Document ID: EPA-HQ-OAR-2007-0562-0436
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2009-11-13T05:00Z

Attachment 1

CALIFORNIA

Area Designations For the 

24-Hour Fine Particle National Ambient Air Quality Standard

Note:  As a basic introduction, the following is a summary table listing
ALL areas and counties proposed for nonattainment in the State.  The
technical analyses for each individual area then follow.  

The table below identifies the counties in California that EPA has
designated as not attaining the 2006 24-hour fine particle (PM2.5)
standard.  A county (or part thereof) is designated as nonattainment if
it has an air quality monitor that is violating the standard or if the
county is determined to be contributing to the violation of the
standard. 



Area 	California  Recommended Nonattainment Counties	EPA’s Final
Designated Nonattainment Counties

Butte County	Butte County - Partial	Butte County - Partial

Imperial County	Imperial County - Partial	Imperial County- Partial

Sacramento County	Sacramento	Sacramento County

Yolo County - Partial

Placer County – Partial

El Dorado County – Partial

Solano County - Partial

San Francisco Bay Area	Sonoma County – Partial

Napa County

Marin County

San Francisco County

Contra Costa County

Alameda County

Santa Clara County

San Mateo County

Solano County - Partial	Sonoma County – Partial

Napa County

Marin County

San Francisco County

Contra Costa County

Alameda County

Santa Clara County

San Mateo County

Solano County - Partial

San Joaquin Valley Air Basin 	San Joaquin County

Stanislaus County

Merced County

Madera County

Fresno County

Kings County

Tulare County

Kern County - Partial

	San Joaquin County

Stanislaus County

Merced County

Madera County

Fresno County

Kings County

Tulare County

Kern County - Partial

South Coast Air Basin	Los Angeles County – Partial

San Bernardino County Partial

Riverside County – Partial

Orange County	Los Angeles County – Partial

San Bernardino County Partial

Riverside County – Partial

Orange County

Yuba County

Sutter County	Yuba County – Partial

Sutter County - Partial	Yuba County – Partial

Sutter County

EPA has designated the remaining counties in the state as
“attainment/unclassifiable.” EPA designated a county as
“unclassifiable” when:  one or more of its monitors recorded a
violation in 2004-2006; all monitors in the county with complete
2005-2007 data showed attainment; and one or more other monitors in the
county had 2005-2007 monitoring data that was not complete and could not
be used for determining compliance with the standard.

EPA Technical Analysis for Chico (Butte County 

Introduction

Pursuant to section 107(d) of the Clean Air Act, EPA must designate as
nonattainment those areas that violate the NAAQS and those nearby areas
that contribute to violations.  This technical analysis for Butte
identifies the counties with monitors that violate the 24-hour PM2.5
standard and evaluates nearby counties for contributions to fine
particle concentrations in the area.  EPA has evaluated these counties
based on the weight of evidence of the following nine factors
recommended in EPA guidance and any other relevant information:  

- pollutant emissions

- air quality data

- population density and degree of urbanization

- traffic and commuting patterns

- growth

- meteorology

- geography and topography

- jurisdictional boundaries

- level of control of emissions sources

Figure 1 is a map of the counties in the area and other relevant
information such as the locations and design values of air quality
monitors, the metropolitan area boundary, and counties recommended as
nonattainment by the State. Figure 2 shows the designated PM 2.5
nonattainment area within Butte County.

  SHAPE  \* MERGEFORMAT   

Figure 1

Figure 1.

 

Figure 2

The California Air Resources Board (CARB), sent a letter to EPA, dated
December 17, 2007 recommending that the City of Chico in Butte County be
designated as “nonattainment” for the 2006 24-hour PM2.5 standard
based on air quality data from 2004-2006.  These data are from Federal
Reference Method (FRM) monitors located in the state. 

In August 2008, EPA notified California of its intended designations. 
In this letter, EPA also requested that if California wished to provide
comments on EPA’s intended designation, it should do so by October 20,
2008.  EPA stated that it would consider any additional information
(e.g., on power plants or partial county areas) provided by the state in
making final decisions on the designations. 

Air quality monitoring data on the composition of fine particle mass are
available from the EPA Chemical Speciation Network and the IMPROVE
monitoring network, as well as from the Chico monitoring site.  Analysis
of these data indicates that the days with the highest fine particle
concentrations occur predominantly in the cold season, and the average
chemical composition of the highest days is characterized by high levels
of organic carbon (e.g., 75%). 

Based on EPA's technical analysis described below and currently
available information, EPA has designated a portion of Butte County as
nonattainment for the 24-hour PM2.5 air-quality standard.

Butte County Area 	California  Recommended Nonattainment Counties
EPA’s Final Designated Nonattainment Counties

Butte County	Butte County (partial)	Butte County (partial)

The following is a technical analysis for Butte County, California.   

Factor 1:  Emissions data

For this factor, EPA evaluated county level emission data for the
following PM2.5 components and precursor pollutants:  “PM2.5 emissions
total,” “PM2.5 emissions carbon,” “PM2.5 emissions other,”
“SO2,” “NOx,” “VOCs,” and “NH3.”  “PM2.5 emissions
total” represents direct emissions of PM2.5 and includes:   “PM2.5
emissions carbon,” “PM2.5 emissions other”, primary sulfate (SO4),
and primary nitrate.  (Although primary sulfate and primary nitrate,
which are emitted directly from stacks rather than forming in
atmospheric reactions with SO2 and NOx, are part of “PM2.5 emissions
total,” they are not shown on the template or data spreadsheet as
separate items).  “PM2.5 emissions carbon” represents the sum of
organic carbon (OC) and elemental carbon (EC) emissions, and “PM2.5
emissions other” represents other inorganic particles (crustal). 
Emissions of SO2 and NOx, which are precursors of the secondary PM2.5
components sulfate and nitrate, are also considered.  VOCs (volatile
organic compounds) and NH3 (ammonia) are also potential PM2.5 precursors
and are included for consideration. 

Emissions data were derived from the 2005 National Emissions Inventory
(NEI), version 1.   See
http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html.

EPA also considered the Contributing Emissions Score (CES) for each
county.  The CES is a metric that takes into consideration emissions
data, meteorological data, and air quality monitoring information to
provide a relative ranking of counties in and near an area.  Note that
this metric is not the exclusive manner for considering data for these
factors.  A summary of the CES is included in Attachment 2, and a more
detailed description can be found at
http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html#C. 

Table 1 shows emissions of PM2.5 and precursor pollutants components
(given in tons per year) and the CES for violating and potentially
contributing counties in the Butte County.  Counties are listed in
descending order by CES.

Table 1.  PM 2.5 24-hour Component Emissions, and CES.

County	State Recommended Nonattainment? 	CES	PM2.5 total

	SOx

	NOx

	Carbon

PM2.5

 	PM2.5

other

	VOCs

	NH3

Butte 	Yes (P)	100	2,974	2,115	8,486	1,513	1,461	9,754	1,757

Tehama 	No	19	1,443	2,087	3,936	823	620	4,150	782

Glenn  	No	14	1,851	1,347	3,882	833	1,017	4,392	2,139

P = partial

Additional data considered in EPA’s analysis of this factor are
summarized in the following table derived from the California Air
Resources Board Almanac of Emissions and Air Quality Data (  HYPERLINK
"http://www.arb.ca.gov/Aqd/almanac/almanac.htm" 
http://www.arb.ca.gov/Aqd/almanac/almanac.htm ).  The following table
further defines, in tons per day, the type of area sources contributing
to PM2.5 emissions in Butte County.  Area sources include residential
fuel combustion, farming operations, construction/demolition, paved road
dust, unpaved road dust, fugitive windblown dust, fires, managed burning
and disposal and cooking.  Area sources represent the dominant emission
source category for direct PM2.5 emissions in Butte County, with
approximately 70% of the total.  Based on Table 2, within the area
source category, residential wood burning is the dominant source of
PM2.5.  This is consistent with the speciation data discussed below.

Table 2. Area Source Emission (tons per day)

SOURCE	PM2.5

Residential Fuel Combustion	2.65

Farming Operations	0.82

Construction/Demolition	0.11

Paved Road Dust	0.53

Unpaved Road Dust	0.76

Fugitive Windblown Dust	0.04

Fires	0.01

Managed Burning & Disposal	1.4

Cooking	0.07

      Total Area Wide	6.4

Area Wide percent of total	68%

Total All	9.9

Source:  ARB Almanac website (2006)   HYPERLINK
"http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm" 
http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm  

Given the significance of NOx emissions in the formation of the PM2.5,
EPA also considered emissions provided in the CARB Recommendation letter
under this factor, along with the NOx data from NEI summarized in Table
1.  Table 3 summarizes NOx emissions from stationary, area, and mobile
source categories for 2006, 2010, and 2020. 

Table 3.  NOx Winter Emissions for Butte County (tons per day)

Source Category	2006	2010	2020

Stationary Sources	1.4	1.4	1.4

Area  Sources	1.7	1.7	1.7

Mobile Sources	23.3	19.9	11.3

Source: California Air Resources Board in their letter of December 17,
2007

The CES shown in Table 1 describes the relative contribution of
emissions from surrounding counties to the high emission days based on a
broad analysis of NOAA HYSPLIT trajectories linking county-wide
emissions from Butte and the surrounding counties and speciated air
monitoring data on high days.  The CES clearly demonstrates a connection
between pollution levels in Chico and sources throughout Butte County. 
The CES shows less of a link between PM2.5 levels in Chico and
neighboring Tehama and Glenn Counties.

Speciation data from the Chico air monitoring station was considered in
evaluating this factor, as a way to link emission sources to high PM2.5
levels.  As shown in the pie chart below (Figure 3), monitored PM2.5 in
Chico is 75% organic carbon, for which the major source is residential
wood burning. Since this source category is associated with population
density, this data supports including urbanized areas and their
surroundings within the nonattainment area.

In addition, 16% of the PM2.5 is ammonium nitrate, formed from precursor
NOx emissions.  Both Table 1 and 3 describe NOx emissions data for Butte
County; mobile sources are the dominant source of NOx emissions.  As
discussed below under Factor 4: Traffic and commuting patterns, most of
these emissions are along the roughly north-south State Route 99
corridor, with substantial additional contribution from commuting
between Chico and the more eastern cities of Paradise and Oroville.

 In light of the commuting patterns discussed under Factor 4 and
illustrated in Figure 3, and in light of the spatial scale of nitrate
formation, mobile source emissions in Butte County are contributing to
the PM2.5 exceedances measured in Chico.

Emission levels and CES values support designation of Butte County as a
24-hour PM2.5 nonattainment area.  However, it does not appear that the
surrounding counties are significantly contributing to the pollution
levels in Butte County. With respect to the CES values, Butte County has
the highest CES score of 100, followed distantly by Glenn and Tehama
Counties, at 14 and 19 respectively.  Glenn and Tehama Counties are
located west of Butte County, over 40 miles away.  These counties have
limited populations and no commuting pattern with Butte County. There is
no evidence that these counties contribute to the PM2.5 air quality
problems in Butte County .  We have eliminated these counties from
further consideration given these facts. 

Factor 2:  Air quality data 

This factor considers the 24-hour PM2.5 design values in micrograms per
cubic meter (µg/m3) for air quality monitors in Butte County based on
data for the 2004-2006 and 2005-2007 period.  A monitor’s design value
indicates whether that monitor attains a specified air quality standard.
The 24-hour PM2.5 standards are met when the 3-year average of a
monitor’s 98th percentile values are 35 µg/m3 or less.  A design
value is only valid if minimum data completeness criteria are met. 

The 24-hour PM2.5 design values for Butte County are shown in Table 2.  

Table 4.  Air Quality Data

County/ City	State Recommended Nonattainment

	24-hour PM2.5 Design Values

2004-06

(µg/m3)	24-hour PM2.5 Design Values

2005-07

(µg/m3)

Butte County, CA

City of Chico 	Yes 	56	55

	

The violating monitor for 2004–2006 and 2005-2007 is located in the
City of Chico in Butte County.  Therefore, Butte County is a candidate
for designation as a nonattainment area.  Tehama and Glenn counties have
no PM2.5 monitors , and consequently no data showing violations.  Given
the air quality data, including consideration of CES values, and the
State’s recommendations,  Tehama and Glenn Counties were not further
considered as nonattainment areas under this factor.  

EPA considered the chemical composition (speciation) of PM2.5 in
evaluating this factor.  As shown in the pie chart below (Figure 3), the
chemical makeup of PM2.5 in Chico is dominated by organic carbon, at 75%
of the total.  This reflects emissions from residential wood burning.
There is also a large ammonium nitrate contribution.  The highest
concentrations occur during the winter months (i.e., November through
February).  As discussed above, the carbon portion supports
nonattainment designation of at least the urban areas and their
surroundings, while the nitrate portion supports at least a large
proportion of the county.

Figure 3

In summary, the air quality factor supports nonattainment designation of
at least large portions of Butte County.  PM2.5 speciation data support
the idea that localized residential wood burning on stagnant winter
nights is what pushes the monitor into violation, but also support a
larger area that includes sources contributing to the ammonium nitrate
portion of violations.

Eligible monitors for providing design value data generally include
State and Local Air Monitoring Stations (SLAMS) at population-oriented
locations with an FRM.  All data from Special Purpose Monitors (SPM)
using an FRM is eligible for comparison to the relevant NAAQS, subject
to the requirements given in the October 17, 2006 Revision to Ambient
Air Monitoring Regulations (71 FR 61236).  All monitors used to provide
data must meet the monitor siting and eligibility requirements given in
71 FR 61236 to 61328 in order to be acceptable for comparison to the
24-hr PM2.5 NAAQS for designation purposes.

Factor 3: Population density and degree of urbanization (including
commercial development)

Population data are relevant in defining the boundaries of the PM2.5
nonattainment area given the correlation between population and the
emission sources contributing to PM2.5 exceedances (i.e., residential
wood burning and mobile sources), as well as the population exposed to
high PM2.5 levels. Table 6 shows the 2005 population for each county in
the area being evaluated, as well as the population density for each
county in that area.  Population data gives an indication of whether it
is likely that population-based emissions might contribute to violations
of the 24-hour PM2.5 standards. 

Table 6.  Population

County	State Recommended Nonattainment	2005 Population	2005 Population
Density 

(pop/sq mi)

Butte 	Yes (P)	214,153	128

	Tehama  	No	60,932	21

Glenn 	No	27,683	21

P= partial

According to Table 3, Butte County has the highest population and
population density.  Tehama County has the next highest population of
the adjacent counties, but significantly below Butte (also in terms of
population density).  Population centers in Butte County include Chico
(population of 59,444 per 2000 US Census), Paradise (population of 26408
per 2000 US Census) and Oroville (population of 13004 per 2000 US
Census). Tehama and Glenn County have the same population density of 21
people per square mile, which is extremely low, compared to Butte County
at 128.   Both Butte and Glenn counties experienced a 5% population
growth from 2000-2005, while Tehama County saw slightly higher growth at
8%. However, the small populations and moderate growth in Tehama and
Glenn counties further supports elimination of these counties from
consideration as nonattainment areas.  The presence of population
centers outside of Chico supports EPA’s recommendation to include
these other population centers in the nonattainment area.  Relatively
little population lives in the eastern high elevation portions of the
county.

Attachment 3 has a chart that shows the area, population, car traffic
and truck traffic for Butte County for the county as a whole, as well as
just for the nonattainment area.  The numbers clearly reflect that the
population and traffic numbers are very high, and that most of the
population and traffic is captured within the nonattainment area. 

Figure 4Factor 4: Traffic and commuting patterns 

This factor considers the number of commuters in each county who drive
to Butte County, the percent of total commuters in each county who
commute to Butte County, as well as the total Vehicle Miles Traveled
(VMT) for each county in millions of miles (see Table 5). A county with
numerous commuters is generally an integral part of an urban area and is
likely contributing to fine particle concentrations in the area.  Such
an area could be an appropriate county for implementing mobile source
emission control strategies, thus warranting inclusion in the
nonattainment area.

Table 5.  Traffic and Commuting Patterns

County	State Rec. NA	2005 VMT

(millions 	Number Commuting to any violating counties 

	Percent

Commuting to any violating counties 

	Number Commuting into statistical area 	Percent

Commuting into statistical area 

Butte County 	Yes (P)	2,078	74,510	91%	73,000	91%

Tehama County	No	599	1,170	6%]	1,140	6%

Glenn County 	No	330	1,770	17%	1,770	17%

P = partial

According to the data in Table 8, Butte County has a significantly
larger number of commuters commuting into the violating area, 75,510 or
92%. Butte County has a large number of commuters traveling to and from
Chico, the location of the violating monitor. There is also significant
traffic into and out of Chico from the Cities of Paradise (on Highway
91) and to Oroville (on Highway 149).

In addition to the contribution of Butte County to traffic levels in the
City of Chico, average daily truck traffic on Highway 162 is in the
range of 5001 to 10,000. This highway travels from Sutter County to
Butte County beyond the city limits of Chico. The daily car and truck
traffic from Chico to Paradise, and from Chico to Oroville is much
lower, in the range of 0 to 2000, but shows a daily traffic pattern. 

Factor 4 further supports eliminating Tehama, and Glenn Counties from
consideration as a nonattainment area.  However, Butte County has
significant commuter and truck traffic which argues for including most
of Butte County as a nonattainment area. Figure 4 shows the traffic
patterns in and around Chico.  There is relatively little traffic in the
eastern high elevation portions of the county.

The 2005 VMT data used for tables 5 and 6 of the technical analysis have
been derived using methodology such as that described in "Documentation
for the  2005 Mobile National Emissions Inventory, Version 2," December
2008, prepared for the Emission Inventory Group, U.S. EPA.  This
document may be found at:   HYPERLINK
"ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile_sector/documentation/20
05_mobile_nei_version_2_report.pdf" 
ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile_sector/documentation/200
5_mobile_nei_version_2_report.pdf 

Factor 5:  Growth rates and patterns  

This factor considers population growth for 2000-2005 and growth in
vehicle miles traveled for 1996-2005 for Butte County and the
surrounding counties, as well as patterns of population and VMT growth. 
A county with rapid population or VMT growth is generally an integral
part of an urban area and likely to be contributing to fine particle
concentrations in the area.  

Table 8 below shows population, population growth, VMT and VMT growth
for counties that are in the area adjacent to Butte County.  Counties
are listed in descending order based on VMT growth between 2000 and
2005.

Table 6. Population and VMT Growth and Percent Change

County	Population (2005)	Population Density	Population % change (2000 -
2005)	2005 VMT

( millions)	% VMT

change

(% 2000-2005

Butte 	214,153	128	5%	2,078	61%

	Tehama 	60,932	21	8%	485	(41)%

Glenn 	27,683	21	5%	253	(40)%

According to Table 6, Butte County has the highest population and
population density.  Tehama County has the next highest population of
the adjacent counties, but significantly below Butte (also in terms of
population density).  Tehama and Glenn County have the same population
density of 21 pop/sq mi, compared to Butte County at 128.   Both Butte
and Glenn counties experienced a 5% population growth from 2000-2005,
while Plumas and Tehama counties also saw slightly higher growth at 8%.
Glenn and Tehama Counties, while having a relatively small increase in
population from 2000 to 2005, also experienced a decline in VMT growth
from 2000 to 2005.  

Based on the analysis under Factor 5, Tehama and Glenn Counties, while
experiencing modest growth in population, also had significant decreases
in VMT which further supports elimination of these counties from
consideration as nonattainment areas.  Plumas County also had slight
growth in population, but saw increased VMT.  However, the total numbers
for Plumas are still very low further supporting its elimination from
consideration as a nonattainment area. Butte County has the largest
population, by far, and also the most significant growth in VMT.  

Factor 6:  Meteorology (weather/transport patterns)

For this factor, EPA considered data from National Weather Service
instruments in the area.  Wind direction and wind speed data for
2004-2006 were analyzed, with an emphasis on “high PM2.5 days” for
each of two seasons (an October-April “cold” season and a
May-September “warm” season).  These high days are defined as days
where any FRM or Federal Equivalent Method (FEM) air quality monitors
had 24-hour PM2.5 concentrations above 95% on a frequency distribution
curve of PM2.5 24-hour values, or were 24-hr values exceeded 35.1
µg/m3.

For each air quality monitoring site, EPA developed a “pollution
rose” to understand the prevailing wind direction and wind speed on
the days with highest fine particle concentrations.  Figure 4 identifies
24-hour PM2.5 values by color; days exceeding 35 ug/m3 are denoted with
a red or black icon.  A dot indicates the day occurred in the warm
season; a triangle indicates the day occurred in the cool season.  The
center of the figure indicates the location of the air quality
monitoring site, and the location of the icon in relation to the center
indicates the direction from which the wind was blowing on that day.  An
icon that is close to the center indicates a low average wind speed on
that day.  Higher wind speeds are indicated when the icon is further
away from the center.

  

The pollution rose for Butte County, shown below, indicates that the
elevated levels of the PM2.5 24-hour values for the Chico monitoring
site occur primarily when the wind is from the south, and occasionally
when the wind is from the north.   The pollutant rose for Butte County
also indicates that elevated PM2.5 24-hour values occur during the cool
season, during time periods of low wind speeds.

 

Figure 5

These data are consistent with the analysis provided by California, and
may also support the CARB position that the organic carbon portion of
the particulate matter problem is localized.  However, as discussed in
Factor 2: Air Quality, above, based on the nitrate portion, emissions
from a larger area contribute to PM2.5 violations. This factor, together
with Factor 2, supports the inclusion of at least major portions of
Butte County in the nonattainment area.

Note:  the meteorology factor is also considered in each county’s
Contributing Emissions Score because the method for deriving this metric
included an analysis of trajectories of air masses for high PM2.5 days.

Factor 7:  Geography/topography (mountain ranges or other air basin
boundaries)

The geography/topography analysis looks at physical features of the land
that might have an effect on the airshed and, therefore, on the
distribution of PM2.5 within Butte County.

Butte County is part of the larger Northern Sacramento Valley Air Basin
(NSVAB), which includes the counties of Butte, Colusa, Glenn, Shasta,
and Tehama. The NSVAB is bounded on north and west by the Coastal
Mountain Range and on the east by the southern portion of the Cascade
Mountain Range and the northern portion of the Sierra Nevada Mountains.
These mountain ranges reach heights in excess of 6,000 feet with peaks
rising much higher.  This provides a substantial physical barrier to
locally created pollution.  

For the areas under consideration, high PM2.5 concentrations mostly
occur during stagnant conditions during winter, with radiation
inversions.  The cooling of the ground, as heat is radiated away,
creates an inversion, since air near the ground is cooler than that
above.  This inhibits mixing and confines pollutants to a relatively
shallow layer near the ground.  EPA considered radar wind profiler data
collected at Chico during CRPAQS study, and analyzed by CARB to derive
mixing heights for the area.  A typical value for maximum mixing height
during high PM2.5 conditions is 300 m (984 ft) AGL (above ground level).
  EPA recognizes that an inversion height is not a rigid boundary
extending through a fixed elevation.  In reality the inversion would be
partly terrain-following, and the degree of stagnation would be subject
to additional influences at the foothill edges, such as strong diurnal
slope flows.  In any case, mixing heights vary by site and date, so any
single height can provide only a scale for comparison, not a definitive
value.  Nevertheless, the inversion height provides an indicator of the
area over which inversions may be enhancing pollution concentrations,
and of the extent of the area that may be contributing to NAAQS
violations.

Because the Butte area has topographical features higher the typical
daytime height of the inversion layer, to help determine an appropriate
eastern boundary EPA considered the inversion height to estimate the
size of the area likely to have similar pollution conditions and to
contribute to NAAQS violations. The eastern portion of Butte County
extends into the foothills of the Sierra Nevada Mountains.  For Chico,
the 300 m AGL (984  ft) inversion layer thickness translates to an
elevation contour of 375 m (1221 ft) MSL (above Mean Sea Level).  Much
of eastern portion Butte County is above this elevation, as shown in
Figure 6 below.  The urbanized area of Paradise is right about at this
line.

In summary, topography is an important factor for Butte given that the
inversion layer, which can lead to winter PM2.5 exceedances in the
Sacramento Valley, is blocked by the Sierra foothills.  In addition to
affecting the City of Chico, similar pollution conditions are expected
throughout Butte County, and areas below or near the inversion height
could contribute to PM2.5 violations.

Figure 6

Factor 8:  Jurisdictional boundaries (e.g., existing PM and ozone areas)

EPA believes consideration also should be given to existing boundaries
and organizations as they may facilitate air quality planning and the
implementation of control measures to attain the standard.  Areas
already designated as nonattainment represent important boundaries for
state air quality planning. To the degree appropriate based upon
violations and contribution to violations of the respective NAAQS, EPA
believes it can be helpful for air planning purposes and for attainment
of both NAAQS for ozone and PM2.5 nonattainment area boundaries to be
consistent.

As compared to EPA’s original intention, the final designation places
little emphasis on the ozone nonattainment area boundary, especially in
setting the boundary within Butte County.  Instead, more weight was
placed on the areas generating pollution likely to contribute to NAAQS
violations and on the topographic barrier of the Sierras.  The lower
elevation portions of Butte County is being recommended for a
nonattainment designation for PM2.5 and is under the jurisdiction of the
Butte County Air Quality Management District (AQMD).  

Factor 9:  Level of control of emission sources 

This factor considers emission controls currently implemented for major
sources in Butte County. There are no large contributing sources that
have been excluded from the Sacramento nonattainment area.  Figure 6
identifies both NOx and PM 2.5 sources within Butte County, as well as
their emissions levels.

The emission estimates in Table 1 (under Factor 1) include any control
strategies implemented by Butte County area before 2005 that may
influence emissions of any component of PM2.5 emissions (i.e., total
carbon, SO2, NOx, and crustal PM2.5).  

Conclusion

EPA is designating the lower elevation portions of Butte County as
nonattainment for the PM2.5 NAAQS.  The chosen area boundaries are
supported by most of the factors EPA considered.  Butter County contains
a violating PM2.5 monitor, and the cities of Paradise and Oroville are
connected by traffic distributions.  These cities have substantial
residential wood smoke emissions of carbon, by far the largest component
of PM2.5 violations. Despite evidence that the effect of these sources
is relatively localized, these sources are not limited to the city
boundaries, nor is their influence.  Also, ammonium nitrate, mainly from
mobile source NOx emissions, is an important PM2.5 component; its larger
spatial scale justifies including relatively large portions of the
counties within the nonattainment area.  The winter inversions that lead
to PM2.5 NAAQS exceedances limit the vertical extent of pollution, as
reflected in additional data provided by CARB.  The Sierra foothills to
the east provide a corresponding topographic barrier.  This and the
relatively small population and emissions in eastern Butte County
justify excluding it from the nonattainment area.

Additional information regarding responses to specific State comments
can be found in EPA's Response to Comments document at   HYPERLINK
"http://www.epa.gov/pmdesignations/2006standards/tech.htm" 
http://www.epa.gov/pmdesignations/2006standards/tech.htm . 

Attachment 2

Description of the Contributing Emissions Score

The CES is a metric that takes into consideration emissions data,
meteorological data, and air quality monitoring information to provide a
relative ranking of counties in and near an area.  Using this
methodology, scores were developed for each county in and around the
relevant metro area.  The county with the highest contribution potential
was assigned a score of 100, and other county scores were adjusted in
relation to the highest county.  The CES represents the relative maximum
influence that emissions in that county have on a violating county.  The
CES, which reflects consideration of multiple factors, should be
considered in evaluating the weight of evidence supporting designation
decisions for each area.

The CES for each county was derived by incorporating the following
significant information and variables that impact PM2.5 transport:

·	Major PM2.5 components:  total carbon (organic carbon (OC) and
elemental carbon (EC)), SO2, NOx, and inorganic particles (crustal).

·	PM2.5 emissions for the highest (generally top 5%) PM2.5 emission
days (herein called “high days”) for each of two seasons, cold
(Oct-Apr) and warm (May-Sept)

·	Meteorology on high days using the NOAA HYSPLIT model for determining
trajectories of air masses for specified days

·	The “urban increment” of a violating monitor, which is the urban
PM2.5 concentration that is in addition to a regional background PM2.5
concentration, determined for each PM2.5 component

·	Distance from each potentially contributing county to a violating
county or counties

A more detailed description of the CES can be found at
http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html#C



Attachment 3: Population and Traffic Data

County	County Area (sq. miles)	Nonattainment Area (sq. miles)

Butte	1,677.50	1,158.33

El Dorado	1,787.99	620.92

Imperial	4,481.67	690.54

Placer	1,501.86	432.38

Sacramento	992.04	992.04

Sutter	608.39	608.39

Yolo	1,023.36	698.67

Yuba	643.57	482.77

Solano (SV)	470.55	470.55

Solano (SF)	419.01	419.01

County	County Population	Nonattainment Area Population

Butte	203,171.00	196,300.00

El Dorado	156,299.00	110,528.00

Imperial	142,361.00	122,775.00

Placer	248,399.00	207,156.00

Sacramento	1,223,499.00	1,223,499.00

Sutter	78,930.00	78,930.00

Yolo	168,660.00	163,193.00

Yuba	60,219.00	56,293.00

Solano (SV)	120,697.00	120,697.00

Solano (SF)	273,845.00	273,845.00

County	County Annual Non-truck Traffic	Nonattainment Area Annual
Non-truck Traffic

Butte	2,237,170.00	2,225,913.00

El Dorado	1,573,738.00	1,547,018.00

Imperial	1,677,333.00	1,229,867.00

Placer	4,777,401.00	4,548,701.00

Sacramento	33,510,398.00	33,510,398.00

Sutter	361,416.00	361,416.00

Yolo	4,677,258.00	4,671,958.00

Yuba	426,377.00	422,677.00

Solano (SV)	3,988,735.00	3,988,735.00

Solano (SF)	12,301,618.00	12,301,618.00

County	County Annual Truck Traffic	Nonattainment Area Annual Truck
Traffic

Butte	169,932.00	169,280.00

El Dorado	86,212.00	84,588.00

Imperial	229,338.00	139,186.00

Placer	422,876.00	400,706.00

Sacramento	2,515,749.00	2,515,749.00

Sutter	33,714.00	33,714.00

Yolo	614,874.00	614,512.00

Yuba	23,724.00	23,036.00

Solano (SV)	369,035.00	369,035.00

Solano (SF)	933,605.00	933,605.00

Sources: U.S. Census Department (2000), Federal Highway Administration
(2002), EPA (2008)

 EPA designated nonattainment areas for the 1997 fine particle standards
in 2005.  In 2006, the 24-hour PM2.5 standard was revised from 65
micrograms per cubic meter (average of 98th percentile values for 3
consecutive years) to 35 micrograms per cubic meter; the level of the
annual standard for PM2.5 remained unchanged at 15 micrograms per cubic
meter (average of annual averages for 3 consecutive years).  

 PAGE   

 PAGE   6 

Concentration:

  > 40 µg/m3

  35 - 40 µg/m3

  30 - 35 µg/m3

  < 30 µg/m3

Season:

     cool (Oct-Apr)

     warm (May-Sep)

2007

2006

2005

RED_BLUFF_MUNICIPAL_ARPT (ID=24216)

Meteorological data from 34.7 miles away

Chico, CA

(due to missing or variable wind data)            

7 exceedance(s) not plotted                       

   55-NA

Value

Design

4

5

4

# days > 35

53.0

59.0

54.0

98th %-ile

2006

2005

2004

Year

Pollution Rose, 2005-2007

Chico, CA [Butte County, CA]

Site 060070002

Wind Speed (mph)

12+

10

8

6

4

2

E

W

S