CHAPTER 8

FUTURE AIR QUALITY -

DESERT NONATTAINMENT AREAS

Introduction

Statement of Problem

Attainment Demonstration

Post-1996 VOC Rate-of-Progress Requirements

Summary of Coachella Valley PM10 Plan

Conclusions
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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INTRODUCTION

The 1990 federal Clean Air Act revised the planning requirements for many areas that 

have not attained National Ambient Air Quality Standards. The South Coast Air Quality 

Management District (District) has jurisdiction over the South Coast Air Basin (Basin), 

and the desert portions of Los Angeles and Riverside counties in the Mojave Desert Air 

Basin and Salton Sea Air Basin, respectively (see Figure 1-1). However, AB 2666 

(Knight) created the Antelope Valley Air Pollution Control District beginning on July 1, 

1997. Until then, the District will continue to address the planning requirements for the 

Antelope Valley. The Antelope Valley, located in the desert portion of Los Angeles 

county, and the Coachella Valley, located in the desert portion of Riverside county, both 

exceed the federal ozone standard. The Antelope Valley is unclassified for PM10. The 

Coachella Valley has attained the federal PM10 standards and a maintenance plan is 

currently being developed as a separate plan.

The federal Clean Air Act requires that the Antelope Valley and Coachella Valley:

 identify specific emission reduction goals; 

 demonstrate reasonable further progress in VOC emission reductions; 

 demonstrate attainment of the federal ozone standard by November 15, 2007; 

and

 provide contingency measures or actions in the event of a failure to attain or to 

meet interim milestones.

This AQMP revision addresses these requirements and satisfies the State Implementation 

Plan requirements under Title I of the Clean Air Act (CAA).

STATEMENT OF PROBLEM

There are a number of circumstances that are unique to the Antelope and Coachella 

valleys which make it difficult to develop a local control strategy that satisfies CAA 

requirements. For example, with little in the way of local emissions, and with the 

significant growth projected for both desert areas it is difficult to satisfy the reasonable 

further progress requirements of the CAA. There is strong evidence that pollutant 

transport from the South Coast Air Basin to the Antelope and Coachella valleys is the 

primary cause of the ozone nonattainment status of both areas. As a result, the District 

believes that aggressive control of the South Coast Air Basin emissions is an effective 

strategy to substantially improve air quality in the Antelope and Coachella valleys. Each 

of these issues is addressed in further detail below.
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Regulatory Requirements

State Implementation Plan requirements under Title I of the CAA depend on the severity 

of the nonattainment problem. For the Antelope Valley and the Coachella Valley, the 

CAA requirements for moderate through severe areas must be addressed. Thus, the areas 

are subject to the reasonable further progress requirements of the CAA, as discussed in 

Chapter 6 for the South Coast Air Basin; these requirements are intended to ensure that 

each ozone nonattainment area provide for sufficient VOC emission reductions to attain 

the ozone national ambient air quality standard. These requirements are more difficult to 

meet for areas with low existing emissions and significant population growth, since the 

VOC reductions are relative to the 1990 emissions and activity levels. For example, the 

CAA requires three percent VOC emission reductions beginning in 1997. If an area 

experiences population growth such that VOC emissions increase by 15 percent over 

1990 levels, then the area must develop regulations that achieve VOC reductions of at 

least 18 percent (i.e., the 3 percent rate-of-progress requirement plus the 15 percent 

increase from population growth). The expected population growth for the Antelope and 

Coachella valleys is significant; thus the rate-of-progress requirements of the CAA 

cannot be met for either area unless further local controls are implemented.

The CAA also requires that “severe-17” ozone nonattainment areas, such as the Antelope 

and Coachella valleys, demonstrate attainment of the federal ozone air quality standard 

by November 15, 2007 using a U.S. EPA-recommended photochemical grid model and 

EPA-approved modeling techniques. The South Coast Air Basin modeling domain, as 

shown in Figure 8-1, was expanded to include the Antelope Valley and Coachella Valley 

so that this CAA requirement could be addressed. It is clear from available data that 

federal ozone standard exceedances in the Antelope and Coachella valleys largely result 

from pollutant transport from the upwind South Coast Air Basin. Photochemical grid 

modeling for the 1994 AQMP, using the U.S. EPA-approved Urban Airshed Model, 

shows that attainment of the ozone standard is possible with the proposed control 

strategy described in the 1994 AQMP for the South Coast Air Basin, and control of 

locally generated emissions via state and federal regulations. This Plan carries forward 

the 1994 AQMP control approach for the Antelope and Coachella valleys.

Population Growth

Both the Antelope Valley and the Coachella Valley are rapidly growing areas, as shown 

in Table 8-1. By 2020, the population in the Antelope Valley is expected to nearly triple 

from 1990 levels and the Coachella Valley population is projected to more than double. 

It is clearly more challenging to meet the rate-of-progress requirements of the CAA in 

such rapidly growing areas.
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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Photochemical Modeling Domain

FIGURE 8-1

Modeling Domain

[Note: A New District (Antelope Valley Air Pollution Control District) was Formed in 

September 1996 and Will Be Effective on July 1, 1997.]

TABLE 8-1

Historical Population and Population Forecasts
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Area 1980 1990 2000 2010 2020

South Coast Air Basin ~10,500,000 13,022,000 14,798,000 16,653,000 18,926,000

Antelope Valley 101,000 235,000

375,000 532,000 706,000

Coachella Valley 139,000 267,000

319,000 389,000 475,000

Pollutant Transport

The following pollutant transport pathways from the South Coast Air Basin to the 

Mojave Desert and Salton Sea air basins have been identified: 1) through Newhall Pass 

to the Antelope Valley; and 2) through Banning Pass to the Coachella Valley.1 The 

transport pathway to the Coachella Valley has been an intensely studied phenomenon. 

An experiment to study this transport pathway concluded that the South Coast Air Basin 

was the source of the observed high oxidant levels in the Coachella Valley.2 Transport 

from Anaheim to Palm Springs was directly identified with an inert sulfur hexafluoride 

tracer release3. The most comprehensive study to date of transport from the South Coast 

Air Basin to the Mojave Desert and Salton Sea air basins confirmed the transport 

pathways to both Antelope and Coachella valleys.4

Ozone pollutant transport to the Antelope and Coachella valleys can be demonstrated by 

examining ozone exceedance frequencies as a function of distance from the source areas. 

Figures 8-2 and 8-3, respectively, show the frequency of exceedances of the federal onehour ozone standard by hour for the period 1991 to 1995. Figure 8-2 represents the 

transport route to the Antelope Valley beginning at the primary source region of 

downtown Los Angeles through Burbank and Santa Clarita and ending at Lancaster in 

the Antelope Valley. The Coachella Valley transport route is represented in Figure 8-3, 

starting at Pico Rivera near the source region and passing through Fontana and Banning 

and finally through Banning Pass to Palm Springs in the Coachella Valley. Note in both 

figures that near the source region exceedances occur most frequently at mid-day (noon 

to 1:00 p.m.) during the peak of incoming solar radiation and therefore the peak of ozone 

production. As one goes downwind of the source region, exceedances occur later and 

later in the day as the ozone cloud is transported downwind. For example, at Lancaster 

exceedances occur most frequently at 3:00 to 4:00 p.m. and Palm Springs exceedances 

 

1 R.W. Keith. 1980. A Climatological Air Quality Profile: California’s South Coast Air Basin. Staff Report, South 

Coast Air Quality Management District.

2 E.K. Kauper. 1971. Coachella Valley Air Quality Study. Final Report, Pollution Res. & Control Corp., Riverside 

County Contract & U.S. Public Health Service Grant No. 69-A-0610 RI.

3

P.J. Drivas and F.H. Shair . 1974. A Tracer Study of Pollutant Transport in the Los Angeles Area. Atmos. Environ.

8: 1155-1163.

4 T.B. Smith et al. 1983. The Impact of Transport from the South Coast Air Basin on Ozone Levels in the Southeast 

Desert Air Basin. CARB Research Library Report No. ARB-R-83-183. ARB Contract to MRI/Caltech.
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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occur most frequently at 6:00 p.m. If these peaks were locally generated they would be 

occurring near mid-day and not in the late afternoon or early evening.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00

Hour of Day

Frequency

Downtown LA Burbank Santa Clarita Lancaster

FIGURE 8-2

Frequency of Federal Ozone Exceedances Along the Antelope Valley Transport Route,

1991-95

Ozone is transported these long distances at fairly high concentrations for two reasons. 

Control of VOCs in the South Coast Air Basin has caused the location of the daily 

maximum ozone to move eastward; thus more pollutants which have not reacted are 

carried to greater distances. The VOC control program in the South Coast Air Basin has 

reduced VOC emissions to the extent that photochemical reaction rates of formation of 

ozone have also slowed. Greater amounts of emissions (although, overall, these 

emissions are lower) are transported downwind as a result. In addition, ozone formed in 

the South Coast Air Basin could remain above the standards during transport in the 

downwind areas since there are fewer oxides of nitrogen sources to react with ozone 

during the nighttime hours.

Table 8-2 compares the 1993 emission inventories of the South Coast Air Basin with 

those for the Antelope Valley and the Coachella Valley. The South Coast Air Basin 

emissions, upwind of the Antelope and Coachella valleys, overwhelm the locallygenerated emissions. Depending on the pollutant, emissions in the South Coast Air 

Basin are 11 (for PM10) to 99 (for SOx) times greater than emissions in the Antelope 
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Valley and 5 (for PM10) to 50 (for SOx) times greater than emissions in the Coachella 

Valley. It is clear that improved air quality in these areas depends on reduced emissions 

in the South Coast Air Basin. This is illustrated by the trends in ozone air quality 

described in the following section.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00

Hour of Day

Frequency

Pico Rivera Fontana Banning Palm Springs

FIGURE 8-3

Frequency of Federal Ozone Exceedances Along the Coachella Valley Transport Route, 

1991-95
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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TABLE 8-2

Comparison of 1993 Annual Average Emissions

Emission Rate (tons/day)

Area VOC NOx CO SOx PM10

South Coast Air Basin 1239 1194 7045 79 416

Antelope Valley 28 30 168 1 28

Coachella Valley 40 54 270 1 88

Trends in Ozone Air Quality

Ozone air quality trends since 1980 are shown in Figures 8-4 and 8-5 for stations along 

the Antelope and Coachella Valley transport routes, respectively. The statistic used here 

to illustrate trends is the average of the 30 highest daily maximum one-hour ozone 

concentrations in each year, referred to as the “Top 30 Mean.” This statistic has been 

identified and recommended by the ARB5as a good trend indicator. Over this time 

period population growth in the Antelope and Coachella valleys was much greater than 

that in the South Coast Air Basin, as shown in Table 8-2. Since emissions are directly 

related to population for many source categories, emissions growth was also greater in 

the Antelope and Coachella valleys relative to the South Coast Air Basin. However, the 

downward trend in the Top 30 Means at Lancaster and Palm Springs parallels the trend 

of the upwind stations which are in the South Coast Air Basin. This observation 

confirms the conclusion that ozone air quality in the Antelope and Coachella valleys is 

largely due to transport from the upwind source region of the South Coast Air Basin and 

that attainment in the valleys is only possible with emission reductions in the Basin.

 

5 ARB. 1992. Ozone Air Quality Trends (1981-1990).
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10

15

20

25

1980198119821983198419851986198719881989199019911992199319941995

Year

Concentration (pphm)

Downtown LA Burbank Santa Clarita Lancaster

FIGURE 8-4

Mean of the Top 30 Daily Peak Ozone Concentrations - Antelope Valley Transport Route

10

15

20

25

30

1980198119821983198419851986198719881989199019911992199319941995

Year

Concentration (pphm)

Fontana Redlands Banning Palm Springs

FIGURE 8-5

Mean of the Top 30 Daily Peak Ozone Concentrations - Coachella Valley Transport Route
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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Figures 8-6 and 8-7 illustrate just how effective the District’s control strategy has been in 

reducing the number of federal one-hour ozone exceedances in the Antelope and 

Coachella valleys since 1980. The number of exceedance days by month in 1980, 1985, 

1990, and 1995 for Lancaster and Palm Springs are shown in Figures 8-6 and 8-7, 

respectively. Both the number of days per month exceeding the standard and the number 

of months in which exceedances are observed have dropped dramatically since 1980. In 

1980, Lancaster experienced exceedances in eight months of the year and Palm Springs 

experienced exceedances in seven months of the year. By 1995, the number of months 

with exceedances had dropped to only three months.

Jan

Feb

Mar

Apr

MayJun

Jul

Aug

Sep

Oct

Nov

Dec

1995

1990

1985

1980

0

5

10

15

20

25

Number of 

Exceedance Days

Month

Year

FIGURE 8-6

Federal Exceedance Days by Month and Year at Lancaster
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1995

1990

1985

1980

0

2

4

6

8

10

12

14

16

18

Number of 

Exceedance Days

Month

Year

FIGURE 8-7

Federal Exceedance Days by Month and Year at Palm Springs

ATTAINMENT DEMONSTRATION

Air quality modeling is an integral part of the planning process to achieve clean air. The 

CAA requires that ozone nonattainment areas designated as serious and above be 

required to use a photochemical grid model to demonstrate attainment. The 

photochemical grid model (or air quality simulation model) recommended by the U.S. 

EPA for ozone analyses is the Urban Airshed Model with the Carbon Bond Mechanism 

IV chemistry (UAM). UAM is an urban-scale, three-dimensional, grid-type, numerical 

simulation model. It is designed for computing ozone concentrations under short-term, 

episodic conditions lasting one to three days. UAM is also the recommended model for 

ozone analysis by the ARB. 

It is desirable to perform ozone air quality analyses using several different 

meteorological episodes. Chapter 5 describes the meteorological episodes used to 

project future air quality. Performance evaluations of the four meteorological episodes 

are discussed in Technical Report V-B of the 1994 AQMP.

Future-year air quality projections in the Antelope and Coachella valleys are presented in 

detail in Appendix V; the results are summarized in Figure 8-8 for the Antelope Valley 

and Figure 8-9 for the Coachella Valley. The peak predicted ozone concentrations are 
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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shown for the baseline and controlled 2007 simulations for each of the four 

meteorological episodes modeled. “Baseline” assumes no further control beyond 

existing rules and regulations and “Control” assumes implementation of the proposed 

control strategy described in Chapters 4 and 7. As illustrated, the federal ozone standard, 

shown by a solid horizontal line at 12 pphm in the figures, will be exceeded in one of the 

four episodes in the Antelope Valley and in two of the four episodes in the Coachella 

Valley if the AQMP control is not implemented. However, with the implementation of 

the control strategy, the federal one-hour ozone air quality standard is attained for all four

episodes in both the Antelope and Coachella valleys.

FED

STD

0

2

4

6

8

10

12

14

Jun-87 Jul-87 Aug-87 Sep-87

Episode

Concentration (pphm)

Baseline Control

FIGURE 8-8

Maximum Predicted Ozone Concentrations for 2007 in the Antelope Valley With and 

Without Implementation of the 1997 AQMP Control Strategy

POST-1996 VOC RATE-OF-PROGRESS REQUIREMENTS

The reasonable further progress requirements in the CAA are intended to ensure that 

each ozone nonattainment area provide for sufficient precursor emission reductions to 

attain the ozone National Ambient Air Quality Standard. More specifically, Section 

182(c)(2) requires that each serious and above ozone nonattainment area achieve actual 

VOC emission reductions of at least three percent per year averaged over each 

consecutive 3-year period beginning six years after enactment of the Act until the area’s 
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attainment date (i.e., November 15, 2007 for the Antelope and Coachella valleys). This 

is called the “post-1996 rate-of-progress” requirement of the CAA.

FED

STD

0

2

4

6

8

10

12

14

Jun-87 Jul-87 Aug-87 Sep-87

Episode

Concentration (pphm)

Baseline Control

FIGURE 8-9

Maximum Predicted Ozone Concentrations for 2007 in the Coachella Valley With and 

Without Implementation of the 1997 AQMP Control Strategy

According to Section 182(c)(2)(C), actual NOx emission reductions which occur after 

1990 can be used to meet post-1996 VOC emission reduction requirements provided the 

NOx reductions satisfy the following criteria. First, the control strategy used to 

demonstrate attainment must consist of both VOC and NOx control measures. More 

specifically, the mix of VOC and NOx emission reductions used to satisfy the post-1996 

rate-of-progress requirements of the CAA must be consistent with the controlled VOC 

and NOx emission levels used in the modeling demonstration. And lastly, the combined 

annual VOC and NOx reductions must average 3 percent per year.

As mentioned a number of times in this chapter, poor ozone air quality in the Antelope 

and Coachella valleys is primarily due to transport of ozone and its precursors from the 

upwind source region of the South Coast Air Basin and attainment in these downwind 

valleys is only possible with substantial emission reductions in the Basin. With this in 

mind, the proposed control strategy consists of two components: 1) an aggressive 

control strategy for VOC and NOx emission sources in the South Coast Air Basin; and 2) 
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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control of locally generated emissions via proposed control measures implemented by 

state and federal actions.

The District’s approach to satisfying the post-1996 rate-of-progress requirement is 

presented in Appendix V; Figures 8-10 (Antelope Valley) and 8-11 (Coachella Valley) 

summarize the results. At each milestone year (1999, 2002, 2005, and 2007) the 

following VOC and NOx emission levels are shown:

 the target level (termed “Target Level” in the figures);

 the projected uncontrolled baseline (termed “Projected Baseline” in the figures); 

and

 the controlled emissions - statewide mobile and stationary control measures and 

control measures for federally regulated sources (termed “Controlled 

Emissions” in the figures).

The rate-of-progress results for the Antelope Valley are shown in Figure 8-10. The 

proposed reduction rates by milestone year are shown in Table 8-3. These rates were 

determined by applying all the creditable VOC reductions at each milestone and 

providing sufficient NOxreductions to satisfy the VOC emission reduction requirements 

of Section 182(c)(2). Comparing the baseline emissions with the target levels for each 

milestone year indicates that additional emission reductions are necessary to achieve 

target levels as illustrated in Figure 8-10. However, with the implementation of the state 

and federal control measures, the post-1996 rate-of-progress requirements are satisfied at 

all milestone years as shown by the controlled emission levels in Figure 8-10.

TABLE 8-3

Percent VOC and NOx Reductions for the

Antelope Valley Post-1996 Rate of Progress Plan

Milestone Year VOC NOx CAA*

1999 15.0 9.0 24.0

2002 0.5 8.5 9.0

2005 5.0 4.0 9.0

2007 0.5 5.5 6.0

* The percent VOC and NOx reductions must equal the CAA percent 

reduction requirements listed here.
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a) VOC

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1999 2002 2005 2007

Milestone Year

Emissions (tpd)

Target Level Projected Baseline Controlled Emissions

b) NOx

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1999 2002 2005 2007

Milestone Year

Emissions (tpd)

Target Level Projected Baseline Controlled Emissions

FIGURE 8-10

Comparison of Baseline and Controlled (a) VOC and (b) NOx Emissions

and CAA Target Levels - Antelope Valley
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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As shown in Figure 8-11, the VOC and NOx emission reductions from existing District 

and ARB rules are sufficient to meet the CAA rate-of-progress requirements for the 

Coachella Valley. The rate-of-progress requirements for all milestone years are met by a 

combination of VOC and NOx reductions from existing District and ARB rules. The 

proposed reduction rates by milestone year are shown in Table 8-4. The control strategy 

provides additional VOC and NOx reductions for all the years beginning with 1999. The 

projected emission reductions beyond the target levels can be used as contingency in the 

event of a milestone failure.

TABLE 8-4

Percent VOC and NOx Reductions for the

Coachella Valley Post-1996 Rate of Progress Plan

Milestone Year VOC NOx CAA*

1999 16.3 7.7 24.0

2002 6.5 2.5 9.0

2005 6.4 2.6 9.0

2007 3.0 3.0 6.0

* The percent VOC and NOx reductions must equal the CAA percent reduction 

requirements listed here.
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a) VOC

0

5

10

15

20

25

30

35

1999 2002 2005 2007

Milestone Year

Emissions (tpd)

Target Level Projected Baseline

b) NOx

0

10

20

30

40

50

60

1999 2002 2005 2007

Milestone Year

Emissions (tpd)

Target Level Projected Baseline

FIGURE 8-11

Comparison of Baseline and Controlled (a) VOC and (b) NOx Emissions 

and CAA Target Levels - Coachella Valley
Chapter 8 Future Air Quality - Desert Nonattainment Areas

8 - 17

SUMMARY OF COACHELLA VALLEY PM10 PLAN

Introduction

The Coachella Valley is currently designated nonattainment for PM10. Unlike the Basin, 

where PM10 exceedances are due primarily to PM10 precursor pollutants, the Coachella 

Valley’s elevated PM10 levels are strongly tied to local fugitive dust problems. 

Accordingly, instead of relying on District rulemaking to achieve attainment, previous 

planning documents have proposed local control to meet the area’s air quality objectives. 

This approach allows local Coachella Valley governments, industry, and citizens to take 

an active part in improving the Valley’s air quality. As a result of this approach, various 

local dust control programs and two District “backstop” rules have been developed. 

These programs have resulted in significant improvements in the Valley’s air quality.

Background

Under the 1990 federal Clean Air Act (CAA), the Coachella Valley was originally 

designated as a “moderate” PM10 nonattainment area. In response to CAA requirements 

for “moderate” areas, the District developed the “State Implementation Plan for PM10 in 

the Coachella Valley” (90-CVSIP) which was adopted by the Governing Board in 

November 1990. The 90-CVSIP proposed implementation of reasonably available 

control measures (RACM) for fugitive dust sources no later than December 10, 1993. 

Modeling contained in the 90-CVSIP demonstrated attainment of the national ambient 

air quality standards (NAAQS) for PM10 would occur by December 31, 1995, one year 

after the statutory limit for moderate nonattainment areas.

The CAA specifies that any area which cannot attain the standards by December 1994 

would subsequently be reclassified as a “serious” nonattainment area. In January 1993, 

the U.S. EPA completed its initial redesignation process, and included the Coachella 

Valley among five nationwide areas redesignated as “serious,” effective February 8, 

1993. The CAA further specifies that a SIP revision is due within 18 months of the 

redesignation date (i.e., August 8, 1994) and that a demonstration of attainment must be 

submitted within four years of the redesignation date (i.e., February 8, 1997). Among 

other requirements, the “serious” area SIP must ensure the implementation of “best 

available control measures” (BACM). The District prepared and later adopted the 1994 

Coachella Valley PM10 SIP revision (94-CVSIP) in July of 1994. 

1997 PM10 Maintenance Plan

Under the CAA, an area can be redesignated as attainment if, among other requirements, 

the U.S. EPA determines that the NAAQS have been attained. Section 175A of the CAA 
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states that any district that submits a request under Section 107(d) for redesignation of a 

nonattainment area to attainment must submit a revision of the applicable SIP that 

demonstrates attainment for at least 10 years after the redesignation. U.S. EPA guidance 

states that a determination of compliance with the NAAQS must be based on three 

complete, consecutive calendar years of quality-assured air quality monitoring data6. Air 

quality is monitored at two locations in the Coachella Valley and results indicate that 

there were no PM10 exceedances in 1993 or 1994. In 1995, the 24-hour standard was 

exceeded once and this led to an exceedance of the annual average standard. This 

exceedance occurred on a day where the maximum hourly wind gusts exceeded 50 mph 

for each hour of the day. 

The U.S. EPA has recently developed a natural events policy7that permits, under certain 

circumstances, the exclusion of air quality data attributable to uncontrollable natural 

events (e.g., volcanic activity, wildland fires, and high wind events). With the exclusion 

of air quality data from the one 24-hour exceedance in 1995, the Coachella Valley has 

experienced three consecutive years without an exceedance of the PM10 standards and, 

consequently, would be eligible for redesignation to attainment. Based on the supporting 

meteorological data regarding the one high wind event in 1995, the District is preparing a 

maintenance plan for the Coachella Valley. In accordance with U.S. EPA guidance, the 

major elements of the plan are as follows:

 a demonstration of attainment with the PM10 standards based on the three most recent 

years of ambient data;

 a maintenance plan, including contingency measures, to ensure continued attainment 

for the next ten years; and

 a Natural Events Action Plan pursuant to the Natural Events Policy.

The Coachella Valley Maintenance plan will be prepared as a separate document. It will 

be released for public review and submitted to the U.S. EPA in lieu of the attainment 

demonstration prior to February 8, 1997.

CONCLUSIONS

The Antelope Valley and the Coachella Valley are designated as “severe-17” ozone 

nonattainment areas and as such must demonstrate reasonable further progress and 

attainment according to federal Clean Air Act requirements. The District’s proposed 

 

6 U.S. EPA, Memorandum to Division Directors, Subject: Procedures for Processing Requests to Redesignate Areas 

to Attainment, Office of Air Quality Planning and Standards, Research Triangle Park, page 2, September 4, 1992.

7 U.S. EPA, Memorandum from Mary Nichols, Assistant Administrator, Subject: Areas Affected by PM10 Natural 

Events, May 30, 1996.
Chapter 8 Future Air Quality - Desert Nonattainment Areas

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control strategy includes two components: a strategy for the South Coast Air Basin as 

described in Chapter 4 and control of locally generated emissions in the Antelope Valley 

and Coachella Valley via regulations at the state and federal level. Photochemical grid 

modeling, using a U.S. EPA-approved model and methodologies, demonstrates that the 

federal one-hour ozone standard will be met by November 15, 2007 for the Coachella 

Valley as required by the CAA. However, the federal ozone air quality standard will be 

met in the Antelope Valley by 2010. For PM10, the Antelope Valley is an unclassified 

area with no current planning requirements; for the Coachella Valley, a PM10

maintenance plan will be submitted with a request to U.S. EPA for redesignation to 

attainment status.