2008 PM2.5 Plan 

Chapter 1 

 

Progress and Current Air Quality 
2008 PM2.5 Plan 

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San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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Chapter 1: Progress and Current Air Quality

1.1 INTRODUCTION 

This chapter presents an overview of the progress that has been made and the current 

state of the San Joaquin Valley’s air quality. Over the past 20 years, the hard work and 

financial and personal investments made by industries, individuals, and agencies are 

producing real and tangible results that yield an improvement in air quality. 

1.2 WHAT IS PM2.5? 

Particulate matter (PM) is any material except pure water that exists in the solid or liquid 

state in the atmosphere. Under current regulations, particulate matter (PM) is 

differentiated by particle size as opposed to composition. PM can be emitted directly as 

primary PM, and it can form in the atmosphere through the reactions of precursors to 

form secondary PM (see Figure 1-1). Since PM occurs as a wide range of compounds, 

PM planning requires an evaluation of emissions inventories for several pollutants: 

direct PM, nitrogen oxides (NOx), volatile organic compounds (VOCs), sulfur dioxide 

(SO2), and ammonia (NH3). Some of these precursors also form other air pollutants, 

such as ozone. Control measures that reduce PM precursor emissions tend to have a 

beneficial impact on ambient PM levels. Air quality modeling and other forms of 

analyses are used to evaluate the benefit of precursor controls on PM levels in 

individual regions (see Chapter 3). 

Figure 1-1 PM2.5 Formation 

PM2.5 Formation Formation

Organic 

compounds

Organic 

compounds

Volatile compounds Volatile compounds

Semivolatile

compounds

Semivolatile

compounds

Semivolatile and 

gaseous compounds

Semivolatile and 

gaseous compounds

Organic Particles Organic Particles

Secondary Organic 

Particles

Secondary Organic 

Particles

NO NO2

Ozone

NH3

SO2 Inorganic 

Sulfate

Inorganic 

Sulfate

Ammonium 

Sulfates

Ammonium 

Sulfates

Ammonium 

Nitrate

Ammonium 

Nitrate

Chemical Deposition

RO2

Chemical Deposition

H2SO4

Inorganic 

Nitrates

Inorganic 

Nitrates

NO3

N2O5

HNO3

È

O2 H2O2 O3

OH H2O

OH

O2

OH

O2
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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The resulting ambient PM mixture includes aerosols (fine airborne solid particles and 

liquid droplets, except pure water) consisting of components of nitrates, sulfates, 

elemental carbons, organic carbon compounds, acid aerosols, trace metals, geological 

materials, etc. Primary PM can be emitted either naturally (windblown dust and 

wildfires) or from human (anthropogenic) activity: agricultural operations, industrial 

processes, combustion of wood and fossil fuels, construction and demolition activities, 

and entrainment of road dust. 

 

PM in the air may eventually be removed from the atmosphere by gravitational settling, 

rainout (attaching to water droplets as they fall to the ground), and washout (being 

absorbed by water molecules in clouds and later falling to the ground with rain). 

However, particles can condense or re-enter the gas phase under different 

environmental conditions. All of these processes contribute to the complexity of 

predicting PM levels in the atmosphere using computer simulation models. 

State and federal air quality standards differentiate two size fractions of PM (see Figure 

1-2): PM that is 10 microns or less in diameter (PM10) and the smaller subset that is 2.5 

microns or less in diameter (PM2.5). The District’s previous PM planning efforts 

focused on PM10, also referred to as “inhalable coarse particles.” Under the control 

strategy put forth in the 2003 PM10 Plan and its amendments, and reaffirmed in the 

2006 PM10 Plan, the Valley has reached attainment of the federal PM10 standards. 

The SB656 report prepared and adopted to meet state requirements in 2006 confirmed 

that the District’s PM10 and precursor strategy is a benchmark for other air districts in 

California. In September 2007, the District Governing Board adopted the 2007 PM10 

Maintenance Plan and Request for Redesignation, which included meteorological 

analysis, a contingency plan, and modeling. This plan demonstrated continued attainment 

through 2020, which is necessary to allow the U.S. Environmental Protection Agency (EPA) 

to officially redesignate the San Joaquin Valley to attainment of the PM10 standards. The 

California Air Resources Board (ARB) approved the PM10 Maintenance Plan on 

October 25, 2007. The 2008 PM2.5 Plan is the District’s first plan focused specifically 

on PM2.5 (also referred to as “fine particles”), although the control strategies of the 

PM10 plans and 2007 Ozone Plan have already improved the Valley’s ambient PM2.5 

levels. 

1.3 ADOPTED RULES 

Since its formation in 1992, the San Joaquin Valley Unified Air Pollution Control District 

(District) has adopted about 500 rules and rule amendments. The District was the 

nation’s first air district to adopt a progressive Indirect Source Review (ISR) program, 

which reduces emissions from new indirect sources Valley-wide, such as commercial, 

industrial, and residential developments. The District was also the first air district in the 

nation to adopt a rule to control emissions of volatile organic compound (VOC) from 

wine production and storage. This rule contains groundbreaking compliance options 

that offer flexibility to operators without sacrificing emission reductions. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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Figure 1-2 Diameter Comparison: Human Hair, Sand, PM10, and PM2.5 

The District was the first air district in the state to regulate emissions from on-field 

agricultural operations. To date, through the Conservation Management Practices 

(CMP) rule, the District has received 6,400 CMP plans from Valley farmers that reduce 

particulate matter emissions from 3.2 million acres of productive agricultural land. The 

District was also the first major air district in the state to regulate the use of residential 

fireplaces. Other major air districts in the state are now using the District’s regulation as 

the benchmark for their regulatory efforts. In addition, the District leads the nation with 

its stringent emission limits on engines, boilers, turbines, and glass-melting furnaces. 

Air quality improvements evidence the success of the District’s innovative rules, as 

discussed in the next section. 

As noted in the ARB staff report on Accelerating San Joaquin Valley Air Quality 

Progress (2007):

“A snapshot of rule stringency taken ten years ago would have shown the South 

Coast District with the State’s most stringent rules, setting the benchmark for 

stationary source control. The San Joaquin Valley District would have been seen 

lagging behind. The picture today looks very different. While the South Coast is 

still pushing the limits of stringency, the San Joaquin Valley District has caught 

up. Since early this decade, the District has set aggressive rulemaking targets in 

its SIPs for ozone and particulate matter.”1

 

1

 California Air Resources Board (ARB) (November 6, 2007). ARB Staff Report to the Air Resources Board: 

Accelerating San Joaquin Valley Air Quality Progress. Page 12. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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1.4 EMISSIONS AND CURRENT AIR QUALITY 

The two major indicators of air quality improvement are emissions inventories and 

ambient air quality data. Emissions inventories are estimates indicating how much 

direct pollution is going into the air as a result of various activities. Ambient air quality 

data, which is measured by monitors, tells us how much pollution is in the air we 

breathe. Together, these data illustrate progress made in improving air quality as well 

as the great challenge we face in meeting future standards. 

1.4.1 Emissions 

An emissions inventory is a tabulation of pollutant emissions into the atmosphere. The 

District uses comprehensive emissions inventories to develop control strategies; 

determine the effectiveness of permitting and control programs; provide input into 

ambient receptor, aerosol, photochemical, and statistical models; fulfill reasonable 

further progress requirements; and screen sources for compliance investigations. 

Emissions inventory data, like ambient monitoring data, are also used as indicators for 

trends in air pollution. 

To reduce the Valley’s PM2.5 levels further, the 2008 PM2.5 Plan presents a control 

strategy that is based on an exhaustive evaluation of the emissions inventories of 

directly emitted PM2.5 as well as relevant PM2.5 precursors. Typically, an emissions 

inventory is organized by emission source category. Source categories consist of 

several broad groups: 

 Mobile sources – motorized vehicles 

o On-road sources include automobiles, motorcycles, buses, and trucks 

o Other or off-road sources include farm and construction equipment, lawn 

and garden equipment, forklifts, locomotives, boats, aircraft, and 

recreational vehicles 

 Stationary sources – fixed sources of air pollution 

o Power plants, refineries, and manufacturing facilities 

o Aggregated point sources - facilities (such as gas stations and dry 

cleaners) that are not typically inventoried individually but are estimated as 

a group and reported as a single source category. 

 Area sources –human activity that takes place over a wide geographic area 

o Includes consumer products, fireplaces, tilling, and unpaved road dust 

 Natural sources – non-anthropogenic, naturally occurring emissions 

o Geogenic sources, such as petroleum seeps 

o Biogenic sources, such as emissions from plants 

o Wildfire sources 

The District has made significant progress in reducing PM2.5 precursor emissions (see 

Figure 1-3). These reductions are a result of the many rules and programs put in place 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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by the District and the California Air Resources Board (ARB). These reductions 

represent an impressive accomplishment, especially in light of the 37% increase in 

population in the San Joaquin Valley over the same time period. 

Figure 1-3 PM2.5 and Precursor Emissions Reductions, 1990-2005 

(Annual Averages, 2006 Almanac, base year 2005) 

0

200

400

600

800

1000

1200

1990 2005

tons per day, annual average

SO2

Direct PM2.5

NOx

Appendix B contains detailed tables showing the emissions inventories for directly 

emitted PM2.5, NOx, VOC, SO2, and ammonia. This appendix also contains 

information on emissions inventory maintenance. Motor vehicle transportation 

conformity budgets, which are required in state implementation plans (SIPs) and are 

based on motor vehicle emissions inventories, will be available in Appendix C in the 

next version of the plan. Emission reduction credits (ERCs) are in Appendix D. 

1.4.2 Air Monitoring Data and Analysis 

The District operates an extensive air monitoring network to measure progress toward 

compliance with the National Ambient Air Quality Standards (NAAQS). Air quality 

monitoring networks are designed to monitor areas with high population densities, areas 

with high pollutant concentrations, areas impacted by major pollutant sources, and 

areas representative of background concentrations. Together, the District and ARB 

operate 11 filter-based PM2.5 monitoring sites throughout the San Joaquin Valley. 

Figure 1-4 shows the Valley’s air quality monitoring sites. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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Figure 1-4 Atmospheric Monitoring Sites within the San Joaquin Valley Air Basin 

PM is measured and expressed as the mass of particles contained in a cubic meter of 

air (micrograms per cubic meter, or μg/m3). The data collected from the District’s 

network of filter-based PM2.5 monitors is used to calculate design values for the 24-

hour and annual PM2.5 standards, as outlined in EPA guidance2

 and regulations. 

To calculate the 24-hour average design values (three-year 24-hour average 98th

percentile): 

1. Determine the 98th percentile PM2.5 concentration value for each year of three 

consecutive years, 

2. Average these three values 

3. Round to the nearest 1.0 μg/m3

 

To calculate annual design values (three-year annual mean values): 

1. Average the data by quarter, 

2. Average the four quarters in a calendar year to determine that year’s average 

3. Average three consecutive years 

4. Round to the nearest 0.1 μg/m3

 

 

2

 EPA, Guideline on Data Handling Conventions for the PM NAAQS, April 1999; Appendix N of 40 CFR Part 50 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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The three-year 24-hour average 98th percentile and three-year annual mean values are 

then compared to their respective National Ambient Air Quality Standard. Rounding 

convention guidelines are also incorporated into the annual and 24-hour calculations. 

Data substitution guidelines are only used in the 24-hour average calculation. 

EPA promulgated the 1997 PM2.5 NAAQS designations based on 2001-2003 data in 

the Federal Register on January 5, 2005, effective April 5, 2005 (70 FR 944-1019). 

Figure 1-5 shows 24-hour and annual PM2.5 design values for each of the District’s 

PM2.5 monitoring sites based on 2004-2006. To meet the attainment test for the 1997 

PM2.5 NAAQS, a site must attain both the 24-hour NAAQS (with a design value less 

than or equal to 65.49 μg/m3

) and the annual NAAQS (with a design value less than or 

equal to 15.0 μg/m3). For the San Joaquin Valley Air Basin to be in attainment, all sites 

in the Valley must attain the PM2.5 NAAQS. Because several monitoring sites do not 

pass the attainment test for the annual PM2.5 standard, the Valley is nonattainment for 

the 1997 PM2.5 NAAQS. 

Figure 1-5 PM2.5 Design Values and Attainment Test 

(based on 2004-2006 monitoring data) 

Attainment Tests 

(Sites must pass both tests) 

24-hour PM2.5 

NAAQS 

Annual PM2.5 

Monitoring Site NAAQS 

Design 

Value 

(μg / m3)

Within the 

NAAQS? 

Design 

Value 

(μg / m3)

Within the 

NAAQS? 

Attainment?

Stockton 41 Yes 12.9 Yes Yes 

Modesto 51 Yes 14.1 Yes Yes 

Merced 45 Yes 14.7 Yes Yes 

Fresno-1st 58 Yes 16.7 No No

Fresno-Winery 59 Yes 17.2 No No

Clovis 57 Yes 16.2 No No

Corcoran 58 Yes 17.2 No No

Visalia 56 Yes 18.2 No No

Bakersfield-Golden 64 Yes 18.5 No No

Bakersfield-California 62 Yes 18.5 No No

Bakersfield-Planz 65 Yes 18.9 No No

San Joaquin Valley Air Basin No 

PM2.5 data review for trend analysis is limited since PM2.5 monitoring has been in 

progress for less than a decade. Figures 1-6 and 1-7 provide 24-hour and annual 

design values by site for 2004, 2005, and 2006: 

 The 2006 24-hour PM2.5 design value is the 3-year average of the 98th

percentile values of 2004, 2005, and 2006. 

 The 2005 24-hour PM2.5 design value is the 3-year average of the 98th

percentile values of 2003, 2004, and 2005. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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 The 2004 24-hour PM2.5 design value is the 3-year average of the 98th

percentile values of 2002, 2003 and 2004. 

Figure 1-6 shows that although the Bakersfield-California site’s data yielded 24-hour 

design values above the standard in 2004 and 2005, all Valley sites showed design 

values below the 24-hour standard in 2006. Figure 1-7 shows that although several 

Valley sites still had design values over the annual standard in 2006, annual design 

values are improving overall. More PM2.5 data analysis is available in Appendix A. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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Figure 1-6 24-hour Design Values at Valley Sites, 2004, 2005, and 2006 

0 10 20 30 40 50 60 70 80

Stockton

Modesto

Merced

Fresno-1st

Fresno-Winery

Clovis

Corcoran

Visalia

Bakersfield-Golden

Bakersfield-California

Bakersfield-Planz

3- Year Average 24 hour 98th Percentile Concentration (μg / m3

)

2004

2005

2006

NAAQS = 65
San Joaquin Valley Unified Air Pollution Control District April 30, 2008

Chapter 1: Progress and Current Air Quality 

2008 PM2.5 Plan 

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Figure 1-7 Annual Design Values at Valley Sites, 2004, 2005, and 2006 

0 5 10 15 20 25

Stockton

Modesto

Merced

Fresno-1st

Fresno-Winery

Clovis

Corcoran

Visalia

Bakersfield-Golden

Bakersfield-California

Bakersfield-Planz

3- Year Average Annual Mean Concentration (μg / m3

)

2004

2005

2006

NAAQS =15.0