1 Attachment 1
CALIFORNIA Area Designations For the 24
- Hour Fine Particle National Ambient Air Q uality Standard Note: As a basic introduction, the following is a summary table listing ALL areas and counties proposed for nonattainment in the State. The t echnical anal ys es 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 ( PM 2.5 ) standard. 1 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.

1 EPA designated nonattainment areas for the 1997 fine particle standards in 2005. In 2006, the 24

- hour PM 2.5 standard was revised from 65 micrograms per cubic meter (average of 98 th percentile values for 3 consecutive years) to 35 micrograms per cubic meter; the level of the annual standard for PM 2.5 remained unchanged at 15 micrograms per cubic meter (average of annual averages for 3 consec utive years).2

Area California Recommended Nonattainment Counties EPA’s Final Designated Nonattainment Counti es 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 rem aining 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 on e 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.3

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 nearb y areas that contribute to violations. This technical anal ys is fo r Butte i dentifies the counties with monitors that violate the 24

- hour PM 2.5 standard and evaluates nearb y 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 an y other relevant information:

- pollutant emissions

- air quality data

- population density and degree of urbanization

- traffic and commuting patterns

- growth

- meteorology

- geograph y 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 non attainment area within Butte County

.

Figure 1

Figure 1.4 Figure 25

T he 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” f or the 2006 24

- hour PM 2.5 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 desi gnations. 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 b y 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 . Anal ys is of these data indicates that the day s with the highest fine particle concentrations occur predominantly in the cold season, and the average chemical composition of the highest day s is characterized by high levels o f organic carbon ( e.g. , 75%)

. Based on EPA's technical analysis described below and currentl y available information , EPA has designated a portion of Butte County as nonattainment for the 24

- hour PM 2.5 air

- quality standard

. Butte County Area California Recommended Nonattainment Counties EPA’s Final Designated Nonattainment Counties Butte County Butte County (p artial ) Butte County (p artial ) The following is a technical anal ys is for Butte County , California

. Factor 1: Emissions data For this fac tor, EPA evaluated county l evel emission data for the following PM 2.5 components and precursor pollutants: “PM 2.5 emissions total,” “PM 2.5 emissions carbon,” “PM 2.5 emissions other,” “SO 2 ,” “NO x ,” “VOCs,” and “NH 3. ” “PM 2.5 emissions total” represents direct emissions of PM 2.5 and includes: “PM 2.5 emissions carbon,” “PM 2.5 emissions other”, primary sulfate ( SO 4 ), and primary nitrate. (Although primary sulfate and primary nitrate, which are emitted directl y from stacks rather than forming in atmospheric reactions with SO 2 and NO x , are part of “PM 2.5 emissions total,” they are not shown on the template or data spreadsheet as separate items ). “PM 2.5 emissions carbon” represents the sum of organic carbon (OC) and elemental carbon (EC) emissions, and “PM 2.5 emissions other” represents other inorganic particles (crustal). Emissions of SO 2 and NO x , which are precursors of the secondary PM 2.5 components sulfate and nitrate, are also considered. VOCs (volatile organic compounds) and NH 3 (ammonia) are also potential PM 2.5 precursors and are included for consideration. Emissions data were derived from the 2005 National Emissio ns Inventory (NEI), version 1. See http://www.epa.gov/ttn/naaqs/pm/pm25_2006_techinfo.html. EPA also considered the Contributing Emissi ons Score (CES) for each county . The CES is a metric that takes into consideration emissions data, meteorological data, and air quality monitoring6

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 PM 2.5 and p recursor 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 b y C ES.
Table 1. PM 2.5 24 - hour Component Emissions, and CES.
County State

Reco mmen ded Nonat tainm ent? CES PM 2.5

total SOx NOx Carbon PM 2.5 PM 2.5

other VOCs NH 3

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 anal ys is of this factor are summarized in the following table derived from the California Air Resources Board Almanac of Emissions and Air Quality Data (http://www.arb.ca.gov/Aqd/almanac/almanac.htm ). The following table further defines, in tons per day , the ty

pe of area sources contributing to PM 2.5 emissions in Butte County. Area sources include residential fuel combustion, farmin g 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 , w ith approximately 70% of the total . Based on Table 2, within the area source category , residential wood burning is the dominant source of PM 2.5 . This is consistent with the speciation data discussed below.
Table 2. A rea Source Emission (tons per day)

SO URCE PM 2.5 Residential Fuel Combustion 2.65 Farm ing Operations 0.82 Construction/Demolition 0.11 Paved Road Dust 0.53 Unpaved Road Dust 0.76 Fugitive W indblown Dust 0.04 Fires 0.01 Managed Burning & Disposal 1.4 Cooking 0.07 Total Area Wi de 6.4 Area W ide percent of total 68%

Total All 9.9 Source: A RB Almanac website (2006 ) http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm7

Given the significance of NOx emissions in th e formation of the PM 2.5 , 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 Boa rd 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 day s based on a broad analy sis of NOAA HYSPLIT trajectories linking count ywide emissions fro m Butte and the surrounding counties and speciated air monitoring data on high day s. The CES clearl y d emonstrates a connection between pollution levels in Chico and sources throughout Butte County. The CES shows less of a link between PM 2.5 levels in Chi co and neighboring Tehama and Glenn Count ies

. S peciation data from the Chico air monitoring station was considered in evaluating this factor , as a way to link emission sources to high PM 2.5 levels. As shown in the pie chart below (Figure 3), monitored PM 2.5 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 PM 2.5 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 roughl y 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 commuti ng 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 PM 2.5 ex ceedances measured in Chico

. E mission levels and CES values s upport designation of Butte County as a 24

- hour PM 2.5 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 th e highest CES score of 100, followed distantly by Glenn and Tehama Counties , at 14 and 19 respectivel y . 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 . T here is no evidence that these counties contribute to the PM 2.5 air quality problems in Butte County . We have eli m inated these counties from further consideration given these facts.8

Factor 2: Air quality data This factor considers th e 24

- hour PM 2.5 design values in micrograms per cubic meter (μg/m 3 ) 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 s tan dard. The 24

- hour PM 2.5 standards are met when the 3

- year average of a monitor’s 98 th percentile values are 35 μg/m 3 or less. A design value is only valid if minimum data completeness criteria are met. The 24

- hour PM 2.5 design values for Butte County are shown in Table 2. Table 4

. Air Quality Data
County/ City State Recommended Nonattainment 24 - hour PM 2.5

Design Values 2004 - 06 (μg/m 3 ) 24 - hour PM 2.5

Design Values 2005 - 07 (μg/m 3 ) Butte County, CA Cit y of Chico Yes 56 55

The violating monit or 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 PM 2.5 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 PM 2.5 in evaluating this factor. As shown in the pie chart below (Figure 3), the chemical makeup of PM 2.5 in Chico is dominated by organic carbon, at 75% of the total. This reflects emissions from residential wood burning. There is also a large ammoni um 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.9 Ave rag e Com pos ition on 14 E xceed an ce D ay

s- Chic o

AmmNi tr ate 16%
AmmS ul fa te

2%

OC 75% Ot her

2% Ge ologi ca l 1% El em

ents 2% EC 2%

PM2.5 Mass= 52 .2 ug/ m3

Sum of Spec ies=51.4 ug/ m3 Figure 3
In summary , the air quality factor supports nonattainment designation of at least large portions of Butte County . PM 2.5 speciation data support the idea that localized resid ential 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 gen erall y i nclude State and L ocal 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 PM 2.5 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 PM 2.5 nonattainment area given the correlation between popu lation and the emission sources contributing to PM 2.5 exceedances (i.e., residential wood burning and mobile sources), as well as the population exposed to high PM 2.5 levels. Table 6 shows the 2005 population for each county in the area being evaluated, as well as the population density for each county i n that area. Population data gives an indication of whether it is likely that population

- based emissions might contribute to violations of the 24

- hour PM 2.5 standards.10

Table 6. Population
County S tate

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 densi ty . Tehama County has the next highest population of the adjacent counties, but significantly below Butte (also in terms of population density). P opulation centers in Butte County include Chico (population of 59,444 per 2000 US Census), Paradise (populat ion 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 p eople per square mi le , which is extremely low, compared to Butte County at 128. Both Butte and Glenn c ounties experienced a 5% population growth from 2000

- 2005, while Tehama C ounty 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 considerati on 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 numbe rs are very high, and that most of the population and traffic is captured within the nonattainment area.11 Figure 412

Factor 4: Traffic and commuting patterns This factor considers the number of commuters in each county who drive to Butte County , the pe rcent of total commuters in each county who commute to Butte County , as well as the total Vehicle Miles Traveled (VMT) for each county i n millions of miles (see Table 5 ). A county with numerous commuters is generall y an integral part of an urban area and i s 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 Commutin g Patterns

County State

Rec. N A 2005

VMT (millions Number

Commutin g to any violating counties Percent

Commuting to any violating counties Number

Commut ing into statistic al area Percent

Commuting into statistical area Butte Count y Yes (P) 2,078 74,510 91% 73,000 91 %

Tehama Count y No 599 1,170 6% ] 1,140 6 % Glenn Count y 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 dail y 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 relativel y l ittle traffic in the eastern high elevation portions of the county. The 2005 VMT data used for tables 5 and 6 of the technical anal ys is have been derived using methodology such as that described in "Documentation for the 2005 Mobile13

National Emissions Inventory , Version 2," December 2008, prepared for the Emission Inventory Group, U.S. EPA. This document may be found at: ftp://ftp.epa.gov/EmisInvento ry /2005_nei/mobile_sector/documentation/2005_mobile_ne i_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 surroun ding counties , as well as patterns of population and VMT growth. A county with rapid population or VMT growth is generall y 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 significantl y 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 slightl y higher growth at 8%. Glenn and Tehama Counties, while having a relativel y small increase in population from 2000 to 2005, also experienced a decline in VMT growth from 2000 to 2005. Based on the anal ys is under Factor 5, Tehama and Glenn Counties, while experiencing modest growth in population , also had significant decreases i n 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 i ts elimination from consideration as a nonattainment area. Butte County has the largest population, by far, and also the most significant growth in VMT.14

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 anal yz ed, with an emphasis on “high PM 2.5 day s” for each of two seasons (an October

- April “cold” season and a May

- September “warm” season). These high d ay s are defined as days where an y FRM or Federal Equivalent Method ( FEM ) air quality monitors had 24

- hour PM 2.5 concentrations above 95% on a frequency distribution curve of PM 2.5 24

- hour values, or were 24

- hr values exceeded 35.1 μg/m 3

. For each air qual ity monitoring site, EPA developed a “pollution rose ” to understand the prevailing wind direction and wind speed on the days with highest fine particle concentrations. F igure 4 identifies 24

- hour PM 2.5 values by color; day s 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 m onitoring site, and the location of the icon in r elation 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 i s further away from the center. The pollution rose for Butte County , shown below, indicates that the elevated levels of the PM 2.5 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 PM 2.5 24

- hour values occur during the cool season, during time periods of low wind speeds.15 Figure 5 Th ese data are consistent with the anal ys is provided by California , and may also support the C ARB 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 PM 2.5 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 analy sis of trajectories of air masses for high PM 2.5 day s. Factor 7: Geography/topography (mountain ranges or other air basin boundaries) The geograph y/topography anal ys is looks at phy sical features of the land that might have an effect on the airshed and, therefore, on the distribution of PM 2.5 within Butte County

. S W E

2 4 6 8 10 12+

Wind Speed (mph) Site 060070002 Chico, CA [Butte County, CA] Pollution Rose, 2005- 2007

Year 2004 2005 200 6 98th %

- ile

54.0 59.0 53.0 # days > 35

4 5 4 Design Value 55

- NA 7 exceedance(s) not plotted (due to missing or v ariable wind data) Chico, CA Meteorological data from 34.7 miles away RED_BLUFF_MUNICIPA L_ARPT (ID=24216) 2005 2006 2007 Concentration : 

### n > 40 μg/m3 n 35

- 40 μg/m3 n 30

- 35 μg/m3 n < 30 μg/m3
Season : cool (Oct

- Apr) warm (May

- Sep)16

Butte County is part of the larger Northern Sacramento Valley Air Basin (NSVAB), which includes the counties of Butte, Colusa, Glenn, Shasta, and Teham a . 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 fe et with peaks rising much higher. This provides a substantial phy sical barrier to locally created pollution. For the areas under consideration, high PM 2.5 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 relativel y s hallow layer near the ground. EPA considered radar wind profile r d ata collected at Chico during CRPAQS study , and anal yz ed b y C ARB to derive mixing heights for the area. A typi cal value for maximum mixing height during high PM 2.5 conditions is 300 m ( 984 ft) AGL (above ground level). EPA recognizes that an inversio n height is not a rigid boundary extending through a fixed elevation. In reality the inversion would be partl y t errain

- following, and the degree of stagnation would be subject to additional influences at the foothill edges, such as strong diurnal slope fl ows. In an y case , mixing heights vary by site and date, so any single height can provide only a scale for comparison, not a definitive value. Nevertheless, th e 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 ty pical day time 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 Chi co, the 3 0 0 m AGL ( 984 ft) inversion layer thickness translates to an elevation contour of 3 75 m (1 221 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 Paradi se is right about at this line. In summary , topograph y i s an important factor for Butte given that the inversion layer, which can lead to winter PM 2.5 ex ceedances in the Sacramento Valley , is blocked b y the Sierra foothills . In addition to affecting the C ity of Chico, similar pollution conditions are expected throughout Butte County , and areas below or near the inversion height could contribute to PM 2.5 violations.17 Figure 618

Factor 8: Jurisdictional boundaries (e.g., existing PM and ozone areas)
E PA 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 d esignated as nonattainment represent impo rtant 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 , especiall y in setting the boundary within Butte County . Instead, more w eight 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 PM 2.5 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 currentl y i mplemented 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 i n Table 1 (under Factor 1) include any control strategies implemented by Butte County area before 2005 that may influence emissions of an y component of PM 2.5 emissions (i.e., total carbon, SO 2 , NOx, and crustal PM 2.5 ).
Conclusion EPA is designating the lower elevation portions of Butte County as n onattainment for the PM 2.5 NAAQS. The chosen area boundaries are supported b y m ost of the factors EPA considered. Butter County contains a violating PM 2.5 monitor, and the cities of Paradise and Oroville are connected by traffic distributions. These cit ies have substantial residential wood smoke emissions of carbon, b y far the largest component of PM 2.5 violations. Despite evidence that the effect of these sources is relativel y l ocalized, 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 PM 2.5 component; its larger spatial scale justifies including relativel y l arge portions of the counties within the nonattainment area. The winter inversions that lead to PM 2.5 NAAQS exceedances limit the vertical extent of pollution, as reflected in additional data provided b y C ARB. The Sierra foothills to the east provide a corresponding topographic barrier. This and the relativel y s mall population and emission s in eastern Butte County justify excluding it from the nonattainment area.19

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

.20 Attachment 2 Description of the Contributing Emissions Score The CES is a metric that takes into consideration emissions data, meteorological data, and air quality m onitoring 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 10 0, and other county s cores 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 c onsidered in evaluating the weight of evidence supporting designation decisions for each area. The CES for each county was derived b y i ncorporating 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 day s (herein called “high day s”) 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 bac kground 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_techin fo.html#C21 At tachment 3: Population and Traffic Data Count y Count y 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 Count y Count y 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 Count y Count y Annual Non

- truck Tra ffic 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
Count y Count y 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)22