a
Update
Hourly
Temperature
and
Humidity
Averages
July
1,
2004
Background
EPA
has
previously
obtained
monthly
average
hourly
temperature
and
relative
humidity
data
for
all
counties
in
the
U.
S.
including
Puerto
Rico
and
the
Virgin
Islands
for
calendar
years
1999
through
2003
for
use
in
National
Emission
Inventory
(
NEI)
calculations
using
the
National
Mobile
Inventory
Model
(
NMIM).
Twenty
year
monthly
average
temperatures
by
hour
were
also
obtained
for
the
1981
through
2000
time
period.

Although
these
hourly
averages
are
sufficient
for
calculating
hourly
emission
rates,
some
calculations
require
accurate
minimum
and
maximum
daily
temperatures.
These
minimums
and
maximums
cannot
be
accurately
determined
from
the
hourly
averages,
since
the
daily
minimum
and
maximum
temperatures
and
humidity
values
do
not
always
occur
in
the
same
hours
of
the
day.
The
averaging
of
temperatures
by
hour
of
the
day
also
reduces
the
range
of
hourly
temperatures
used
for
the
monthly
averages.

Data
The
contractor
shall
use
the
hourly
temperature
and
dewpoint
data,
as
well
as
location
(
latitude
and
longitude),
for
all
1st
Order
weather
stations
across
the
United
States
from
the
National
Climatic
Data
Center
(
NCDC)
for
all
of
the
cities
across
the
U.
S.
(
including
Alaska,
Hawaii,
Puerto
Rico
and
the
Virgin
Islands).
Data
from
2nd
order
automated
weather
stations
may
also
be
used
for
the
more
recent,
shorter
analysis
periods.
For
consistency,
the
data
must
be
organized
as
it
was
in
the
previous
work.

If
necessary,
EPA
will
provide
the
summaries
of
the
data
that
were
produced
by
AIR
in
that
previous
work.

If
necessary,
EPA
will
provide
a
list
of
the
counties
used
in
the
1999
NEI
analysis,
including
Alaska,
Hawaii,
Puerto
Rico
and
the
Virgin
Islands.

Analysis
In
order
to
obtain
accurate
monthly
average
daily
minimum
and
maximum
temperature
and
humidity
values,
these
statistics
will
be
obtained
directly,
independent
of
the
hour
of
the
day.
The
monthly
average
daily
minimum
and
maximum
temperature
and
humidity
values
will
be
determined
for
every
month
for
calendar
years
1999
through
2003
separately
and
for
a
20
year
average.
If
data
from
all
20
years
is
not
available,
a
shorter
time
period
may
be
used.
Separate
averages
will
be
obtained
for
each
of
the
3,222
counties
in
the
1999
NEI
analysis,
including
Alaska,
Hawaii,
Puerto
Rico
and
the
Virgin
Islands.

Using
the
newly
calculated
monthly
average
daily
minimum
and
maximum
temperature
and
humidity
values,
each
of
the
monthly
average
hourly
temperature
and
humidity
values
(
calculated
in
the
previous
work
assignment)
shall
be
adjusted
so
that
the
maximum
and
minimum
hourly
temperatures
and
humidity
values
for
each
month
match
the
monthly
average
daily
minimum
and
maximum
temperature
and
humidity
values.
This
is
done
by
applying
the
ratio
of
the
temperature
span
of
the
maximum
and
minimum
values
in
the
hourly
averages
and
the
actual
monthly
average
daily
minimum
and
maximum
values.

T
=
MinT
+
(
t­
mint)*
[
(
MaxT­
MinT)/(
maxt­
mint)
]
b
H
=
MinH
+
(
h­
minh)*
[
(
MaxH­
MinH)/(
maxh­
minh)
]

Where
:

T
:
The
adjusted
monthly
average
temperature
for
an
hour
in
a
month.
t
:
The
average
temperature
for
an
hour
in
the
month.
MaxT
:
The
monthly
average
daily
maximum
temperature.
MinT
:
The
monthly
average
daily
minimum
temperature.
maxt
:
The
maximum
monthly
average
hourly
temperature.
mint
:
The
minimum
monthly
average
hourly
temperature.

H
:
The
adjusted
monthly
average
humidity
for
an
hour
in
a
month.
h
:
The
average
humidity
for
an
hour
in
the
month.
MaxH
:
The
monthly
average
daily
maximum
humidity.
MinH
:
The
monthly
average
daily
minimum
humidity.
maxh
:
The
maximum
monthly
average
hourly
humidity.
minh
:
The
minimum
monthly
average
hourly
humidity.

It
is
extremely
important
that
the
daily
minima
and
maxima
values
shall
be
based
on
the
hourly
measurements,
rather
than
the
absolute
daily
minimum
and
maximum
measurements.

Reporting
The
contractor
shall
provide
the
results
in
an
Microsoft
Excel
spreadsheet,
or
other
format
approved
by
EPA.
All
values
shall
include
at
least
one
decimal
place.
Separate
spreadsheets
may
be
used
for
each
calendar
year
and
for
the
multiple
year
averages.
