Ozone
and
Carbon
Monoxide
Design
Value
Calculations
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
Office
of
Air
Quality
Planning
and
Standards
Research
Triangle
Park,
North
Carolina
27711
June
18,
1990
MEMORANDUM
SUBJECT:
Ozone
and
Carbon
Monoxide
Design
Value
Calculations
FROM:
William
G.
Laxton,
Director
Technical
Support
Division
(
MD­
14)

TO:
See
Below
In
discussions
related
to
the
Clean
Air
Act
legislation,
design
values
for
ozone
and
carbon
monoxide
are
receiving
particular
attention.
Previously,
it
sufficed
to
designate
areas
as
either
attainment
or
nonattainment
but
now
areas
will
be
further
classified
into
different
categories
based
upon
the
magnitude
of
the
appropriate
design
value.
This
additional
classification
step
places
added
emphasis
on
the
need
to
accurately
determine
these
design
values.
The
classification
will
be
done
according
to
concentration
cutpoints,
and
on
a
schedule,
specified
in
the
legislation.

Obviously,
once
this
process
is
set
in
motion
we
will
be
working
very
closely
with
you
to
develop
these
design
values.
However,
I
thought
it
would
be
appropriate
to
reiterate
our
design
value
computation
procedures
in
advance
to
help
people
anticipate
the
types
of
data
review
questions
that
may
arise.
The
computation
procedures
stated
here
are
consistent
with
our
previous
methods.
There
are
differences
between
the
procedures
for
ozone
and
carbon
monoxide
because
the
National
Ambient
Air
Quality
Standard
(
NAAQS)
is
structured
in
terms
of
expected
exceedances
while
the
carbon
monoxide
NAAQS
uses
the
older
"
once
per
year"
format.
The
most
apparent
difference
is
that
the
CO
design
values
are
based
upon
2
years
of
data
while
design
values
for
ozone
use
3
years.
Another
difference
is
that
the
ozone
NAAQS
uses
the
daily
maximum
ozone
value
while
the
CO
NAAQS
considers
running
8­
hour
averages
so
that,
even
though
they
must
be
non­
overlapping,
it
is
possible
to
have
more
than
one
CO
exceedance
per
day.
Because
of
these
differences,
it
is
convenient
to
discuss
each
pollutant
separately.
With
respect
to
terminology,
you
may
hear
the
CO
design
value
approach
referred
to
as
"
the
highest
of
the
second
highs',
while
the
ozone
design
value
is
frequently
simplified
as
"
the
fourth
high
in
3
years."

One
point
to
remember
is
that
all
locations
within
an
area
have
to
meet
the
standard
(
NAAQS).
Therefore,
when
we
do
our
evaluations,
we
look
at
each
individual
site
to
make
sure
that
every
site
meets
the
standard.
A
separate
design
value
is
developed
for
each
site
that
does
not
meet
the
NAAQS,
and
the
highest
of
these
design
values
is
the
design
value
for
the
area.

Page
2
Carbon
Monoxide
CO
design
values
are
discussed
in
terms
of
the
8­
hour
CO
NAAQS,
rather
that
the
1­
hour
NAAQS,
because
the
8­
hour
NAAQS
is
typically
the
standard
of
concern.
However,
a
1­
hour
design
value
would
be
computed
in
the
same
manner.
For
8­
hour
CO,
we
simply
look
at
the
maximum
and
second
maximum
(
non­
overlapping)
8­
hour
values
at
a
site
for
the
most
recent
2
years
of
data.
These
values
may
be
readily
found
on
an
AIRS
AMP450,
"
Quick
Look",
printout.
Then
we
choose
the
highest
of
the
second
highs
and
use
this
as
our
design
value
for
that
site.
We
then
look
at
all
design
values
within
an
area
and
the
highest
of
these
serves
as
the
design
value
for
the
area.
Note
that,
for
each
site,
individual
years
of
CO
data
are
considered
separately
to
determine
the
second
maximum
for
each
year
­
CO
data
are
not
combined
from
different
years.
It
is
probably
worth
commenting
on
this.
The
CO
NAAQS
requires
that
not
more
than
one
8­
hour
average
per
year
can
exceed
9
ppm
(
greater
than
or
equal
to
9.5
ppm
to
adjust
for
rounding).
We
evaluate
attainment
over
a
2­
year
period.
If
an
area
has
a
design
value
greater
that
9
ppm,
it
means
there
was
a
monitoring
site
where
the
second
highest
(
non­
overlapping)
8­
hour
average
was
greater
that
9
ppm
in
at
least
1
year.
Therefore,
there
were
at
least
two
values
above
the
standard
during
1
year
at
that
site
and
thus
the
standard
was
not
met.

Hypothetical
Case
(
two
CO
sites
in
an
area)

(
8­
Hour
Averages)
MAX
2nd
High
SITE
1
1987
14.6
8.9
1988
13.9
10.9
10.9
is
the
Design
Value
for
Site
1
(
8­
Hour
Averages)
MAX
2nd
High
SITE
2
1987
12.2
11.1
1988
10.8
10.4
11.1
is
the
Design
Value
for
Site
2
11.1
ppm
would
be
the
design
value
for
the
area.

Ozone
The
form
of
the
ozone
NAAQS
requires
the
use
of
a
3­
year
period
to
determine
the
average
number
of
exceedances
per
year.
In
its
simplest
form,
the
ozone
standard
requires
that
the
average
number
of
exceedances
over
a
3­
year
period,
cannot
be
greater
than
1.0.
An
area
with
four
exceedances
during
a
3­
year
period,
therefore,
does
not
meet
the
ozone
standard
because
four
exceedances
in
3
years
averages
out
to
more
than
once
per
year.
Now,
if
the
fourth
highest
value
was
equal
to
the
level
of
the
ozone
standard,
i.
e.
0.12
ppm,
then
the
area
would
have
no
more
than
three
exceedances
during
the
3­
year
period
and
the
average
number
of
exceedances
per
year
would
not
be
greater
3
Page
3
than
one.
This
assumes
no
missing
data
and
is
how
the
fourth
high
value
in
3­
years
came
to
be
used
as
the
design
value.
Actually,
an
adjustment
is
specified
in
the
ozone
NAAQS
to
account
for
missing
data
in
determining
the
expected
exceedances
for
ozone.
Because
of
considerations
associated
with
control
strategy
modeling,
the
following
basic
approach
for
ozone
design
values
has
been
in
use
since
1981.
If
there
are
3
complete
years
of
ozone
data,
then
the
fourth
highest
daily
maximum
during
the
3­
year
period
is
the
data,
then
the
fourth
highest
daily
maximum
during
the
3­
year
period
is
the
design
value
for
that
site.
If
only
2
complete
years
of
data
are
available,
then
the
third
highest
is
used
and,
if
only
one
complete
year
is
available,
then
the
second
highest
is
used.
In
this
approach,
a
year
of
ozone
data
is
considered
complete
if
valid
daily
maximums
are
available
for
at
least
75
percent
of
the
ozone
season.
Note
that
because
of
the
form
of
the
ozone
NAAQS,
data
are
combined
over
multiple
years
but
they
are
not
combined
from
different
sites.

Hypothetical
Case
(
two
O3
sites
in
an
area,
each
year
at
least
75%
complete)

FOUR
HIGHEST
DAILY
MAXIMUM
VALUES
Max
2nd
Hi
3rd
Hi
4th
Hi
SITE
1
1986
.127
.123
.122
.110
1987
.129
.124
.121
.116
1988
.142
.136
.134
.115
The
design
value
for
Site
1
is
0.129
ppm,
the
fourth
highest
daily
maximum
value
during
the
three
year
period.

FOUR
HIGHEST
DAILY
MAXIMUM
VALUES
Max
2nd
Hi
3rd
Hi
4th
Hi
SITE
2
1986
.110
.100
.095
.090
1987
.110
.100
.095
.090
1988
.180
.175
.160
.110
The
design
value
for
Site
2
is
0.110,
the
fourth
highest
value
during
the
three
year
period.

0.129
ppm
would
be
the
design
value
for
the
area.

There
are
a
few
additional
comments
warranted
on
the
ozone
example.
First,
note
that
data
from
each
site
was
treated
independently
in
computing
the
design
value
for
that
site.
Assuming
no
missing
data,
the
second
site
would
meet
the
ozone
NAAQS
but
the
area
would
not
because
the
other
site
shows
that
the
NAAQS
is
not
being
met.
Also,
it
should
be
noted
that
the
high
Page
4
values
for
a
year
are
considered
even
if
the
data
for
that
year
did
not
satisfy
the
75
percent
data
completeness
criterion.
For
example,
if
a
site
had
2
years
of
data
that
met
the
75
percent
data
completeness
requirement
and
1
year
that
did
not,
then
the
third
highest
value
during
the
3­
year
period
would
be
the
design
value
because
there
were
only
2
complete
years
of
data
but
the
data
from
all
3
years
would
be
considered
when
determining
the
third
highest
value.
This
ensures
that
valid
high
ozone
measurements
in
a
particular
year
are
not
ignored
simply
because
other
data
in
that
year
were
missing.
When
computing
data
completeness,
the
number
of
valid
days
can
be
increased
to
include
days
that
may
be
assumed
to
be
less
than
the
standard
level
as
stated
in
the
ozone
NAAQS.
Also,
for
new
sites
that
have
just
come
on
line,
the
75
percent
data
completeness
requirement
for
the
start­
up
year
may
be
applied
beginning
with
the
first
day
of
actual
monitoring
as
long
as
the
data
set
is
at
least
75
percent
complete
for
June
through
August.

A
final
practical
complication
that
must
be
addressed
in
determining
ozone
design
values
is
the
case
where
a
site
reports
data
but
has
no
year
that
meets
the
75
percent
data
completeness
requirement.
Admittedly,
this
is
an
unusual
situation
but,
for
the
sake
of
completeness,
it
needs
to
be
addressed.
At
the
same
time,
however,
the
reason
for
this
consistent
data
completeness
problem
should
be
examined
because
ozone
monitoring
data
completeness
is
typically
greater
that
90
percent.
In
general,
if
a
site
has
no
complete
years
of
data
and
fewer
than
90
days
of
data
during
the
3­
year
period,
the
design
value
will
be
determined
on
a
case
by
case
basis.
In
such
cases,
the
data
base
is
so
sparse
that
it
would
be
extremely
difficult
to
describe
general
rules
that
would
apply
and
a
careful
evaluation
would
have
to
be
made
to
determine
why
this
situation
occurred
and
what
is
the
most
appropriate
way
to
use
the
data.
For
a
site
without
a
single
complete
year
of
data
but
at
least
90
days
of
data
during
the
3­
year
period,
the
following
steps
are
followed
in
determining
the
ozone
design
value:

1.
Divide
the
number
of
valid
daily
maximums
during
the
3­
year
period
by
the
required
number
of
monitoring
days
per
year.
As
noted
earlier,
the
number
of
valid
days
can
be
increased
by
including
the
number
of
days
that
may
be
assumed
to
be
less
than
the
standard
level
as
specified
in
the
ozone
NAAQS.

2.
Add
1.0
to
the
above
total
and
then
use
the
integer
portion
of
the
result
as
the
rank
of
the
design
value.

These
steps
are
not
as
complicated
as
they
may
initially
appear.
For
example,
suppose
a
site
with
a
required
ozone
monitoring
season
of
214
days
each
year
reports
0,
121,
and
130
valid
days
of
ozone
data
during
the
3­
year
period.
Step
1
would
give
(
0+
121+
130)/
214=
1.17.
In
step
2,
1.0
is
added
to
this
total
giving
2.17.
The
integer
portion
of
2.17
is
2
and
so
the
design
value
is
the
second
highest
value
during
the
three
year
period.
Again,
this
type
of
situation
should
not
occur
that
often
and
the
reasons
for
the
data
completeness
problems
should
be
identified.

When
discussing
data
completeness
for
ozone,
it
is
important
to
recognize
that
monitoring
sites
are
occasionally
discontinued
for
valid
Page
5
practical
reasons.
In
such
cases,
if
data
are
available
from
another
site
that
is
representative
of
the
same
situation,
then
data
from
the
discontinued
site
may
be
superceded
by
data
from
the
other
site.
The
intent
is
to
ensure
that
a
single
year
of
data
from
a
monitor
that
was
discontinued
2
years
ago,
does
not
dictate
the
design
value
if
data
are
available
from
another,
equally
representative,
site.
This
is
not
intended
to
eliminate
the
missing
data
penalty
when
a
site
is
discontinued
and
there
is
no
data
available
from
a
similar
monitor.

I
have
not
discussed
certain
basic
data
handling
conventions,
such
as
computing
8­
hour
CO
averages
with
missing
data,
determining
the
non­
overlapping
second
maximum
8­
hour
average,
or
the
definition
of
a
valid
daily
maximum
1­
hour
ozone
daily
maximum.
All
of
these
conventions
have
been
in
place
since
the
1970'
s
and
are
routinely
incorporated
into
AIRS
outputs
so
I
have
not
bothered
to
discuss
these
points.

Addressees:
Director,
Environmental
Services
Division,
Regions
I­
VIII,
X
Director,
Office
of
Policy
and
Management,
Region
IX
Director,
Air
Management
Division,
Region
III
Director,
Air
and
Waste
Management
Division,
Region
II
Director,
Air,
Pesticides
and
Toxics
Management
Division,
Regions
I
and
IV
Director,
Air
and
Radiation
Division,
Region
V
Director,
Air,
Pesticides
and
Toxics
Division,
Region
VI
Director,
Air
and
Toxics
Division,
Regions
VII,
VIII,
IX,
and
X
cc:
J.
Calcagni
(
MD­
15)
R.
Campbell
(
MD­
10)
T.
Curran
(
MD­
14)
D.
DeVoe
(
ANR­
443)
J.
Farmer
(
MD­
13)
T.
Helms
(
MD­
15)
W.
Hunt
(
MD­
14)
S.
Meiburg
(
MD­
11)
R.
Ossias
(
LE­
132A)

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end
of
original
document
­­­­­­­­­­­­­­­­­
