Document ID: EPA-HQ-OAR-2003-0049-0393
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2005-04-29T04:00Z

Transportation
Conformity
Rule
Amendments
for
the
New
PM2.5
National
Ambient
Air
Quality
Standard:
PM2.5
Precursors
Response
to
Comments
Document
Docket
ID
No.
OAR­
2003­
0049
April
29,
2005
1The
speciation
trends
network
consists
of
over
50
monitoring
sites
in
urban
areas
and
provides
nationally
consistent
data
on
PM2.5
constituents
by
type
(
i.
e.,
"
speciated")
including
nitrates,
elemental
carbon,
organic
carbon
and
sulfates.

Page
2
Required
Precursors
Comment:
Two
comments
received
on
the
November
5,
2003,
proposed
conformity
rulemaking
(
68
FR
62690)
indicated
support
for
identifying
NOx,
VOCs,
SOx
and
ammonia
as
potential
transportation­
related
PM2.5
precursors.

Response:
EPA
agrees
with
these
comments.
Based
on
data
collected
from
monitoring
sites
in
the
national
speciation
trends
network,
1
secondary
particles
from
precursors
commonly
account
for
over
half
of
the
total
fine
particle
mass
from
all
emissions
sources
measured
at
these
sites.
Therefore,
we
expect
that
areas
may
need
to
address
on­
road
emissions
of
relevant
precursors
(
i.
e.,
NOx,
VOC,
SOx
and
ammonia)
in
their
SIPs
and
in
conformity.

Comment:
EPA
received
a
number
of
comments
on
the
proposed
options
for
addressing
precursors
during
the
period
before
PM2.5
SIPs
are
submitted
and
emissions
budgets
are
found
adequate
or
approved.
The
majority
of
commenters
supported
option
2
included
in
the
November
5,
2003
conformity
proposal.
Option
2
would
have
required
significance
findings
for
any
of
the
four
precursors
(
i.
e.,
NOx,
VOC,
SOx
and
ammonia)
to
be
analyzed
in
conformity
determinations
prior
to
EPA
finding
emissions
budgets
in
a
PM2.5
SIP
adequate
or
EPA's
approval
of
that
SIP.
Some
commenters
that
supported
option
2
believed
that
limited
resources
would
be
best
used
by
determining
which
precursors
contribute
significantly
to
an
area's
air
quality
problem
before
conformity
for
those
precursors
was
required.
A
number
of
commenters
also
supported
the
proposed
option
1.
Option
1
would
have
required
NOx
and
VOCs
to
be
analyzed
in
conformity
determinations
prior
to
the
submission
of
PM2.5
SIPs
unless
one
or
both
precursors
was
determined
to
be
insignificant.
This
option
also
would
not
have
required
SOx
or
ammonia
to
be
analyzed
for
conformity
prior
to
a
submitted
SIP
unless
one
or
both
precursors
was
found
significant.
Two
supporters
of
option
1
believed
sufficient
air
quality
data
exists
for
their
areas
to
support
requiring
analysis
of
NOx
and
VOCs
in
conformity
determinations
prior
to
the
Page
3
submission
of
a
PM2.5
SIP.
One
commenter
recommended
that
to
properly
implement
the
Clean
Air
Act
in
all
PM2.5
areas,
conformity
determinations
should
be
required
for
all
four
precursors
prior
to
the
submission
of
a
PM2.5
SIP
unless
a
precursor
was
found
to
be
insignificant.
This
commenter
believed
that
it
would
be
unreasonable
to
allow
an
area
to
opt
out
of
conducting
an
analysis
by
default
for
a
precursor
that
could
be
responsible
for
a
large
portion
of
PM2.5.
Additionally,
two
commenters
indicated
that
SOx
should
be
addressed
in
conformity
determinations
prior
to
submission
of
a
PM2.5
SIP
unless
it
is
found
to
be
insignificant.
One
commenter
stated
that
ammonia
should
be
included
in
conformity
determinations
as
soon
as
modeling
and
analysis
tools
are
available.
Another
commenter
opined
that
the
only
pollutant
that
should
require
a
significance
finding
prior
to
the
submission
of
a
PM2.5
SIP
is
ammonia.

Response:
The
final
rule
allows
for
the
consideration
of
the
four
precursors
in
conformity
prior
to
PM2.5
SIPs
when
such
precursors
are
significant:
NOx
is
considered
significant
in
the
absence
of
a
finding;
VOCs,
SOx
and
ammonia
must
be
found
significant
to
be
included.
In
finalizing
this
rule
EPA
attempted
to
strike
a
balance
between:
1)
expeditiously
addressing
transportation­
related
emissions
that
could
exacerbate
the
PM2.5
air
quality
problem
before
a
SIP
is
established,
and
2)
targeting
conformity
requirements
in
PM2.5
areas
in
an
efficient
and
reasonable
manner.
EPA
based
its
decision
on
a
number
of
factors.
For
example,
EPA
considered
the
environmentally
conservative
nature
of
requiring
conformity
determinations
for
all
four
precursors
prior
to
the
submission
of
a
SIP
unless
a
finding
is
made
that
on­
road
emissions
of
a
precursor
or
precursors
is
insignificant,
rather
than
only
for
NOx.
Requiring
that
all
four
precursors
be
addressed
in
conformity
prior
to
the
submission
of
a
SIP
may
be
a
more
environmentally
protective
approach
to
meeting
the
Clean
Air
Act's
conformity
requirements
because
any
significant
precursors
would
automatically
be
addressed
without
the
need
for
a
significance
finding
to
be
made
by
the
state
air
agency
or
the
EPA
regional
office.
On
the
other
hand,
requiring
significance
findings
for
the
precursors
VOCs,
SOx
and
ammonia
better
accounts
for
regional
variability
in
air
quality
and
better
targets
resources
to
the
precursors
that
are
most
important
in
an
individual
area.
Also,
requiring
significance
findings
for
these
three
precursors
could
help
areas
avoid
adopting
on­
road
control
measures
to
address
a
particular
precursor
before
a
SIP
is
submitted
that
ultimately
prove
to
be
unnecessary
after
a
SIP
is
developed,
if
emissions
of
the
targeted
precursor
are
ultimately
found
to
be
insignificant.
In
addition,
EPA
also
considered
with
2In
addition,
California
has
adopted
its
own
rule
which
addresses
the
sulfur
content
of
gasoline
in
that
state.
California's
regulation
is
similar
in
stringency
to
the
federal
regulation.

3EPA
420­
R­
00­
020,
October
2002,
"
Procedures
for
Developing
Base
Year
and
Future
Year
Mass
and
Modeling
Inventories
for
the
Heavy­
Duty
Engine
and
Vehicle
Standards
and
Highway
Diesel
Fuel
(
HDD)
Rulemaking."

Page
4
respect
to
each
precursor
the
chemistry
of
secondary
particle
formation,
the
results
of
speciated
air
quality
monitoring
and
on­
road
emissions
inventory
data.
In
addition
to
the
information
provided
below,
the
November
2003
notice
of
proposed
rulemaking
contains
a
more
detailed
discussion
of
speciated
air
quality
data
and
on­
road
emissions
data
(
68
FR
62706
through
62708).
Please
refer
to
the
notice
of
proposed
rulemaking
for
additional
details.
Sulfur
dioxide.
While
speciated
air
quality
data
show
that
sulfate
is
a
relatively
significant
component
(
e.
g.
ranging
from
nine
to
40
percent)
of
PM2.5
mass
in
all
regions
of
the
country,
emissions
inventory
data
and
projections
show
that
on­
road
emissions
of
SOx
constitute
a
"
de
minimis"
(
i.
e.,
extremely
small)
portion
of
total
SOx
emissions.
Emissions
inventory
data
for
1999
for
the
372
potential
PM2.5
nonattainment
counties
for
PM2.5
(
based
on
1999­
2001
air
quality
data)
show
that
on­
road
sources
were
responsible
for
only
two
percent
of
total
SOx
emissions.
By
comparison,
fuel
combustion
sources
(
e.
g.,
electric
utility
and
industrial
combustion
of
coal
and
oil)
contributed
approximately
88
percent
of
the
SOx
emissions
in
1999
in
these
same
counties.
Furthermore,
EPA
has
already
adopted
two
regulations
that
will
greatly
reduce
emissions
of
SOx
from
on­
road
sources
by
the
time
such
regulations
are
both
in
full
effect
in
2009.
First,
in
2004
the
low
sulfur
gasoline
program
began
to
be
phased
in
and
will
be
fully
effective
in
2007
(
February
10,
2000,
65
FR
6697).
This
regulation
will
reduce
the
sulfur
content
of
gasoline
by
approximately
90
percent
when
fully
effective.
2
Second,
in
2006
the
low
sulfur
diesel
program
will
begin
to
be
phased
in
and
will
be
fully
effective
by
2009
(
January
18,
2001,
66
FR
5001).
This
regulation
will
reduce
the
sulfur
content
of
diesel
fuel
by
approximately
97
percent
nationally
when
fully
effective.
Projections
of
on­
road
emissions
of
SO2
in
2020
indicate
that
on­
road
sources
will
be
responsible
for
less
than
one
percent
of
the
total
SO2
emissions
in
2020
in
the
372
potential
PM2.5
nonattainment
counties
(
based
on
1999­
2001
air
quality
data).
3
These
projections
confirm
that
the
implementation
of
the
fuel
regulations
discussed
above
will
ensure
that
as
a
general
Page
5
matter
SO2
emissions
from
on­
road
sources
remain
at
insignificant
levels
in
all
areas.
Therefore,
states
are
not
required
to
include
SOx
in
conformity
determinations
prior
to
submission
of
a
SIP
unless
the
state
air
agency
or
EPA
regional
office
makes
a
finding
that
on­
road
emissions
of
SOx
are
a
significant
contributor
to
an
area's
PM2.5
problem.
If
a
state
determines
through
its
SIP
development
process
that
on­
road
emissions
of
SOx
are
significant
and
the
SIP
includes
an
adequate
or
approved
emissions
budget
for
SOx,
then
future
conformity
determinations
will
be
required
to
include
a
regional
emissions
analysis
for
SOx.
Nitrogen
oxides.
Based
on
a
review
of
speciated
monitoring
data
analyses,
nitrate
concentrations
vary
significantly
across
the
country.
For
example,
in
some
southeastern
locations,
annual
average
nitrate
levels
range
from
six
to
eight
percent
of
total
PM2.5
mass,
whereas
nitrate
comprises
40
percent
or
more
of
PM2.5
mass
in
certain
California
locations.
Nitrate
formation
is
favored
by
the
availability
of
ammonia,
low
temperatures,
and
high
relative
humidity.
Nitrate
formation
also
depends
upon
the
amount
of
nearby
SO2
emissions
because
ammonia
reacts
preferentially
with
SO2
over
NOx
(
i.
e.,
ammonia
first
reacts
to
form
ammonium
sulfate
and
then
reacts
to
form
ammonium
nitrate).
The
sources
of
NOx
are
numerous
and
widespread,
including
motor
vehicles,
power
plants,
and
many
other
combustion
activities.
We
believe
these
source
categories
and
the
potential
for
significant
impacts
on
air
quality
exist
in
many
nonattainment
areas.
The
analysis
of
speciated
air
quality
data
and
the
discussion
of
emission
inventory
data
in
the
November
2003
transportation
conformity
notice
of
proposed
rulemaking
provide
an
appropriate
basis
for
deciding
that
states
must
include
NOx
in
conformity
determinations
made
before
SIPs
are
submitted
and
emissions
budgets
are
found
adequate
or
approved,
unless
the
state
air
agency
and
the
EPA
regional
office
find
that
on­
road
emissions
of
NOx
are
not
a
significant
contributor
to
the
area's
PM2.5
problem.
EPA
believes
that
requiring
both
the
state
air
agency
and
the
EPA
regional
office
make
an
insignificance
finding
for
NOx
is
warranted
because
in
this
rulemaking
EPA
has
initially
determined
that
NOx
is
a
significant
precursor
for
all
PM2.5
nonattainment
areas.
Additionally,
all
other
insignificance
findings
require
both
state
air
agency
and
EPA
regional
office
action
because
they
are
made
through
either
a
motor
vehicle
emission
budget
adequacy
finding
or
a
SIP
approval
as
required
by
§
93.109(
k)
of
the
conformity
regulation.
Therefore,
EPA
believes
that
it
is
necessary
that
both
the
state
air
agency
and
the
EPA
regional
office
make
a
finding
that
on­
road
emissions
of
NOx
are
an
insignificant
contributor
to
an
area's
PM2.5
air
quality
problem
prior
to
the
submission
of
a
SIP.
A
finding
made
by
both
Page
6
agencies
provides
assurance
that
on­
road
emissions
of
NOx
are
in
fact
insignificant
contributors
to
an
area's
PM2.5
air
quality
problem
and
therefore
may
be
omitted
from
conformity
determinations
prior
to
the
submission
of
a
SIP
for
the
area.
After
a
PM2.5
SIP
is
submitted,
conformity
determinations
will
be
required
for
on­
road
emissions
of
NOx
if
the
SIP
includes
emissions
budgets
that
are
found
adequate
or
are
approved.
Volatile
Organic
Compounds.
In
2003,
EPA
estimates
that
onroad
motor
vehicles
accounted
for
28
percent
of
total
VOCs
nationwide.
Carbonaceous
particles,
which
result,
in
part,
from
reactions
involving
VOCs,
account
for
25­
70%
of
constructed
fine
particle
mass
measured
at
specific
Speciation
Trends
Network
sites.
The
highest
percentages
of
carbonaceous
particles
tend
to
be
in
the
western
United
States,
while
the
lowest
percentages
tend
to
be
in
the
eastern
United
States.
Although
research
clearly
indicates
that
VOCs
can
contribute
to
the
formation
of
carbonaceous
secondary
PM2.5
compounds,
the
current
science
is
still
incomplete
in
its
understanding
of
the
fraction
of
particulate
organic
compounds
that
began
as
VOCs.
A
major
reason
for
this
existing
deficiency
is
the
varying
degrees
of
volatility
of
organic
compounds,
as
well
as
our
inability
to
model
collectively
the
reactivity
of
these
different
groups
of
compounds.
For
example,
there
are
highly
reactive
volatile
compounds
with
six
or
fewer
carbon
atoms
that
indirectly
contribute
to
PM
formation
through
reaction
with
oxidizing
compounds
such
as
the
hydroxyl
radical
and
ozone.
There
are
also
semi­
volatile
compounds
with
between
seven
and
24
carbon
atoms
that
can
exist
in
particle
form
and
can
readily
be
oxidized
to
form
other
low
volatility
compounds.
Finally,
high
molecular
weight
organic
compounds
(
with
25
carbon
atoms
or
more
and
low
vapor
pressure)
are
emitted
directly
as
primary
organic
particles
and
exist
primarily
in
the
condensed
phase
at
ambient
temperatures.
For
this
reason,
these
high
molecular
weight
organic
compounds
are
generally
considered
to
be
primary
particles
and
not
VOCs.
The
relative
importance
of
each
of
these
groups
of
organic
compounds
in
the
formation
of
organic
particles
varies
from
area
to
area.
In
addition,
the
contribution
of
onroad
source
emissions
to
each
of
these
three
groups
of
organic
compounds
may
also
vary
from
area
to
area.
Current
scientific
and
technical
information
clearly
shows
that
carbonaceous
material
is
a
significant
fraction
of
total
PM2.5
mass
in
most
areas,
and
that
certain
aromatic
VOC
emissions
such
as
toluene,
xylene,
and
trimethyl­
benzene
are
precursors
to
the
formation
of
secondary
PM2.5
(
secondary
organic
aerosols).
However,
while
significant
progress
has
been
made
in
understanding
the
role
of
gaseous
organic
material
in
the
formation
of
organic
PM,
this
relationship
is
complex
and
requires
further
research
and
technical
tools
to
determine
the
4McMurry,
P.,
Shepherd,
M.,
Vickery,
J.
(
ed.)
Particulate
Matter
Science
for
Policy
Makers
­
A
NARSTO
Assessment.
Cambridge:
Cambridge
University
Press,
2004.

5Cabada
J.
C.,
S.
N.
Pandis,
R.
Subramanian,
A.
L.
Robinson,
A.
Polidori,
and
B.
Turpin
(
2004)
Estimating
the
secondary
organic
aerosol
contribution
to
PM2.5
using
the
EC
tracer
method,
Aerosol
Sci.
Technol.,
38S,
140­
155.

6Millet
D.
B.,
N.
M.
Donahue,
S.
N.
Pandis,
A.
Polidori,
C.
O.
Stanier,
B.
J.
Turpin,
and
A.
H.
Goldstein
(
2005)
Atmospheric
volatile
organic
compound
measurements
during
the
Pittsburgh
Air
Quality
Study:
Results,
interpretation,
and
quantification
of
primary
and
secondary
contributions,
J.
Geophys.
Res.,
110,
D07SO7,
10.1029/
2004JD004601.

7"
Sources
of
carbon
in
PM2.5
based
on
14C
and
tracer
analysis,"
Edgerton,
Eric
S.,
John
J.
Jansen,
Mei
Zheng
and
Benjamin
E.
Hartsell
(
September
2004),
8th
International
Conference
on
Carbonaceous
Particles
in
the
Atmosphere,
Vienna,
Austria.

8"
Source
apportionment
of
PM2.5
using
a
three­
dimensional
air
quality
model
and
a
receptor
model,"
Park,
S­
K,
L.
Ke,
B.
Yan,
A.
G.
Russell,
M.
Zheng
(
2005),
Proceedings
of
an
AAAR
international
specialty
conference
­­
Particulate
Matter
Supersites
Program
and
Related
Studies,
Atlanta,
Georgia.

Page
7
extent
of
the
contribution
of
specific
VOC
compounds
to
organic
PM
mass,
prior
to
EPA
being
able
to
determine
the
extent
of
the
contribution
of
VOCs
to
nonattainment
problems
in
all
PM2.5
areas.
Additional
research
is
also
needed
to
determine
the
sources
of
VOC
emissions
that
contribute
most
to
PM2.5
air
quality
issues.
For
example,
according
to
the
NARSTO
Fine
Particle
Assessment,
4
secondary
sources
may
contribute
up
to
50
percent
of
secondary
organic
mass,
particularly
in
areas
where
photochemical
transformations
of
emissions
from
biogenic
sources
(
e.
g.,
trees)
are
significant.
In
addition,
data
obtained
from
the
Particulate
Matter
Supersites
Program
suggest
that
biogenic
emissions
may
contribute
significantly
to
secondary
organic
aerosols
during
days
of
peak
PM2.5.
Analysis
of
air
quality
samples
collected
in
Pittsburgh
from
2001
through
2002
indicates
that
as
much
as
half
of
the
organic
aerosol
during
peak
periods
may
be
attributable
to
biogenic
sources
(
e.
g.,
trees)
as
opposed
to
anthropogenic
sources
(
i.
e.,
man­
made
sources
such
as
power
plants
and
motor
vehicles).
5,6
The
Supersites
Program
has
also
collected
data
on
the
contribution
of
biogenic
source
emissions
in
other
locations
in
the
U.
S.,
including
Atlanta,
Georgia.
7,8
However,
these
Page
8
findings
have
not
yet
been
published
and
peer­
reviewed.
The
contribution
of
biogenic
emissions
to
PM2.5
air
quality
issues
is
important
because
biogenic
emissions
cannot
be
controlled.
EPA
acknowledges
that
analytical
tools
are
evolving
to
enable
areas
to
adequately
model
the
contribution
of
VOCs
to
PM2.5
formation.
Researchers
in
the
field
anticipate
that
within
the
next
five
years
the
ability
of
models
to
simulate
various
components
of
PM2.5
will
improve
greatly,
as
will
their
ability
to
estimate
the
effectiveness
of
various
control
measures.
These
model
improvements
are
particularly
significant
for
secondary
organic
aerosols
and
biogenic
and
anthropogenic
emissions
of
VOCs.
However,
until
such
model
improvements
are
made
and
our
understanding
of
VOC
secondary
particle
formation
improves,
EPA
believes
it
is
not
appropriate
to
require
regional
conformity
analyses
for
VOCs
in
PM2.5
nonattainment
areas
prior
to
the
submission
of
a
PM2.5
SIP
and
emissions
budgets
for
VOCs
being
found
adequate
or
approved,
unless
the
state
air
agency
or
EPA
regional
office
finds
that
VOCs
are
a
significant
contributor
to
an
area's
PM2.5
problem.
If
a
state
determines
through
its
SIP
development
process
that
on­
road
emissions
of
VOCs
are
significant
and
the
SIP
includes
an
adequate
or
approved
emissions
budget
for
VOCs,
then
future
conformity
determinations
will
be
required
to
include
a
regional
emissions
analysis
for
VOCs.
Ammonia.
We
believe
a
case­
by­
case
approach
is
also
appropriate
for
ammonia
because
there
is
sufficient
uncertainty
about
emissions
inventories
and
about
the
potential
efficacy
of
control
measures
from
location
to
location.
Reductions
of
ammonia
may
be
effective
primarily
in
areas
where
nitric
acid
is
in
abundance
and
ammonia
is
the
limiting
factor
to
ammonium
nitrate
formation
(
ammonium
nitrate
is
a
type
of
particulate
matter).
Although
ammonia
reductions
may
be
appropriate
in
selected
locations,
in
other
locations
such
reductions
may
lead
to
increased
atmospheric
acidity,
exacerbating
acidic
deposition
problems.
In
other
words,
states
should
evaluate
the
benefits
of
including
ammonia
in
conformity
determinations
prior
to
the
submission
of
SIPs
and
emissions
budgets
being
found
adequate
or
approved.
Therefore,
states
are
not
required
to
include
ammonia
in
conformity
determinations
prior
to
submission
of
a
SIP
unless
the
state
air
agency
or
EPA
regional
office
makes
a
finding
that
on­
road
emissions
of
ammonia
are
a
significant
contributor
to
an
area's
PM2.5
problem.
If
a
state
determines
through
its
SIP
development
process
that
on­
road
emissions
of
ammonia
are
significant
and
the
SIP
includes
an
adequate
or
approved
emissions
budget
for
ammonia,
then
future
conformity
determinations
will
be
required
to
include
a
regional
emissions
analysis
for
ammonia.
Page
9
Comment:
Several
commenters
believed
that
SIP
budgets
for
one
or
more
of
the
PM2.5
precursors
should
be
established
before
conformity
is
required
for
those
precursors.
Specifically,
two
commenters
believed
that
SOx
and
ammonia
should
be
evaluated
for
significance
and
have
SIP
budgets
before
conformity
is
required.
Three
other
commenters
believed
that
conformity
determinations
should
not
be
required
for
any
PM2.5
precursors
prior
to
the
submission
of
a
SIP
and
emissions
budgets
being
found
adequate
or
approved.
One
of
these
commenters
stated
that
§
§
93.102(
b)(
2)(
iii)­(
v)
and
93.102(
b)(
3)
should
refer
to
budgets
because
conformity
should
only
be
required
if
there
is
an
explicit
motor
vehicle
emissions
budget
that
is
intended
to
be
a
ceiling
on
future
emissions.

Response:
EPA
disagrees
with
these
commenters.
Clean
Air
Act
section
176(
c)(
6)
requires
that
conformity
apply
in
new
nonattainment
areas
one
year
after
the
effective
date
of
the
nonattainment
designation,
even
prior
to
the
submission
of
SIPs
establishing
budgets
for
a
particular
pollutant
or
precursor.
Clean
Air
Act
section
176(
c)(
4)
provides
EPA
with
the
authority
to
establish
conformity
tests
that
will
ensure
that
transportation
plans,
TIPs
and
projects
do
not
result
in
new
violations
of
an
air
quality
standard,
increase
the
frequency
or
severity
of
an
existing
violation,
or
delay
timely
attainment
of
a
standard
during
the
period
before
a
SIP
is
submitted.
While
the
contribution
of
mobile
sources
to
PM2.5
nonattainment
problems
is
likely
to
vary
from
area
to
area,
on­
road
emissions
of
at
least
NOx,
and
perhaps
other
precursors,
are
likely
to
make
a
significant
contribution
to
PM2.5
problems
in
most
areas.
Therefore,
EPA
believes
it
is
both
required
by
the
Clean
Air
Act
and
necessary
to
protect
public
health
for
PM2.5
areas
to
begin
considering
the
role
of
on­
road
emissions
of
PM2.5
precursors
in
their
PM2.5
air
quality
problems,
and
to
demonstrate
conformity
for
those
precursors
that
make
a
significant
contribution
to
their
air
quality
problems
once
conformity
applies
for
PM2.5.
Before
adequate
or
approved
SIP
budgets
are
established,
PM2.5
areas
must
use
one
of
the
interim
emissions
tests
in
§
93.119
to
fulfill
this
statutory
requirement.

Comment:
One
commenter
opined
that
requiring
conformity
for
additional
precursors
results
in
additional
burden.
The
commenter
stated
that
any
additional
pollutant
or
precursor
that
has
to
be
included
in
a
conformity
determination
leads
to
additional
modeling
runs,
additional
documentation
of
results,
additional
explanation
to
the
public
and
regional
decision
makers
and
an
additional
opportunity
for
a
conformity
lapse.
This
commenter
believed
that
EPA
should
not
minimize
these
resource
Page
10
requirements
or
use
this
argument
to
support
the
inclusion
of
PM2.5
precursors
in
conformity
determinations
prior
to
a
SIP
submission.

Response:
EPA
understands
the
commenter's
concerns
and
has
attempted
to
structure
requirements
for
PM2.5
precursors
so
that
human
health
and
air
quality
are
protected
while
targeting
regional
emissions
analyses
to
only
those
precursors
from
on­
road
emissions
that
make
a
significant
contribution
to
an
area's
PM2.5
air
quality
problem.
However,
EPA
continues
to
believe
as
stated
in
the
November
2003
proposal
that
including
PM2.5
precursors
in
PM2.5
regional
emissions
analyses
prior
to
the
submission
of
a
SIP
should
not
result
in
any
additional
transportation
or
emissions
modeling
because
PM2.5
areas
will
already
be
producing
VMT
and
emissions
estimates
for
direct
PM2.5
(
68
FR
62706).
The
same
VMT
estimates
would
be
used
in
calculating
emissions
of
any
and
all
precursors.
Additionally,
emission
factors
for
the
relevant
precursors
would
generally
be
produced
in
the
same
model
runs
as
the
emission
factors
for
direct
PM2.5.
EPA
recognizes
that
there
would
be
some
small
increase
in
burden
in
documenting
these
results
and
in
discussing
these
precursors
with
regional
decision
makers
and
the
public,
but
we
believe
this
small
increase
is
merited
if
a
precursor
is
a
significant
contributor
to
an
area's
air
quality
problem.
EPA
also
recognizes
that
it
is
possible
that
an
area
could
lapse
because
it
may
not
be
able
to
demonstrate
conformity
for
one
or
more
of
the
PM2.5
precursors.
EPA
and
DOT
always
attempt
to
work
with
areas
that
are
experiencing
problems
demonstrating
conformity
in
order
to
resolve
problems
before
a
lapse
occurs.
However,
the
Clean
Air
Act's
conformity
requirements
are
intended
to
ensure
that
the
use
of
federal
transportation
funds
does
not
cause
new
air
quality
problems,
make
existing
problems
worse,
or
delay
meeting
a
Clean
Air
Act
requirement
such
as
attainment.
Therefore,
if
one
or
more
precursors
is
a
significant
contributor
to
an
area's
air
quality
problem,
the
inability
to
demonstrate
conformity
for
such
precursors
would
be
consistent
with
the
Clean
Air
Act's
intended
purpose
of
the
conformity
process.
In
other
words,
if
conformity
cannot
be
demonstrated
for
a
significant
precursor,
federal
transportation
funds
could
not
be
spent
on
transportation
activities
that
potentially
would
cause
a
new
air
quality
problem,
worsen
an
existing
problem,
or
delay
attainment
or
other
emission
reduction
milestone.
The
inability
to
demonstrate
conformity
would
indicate
that
further
action
is
needed
before
federal
transportation
funding
and
approvals
can
occur
so
that
ultimately
both
transportation
and
air
quality
goals
are
achieved.
Page
11
Significance
Findings
Comment:
A
number
of
commenters
expressed
support
for
significance
findings
to
be
made
by
either
the
state
air
agency
or
the
EPA
regional
office
before
a
PM2.5
SIP
is
submitted.
However,
commenters
also
suggested
different
options
for
making
significance
findings.
Thirteen
commenters
stated
that
both
the
state
air
agency
and
the
EPA
regional
office
should
make
the
finding,
while
two
commenters
stated
that
the
finding
should
be
made
through
an
area's
interagency
consultation
process.
Another
commenter
recommended
that
only
the
state
should
have
the
ability
to
make
significance
findings.

Response:
EPA
is
making
one
change
with
regard
to
insignificance
findings.
EPA
has
determined
that
insignificance
findings
for
NOx
should
be
made
by
both
the
state
air
agency
and
the
EPA
regional
office.
EPA
believes
that
requiring
both
the
state
air
agency
and
the
EPA
regional
office
to
make
an
insignificance
finding
for
NOx
is
appropriate
because,
as
stated
above
in
this
rulemaking,
EPA
has
initially
determined
that
NOx
is
a
significant
precursor
for
all
PM2.5
nonattainment
areas.
Additionally,
all
other
insignificance
findings
made
within
the
transportation
conformity
and
SIP
processes
require
both
state
air
agency
and
EPA
regional
office
action
because
they
are
made
through
either
a
motor
vehicle
emission
budget
adequacy
finding
or
a
SIP
approval
as
required
by
§
93.109(
k)
of
the
conformity
regulation.
Therefore,
EPA
believes
that
it
is
necessary
that
both
the
state
air
agency
and
the
EPA
regional
office
make
a
finding
that
on­
road
emissions
of
NOx
are
an
insignificant
contributor
to
an
area's
PM2.5
air
quality
problem
prior
to
the
submission
of
a
SIP.
A
finding
made
by
both
agencies
provides
assurance
that
on­
road
emissions
of
NOx
are
in
fact
insignificant
contributors
to
an
area's
PM2.5
air
quality
problem
and
therefore
may
be
omitted
from
conformity
determinations
prior
to
the
submission
of
a
SIP
for
the
area.
Finally,
EPA
believes
that
an
insignificance
finding
for
NOx
should
be
made
by
both
the
state
air
agency
and
the
EPA
regional
office
because
NOx
is
the
only
pollutant/
precursor
for
which
a
regional
analysis
is
avoided
if
a
finding
is
made.
That
is,
the
conformity
rule
allows
NOx
to
be
found
insignificant
before
a
SIP
is
submitted
and
therefore
not
be
included
in
subsequent
conformity
determinations.
For
all
other
pollutants/
precursors
covered
by
the
conformity
rule
(
i.
e.,
VOCs,
SOx
and
ammonia
as
PM2.5
precursors;
NOx
and
VOCs
as
PM10
precursors
and
road
dust
as
a
contributor
to
PM2.5
air
quality
problems)
either
the
state
air
Page
12
agency
or
the
EPA
regional
office
can
decide
if
emissions
are
significant
and
therefore
should
be
included
in
conformity
determinations
prior
to
the
submission
of
a
SIP
and
emissions
budgets
being
found
adequate
or
approved.
However,
a
finding
for
NOx
(
in
this
case,
a
finding
of
insignificance)
would
lead
to
a
less
environmentally
protective
result
where
NOx
would
no
longer
be
considered
in
conformity
determinations.
In
contrast,
consistent
with
the
rule's
requirements
for
significance
findings
for
other
precursor
emissions
and
the
November
5,
2003,
proposal,
today's
action
specifies
that
significance
findings
for
VOCs,
SOx
and
ammonia
as
PM2.5
precursors
can
be
made
by
either
the
state
air
agency
or
the
EPA
regional
office.
We
believe
that
changes
to
the
procedures
for
finding
VOCs,
SOx
and
ammonia
precursor
emissions
significant
in
response
to
comments
are
unnecessary
because
such
findings
would
result
in
the
inclusion
of
one
or
more
precursors
in
conformity
which
would
be
more
environmentally
protective.
Furthermore,
allowing
significance
findings
for
VOCs,
SOx
and
ammonia
to
be
made
by
either
the
state
air
agency
or
the
EPA
regional
office
acknowledges
the
state's
authority
as
well
as
EPA's
role
in
ensuring
national
consistency
in
such
decisions.
The
language
used
in
the
final
rule
for
these
three
PM2.5
precursors
is
consistent
with
how
such
findings
have
been
made
for
PM10
precursors,
since
the
original
1993
conformity
rule
(
58
FR
62188).
Today's
final
rule
for
these
three
precursors
is
also
consistent
with
how
such
findings
are
to
be
made
for
PM2.5
road
dust.
The
road
dust
requirements
were
finalized
in
the
July
1,
2004,
conformity
final
rule
(
69
FR
40004).
EPA
believes
that
maintaining
consistency
in
cases
where
precursors
are
determined
to
be
significant
will
facilitate
implementation
of
the
conformity
rules
with
no
adverse
impacts,
in
light
of
the
role
interagency
consultation
will
play
in
such
findings
as
explained
in
Section
III.
A.
of
this
final
rule.

Comment:
One
commenter,
who
favored
including
all
precursors
in
conformity
determinations
prior
to
the
submission
of
a
SIP,
stated
that
a
precursor
could
be
found
to
be
insignificant
if
current
on­
road
emissions
are
less
than
five
percent
of
total
PM2.5
and
no
increases
are
expected
on
a
percentage
basis
during
the
period
covered
by
the
SIP
or
the
conformity
determination
for
the
area.

Response:
EPA
disagrees
with
this
suggested
approach.
Merely
using
a
percentage
level
as
a
basis
for
a
significance
or
insignificance
finding
ignores
many
other
aspects
of
an
area's
nonattainment
problem.
Rather,
EPA
believes
that
a
combination
of
the
criteria
for
insignificance
findings
contained
in
Page
13
§
93.109(
k)
of
the
conformity
rule
and
the
discussion
of
insignificance
and
significance
findings
as
they
apply
to
PM2.5
precursors
contained
in
this
notice
provide
the
appropriate
basis
for
deciding
whether
or
not
a
PM2.5
precursor
is
significant
or
insignificant
in
a
given
area.
Discussion
of
EPA's
rationale
for
establishing
criteria
for
significance
and
insignificance
findings
can
be
found
in
the
preamble
to
the
July
1,
2004,
conformity
final
rule
(
69
FR
40061
through
40063).
Therefore,
EPA
is
not
adopting
the
criteria
suggested
by
the
commenter.

Comment:
One
commenter
believed
that
if
all
precursors
were
considered
in
conformity
prior
to
a
SIP
submission
it
could
be
presumed
that
these
precursors
will
ultimately
be
included
in
the
SIP
for
the
area.
In
such
a
case,
the
commenter
believed
it
would
be
difficult
to
justify
not
including
the
precursors
in
the
SIP
for
the
area
if
the
state
presumptively
includes
all
of
them
in
the
first
conformity
determination.

Response:
Under
this
final
rule
any
significance
finding
made
prior
to
EPA's
adequacy
finding
for
budgets
in
a
SIP,
or
EPA's
approval
of
the
SIP,
should
not
be
viewed
as
the
ultimate
determination
of
the
significance
of
precursor
emissions
in
a
given
area.
State
and
local
agencies
may
find
through
the
SIP
development
process
that
emissions
of
one
or
more
precursors
are
significant,
even
if
a
precursor
had
previously
been
considered
insignificant.
In
such
a
case,
the
PM2.5
SIP
would
establish
a
motor
vehicle
emissions
budget
for
that
precursor
and
a
regional
emissions
analysis
for
that
precursor
would
be
included
in
subsequent
conformity
determinations.
Similarly,
state
and
local
agencies
may
find
that
a
precursor
is
insignificant
when
preparing
the
SIP,
even
if
previously
found
significant
prior
to
the
SIP's
preparation.

Comment:
One
commenter
stated
that
the
insignificance
policy
should
be
applied
to
precursor
emissions
in
PM2.5
nonattainment
and
maintenance
areas
for
a
variety
of
reasons
such
as
the
need
for
additional
information
on
the
nature
and
cause
of
an
area's
PM2.5
problem,
speciation
of
PM2.5
and
availability
of
PM2.5
control
measures.

Response:
EPA
agrees
with
this
commenter.
This
final
rule
allows
nonattainment
areas
to
make
findings
on
the
significance
of
each
of
the
four
precursors
to
their
PM2.5
air
quality
problem
during
the
period
before
a
SIP
is
submitted
and
budgets
are
found
adequate.
The
insignificance
policy
also
generally
applies
after
a
SIP
is
submitted,
via
the
decisions
about
precursors
that
are
Page
14
determined
in
the
SIP.

Comment:
One
commenter
requested
additional
guidance
on
significance
and
insignificance
findings.

Response:
EPA
does
not
believe
that
additional
guidance
on
significance
and
insignificance
findings
is
necessary
at
this
time.
EPA
has
described
the
criteria
to
be
considered
and
the
process
to
be
used
in
making
these
findings
in
§
93.109(
k)
of
the
conformity
rule
and
in
the
preamble
to
this
final
rule.
Additional
discussion
and
details
on
insignificance
findings
can
be
found
in
the
preamble
to
the
July
1,
2004,
final
rule
(
69
FR
40061
through
40063).
Page
15
Precursors
in
SIPs
Comment:
One
commenter
stated
that
after
PM2.5
SIPs
are
submitted,
areas
should
consider
all
four
precursors
in
conformity
determinations
unless
the
SIP
clearly
states
that
one
or
more
precursors
are
insignificant.

Response:
EPA
is
not
making
any
changes
to
the
conformity
rule
in
response
to
this
comment.
EPA
does
not
believe
that
it
is
necessary
for
a
SIP
to
explicitly
state
that
a
precursor
is
insignificant.
Instead,
EPA
believes
that
states
will
consider
the
on­
road
contribution
of
all
four
precursors
to
the
PM2.5
problem
as
they
develop
their
SIPs.
If
through
the
SIP
process
a
state
concludes
that
on­
road
emissions
of
one
or
more
precursors
needs
to
be
addressed
in
order
to
attain
the
PM2.5
standard
as
expeditiously
as
practicable,
then
EPA
expects
that
the
state
will
include
an
emissions
budget
in
the
SIP
for
each
of
the
relevant
precursors.
A
conformity
determination
will
then
be
required
for
each
precursor
for
which
there
is
a
budget,
after
the
emissions
budgets
are
found
adequate
or
approved.
In
making
a
decision
about
each
precursor,
states
should
consider
the
insignificance
criteria
contained
in
§
93.109(
k)
of
the
conformity
rule
and
the
current
state
of
the
science
concerning
the
precursor's
role
in
the
formation
of
PM2.5.
Once
SIPs
are
submitted
and
found
adequate
or
approved
the
conformity
rule
requires
that
conformity
be
assessed
against
the
budgets
in
the
applicable
SIP.
Conformity
determinations
must
then
address
all
precursors
for
which
the
SIP
establishes
a
budget,
and
need
not
address
any
possible
precursor
for
which
the
state
has
not
established
a
budget
because
the
emissions
of
that
precursor
are
insignificant.
EPA
notes
that,
if
inventory
and
modeling
analyses
demonstrating
reasonable
further
progress,
attainment
or
maintenance
indicate
a
level
of
emissions
of
a
precursor
that
must
be
maintained
to
demonstrate
compliance
with
the
applicable
requirement,
then
that
level
of
emissions
should
be
clearly
identified
in
the
SIP
as
a
motor
vehicle
emissions
budget
for
transportation
conformity
purposes
consistent
with
§
93.118(
e)
even
if
the
SIP
does
not
establish
particular
controls
for
the
given
precursor.
If
the
state
fails
to
identify
such
a
level
of
emissions
as
a
motor
vehicle
emissions
budget,
EPA
will
find
the
submitted
SIP
budgets
inadequate
because
the
SIP
fails
to
clearly
identify
the
motor
vehicle
emissions
budget
as
required
by
conformity
rule
§
93.118(
e)(
4)(
iii).
Page
16
Comment:
Several
commenters
raised
concerns
about
SIP
development
and
regional
emissions
analyses
in
areas
that
are
nonattainment
for
both
8­
hour
ozone
and
PM2.5.
One
of
these
commenters
asked
if
NOx
and
VOC
conformity
analyses
would
be
the
same
for
both
pollutants
in
these
areas.
Another
commenter
asked
if
NOx
and
VOC
budgets
would
be
the
same
for
8­
hour
ozone
and
PM2.5
SIPs
in
these
areas.

Response:
EPA
does
not
expect
that
either
regional
emissions
analyses
or
budgets
for
NOx
and
VOCs
will
be
the
same
for
8­
hour
ozone
and
PM2.5
standards
in
areas
that
are
nonattainment
for
both
pollutants,
for
several
reasons.
First,
it
is
likely
that
most
areas
will
have
different
attainment
dates
for
each
of
the
two
pollutants,
which
means
that
it
is
likely
that
analyses
and
budgets
will
be
required
for
different
years.
Second,
it
is
possible
that
in
many
cases
the
boundaries
of
the
nonattainment
area
for
each
pollutant
may
be
different.
For
example,
the
8­
hour
ozone
nonattainment
area
may
contain
more
counties
than
the
PM2.5
nonattainment
area
or
vice
versa.
Finally,
VOC
and
NOx
regional
emissions
analyses
and
budgets
for
8­
hour
ozone
and
PM2.5
areas
will
most
likely
be
developed
using
different
meteorological
conditions
and,
in
some
areas,
different
travel
patterns.
For
example,
because
in
most
areas,
ozone
is
a
summertime
pollutant,
NOx
and
VOC
regional
emissions
and
budgets
in
8­
hour
ozone
areas
would
be
calculated
using
meteorological
and
travel
data
for
a
"
typical"
summer
day.
In
contrast,
NOx
and
VOC
regional
emissions
and
budgets
for
PM2.5
areas
may
be
established
using
annual
averages
for
meteorological
and
traffic
conditions,
rather
than
conditions
for
only
a
particular
season,
because
most
PM2.5
nonattainment
areas
are
violating
the
annual
PM2.5
standard
instead
of
the
24­
hour
standard.

Comment:
One
commenter
stated
that
there
was
an
error
in
the
proposed
option
1
language
in
§
93.102(
b)(
iv)
of
the
November
2003
rulemaking.
Specifically,
the
commenter
suggested
that
the
proposed
language
appeared
to
require
conformity
determinations
for
NOx
and
VOCs
if
a
submitted
SIP
does
not
contain
emissions
budgets
for
NOx
and
VOCs.

Response:
EPA
disagrees;
the
language
as
proposed
for
NOx
and
VOCs
is
correct
and
we
are
retaining
that
language
for
NOx
in
this
final
rule.
We
believe
that
the
commenter
misunderstood
the
proposal.
The
language
in
§
93.102(
b)(
iv)
that
is
finalized
today
requires
that
conformity
determinations
be
made
for
NOx
unless:
1)
during
the
period
before
a
SIP
is
submitted
and
budgets
are
found
adequate
or
approved
the
state
air
agency
and
EPA
regional
Page
17
office
make
a
finding
that
on­
road
emissions
of
NOx
are
not
significant
contributors
to
an
area's
air
quality
problem;
and/
or
2)
the
area's
SIP
does
not
establish
an
emissions
budget
for
onroad
emissions
of
NOx.
In
other
words,
if
the
SIP
includes
an
adequate
or
approved
emissions
budget
for
NOx,
then
NOx
must
be
analyzed
in
conformity
determinations
in
PM2.5
nonattainment
areas.
In
contrast,
if
the
SIP
does
not
contain
a
budget
for
NOx
and
instead
concludes
that
emissions
of
NOx
could
rise
to
any
level
without
impairing
reasonable
further
progress
or
attainment,
EPA
would
make
an
insignificance
finding,
either
through
a
motor
vehicle
emissions
budget
adequacy
finding
or
through
a
SIP
approval,
and
NOx
would
not
have
to
be
considered
for
conformity
purposes.
Page
18
Modeling
Concerns
Comment:
Several
commenters
expressed
concerns
about
generating
estimates
for
PM2.5
precursors.
One
commenter
stated
that
few
areas
have
experience
using
MOBILE6
to
evaluate
PM2.5
emissions
and
that
unexpected
issues
and
problems
will
arise
from
the
use
of
MOBILE6.
The
commenter
believed
that
difficulties
will
come
from
both
model
shortcomings
and
inexperience
of
the
users.
Another
commenter
had
concerns
about
relying
on
a
future
release
of
MOBILE6.2
or
other
future
guidance
for
estimating
precursor
emissions.
A
third
commenter
stated
that
there
is
a
need
for
guidance
on
analysis
techniques
for
ammonia
and
SOx.

Response:
Since
the
conformity
proposal
to
this
final
rule
was
published
in
November
2003,
EPA
has
released
MOBILE6.2.
MOBILE6.2
is
based
on
the
latest
available
information
concerning
vehicle
emissions
and
is
therefore
the
best
available
tool
at
this
time
for
calculating
on­
road
emissions
of
PM2.5
precursors
(
in
all
states
except
California).
The
Federal
Register
notice
announcing
the
release
of
the
model
was
published
on
May
19,
2004
(
69
FR
28830).
EPA
released
SIP
and
conformity
policy
guidance
on
the
use
of
MOBILE6.2
on
February
24,
2004,
entitled,
"
Policy
Guidance
on
the
Use
of
MOBILE6.2
and
the
December
2003
AP­
42
Method
for
Re­
Entrained
Road
Dust
for
SIP
Development
and
Transportation
Conformity."
EPA
released
technical
guidance
on
the
use
of
the
MOBILE6.2
model
in
August
2004.
Information
on
training
in
the
use
of
MOBILE6.2,
related
policy
memoranda
and
the
technical
guidance
in
the
use
of
the
model
are
available
on
EPA's
MOBILE
website
at
http://
www.
epa.
gov/
otaq/
m6.
htm.
EPA
understands
the
concerns
that
these
commenters
have
expressed
about
estimating
precursors.
However,
we
believe
there
is
adequate
time
for
new
areas
to
gain
MOBILE
experience
and
conduct
conformity
analyses
for
the
PM2.5
standard
before
the
end
of
the
one­
year
conformity
grace
period.
We
believe
that
the
material
described
above
contains
sufficient
information
for
the
states
that
use
MOBILE
to
conduct
modeling
of
on­
road
emissions
of
ammonia
and
SOx.
Therefore,
we
believe
that
additional
guidance
or
analytical
techniques
for
estimating
these
precursors
is
unnecessary.
EPA
recognizes,
however,
that
California
needs
to
complete
the
development
of
a
methodology
for
estimating
onroad
emissions
of
ammonia
before
ammonia
would
be
included
in
conformity
determinations
in
California,
as
discussed
further
in
Section
III.
A.
of
this
final
rule.
9USEPA,
2003.
Air
Quality
Criteria
for
Particulate
Matter
(
Fourth
External
Review
Draft).
EPA/
600/
P­
99/
002aD
and
bD.
U.
S.
Environmental
Protection
Agency,
Office
of
Research
and
Development,
National
Center
For
Environmental
Assessment,
Research
Triangle
Park
Office,
Research
Triangle
Park,
NC.
June
2003.
Available
electronically
at
http://
cfpub.
epa.
gov/
ncea/
cfm/
partmatt.
cfm.

10
North
American
Research
Strategy
for
Tropospheric
Ozone
(
NARSTO)
and
Particulate
Matter,
Particulate
Matter
Science
for
Policy
Makers
 
A
NARSTO
Assessment,
Parts
1
and
2.
NARSTO
Management
Office
(
Envair),
Pasco,
Washington.
February
2003.

Page
19
State
of
the
Science
Comment:
Two
commenters
expressed
concern
about
the
current
understanding
of
the
formation
of
secondary
particles.
One
commenter
stated
that
the
role
of
ammonia
needs
to
be
evaluated
quickly
so
that
states
can
have
all
information
possible
while
they
plan
to
attain
the
PM2.5
standard.
The
other
commenter
stated
that
there
is
a
lack
of
understanding
about
the
formation
of
secondary
particles.
This
commenter
believed
that
unnecessary
analysis
of
potential
PM2.5
precursors
would
be
time
consuming
and
overly
burdensome
without
producing
substantial
air
quality
benefits.

Response:
EPA
acknowledges
that
our
understanding
of
the
formation
of
secondary
particles
is
not
complete.
However,
EPA
believes
that
this
final
rule
strikes
an
appropriate
balance
between
preserving
limited
state
and
local
resources
and
environmental
protection.
Our
incomplete
understanding
of
the
role
of
VOCs
and
ammonia
in
the
formation
of
secondary
particles
is
one
of
the
reasons
that
we
determined
that
PM2.5
nonattainment
areas
should
not
be
required
to
address
those
precursors
in
conformity
determinations
before
SIP
budgets
are
available
unless
a
significance
finding
is
made.
On
the
other
hand,
EPA
believes
that
there
is
clear
evidence
and
a
substantial
understanding
of
the
role
of
NOx
and
SOx
in
the
formation
of
secondary
particles.
Additional
information
on
the
role
of
each
of
the
precursors
can
be
found
in
the
US
EPA
Criteria
Document,
9
and
in
the
NARSTO
Fine
Particle
Assessment.
10
EPA
agrees
that
further
research
is
needed
on
the
role
of
ammonia
in
particle
formation
and
the
benefits
of
ammonia
control
measures.
Ongoing
research
is
expected
to
greatly
improve
our
understanding
of
ammonia
control
measures
as
well
as
our
Page
20
understanding
of
the
role
of
ammonia
in
aerosol
formation.
However,
as
states
and
EPA
develop
a
greater
understanding
over
the
coming
years
about
the
air
quality
effects
of
reducing
ammonia
emissions
in
specific
nonattainment
areas,
it
may
be
appropriate
for
ammonia
reduction
strategies
to
be
included
in
future
SIPs
and
it
may
be
appropriate
to
include
ammonia
in
future
conformity
determinations.
Page
21
Comment
Period
Comment:
One
commenter
requested
an
additional
comment
period
for
PM2.5­
related
requirements.

Response:
As
stated
in
the
July
1,
2004,
Federal
Register
notice,
EPA
determined
that
it
is
not
necessary
to
reopen
the
comment
period
on
the
proposed
options
for
addressing
PM2.5
precursors
in
conformity
determinations
(
69
FR
40032).
EPA
published
a
supplemental
proposal
on
PM2.5
hot­
spot
analyses
on
December
13,
2004,
providing
the
public
with
an
opportunity
to
comment
on
the
proposed
options
for
hot­
spot
analyses
(
69
FR
72140).
Additionally,
when
EPA
publishes
the
proposed
PM2.5
implementation
strategy
the
public
will
have
the
opportunity
to
comment
on
that
proposal
as
well.
EPA
concludes
that
the
comment
periods
for
these
rulemakings
has
provided
the
public
with
adequate
time
to
comment
on
additional
issues
related
to
PM2.5.