Enclosure
2­
1
Enclosure
2
State
of
California
Information
to
Support
Recommendations
for
Federal
PM2.5
Nonattainment
Area
Boundaries
This
document
discusses
our
rationale
for
the
recommended
boundaries
for
each
of
the
four
preliminary
fine
particulate
matter
(
PM2.5)
nonattainment
areas
in
California.
The
U.
S.
Environmental
Protection
Agency's
(
U.
S.
EPA)
guidance
memorandum
(
April
1,
2003,
Designations
for
the
Fine
Particle
National
Ambient
Air
Quality
Standards,
Memorandum
from
Jeffrey
R.
Holmstead,
Assistant
Administrator,
Office
of
Air
and
Radiation
to
Regional
Administrators,
Regions
I­
X)
sets
out
criteria
for
determining
appropriate
nonattainment
area
boundaries.
In
short,
the
memorandum
indicates
that
nonattainment
areas
must
be
large
enough
to
capture
the
entire
area
violating
the
standard
as
well
as
sources
contributing
to
violations.

The
guidance
goes
on
to
describe
the
association
of
higher
PM2.5
levels
with
greater
levels
of
urban
activity
and
states
that
the
presumptive
boundaries
for
urbanized
areas
violating
the
PM2.5
standards
is
the
Metropolitan
Statistical
Area
(
or
Consolidated
Metropolitan
Statistical
Area
where
appropriate.)
U.
S.
EPA's
guidance
also
suggests
consideration
of
eight­
hour
nonattainment
boundaries
to
support
coordination
of
control
strategies
for
ozone
and
PM2.5.
For
U.
S.
EPA
to
consider
an
alternative
boundary,
the
memorandum
calls
on
states
to
evaluate
the
following
criteria
to
support
its
recommendations
for
the
geographic
extent
of
a
nonattainment
area.

 
Emissions
 
Air
quality
 
Population
density
 
Traffic
and
commuting
patterns
 
Expected
growth
 
Meteorology
 
Geography/
topography
 
Jurisdictional
boundaries
 
Level
of
emission
control
In
California,
the
primary
considerations
for
air
quality
planning
are
air
basin
and
air
district
boundaries
if
the
pollution
problem
is
regional
in
nature.
Under
State
law,
air
basins
are
based
on
a
rigorous
scientific
assessment
of
geography
and
meteorology,
with
consideration
of
political
jurisdictions.
Basin
boundaries
are
formally
adopted
by
ARB
in
regulation.
Air
districts
were
established
by
State
statute.
ARB
typically
uses
a
combination
of
air
basin
and
air
district
lines
to
set
boundaries
for
areas
that
violate
California
air
quality
standards,
with
exceptions
when
a
single
city
or
community
has
a
unique
air
pollution
problem
distinct
from
the
region.

We
evaluated
the
specific
criteria
in
U.
S.
EPA
guidance,
as
well
as
State
conventions,
to
identify
the
most
appropriate
and
effective
boundary
for
each
PM2.5
nonattainment
area.
We
recommend
the
air
basin
boundaries
for
South
Coast,
San
Joaquin
Valley,
and
San
Diego
to
reflect
the
regional
nature
of
PM2.5
pollution
in
these
areas.
We
Enclosure
2­
2
recommend
a
focused
nonttainment
area
for
the
City
of
Calexico
to
reflect
the
localized
nature
of
the
PM2.5
problem
there.

South
Coast
Air
Basin
The
federal
PM2.5
standards
are
exceeded
broadly
across
the
basin.
Consideration
of
U.
S.
EPA's
factors,
especially
population
and
emission
densities
within
the
basin,
which
indicate
broad
regional
contribution
to
elevated
PM2.5
levels,
support
use
of
the
air
basin
boundary.

The
recommended
South
Coast
Air
Basin
PM2.5
nonattainment
area
includes
Western
Los
Angeles
(
including
Catalina
and
San
Clemente
Islands),
Orange,
Southwestern
San
Bernardino,
and
Western
Riverside
Counties.
This
area
is
under
the
jurisdiction
of
the
South
Coast
Air
Quality
Management
District.
The
recommended
boundary
corresponds
to
the
recently
modified
federal
one­
hour
ozone
nonattainment
boundary
and
the
proposed
eight­
hour
ozone
boundary.

San
Joaquin
Valley
Air
Basin
The
federal
PM2.5
standards
are
exceeded
broadly
across
the
basin.
Consideration
of
U.
S.
EPA's
factors,
especially
population
and
emission
densities
within
the
basin,
which
indicate
broad
regional
contribution
to
elevated
PM2.5
levels,
support
use
of
the
air
basin
boundary.

The
recommended
San
Joaquin
Valley
PM2.5
nonattainment
area
consists
of
San
Joaquin,
Stanislaus,
Merced,
Madera,
Fresno,
Kings,
Tulare
and
Western
Kern
Counties.
The
area
is
under
the
jurisdiction
of
the
San
Joaquin
Valley
Unified
Air
Pollution
Control
District.
The
recommended
boundary
for
this
area
coincides
with
the
existing
federal
one­
hour
ozone
nonattainment
boundary
and
ARB's
proposed
eighthour
ozone
boundary.

San
Diego
County
The
federal
annual
PM2.5
standard
is
exceeded
broadly
across
the
basin.
Consideration
of
U.
S.
EPA's
factors,
especially
population
and
emission
densities
within
the
basin,
which
indicate
broad
regional
contribution
to
elevated
PM2.5
levels,
support
use
of
the
County
boundary,
which
is
the
same
as
the
air
basin
boundary.

The
proposed
PM2.5
nonattainment
area
would
include
all
of
San
Diego
County,
under
the
jurisdiction
of
the
San
Diego
Air
Pollution
Control
District.
This
corresponds
to
the
existing
federal
one­
hour
ozone
maintenance
area
boundary
and
the
proposed
eighthour
ozone
boundary.
Enclosure
2­
3
City
of
Calexico
The
City
of
Calexico
is
on
the
U.
S­
Mexico
border,
at
the
southern
end
of
Imperial
County.
The
County
is
under
the
jurisdiction
of
the
Imperial
County
Air
Pollution
Control
District
and
is
part
of
the
Salton
Sea
Air
Basin
(
which
also
includes
a
portion
of
Riverside
County).
Imperial
County
is
generally
rural
with
relatively
small
incorporated
regions
­­
only
El
Centro
is
included
in
a
Metropolitan
Statistical
Area.

Imperial
County
is
a
federal
PM10
nonattainment
area,
with
peak
PM10
levels
occurring
in
Calexico
and
occasional
PM10
exceedances
elsewhere
in
the
County
(
exacerbated
by
transport
from
Mexico).
Within
Imperial
County,
Calexico
is
just
over
the
annual
PM2.5
standard
for
2000­
2002,
while
monitors
in
the
Brawley
and
El
Centro
record
levels
significantly
below
this
standard.
None
of
the
Imperial
County
monitors
have
recorded
violations
of
the
24­
hour
PM2.5
standards.
Data
from
the
portion
of
Riverside
County
in
the
basin
show
attainment
of
both
PM2.5
standards.

Based
on
the
available
information,
we
believe
that
violations
of
the
PM2.5
standard
are
localized
in
Calexico
and
the
much
larger
adjacent
city
of
Mexicali,
Mexico.
As
a
result,
the
federal
PM2.5
nonattainment
area
should
be
limited
to
the
part
of
this
urban
area
on
the
U.
S.
side
of
the
border
 
the
City
of
Calexico.

We
discuss
this
recommendation
in
the
context
of
U.
S.
EPA's
boundary
criteria
below,
specifically
the
basis
for
recommending
a
nonattainment
area
smaller
than
the
full
Imperial
County.
The
Calexico/
Mexicali
urban
area
is
easily
distinguished
from
the
rest
of
Imperial
County.
Since
current
emission
statistics
for
Mexicali
are
not
readily
available,
we
relied
on
a
1999
report
Program
to
Improve
Air
Quality
in
Mexicali
2000­
2005
that
was
developed
by
the
Mexican
government
and
posted
on
U.
S.
EPA's
website.
We
then
compared
data
for
the
appropriate
corresponding
year
in
Calexico
and
Imperial
County.

Population
Density
From
an
air
quality
perspective,
Calexico
and
Mexicali,
Mexico
form
one
urbanized
region
divided
by
an
international
border.
According
to
2000
U.
S.
Census
data,
Calexico's
population
is
approximately
27,000.
The
official
2000
Mexican
Census
placed
Mexicali's
population
at
760,000,
with
3
percent
annual
growth
expected.
In
2000,
the
entire
Imperial
County
population
was
142,000.
Considering
the
geographic
size
of
the
two
areas
as
well,
the
Mexicali
population
density
is
two
and
a
half
times
the
density
for
all
of
Imperial
County.

Air
Quality
We
calculate
that
the
high
PM10
site
in
Mexicali
exceeded
the
level
of
the
U.
S.
federal
PM10
standard
on
258
days
in
2001.
During
the
same
year
in
Imperial
County,
there
were
18
calculated
exceedances
at
the
Calexico
high
monitor,
zero
days
at
Brawley,
and
6­
7
days
at
El
Centro,
Niland,
and
Westmorland.

Chemical
mass
balance
speciated
data
indicate
Calexico
PM2.5
is
dominated
by
organic
carbon
particles.
They
are
a
significant
contributor
to
elevated
PM2.5
levels
throughout
the
year,
peaking
during
the
winter
months.
On
an
annual
basis,
these
Enclosure
2­
4
carbon
particles
make
up
approximately
60
percent
of
total
PM2.5
mass.
Organic
carbon
sources
in
urban
areas
include
burning,
cooking,
and
motor
vehicle
exhaust.
Geologic
material
(
dust)
is
a
smaller
portion
of
total
PM2.5
in
Calexico,
making
up
less
than
20
percent
of
total
PM2.5
mass
on
an
annual
average
basis.

Emissions
Calexico
(
and
Mexicali)
are
distinct
from
the
rest
of
Imperial
County
based
on
the
distribution
and
nature
of
emission
sources.
Imperial
County
is
largely
rural
with
widespread
agricultural
activity
and
the
associated
emissions
profile.
Urban
activities
and
their
associated
emissions
are
found
only
in
the
few
developed
areas:
Calexico
(
and
Mexicali),
El
Centro,
City
of
Imperial,
and
Brawley.
The
Mexicali
inventory
for
oxides
of
nitrogen
(
NOx)
is
about
30
percent
greater
than
all
of
Imperial
County's.
The
Mexicali
hydrocarbon
(
HC)
inventory
is
about
60
percent
greater
than
all
of
Imperial
County's.
Finally,
the
urban
Mexicali
direct
PM10
inventory
is
nearly
the
same
as
Imperial
County's.

Traffic
and
Commuting
Patterns
Calexico/
Mexicali
is
home
to
a
busy
U.
S.­
Mexico
border
crossing.
In
1996,
the
border
crossing
handled
almost
7
million
vehicles.
Mexicali
has
over
three
times
as
many
motor
vehicles
as
all
of
Imperial
County.

Level
of
Control
Imperial
County
has
motor
vehicle
emission
controls
that
are
consistent
with
the
rest
of
California.
Vehicles
must
meet
California
standards;
both
cars
and
heavy
trucks
are
subject
to
in­
use
inspection
programs.
The
Imperial
County
District
administers
a
smoke
management
program
for
open
burning,
consistent
with
the
ARB's
statewide
regulation.
Vehicles
in
Mexicali
are
typically
older
California
vehicles
and
there
is
no
in­
use
inspection
program.
Finally,
Mexicali
open
burning
is
widespread
and
uncontrolled.
This
is
particularly
significant
given
the
large
organic
fraction
found
in
Calexico
PM2.5.

The
table
below
summarizes
how
all
of
Imperial
County
compares
to
Mexicali.

Imperial
County/
Mexicali
Statistical
Comparison
Imperial
County
(
entire
county)
Mexicali
(
city
only)
2000­
Population
142,000
760,000
Population
Density*
20
inhabitants/
km
2
50
inhabitants/
km
2
2001­
days
of
PM10
over
150
ug/
m3
at
high
monitor
18
days
@
Calexico
Ethel
258
days
at
Mexicali
Progreso
1996
NOx
Emissions*
35
tons
per
day
51
tons
per
day
1996
HC
Emissions*
54
tons
per
day
140
tons
per
day
1996
PM10
Emissions*
220
tons
per
day
195
tons
per
day
Vehicle
Population*
71,000
241,000
*
Source:
Program
to
Improve
Air
Quality
in
Mexicali
2000­
2005
Based
on
all
of
these
factors,
ARB
staff
has
concluded
that
Calexico
exceedances
of
the
federal
PM2.5
standards
are
the
result
of
urban
activity
associated
with
the
densely
populated
international
Calexico/
Mexicali
border
region.
Within
Imperial
County,
the
level
of
urban
activity
is
unique
to
the
area
and
is
not
representative
of
the
air
quality
of
the
rest
of
Imperial
County
or
the
Salton
Sea
Air
Basin.
