Document ID: EPA-HQ-OAR-2003-0049-0297
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2004-09-02T04:00Z

Mr.
Leonard
Seitz
1500
7th
St.,
Apt
12J
Sacramento,
CA
95814
Dear
Mr.
Seitz:

At
the
conformity
training
session
in
held
on
August
4­
5,
2004
in
Oakland,
CA,
you
asked
about
the
Environmental
Protection
Agency's
(
EPA's)
response
to
the
comment
you
submitted
on
the
proposed
new
standards
conformity
rule.
We
have
checked
our
response
to
comments
document,
and
it
appears
that
our
response
to
your
comment
was
not
included.
However,
we
are
responding
to
you
with
this
letter
and
will
add
the
letter
to
the
docket
as
our
response
to
your
comment.

We
agree
that
actual
ozone
concentrations
in
an
area
depend
on
many
factors
including
meteorology,
time
and
location
of
emissions,
speciation
of
emissions,
and
total
emissions
from
all
sources,
including
stationary,
area,
on­
road
mobile,
off­
road
and
biogenic.
Air
quality
analyses
done
for
the
development
of
state
implementation
plans
(
SIPs)
necessarily
includes
most
or
all
of
these
factors,
depending
on
availability
of
data
and
the
demands
of
the
air
quality
models
used.
Including
emissions
from
all
these
types
of
sources
in
regional
emissions
analyses
done
for
transportation
conformity,
however,
would
confound
the
purpose
of
transportation
conformity,
which
is
to
ensure
that
transportation
plans
and
transportation
improvement
programs
conform
to
the
purpose
of
the
SIP.
In
other
words,
in
transportation
conformity,
only
on­
road
motor
vehicle
emissions
are
estimated
because
the
Clean
Air
Act
specifically
requires
that
the
air
quality
impacts
of
transportation
activities
alone
be
considered
by
transportation
agencies.
It
would
be
difficult
to
determine
whether
changes
in
future
emissions
were
the
result
of
changes
in
the
transportation
plan
or
in
the
emissions
of
other
sources
if
grid­
based
photochemical
modeling
were
to
be
used
in
the
regional
emissions
analysis
done
for
transportation
conformity.

EPA
does
not
agree
with
the
assertion
that
the
regional
emissions
analysis
gives
a
false
sense
that
concentrations
are
proportional
to
emissions
or
to
vehicle
miles
traveled
(
VMT).
In
a
regional
emissions
analysis,
concentrations
are
not
examined,
only
the
overall
emissions
produced
from
the
transportation
sector.
Hot
starts,
cold
starts,
soak
times,
average
speeds,
climate
conditions
such
as
temperature
and
humidity
and
many
other
factors
that
affect
on­
road
mobile
source
emissions
are
all
taken
into
account
in
the
modeling
process
that
produces
the
motor
vehicle
budget
and
the
projected
regional
motor
vehicle
emissions
that
are
compared
to
the
budget.
Changes
in
these
factors
and
in
VMT
are
going
to
have
the
greatest
impact
on
motor
vehicle
emissions
as
they
affect
regional
air
quality.

Finally,
EPA
does
not
believe
that
basing
conformity
determinations
on
grid­
based
photochemical
modeling
is
feasible.
While
such
an
air
quality
analysis
is
necessary
for
producing
an
attainment
SIP,
it
is
also
very
resource
intensive.
States
have
three
years
after
designation
in
which
to
produce
their
attainment
SIP,
and
for
many
states
a
substantial
portion
of
that
time
will
be
spent
developing
all
the
data
needed
for
the
air
quality
analysis
and
analyzing
the
results.
Attainment
SIPs
are
done
relatively
infrequently.
On
the
other
hand,
transportation
conformity
determinations
occur
regularly,
at
least
every
three
years.
Each
transportation
conformity
analysis
also
examines
multiple
analysis
years,
which
would
be
especially
complex
if
photochemical
grid­
based
air
quality
analyses
were
required.

Many
areas
use
photochemical
modeling
when
they
calculate
what
emission
reductions
are
needed
to
attain
the
air
quality
standard.
However,
the
transportation
sector
needs
to
know
what
level
of
emissions
can
be
permitted
and
an
emissions
budget
is
the
best
way
to
establish
this
level.
Modeling
done
for
conformity
analyses
does
not
allow
for
detailed
spatial
or
temporal
control
strategies,
but
it
does
allow
for
the
estimation
of
the
emissions
impact
of
control
strategies
that
can
be
applied
consistently
across
a
nonattainment
area
in
a
predictable
manner.
Transportation
planners
need
a
clear
test
for
determining
whether
their
planned
transportation
activities
conform,
to
be
able
to
meet
both
the
transportation
and
the
air
quality
needs
of
an
area.
EPA
believes
the
budget
test
serves
this
goal.
As
we
outlined
in
a
proposed
rule
on
July
9,
1996,
EPA
believes
that
consistency
with
motor
vehicle
emissions
budgets
in
SIPs
satisfies
Clean
Air
Act
requirements.
Specifically,
EPA
believes
consistency
with
budgets
established
in
an
attainment
demonstration
or
maintenance
plan
ensures
that
existing
violations
will
not
be
worsened
because
these
budgets
represent
levels
that
are
consistent
with
attainment
of
the
standards
(
61
FR
36115).

EPA
does
not
agree
with
the
idea
that
the
regional
emissions
analysis
done
for
conformity
determinations
is
an
inherently
inferior
analysis.
While
it
is
less
detailed
than
a
photochemical
air
quality
analysis,
EPA
believes
that
requiring
areas
to
estimate
the
total
emissions
from
motor
vehicles
in
the
regional
emissions
analysis
is
appropriate
for
the
reasons
given
above:
it
allows
isolation
of
the
on­
road
motor
vehicle
emissions
into
a
budget
for
control
purposes;
it
addresses
the
factors
that
have
the
most
affect
on
motor
vehicle
emissions;
it
is
less
resource
intensive
and,
therefore,
a
more
practical
approach
to
an
analysis
that
must
be
done
relatively
frequently;
and
it
meets
the
requirements
of
the
Clean
Air
Act.

Thank
you
for
your
interest
in
this
issue.
If
you
have
other
questions,
please
feel
free
to
contact
me
at
kapichak.
rudolph@
epa.
gov
or
Joe
Pedelty
at
pedelty.
joe@
epa.
gov.

Sincerely
yours,

Rudolph
Kapichak
Conformity
Team
Leader
State
Measures
and
Conformity
Group