MEMORANDUM
FROM:
Patrick
Dolwick,
Physical
Scientist
TO:
CAIR
Reconsideration
Docket
(
OAR­
2003­
0053)

RE:
Impacts
of
a
Discrepancy
in
the
Analysis
Assessing
Significance
of
Upwind
State
Ozone
Contributions
EPA
has
uncovered
a
small
discrepancy
in
the
final
rule's
technical
analysis
for
assessing
significance
of
upwind
states'
contribution
to
downwind
states'
ozone
nonattainment.
This
discrepancy
does
not
affect
the
ultimate
conclusions
as
to
which
States
should
be
included
in
the
CAIR
ozone
control
region.

As
explained
in
the
support
documentation
for
the
rule1,
EPA
used
an
air
quality
model
to
calculate
specific
metrics
to
determine
how
individual
States
affected
projected
residual
8­
hour
ozone
nonattainment
areas.
Various
criteria
were
established
to
determine
if
these
impacts
were
significant
from
an
air
quality
perspective
based
on
the
magnitude,
frequency,
and
relative
contribution
of
the
impacts.
See
generally
70
FR
at
25191­
192.
One
of
metrics
used
to
consider
the
relative
contribution
was
the
average
percent
contribution
to
nonattainment
from
source
apportionment
modeling.
This
metric
was
one
of
several
metrics
in
the
initial
screening
test.
Values
of
the
average
percent
contribution
metric
that
were
less
than
1%
(
after
rounding
to
the
nearest
integer)
were
determined
not
to
be
significant
and
were
dropped
from
further
evaluation.
For
the
final
CAIR
modeling,
values
of
this
metric
were
calculated
to
one
place
to
the
right
of
the
decimal,
after
rounding.
EPA
then
rounded
these
data
to
the
nearest
integer.
The
net
effect
was
an
inappropriate
"
double
rounding"
for
values
that
were
between
0.450
and
0.499
percent2.

EPA
has
recalculated
the
values
for
the
average
percent
contribution
metric
without
the
inappropriate
double
rounding.
Twenty
upwind
State­
to­
downwind
nonattainment
area
linkages
had
average
percent
contribution
values
between
0.450
and
0.499
percent
that
were
erroneously
rounded
to
1%
(
rather
than
0%).
Of
these
twenty
linkages,
19
did
not
pass
other
screening
criteria,
so
the
linkages
were
correctly
categorized
as
not
significant
despite
the
"
double
rounding"
in
the
calculation
of
the
average
percent
contribution
metric.
The
remaining
linkage
(
Mississippi's
contribution
to
Fulton
Co.,
GA)
did
pass
the
other
screening
tests,
but
was
subsequently
determined
via
other
criteria
not
to
be
significant
based
on
EPA's
evaluation
of
all
of
the
contribution
metrics.
The
table
presented
below
summarizes
the
significance
assessment
for
these
20
linkages.

1
U.
S.
Environmental
Protection
Agency:
Technical
Support
Document
for
the
Final
Clean
Air
Interstate
Rule
 
Air
Quality
Modeling,
EPA
Docket
#
2003­
0053,
March
2005,
Research
Triangle
Park,
NC,
27711,
pp
26­
40.
2
The
"
double
rounding"
of
the
average
percent
contribution
metric
did
not
occur
in
the
calculations
performed
as
part
of
the
ozone
significant
contribution
analysis
in
the
CAIR
proposal.
While
the
"
double
counting"
discrepancy
did
not
ultimately
affect
the
significance
of
any
individual
State­
receptor
linkage,
EPA
does
plan
to
correct
the
ozone
contribution
metrics
tables
in
Appendix
G
of
the
CAIR
Air
Quality
Modeling
Technical
Support
Document,
as
part
of
the
overall
CAIR
reconsideration
process.

Upwind
State
Projected
2010
Residual
Nonattainment
Area
Average
Percent
Contribution
(
2
digits)
Average
%
Contribution
(
correctly
rounded
to
nearest
integer)
Pass
All
Other
Screening
Tests?
Determined
to
be
Significant
in
CAIR
Final?
AR
Anne
Arundel
MD
0.45%
0%
NO
NO
AR
Sheboygan
WI
0.49%
0%
NO
NO
IA
Kent
RI
0.46%
0%
NO
NO
IA
Middlesex
CT
0.47%
0%
NO
NO
IN
Galveston
TX
0.47%
0%
NO
NO
KY
Hunterdon
NJ
0.48%
0%
NO
NO
MA
Middlesex
CT
0.46%
0%
NO
NO
MI
Sheboygan
WI
0.46%
0%
NO
NO
MO
New
Haven
CT
0.47%
0%
NO
NO
MO
Kent
RI
0.48%
0%
NO
NO
MO
Middlesex
CT
0.48%
0%
NO
NO
MO
Suffolk
NY
0.48%
0%
NO
NO
MS
Fulton
GA
0.49%
0%
YES
NO
MS
Macomb
MI
0.49%
0%
NO
NO
PA
Harris
TX
0.49%
0%
NO
NO
TN
Anne
Arundel
MD
0.47%
0%
NO
NO
TN
Arlington
VA
0.47%
0%
NO
NO
WI
Middlesex
CT
0.47%
0%
NO
NO
WI
Arlington
VA
0.49%
0%
NO
NO
WV
Galveston
TX
0.46%
0%
NO
NO
Note:
In
the
"
Pass
all
other
screening
tests"
column,
a
"
no"
means
that
the
upwind
State
to
downwind
nonattainment
linkage
is
not
significant
based
on
the
initial
screening
test.
"
Yes"
means
that
the
linkage
was
evaluated
further
using
all
the
metrics
to
determine
whether
or
not
the
linkage
was
significant.
