
quality
management,
including
air
quality
monitoring
and
data
analysis;
and,
as
discussed
below,
to
Tribal
air
quality
agencies
where
appropriate.

This
proposed
rule
would
also
govern
EPA's
actions
in
reviewing
and
approving
or
disapproving
the
relevant
actions
taken
or
requested
by
States.
Where
EPA
implements
air
quality
management
programs
on
Tribal
lands,
this
proposed
rule
would
govern
those
actions
as
well.

At
present,
only
the
NAAQS
for
ozone
and
PM
contain
provisions
which
allow
for
the
special
handling
of
air
quality
data
affected
by
exceptional
events
(
40
CFR
part
50,
appendices
K,
I,
and
N).
The
language
of
section
319
of
the
CAA
is
broad
in
terms
of
making
its
provisions
applicable
to
events
that
"
affect
air
quality"
and
to
exceedances
or
violations
of
"
the
national
ambient
air
quality
standards"
(
42
U.
S.
C.
7619(
b)(
1)(
A)(
i),

(
b)(
3)(
B)(
iv)).
Thus,
its
provisions
can
apply
to
the
23
NAAQS
for
any
criteria
pollutant.
Because
the
NAAQS
established
for
other
criteria
pollutants
do
not
currently
contain
provisions
permitting
the
discounting
or
exclusion
of
data
due
to
exceptional
events,
we
are
proposing
to
only
apply
the
provisions
of
this
rule
initially
to
ozone
and
PM.
As
we
review
and
consider
the
need
for
revisions
to
the
NAAQS
for
other
pollutants,
we
will
include
provisions
to
address
exceptional
events
in
those
NAAQS
in
accordance
with
section
319,
as
appropriate
at
that
time.
Because
issuance
of
a
new
or
revised
NAAQS
will
necessitate
the
initiation
of
the
designation
process,
EPA
believes
that
the
NAAQS
rules
are
an
appropriate
place
to
make
provision
for
exceptional
events
in
the
evaluation
of
air
quality
data.
In
the
interim,
where
exceptional
events
result
in
exceedances
or
violations
of
NAAQS
that
do
not
currently
provide
for
special
treatment
of
the
data,
we
intend
to
use
our
discretion
as
outlined
under
section
107(
d)(
3)
not
to
redesignate
affected
areas
as
nonattainment
based
on
these
events.

B.
How
Does
This
Rule
Relate
to
Indian
Tribes?

Under
the
CAA
and
the
Tribal
Authority
Rule
(
TAR),

eligible
Indian
Tribes
may
develop
and
submit
Tribal
Implementation
Plans
(
TIPs)
for
EPA
approval,
to
administer
requirements
under
the
CAA
on
their
reservations
and
other
24
areas
under
their
jurisdiction.
However,
Tribes
are
not
required
to
develop
TIPs
or
otherwise
implement
relevant
programs
under
the
CAA.
The
EPA
has
stated
that
it
will
continue
to
ensure
the
protection
of
air
quality
throughout
the
nation,
including
in
Indian
country,
and
will
issue
Federal
Implementation
Plans
(
FIPs)
as
necessary
or
appropriate
to
fill
gaps
in
program
implementation
in
affected
areas
of
Indian
country
(
63
FR
7254,
7265;

February
12,
1998).

In
cases
where
a
Tribal
air
quality
agency
has
implemented
an
air
quality
monitoring
network
which
is
affected
by
emissions
from
exceptional
events,
the
criteria
and
procedures
identified
in
this
proposed
rule
may
be
used
to
exclude
or
discount
data
for
regulatory
purposes.

Certain
Tribes
may
implement
all
relevant
components
of
an
air
quality
program
for
purposes
of
meeting
the
various
requirements
of
this
proposed
rule.
In
some
cases,

however,
a
Tribe
may
implement
only
portions
of
the
relevant
program
and
may
not
be
in
a
position
to
address
each
of
the
procedures
and
requirements
associated
with
excluding
or
discounting
emissions
data
(
e.
g.,
a
particular
Tribe
may
operate
a
monitoring
network
for
purposes
of
gathering
and
identifying
appropriate
data,
but
may
not
implement
relevant
programs
for
the
purpose
of
mitigating
25
the
effects
of
exceptional
events
required
under
this
proposed
rule).
The
EPA
intends
to
work
with
Tribes
on
the
implementation
of
this
proposed
rule,
which
may
include
appropriate
implementation
by
EPA
of
program
elements
ensuring
that
any
exclusion
or
discounting
of
data
in
Indian
country
areas
with
air
quality
affected
by
exceptional
events
comports
with
the
procedures
and
requirements
of
this
proposed
rule.

C.
What
is
an
Exceptional
Event?

In
accordance
with
the
language
in
section
319,
EPA
is
proposing
to
define
the
term
"
exceptional
event"
to
mean
an
event
that:

(
i)
affects
air
quality;

(
ii)
is
not
reasonably
controllable
or
preventable;

(
iii)
is
an
event
caused
by
human
activity
that
is
unlikely
to
recur
at
a
particular
location
or
a
natural
event;
and
(
iv)
is
determined
by
the
Administrator
through
the
process
established
in
these
regulations
to
be
an
exceptional
event.

It
is
important
to
note
that
natural
events,
which
are
one
form
of
exceptional
events
according
to
this
definition,

may
recur,
sometimes
frequently
(
e.
g.,
western
wildfires).

For
purposes
of
this
rule,
EPA
is
proposing
to
define
26
"
natural
event"
as
an
event
in
which
human
activity
has
no
substantial
or
direct
causal
connection
to
the
event
in
question.
We
recognize
that
over
time,
certain
human
activities
may
have
had
some
impact
on
the
conditions
which
later
give
rise
to
a
"
natural"
air
pollution
event.

However,
we
do
not
believe
that
small
historical
human
contributions
should
preclude
an
event
from
being
deemed
"
natural."

In
this
proposed
rule,
EPA
also
defines
the
term
"
exceedance"
with
respect
to
compliance
with
the
NAAQS
and
establishes
criteria
for
determining
when
an
event
can
be
said
to
"
affect
air
quality."
We
are
not
proposing
more
detailed
requirements
for
determining
when
an
event
is
"
not
reasonably
controllable
or
preventable"
because
we
believe
that
such
determinations
will
necessarily
be
dependent
on
specific
facts
and
circumstances
that
cannot
be
prescribed
by
rule.
In
adopting
section
188(
f)
of
subpart
4
of
the
1990
amendments
to
the
CAA,
Congress
recognized
and
provided
for
distinctions
between
these
types
of
activities,
while
discussing
circumstances
under
which
events
should
or
should
not
be
considered
natural
(
see
Public
Law
101­
549,
CAA
Amendments
of
1990
House
Report
No.

101­
290(
l),
May
17,
1990;
and
discussion
of
Mono
Lake,

California
therein).
27
D.
Examples
of
Exceptional
Events
The
EPA
believes
that
the
following
types
of
events
meet
the
definition
of
exceptional
events,
as
defined
above.
This
means
that
air
quality
data
affected
by
these
types
of
events
may
qualify
for
exclusion
under
this
proposed
rule
if
all
other
requirements
of
the
rule
are
met.
The
AQS
data
base
also
contains
a
more
detailed
list
of
other
similar
events
that
may
be
flagged
for
special
consideration
(
http://
www.
epa.
gov/
ttn/
airs/
airsaqs/
manuals/

codedescs.
htm).

1.
Chemical
Spills
and
Industrial
Accidents
Emissions
that
result
from
accidents
such
as
fires,

explosions,
power
outages,
train
derailments,
vehicular
accidents,
or
combinations
of
these
may
be
flagged
as
an
exceptional
event.

2.
Structural
Fires
Structural
fires
include
any
accidental
fire
involving
a
manmade
structure.

3.
Exceedances
Due
to
Transported
Pollution
Transported
pollution,
whether
national
or
international
in
origin
and
whether
from
natural
or
anthropogenic
sources,
may
cause
exceedances
which
are
eligible
for
exclusion
under
this
rule
as
long
as
the
other
criteria
and
requirements
for
exceptional
events
under
this
28
rule
are
met.
For
example,
States
may
flag,
and
EPA
may
exclude,
data
associated
with
fires
occurring
outside
of
the
borders
of
the
United
States,
such
as
forest
fires
in
Mexico,
Central
America,
and
Canada;
or
transport
events
such
as
African
dust
and
Asian
dust
which
contribute
significantly
to
ambient
concentrations
of
a
pollutant,

leading
to
exceedances
or
violations
of
the
NAAQS.
An
example
of
interstate
transported
emissions
which
may
be
flagged
as
due
to
an
exceptional
event
would
be
emissions
due
to
smoke
from
wildland
fires
which
cause
exceedances
or
violations
at
monitoring
sites
in
other
States.
Other
types
of
events
may
be
considered
on
a
case­
by­
case
basis.

4.
Exceedances
Due
to
a
Terrorist
Attack
Emissions
that
result
from
a
terrorist
attack
such
as
smoke
from
fires,
dust,
explosions,
power
outages,
train
derailments,
vehicular
accidents,
or
combinations
of
these
may
be
flagged
as
an
exceptional
event.

5.
Natural
Events
The
natural
events
addressed
by
this
proposed
rule
are:
(
1)
volcanic
and
seismic
activities;
(
2)
natural
disasters
and
associated
cleanup
activities;
(
3)
high
wind
events;
(
4)
unwanted
fires;
and
(
5)
stratospheric
ozone
intrusions.
The
EPA
will
consider
other
types
of
natural
events
on
a
case­
by­
case
basis.
29
a.
Volcanic
and
Seismic
Activities.
Ambient
concentrations
of
particulate
matter
for
which
volcanic
eruptions
or
seismic
activity
caused
or
contributed
to
high
levels
of
particulate
matter
in
an
affected
area
will
be
treated
as
natural
events.
While
not
occurring
frequently,

volcanic
and
seismic
activity
can
affect
air
quality
data
related
to
the
particulate
matter
NAAQS
for
an
extended
period
of
time
after
an
event.
Volcanic
eruptions
contribute
to
ambient
concentrations
in
two
ways;

concentrations
due
to
primary
emissions
(
e.
g.,
ash);
and
emissions
of
precursor
pollutants
(
e.
g.,
sulfur
dioxide)

that
contribute
to
the
secondary
formation
of
particulate
matter.
Seismic
activity
(
e.
g.,
earthquakes)
can
also
contribute
to
ambient
particulate
matter
concentrations
by
shaking
the
ground,
causing
structures
to
collapse
and
otherwise
raising
dust.

b.
Natural
Disasters
and
Associated
Clean­
up
Activities.

For
the
purpose
of
flagging,
major
natural
disasters,

such
as
hurricanes
and
tornados
for
which
State,
local,
or
Federal
relief
has
been
granted,
and
clean­
up
activities
associated
with
these
events
may
be
considered
exceptional
events.

c.
High
Wind
Events.
High
wind
events
are
events
that
affect
ambient
particulate
matter
concentrations
through
30
re­
entrainment
of
material,
i.
e.,
by
raising
dust.

Concentrations
of
coarse
particles,
i.
e.,
PM10­
2.5
and
PM10
in
some
locations,
are
most
likely
affected
by
these
types
of
events,
although
PM2.5
standards
may
be
exceeded
under
such
circumstances
as
well.

d.
Unwanted
Fires.
Ambient
particulate
matter
concentrations
caused
by
smoke
from
wildland
fires
will
be
treated
as
due
to
natural
events
if
the
fires
are
determined
to
be
unwanted
fires,
designated
wildland
fire
use
fires,
not
designated
or
managed
as
prescribed
fires,

or
requiring
appropriate
suppression
action
by
a
wildland
manager.
8
The
question
of
what
is
a
natural
versus
an
anthropogenic
fire
has
particular
significance
in
considering
the
impacts
of
wildland
fires
on
air
quality
and
how
they
should
be
regarded
under
today's
proposed
rule.
Federal
land
managers
have
given
recognition
to
several
different
types
of
wildland
fires,
depending
on
their
causal
circumstances
and
the
role
that
such
fires
play
in
the
affected
ecosystems.
"
Wildfires"
are
described
as
unplanned,
unwanted
wildland
fires,
and
include
8
It
should
be
noted
that
this
rule
does
not
cover
agricultural
burning.
To
the
extent
that
it
is
necessary
for
EPA
to
address
this
issue,
we
will
do
so
in
the
future
via
separate
guidance
or
rulemaking.
31
unauthorized
burns
(
such
as
arson
or
acts
of
carelessness
by
campers),
prescribed
burns
that
escape
control
due
to
unforeseen
circumstances,
or
other
wildland
fires
where
the
primary
objective
is
to
suppress
the
fire
as
quickly
as
possible.

In
contrast,
"
wildland
fire
use"
fires
are
those
which
were
ignited
naturally
or
unintentionally
(
e.
g.,
as
the
result
of
lightning)
and
are
allowed
to
continue
burning
without
suppression
efforts
in
locations
that
have
been
designated
in
fire
management
plans
as
areas
where
fires
are
necessary
and
desirable
to
accomplish
specific
resource
management
objectives.
"
Prescribed
fires"
are
those
ignited
purposely
to
accomplish
specific
management
objectives,
and
have
been
subject
to
written,
approved
prescribed
fire
plans
("
Interagency
Strategy
for
Directives
Task
Group,"
Memorandum
from
National
Fire
and
Aviation
Executive
Board
to
Agency
Personnel:
Bureau
of
Indian
Affairs,
Bureau
of
Land
Management,
National
Park
Service,

U.
S.
Fish
and
Wildlife
Service,
USDA
Forest
Service,
April
18,
2005).
Under
these
classifications,
we
believe
that
wildfires
due
to
whatever
causes
them
clearly
fall
within
the
meaning
of
"
natural
events"
as
that
term
is
used
in
section
319.
Similarly,
we
believe
that
wildland
fire
use
fires
qualify
as
"
natural
events"
by
virtue
of
their
32
natural
origins.

Prescribed
fires,
however,
cannot
be
classified
as
"
natural,"
given
their
clearly
anthropogenic
origins.

Nonetheless,
we
believe
that
prescribed
fires
are
not
automatically
excluded
from
the
definition
of
exceptional
events.
If
a
prescribed
fire
meets
the
statutory
criteria
of
being
"
unlikely
to
recur
at
the
same
location"
or
"
not
reasonably
controllable
or
preventable,"
and
the
measures
specified
below,
it
may
qualify
as
an
exceptional
event.

Prescribed
fires
carried
out
for
resource
management
objectives
are
frequently
designed
to
restore
the
role
of
wildland
fires
as
they
once
occurred
under
natural
conditions.
As
such,
their
expected
frequency
can
vary
widely,
depending
on
the
fire
regenerative
cycle
of
a
particular
landscape
or
wildland
ecosystem.
The
natural
fire
cycle
can
range
from
once
every
year
to
less
frequently
than
once
in
35­
60
years.
Thus
in
many,
though
not
all,
cases
it
may
be
demonstrated
that
the
likelihood
of
recurrence
is
sufficiently
small
that
these
events
should
be
accorded
special
consideration
under
the
rule.

Since
a
prescribed
fire
is
being
deliberately
ignited,

it
does
not
qualify
as
"
natural,"
and
one
view
is
that
it
cannot
qualify
as
"
not
reasonably
controllable
or
preventable."
However,
a
different
interpretation
of
this
33
provision
of
section
319
examines
whether
there
are
any
reasonable
alternatives
to
the
use
of
fire
in
light
of
the
needs
and
objectives
to
be
served
by
it.
For
instance,

there
may
be
a
sufficient
build­
up
of
forest
fuels
in
a
particular
area
that
if
left
unaddressed
would
pose
an
unacceptable
risk
of
catastrophic
wildfire,
which
result
in
adverse
impacts
of
much
greater
magnitude
and
severity
than
would
result
from
the
careful
use
of
prescribed
fires.
A
particular
ecosystem
may
also
be
highly
dependent
on
a
natural
fire
cycle
to
maintain
a
sustainable
natural
species
composition.
Alternatively,
pest
or
disease
outbreaks
in
an
area
may
be
such
that
there
are
no
reasonable
alternatives
to
fire.
In
some
cases,
other
legal
requirements
may
preclude
the
use
of
mechanical
fuel
reduction
methods
such
as
in
designated
wilderness
or
National
Parks.
Where
such
ecological
conditions
exist,
or
where
mechanical
or
other
treatments
are
not
reasonably
feasible
for
reasons
that
include,
but
are
not
limited
to,

a
lack
of
access
or
severe
topography,
we
believe
that
it
would
be
appropriate
to
exclude
the
impacts
from
wellmanaged
prescribed
fires
to
address
them.
Well­
managed
prescribed
fires
are
those
that
consider
smoke
impacts
prior
to
and
during
the
burn,
barring
unforeseen
circumstances,
and
when
the
prescribed
fire
is
in
34
compliance
with
a
Smoke
Management
Plan
(
SMP).

The
EPA
is
proposing
in
this
action
that
States
continue
to
follow
the
smoke
management
provisions
described
in
the
"
Interim
Air
Quality
Policy
on
Wildland
and
Prescribed
Fires,"
issued
May
15,
1998
(
Wildland
and
Prescribed
Fire
Policy).
This
policy
provides
that
EPA
will
allow
exceedances
to
be
discounted
that
have
been
flagged
by
a
State
as
having
been
caused
by
prescribed
fires
used
for
purposes
of
resource
management
provided
that
the
State
certifies
that
it
has
adopted
and
is
implementing
a
certified
SMP
as
described
in
our
policy.

Under
our
proposal,
if
a
State,
local,
or
Tribal
air
quality
agency
does
not
certify
that
a
basic
SMP
is
being
implemented,
or
that
basic
smoke
management
practices
are
being
employed
by
burners,
EPA
would
not
exclude
data
related
to
exceedances
or
violations
attributed
to
prescribed
fires
managed
for
resource
benefits.

We
request
comments
on
the
interpretation
of
prescribed
fire
described
above
on
the
proposed
requirements
for
SMPs,
and
on
any
additional
criteria
or
conditions
that
should
be
considered
in
determining
whether
and
under
what
circumstances
prescribed
fires
should
be
considered
to
be
exceptional
events.
35
e.
Stratospheric
Ozone
Intrusions.
Stratospheric
ozone
intrusion
is
considered
to
be
a
natural
event.
A
stratospheric
ozone
intrusion
occurs
when
a
parcel
of
air
originating
in
the
stratosphere,
which
is
at
an
average
height
of
20
km
or
12.4
miles,
is
re­
entrained
directly
to
the
surface
of
the
earth.
Stratospheric
ozone
intrusions
are
very
infrequent,
localized
events
of
short
duration.

They
are
typically
associated
with
strong
frontal
passages
and,
thus,
may
occur
primarily
during
the
spring
season.

IV.
The
Management
of
Air
Quality
Data
Affected
by
Exceptional
Events
The
EPA
is
proposing
that,
in
order
to
exclude
air
quality
data
from
consideration
for
regulatory
purposes,

States
must
follow
the
procedures,
timelines,
and
other
requirements
described
in
this
proposed
rule.

Specifically,
States
must
clearly
identify,
or
"
flag,"
data
they
believe
to
be
influenced
by
such
events;
they
must
show
that
they
have
flagged
days
on
which
air
quality
has
been
"
affected"
by
exceptional
events
according
to
EPA
criteria;
and
they
must
submit
appropriate
documentation
demonstrating
that
the
exceptional
event
caused
the
exceedance
or
violation
of
the
NAAQS
in
question.
Each
of
these
steps
is
described
in
detail
below.
36
A.
Flagging
of
Data
in
the
AQS
Data
Base
Air
quality
data
are
required,
pursuant
to
40
CFR
part
58.35,
to
be
submitted
to
EPA
by
each
State
on
a
calendar
quarterly
basis,
with
submissions
due
not
later
than
90
days
after
the
end
of
a
quarterly
reporting
period.
Once
air
quality
data
have
been
submitted
to
EPA,
it
is
possible
to
"
flag"
specific
values
for
various
purposes.
"
Data
flagging"
refers
to
the
act
of
making
a
notation
in
a
designated
field
of
an
electronic
data
record.
The
principal
purpose
of
the
data
flagging
system
in
the
AQS
data
base
is
to
identify
those
air
quality
measurements
for
which
special
attention
or
handling
is
warranted.
These
include,
but
are
not
limited
to,
those
measurements
that
are
influenced
by
exceptional
events.
In
the
case
of
exceptional
events,
States
place
the
initial
flag
on
the
data
in
the
AQS
data
base.
Following
an
evaluation
of
the
supporting
documentation,
EPA
will
decide
whether
to
concur
with
the
flag;
concurrence
will
be
marked
by
the
placement
of
a
second
flag
in
the
AQS
data
base
by
EPA.
Once
EPA
has
concurred
on
the
flag,
the
data
will
be
excluded
from
regulatory
decisions
such
as
determinations
of
attainment
or
nonattainment.

While
the
flagging
of
data
by
the
State
is
the
first
step
in
an
exceptional
events
demonstration,
it
is
37
insufficient
by
itself
to
allow
for
the
exclusion
of
data.

In
order
to
have
EPA
concur
on
a
flag,
States
must
meet
the
additional
requirements
described
below.
As
explained,
the
State
has
the
responsibility
to
document
both
the
occurrence
of
the
event
and
the
causal
connection
to
the
monitoring
data
under
consideration.
Because
the
initial
step
of
flagging
the
data
is
a
relatively
simple
one,

States
may
flag
many
more
days
than
the
number
of
days
for
which
they
ultimately
submit
documentation
to
support
exclusion.

B.
What
Does
it
Mean
for
an
Event
to
"
Affect
Air
Quality"?

It
is
important
to
recognize
that
any
emissionsproducing
event
has
the
potential
to
have
some
influence
on
downwind
air
quality.
Indeed,
on
any
given
day,
measured
air
quality
at
any
given
location
will
reflect
the
influences
of
a
variety
of
activities,
including
both
natural
and
anthropogenic
emissions
from
both
local
and
remote
upwind
sources.
The
EPA
believes
that
it
would
be
unreasonable
to
exclude
data
affected
by
an
exceptional
event
simply
because
of
a
trivial
contribution
of
the
event
to
air
quality.
Furthermore,
we
also
believe
that
it
would
be
unreasonable
to
exclude
more
significant,
but
routine
background
air
quality
impacts,
as
this
would
disregard
an
important
part
of
the
public's
exposure
to
air
pollution
38
upon
which
EPA's
air
quality
standards
are
based.
The
effect
of
such
exclusion
would
be
an
inappropriate
reduction
in
the
stringency
of
the
NAAQS,
rather
than
providing
specific
relief
under
the
circumstances
provided
in
section
319
for
which
States
should
not
be
designated
nonattainment
or
be
required
to
prepare
control
strategies.

Neither
section
319
nor
its
legislative
history
provides
precise
guidance
on
what
should
be
considered
when
determining
whether
an
event
"
affects
air
quality"
and
thus
qualifies
to
be
considered
for
exclusion
or
special
treatment.
However,
section
319(
b)(
3)(
B)(
ii)
and
(
iv)

provide
that
there
must
be
a
"
clear
causal
relationship"

between
a
measured
exceedance
of
a
standard
and
the
event
to
show
that
the
event
"
caused
a
specific
air
pollution
concentration;"
and
it
must
be
shown
that
the
data
in
question
are
"
directly
due"
to
an
exceptional
event.

Moreover,
one
of
the
principles
provided
by
section
319(
b)(
3)(
A)
indicate
that
the
protection
of
public
health
is
the
highest
priority.
For
these
reasons,
we
are
proposing
that
for
an
event
to
qualify
as
"
exceptional"
for
purposes
of
special
regulatory
consideration,
its
air
quality
impact
must
fall
both
above
the
level
of
the
applicable
standard
(
i.
e.,
must
be
an
"
exceedance"
as
required
by
section
319)
and
significantly
beyond
the
39
normal
fluctuating
range
of
air
quality,
including
background
air
quality
concentrations,
and
should
be
large
enough
so
that
without
it
there
would
have
been
no
exceedance.
We
next
provide
several
alternative
approaches
to
determining
whether
and
when
air
quality
is
"
affected
by"
exceptional
events,
and
request
comment
on
which
of
these
approaches
is
most
suitable
for
demonstrating
such
impacts.

1.
Option
1:
95th
Percentile
Criterion
The
first
proposed
approach
is
essentially
a
test
for
statistical
deviations
from
the
norm.
For
measurement
days
on
which
the
event
can
be
shown
to
have
an
air
quality
impact,
the
measurement
would
be
compared
to
the
95th
percentile
of
measurements
typical
of
days
in
the
particular
calendar
quarter
that
are
not
influenced
by
exceptional
events
("
non­
event
days").
The
typical
days
could
be
based
on
a
3­
5
year
period
of
record
which
exclude
days
influenced
by
exceptional
events.
Under
this
option,

only
an
event
whose
resulting
concentrations
meet
or
exceed
the
95th
percentile
criterion,
along
with
meeting
the
other
criteria
in
this
proposed
rule
would
qualify
for
exclusion
from
regulatory
consideration.

In
evaluating
available
air
quality
data,
we
have
found
that
by
limiting
consideration
to
those
40
concentrations
above
the
95th
percentile,
only
those
concentrations
that
fall
approximately
two
standard
deviations
above
the
mean
of
concentrations
for
that
quarter
would
generally
be
excluded
(
See
memo
from
Mark
Schmidt,
OAQPS,
to
docket
entitled
"
Analysis
of
Flagged
Particulate
Matter
Data,"
February
10,
2006).
Excluding
days
on
which
concentrations
caused
by
exceptional
events
exceed
the
95th
percentile
threshold
employs
a
general
test
of
statistical
significance
and
has
the
effect
of
ensuring
that
such
concentrations
would
clearly
fall
beyond
the
range
of
normal
expectations
for
air
quality
during
a
particular
time
of
year.

In
our
analysis
of
flagged
and
excluded
air
quality
data
for
the
period
1999­
2004,
we
found
that
application
of
the
95th
percentile
criterion
would
result
in
the
exclusion
of
approximately
85
percent
of
data
previously
flagged
by
States
and
concurred
on
by
EPA.
Thus,
this
approach
would
result
in
a
somewhat
more
rigorous
qualification
requirement
than
is
reflected
in
EPA's
past
case­
by­
case
approach.
Previously,
EPA
did
not
have
a
concentration
threshold
or
other
quantitative
criteria
to
determine
which
days
would
be
eligible
for
exclusion
due
to
exceptional
events.
As
indicated
above,
approximately
15
percent
of
the
flags
that
were
concurred
on
were
concentrations
that
41
were
not
necessarily
statistically
distinguishable
from
routine
levels.
The
95th
percentile
approach
could
also
help
to
eliminate
some
of
the
variability
from
State
to
State
and
Region
to
Region:
as
described
in
Schmidt
(
2006),
rates
of
flagging
and
the
severity
of
pollution
on
flagged
days
have
varied
significantly
among
States
and
regions
in
the
past.
For
PM2.5,
for
example,
many
States
flagged
no
days
between
1999­
2004,
while
Puerto
Rico
flagged
15
percent
of
all
of
its
PM2.5
data.
Also,
while
most
PM2.5
flags
during
this
period
were
above
the
95th
percentile,
some
States
flagged
data
at
the
75th
percentile
or
lower.
(
See
memo
from
Mark
Schmidt,
OAQPS,
to
docket
entitled
"
Analysis
of
Flagged
Particulate
Matter
Data,"

February
10,
2006.)

2.
Option
2:
75th
Percentile/
95th
Percentile
Tiered
Approach
Under
this
approach,
we
propose
to
retain
flexibility
to
determine
whether
concentrations
less
than
the
95th
percentile
but
above
the
norm
should
qualify
for
exclusion
as
"
affecting
air
quality."
In
particular,
multiple
measurement
values
over
time
with
relatively
small
individual
event
impacts
may
collectively
affect
an
annual
average
concentration
to
a
significant
degree.
States
may
wish
to
consider
whether
to
exclude
such
impacts
if
the
42
average
concentration
is
close
to
the
level
of
the
annual
NAAQS.
Therefore,
we
are
soliciting
comment
on
a
second
approach
whereby
measured
values
are
compared
both
to
the
historical
95th
percentile
of
non­
event
days
and
to
the
75th
percentile
of
such
days.

Where
concentrations
caused
by
an
exceptional
event
meet
or
exceed
the
95th
percentile
criterion,
they
would
be
conclusively
determined
to
qualify
for
exclusion
subject
to
the
other
requirements
of
this
proposed
rule.
Where
concentrations
caused
by
an
exceptional
event
do
not
meet
the
95th
percentile
criterion,
we
would
provide
a
further
opportunity
for
States
to
make
demonstrations
which
satisfy
the
other
criteria
in
this
proposed
rule,
so
long
as
values
exceeded
the
75th
percentile
of
non­
event
days.
This
approach
would
provide
for
a
more
flexible
approach
and
would
rely
on
a
weight­
of­
evidence
demonstration
that
would
permit
States
to
make
other
sorts
of
showings
that
the
concentrations
caused
by
the
event
were
in
some
way
unusual
or
not
representative
of
normal
air
quality
and
thus
should
not
result
in
additional
regulatory
requirements.

When
we
applied
the
75
percent
percentile
criterion
to
our
analysis
of
flagged
and
excluded
air
quality
data
for
the
period
1999­
2004,
we
found
that
this
criterion
would
make
nearly
all
of
the
data
previously
flagged
by
States
43
and
concurred
on
by
EPA
eligible
for
exclusion.
Thus,
we
expect
this
approach
would
have
a
result
that
is
roughly
consistent
with
EPA's
past
case­
by­
case
approach.

3.
Option
3:
Case­
by­
Case
Approach
Based
on
Weight
of
Evidence
The
third
option
is
to
permit
the
more
general
caseby
case
evaluation,
without
threshold
criteria,
that
may
be
guided
by
the
magnitude
of
the
measured
concentration
on
days
affected
by
exceptional
events
relative
to
historical,

seasonally
adjusted
air
quality
levels.
This
approach
is
most
nearly
analogous
to
our
historical
treatment
of
exceptional
events
but,
in
contrast
to
Options
1
and
2,

provides
the
least
definitive
guidance
to
assist
States
in
their
evaluations.
Nevertheless,
the
case­
by­
case
approach
allows
for
consideration
of
days
with
ambient
concentrations
which
are
not
necessarily
among
the
highest
concentrations
that
have
been
historically
observed.
In
fact,
25
percent
of
days
have
concentrations
greater
than
the
median
value
but
less
than
the
75th
percentile.
While
such
days
are
unlikely
to
impact
short­
term
standards,

discounting
such
days
can
certainly
have
an
impact
on
an
annual
average
concentration.
In
general,
however,

demonstration
that
an
event
caused
a
concentration
which
is
essentially
indistinguishable
from
routine
air
quality
44
would
be
very
difficult
to
document,
and
this
approach
may
make
it
difficult
for
EPA
regions
to
be
consistent
when
determining
whether
to
concur
on
a
flag.

We
request
comment
on
which
of
these
proposed
options
should
be
included
in
the
final
rule,
including
the
appropriateness
of
proposed
statistical
criteria,
the
period
of
record
on
which
to
base
the
95th
and
75th
percentile
and
conclusions
about
normal
air
quality
expectations
(
e.
g.,
3
years,
5
years,
or
some
longer
period
of
record),
and
any
other
criteria
or
procedures
we
should
consider
adopting
along
with
one
of
these
options.

C.
Use
of
a
"
But
For"
Test
There
may
be
instances
in
which
exceptional
events
may
have
a
significant
impact
on
air
quality
on
days
when
concentrations
are
already
above
the
applicable
standard
in
the
absence
of
the
influence
of
such
events.
In
such
cases,
it
is
important
to
preserve
and
consider
all
valid
air
quality
data
influenced
by
activities
which
properly
fall
within
the
responsibilities
of
States
to
manage
for
purposes
of
air
quality
attainment
and
maintenance.
For
this
reason,
we
are
proposing
to
require
that
air
quality
data
may
not
be
excluded
except
where
States
show
that
exceedances
or
violations
of
applicable
standards
would
not
have
occurred
"
but
for"
the
influence
of
exceptional
45
events.
In
other
words,
to
the
extent
it
is
possible
to
determine
that
the
resulting
air
quality
concentrations
and
appropriate
design
values
for
an
area
would
be
above
the
level
of
the
standards
even
without
the
influence
of
the
exceptional
event,
the
air
quality
data
for
the
day(
s)
in
question
should
not
be
excluded.
However,
consideration
of
the
impacts
of
exceptional
events
on
air
quality
values
for
control
strategy
planning
purposes
may
be
appropriate,
and
States
are
encouraged
to
consult
with
the
appropriate
EPA
regional
offices
to
further
discuss
this
issue.

D.
Schedules
and
Procedures
for
Flagging
and
Requesting
Exclusion
of
Data
In
establishing
procedures
and
timetables
for
States
to
request,
and
EPA
to
grant,
exclusion
of
data
affected
by
exceptional
events,
we
are
guided
by
two
competing
considerations:
ensuring
States
have
adequate
time
and
opportunity
to
compile
and
evaluate
all
relevant
and
available
information
in
support
of
such
requests;
and
making
determinations
in
a
timely
manner
so
that
all
pertinent
and
valid
air
quality
data
would
be
appropriately
considered
in
regulatory
determinations.
To
assist
EPA
in
determining
the
best
approach
to
managing
the
data
flagging
process
and
submissions
of
demonstrations
for
the
final
rule,
we
are
proposing
three
alternatives
for
public
review
46
and
comment.

1.
Option
1:
Early
Data
Flagging
and
Demonstration
Submission
The
first
approach
would
establish
a
two­
step
process
for
identification
of
data
and
submission
of
demonstrations.
This
process
provides
for
the
early
flagging
of
data
and
the
notification
of
the
appropriate
EPA
Regional
Office
concerning
the
State's
intention
to
seek
exclusion
of
data,
followed
by
a
longer
timeframe
for
States
to
prepare
and
submit
their
demonstrations.

Under
this
approach,
we
would
require
a
State
to
flag
the
data
that
they
believe
to
be
affected
by
exceptional
events
at
the
time
of
submission
of
the
air
quality
data
to
EPA's
AQS
data
base,
in
accordance
with
the
schedule
described
in
40
CFR
part
50.35,
which
is
generally
no
later
than
90
days
after
the
end
of
the
calendar
quarter.
This
approach
would
ensure
that
the
flagging
process
remains
consistent
with
the
timeline
set
forth
in
rules
governing
data
submission
requirements.

Just
as
the
scope
and
substance
of
demonstrations
in
support
of
requests
for
exclusion
will
vary
depending
on
facts
and
circumstances
(
see
section
IV.
F.
below),
so,
too,

will
the
time
required
for
such
demonstrations.
Where
air
quality
in
an
area
is
influenced
by
a
relatively
small
set
47
of
emission
sources
with
well­
defined
emission
profiles
and
limited
pollutant
species,
a
demonstration
that
an
air
quality
measurement
influenced
by
a
particular
event
merits
exclusion
may
be
relatively
simple
to
make.
In
other
cases,
such
as
where
the
number
and
types
of
sources
contributing
to
measured
air
quality
concentrations
are
extremely
complex
and
varied,
making
it
more
difficult
to
distinguish
between
the
effects
of
routine
activities
and
unusual
ones,
more
time
and
effort
will
be
needed
for
a
State
to
provide
an
adequate
demonstration
in
support
of
its
request.

For
these
reasons,
we
are
proposing
under
this
option
to
require
States
to
notify
the
appropriate
EPA
Regional
Office
of
their
intent
to
seek
exclusion
of
data
due
to
exceptional
events
at
the
time
of
submission
of
quarterly
air
quality
data
to
the
AQS
data
base.
We
are
also
proposing
to
require
the
State
to
consult
with
the
EPA
Regional
Office
as
soon
as
reasonably
possible
after
notification
about
the
event,
its
suspected
air
quality
impact,
and
the
demonstration
needed
to
justify
a
decision
to
exclude
the
data
from
regulatory
consideration.
This
is
intended
to
enable
the
State
and
EPA
to
work
together
during
the
process
of
data
analysis
and
documentation
to
ensure
that
a
complete
and
well­
supported
demonstration
is
48
submitted
in
a
timely
manner.

With
respect
to
demonstrations
in
support
of
requests
for
exclusion
of
data,
we
are
proposing
under
this
option
to
provide
States
with
more
time
to
submit
the
necessary
demonstration.
We
propose
that
States
submit
complete
demonstrations
to
EPA
not
later
than
180
days
following
the
close
of
the
quarter
in
which
the
event
occurred.
Based
on
past
experience
with
exceptional
events
and
associated
data
analyses,
we
believe
that
this
will
provide
adequate
time
in
most
cases
for
States
to
identify,
compile,
and
evaluate
all
relevant
factors
pertaining
to
an
exceptional
event
and
its
impacts.
However,
in
special
circumstances
where
additional
time
is
required
to
make
a
complete
submission,

and
where
the
outcome
of
such
additional
efforts
is
likely
to
have
a
substantial
impact
on
the
demonstration,
we
are
proposing
to
allow
States
to
request
extensions
of
up
to
90
additional
days.
We
expect
that
such
extensions
under
this
option
would
be
the
exception,
rather
than
the
rule,
and
that
they
will
be
limited
to
special
circumstances
necessitating
more
complex
and
sophisticated
analyses,
such
as
where
the
collection
and
analysis
of
species­
specific
data
in
urban
areas
may
be
needed
in
order
to
characterize
and
quantify
an
event's
contribution
to
air
quality
at
a
particular
location.
Under
this
option,
as
well
as
the
49
options
addressed
below,
once
EPA
receives
a
State's
demonstration,
EPA
will
then
have
a
30­
day
period
to
review
the
demonstration
and
provide
a
concurrence
or
nonconcurrence
on
the
flag
in
the
AQS
data
base.
The
EPA
expects
that,
in
most
cases,
a
period
of
30
days
will
be
enough
time
to
review
and
provide
a
concurrence
related
to
a
State's
request
to
exclude
data
affected
by
an
exceptional
event.
However,
for
more
complex
demonstrations,
EPA
may
require
more
time
for
its
review.

In
such
cases,
EPA
may
extend
the
time
for
its
review
by
not
more
than
an
additional
30
days.

2.
Option
2:
Early
Data
Flagging
and
Delayed
Demonstration
Submission
Under
this
option,
we
are
proposing
the
same
requirements
for
the
flagging
of
data
and
notification
of
the
appropriate
EPA
Regional
Office
as
described
in
Option
1.
However,
under
Option
2,
we
propose
to
allow
up
to
3
years
following
the
quarter
in
which
the
event
occurred
for
the
submission
of
exceptional
events
demonstrations.
The
reason
for
providing
more
time
under
this
option
is
that
for
most
existing
air
quality
standards,
decisions
regarding
whether
or
not
an
area
is
attaining
the
applicable
standard
are
based
on
the
most
recent
3
years
of
air
quality
data.
Providing
3
years
for
submission
of
50
demonstrations
would
provide
States
with
an
opportunity
to
evaluate
whether
the
influence
of
one
or
more
exceptional
events
will
be
relevant
to
determinations
of
attainment
or
nonattainment
before
undertaking
the
effort
of
preparing
and
submitting
demonstrations.

3.
Option
3:
Delayed
Data
Flagging
and
Demonstration
Submission
Under
this
option,
we
are
proposing
to
decouple
the
process
of
flagging
and
demonstrations
from
the
regular
submission
of
air
quality
data
to
the
AQS
data
base
and
to
require
instead
that
data
be
flagged
and
exceptional
events
demonstrations
be
submitted
not
later
than
6
months
prior
to
the
date
when
regulatory
decisions
using
the
air
quality
data
must
be
made.
This
option
is
based
on
the
recognition
that
while
data
flagging
itself
may
not
be
a
particularly
burdensome
exercise,
it
triggers
a
more
extensive
process
of
collection
and
analysis
of
other
information
to
determine
and
demonstrate
whether,
in
fact,
an
exceptional
event
has
occurred
which
affects
air
quality
data
in
a
way
that
justifies
exclusion
of
the
data.
It
may
be
that
although
certain
events
occurred
which
do
indeed
affect
air
quality
in
significant
ways,
their
impact
on
regulatory
decisions
may
not
be
known
for
a
significant
period
of
time,
i.
e.,
until
a
relevant
3­
year
period
of
record
is
51
compiled
and
the
need
for
a
regulatory
decision
is
identified.
Thus
under
this
option,
it
would
be
less
burdensome
for
the
States
and
EPA
if
demonstrations
were
not
required
unless
and
until
it
became
apparent
that
potentially
affected
measurements
would
be
used
in
making
regulatory
findings
of
attainment
or
nonattainment
(
e.
g.,

where
a
State
with
an
existing
area
designated
as
nonattainment
seeks
to
have
that
area
redesignated
as
attainment
and
the
existence
of
one
or
more
exceptional
events
may
affect
its
ability
to
provide
the
requisite
3
years
of
clean
air
quality
data).

We
request
comment
on
which
of
the
above
three
proposed
options
EPA
should
promulgate
and
on
what,
if
any,

modifications
to
these
options
we
should
make
prior
to
the
final
rule.

E.
Exclusion
of
Entire
24­
Hour
Value
as
Opposed
to
a
Partial
Adjustment
of
the
24­
Hour
Value
The
EPA's
historical
practice
has
been
to
exclude
a
daily
measured
value
in
its
entirety
when
that
value
is
found
to
be
largely
caused
by
an
exceptional
event,
and
we
are
proposing
to
retain
this
approach
in
today's
proposed
rule.
With
this
approach,
a
determination
is
made
that
emissions
from
the
event
are
largely
responsible
for
the
resultant
ambient
air
pollutant
concentration.
For
52
example,
if
the
observed
concentration
is
200
µ
g/
m3
PM2.5
and
is
associated
with
a
nearby
forest
fire,
then
EPA
would
concur
with
the
claim
that
the
event
was
responsible
for
the
ambient
concentration.
The
measured
value
would
be
excluded
in
its
entirety
from
the
data
used
to
judge
attainment
(
as
per
40
CFR
50,
appendix
N),
although
the
measurement
day
would
still
count
towards
meeting
minimum
data
capture
requirements.

We
believe
it
would
be
desirable
to
adjust
the
daily
value
to
exclude
only
those
portions
of
the
data
that
are
attributable
to
the
exceptional
event
in
question,
and
to
retain
the
remainder
of
the
day's
measurement
if
appropriate
and
accurate
methods
were
available
to
make
such
adjustments.
For
example,
if
an
area
affected
by
a
forest
fire
had
a
measured
24­
hour
PM2.5
concentration
of
50
µ
g/
m3
and
the
estimated
event
impact
was
30
µ
g/
m3,
then
the
expected
value
which
would
have
occurred
but
for
the
event
would
have
been
20
µ
g/
m3.
Normal
air
quality
for
this
location
might
be
16
µ
g/
m3
and,
therefore,
the
"
but­
for"

concentration
of
20
µ
g/
m3
is
above
average.
Discounting
the
entire
event
day
could,
therefore,
inappropriately
bias
a
determination
of
nonattainment
with
the
annual
PM2.5
NAAQS
(
currently
set
at
15
µ
g/
m3).
We
are
currently
seeking
to
develop
and
evaluate
new
analytical
methods
that
would
53
allow
us
to
discount
only
the
portion
of
the
daily
value
attributable
to
the
exceptional
event.
However,
at
present,
we
are
not
aware
of
the
existence
of
adequate
and
universally
applicable
techniques
that
are
administratively
and
technically
feasible
and
that
could
support
partial
adjustment
of
air
quality
data
except
perhaps
in
limited
cases,
such
as
where
the
number
and
type
of
pollutant
species
and
contributing
sources
are
relatively
less
complex
or
potentially,
when
sufficient
spatial,
temporal,

meteorological
and
chemical
data
are
available
[
See
memo
to
docket,
Husar
et
al.
2006,
(
www.
regulations.
gov,
Epa­

HQOar
2003­
0061­
0733
thru
0733.5)].
When
we
determine
that
techniques
for
adjustment
of
air
quality
data
are
sufficiently
well­
demonstrated
for
use
in
exceptional
events
determinations,
we
will
publish
a
notice
of
proposed
rulemaking
to
seek
comment
on
the
appropriateness
and
scope
of
such
use.

F.
What
Should
States
be
Required
to
Submit
in
Their
Exceptional
Events
Demonstrations?

Section
319
requires
that,
in
order
to
have
a
flagged
value
excluded
from
regulatory
determinations,
a
State
must
make
an
affirmative
demonstration
that
an
event
occurred
(
as
shown
by
reliable
and
accurate
data
that
is
promptly
produced)
and
that
there
is
a
clear
causal
relationship
54
between
measured
exceedances
or
violations
of
a
standard
and
the
exceptional
event
in
question
to
"
demonstrate
that
the
exceptional
event
caused
a
specific
air
pollution
concentration."
(
42
U.
S.
C.
7619(
b)(
3)(
B)(
ii),
(
iv)).

Section
319
also
indicates
that
regulations
promulgated
under
the
section
should
provide
for
criteria
and
procedures
to
exclude
air
quality
monitoring
data
"
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."

Therefore,
after
flagging
data
in
the
AQS
data
base,

States
are
expected
to
develop
appropriate
documentation
to
support
each
individual
flag.
As
a
general
matter,
we
believe
that
such
demonstrations
should
include
documentation
showing
that
the
event
in
fact
occurred
and
that
emissions
related
to
the
event
were
transported
in
the
direction
of
the
monitor(
s)
where
measurements
were
recorded;
the
size
of
the
area
affected
by
the
transported
emissions;
the
relationship
in
time
between
the
event,

transport
of
emissions,
and
recorded
concentrations;
and,

as
appropriate,
pollutant
species­
specific
information
supporting
a
causal
relationship
between
the
event
and
the
measured
concentration.
The
latter
information
could
be
based
on
available
data
provided
by
routine
speciation,
55
monitoring
networks,
or
from
selective
laboratory
analysis
of
archived
particulate
matter
filters
for
the
day
thought
to
be
impacted
by
specific
events.
In
certain
situations,

such
data
might
be
useful
for
evaluation
of
impacts
from
exceptional
events,
e.
g.,
to
distinguish
between
impacts
caused
by
natural
fires
versus
impacts
caused
by
industrial
sources.
Depending
on
which
option
is
finalized
pursuant
to
section
V
below,
States
may
also
need
to
show
that
appropriate
mitigation
actions
were
taken
at
the
time
that
the
event
occurred,
or
after
an
event
occurred
in
order
to
protect
public
health.

The
following
examples
are
intended
to
further
illustrate
the
kinds
of
information
that
States
could
consider
in
preparing
their
demonstrations:

1.
Information
demonstrating
the
occurrence
of
the
event
and
its
subsequent
transport
to
the
affected
monitors.
This
could
include,
for
instance,
documentation
from
land
owners/
managers,
satellite­
derived
pixels
(
portions
of
digital
images)
indicating
the
presence
of
fires;
satellite
images
of
the
dispersing
smoke
and
smoke
plume
transport
or
trajectory
calculations
(
calculations
to
determine
the
direction
of
transport
of
pollutant
56
emissions
from
their
point
of
origin)
connecting
fires
with
the
receptors.

2.
Identification
of
the
spatial
pattern
of
the
affected
area
(
the
size,
shape,
and
area
of
geographic
coverage).
This
could
include,
for
instance,
the
use
of
satellite
or
surface
measurement
data.

3.
Information
about
temporal
patterns
(
e.
g.,
the
time
and
duration
of
an
event
in
relation
to
measured
downwind
concentrations,
air
quality
trends
over
time
and
space).
This
could
include,

for
instance,
observed
sequential
concentration
spikes
at
multiple
locations
in
a
downwind
direction.

4.
Identification
of
the
chemical
composition
of
measured
concentrations.
This
could
include,
for
instance,
organic
or
crustal
material
in
excess
of
typically
observed
quantities
to
differentiate
from
other
high
concentration
events.

5.
Extremely
high
wind
speeds,
or
unusual
transport
conditions
relative
to
historically
typical
levels
for
the
season
of
the
year
in
which
the
claimed
event
occurred.

This
list
is
not
exhaustive
and
not
all
of
these
kinds
57
of
information
and/
or
documentation
will
need
to
be
provided
in
every
instance.
A
particular
instance
may
require
more
or
less
documentation,
depending
on
the
particular
facts
or
circumstances
in
that
instance.
The
simplest
demonstrations
could
consist
of
newspaper
accounts
or
satellite
images
to
demonstrate
that
an
event
occurred
together
with
daily
and
seasonal
average
ambient
concentrations
to
demonstrate
an
unusually
high
ambient
concentration
level
which
is
clearly
indicative
of
an
exceptional
impact.
Such
is
the
case
with
events
such
as
volcanic
eruptions
and
nearby
forest
fires.
In
one
instance,
we
determined
that
wildfires
upwind
of
the
San
Diego
area
caused
high
concentrations
of
particulate
matter
measured
in
October
2003
based
on
the
actual
physical
damage
caused
by
fire
to
the
ambient
monitor.
Depending
on
the
nature
of
the
event,
meteorological
conditions,

severity
and
spatial
extent
of
measured
ambient
concentrations
(
including
relevant
chemical
components
when
available)
relative
to
what
typically
occurs
in
the
area,

and
on
emissions
of
pollutants
from
the
exceptional
event
which
have
similar
characteristics
to
those
of
other
sources
in
the
area,
additional
showings
could
be
required
on
a
case­
by­
case
basis.
In
particular,
we
anticipate
that
significantly
more
effort
will
be
needed
to
establish
that
58
an
exceptional
event
caused
a
particular
concentration
in
an
urban
area
in
which
there
are
numerous
and
diverse
sources
and
complex
meteorology
and
topography,
and
where
the
emissions
from
the
event
in
question
may
well
be
similar
to
those
from
other
sources
contributing
to
measured
concentrations,
as
compared
to
an
area
that
has
relatively
few
sources,
simple
terrain
and
less
complex
meteorology,
and
where
emissions
associated
with
the
event
are
both
substantially
greater
than
and
different
in
composition
from
those
of
other
nearby
sources.
Because
of
the
variability
in
the
nature
of
exceptional
events
and
the
resulting
demonstration
requirements,
States
should
consult
with
the
appropriate
EPA
Regional
Office
early
in
the
process
of
preparing
their
demonstrations.

We
are
not
proposing
to
specify
what
will
be
required
as
a
minimum
level
of
documentation
in
all
cases
because
facts
and
circumstances
will
vary
significantly
based
on,

among
other
things,
geography,
meteorology
and
the
relative
complexity
of
source
contributions
to
measured
concentrations
in
any
particular
location.
However,
we
request
comment
on
whether
we
should
adopt
a
set
of
minimum
demonstration
requirements
to
ensure
a
reasonable
degree
of
national
consistency
in
approaches
to
demonstrating
exceptional
events,
and
if
so,
what
elements
should
be
59
included
in
the
demonstration.
We
believe,
however,
that
at
a
minimum,
the
elements
of
such
a
demonstration
should
include
a
showing
that
an
event
occurred
at
a
time
when
meteorological
conditions
were
conducive
to
transporting
emissions
from
the
event
downwind
to
the
monitor
recording
a
high
concentration
of
one
or
more
criteria
pollutants.

G.
Special
Considerations
Relevant
to
Proposed
Standards
for
PM10­
2.5
As
noted
in
EPA's
notice
of
proposed
rulemaking
reviewing
the
NAAQS
for
particulate
matter
(
71
FR
2620;

January
17,
2006),
fine
particles
(
PM2.5)
are
produced
chiefly
by
combustion
processes
and
by
atmospheric
reactions
of
various
gaseous
pollutants,
whereas
thoracic
coarse
particles
(
PM10­
2.5)
are
generally
emitted
directly
as
particles
as
a
result
of
mechanical
processes
that
crush
or
grind
larger
particles
or
the
resuspension
of
dusts.

Sources
of
fine
particles
include,
for
example,
motor
vehicles,
power
generation,
combustion
sources
at
industrial
facilities,
and
residential
fuel
burning.

Sources
of
thoracic
coarse
particles
include,
for
example,

resuspension
of
traffic­
related
emissions
such
as
tire
and
brake
lining
materials,
and
direct
emissions
from
industrial
operations,
construction
and
demolition
activities.
Fine
particles
can
remain
suspended
in
the
60
atmosphere
for
days
to
weeks
and
can
be
transported
thousands
of
kilometers,
whereas
thoracic
coarse
particles
generally
deposit
rapidly
on
the
ground
or
other
surfaces
and
are
not
readily
transported
across
urban
or
broader
areas
(
71
FR
2620,
2625;
January
17,
2006).

Based
on
preliminary
analysis,
we
generally
anticipate
that
demonstrations
that
ambient
concentrations
of
PM10­
2.5
have
been
affected
by
exceptional
events
will
involve
similar
analytical
steps
to
demonstrations
for
PM2.5
but
will
be
simpler
than
demonstrations
for
PM2.5.9
This
conclusion
is
based
on
preliminary
evaluation
of
estimated
PM10­
2.5
concentrations
derived
from
historical
PM10
and
PM2.5
data.
We
examined
those
days
on
which
PM10
exceedances
were
flagged
as
due
to
exceptional
events
but
where
PM2.5
concentrations
were
not
also
flagged,
indicating
that
the
event
in
question
was
dominated
by
coarse
particles.
The
results
of
this
analysis
suggest
that
exceptional
events
related
to
PM10­
2.5
are
relatively
infrequent,
occur
predominantly
in
the
western
States
and
are
overwhelmingly
high
wind
events.
Thus,
with
the
exception
of
western
areas,
we
do
not
anticipate
that
exceptional
events
will
be
9
The
demonstrations
related
to
PM
10­
2.5
are
contingent
upon
the
final
outcome
related
to
the
rulemaking
on
the
NAAQS
for
PM
10­
2.5
.
61
a
predominate
factor
in
decisions
made
related
to
attainment
or
nonattainment
determinations
for
the
proposed
PM10­
2.5
standards
(
See
memo
from
Mark
Schmidt,
OAQPS,
to
docket
entitled
"
Analysis
of
Flagged
Particulate
Matter
Data,"
February
10,
2006).
Moreover,
in
light
of
the
above
analysis
and
the
evidence
on
which
it
is
based,
we
believe
that
exceptional
events
demonstrations
for
PM10­
2.5
will
involve
relatively
straightforward
showings
that
when
high
concentrations
occurred
at
the
affected
monitors,

concentrations
at
available
rural
monitors
(
e.
g.,
IMPROVE
network
monitors)
were
also
elevated
and
that
meteorological
conditions
(
i.
e.,
wind
speed
and
wind
direction)
were
conducive
to
transport
from
upwind
sources
of
re­
entrained
coarse
particles.
It
may
be
beneficial
to
examine
continuous
PM10­
2.5
monitoring
data
as
well,
as
they
may
indicate
extremely
high
short­
term
values
(
e.
g.,
1
hour
or
less)
that
heavily
influence
24­
hour
concentrations
and
are
consistent
with
extreme
high
wind
events.
For
instance,
when
we
examined
air
quality
concentrations
recorded
in
El
Paso,
Texas
during
a
dust
storm
that
occurred
on
April
26­
27,
2002
we
found
two
consecutive
24­

hour
average
concentrations
of
PM10
(
654
µ
g/
m3)
and
PM2.5
(
56
µ
g/
m3)
which
were
dominated
by
a
peak
1­
hour
concentration
of
2700
µ
g/
m3
which
occurred
in
the
late
evening
of
April
62
26­
27.

H.
Public
Availability
of
Air
Quality
Data
and
Demonstrations
Related
to
Exceptional
Events
Sections
40
CFR
parts
58.35
and
58.28
of
EPA's
air
quality
monitoring
rules
state
that
all
data,
flagged
or
unflagged,
should
be
available
to
the
public
for
comparison
to
the
NAAQS
to
determine
if
exceedances
have
occurred.

The
EPA
is
proposing
to
require
that
all
relevant
flagged
data,
along
with
the
reasons
for
the
data
being
flagged,

and
a
demonstration
that
the
flagged
data
are
caused
by
exceptional
events
be
made
available
by
the
State
for
public
review
and
comment
prior
to
the
demonstration
being
submitted
to
EPA
for
a
decision
concerning
whether
to
exclude
the
data
from
regulatory
consideration.
Notice
and
availability
of
such
data
and
demonstrations
must
be
adequate
and
consistent
with
States'
administrative
procedures
governing
similar
submissions.
EPA
is
not
proposing
to
require
that
public
hearings
be
held
on
exceptional
events
demonstrations,
but
leaves
this
matter
to
the
States'
discretion.

V.
Additional
Requirements
Pursuant
to
section
319,
EPA
is
proposing
new
regulations
to
address
exceptional
events.
Also
EPA
is
proposing
one
option,
and
is
taking
comments
on
three
63
alternative
options,
to
address
the
issue
of
whether,
and
to
what
extent,
States
might
be
required
to
adopt
specific
mitigation
plans
or
measures.
Section
319
states
that
EPA
must
promulgate
regulations
that
are
consistent
with
paragraph
3
which
enumerates
certain
principles
and
minimum
regulatory
requirements.
The
first
part
of
paragraph
3
states
that
in
promulgating
regulations
under
section
319,

EPA
shall
follow
five
principles,
including
the
principle
that
each
State
"
must
take
necessary
measures
to
safeguard
public
health
regardless
of
the
source
of
air
pollution."

Section
319(
b)(
3)(
A).
This
section
does
not,
however,

specify
what
measures
may
be
"
necessary"
in
this
context.

In
order
to
address
this
principle,
EPA
is
proposing
to
exclude
trivial
and
more
routine
background
air
quality
impacts
from
qualifying
as
an
exceptional
event
and
is
also
proposing
a
"
but
for"
test
as
a
precondition
to
qualification
as
an
exceptional
event
(
See:
section
IV).

In
addition,
EPA
is
also
proposing
one
approach
and
is
taking
comments
on
three
other
alternative
options
concerning
State
actions
in
anticipation
of
or
in
response
to
exceptional
events.
These
proposed
options
range
from
being
very
detailed
and
more
prescriptive
to
very
flexible
and
less
prescriptive.
While
EPA
does
not
believe
section
319(
b)(
3)(
A)
explicitly
requires,
in
and
of
itself,
that
64
States
develop
mitigating
measures
or
plans
under
options
(
1),
(
2),
and
(
3)
as
discussed
below,
EPA
solicits
comment
on
whether
this
subparagraph
supports
the
exertion
of
other
legal
authority
to
require
mitigating
actions
or
plans
and
solicits
comment
on
issues
regarding
its
legal
authority
to
require
mitigation
measures
and
plans,
and
the
legal
basis
for
not
requiring
mitigation
measures
or
plans.
We
are
also
requesting
comments
on
the
proposed
approach
and
the
three
alternatives,
and
on
any
modifications
to
or
combinations
of
any
of
the
four
approaches.

A.
Option
1:
Proposed
Option:
Require
Public
Notification,
Education
and
Appropriate
and
Reasonable
Measures
In
cases
where
exceedances
or
violations
of
a
NAAQS
are
caused
by
an
exceptional
event,
EPA
is
proposing
that
once
a
State
becomes
aware
that
an
exceptional
event
is
occurring,
is
predicted
to
occur,
or
has
occurred,
the
State
must
take
appropriate
action
to:

1.
Provide
notice
to
the
public
of
the
event.
This
may
include,
but
is
not
limited
to,
using
the
media
to
alert
the
public
of
the
event.

2.
Provide
public
education
concerning
the
potential
health
risks
associated
with
being
exposed
to
high
ambient
concentrations
of
pollutant(
s)
65
related
to
the
event.
This
may
include,
but
is
not
limited
to,
providing
information
to
sensitive
populations
related
to
the
health
risks
associated
with
the
event.

3.
Take
appropriate
and
reasonable
measures
to
abate
or
minimize
the
exposure
of
the
public
to
high
concentrations
of
air
pollution
associated
with
the
exceptional
event.
This
may
include,
but
is
not
limited
to,
taking
reasonable
and
appropriate
actions
to
implement
control
measures
on
significant
contributing
anthropogenic
sources
to
reduce
potential
exposure
of
the
public
to
emissions
associated
with
natural
events.
For
example,
in
the
case
of
volcanic
or
seismic
activity,
this
may
include,
but
is
not
limited
to,
providing
for
prompt
clean
up
of
the
ash
deposits
related
to
the
event
to
prevent
reentrainment

Under
this
option,
where
a
State
is
requesting
that
air
quality
data
be
excluded
as
an
exceptional
event,
the
State
must
submit,
as
part
of
its
demonstration,
the
appropriate
documentation
to
show
that
the
State
provided
appropriate
public
notice
and
public
education
concerning
the
event
in
question,
and
that
the
State
took
reasonable
66
measures
to
abate
or
minimize
the
exposure
of
the
public,

where
appropriate.

The
concept
of
having
States
take
steps
to
reduce
emissions,
where
appropriate,
and
to
develop
mitigation
plans
to
address
impacts
associated
with
exceptional
events
was
first
instituted
under
the
PM10
Natural
Events
Policy.

The
mitigation
plans
required
under
the
PM10
Natural
Events
Policy
were
called
Natural
Events
Action
Plans
(
NEAPS).
In
instances
where
a
State
requested
that
air
quality
data
influenced
by
a
natural
event
be
excluded,
the
State
was
required
to
develop
and
implement
a
NEAP.

In
developing
a
NEAP,
States
were
expected
to:

establish
a
public
notification
and
education
program
related
to
natural
events;
minimize
public
exposure
to
high
concentrations
of
pollutants
related
to
natural
events;

provide
a
process
for
abatement
of
controllable
anthropogenic
sources
related
to
natural
events;
identify,

study,
and
implement
practical
mitigation
measures
as
necessary;
and
provide
for
a
periodic
re­
evaluation
of
the
NEAP
every
3­
5
years.

Due
to
past
success
with
the
implementation
of
NEAPs,

EPA
is
proposing
to
base
the
requirements
to
mitigate
the
impact
of
exceptional
events
on
the
general
concepts
and
elements
described
above
from
the
PM10
Natural
Events
67
Policy.
The
EPA
is
proposing
this
approach
to
provide
flexibility
to
the
States
to
implement
those
measures
that
it
considers
to
be
reasonable
and
appropriate
under
particular
circumstances
to
protect
public
health
in
the
event
of
an
exceptional
event.
The
EPA
believes
that
this
approach
allows
States
to
use
their
experience
in
addressing
those
exceptional
events
that
occur
most
frequently
in
their
respective
jurisdictions,
and
in
providing
notice
to
sensitive
populations
concerning
the
harmful
effects
of
prolonged
exposure
to
high
concentrations
of
pollution
associated
with
various
types
of
exceptional
events,
yet
could
be
consistent
with
both
the
principles
and
requirements
of
section
319.
The
proposed
approach
also
allows
EPA
to
fulfill
its
oversight
responsibility,
while
still
providing
flexibility
to
States
to
implement
reasonable
measures
to
address
the
effects
of
exceptional
events
on
public
health.
A
possible
disadvantage
of
this
option
is
that
it
has
the
potential
to
result
in
inconsistencies
in
the
way
that
exceptional
events
are
addressed
by
States
and
in
the
actions
that
are
taken
to
mitigate
public
health
impacts
associated
with
exceptional
events,
although
such
inconsistencies
exist
in
any
program
that
allows
flexibility
of
any
kind.
We
believe
that
despite
this,
such
flexibility
makes
for
a
68
better
and
more
efficient
program
in
terms
of
taking
specific
mitigation
actions
that
fit
the
circumstances
of
each
case.

B.
Option
2:
The
Development
of
a
Mitigation
Plan
by
States
under
Section
110
of
the
CAA
Under
this
option,
States
would
be
required
to
adopt
a
general
mitigation
plan
to
address
exceptional
events
before
the
occurrence
of
an
event
as
a
part
of
the
State's
SIP
required
under
section
110(
a)(
1)
of
the
CAA.
Section
110(
a)(
1)
requires
States
to
adopt
and
submit
to
EPA,

within
3
years
following
the
promulgation
of
a
new
or
revised
NAAQS,
a
plan
which
provides
for
the
implementation,
maintenance,
and
enforcement
of
the
standard
in
each
air
quality
region
within
the
State.
The
EPA
believes
that
section
110(
a)(
1)
of
the
CAA
provides
EPA
with
the
statutory
authority
to
require
States
to
submit
plans
to
address
the
mitigation
of
public
health
impacts
due
to
exceptional
events
that
cause
exceedances
or
violations
of
the
NAAQS,
because
such
plans
assist
in
the
maintenance
and
enforcement
of
the
NAAQS
and
could
be
consistent
with
both
the
principles
and
requirements
of
section
319.
Under
this
alternative,
States
would
be
required
to
develop
and
adopt
the
general
requirements
and
procedures
necessary
for
the
implementation
of
a
mitigation
69
plan
as
a
part
of
its
section
110(
a)(
1)
SIP
to
address
a
new
or
revised
NAAQS.
As
a
part
of
this
plan,
EPA
would
require
States
to
identify
the
actions
the
State
intends
to
take
to
reduce
the
impact
of
exceptional
events
on
public
health.
Since
the
precise
nature
and
cause
of
exceptional
events
may
not
be
foreseeable,
in
many
cases,
these
requirements
would
be
general,
and
similar
to
the
types
of
actions
that
States
have
already
identified
and
adopted
in
their
section
110
plans
intended
to
address
emergency
episodes
as
required
under
section
110(
g)
and
40
CFR
part
51.152.
Once
the
general
requirements
of
the
mitigation
plan
are
in
place
under
section
110,
the
State
would
only
need
to
take
action
on
an
episodic
basis
to
implement
the
requirements
of
the
mitigation
plan
for
the
affected
area
following
the
occurrence
of
an
exceptional
event.

The
general
plan
requirements
would
include
provisions
for
providing
public
notification
of
an
event;
providing
a
program
to
educate
the
public
on
the
harmful
effects
of
prolonged
exposure
to
emissions
associated
with
an
exceptional
event;
and
implementing
reasonable
measures
to
mitigate
the
public
health
impacts
of
an
exceptional
event
(
e.
g.,
the
implementation
of
control
measures
to
abate
or
minimize
the
effect
of
high
concentrations
of
emissions
associated
with
an
exceptional
event).
In
cases
where
70
control
measures
are
required
to
address
the
impacts
associated
with
an
exceptional
event,
the
State
would
implement
the
required
measures
on
an
episodic
basis,

meaning
in
response
to
a
specific
event
that
affects
the
air
quality
of
a
particular
area.

In
cases
where
anthropogenic
sources
contribute
to
emissions
related
to
a
recurring
natural
event,
appropriate
control
measures
would
have
to
be
implemented
on
all
significant
contributing
anthropogenic
sources
related
to
the
event
in
the
affected
area.
10
Natural
events,
which
are
defined
as
a
class
of
exceptional
events
under
this
rule,

may
recur
frequently
in
affected
areas.
Under
this
option,

as
well
as
under
Option
3
below,
after
a
natural
event
occurs,
and
it
is
determined
that
anthropogenic
sources
have
significantly
contributed
to
the
emissions
associated
with
that
event,
EPA
is
proposing
that
at
a
minimum,

Reasonably
Available
Control
Measures
(
RACM)
must
be
implemented
on
the
anthropogenic
sources
that
contributed
to
the
emissions
associated
with
the
event.
Reasonable
Available
Control
Measures
are
defined
as
those
control
measures
that
are
considered
to
be
reasonable,
and
71
economically
feasible,
to
implement
in
an
area
for
a
given
source
type.
States
should
consult
the
most
recent
EPA
control
guidance
for
the
affected
pollutant
to
determine
what
control
measures
might
be
considered
as
RACM
for
the
affected
source
types
associated
with
emissions
due
to
a
natural
event.
This
requirement
is
also
consistent
with
the
policy
currently
being
implemented
under
the
"
PM10
Natural
Events
Policy."

Also,
EPA
requests
comments
on
whether,
instead
of
RACM,
the
appropriate
level
of
controls
that
should
be
implemented
on
these
source
types
is
Best
Available
Control
Measures
(
BACM).
Best
Available
Control
Measures
is
a
term
first
identified
in
the
CAA
under
part
D,
subpart
4,

related
to
the
implementation
of
the
PM10
standard.
For
PM10,
BACM
are
defined
as
techniques
that
achieve
the
maximum
degree
of
emissions
reductions
from
a
source
as
determined
on
a
case­
by­
case
basis,
considering
both
the
technological
and
economic
feasibility
of
implementing
the
control
measures
for
the
affected
source
(
59
FR
42010;

August
16,
1994).
Currently,
EPA
requires
the
10
In
the
case
of
the
proposed
NAAQS
for
PM10­
2.5,
these
options
would
not
apply
to
sources
which
are
proposed
to
be
excluded
from
consideration,
e.
g.,
agriculture
and
mining
activities.
72
implementation
of
BACM
on
contributing
anthropogenic
sources
under
the
PM10
Natural
Events
Policy
for
high
wind
events.
Under
this
option,
as
well
as
under
Option
3
below,
the
State
would
also
be
required
to
submit
the
mitigation
plan
for
the
affected
area
to
the
appropriate
EPA
Regional
Office
for
review
and
concurrence.
Once
the
State
has
received
concurrence
from
the
Regional
Office
on
the
control
measures
identified
for
the
anthropogenic
sources
contributing
to
exceedances
associated
with
natural
events,
the
State
would
be
required
to
include
the
measures
as
a
part
of
its
section
110(
a)(
1)
SIP
related
to
the
mitigation
plan
for
the
area.
As
is
the
case
with
the
control
plans
required
for
emergency
episode
plans
under
section
110(
g),
the
State
will
not
be
required
to
submit
the
specific
control
measures
as
a
part
of
the
mitigation
plan
to
EPA
to
be
made
federally
enforceable.
Pursuant
to
section
107(
d)(
3)
and
section
319
(
b)(
3)(
B)
of
the
CAA,
it
is
EPA's
intention
to
adopt
a
flexible
approach
and
not
redesignate
an
area
as
nonattainment,
or
seek
a
SIP
call
for
an
area,
so
long
as
the
State
continues
to
implement
the
requirements
related
to
the
mitigation
plan
for
the
area,
as
well
as
the
control
measures
for
significant
contributing
anthropogenic
sources
related
to
a
natural
event.
73
Where
a
State
provides
adequate
documentation
to
show
that
RACM
was
being
implemented
for
the
affected
sources
at
the
time
that
the
natural
event
in
question
occurred,
a
State
need
not
implement
further
control
measures
in
the
area
related
to
the
natural
event.
In
cases
where
RACM
was
not
implemented
for
contributing
anthropogenic
sources
at
the
time
of
the
natural
event,
the
State
would
be
required
to
implement
RACM
as
expeditiously
as
practicable,
but
in
no
case
later
than
18
months
from
the
end
of
the
calendar
quarter
in
which
the
event
occurred.
The
EPA
requests
comments
on
whether
this
proposed
time
period
is
appropriate
for
the
implementation
of
RACM
for
significant
contributing
anthropogenic
sources
under
this
option
or
whether
another
time
period
is
more
appropriate.

The
advantage
of
this
particular
option
is
that
all
States
would
have
a
general
plan
in
place
for
how
to
address
exceptional
events
once
they
occur
and
could
take
immediate
action
to
protect
public
health.
It
would
also
allow
States
to
evaluate
proactively
what
actions
need
to
be
taken
to
address
anthropogenic
sources
related
to
exceptional
events,
and
to
consider
the
most
efficient
and
effective
ways
to
educate
the
sensitive
populations
most
likely
to
be
harmed
should
an
event
occur.

It
is
important
to
note
that
if
we
selected
Option
3
74
regarding
the
timeline
for
flagging
of
data
and
submission
of
demonstrations,
a
disadvantage
would
be
that
flagging
and
demonstrations
could
potentially
be
delayed
significantly
past
the
time
when
States
would
be
required
to
implement
RACM
under
this
option
for
mitigation
plans.

We
request
comment
on
when
RACM
should
be
implemented
by
States
in
the
event
that
we
select
Flagging
and
Demonstration
Option
3.

C.
Option
3:
The
Development
of
a
Mitigation
Plan
for
Episodic
Events
Under
this
option,
where
appropriate,
EPA
would
require
a
State
to
develop
and
implement
a
mitigation
plan
for
an
area
following
the
occurrence
of
an
exceptional
event.
This
is
in
contrast
to
Option
2
above,
which
would
require
each
State
to
adopt
a
plan
under
section
110
of
the
CAA
containing
the
general
provisions
of
a
mitigation
plan
in
advance
of
the
occurrence
of
any
exceptional
event.

Under
this
third
option,
the
mitigation
plan
would
only
be
developed
by
the
State
following
the
occurrence
of
an
exceptional
event
for
which
a
State
requested
exclusion
of
air
quality
data.
The
mitigation
plan
would
be
required
to
address
the
actions
that
would
be
taken
by
the
State
related
to
future
similar
events,
yet
could
be
consistent
with
the
principles
and
requirements
of
section
319.
The
75
mitigation
plan
under
this
option
would
have
the
same
provisions
to
plans
developed
under
Option
2
above,

including
the
requirements
to
notify
the
public
that
an
event
is
expected
to
occur,
or
is
occurring,
or
has
occurred,
to
provide
for
public
education
related
to
the
health
effects
associated
with
the
event,
and
to
identify
the
actions
that
would
be
taken
by
the
State
to
mitigate
the
impact
of
any
recurrence
of
the
event
on
public
health.

The
mitigation
plan
must
include
a
detailed
description
of
planned
actions
that
would
be
implemented
if
the
event
recurs.
It
would
also
provide
for
an
implementation
schedule
which
identifies
the
actions
that
would
be
taken
related
to
the
recurrence
of
an
event,
and
it
should
identify
the
principal
parties
that
would
be
responsible
for
carrying
out
the
stated
actions
under
the
mitigation
plan.

In
cases
where
a
State
intends
to
request
that
EPA
exclude
data
from
regulatory
consideration
that
has
been
affected
by
an
exceptional
event
under
this
option,
the
State
must
submit
the
plan
to
EPA
for
review
and
concurrence.
However,
EPA
will
not
take
action
to
make
the
mitigation
plan
federally
enforceable.
Under
this
option
States
would
develop
a
mitigation
plan
for
an
area
where
an
exceptional
event
has
caused
an
exceedance
or
violation
of
76
a
NAAQS
no
later
than
18
months
following
the
end
of
the
calendar
quarter
in
which
the
event
occurred.
The
EPA
requests
comments
on
whether
18
months
is
an
appropriate
time
period
for
the
development
and
adoption
of
a
mitigation
plan
under
this
option
or
whether
another
time
period
is
more
appropriate.

As
stated
in
Option
2
above,
in
cases
where
anthropogenic
sources
contribute
to
emissions
related
to
a
recurring
natural
event,
RACM
must
be
implemented
for
all
significant
contributing
anthropogenic
sources.
Where
a
State
provides
adequate
documentation
to
show
that
RACM
was
being
implemented
for
the
affected
sources
in
the
area
at
the
time
that
the
event
occurred,
no
action
would
be
required
by
the
State
to
implement
further
control
measures
related
to
the
event
for
the
affected
area.
In
cases
where
a
determination
is
made
that
RACM
was
not
being
implemented
for
significant
contributing
anthropogenic
sources
at
the
time
of
the
event,
the
State
would
be
required
to
adopt
and
implement
RACM
as
expeditiously
as
practicable,
but
in
no
case
later
than
3
years
following
the
end
of
the
calendar
quarter
in
which
the
event
occurred.
The
EPA
requests
comment
on
the
appropriateness
of
the
time
period
being
proposed
for
the
implementation
of
control
measures
related
to
significant
contributing
anthropogenic
sources
77
associated
with
a
recurring
natural
event
under
this
option.

An
advantage
of
this
alternative
is
that
a
State
can
more
carefully
tailor
the
actions
that
it
will
take
to
mitigate
the
effect
of
the
exceptional
event
based
on
its
prior
experience,
which
will
help
ensure
protection
of
public
health.
However,
the
disadvantage
of
this
particular
option
is
that
it
would
apply
more
specifically
to
one
type
of
event,
so
that
if
a
new
or
different
type
of
exceptional
event
occurred,
there
would
be
no
provisions
in
place
under
the
mitigation
plan
to
address
it.
Each
time
a
new
type
of
event
occurs,
the
State
would
need
to
submit
or
revise
the
plan
to
address
the
new
event.

D.
Option
4:
Do
Not
Require
States
to
Adopt
and
Implement
Specific
Mitigation
Plans
or
Measures
under
this
Rule
Under
this
option,
EPA
would
not
require
a
State
to
develop
and
implement
a
mitigation
plan
for
exceptional
events,
or
to
take
specific
mitigation
measures
as
described
in
options
1­
3
in
order
for
EPA
to
exclude
data
from
regulatory
consideration
because
it
results
from
an
exceptional
event.
This
approach
would
allow
States
to
have
the
maximum
degree
of
flexibility
in
determining
what
actions
should
be
taken
to
mitigate
the
impacts
of
exceptional
events,
e.
g.,
public
notification,
public
78
education,
efforts
to
reduce
exposures,
or
other
necessary
measures
to
safeguard
public
health.
Thus,
States
would
not
be
obligated
to
take
any
particular
actions
to
mitigate
exposures
such
as
those
in
Option
1,
to
develop
and
implement
a
formal
mitigation
plan
as
part
of
the
SIP
such
as
that
in
proposed
Option
2,
or
to
develop
a
more
formal
plan
with
requirements
not
a
part
of
the
SIP
such
as
that
in
proposed
Option
3.

This
proposed
approach
would
require
a
much
less
formal
method
for
States
to
take
necessary
measures
to
safeguard
public
health,
yet
could
be
consistent
with
both
the
principles
and
requirements
of
section
319.
The
statute
does
not
identify
specific
ways
in
which
EPA
must
satisfy
its
principles
and
requirements.
Moreover,
as
detailed
above,
EPA
is
proposing
to
exclude
only
certain
types
of
exceptional
events
from
regulatory
determinations
with
respect
to
the
NAAQS.
In
section
IV,
EPA
is
proposing
options
for
percentile
criteria,
case­
by­
case
evaluation,

and
establishment
of
a
"
but
for"
test
in
order
for
an
event
to
qualify
as
an
exceptional
event
for
which
data
can
be
excluded
with
respect
to
exceedences
or
violations
of
the
NAAQS.
These
requirements,
in
and
of
themselves,
may
offer
appropriate
protection
of
public
health.
Under
this
view,

EPA
should
give
States
broad
flexibility
in
determining
how
79
best
to
respond
to
individual
exceptional
events.
Given
the
States'
concern
with
the
health
of
their
citizens,
and
taking
into
consideration
the
other
requirements
of
this
rule,
in
this
view
States
would
have
sufficient
incentive
to
take
appropriate
actions
to
protect
public
health.

One
benefit
of
this
option
is
that
it
would
allow
States
to
maintain
the
maximum
degree
of
flexibility
to
respond
to
exceptional
events
and
to
take
appropriate
actions
to
protect
public
health
without
unnecessarily
limiting
their
ability
to
seek
exceptional
events
treatment
for
the
data.
One
potential
limitation
of
this
proposed
approach
is
that
it
might
result
in
inconsistencies
among
States
in
addressing
exceptional
events
and
in
mitigating
the
impacts
of
those
events.

The
EPA
requests
comments
on
all
options
described
above.
Additionally,
EPA
requests
comments
on
specific
modifications
that
should
be
made
to
one
or
more
of
the
options
provided
above,
or
on
any
combination
of
these
options.

VI.
Special
Treatment
of
Certain
Events
Under
this
Rule
As
stated
in
section
III.
C.,
above,
this
proposed
rule
applies
to
data
affected
by
natural
events,
which
are
a
subset
of
exceptional
events,
at
air
quality
monitoring
sites
where
it
has
been
determined
that
concentrations
due
80
to
these
events
have
caused
or
substantially
contributed
to
exceedances
or
violations
of
the
NAAQS
in
an
affected
area.

This
proposed
rule
applies
to
several
types
of
natural
events,
including
volcanic
and
seismic
actives,
natural
disasters,
high
wind
events,
unwanted
fires,
and
stratospheric
ozone
intrusions,
and
to
transported
pollution
originating
from
national
and
international
sources
that
otherwise
meets
the
criteria
and
requirements
for
exceptional
events.
Some
types
of
exceptional
events
have
unusual
characteristics
which
require
special
consideration
in
the
context
of
this
proposed
rulemaking.

We
discuss
each
of
these
special
issues,
and
the
necessary
accommodations,
below
A.
Volcanic
and
Seismic
Activities
Volcanic
and
seismic
activities
may
affect
air
quality
for
an
extended
period
of
time
after
the
initial
occurrence
of
the
event
in
question.
Therefore,
EPA
believes
it
is
appropriate
to
consider
an
extended
timeframe
for
flagging
and
exclusion
of
data
associated
with
such
events.

Specifically,
EPA
is
proposing
that
emissions
attributed
to
anthropogenic
activities
that
re­
entrain
volcanic
ash
and
dust
from
seismic
activity
during
the
first
year
(
12
months)
following
an
event
will
be
treated
as
due
to
the
natural
event.
Based
on
prior
experiences,
and
on
81
consultation
with
States,
we
believe
that
1
year
is
an
adequate
amount
of
time
for
cleaning
ash
deposits
from
areas
where
anthropogenic
activities
(
e.
g.,
vehicle
traffic)
may
cause
re­
entrainment
and
possible
exceedances
of
the
particulate
matter
NAAQS.
After
a
year,
however,

exceedances
or
violations
due
to
re­
entrainment
of
ash
deposits
will
not
be
provided
special
consideration
under
this
rule.
The
EPA,
however,
requests
comments
on
whether
another
time
period
is
more
appropriate
and
reasonable
to
allow
for
clean
up
of
ash
deposits
following
volcanic
or
seismic
activity.

B.
High
Wind
Events
Where
high
wind
events
result
in
exceedances
or
violations
of
PM2.5
standards,
we
are
proposing
that
they
will
be
treated
as
natural
events
pursuant
to
this
proposed
rule
if
there
is
a
clear
causal
relationship
demonstrated
between
the
exceedances
measured
and
the
high
wind
event
in
question,
and
if
anthropogenic
activities
which
contribute
to
PM2.5
emissions
in
conjunction
with
the
high
wind
event
are
reasonably
well
controlled.

For
the
proposed
24­
hour
PM10­
2.5
standard,
we
propose
to
exclude
measured
exceedances
from
consideration
if
it
is
demonstrated
that
high
winds
resulted
in
the
transport
of
airborne
particulate
matter
in
concentrations
that
caused
82
an
exceedance
or
violation
of
the
NAAQS.
11
States
would
be
expected
to
control
emissions
from
contributing
anthropogenic
sources
as
appropriate
under
the
definition
of
the
proposed
PM10­
2.5
indicator.

C.
Stratospheric
Ozone
Intrusion
Consideration
of
stratospheric
ozone
intrusions
applies
only
to
the
8­
hour
ozone
standard.
The
occurrence
of
such
inversions
is
extremely
difficult
to
measure
or
document
given
currently
measured
meteorological
parameters.
The
infrequence,
short
duration,
and
localized
nature
of
such
events
makes
it
difficult
to
use
currently
available,
general
meteorological
data,
which
are
usually
collected
at
isolated
locations
like
airports,
to
determine
whether
a
stratospheric
ozone
intrusion
has
occurred.
The
EPA
believes
it
is
important
to
differentiate
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
showing
the
result
of
stratospheric
11
As
discussed
in
rules
proposed
at
71
FR
2665­
2668,
January
17,
2006,
and
71
FR
2710
at
2731,
2736­
40,
January
17,
2006,
where
properly
sited
monitors
show
exceedances
or
violations
of
proposed
PM10­
2.5
standards,
it
will
generally
be
presumed
that
such
concentrations
are
due
to
emissions
of
urban
origin
and
therefore
subject
to
regulation,
unless
shown
to
be
due
to
an
exceptional
event.
83
ozone
intrusion,
no
standard
definition
or
criteria
have
been
established
for
concrete
identification.
Therefore,

EPA's
determination
of
whether
a
stratospheric
ozone
intrusion
has
occurred
is
a
case­
by­
case
decision
based
on
reasonable
judgment
considering
the
season
of
the
year;

time
of
day;
persistence,
duration,
type
and
severity
of
accompanying
meteorological
conditions
associated
with
the
ozone
measurement
in
question;
and
other
data
showing
that
conditions
were
not
conducive
to
local
high
ozone
production
but
for
this
intrusion.

VII.
Treatment
of
Fireworks
Displays
While
we
are
not
including
fireworks
displays
in
our
proposed
rule
governing
exceptional
events,
we
are
proposing
as
a
policy
matter
to
address
certain
displays
in
a
manner
similar
to
exceptional
events.
Some
national
and/
or
cultural
traditions,
such
as
July
4th
Independence
Day
and
Chinese
New
Year,
have
long
included
fireworks
displays
as
important­­
indeed,
many
might
assert
essential­

­
elements
of
their
observances.
While
this
issue
is
not
specifically
covered
in
CAA
section
319,
EPA
believes
that
Congress
did
not
intend
to
require
EPA
to
consider
air
quality
violations
associated
with
such
cultural
traditions
in
regulatory
determinations
to
prohibit
these
activities.

We
are
not
aware
of
any
information
showing
adverse
84
air
quality
impacts
caused
by
individual
use
of
fireworks
in
relatively
small
quantities.
However,
analyses
of
monitoring
data
collected
on
July
4th
and
July
5th
indicates
that
large
fireworks
displays,
in
combination
with
other
sources,
can
in
some
circumstances
be
potentially
significant
sources
of
air
pollutant
emissions.

For
this
reason,
States
are
encouraged
to
take
reasonable
precautions
to
minimize
exposures
to
emissions
from
fireworks
displays,
as
well
as
to
manage
associated
activities
that
may
have
significant
impact
in
the
areas
where
these
events
are
held.
Such
actions
may
include
alerting
the
public
to
the
potential
for
short­
term
air
quality
impacts
that
may
result
from
the
discharge
of
fireworks
at
large
displays,
monitoring
prevailing
winds,

and
locating
displays
downwind
of
concentrations
of
people.

States
are
encouraged,
too,
to
explore
the
use
of
loweremitting
fireworks,
such
as
those
developed
for
frequent
use
at
amusement
parks.

For
these
reasons,
where
States
can
show
that
the
use
of
fireworks
displays
is
integral
to
significant
traditional
national,
ethnic,
or
other
cultural
events,
we
are
proposing
that
air
quality
data
associated
with
such
events
could
be
excluded.
We
request
comments
on
alternative
approaches
to
addressing
emissions
from
85
fireworks
at
such
events.

VIII.
Statutory
and
Executive
Order
Reviews
A.
Executive
Order
12866:
Regulatory
Planning
and
Review
Under
Executive
Order
12866
(
58
FR
51735,
October
4,

1993),
EPA
must
determine
whether
the
regulatory
action
is
"
significant"
and,
therefore,
subject
to
the
Office
of
Management
and
Budget
(
OMB)
review
and
the
requirements
of
the
Executive
Order.
The
order
defines
"
significant
regulatory
action"
as
one
that
is
likely
to
result
in
a
rule
that
may:

(
1)
have
an
annual
effect
on
the
economy
of
$
100
million
or
more
or
adversely
affect
in
a
material
way
the
economy,
a
sector
of
the
economy,

productivity,
competition,
jobs,
the
environment,

public
health
or
safety,
or
State,
local,
or
Tribal
governments
or
communities;

(
2)
create
a
serious
inconsistency
or
otherwise
interfere
with
an
action
taken
or
planned
by
another
agency;

(
3)
materially
alter
the
budgetary
impact
of
entitlements,
grants,
user
fees,
or
loan
programs
or
the
rights
and
obligations
of
recipients
thereof;
or
(
4)
raise
novel
legal
or
policy
issues
arising
out
of
86
legal
mandates,
the
President's
priorities,
or
the
principles
set
forth
in
the
Executive
Order.

Pursuant
to
the
terms
of
Executive
Order
12866,
it
has
been
determined
that
the
proposed
rule
is
a
"
significant
regulatory
action."
As
such,
this
proposed
rule
was
submitted
to
OMB
for
review
under
Executive
Order
12866.

B.
Paperwork
Reduction
Act
This
action
does
not
impose
an
information
collection
burden.
The
information
being
requested
under
this
rule
is
consistent
with
current
requirements
related
to
information
needed
to
verify
the
authenticity
of
monitoring
data
submitted
to
EPA's
AQS
data
base,
and
to
justify
data
that
has
been
flagged
as
being
affected
by
exceptional
or
natural
events.
The
OMB
has
previously
approved
the
information
collection
requirements
contained
in
the
existing
regulations
at
40
CFR
part
58.01,
subparts
A
through
E,
under
the
provisions
of
the
Paperwork
Reduction
Act,
44
U.
S.
C.
3501
et
seq.
and
assigned
OMB
control
number
2060­
0084,
EPA
ICR
number
940.17.
A
copy
of
the
OMB
approved
Information
Collection
Request
(
ICR)
may
be
obtained
from
Susan
Auby,
Collection
Strategies
Division;

U.
S.
Environmental
Protection
Agency
(
2822T);
1200
Pennsylvania
Ave.,
NW,
Washington,
DC
20460
or
by
calling
(
202)
566­
1672.
87
Burden
means
that
total
time,
effort,
or
financial
resources
expended
by
persons
to
generate,
maintain,

retain,
or
disclose
or
provide
information
to
or
for
a
Federal
agency.
This
includes
the
time
needed
to
review
instructions;
develop,
acquire,
install,
and
utilize
technology
and
systems
for
the
purposes
of
collecting,

validating,
and
verifying
information,
processing
and
maintaining
information,
and
disclosing
and
providing
information;
adjust
the
existing
ways
to
comply
with
any
previously
applicable
instructions
and
requirements;
train
personnel
to
be
able
to
respond
to
a
collection
of
information;
search
data
sources;
complete
and
review
the
collection
of
information;
and
transmit
or
otherwise
disclose
the
information.
An
Agency
may
not
conduct
or
sponsor,
and
a
person
is
not
required
to
respond
to
a
collection
of
information
unless
it
displays
a
currently
valid
OMB
control
number.
The
OMB
control
numbers
for
EPA's
regulations
in
the
CFR
are
listed
in
40
CFR
part
9.

C.
Regulatory
Flexibility
Act
The
Regulatory
Flexibility
Act
(
RFA)
generally
requires
an
agency
to
prepare
a
regulatory
flexibility
analysis
of
any
rule
subject
to
notice
and
comment
rulemaking
requirements
under
the
Administrative
Procedures
Act
(
APA)
or
any
other
statute
unless
the
EPA
certifies
that
the
rule
will
not
88
have
a
significant
economic
impact
on
a
substantial
number
of
small
entities.
Small
entities
include
small
businesses,
small
organizations,
and
small
governmental
jurisdictions.
For
the
purpose
of
assessing
the
impacts
of
today's
proposed
rule
on
small
entities,
small
entity
is
defined
as:
(
1)
a
small
business
that
is
a
small
industry
entity
as
defined
in
the
U.
S.
Small
Business
Administration
(
SBA)
size
standards.
(
See
13
CFR
121);
(
2)
a
small
governmental
jurisdiction
that
is
a
government
of
a
city,

county,
town,
school
district
or
special
district
with
a
population
of
less
than
50,000;
and
(
3)
a
small
organization
that
is
any
not­
for­
profit
enterprise
which
is
independently
owned
and
operated
and
is
not
dominate
in
its
field.

Courts
have
interpreted
the
RFA
to
require
a
regulatory
flexibility
analysis
only
when
small
entities
will
be
subject
to
the
requirements
of
the
rule.
See,

Michigan
v.
EPA,
213
F.
3d
663,
668­
69
(
D.
C.
Cir.,
2000),

cert.
den.,
532
U.
S.
903
(
2001).
This
rule
would
not
establish
requirements
applicable
to
small
entities.

Instead,
this
rule
provides
the
criteria
necessary
for
State,
local,
or
Tribal
air
quality
agencies
to
meet
in
order
to
properly
flag
data
as
being
influenced
by
an
exceptional
or
natural
event.
The
rule
also
provides
89
information
concerning
what
action
should
be
taken
by
a
State,
local,
or
Tribal
air
quality
agency
to
protect
public
health
once
EPA
has
provided
a
concurrence
on
data
that
has
been
flagged
as
being
influenced
by
an
exceptional
or
natural
event.
Because
affected
States
would
have
discretion
to
choose
the
sources
that
may
need
to
be
regulated
and
the
emissions
reductions
each
selected
source
would
have
to
achieve
using
RACM
or
BACM
related
to
anthropogenic
sources
in
the
area
determined
to
be
influenced
by
an
exceptional
or
natural
event,
EPA
could
not
predict
the
effect
of
the
rule
on
small
entities.

After
considering
the
economic
impacts
of
today's
proposed
rule
on
small
entities,
I
certify
that
this
rule
will
not
have
a
significant
economic
impact
on
a
substantial
number
of
small
entities.

D.
Unfunded
Mandates
Reform
Act
Title
II
of
the
Unfunded
Mandates
Reform
Act
of
1995
(
UMRA),
Public
Law
104­
4,
establishes
requirements
for
Federal
Agencies
to
assess
the
effects
of
their
regulatory
actions
on
State,
local
and
Tribal
governments
and
the
private
sector.
Under
section
202
of
the
UMRA,
EPA
generally
must
prepare
a
written
statement,
including
a
cost­
benefit
analysis,
for
proposed
and
final
rules
with
"
Federal
mandates"
that
may
result
in
expenditures
to
State
90
governments,
in
the
aggregate,
or
to
the
private
sector,
of
$
100
million
or
more
in
any
1
year.
Before
promulgating
an
EPA
rule
for
which
a
written
statement
is
needed,
section
205
of
the
UMRA
generally
requires
EPA
to
identify
and
consider
a
reasonable
number
of
regulatory
alternatives
and
adopt
the
least
costly,
most
cost­
effective
or
least
burdensome
alternative
that
achieves
the
objectives
of
the
rule.
The
provisions
of
section
205
do
not
apply
when
they
are
inconsistent
with
applicable
law.
Moreover,
section
205
allows
EPA
to
adopt
an
alternative
other
than
the
least
costly,
most
cost­
effective
or
least
burdensome
alternative
if
the
Administrator
publishes
with
the
final
rule
an
explanation
of
why
that
alternative
was
not
adopted.

Before
EPA
establishes
any
regulatory
requirements
that
may
significantly
or
uniquely
affect
small
governments,

including
Tribal
governments,
it
must
have
developed
under
section
203
of
the
UMRA
a
small
government
agency
plan.

The
plan
must
provide
for
notifying
potentially
affected
small
governments
to
have
meaningful
and
timely
input
in
the
development
of
EPA
regulatory
proposals
with
significant
Federal
intergovernmental
mandates,
and
informing,
educating,
and
advising
small
government
on
compliance
with
regulatory
requirements.

Today's
action
does
not
include
a
Federal
mandate
91
within
the
meaning
of
UMRA
that
may
result
in
expenditures
of
$
100
million
or
more
in
any
1
year
by
either
State,

local,
or
Tribal
governments
in
the
aggregate
or
to
the
private
sector,
and
therefore,
is
not
subject
to
the
requirements
of
sections
202
and
205
of
the
UMRA.

Inasmuch
as
this
action
simply
provides
the
criteria
for
State,
local,
or
Tribal
air
quality
agencies
to
flag
data
to
be
discounted
for
regulatory
purposes
that
is
being
influenced
by
exceptional
or
natural
events,
this
proposed
Federal
action
will
not
impose
mandates
that
will
require
expenditures
of
$
100
million
or
more
in
the
aggregate
in
any
1
year.

E.
Executive
Order
13132:
Federalism
Executive
Order
13132,
entitled
"
Federalism"
(
64
FR
43255,
August
10,
1999),
requires
EPA
to
develop
an
accountable
process
to
ensure
"
meaningful
and
timely
input
by
State
and
local
officials
in
the
development
of
regulatory
policies
that
have
federalism
implications."

"
Policies
that
have
federalism
implications"
is
defined
in
the
Executive
Order
to
include
regulations
that
have
"
substantial
direct
effects
on
the
States,
or
the
relationship
between
the
national
government
and
the
States,
or
on
the
distribution
of
power
and
responsibilities
among
the
various
levels
of
government."
92
This
proposed
rule
does
not
have
federalism
implications.
It
will
not
have
substantial
direct
effects
on
the
States,
on
the
relationship
between
the
national
government
and
the
States,
or
on
the
distribution
of
power
and
responsibilities
among
the
various
levels
of
government,
as
specified
in
Executive
Order
13132.
The
CAA
establishes
the
scheme
whereby
States
take
the
lead
in
developing
plans
to
meet
the
NAAQS.
This
rule
will
not
modify
the
relationship
of
the
States
and
EPA
for
purposes
of
developing
programs
to
implement
the
NAAQS.
Thus,

Executive
Order
13132
does
not
apply
to
this
rule.

F.
Executive
Order
13175:
Consultation
and
Coordination
with
Indian
Tribal
Governments
Executive
Order
13175,
entitled
"
Consultation
and
Coordination
with
Indian
Tribal
Governments"
(
65
FR
67249,

November
9,
2000),
requires
EPA
to
develop
an
accountable
process
to
ensure
"
meaningful
and
timely
input
by
Tribal
officials
in
the
development
of
regulatory
policies
that
have
Tribal
implications."
This
proposed
rule
does
not
have
"
Tribal
implications"
as
specified
in
Executive
Order
13175.
The
rule
provides
information
concerning
what
action
should
be
taken
by
a
State,
local,
or
Tribal
air
quality
agency
implementing
relevant
air
quality
programs
to
protect
public
health
once
EPA
has
provided
a
93
concurrence
on
data
that
has
been
flagged
as
being
influenced
by
an
exceptional
or
natural
event.
The
CAA
and
the
Tribal
Authority
Rule
(
TAR)
give
Tribes
the
opportunity
to
develop
and
implement
CAA
programs,
but
it
leaves
to
the
discretion
of
the
Tribe
whether
to
develop
these
programs
and
which
programs,
or
appropriate
elements
of
a
program,

the
Tribe
will
adopt.

This
rule
does
not
have
Tribal
implications
as
defined
by
Executive
Order
13175.
It
does
not
have
a
substantial
direct
effect
on
one
or
more
Indian
Tribes,
because
no
Tribe
has
implemented
an
air
quality
management
program
related
to
the
PM
NAAQS
at
this
time.
Furthermore,
this
rule
does
not
affect
the
relationship
or
distribution
of
power
and
responsibilities
between
the
Federal
government
and
Indian
Tribes.
The
CAA
and
the
TAR
establish
the
relationship
of
the
Federal
government
and
Tribes
in
developing
plans
to
attain
the
NAAQS,
and
this
rule
does
nothing
to
modify
that
relationship.
Because
this
rule
does
not
have
Tribal
implications,
Executive
Order
13175
does
not
apply.

G.
Executive
Order
13045:
Protection
of
Children
from
Environmental
Health
and
Safety
Risks
Executive
Order
13045:
"
Protection
of
Children
From
Environmental
Health
and
Safety
Risks"
(
62
FR
19885,
April
94
23,
1997)
applies
to
any
rule
that
(
1)
is
determined
to
be
"
economically
significant"
as
defined
under
Executive
Order
12866,
and
(
2)
concerns
an
environmental
health
and
safety
risk
that
EPA
has
reason
to
believe
may
have
a
disproportionate
effect
on
children.
If
the
regulatory
action
meets
both
criteria,
EPA
must
evaluate
the
environmental
health
or
safety
effects
of
the
planned
rule
on
children,
and
explain
why
the
planned
regulation
is
preferable
to
other
potentially
effective
and
reasonably
feasible
alternatives
considered
by
EPA.

This
action
is
not
subject
to
Executive
Order
13045
because
it
is
not
economically
significant
as
defined
in
Executive
Order
12866,
and
because
EPA
does
not
have
reason
to
believe
that
the
environmental
health
risks
or
safety
risks
addressed
by
this
rule
present
a
disproportionate
risk
or
safety
risk
to
children.
The
rule
provides
information
concerning
what
action
should
be
taken
by
a
State,
local,
or
Tribal
air
quality
agency
to
protect
public
health
once
EPA
has
provided
a
concurrence
on
data
that
has
been
flagged
as
being
influenced
by
an
exceptional
or
natural
event.

H.
Executive
Order
13211:
Actions
that
Significantly
Affect
Energy
Supply,
Distribution,
or
Use
This
rule
is
not
a
"
significant
energy
action"
as
95
defined
in
Executive
Order
13211,
"
Actions
that
Significantly
Affect
Energy
Supply,
Distribution,
or
Use,"

(
66
FR
28355,
May
22,
2001)
because
it
is
not
likely
to
have
a
significant
adverse
effect
on
the
supply,

distribution,
or
use
of
energy.
Further,
we
have
concluded
that
this
rule
is
not
likely
to
have
any
adverse
energy
effects.

I.
National
Technology
Transfer
Advancement
Act
Section
12(
d)
of
the
National
Technology
Transfer
Advancement
Act
of
1995
(
NTTAA),
Public
Law
No.
104­
113,

section
12(
d)
(
15
U.
S.
C.
272
note)
directs
EPA
to
use
voluntary
consensus
standards
(
VCS)
in
its
regulatory
activities
unless
to
do
so
would
be
inconsistent
with
applicable
law
or
otherwise
impracticable.
Voluntary
consensus
standards
are
technical
standards
(
e.
g.,

materials
specifications,
test
methods,
sampling
procedures,
and
business
practices)
that
are
developed
or
adopted
by
VCS
bodies.
The
NTTAA
directs
EPA
to
provide
Congress,
through
OMB,
explanations
when
EPA
decides
not
to
use
available
and
applicable
VCS.
96
The
Treatment
of
Data
Influenced
by
Exceptional
and
Natural
Events
pg.
96
of
109
pgs.

This
action
does
not
involve
technical
standards.

Therefore,
EPA
did
not
consider
the
use
of
any
VCS.

List
Of
Subjects
in
40
CFR
Parts
50
and
51
Environmental
protection,
Air
pollution
control,
National
parks,
Wilderness
areas.

___________________________________

Dated:

____________________________________

Stephen
L.
Johnson,
Administrator
97
In
consideration
of
the
foregoing,
the
Environmental
Protection
Agency
proposes
to
amend
40
CFR
parts
50
and
51
as
follows:

PART
50
­
NATIONAL
PRIMARY
AND
SECONDARY
AMBIENT
AIR
QUALITY
STANDARDS
1.
The
authority
citation
for
part
50
continues
to
read
as
follows:

Authority:
42
U.
S.
C.
7401,
et
seq.

2.
Amend
§
50.1
to
add
paragraphs
(
j)
and
(
k)
to
read
as
follows:

§
50.1
Definitions.

*
*
*
*
*

(
j)
Exceptional
event
means
an
event
that
affects
air
quality;
is
not
reasonably
controllable
or
preventable;
is
a
natural
event
or
an
event
caused
by
human
activity
that
is
unlikely
to
recur
at
a
particular
location;
and
is
determined
by
the
Administrator
in
accordance
with
40
CFR
50.13
to
be
an
exceptional
event;
it
does
not
include
stagnation
of
air
masses
or
meteorological
inversions;
a
meteorological
event
involving
high
temperatures
or
lack
of
precipitation;
or
air
pollution
relating
to
source
noncompliance.

(
k)
Natural
event
means
an
event
in
which
human
activity
plays
little
or
no
direct
causal
role.
98
(
l)
Exceedance
with
respect
to
a
national
ambient
air
quality
standard
means
one
occurrence
of
a
measured
or
modeled
concentration
that
exceeds
the
specified
concentration
level
of
such
standard
for
the
averaging
period
specified
by
the
standard.

3.
Add
§
50.14
to
read
as
follows:

§
50.14
Treatment
of
air
quality
monitoring
data
influenced
by
exceptional
events.

(
a)
Requirements.

(
1)
A
State
may
request
EPA
to
exclude
data
showing
exceedances
or
violations
of
the
national
ambient
air
quality
standards
that
are
directly
due
to
an
exceptional
event
from
use
in
determinations
by
demonstrating
to
EPA's
satisfaction
that
such
event
caused
a
specific
air
pollution
concentration
at
a
particular
air
quality
monitoring
location.

(
2)
Demonstrations
may
include
any
reliable
and
accurate
data,
but
must
demonstrate
a
clear
causal
relationship
between
the
measured
exceedance
or
violation
of
such
standards
and
the
event.

(
b)
Determinations
by
EPA.

(
1)
EPA
shall
exclude
data
due
to
such
event
from
use
in
determinations
where
a
State
demonstrates:

(
i)
That
an
exceptional
event
caused
a
specific
air
99
pollution
concentration
resulting
in
an
exceedance
or
violation
of
the
national
ambient
air
quality
standards
at
a
particular
air
quality
monitoring
location;
and
(
ii)
That
it
has
taken
appropriate
actions
to
protect
public
health.

(
2)
[
Reserved]

(
c)
Schedules
and
Procedures.

(
1)
Public
notification.

(
i)
All
States
and,
where
applicable,
their
political
subdivisions
must
notify
the
public
promptly
whenever
an
event
occurs
or
is
reasonably
anticipated
to
occur
which
may
result
in
the
exceedance
of
an
applicable
air
quality
standard.

(
ii)
[
Reserved]

OPTION
1
for
paragraph
(
c)(
2):

(
2)
Flagging
of
data.

(
i)
A
State
shall
notify
EPA
of
its
intent
to
exclude
one
or
more
measured
exceedances
of
an
applicable
ambient
air
quality
standard
as
being
due
to
an
exceptional
event
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
of
concern
in
accordance
with
the
schedules
for
submission
of
data
to
the
AQS
data
base
in
40
CFR
58.35.
100
(
ii)
Flags
placed
on
data
in
accordance
with
this
section
shall
be
deemed
informational
only,
and
the
data
shall
not
be
excluded
from
determinations
with
respect
to
exceedances
or
violations
of
the
national
ambient
air
quality
standards
unless
and
until
EPA
notifies
the
State
of
its
concurrence
by
placing
a
concurrence
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
3)
Submission
of
demonstrations.

(
i)
A
State
that
has
flagged
data
as
being
due
to
an
exceptional
event
shall,
after
notice
and
opportunity
for
public
comment,
submit
a
complete
demonstration
to
EPA
in
support
of
its
request
for
exclusion
not
later
than
180
days
following
the
end
of
the
calendar
quarter
in
which
the
flagged
concentration
was
recorded.

(
A)
Extensions.
Where
a
State
demonstrates
to
the
satisfaction
of
EPA
that
additional
time
is
needed
to
obtain
information
or
complete
analyses
to
demonstrate
that
an
exceptional
event
caused
an
exceedance
or
violation
of
an
ambient
air
quality
standard,
and
that
such
information
is
likely
to
have
101
significant
probative
value,
then
EPA
may
grant
an
extension
of
the
date
for
submission
of
demonstrations
of
not
more
than
an
additional
90
days.

(
B)
[
Reserved]

(
ii)
[
Reserved]

(
4)
EPA
review
and
concurrence
or
nonconcurrence.

(
i)
EPA
shall
complete
its
review
and
concur
or
nonconcur
with
a
State's
request
for
exclusion
not
later
than
30
days
following
receipt
of
a
complete
submission
from
the
State.
EPA
shall
notify
the
State
of
its
concurrence
or
nonconcurrence
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
A)
Extensions.
Where
additional
time
is
needed
to
complete
its
review
of
the
State's
demonstration,
EPA
may
extend
the
time
for
review
by
not
more
than
an
additional
30
days.

(
B)
[
Reserved]

(
ii)
[
Reserved]

OPTION
2
for
paragraph
(
c)(
2):

(
2)
Flagging
of
data.
102
(
i)
A
State
shall
notify
EPA
of
its
intent
to
exclude
one
or
more
measured
exceedances
of
an
applicable
ambient
air
quality
standard
as
being
due
to
an
exceptional
event
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
of
concern
in
accordance
with
the
schedules
for
submission
of
data
to
the
AQS
data
base
in
40
CFR
58.35.

(
ii)
Flags
placed
on
data
in
accordance
with
this
section
shall
be
deemed
informational
only,
and
the
data
shall
not
be
excluded
from
determinations
with
respect
to
exceedances
or
violations
of
the
national
ambient
air
quality
standards
unless
and
until
EPA
notifies
the
State
of
its
concurrence
by
placing
a
concurrence
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
3)
Submission
of
demonstrations.

(
i)
A
State
that
has
flagged
data
as
being
due
to
an
exceptional
event
shall,
after
notice
and
opportunity
for
public
comment,
submit
a
complete
demonstration
to
EPA
in
support
of
its
request
for
exclusion
not
later
than
3
years
following
the
end
of
the
calendar
quarter
in
which
the
flagged
concentration
was
recorded.
103
(
ii)
[
Reserved]

(
4)
EPA
review
and
concurrence
or
nonconcurrence.

(
i)
EPA
shall
complete
its
review
and
concur
or
nonconcur
with
a
State's
request
for
exclusion
not
later
than
30
days
following
receipt
of
a
complete
submission
from
the
State.
EPA
shall
notify
the
State
of
its
concurrence
or
nonconcurrence
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
A)
Extensions.
Where
additional
time
is
needed
to
complete
its
review
of
the
State's
demonstration,
EPA
may
extend
the
time
for
review
by
not
more
than
an
additional
30
days.

(
B)
[
Reserved]

(
ii)
[
Reserved]

OPTION
3
for
paragraph
(
c)(
2):

(
2)
Flagging
of
data.

(
i)
A
State
shall
notify
EPA
of
its
intent
to
exclude
one
or
more
measured
exceedances
of
an
applicable
ambient
air
quality
standard
as
being
due
to
an
exceptional
event
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
of
concern
104
not
later
than
180
days
prior
to
the
date
on
which
EPA
intends
to
propose
determinations
with
respect
to
violations
of
applicable
national
ambient
air
quality
standards.

(
ii)
Flags
placed
on
data
in
accordance
with
this
section
shall
be
deemed
informational
only,
and
the
data
shall
not
be
excluded
from
determinations
with
respect
to
exceedances
or
violations
of
the
national
ambient
air
quality
standards
unless
and
until
EPA
notifies
the
State
of
its
concurrence
by
placing
a
concurrence
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
3)
Submission
of
demonstrations.

(
i)
A
State
that
has
flagged
data
as
being
due
to
an
exceptional
event
shall,
after
notice
and
opportunity
for
public
comment,
submit
a
complete
demonstration
to
EPA
in
support
of
its
request
for
exclusion
not
later
than
180
days
prior
to
the
date
on
which
EPA
intends
to
propose
determinations
with
respect
to
violations
of
applicable
national
ambient
air
quality
standards.

(
ii)
[
Reserved]
105
(
4)
EPA
review
and
concurrence
or
nonconcurrence.

(
i)
EPA
shall
complete
its
review
and
concur
or
nonconcur
with
a
State's
request
for
exclusion
not
later
than
30
days
following
receipt
of
a
complete
submission
from
the
State.
EPA
shall
notify
the
State
of
its
concurrence
or
nonconcurrence
by
placing
a
flag
in
the
appropriate
field
for
the
data
record
in
the
AQS
data
base.

(
A)
Extensions.
Where
additional
time
is
needed
to
complete
its
review
of
the
State's
demonstration,
EPA
may
extend
the
time
for
review
by
not
more
than
an
additional
30
days.

(
B)
[
Reserved]

(
ii)
[
Reserved]

PART
51
NATIONAL
PRIMARY
AND
SECONDARY
NATIONAL
AMBIENT
AIR
QUALITY
STANDARDS
1.
The
authority
citation
for
part
51
continues
to
read
as
follows:

Authority:
42
U.
S.
C.
7401,
et
seq.

2.
Adding
Subpart
Y
consisting
of
§
51.920
as
follows
Subpart
Y
 
Exceptional
Events
OPTION
1
for
§
51.920:
106
§
51.920
Mitigation
of
Exceptional
Events.

(
a)
As
a
condition
for
EPA's
approval
of
a
request
to
exclude
air
quality
data
due
to
exceptional
events
from
use,
each
State
must
take
appropriate
and
reasonable
actions
to
protect
public
health
from
exceedances
or
violations
of
the
national
ambient
air
quality
standards
due
to
exceptional
events.
The
State
must:

(
1)
Provide
for
prompt
public
notification
whenever
air
quality
concentrations
exceed
or
are
expected
to
exceed
an
applicable
ambient
air
quality
standard.

(
2)
Provide
for
public
education
concerning
actions
that
individuals
may
take
to
reduce
exposures
to
unhealthy
levels
of
air
quality
during
and
following
an
exceptional
event.

(
3)
Provide
for
the
implementation
of
reasonable
measures
to
protect
public
health
from
exceedances
or
violations
of
ambient
air
quality
standards
caused
by
exceptional
events.

(
b)
[
Reserved]

OPTION
2
for
§
51.920:

§
51.920
Mitigation
of
Exceptional
Events.

(
a)
As
a
condition
for
EPA's
approval
of
a
request
to
107
exclude
air
quality
data
due
to
exceptional
events
from
use,
each
plan
must
include
a
mitigation
action
plan
which
provides
for
appropriate
actions
to
protect
public
health
from
exceedances
or
violations
of
the
national
ambient
air
quality
standards
due
to
exceptional
events.
Each
mitigation
action
plan
must:

(
1)
Provide
for
prompt
public
notification
whenever
air
quality
concentrations
exceed
or
are
expected
to
exceed
an
applicable
ambient
air
quality
standard.

(
2)
Provide
for
public
education
concerning
actions
that
individuals
may
take
to
reduce
exposures
to
unhealthy
levels
of
air
quality
during
and
following
an
exceptional
event.

(
3)
Describe
the
procedures
by
which
appropriate
actions
will
be
identified
and
taken
to
prevent
or
mitigate
public
health
threats
associated
with
exceptional
events.

(
4)
Provide
for
the
implementation
of
reasonably
available
control
measures
to
reduce
emissions
from
those
anthropogenic
sources
which
are
not
exempt
under
§
50.13(
a)(
2)(
ii)
and
which
interact
with
recurring
natural
events
to
contribute
to
exceedances
or
violations
of
applicable
national
108
ambient
air
quality
standards.

(
b)
States
should
periodically
reevaluate
mitigation
action
plans
for
adequacy
and
revise
them
as
necessary
and
appropriate.

OPTION
3
for
§
51.920:

§
51.920
Mitigation
of
Exceptional
Events.

(
a)
As
a
condition
for
EPA's
approval
of
a
request
to
exclude
air
quality
data
due
to
exceptional
events
from
use
in
determinations
with
respect
to
exceedances
or
violations
of
the
national
ambient
air
quality
standards,
each
State
must
adopt
and
implement
a
mitigation
action
plan
for
an
affected
area
which
provides
for
appropriate
actions
to
protect
public
health
from
exceedances
or
violations
of
national
ambient
air
quality
standards
due
to
exceptional
events
which
is
to
be
implemented
in
an
affected
area
on
an
episodic
basis.
Mitigation
action
plans
need
not
be
incorporated
into
the
applicable
implementation
plan,
but
each
mitigation
action
plan
must:

(
1)
Provide
for
prompt
public
notification
whenever
air
quality
concentrations
exceed
or
are
expected
to
exceed
an
applicable
ambient
air
quality
standard.

(
2)
Provide
for
public
education
concerning
actions
109
that
individuals
may
take
to
reduce
exposures
to
unhealthy
levels
of
air
quality
during
and
following
an
exceptional
event.

(
3)
Describe
the
procedures
by
which
appropriate
actions
will
be
identified
and
taken
to
prevent
or
mitigate
public
health
threats
associated
with
exceptional
events.

(
4)
Provide
for
the
implementation
of
reasonably
available
control
measures
to
reduce
emissions
from
those
anthropogenic
sources
which
are
not
exempt
under
§
50.13(
a)(
2)(
ii)
and
which
interact
with
recurring
natural
events
to
contribute
to
exceedances
or
violations
of
applicable
national
ambient
air
quality
standards.

(
b)
States
should
periodically
reevaluate
mitigation
action
plans
for
adequacy
and
revise
them
as
necessary
and
appropriate.
