Enclosure V 

ARB Staff Report 
State of California 

California Environmental Protection Agency

AIR RESOURCES BOARD 

Staff Report 

Analysis of the 

Sacramento Metropolitan Air Quality 

Management District 

PM10 Implementation/Maintenance Plan 

and Redesignation Request 

for Sacramento County 

Release Date: October 29, 2010 

Scheduled for Consideration: November 18-19, 2010 
This document has been reviewed by the staff of the California Air Resources Board 

and approved for publication. Approval does not signify that the contents necessarily 

reflect the views and policies of the Air Resources Board, nor does the mention of trade 

names or commercial products constitute endorsement or recommendation for use. 
TABLE OF CONTENTS 

EXECUTIVE SUMMARY 1 

I. BACKGROUND 2 

II. REDESIGNATION REQUIREMENTS 3 

III. EVALUATION OF THE SACRAMENTO PM10 PLAN 4 

A. Sacramento County Attains the 24-Hour PM10 Standard 4 

B. The State Has Met Applicable Act Requirements 6 

C. Improvement in Sacramento PM10 Air Quality is Due to 

 Permanent and Enforceable Reductions in Emissions 6 

D. Maintenance Plan 7 

1. Attainment Emission Inventory 7 

2. Maintenance Demonstration 8 

3. PM10 Monitoring Network 9 

4. Verification of Continued Attainment 10 

5. Contingency Provisions 10 

6. Transportation Conformity Budgets 10 

IV. STAFF RECOMMENDATION 12 
EXECUTIVE SUMMARY 

The Sacramento Metropolitan Air Quality Management District (District) shares the 

same jurisdictional boundary as Sacramento County (County) and has prepared 

documentation to demonstrate that the County now meets the remaining federal health 

standard for particulate matter of 10 microns in diameter or smaller (PM10) and should 

be redesignated to attainment. On July 1, 1987, the United States Environmental 

Protection Agency (U.S. EPA) adopted the PM10 national ambient air quality standard 

(NAAQS or standard) consisting of an annual average standard of 50 μg/m3, and a 

24-hour standard of 150 μg/m3. Subsequently, on December 18, 2006, U.S. EPA 

revoked the national annual average PM10 standard. 

In 1994, U.S. EPA designated the County a moderate nonattainment area, with an 

attainment deadline of December 31, 2000. Effective March 18, 2002, U.S. EPA 

officially determined that monitors in the County measured air quality attaining the 

24-hour PM10 standard by the moderate area deadline. The District must provide 

documentation specified in the federal Clean Air Act (the Act) demonstrating the 

24-hour PM10 standard can be maintained in order to request that U.S. EPA 

redesignate the County to attainment. 

The District prepared the PM10 Implementation/Maintenance Plan and Redesignation 

Request for Sacramento County (Sacramento PM10 Plan or Plan) as required. The 

Plan affirms the County has attained the standard and demonstrates that existing 

federal, State, and local control measures will maintain the 24-hour PM10 standard in 

the District. On October 28, 2010, the District Board adopted the Plan at a public 

hearing. 

The Plan contains all elements needed for redesignation to attainment: 

 Demonstration that PM10 attainment concentrations measured between 2007 

and 2009 will be maintained for ten years after redesignation; 

 Commitment that the monitoring network will be maintained to track attainment 

for at least ten years after redesignation; 

 Contingency provisions for correcting any future violations of the PM10 NAAQS; 

 Emission inventories for PM10 and nitrogen oxides (NOx); 

 Transportation conformity budgets which sets limits for mobile source emissions 

of PM10 and NOx through 2022. 

In addition, eight years after the U.S. EPA redesignates the area as attainment, the 

District will submit a revised maintenance plan providing for continued attainment for an 

additional ten years. 

ARB staff concurs with the District’s Sacramento PM10 Plan and recommends the 

Board approve the Plan, as a revision to the California State Implementation Plan (SIP), 

for submittal to U.S. EPA. 

October 29, 2010 Page 1 
I. BACKGROUND 

Sacramento County, as shown in Figure 1, was initially designated as a moderate PM10 

nonattainment area in 1994 with an attainment date of December 31. 2000. The County 

is approximately 994 square miles in size. The population of about 1,443,000 residents 

has grown rapidly, increasing almost 40 percent in the past twenty years. The 

urbanized areas are surrounded by agricultural croplands and ranchlands. Four major 

interstate highways cross the county and the major economic activities are related to 

government services, retail trade, agriculture, construction materials, and other 

industrial uses. Despite the changes in land use over time, there have been no 

violations of the 24-hour average PM10 NAAQS since the mid-1990s. 

Figure 1 

Location of Sacramento County 

October 29, 2010 Page 2 
On March 18, 2002, U.S. EPA determined that Sacramento County had attained the 

PM10 standard by the 2000 deadline. Based on this clean data finding, certain 

nonattainment area requirements do not apply, including those for reasonable further 

progress, an attainment demonstration, reasonably available control measures, and 

contingency measures, because these provision’s sole purpose is to achieve attainment 

of the standard. On October 28, 2010, the District adopted the Sacramento County 

PM10 Plan. The Plan officially requests that this area be redesignated to attainment for 

the PM10 standard and charts the course for continued maintenance of the standard. 

The State mobile source control strategy and local District rules have resulted in 

Sacramento County attaining the 24-hour PM10 standard based on both past and 

current data. 

II. REDESIGNATION REQUIREMENTS 

The Act sets the general framework for redesignation requests. In 1992, U.S. EPA 

provided guidance for processing redesignation requests1

. ARB staff reviewed the 

Sacramento PM10 Plan within the context of the Act and the U.S. EPA guidance, which 

identify the following requirements an area must meet for formal redesignation to 

attainment: 

A. The PM10 standard has been attained; 

B. The District has an approved State Implementation Plan (SIP) and the State has 

met all applicable Act requirements for PM10 in the nonattainment area; 

C. The improvement in PM10 air quality is due to permanent and enforceable 

emission reductions; and 

D. U.S. EPA has approved a Maintenance Plan which includes these elements: 

1. Attainment emission inventory; 

2. Demonstration that PM10 attainment concentrations at federal reference 

monitoring stations will be maintained for ten years after redesignation; 

3. Commitment to ongoing monitoring network operation; 

4. Continued verification of attainment; 

5. Contingency plan to promptly correct any violation of the PM10 NAAQS that 

occurs after the area has been redesignated to attainment; and 

6. Transportation conformity budgets for the ten years following the anticipated 

year of U.S. EPA approval of the submittal. 

 

1

 A principal source of EPA guidance with respect to redesignations to attainment can be found in a 

Memorandum from U.S. EPA Office of Air Quality Planning and Standards entitled “Procedures for 

Processing Requests to Redesignate Areas to Attainment,” John Calcagni, Director, Air Quality 

Management Division, U.S. EPA, Research Triangle Park, North Carolina September 4, 1992.

October 29, 2010 Page 3 
III. EVALUATION OF THE SACRAMENTO PM10 PLAN 

Based on review of the Sacramento PM10 Plan and the District’s supporting technical 

analysis, ARB staff concur that the Plan meets the Act’s requirements. The following 

sections indicate how the Plan meets the redesignation and maintenance plan 

requirements. 

A. Sacramento County Attains the 24-Hour PM10 Standard 

Currently, PM10 concentrations are measured at six monitoring sites using federal 

reference method monitors (FRMs). These filter-based, high-volume, size-selective 

inlet samplers collect PM10 samples on an hourly basis, for a 24-hour period, every six 

days. Figure 2 shows the location of all the ambient air monitors in Sacramento County 

with the FRMs for PM10 outlined in the key. 

Table 1 lists the highest 24-hour average PM10 concentration during each year for the 

three-year period of 2007-2009. The 24-hour PM10 standard is met when the 

estimated number of exceedances measured over a three-year period averages one or 

less per year. The FRMs’ data demonstrate that the County attains the 24-hour PM10 

standard. 

October 29, 2010 Page 4 
Figure 2 

PM10 Monitoring Stations in Sacramento County 

October 29, 2010 Page 5 
Table 1 

FRM PM10 Data from 2007 to 2009 

Maximum 24-hour Average 

Concentration (μg/m3) Monitoring Station Name 

2007 2008 2009 

Three-year 

Total Number of 

Days Exceeding 

the Standard 

Branch Center Road 56 89 76 0 

Del Paso Manor 70 71 45 0 

Goldenland Court* -- 56 48 0 

North Highlands 56 97 33 0 

Stockton Blvd 56 88 45 0 

T Street 53 73 47 0 

* The Goldenland Court monitor replaced the Airport Road monitor starting in October 2008. 

B. The State Has Met Applicable Act Requirements 

The Sacramento PM10 Plan serves both the implementation and maintenance plan 

functions prescribed by the Act, since U.S. EPA determined that the PM10 standard 

was met by the 2000 deadline. ARB and the District have also met all of the Act 

requirements applicable for a moderate PM10 nonattainment area to be considered for 

redesignation to attainment. 

C. Improvement in Sacramento PM10 Air Quality is Due to Permanent and 

Enforceable Reductions in Emissions 

Current District rules controlling emissions of particulate matter and precursor gases 

(NOx, sulfur oxides (SOx), and reactive organic gases (ROG)) from stationary sources, 

and ARB-adopted measures governing mobile sources, have all resulted in emission 

reductions. In addition, the District adopted a residential wood-burning measure that 

curtails wood smoke during winter months, when residential wood smoke contributes to 

PM10 levels. The adopted measures are fully enforceable and are explained in detail in 

the Plan. 

The benefit of these emissions reductions are indicated by the downward trend of the 

highest average 24-hour concentration each year at the peak Sacramento monitoring 

site as shown in Figure 3. These measures have provided for continuous attainment of 

the 24-hour PM10 standard in the region since the early 1990s. Based on analyses of 

long-term meteorological variables, including precipitation, wind speed and direction, 

temperature, and stagnation, the District found that meteorological conditions during the 

2007-2009 period were not unusually favorable to lower PM10 levels. Therefore, air 

quality improvements leading to PM10 attainment in the District are due to emission 

reductions from adopted, fully enforceable control measures. 

October 29, 2010 Page 6 
Figure 3 

Peak 24-Hour Average PM10 Concentrations 

Sacramento County 1989-2009 

Note: The peak 1999 concentration of 141 μg/m3 occurred on July 5th at the Del Paso Manor monitoring 

site, and was likely impacted by emissions from the Fourth of July fireworks. 

D. Maintenance Plan 

The Sacramento PM10 Plan includes the following components: attainment emission 

inventory; maintenance demonstration; commitment to continue monitoring network 

operation; commitment for verification of continued attainment; a contingency plan; and 

transportation conformity budgets. 

1. Attainment Emission Inventory 

The Plan must demonstrate that the PM10 standard is attained and maintained, despite 

future growth in the emissions inventory. The emissions inventory is a systematic listing 

of the sources of air pollutants along with the amount of pollutants emitted from each 

source or category over a given period of time. The inventory is a critical tool used to 

indicate trends, measure control efficacy, and evaluate air pollution mitigation. To 

determine the expected emissions in future years, projected emission inventories 

incorporate the effects of growth and existing regulations on a baseline inventory. 

Emission inventories are estimates of the air pollutant emissions released into the 

environment – they are not direct ambient concentration measurements. However, if 

the inventory is reviewed in conjunction with the actual pollutant concentrations 

measured by the monitoring network, proportional relationships can be developed to 

October 29, 2010 Page 7 
predict future concentrations of pollutants. This exercise, detailed in the Plan, 

demonstrates continued attainment of the standard into the future. 

In Sacramento County, the emissions inventory was analyzed for directly-emitted PM10 

and NOx (as a precursor to ammonium nitrate). The District prepared seasonal 

emission inventory projections for a winter day since 24-hour PM10 average 

concentrations have historically been the highest during this time. The main emissions 

source types contributing to winter PM10 air quality in the County are secondary 

ammonium nitrate particles and directly emitted particles from motor vehicle exhaust 

and wood smoke. Typical wintertime weather conditions in Sacramento County include 

high atmospheric stability, low wind dispersion, and colder temperatures which are 

conducive to PM10 pollutant build-up, especially for ammonium nitrate particles. 

 

The Plan used 2008 as the base year from which emission inventories were projected 

into the future for 2012 and 2022. The 2008 emissions inventory is the most recent 

available. The future years of 2012 and 2022 bracket the ten-year maintenance period 

which would start in 2012, the first year after U.S. EPA’s anticipated approval of 

redesignation to attainment. The District inventory updates include the latest point and 

area source emissions information; ARB’s EMFAC mobile source emission outputs; and 

planning assumptions in the Sacramento Area Council of Governments’ (SACOG) most 

recent Regional Transportation Plan. Emissions reduction credits established prior to 

2008 through the regulatory control measures to offset future growth were included in 

the emissions inventory forecasts, so as not to underestimate future emissions for the 

maintenance demonstration for the years 2012 and 2022. 

2. Maintenance Demonstration 

The Act requires the District to show that the PM10 24-hour standard can be maintained 

for at least 10 years after the redesignation request is approved by U.S. EPA. The 

District analyzed the future mix of sources and emission rates and used proportional 

rollback modeling to show that the emissions would not result in a violation of the 

standard during the maintenance planning period years, 2012-2022. The premise of 

proportional rollback is that changes in emissions from individual pollution sources over 

time are directly proportional to the change in associated ambient concentrations due to 

that individual source. 

The source categories were determined by receptor modeling using the Chemical Mass 

Balance (CMB) model and the apportionment determined for the winter season in 

Sacramento.2

 The PM10 component species were matched to the appropriate 

emission inventory categories in the rollback analysis. The PM10 and precursor 

emissions source categories were assumed to vary directly with the matching CMB 

ambient PM10 speciation categories, thereby determining the proportional contributions 

to overall mass measured at a typical monitor. The emissions inventory projections for 

these source categories include the effects of adopted and enforceable controls of ARB, 

 

2

 Motallebi, Nehzat. “Wintertime PM2.5 and PM10 Source Apportionment at Sacramento California”. Air 

and Waste Management Association 1999: 25-34.

October 29, 2010 Page 8 
the District, and other local measures already in place. They also take into account an 

additional 1.5 tons of PM10 in 2022 which can be added to the inventory projections for 

transportation conformity purposes when the planning horizon for regional 

transportation plans exceed the maintenance plan period. 

Table 2 shows the 2012 and 2022 projected maximum 24-hour average PM10 

concentration compared with the base year 2008. The projected changes in peak 

concentration reflect the projected changes in the emissions inventory. The predicted 

peak PM10 average daily concentrations do not exceed 150 μg/m3. This demonstrates 

continued attainment of the 24-hour PM10 NAAQS in Sacramento County. 

Table 2 

Projected Maintenance of 24-hour PM10 NAAQS in Sacramento County 

PM10 CMB 

Analysis Percent of 

PM10 Mass

Peak 

Monitored 

Value 

Concentration

2012 

Projected Peak 

Concentration 

2022 

Projected Peak 

Concentration

Source Category (% total) (μg/m3) (μg/m3) (μg/m3) 

Ammonium Nitrate 24.4% 26.6 23.7 18.1 

Motor Vehicles 24.5% 26.7 24.9 20.7 

Wood Smoke 17.8% 19.4 18.1 20.0 

Fugitive Dust 15.1% 16.5 16.7 18.6 

Ammonium Sulfate 1.3% 1.4 2.2 2.4 

Unidentified Other 16.9% 18.4 18.2 18.9 

TOTAL PM10 100.0% 109* 104 99 

* 109 μg/m3 was the peak monitored value in Sacramento County from the three-year period ending in 

the 2008 base year, using ambient air monitoring data from the T Street monitor in 2006.

3. PM10 Monitoring Network 

The District commits to continue PM10 monitoring to verify sustained attainment of the 

PM10 standard in the County. The existing PM10 monitoring network in Sacramento 

includes six FRM monitors (Figure 2). The minimum number of monitors required is two 

to four monitors based on the population of the Metropolitan Statistical Area containing 

Sacramento County3

. Therefore, the current number of monitors within the County is 

greater than the PM10 monitoring network requirement for the area. The District 

commits to continue to maintain and operate a PM10 ambient monitoring network in 

Sacramento County that meets or exceeds the minimum monitoring requirements. 

 

3 “Network Design Criteria for Ambient Air Quality Monitoring”, 40 CFR Part 58, Appendix D.

October 29, 2010 Page 9 
4. Verification of Continued Attainment 

To verify continued attainment of the PM10 standards, the District commits to 

reevaluate the Plan in accordance with requirements for maintenance plans found in the 

Act. The District will review the assumptions and data for the PM10 maintenance 

demonstration in 2015 and 2018 to fulfill the verification and tracking requirements. 

Eight years after the County has been redesignated to attainment, the District will 

submit to U.S. EPA the required revision to the Plan demonstrating maintenance of the 

standard for the following ten-year period. On a regular basis, the District will continue 

to analyze PM10 data from FRMs and compare daily PM10 values to the level of the 

24-hour standard. This includes tracking the indicator for triggering the maintenance 

contingency plan. In addition, the District may also evaluate data from continuous 

monitors to aid in the analysis of air quality trends. 

5. Contingency Plan 

The Act requires a maintenance plan to include contingency provisions for prompt 

correction of any PM10 standard violation that might occur after the area has been 

redesignated to attainment. The maintenance plan is not required to contain fully 

adopted contingency control measures that will go into effect without further state action 

as is required in attainment SIPs. Instead, for maintenance plans, the area must have a 

plan to ensure that contingency actions occur once they are triggered. The Plan 

identifies the specific indicator or trigger which will be used to determine when 

contingency provisions should be implemented. 

The trigger will be any violation of the 24-hour PM10 standard at a PM10 monitor, 

verified through filter sampling, weighing and processing. If the data point cannot be 

flagged and approved as an exceptional event, then the District will analyze the event to 

determine the possible causes and whether applicable emissions reductions from 

existing measures due to be implemented would be sufficient to prevent future PM10 

violations. If not, the District would proceed with selecting specific measures for 

adoption and implementation to address the PM10 problem. The Plan contains a 

timeline for this process along with a suggested list of reasonably available control 

measures that may provide cost-effective, particulate matter emissions reductions 

benefits, according to the circumstances associated with the violation. 

6. Transportation Conformity Budgets 

The Act requires that transportation plans, programs, and projects receiving federal 

funding or requiring federal approval must be found to be fully consistent with the SIP. 

The federal Transportation Conformity Rule4

 requires SIPs to specify on-road motor 

vehicle emission budgets (transportation conformity budgets) that are consistent with 

the attainment and maintenance demonstrations in the SIP. The conformity regulation 

requires metropolitan planning organizations (MPO) to demonstrate that emissions from 

regional transportation plans and programs do not exceed these emissions budgets. 

 

4

 The Transportation Conformity Regulation is found at 40 CFR Parts 51 and 93. 

October 29, 2010 Page 10 
The MPO for Sacramento County is SACOG, whose forecasts of vehicle miles travelled 

(VMT) were developed from the MPO’s projections of future population, dwelling units, 

and employment. These VMT forecasts were used to develop the transportation 

conformity budgets for future years for PM10 and NOx using ARB’s latest on-road 

mobile source emission factor model EMFAC2007 and transportation activity data from 

the August 2009 Metropolitan Transportation Improvement Program analysis. 

SACOG’s travel demand model predicts that growth in vehicle trips and vehicle miles 

traveled will be slightly lower than the population growth rate for the Sacramento region 

through 2035. 

The transportation conformity budgets reflect emission reductions from control 

measures already adopted through federal, State and District regulations applied to 

projected growth in emissions from re-entrained dust from travel on paved and unpaved 

roads, vehicular exhaust, and road construction. The Transportation Conformity Rule 

requires that PM10 from construction-related fugitive dust be included in the budget 

because it was identified as a contributor to the non-attainment problem. NOx is the 

only precursor included in the budgets, because ammonium nitrate was shown to 

contribute significantly to peak PM10 concentrations. 

Table 3 shows the proposed transportation conformity budgets for NOx and PM10 

average winter day emissions for Sacramento County. If U.S. EPA determines these 

budgets to be adequate, future transportation plan amendments and updates in 

Sacramento County will need to conform to these budgets. SACOG must ensure that 

the aggregate transportation wintertime emissions in the County do not exceed these 

levels when approving new metropolitan transportation plans and transportation 

programs, even if the mix of projects changes or growth increases. These budgets will 

remain in effect until other budgets are found adequate through approval by U.S. EPA. 

Table 3 

Motor Vehicle Emission Budgets for Maintenance of the 24-hour PM10 NAAQS 

Sacramento County 2008 2012 2022 

NOx PM10 NOx PM10 NOx PM10 

Average Emissions in 

Tons per Winter Day 50 15 38 15 19 17 

For transportation conformity purposes, an additional 1.5 tons per day of PM10 were 

added to the 2022 budget to account for potential emissions increases in dust from 

paved roads and construction. This accommodation is only allowed for transportation 

conformity purposes when the emissions forecasts and budgets will be lower than the 

emissions level needed to provide continued maintenance of the standard. These 

emissions are also accounted for in the maintenance emissions inventory forecasts. 

Figure 4 illustrates that the future NOx emissions inventory is projected to decrease at a 

considerably faster rate than projected growth in the PM10 inventory, thereby 

October 29, 2010 Page 11 
October 29, 2010 Page 12 

maintaining emissions at a level that will not result in a violation of the 24-hour PM10 

NAAQS. 

Figure 4 

PM10 and NOx Precursor Emissions for Sacramento County 1990-2022* 

 * Data for 1990, 2000, and 2008 are historical, while data for 2012 and 2022 are projections 

IV. STAFF RECOMMENDATION 

ARB staff has reviewed the Plan prepared by the District and consulted with the District 

staff during this review. ARB staff concurs with the District’s Plan and finds that the 

Plan meets all applicable Act requirements. ARB staff believes that implementation of 

this Plan will continue to maintain PM10 levels below the national air quality standard in 

Sacramento County. Therefore, ARB staff recommend that the Board approve the 

Sacramento PM10 Plan, including the transportation conformity budgets for the County, 

as a revision to the California SIP for submittal to U.S. EPA. In addition, ARB staff 

recommends that the Board approve the District’s request to U.S. EPA that Sacramento 

County be redesignated from nonattainment to attainment for the national PM10 

standard.