2007 Ozone Plan 

Chapter 3 

 

What is Needed to Demonstrate Attainment? 
2007 Ozone Plan 

This page intentionally blank.
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-1

Chapter 3: What is Needed to Demonstrate 

Attainment?

3.1 INTRODUCTION 

This chapter describes what is needed to demonstrate that the San Joaquin Valley can 

attain the federal air quality standards for 8-hour ozone by the statutory attainment date. 

To understand the scope of this effort, it is helpful to consider local challenges, such as 

the San Joaquin Valley’s natural conditions, population growth, and jurisdictional 

limitations. Computer modeling is used to determine the quantity of emissions 

reductions that the District will need to demonstrate attainment of the standards. 

3.2 CHALLENGES 

3.2.1 Natural Conditions 

The topography and climate in the San Joaquin Valley create ideal conditions for 

generating and trapping 

ozone precursors, and then 

creating and retaining ozone 

air pollution. Comprising 

nearly 25,000 square miles, 

the San Joaquin Valley Air 

Basin (SJVAB) is a 

continuous inter-mountain 

valley (Figure 3-1). On the 

western edge is the Coast 

Mountain range, with peaks 

reaching 5,020 feet, and on 

the east side of the Valley is 

the Sierra Nevada range 

with some peaks exceeding 

14,000 feet. The Tehachapi 

Mountains form the southern 

boundary of the Valley. This 

mountain range includes 

peaks over 6,000 feet and 

contains mountain passes to 

the Los Angeles basin and 

the Mojave Desert. 

Figure 3-1 San Joaquin Valley Topography 

San Joaquin

 Stanislaus

 Merced Madera 

 Fresno 

Tulare Kings 

Kern
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-2

Low precipitation levels, high temperatures, and light winds in the SJVAB are conducive 

to elevated ozone levels. The SJVAB averages over 260 sunny days per year. Nearly 

90 percent of the annual precipitation in the SJVAB falls between the months of 

November through April, although average annual rainfall for the entire SJVAB is about 

10 inches on the valley floor. Annual rainfall totals vary from north to south, with 

northern counties experiencing as much as 11 inches of rainfall and southern counties 

experiencing as little as four inches per year (District 2003). The eastern SJVAB 

experiences more rainfall than western areas. 

The Valley floor experiences hot, dry summers and foggy winters. The average 

temperature for Fresno from 1948 to 2004 was 63.3°F. Over the same time period, 

Fresno averaged 106.3 days per year with temperatures over 90°F. Daily high 

temperature readings in July averaged 98°F. Fresno averages 36 days per year with 

temperatures 100°F or hotter (Western Regional Climate Center 2005). 

Inversion layers and vertical mixing can also influence ambient air quality. Whereas 

temperatures in the atmosphere usually decrease with height above the surface, a 

temperature inversion is when temperature increases with height in part of the 

atmosphere (Figure 3-2). The base of the inversion, which is also known as the mixing 

height, acts as a lid on the atmosphere, trapping pollution by limiting vertical dispersion. 

During inversion events, air pollutant emissions build up, ozone precursors then react to 

form ozone, and ozone levels increase from day to day. 

Winds (at ground level or at higher altitudes) transport pollutants from other basins into 

the Valley, within the Valley to areas downwind, and from the Valley into other regions. 

Figure 3-3 depicts typical wind flow patterns for day and night during the ozone season 

in the SJVAB. 

Figure 3-2 Vertical Dispersion, With and Without Temperature Inversion (b) without inversion (a) inversion 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-3

Figure 3-3 San Joaquin Valley Wind Patterns During Ozone Season 

Source: SJVAQSPC 1996 

The amount of pollution transported from other areas into the Valley varies. During the 

daytime, surface winds pick up ozone precursors emitted in the Bay Area and transports 

them down the SJVAB where they can eventually form ozone. The impact of pollutants 

transported from other air basins into the Valley generally declines from north to south 

(ARB 2001). 

Precursors originating in the SJVAB are also transported within the Valley. Local 

emissions are thought to be more responsible for the Valley’s worst ozone air quality. 

Transport moves precursor emissions from Valley source areas (Stockton, Modesto, 

Merced, etc.) south towards areas southeast of Fresno and around Bakersfield, where 

they are converted to ozone. Monitoring locations for Parlier, Edison, and Arvin (see 

Figure 1-3) often experience the highest ozone levels in the SJVAB. 

Transport can also move Valley pollution into other air basins. During the daytime, 

heated air rises into the mountains and transports ozone and other pollutants up the 

Sierra Nevada, Tehachapi, and Coastal Mountains. According to the ARB, the Valley’s 

pollution can affect ozone air quality in the broader Sacramento area, the Great Basin 

valleys, the mountain counties, the Mojave Desert, and the north central and south 

central coasts, depending on meteorological conditions (ARB 2001). 

However, some pollution is not transported into other basins, but back into other parts of 

the Valley. At night, the air is no longer able to exit the southern end of the SJVAB 

because it encounters cooler drainage winds from the surrounding mountains, so it is 

forced back north in a circular flow pattern (Figure 3-3) known as the Fresno eddy. The 

eddy circulates pollutants in a counterclockwise pattern and returns polluted air to urban 

areas where more precursors are added the next day. Throughout the Valley, some of 

the pollutants transported to higher altitudes from daytime heating return to the Valley 

floor at night because of drainage winds from the mountains. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-4

Transport studies increase understanding of how pollution from other areas may impact 

the Valley as well as how pollution originating in Valley areas may impact other places 

both within and beyond the Valley. Improved emissions inventories, improved 

databases on meteorological behavior and atmospheric chemistry, and improved gridbased photochemical models all contribute to ongoing studies that will enhance our 

understanding of pollutant transport. Future District plans will incorporate any 

significant advances in knowledge regarding transport as it becomes available from 

ARB and other agencies. 

3.2.2 Population Growth 

Increased population, which results in increased vehicle activity and more consumer 

product use, leads to increased emissions of ozone precursors, undermining the 

progress made by regulations. Table 3-1 shows population estimates for the eight 

counties of the SJVAB by county, including projections to 2020. In 2006, 9.9% of 

California’s population resided in the SJVAB (California Department of Finance 2005). 

This is projected to grow slightly, with 11% of California’s total population residing in the 

San Joaquin Valley in 2020. Between 2002 (the base year for 8-hour ozone planning 

purposes) and 2020, the population of the San Joaquin Valley will grow by 43%. In 

contrast, the total population for the State of California will grow 24% over the same 

time period. 

 

Table 3-1 SJVAB Population by County 

% Change, 

County 2002 2008 

Projection

2014 

Projection

2020 

Projection 2002-2020 

Fresno 837,459 925,588 1,015,838 1,114,654 33 

Kern a 580,794 653,864 718,656 789,068 36 

Kings 135,218 152,181 167,701 184,751 37 

Madera 129,728 146,654 163,753 183,966 42 

Merced 224,488 264,195 310,961 360,831 61 

San Joaquin 608,594 713,435 844,074 989,462 63 

Stanislaus 479,203 539,425 596,967 653,841 36 

Tulare 384,650 433,356 485,889 543,749 41 

TOTAL 3,380,134 3,828,698 4,303,839 4,820,322 43 a

 Valley portion; Kern County has portions located outside of the San Joaquin Valley Air Basin. 

Source: Developed using Population Trends Reports, California Department of Finance (2005)

3.2.3 Jurisdictional Limits and Regulatory Authority 

Attainment of air quality standards for 8-hour ozone and the reduction of precursor 

emissions in the SJVAB require the cooperation of local and/or regional, state, and 

federal governments. At the federal level, the EPA is responsible for establishing 

federal motor vehicle emission standards. The EPA is also responsible for reducing 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-5

emissions from locomotives, aircraft, heavy duty vehicles used in interstate commerce, 

and other sources such as off-road engines that are either preempted from state control 

or best regulated at the national level. 

The ARB establishes emission standards for on-road motor vehicles and some off-road 

sources. The ARB also establishes fuel specifications and develops consumer product 

standards for meeting air quality goals in California. Other state agencies such as the 

Department of Pesticide Regulation (DPR), California Department of Transportation 

(CalTrans), and the Bureau of Automotive Repair also have responsibility for certain 

emissions sources. 

Districts like the San Joaquin Valley Air Pollution Control District have authority to 

regulate stationary sources and some area sources of emissions. Districts cooperate 

with Regional Transportation Planning Agencies (TPAs) to develop measures affecting 

local transportation activity that are included in a SIP. In turn, the TPAs coordinate the 

process to identify and evaluate potential control measures and compile local 

government commitments that will be included in the local or regional air quality plan. 

The primary jurisdiction of the District is therefore limited to just part of the total 

emissions inventory (Figure 3-4). Based on summer-average 2005 inventories 

developed for this plan, 20% of the total NOx inventory for the SJVAB is under the 

primary regulatory jurisdiction of the District, and 55% of the total VOC inventory for the 

SJVAB is under the primary regulatory jurisdiction of the District. 

Figure 3-4 Ozone Precursors by Source Type1

 

(Based on Summer Emissions Inventories, O3 SIP (v1.06_RF980)) 

 

1

 Please note that Mobile Sources includes on-road and off-road sources. For NOx, 67% of the total mobile source 

emissions in 2005 come from on-road sources, and 33% of the total mobile source emissions come from other mobile 

sources. For VOC, 57% of the total mobile source emissions come from on-road sources, and 43% of the total 

mobile source emissions comes from other mobile sources. 

Oxides of Nitrogen (NOx)

Stationary & 

Area 

Sources

20%

Mobile 

Sources

80%

Volatile Organic Compounds

Stationary & 

Area 

Sources

55%

Mobile 

Sources

45%
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-6

Although the responsibility for establishing the tailpipe emissions standards for the 

mobile sources belongs to state and federal governments, additional reductions are 

needed to reach attainment. Therefore, the District is also proposing measures, such 

as trip reduction, green contracting, and enhanced indirect source review, to provide 

additional mobile source emissions reductions for this plan and will continue to use 

incentive programs to accelerate mobile source emissions reductions. 

3.3 MODELING 

Air quality models simulate the formation, transport, and removal of ozone from the 

lower atmosphere to predict ozone concentrations in future years. The models are 

computer programs that estimate the contribution of ozone from emissions, natural 

conditions, and chemical changes. Modelers used state of the art procedures to 

perform modeling for this plan, including implementing a comprehensive measurement 

program, formulating and formatting model ready data inputs, running the model, 

comparing the model prediction to the base case, developing future year emissions 

scenarios, and running those with the model to predict future ozone levels. The goal of 

these modeling exercises is to formulate a controlled emissions scenario where ozone 

levels will achieve the federal 8-hour ozone standards. Appendix F provides more 

information on the modeling conducted for this plan. 

3.3.1 Model Choice 

The EPA-approved “Comprehensive Air Quality Model with Extensions” (CAMx) 

modeling system was chosen to estimate the amount of emissions reductions needed to 

achieve standards. A meteorological model, Mesoscale Model version 5 (MM5), was 

used to drive the transport and dispersion in the CAMx model. Modelers choose the 

[California] Statewide Air Pollution Research Center (SAPRC) chemical mechanism for 

final run, which is slower computationally than other mechanisms but treats the 

chemical production of ozone in more detail. The choice of the modeling system was a 

consensus among the modelers and stakeholders in Central California. Discussion of 

these choices in models occurred through the Central California Ozone Study (CCOS) 

and the Northern California SIP/Transport Working Groups. In addition to calculating 

ozone and other pollutant concentrations, this model also has the ability to diagnose 

problems with individual processes that simulate the creation, dispersion, and 

deposition of pollutants. 

3.3.2 Base Case 

Two modeling episodes were chosen for use in this plan: July 31-August 2, 2000 and 

July 11-12, 1999. Another episode in September 2000 was attempted, but to date, 

model performance has been poor and consequently this episode has not been used. 

Episodes in 2000 were partially chosen because they fall within the intensive CCOS 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-7

monitoring period where a comprehensive data set to use in modeling is available. The 

1999 episode was chosen because the Bay Area Air Quality Management District 

(BAAQMD) believed ozone was representative of their concentrations. In addition to 

selecting the model, the CCOS technical committee and Northern California 

SIP/Transport working group chose these episodes. 

For both the 1999 and 2000 episodes, emissions and meteorological conditions 

simulated ozone levels that were near design values at key air monitoring sites. In 

general, modeling of these episodes met performance standards, but some 

concentrations were under-predicted at sites in the SJVAB. During the July – August 

2000 episode, meteorology was unusually conducive to creating ozone. A comparison 

of this episode to historical cases indicates that some days of the episode were extreme 

meteorological and pollutant events. For July 1999, statistical analyses also showed 

that meteorology was unusually conducive for forming ozone. According to EPA 

guidelines, although unusual, these pollutant and meteorological characteristics are the 

average worst case, which make them good candidates for modeling. However, for 

these episodes, typical meteorological features that have been seen in the past, such 

as, slope, eddy, and marine flows were evident. The episodes did represent the 

transport and dispersion that have been observed historically in Central California. In 

accordance with EPA guidance, modelers now use a relative reduction factor (RRF), 

which scales the reductions required to achieve the standard to the present design 

value, to address issues regarding the representativeness of the ozone concentrations 

measured in the episodes (see Section 3.3.4 and Appendix F). 

During the July 30-August 2, 2000 base case, a large wildfire produced ozone 

precursors that affected air quality in the San Joaquin Valley. Future year modeling was 

done with wildfires removed. Additional days were modeled to include the ramp up of 

ozone during these events. 

3.3.3 Weight of Evidence 

A weight of evidence approach compares conceptual descriptions, episode 

categorization techniques, adjusted air quality trends, and hydrocarbon analysis to 

modeling results. The purpose of these additional analyses is to provide additional (i.e. 

beyond photochemical modeling) insights into ozone behavior in the atmosphere. As 

noted in EPA’s modeling guidance for 8-hour ozone, “Corroborative evidence should 

accompany all modeled attainment demonstrations” (EPA 2005). Please see Appendix 

F for more information on weight of evidence. 

3.3.4 RRF 

The relative reduction factor (RRF) is a monitor-specific value that is calculated by 

dividing the average simulated, future year daily peak 8-hour ozone concentration by 

the average simulated base year daily peak concentration. The baseline year 

monitored design values are then multiplied by the RRFs to predict future-year 8-hour 

design values for each monitor site. Use of RRF allows the output of photochemical 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-8

models to be used in a relative, rather than absolute, sense. See Appendix F for more 

information on RRF. 

3.4 CARRYING CAPACITY 

Using the most recent emission inventory available, modelers ran various combinations 

of NOx and VOC emissions reductions. The combinations generated a data set of 

predicted ozone levels as a function of percentage reductions of anthropogenic NOx 

and VOC emissions. The data was plotted as carrying capacity diagrams, which shows 

the level of emissions that the atmosphere can “carry” and still demonstrate attainment. 

Planners looked at the combinations of VOC and NOx percentage reductions that are 

needed to attain the standard and then developed a corresponding control strategy. 

The carrying capacity modeling runs were conducted with an episode-specific emission 

inventory based on O3SIP 1.06 (Table B-4). The 2020 baseline emission inventory 

values used in the modeling were 302 tons per day of NOx and 308 tons per day of 

VOC. The 2023 modeling recently provided by ARB used baseline values of 300 tons 

per day NOx and 415 tons per day VOC. For both modeling exercises, the baseline 

values were cut in 20% increments, and the Valley’s NOx carrying capacity for ozone 

was estimated as ranging between 180 tons per day with a 50% anthropogenic VOC 

reduction, and approximately 160 tons per day with no VOC reductions. 

Although all sites in the Valley must be within the standard for the Valley to be 

redesignated into attainment, some sites will be within the standard before others. As 

shown in Appendix F, carrying capacity diagrams show that approximately 49% 

reduction of NOx emissions from the 2020 baseline throughout the Central California 

modeling domain is needed to achieve the 8-hour average ozone NAAQS in the San 

Joaquin Valley. 2023 modeling indicates that a 47% reduction is needed from the 

baseline inventory used for 2023 modeling. This amount of control is driven by the 

reductions needed to achieve the NAAQS at the air quality monitor location near Arvin 

(see Figure 1-3 in Chapter 1 for the Arvin monitoring site location). Other sites will be 

within the standard earlier, with fewer reductions. For instance, a 15% domain-wide 

reduction of 2020 NOx emissions is needed to demonstrate concentrations within the 8-

hour ozone NAAQS at Parlier, the monitoring site downwind of Fresno in the central 

portion of the Valley with historically the worst air quality in the Central San Joaquin 

Valley. By 2020, the carrying capacity diagrams suggest that the Fresno-Sierra Sky 

Park monitoring site will need the most reductions to achieve the NAAQS in the Central 

SJV. The details of the amount of reductions needed for Fresno-Sierra Sky Park are 

discussed below. Sites further north, such as Merced, Modesto, and Stockton are 

projected to be in attainment for the NAAQS by 2020. 

Carrying capacity diagrams (available in Appendix F) also indicate qualitatively whether 

a strategy of reducing only VOC emissions, a NOx-only strategy, or a combination 

strategy is needed to achieve the NAAQS. When the lines on the diagrams are more 

horizontal, this indicates that more NOx control is needed. When they are more vertical, 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-9

a control strategy requires more VOC control. For some areas that are still out of 

attainment in 2020, the attainment (85 ppb) lines on the carrying capacity diagrams are 

flat indicating a need for NOx control. However, the carrying capacity diagrams also 

show that the lines are curved in the upper right hand portion of the plots. This 

indicates VOC control would be advantageous in the beginning years of the control 

program.2

 Thus, for 2020, a strategy based on only NOx control is our principal interest. 

VOC controls are considered for the purpose of decreasing ozone levels faster in the 

initial stages of the control strategy. 

Figures 3-5 and 3-6 show that for the sites near Arvin and at Fresno-Sierra Sky Park 

that are projected to have the worst air quality problems in 2020, reductions in VOC 

emissions will assist in reducing ozone levels early on in the control program, but will 

not change the NOx carrying capacity measurably. These carrying capacity diagrams 

are used to assess the amounts of NOx and VOC reductions needed to achieve the 

NAAQS. The x-axis is the percentage of anthropogenic VOC emissions that were run 

through the ozone model and y-axis is the percentage of anthropogenic NOx emissions. 

Lines on the plots represent equal concentrations of eight-hour averaged ozone in ppb. 

These lines are the projection of the design value for each pair of NOx and VOC 

emissions inventory percentages. The broad solid red line on the plots is 85 ppb, below 

which the NAAQS for eight-hour average ozone is attained; the other solid red lines 

indicate regions of emissions control that exceed the NAAQS. The dashed green lines 

represent areas on the plots where attainment is projected to be reached given that 

percentage of NOx and VOC inventories. Each point below on the bolded line would 

represent the amount of VOC and NOx needed to achieve the NAAQS. For instance, at 

Fresno-Sierra Sky Park, 75% of the NOx inventory would achieve attainment at VOC 

inventories of 75% or less. As an alternative, 80% of the NOx inventory and 60% of the 

VOC inventory would achieve attainment. 

The carrying capacity diagrams show that as NOx reductions are first achieved VOC 

reductions are useful for control of ozone. This is indicated by the curved lines in the 

upper right hand corner of the graphs. However, as more NOx is reduced the curved 

lines transition to flat indicating that further VOC emissions reductions are not useful. 

For example, on the carrying capacity diagram for the Arvin monitoring location, starting 

from the top right hand corner, the fastest route to the next line (representing 98 ppb) 

would be to reduce both VOC and NOx by about 2% or 98% of the inventory. The lines 

on the curves become much straighter at about 80% indicating that at that point a NOx 

control strategy would be more advantageous. 

 

2

 Carrying capacity diagrams produced for the District’s 2004 Extreme Ozone Attainment Demonstration Plan (for 1-

hour ozone) indicated a need for NOx and VOC emission reductions for demonstrating 2010 attainment of the 1-hour 

ozone NAAQS (using the Bakersfield location). 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-10

Figure 3-5 Arvin Monitoring Location Carrying Capacity, 2020 

Figure 3-6 Fresno-Sierra Sky Park Carrying Capacity, 2020 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-11

For other sites in the SJV that are nearer attainment, NOx and VOC reductions are 

needed to achieve the NAAQS. Appendix F, shows that attainment lines for those sites 

that are projected to be in attainment by 2020 are curved or slanted in a way indicating 

that both NOx and VOC reductions are needed. Plots of nonattainment sites other than 

Arvin and Sierra Sky Park indicate that the region around the attainment line would 

benefit from both NOx and VOC controls. Using the RRF, and 40 ppb offset3

, the 

preferred method of calculating attainment, as shown in the lower right of the carrying 

capacity pages in Appendix F, one would conclude that for sites other than the highest 

ozone sites, a NOx and VOC reduction strategy would be the most expeditious route to 

attainment.4 This would support the conclusion that VOC controls in early years would 

be beneficial to attaining the NAAQS. Recent modeling for 2023 confirms results 

established from 2020 modeling. 

As described to this point, carrying capacity diagrams typically only show how ozone 

responds to percent reductions off of a particular emission inventory. These same 

graphs can also show absolute carrying capacities in tons per day of emissions. This 

type of carrying capacity diagram is created by multiplying percent reductions by the 

baseline emission inventory used for modeling. Figure 3-7 and Figure 3-8 show 

modeling responses for the monitoring site near Arvin with emission units in tons per 

day of VOC and NOx instead of percent. One item that becomes evident when looking 

at tonnage based carrying capacity diagrams is that the baseline emission totals play a 

critical role in establishing the range of emissions over which ozone concentration 

information can be obtained. For example, since 2020 is expected to have significantly 

fewer emissions than currently exist in the inventory, 2020 modeling results cannot be 

used to evaluate ozone responses at current emission levels near 600 tpd of NOx. 

In order to compare changing emission levels at numerous sites, the attainment target 

(85 ppb 8-hour ozone line) can be extracted from site-specific carrying capacity 

diagrams and displayed on the same graph. Figure 3-9 and Figure 3-10 combine the 

attainment lines from the Arvin, Edison, Bakersfield-California, Fresno-Sierra Sky Park 

and Parlier carrying capacity diagrams of Appendix F onto one graph. Because many 

sites in the valley were modeled in attainment with the 2020 and 2023 inventories their 

carrying capacities cannot be determined because their attainment lines are at emission 

levels that are higher than those modeled. In order to show the attainment lines for sites 

in attainment in 2020 and 2023, the 85 ppb line was acquired from preliminary 2012 

modeling. Merced, Visalia and Turlock were selected from the preliminary 2012 

modeling to add to the graph. Because the attainment lines for these locations are 

based on preliminary modeling using older inventories and a different modeling year 

their carrying capacities have been used as guidance only. 

 

3

 The lower right hand corner plots shown in Appendix F use the RRF and a 40 ppb offset to predict the future design 

value ozone concentration. This method was agreed to by ARB and District modelers to be the best representation 

of the amount of ozone precursor emission reduction needed to achieve the NAAQS. This method of estimation 

subtracts 40 ppb background levels from the RRF calculation and then adds it back in again after the design value is 

scaled by the RRF. In this manner, the background in the model is correctly not affected by the control of 

anthropogenic emissions. Modelers generally consider 40 ppb to be a viable background ozone concentration. 

4

 Carrying capacity diagrams in Appendix F that have ozone isopleths (plots for sites in attainment have no isopleths), 

other than Arvin or Fresno Sierra-Skypark, show isopleths that are not completely horizontal. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-12

Figure 3-7 Arvin Monitoring Location Carrying Capacity (TPD), 2020 

Figure 3-8 Arvin Monitoring Location Carrying Capacity (TPD), 2023 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-13

To evaluate the effectiveness of attainment strategies, the baseline emission inventory 

and the proposed SIP strategy were also plotted on Figure 3-9 and Figure 3-10. The 

SIP Strategy is shown in black and the baseline emissions inventory is gray. The SIP 

Strategy emission line from 2020 and 2023 is shown as a dashed line to indicate 

Advanced Technology as described in other parts of this plan. By following the emission 

inventory projections on the graph, one can determine which sites will be in attainment 

for a given year and how variations in the control strategy can produce different 

attainment results. This type of analysis assumes that the atmosphere can only hold a 

limited about of VOC and NOx before enough ozone is produced to exceed the 

attainment standard. The amounts of emissions dictate the attainment status, not the 

year. The year is only important because it is used to estimate the level of emissions for 

that year. For example, the site near Arvin can only hold about 160 tons per day of NOx 

before the standard is exceeded. It does not matter what year 160 tons per day is 

reached, only that attainment will not occur until NOx emissions drop to near 160 tons 

per day. 

To utilize this type of analysis, it is assumed that emission patterns, VOC reactivity and 

other modeling parameters hold constant over time. This assumption implies that 

controls are applied evenly throughout the Valley and that similar types of 

anthropogenic emissions exist in years leading up to and including the modeling year. 

For example, if transportation patterns in 2008 are extremely different from those of 

2020 (the modeling year) it might not be reasonable to assume that 300 tons per day of 

NOx in 2008 would produce that same ozone concentration at the same site in 2020. 

When considering all uncertainties in modeling, however, this variation is considered 

minor. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-14

Figure 3-9 Attainment Carrying Capacities for Selected Sites, 2020 Modeling 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-15

Figure 3-10 Attainment Carrying Capacities for Selected Sites, 2023 Modeling 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Chapter 3: What is Needed to Demonstrate Attainment? 

2007 Ozone Plan 

3-16

3.5 PM2.5 CONSIDERATIONS 

In preparing the 2007 Ozone Plan, consistent with our guiding principle number 7, the 

control strategy in this plan is developed with utmost consideration to future needs for 

the upcoming PM2.5 attainment plan. The District elected not to prepare an integrated 

PM2.5/8-hr ozone plan for June 15, 2007 delivery to EPA for a variety of reasons. First, 

the standard is in flux. On October 17, 2006 EPA announced that it is lowering the 24-

hr PM2.5 standard from 65 micrograms/cubic meter (this level is also referred to as the 

1997 PM2.5 standard) to 35 micrograms per cubic meter, and that it would retain the 

annual PM2.5 standard of 15 micrograms/cubic meter (effective December 18, 2006). 

Second, although PM2.5 plans for the 1997 PM2.5 standards are due April 5, 2008, 

EPA still has not released the rule implementing these standards, and release of the 

rule may be further delayed by the December 22, 2006 U.S. Court of Appeals for the 

D.C. Circuit Court decision vacating the Phase I rule implementing the 8-hr ozone 

standard. Implementation rules for standards describe and finalize the planning 

requirements for the standards, so it is often prudent to develop the planning documents 

after the implementation rule is finalized. Third, the state of PM2.5 modeling for the San 

Joaquin Valley Air Basin is such that preliminary modeling results will not be available 

until the summer of 2007 at the earliest. This modeling is using state of the science 

tools developed with data gathered from the $30 million field programs studying air 

pollution in the San Joaquin Valley. The District plans to begin work in earnest on the 

PM2.5 Plan after the 2007 Ozone Plan is adopted and transmitted to ARB. 

Even though the District did not develop a combined PM2.5 and 8-hr ozone plan, the 

District wanted some indication (order of magnitude estimates) of the Valley’s PM2.5 

carrying capacity so that the District could gauge the effects of the Valley’s 8-hr ozone 

emission control strategy on PM2.5 attainment. As a result, a simplified modeling 

exercise was conducted to help estimate the Valley’s carrying capacity for PM2.5. The 

modeling exercise5

 indicated that the Valley’s NOx carrying capacity for PM2.5 is 

between 370 and 420 tons per day. 

Consequently, the San Joaquin Valley control strategy to attain the federal 8-hr ozone 

standard produces NOx emissions reductions that are close to what is needed for 

attainment of the 1997 PM2.5 standards by the maximum possible statutory attainment 

date of April 5, 2015. This suggests that the ozone control strategy will provide most – if 

not all - of the reductions needed to attain the PM2.5 annual standard, based on simple 

modeling exercises. There is a possibility that some additional NOx emissions 

reductions from incentive-based measures may be needed to demonstrate attainment 

of the 1997 annual PM2.5 standard. Results from more sophisticated modeling to be 

released later in 2007 may change these conclusions and findings. 

References 

California Air Resources Board (ARB) (April 2001), Ozone Transport, California Environmental Protection 

Agency, Sacramento, California. 

 

5

 The modeling that ARB conducted was a simplified version of what was done for the District’s 2006 PM10 Plan. For 

more information on this technique, see Chapter 5 and Appendix C in the 2006 PM10 Plan.