CHAPTER 10

LOOKING BEYOND CURRENT REQUIREMENTS

Introduction

Uncertainties Associated with the Technical Analysis

A First Look at the Year 2020 Ozone Air Quality

Potential New Air Quality Standards for Ozone

 and Fine Particulates
Chapter 10 Looking Beyond Current Requirements 

10 - 1

INTRODUCTION

This Chapter presents additional analyses which have important future considerations, 

but which are not currently required under law to be included in the AQMP. 

Uncertainties associated with the technical analysis provided in the AQMP are discussed 

in this chapter. In addition, a first look at the year 2020 is provided. The 2020 air 

quality analysis is provided for informational purposes only and does not serve as a 

maintenance plan at this time. Lastly, the District has attempted to anticipate certain 

future federal requirements and has incorporated this information into the 1997 AQMP. 

In anticipation of federal changes regarding PM10 and ozone ambient air quality 

standards, a preview of future technical considerations and possible planning 

implications is provided in this chapter.

UNCERTAINTIES ASSOCIATED WITH THE TECHNICAL ANALYSIS

As with any plan update there are uncertainties associated with the technical analysis. 

Projecting air quality concentrations into the future has associated uncertainties. These 

uncertainties exist in the demographic and growth projections for the future base years. 

As projections are made to longer periods (i.e., over ten or more years), the uncertainty 

of the projections become greater. Examples of these types of uncertainties include:

 the location of new sources;

 military base reuse plans; and

 economic prosperity.

In addition to the above, there are also uncertainties in the technical information gathered 

for the air quality analysis. The three major input elements of any air quality modeling 

analysis (ambient air quality monitoring data, meteorological measurements, and 

emissions inventory) all have various levels of uncertainties. Generally, ambient air 

quality measurements are within plus or minus half of a unit of measurement (e.g., for 

ozone usually reported in units of pphm would be accurate to within 0.5 pphm). Due to 

this uncertainty, the Basin’s ozone attainment status based on ambient monitoring data 

would be achieved if all ozone monitors reported ozone concentration levels less than or 

equal to 12.4 pphm. Examples of meteorological uncertainties include:

 averaging of instantaneous wind speeds and directions to hourly averaged values 

and

 directional consistency during low (stagnant) wind conditions.
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As discussed in Chapter 3, large uncertainties in the mobile source emissions inventory 

estimates have been observed as evident with the latest EMFAC7G release. On-road 

mobile source emission estimates have increased with each new EMFAC release. Onroad mobile source emissions have inherent uncertainties also with the current 

methodologies used to estimate vehicle activity such as vehicle miles traveled. 

Stationary (or point) source emission estimates have less associated uncertainties 

compared to area source emission estimates. Major stationary sources report emissions 

annually whereas area source emissions are, in general, estimated based on sales or 

population information.

The air quality model used for ozone air quality analysis (the Urban Airshed Model) is a 

sophisticated, complex 3-dimensional model requiring 3-dimensional meteorological 

data. Meteorological measurements collected at various locations throughout the Basin 

are used to generate 3-dimensional flow fields. In addition to uncertainties in model 

input data, air quality models contain inherent uncertainties due to the model 

formulations which rely on numerical methods to solve complex mathematical equations 

of motion. Examples of these types of uncertainty sources are as follows:

(1) Estimations of 3-dimensional wind fields from a limited number of 

measurements.

(2) Chemical reactions based on experimental data.

(3) Application of numerical solutions to complex physical processes.

It should be noted that uncertainties run in two directions and comparisons with recent 

year projections show that the air quality is improving at a greater rate than was 

projected. This would indicate that uncertainties are not significantly affecting the 

integrity of the Plan.

Furthermore, the concerns regarding uncertainties in the technical analysis are reduced 

with future AQMP revisions. For each AQMP revision, the best available technical 

information is used. Under state law, the AQMP revision process is a dynamic process 

with revisions occurring every three years. The AQMP revision represents a “snapshot 

in time” providing the progress achieved since the previous AQMP revision and efforts 

still needed in order to attain air quality standards. 

Under the federal Clean Air Act, a state implementation plan (SIP) is prepared for each 

criteria pollutant. The SIP is not updated on a routine basis under the federal Clean Air 

Act. However, the federal Clean Air Act recognizes that uncertainties do exist and 

provides safeguards if a nonattainment area does not meet an applicable milestone or 

attain federal air quality standards by their applicable dates. Contingency (or backstop) 

measures are required in the AQMP and must be developed into regulations such that 
Chapter 10 Looking Beyond Current Requirements 

10 - 3

they will take effect if a nonattainment area does not meet an applicable milestone or 

attainment date. In addition, federal sanctions may be imposed until an area meets 

applicable milestone targets.

U.S. EPA recently released a guidance document on the use of modeled results to 

demonstrate attainment of the federal ozone air quality standard1 The guidance 

document recognized that there will be uncertainties with ozone modeling analysis. For 

severe and extreme ozone nonattainment areas, the U.S. EPA recommends that at least 

one “mid-course” review of air quality, emissions and modeled data be conducted. A 

second review, shortly before the attainment date, should be conducted also. 

A FIRST LOOK AT THE YEAR 2020 OZONE AIR QUALITY

With continued growth in the South Coast Air Basin beyond 2010, concerns have been 

raised whether the South Coast Air Basin can maintain the federal ozone air quality 

standard. As such, an ozone air quality analysis for 2020 was performed. Data on the 

projected growth in the Basin and surrounding areas were provided by SCAG. Future 

year ozone air quality projections are provided in Figure 10-1.

0

5

10

15

20

25

30

1987 2000 2010 2020

Year

Concentration (pphm)

June 23-25, 1987 August 26-28, 1987

FED

STD

FIGURE 10-1

Basinwide Maximum Ozone Concentration with Proposed Emission Controls

 

1 U.S. EPA, Guidance on Use of Modeled Results to Demonstrate Attainment of the Ozone NAAQS, EPA-454/B95-007, June 1996
FINAL 1997 AQMP

10 - 4

The baseline inventory for the year 2020 is shown in Table 10-1, and the remaining 

emissions with implementation of the 1997 AQMP control strategy is shown in Table 

10-2.

TABLE 10-1

2020 Baseline Emissions for the South Coast Air Basin

Planning Inventory (tons/day)

Summer Winter

VOC NOx CO

Stationary Source Emissions 689 122 365

On-Road Emissions 117 364 1,730

Off-Road Emissions 159 282 1,761

Total Emissions 965 768 3,856

TABLE 10-2

2020 Remaining Emissions for the South Coast Air Basin

with the Implementation of the 1997 AQMP Control Strategy

Ozone Planning Inventory (tons per day)

VOC NOx

Stationary Source Emissions 314 92

On-Road Emissions 57 268

Off-Road Emissions 72 174

Total Remaining Emissions 443 534

POTENTIAL NEW AIR QUALITY STANDARDS FOR OZONE AND FINE 

PARTICULATES

During the timeframe for development of the 1997 AQMP, the U.S. EPA is reviewing 

the current air quality standards for ozone and particulate matter. As part of the 

requirements of the CAA, every five years the U.S. EPA must review the current ambient 

air quality standards and propose revisions where necessary. This review process 

includes a comprehensive evaluation of the latest health studies; a redrafting, if 

appropriate, of the relevant pollutant criteria document; and a staff report recommending 

the position of the U.S. EPA staff. Both the criteria document and the staff report are 

reviewed by the CAA-authorized Clean Air Science Advisory Committee (CASAC), an 

independent panel of experts. Generally, for the U.S. EPA to proceed with the new air 

quality standard setting process, consensus approval must first be given by CASAC on 
Chapter 10 Looking Beyond Current Requirements 

10 - 5

both the criteria document and the staff report. At this point in time, these actions have 

occurred.

In the current process, both ozone and fine particulates are being considered for new 

standards. The U.S. EPA in June 1996 issued an Advanced Notice of Proposed 

Rulemaking (ANPR) regarding possible new ambient air quality standards for ozone and 

fine particulates. In the ANPR, U.S. EPA announced that proposed action would be 

issued in November 1996. Should the proposed action include recommendations for new 

standards, then final action would occur in June 1997. If new standards are proposed, a 

new set of planning requirements will also be proposed. Under the CAA, for new 

standards, new plans must be developed within three to six years from the date of final 

promulgation.

Health Basis

The U.S. EPA recently completed a review of the scientific and technical information on 

the known and potential adverse health effects of ozone and PM10 because results from 

recent studies have suggested that attainment of the existing NAAQS for these pollutants 

may not provide adequate public health protection. A brief summary of the effects 

associated with these pollutant exposures at levels observable in Southern California is 

presented. A more detailed discussion of health effects is provided in Appendix I.

Ozone

People exercising outdoors, children and persons with preexisting lung disease such as 

asthma are considered to be susceptible sub-groups for ozone effects. Identified in 

human and/or animal studies with varying exposure duration the adverse health effects 

which are either induced by ozone or associated with ambient ozone exposures include: 

breathing pattern changes; reduction in breathing capacity and exercise performance; 

increase in airway resistance; susceptibility to infections; excess hospital admissions and 

emergency room visits; and acute inflammation of the respiratory tract including some 

cellular changes.

The lowest range of ozone exposure within which lung functional changes (decrease in 

breathing lung volumes and increase in airway resistance) are observed is 0.08 to 0.12 

ppm for 6-8 hours under moderate exercising conditions. Under similar exposure 

conditions, biochemical indicators of lung inflammation are induced in healthy adults 

exposed to ozone in the range of 0.08 to 0.10 ppm. Excess hospital admissions and 

emergency room visits are observed when hourly ozone concentrations are as low as 0.08 

to 0.10 ppm. Thus, the attainment of the current NAAQS (0.12 ppm) is not likely to 

prevent all the adverse effects indicated from ozone exposure. 
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Particulate Matter

The major categories of adverse health effects associated with PM10 include: increase in 

mortality associated with acute and chronic exposures; exacerbation of preexisting 

respiratory and cardiovascular diseases leading to an increase in hospital admissions and 

emergency room visits; school absences; work loss days and restricted activity days; 

changes in lung function and structure; and altered lung defense mechanisms. 

A review and statistical analysis of recent population studies published on acute adverse 

effects of PM10 indicates that an incremental increase of PM10 by 10 μg/m3can lead to a 

significant increase in both mortality and morbidity risks. The elderly, people with 

preexisting respiratory and/or cardiovascular disease(s) and children appear to be most 

susceptible to the effects of PM10. These findings suggest that even when an area meets 

the existing NAAQS for PM10 the community is likely to continue to have the adverse 

impact from ambient PM10 exposures. 

A limited number of studies which have employed both PM10 and PM2.5 indices for 

pollution suggest that the adverse effects show a better correlation with the latter. A 

growing consensus exists among the scientific community that the fine fraction of PM10

is relatively more toxic than the coarse fraction and is responsible for the majority of 

PM10 effects observed.

In addition, U.S. EPA in its recent PM10 NAAQS review has concluded that the 

difference in exposure relationships, and the strong likelihood of fine mode fraction of 

PM10 being significant contributors to PM-related health effects in sensitive populations, 

are sufficient to justify the consideration of fine and coarse mode particles in PM10 as 

separate classes of pollutants. Hence, U.S. EPA has recommended additional PM2.5

NAAQS.

Assessment of Potential New Standards

Ozone 

The U.S. EPA is considering replacing the current 1-hour federal ozone standard of 0.12 

ppm with an 8-hour standard. At this time, U.S. EPA is considering the level of the 

standard to be in the range of 0.07 to 0.09 ppm, with the most likely value at 0.08 ppm. 

In addition, U.S. EPA is considering a change in the form of the standard, from an 

exceedance-based to a concentration-based form. Under this scenario, if the 5th highest 

8-hour average, as averaged over the three most recent years of record, is above 0.08 

ppm, then the area would be deemed to be in violation of the standards. U.S. EPA is also 

considering the 2nd highest 8-hour average, averaged over three years, and if the 2nd 

highest value is below 0.08 ppm, then an area will be deemed to be in attainment of the 
Chapter 10 Looking Beyond Current Requirements 

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standard. What happens if an area records values between these two bands has not been 

specifically delineated.

The District has evaluated the differences between the current 1-hour standard and the 

possible 8-hour standard for both 1995 (actual) and 2010 (projected). These are 

summarized in Table 10-3. Currently, the 1-hour standards are exceeded by 116 percent. 

The maximum 8-hour would exceed the possible new standard by 155 percent. Future 

year projections show that the 1-hour standard would be met in 2010, but the maximum 

8-hour standard would still be exceeded by 31 percent. Because federal guidance has not 

yet been developed for modeling attainment demonstrations of a 5th highest value, a 

projection of this value cannot be made at this time.

TABLE 10-3

Comparison of Ozone Standards

___________1995____________ ___________2010____________

Standard

(ppm)

Max Value

(ppm)

% above

Standard

Max Value

(ppm)

% above

Standard

Current 1-hour 0.12 0.26 116 0.118 Met

Possible 8-hour

(maximum)

0.08 0.204 155 0.105 31

Possible 8-hour

(5th highest)

0.08 0.165 106 * *

*Future-year federal guidance for attainment demonstration not available.

Particulate Matter

The U.S. EPA is currently recommending that new fine particulate standards be 

established at a cut-point of 2.5 micrometers (PM2.5). The latest recommendations would 

establish a PM2.5 annual average at a value between 12.5 and 20 μg/m3, and a PM2.5 24-

hour average at a value between 18 and 65 μg/m3. The PM10 annual average is likely to 

be retained, but the 24-hour PM10 standard may be deleted.

A comparison of the current PM10 standards and the possible new PM2.5 standards for 

1995 and 2006 are shown in Table 10-4. The 1995 values are derived from the 

measurements taken during the PTEP study; the 2006 PM2.5 values are estimated from 

the PM10 model application coupled with PM10-to-PM2.5 conversion factors applied on a 

component basis, as derived from the PTEP data. Currently, the PM10 standards are 

exceeded by 38 percent, and attainment can be demonstrated by 2006. If the new PM2.5
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standards are promulgated, the PM2.5 annual standard in 2006 with the current control 

strategy would be exceeded by 25 percent at the upper (or least stringent) end of the 

range, while the 24-hour average would be exceeded by 51 percent at the upper end of 

the range. At the lower end of the range (most stringent), the percent above standards 

would be 100 percent for the annual average, and 444 percent for the 24-hour average.

TABLE 10-4

Comparison of Particulate Matter Standard

___________1995___________ ___________2006____________

Standard

(μg/m3)

Max Value

(μg/m3)

% above

Standard

Max Value

(μg/m3)

% above

Standard

Current PM10

(24-hour)

150 207 38 143 Met

Current PM10

(Annual)

50 69 38 48 Met

Possible PM2.5

(24-hour)

upper range

lower range

65

18

125

92

594

98

51

444

Possible PM2.5

(Annual)

upper range

lower range

20

12.5

40

100

220

25

25

100

It is also important in looking into the future to understand the significant components of 

PM2.5 as projected for the year 2006. These are shown in Figure 10-2. The ammonium 

and nitrate portions represent the dominant fraction of PM2.5 on both an annual and 

episodic (24-hour) basis. Note, too, that the crustal component, as identified within the 

category labeled “others,” and which represents a significant fraction of PM10, plays a 

very small role in the PM2.5 picture. For the 24-hour standard, it is evident that 

significant reductions in ammonium nitrate will be needed over and above the current 

PM10 control strategy in order to attain a possible PM2.5 standard. Appreciable 

reductions will also be needed for both organic and elemental carbon, the former from 

VOC emissions and the latter from soot emissions, primarily from diesel exhaust.
Chapter 10 Looking Beyond Current Requirements 

10 - 9

Annual Average

7% 9%

17%

12%

39%

16%

Predicted Annual Average

25 μg/m3

Predicted Maximum 24hr

98 μg/m3

51%

21%

16% 7%

5%

0%

SO4

NO3

NH4

OC

EC

Others

Max. 24hr Average

FIGURE 10-2

Estimated PM2.5 Components in 2006

Implementation

With any new standard, U.S. EPA provides “interim” guidance on the transition from the 

old to the new standard. To better address the concerns and implications of a transition 

policy as well as other implementation issues regarding ozone, fine particulates, and 

regional haze, U.S. EPA has assembled an advisory committee under the Federal 

Advisory Committee Act (FACA). The FACA Committee represents over 50 

representatives from state and local air regulatory agencies, industry, environmental 

organizations, consulting organizations, academia, and federal agencies. In addition, 

four subgroups have been formed to focus on: (1) Base Programs and Policies; (2) 

National and Regional Strategies; (3) Science and Technology; and (4) Communications 

and Outreach. In addition, a Coordination work group integrates the results from the 

subgroups. It is anticipated that U.S. EPA will rely on the FACA process in developing 

new guidance and policies should new standards be promulgated. The District staff are 

actively participating/following the subgroup activities to ensure consideration of South 

Coast Air Basin conditions.