CHAPTER 5

FUTURE AIR QUALITY

Introduction

Modeling Approach

Future Air Quality

Summary and Conclusions

Basin Emissions Carrying Capacity (Emissions Budget)

Projected Emission Trends Through 2010
Chapter 5 Future Air Quality

5 - 1

INTRODUCTION

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

mentioned in Chapter 1, the submittal of the 1994 California Ozone SIP served as the 

ozone attainment demonstration for the South Coast Air Basin and those portions of the 

Southeast Desert Modified Nonattainment Area which are under the District’s 

jurisdiction. The attainment demonstrations provided in this Plan reflect the updated 

emissions baseline estimates, new technical information and enhanced air quality 

modeling techniques, and the control strategy provided in Chapter 4.

The Basin is currently in nonattainment for nitrogen dioxide1, PM10, ozone, and carbon 

monoxide. Three of these pollutants - nitrogen dioxide, PM10, and ozone - are linked to 

common precursor emissions. The District’s goal is to develop an integrated control 

strategy which: 1) ensures that ambient air quality standards for all criteria pollutants are 

met by the established deadlines in the federal Clean Air Act (CAA); and 2) achieves an 

appropriate rate of reduction in excess exposure to PM10 and ozone over the next five to 

ten years. The overall control strategy is designed so that efforts to achieve the standard 

for one criteria pollutant do not cause the deterioration of another. A three-step 

modeling process was originally developed in the 1989 AQMP to develop the control 

strategy. The three-step process begins with an analysis of future nitrogen dioxide air 

quality, followed by PM10 air quality, and lastly, future ozone air quality. Air quality 

analyses under the 1997 AQMP are performed in keeping with this three-step modeling 

approach.

While attainment of all federal criteria pollutant air quality standards is the goal of all 

AQMP revisions, previous AQMP revisions placed greater emphasis on ozone air quality 

modeling due to the complex chemical and physical interactions of volatile organic 

compounds (VOCs) and oxides of nitrogen. However, over the past ten years, a better 

understanding of the complex nature of PM10 formation has led to a need to acquire 

enhanced technical information on PM10 and particulate air quality modeling techniques.

The control strategy to meet federal and state carbon monoxide standards is independent 

of the nitrogen dioxide/PM10/ozone strategy. A photochemical grid model is used to 

project future carbon monoxide (CO) air quality. As mentioned previously, the Basin 

has not exceeded the federal annual standard for nitrogen dioxide since 1991 and the 

state one-hour standard has not been exceeded since 1993. Air quality modeling is 

provided here to demonstrate continuing maintenance of the federal and state nitrogen 

dioxide standards. Visibility impairment analyses are also performed even though 

 

1 The nonattainment designation for NO2 is based on the current federal classification, but the basin met both the federal 

and state NO2 standards since 1993.
FINAL 1997 AQMP

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neither the CAA nor the California Clean Air Act (CCAA) specifically require that 

visibility be addressed for planning purposes.

Detailed information on the modeling approach, data gathering, model development and 

enhancement, model application, and interpretation of results is presented in Appendix 

V. The following sections summarize the results of the modeling efforts. Future air 

quality projections for the Antelope Valley and Coachella Valley are presented in 

Chapter 8 and Appendix V.

MODELING APPROACH

Nitrogen Dioxide

A linear rollback approach is used to evaluate future nitrogen dioxide concentrations. It 

assumes that the ambient concentrations above background levels are directly 

proportional to the emissions in the immediately adjacent areas. In mathematical terms, 

the rollback relationship can be written as follows:

Cp = [(Cb -k)· Qp/Qb]+k (1)

where Cpand Cbare the future year and baseline oxides of nitrogen (NOx)

concentrations, respectively, Qpand Qbare the future year and baseline NOx emission 

rates, respectively, and k denotes the background. For the nitrogen dioxide analysis, the 

background concentrations are assumed negligible.

Projections are made for several key locations in the Basin representative of areas with 

recent nitrogen dioxide violations. Future-year annual average nitrogen dioxide 

concentrations were determined from projected total NOx concentrations using averaged 

NO2/NOx ratios for the period 1992 to 1994 at each of the locations. The reader is 

referred to Appendix V for additional details on the technical approach.

PM10

Within the Basin, PM10 particles are either directly emitted into the atmosphere (e.g., 

primary particles), or are formed through atmospheric chemical reactions from precursor 

gases (e.g., secondary particles). Primary PM10 includes road dust, diesel soot, 

combustion products, and other sources of fine particles. Secondary products, such as 

sulfates, nitrates, and complex carbon compounds are formed from reactions with oxides 

of sulfur, oxides of nitrogen, VOCs, and ammonia.
Chapter 5 Future Air Quality

5 - 3

Because of the dual nature of PM10, a combination of different modeling techniques 

(receptor and photochemical grid models) is used to estimate the source contributions to 

ambient PM10 levels as measured at different monitoring sites. In addition, the air 

quality projections using the various modeling techniques are compared to a modified 

emissions rollback method (similar to that described for nitrogen dioxide, except that the 

rollback is performed on a component-by-component basis) to provide assurance that the 

modeling techniques are giving directionally appropriate conclusions. This speciated 

rollback methodology is described in more detail in Appendix V. It should be noted that 

this methodology cannot distinguish between primary and secondary carbon as compared 

to measured organic carbon levels. Since the distinction between primary and secondary 

organics can only be estimated, the speciated rollback technique was applied under two 

assumptions: primary carbon domination and secondary carbon domination.

The following section summarizes the PM10 modeling studies conducted in preparation 

for this Plan. Details of the PM10 modeling are presented in Appendix V.

PM10 Technical Enhancement Program (PTEP) Modeling Studies

Due to the complex nature of PM10, a variety of air quality modeling techniques can be 

used. Nonreactive PM10 components such as fugitive dust can be estimated using 

chemical mass balance or source-receptor techniques where fingerprinting of various 

source profiles is necessary to identify source contributions. In addition, dispersion 

models (both 2-dimensional and 3-dimensional) can also be used to estimate nonreactive 

PM10 component concentrations. Traditionally, simple linear rollback techniques (such 

as that used for nitrogen dioxide) are used to estimate nonreactive PM10 components 

also. For PM10 components that are secondary in nature (i.e., species formed through 

chemical transformation), air quality models which have the capability to handle PM10

chemical and physical processes. Many of these models have been developed under 

research sponsorship and have not been extensively applied to-date.

In 1995, the District embarked on a PM10 Technical Enhancement Program (PTEP) to 

acquire new PM10 air quality models or enhance the current PM10 models in order to 

project future-year PM10 concentrations. Several projects were undertaken including the 

acquisition of an episodic aerosol model, a fugitive dust model, a source apportionment 

model, enhancements to the chemical mass balance (CMB) source profiles, and updating 

the secondary sulfate and nitrate chemistry used in the particle-in-cell dispersion model. 

These projects provided a suite of PM10 air quality modeling techniques that could be 

used to assess PM10 air quality.

Since the 1989 AQMP, the District has been applying a particle-in-cell (PIC) dispersion 

model to examine annual secondary sulfate and nitrate concentrations. The PIC model 

has limited capabilities in examining large regions (beyond the boundaries of the South 

Coast Air Basin) due to the model’s formulation and simple treatment of meteorology. 
FINAL 1997 AQMP

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As part of the PTEP, the District embarked on modifying the Urban Airshed Model 

(UAM), the photochemical grid model used for ozone air quality analysis. The UAM is 

a proven air quality model capable of modeling large complex regions. However, the 

chemical mechanism in the UAM does not estimate secondary sulfate and nitrate 

concentrations. As such, the PTEP sponsored the enhancement of a set of empirical 

relationships between precursor emissions and sulfate and nitrate formation. (A similar 

set of empirical relationships was developed for the PIC model.) The enhanced 

empirical relationships are incorporated into the UAM replacing the ozone 

photochemical mechanism. Model performance evaluations with the 1995 PTEP 

ambient measurements indicate that the modified UAM (known as UAM/LC) provides 

reasonable estimates of the annual sulfate and nitrate concentrations. In addition, the 

UAM/LC has the ability to model primary PM10 emissions. While the UAM/LC was 

developed to estimate annual sulfate and nitrate concentrations, the UAM/LC can also be 

used for shorter-term sulfate and nitrate concentrations. However, intensive efforts must 

be undertaken to prepare meteorological and air quality inputs needed to perform the 

model evaluation. The UAM/LC model evaluations are discussed in Appendix V.

Previous AQMP revisions also used the Chemical Mass Balance (CMB) model to assess 

source-receptor relationships. The CMB relies on source profiles to relate the 

contributions from various sources to measurements at a given location. As part of the 

PTEP, some of the CMB speciation profiles were updated.

In order to analyze local fugitive dust impacts, the PTEP identified a need for a fugitive 

dust model. The fugitive dust model has the capability to analyze fugitive dust impacts 

on a very localized area which is smaller than the resolution of most more complex 3-

dimensional grid models. The PTEP envisioned that if the episodic aerosol model tended 

to underestimate fugitive dust concentrations, then the fugitive dust model results would 

substitute the fugitive dust results of the episodic aerosol model. 

The third air quality model in the suite of PM10 air quality models is the source 

apportionment model. The source apportionment model provides the additional 

capability to analyze the impacts of various sources at a given location. While the source 

apportionment model can simulate 24-hour PM10 concentrations, the primary purpose of 

the model is to evaluate different control strategies and the relative contributions from 

the sources affected by the control strategies.

To analyze 24-hour PM10 concentrations, an episodic aerosol model application study 

was sponsored under the PTEP. The episodic aerosol model has been under 

development since 1989 with sponsorship from both the District and the Air Resources 

Board (ARB). The episodic aerosol model has the capability to model all major PM10

species. However, since the model is a 3-dimensional grid model, it is inherently a 

resource intensive model and cannot readily be used to estimate 24-hour PM10

concentrations. While the PTEP project advanced the state-of-science of episodic 
Chapter 5 Future Air Quality

5 - 5

aerosol model development, at this time, continued research is needed before the model 

can be relied upon as the primary approach to simulate 24-hour PM10 concentrations. In 

addition, techniques must be developed to expand the episodic PM10 concentration 

estimates to an annual average value.

Draft working papers for the 1997 AQMP provide discussions on each of the PTEP 

modeling projects.

AQMP Modeling Approach

Receptor models require specific knowledge about the chemical components of the 

ambient PM10 samples and of all sources emitting primary PM10. Special studies were 

conducted to develop a data base and a comprehensive library of chemical profiles for 

specific sources of PM10 emissions. Using the CMB model, ambient PM10

concentrations at each site can be apportioned according to the contributing sources.

For secondary PM10 components (sulfates and nitrates) and primary PM10 emissions, the 

UAM/LC is used to project annual concentrations in the South Coast Air Basin and 

Coachella Valley. Based on the change in PM10 concentrations from the base year and 

future-year projected by the UAM/LC, the projected future-year 24-hour PM10

concentrations can also be estimated.

Using the CMB and the UAM/LC, the major secondary PM10 components: nitrates, 

sulfates, secondary organics, and the primary, nonreactive, components can be estimated.

These models are used in combination with emissions projections to determine future 

PM10 air quality for a given future-year baseline or control scenario. For secondary 

organics, a linear rollback technique is applied to the CMB results to obtain future year 

projections while the UAM/LC is used to project the other components. Measurements 

from the five PTEP monitoring stations are used (Los Angeles, Anaheim, Diamond Bar, 

Rubidoux, and Fontana). The 1995 annual PM10 concentrations represent the PM10

design values for the South Coast Air Basin and all future-year PM10 air quality 

projections are compared to the 1995 concentrations. Detailed discussions of the model 

results are provided in Appendix V.

Ozone

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

UAM. UAM is an urban scale, three-dimensional, grid-type, numerical simulation 

model. It is designed for computing ozone concentrations under short-term, episodic 
FINAL 1997 AQMP

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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. Only one episode was modeled for the 1989 AQMP. Since 

then, measurement data from the 1987 Southern California Air Quality Study (SCAQS) 

(Lawson, 1990) became available for modeling purposes. For the 1991 AQMP, three 

ozone meteorological episodes were used to predict future air quality; two 

meteorological episodes during the SCAQS were used to complement the single episode 

from the 1989 AQMP. For the 1994 AQMP, two additional episodes are added to the 

analysis.

For the 1997 AQMP, the first modeling episode developed for the 1989 AQMP (the June 

5-7, 1985 episode) is dropped from further use since the meteorological conditions rarely 

occur in the Basin. The current form of the federal ozone air quality standard allows for 

one exceedance per year to account for these rare meteorological events. As such, a peak 

ozone concentration due to meteorological conditions in the June 1985 episode would be 

accounted for in the current form of the standard. In addition, the U.S. EPA modeling 

guidelines recommend that meteorological episodes from 1987 to present be used for 

attainment demonstration Table 5-1 lists the four meteorological episodes used for 

ozone air quality analysis, along with their peak measured ozone concentrations in the 

South Coast Air Basin, Antelope Valley, and Coachella Valley.

TABLE 5-1

Ozone Meteorological Episodes Used for the Ozone Attainment Demonstration

 Peak Concentration Peak (pphm)

Episode South Coast A.B. Antelope Valley Coachella Valley Introduced in the

August 26-28, 1987 29 10 16 1991 AQMP

June 23-25, 1987 24 15 16 1991 AQMP

July 13-15, 1987 25 12 16 1994 AQMP

September 7-9, 1987 33 12 15 1994 AQMP

Performance evaluations of the four meteorological episodes are provided in the 1994 

AQMP and the detailed UAM results for the various future year baseline and control 

scenarios are presented in Appendix V.

Carbon Monoxide

The CAA requires the use of an areawide model to describe the accumulation of 

emissions over several hours and kilometers within the region, as well as estimates of 
Chapter 5 Future Air Quality

5 - 7

roadway impacts within a few hundred meters of the roadway intersection. Based on 

U.S. EPA modeling guidelines, the UAM is used for the areawide analysis, and 

CAL3QHC, a roadway intersection model, is used to calculate carbon monoxide 

concentrations near the intersection. The UAM results are used to evaluate the 

effectiveness of control measures in attaining the federal 8-hour air quality standard for 

carbon monoxide in the year 2000. Carbon monoxide attainment demonstrations were 

submitted to the U.S. EPA in 1992 and 1994. Since that time, newer emission estimates 

have become available. Thus, the 1997 AQMP contains a revised attainment 

demonstration which will replace the prior submittals. A complete description of the 

modeling analysis is presented in Appendix V.

Visibility

Future-year visibility in the Basin is projected using the results derived from a regression 

analysis of visibility with air quality measurements. The regression data set consisted of 

aerosol composition data collected during a special monitoring program conducted 

concurrently with visibility data collection (prevailing visibility observations from 

airports and visibility measurements from District monitoring stations). A full 

description of the visibility analysis is given in Technical Report V-C of the 1994 

AQMP.

FUTURE AIR QUALITY

Nitrogen Dioxide

Under the federal Clean Air Act, the Basin must comply with the federal annual nitrogen 

dioxide air quality standard by November 15, 1995 [Section 192(b)]. Since the annual 

standard is based on the calendar year, attainment must be demonstrated for calendar 

year 1994. As discussed in Chapter 2, the Basin has met the federal annual standard the 

last four years (i.e., 1992 through 1995) and the state one-hour standard the last two 

years (i.e., 1994 and 1995). The modeling results discussed next show that the Basin will 

continue to meet federal and state nitrogen dioxide standards.

Figure 5-1 presents the predicted annual average nitrogen dioxide concentrations for 

2000 and 2010 with and without controls. Maximum 1-hour nitrogen dioxide 

concentrations are projected from the baseline maximum 1-hour concentrations using 

linear rollback. The predicted maximum 1-hour nitrogen dioxide concentrations for the 

future-year baseline conditions with and without controls are shown in Figure 5-2.
FINAL 1997 AQMP

5 - 8

(Federal Standard = 5.3 pphm)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Los Angeles Burbank Pomona Pico Rivera

Site

Concentration (pphm)

1993 Baseline 2000 Baseline 2010 Baseline

2000 Control 2010 Control

FIGURE 5-1

Annual Average NO2 Concentration Projections

0

5

10

15

20

25

30

Los

Angeles

Burbank Pomona Pico

Rivera

Site

Concentration (pphm)

1993 Baseline 2000 Baseline 2010 Baseline

2000 Control 2010 Control

CAL

STD

FIGURE 5-2

Maximum 1-Hour NO2 Concentration Projections
Chapter 5 Future Air Quality

5 - 9

The trend analysis was performed using the highest nitrogen dioxide concentrations 

observed in the last three-year period. Based on the more recent nitrogen dioxide 

measurements as discussed in Chapter 2, nitrogen dioxide concentrations continue to 

decrease over time.

The results indicate that the federal annual nitrogen dioxide standard will be met 

throughout the Basin through the year 2010 without additional emission controls. 

However, implementation of proposed controls after 1997 would further reduce nitrogen 

dioxide concentrations in the Basin.

Based on projected future-year maximum 1-hour nitrogen dioxide concentrations 

assuming no further controls, the Basin will be in compliance with the state 1-hour 

standard through the year 2010. Implementation of proposed controls after 1997 would 

further reduce nitrogen dioxide concentrations in the Basin.

PM10

Under the federal Clean Air Act, the Basin must comply with the federal PM10 air quality 

standards by December 31, 2001 [Section 188(c)(2)]. A five-year extension could be 

granted if attainment cannot be demonstrated and several other conditions are satisfied 

[Section 188(e)]. Figures 5-3 and 5-4 depict future annual average PM10 air quality 

projections at five PM10 monitoring sites compared to federal and state annual PM10

standards, respectively. Although each standard is based on an annual average, separate 

calculations are required because the federal standard is based on an arithmetic average, 

whereas the state standard is based on a geometric average. In general, geometric 

averages are slightly less than arithmetic averages. Shown in each figure are the 

estimated baseline conditions for the years 1995, 2000, 2006 and 2010, along with 

projections for 2000, 2006, and 2010 with control measures in place. All areas will 

attain the federal annual standard by the year 2000, except Rubidoux, which will be in 

compliance by 2006. Relative to the state annual standard (μg/m3), Los Angeles, 

Anaheim, and Diamond Bar are projected to attain by 2006. Rubidoux and Fontana will 

not be in compliance by 2010.

The projections for the 24-hour state and federal standards are shown in Figure 5-5. The 

results are similar to those for the annual standards. All areas will be in attainment of the 

federal 24-hour standard (150 μg/m3), except Rubidoux, which will be in compliance by 

2006. With respect to the state 24-hour standard (50 μg/m3), none of the sites will be in 

attainment by 2010.
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0

10

20

30

40

50

60

70

Los

Angeles

Anaheim Diamond

Bar

Rubidoux Fontana

Site

Concentration

1995 Baseline 2000 Baseline 2006 Baseline 2010 Baseline

2000 Control 2006 Control 2010 Control

FED

STD

FIGURE 5-3

Annual Arithmetic Average PM10 Concentrations 

0

10

20

30

40

50

60

Los

Angeles

Anaheim Diamond

Bar

Rubidoux Fontana

Monitoring Site

Concentration

1995 Baseline 2000 Baseline 2006 Baseline 2010 Baseline

2000 Control 2006 Control 2010 Control

CAL

STD

FIGURE 5-4

Annual Geometric Average PM10 Concentrations
Chapter 5 Future Air Quality

5 - 11

0

50

100

150

200

250

Los

Angeles

Anaheim Diamond

Bar

Rubidoux Fontana

Monitoring Site

Concentration

1995 Baseline 2000 Baseline 2006 Baseline 2010 Baseline

2000 Control 2006 Control 2010 Control

FED

STD

CAL

STD

FIGURE 5-5

Maximum 24-Hour PM10 Concentrations

Ozone

As the only ozone nonattainment area designated as extreme, the Basin must comply 

with the federal ozone air quality standard by November 15, 2010. The attainment 

demonstration shown here addresses this requirement. As discussed earlier, four 

meteorological episodes are used in the ozone attainment demonstration. The modeling 

results for each of the episodes exhibit similar ozone air quality projections. The results 

for the June 23-25, 1987 and August 26-28, 1987 episodes are presented here since these 

two episodes are more limiting than the other two episodes (i.e., July 13-15, 1987 and 

September 7-9, 1987). The modeling results for all episodes are presented in Appendix 

V.

The ozone modeling discussion that follows is divided into two sections: projected 

baseline concentrations and predicted controlled concentrations. The baseline 

projections assume no further controls in the future years and the predicted controlled 

concentrations assume the implementation of the 1997 AQMP control strategy at the 

appropriate level for the year modeled.

Table 5-2 shows the total VOC and NOx emissions in the Basin on the first day of the 

June 23-25, 1987 episode. The emissions presented in Table 5-2 are episode-specific 
FINAL 1997 AQMP

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and therefore differ from the planning inventories reported in Chapter 3. The modeling 

results indicate that without additional controls, there will be some air quality 

improvement relative to peak ozone concentrations from 1987 to 2010 as VOC emissions 

decrease. However, after 2010 the ozone air quality is projected to degrade slightly.

TABLE 5-2

Precursor Emissions and Model-Predicted Ozone Concentrations

Peak Ozone

concentration*

Year/Scenario VOC NOx (pphm)

1987 Historical Year 1976 1379 24**

2000 Baseline 974 924 15.0

2010 Baseline 905 739 15.1

2000 Control 919 899 14.6

2010 Control 402 502 11.8

* Peak ozone concentrations for future years are for the last day of the June 1987 episode.

** Peak measured ozone concentration.

The VOC emission reductions are due mainly to decreases in mobile source emissions 

whereas the oxides of nitrogen emissions decrease more slowly due to increases in offroad activities (see Chapter 3 for a discussion of future-year emission estimates).

Figure 5-6 depicts the predicted baseline basinwide maximum ozone without further 

AQMP measures for the June and August 1987 meteorological episodes modeled. As 

shown, basinwide peak ozone concentrations are on the order of 15-16 pphm from 2000 

to 2010. Similar modeling results are seen for the other two 1987 meteorological 

episodes (see Appendix V).

Control Strategy Impacts

Figure 5-7 shows the predicted Basinwide maximum ozone for the June and August 

1987 meteorological episodes for the years 2000, and 2010, with proposed emission 

controls in place. The maximum ozone concentrations and emission levels are also 

presented in Table 5-2. The results indicate that the proposed control strategy will 

almost eliminate health advisories (> 15 pphm) around the year 2000 and will bring the 

entire Basin into compliance with the federal ozone standard by the year 2010. Regional 

maximum ozone concentrations in the year 2010 will be between 9 and 12 pphm for the 

four meteorological episodes. With implementation of the proposed control strategy, the 

peak ozone value for the June 1987 episode is 11.8 pphm.
Chapter 5 Future Air Quality

5 - 13

0

5

10

15

20

25

30

1987 2000 2010

Year

Concentration (pphm)

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

FED

STD

FIGURE 5-6

Baseline Basinwide Maximum Ozone Concentrations

0

5

10

15

20

25

30

1987 2000 2010

Year

Concentration (pphm)

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

FED

STD

FIGURE 5-7

Basinwide Maximum Ozone Concentration with Proposed Emissions Controls
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Spatial distributions of maximum ozone concentrations for the 1987 historical year are 

shown in Figure 5-8. Future year ozone air quality projections for 2000 and 2010 with 

and without implementation of all control measures are presented in Figures 5-9 and 5-

10, respectively. The predicted ozone concentration will be significantly reduced in the 

future years in all parts of the Basin, the Mojave Desert Air Basin, and the Salton Sea Air 

Basin with the implementation of proposed control measures in the South Coast Air 

Basin. Similar results occur for the other meteorological episodes.

Assessment of Mobile Emission Uncertainties

As discussed in the 1994 AQMP, recent studies indicate that current and historical onroad mobile source emissions may be underestimated by as much as 60 percent for VOCs 

and 8 percent for oxides of nitrogen. For the 1997 AQMP, an updated version of the 

emissions factor program (EMFAC7G) indicates that all on-road motor vehicle precursor 

emissions have increased compared to the on-road motor vehicle emissions estimated in 

the 1994 AQMP. However, the emission increases are still uncertain given the 

uncertainties in the transportation model assumptions and the assumptions inherent to the 

current on-road motor vehicle emissions estimation procedures. As faster computer 

systems become available, more sophisticated procedures for estimating on-road motor 

vehicle emissions will also become available.

Future-year emission estimates for on-road mobile sources will most likely be more 

accurate as emission controls become more efficient. As newer on-road vehicles are 

introduced, on-road emissions are expected to decrease and deterioration rates will be 

smaller. It is not expected that future-year on-road emissions will be as grossly 

underestimated. Future AQMP revisions will reassess the impacts of the mobile source 

underestimations as newer revisions to the mobile source estimations become available.

Assessment of Weekend Emissions Effects

In recent years ambient ozone measurements indicate a faster decrease in Stage I 

episodes (days with ozone concentrations greater than 20 pphm) on weekdays compared 

to weekends. To address concerns that future ozone exceedances may occur more often 

on weekends, a sensitivity analysis using the June 1987 and August 1987 ozone 

meteorological episodes was conducted. Since meteorology varies independent of the 

day of the week, differences between weekday and weekend emissions are likely key. 

During the work week, stationary source emissions are higher as more businesses 

operate. Motor vehicle emissions peak in the morning and evening rush hours. On 

weekends, stationary source emissions are lower and motor vehicle emissions build up to 

a plateau level sustained through much of the day. Sufficient information to generate a 

weekend stationary and area source emissions inventory are available. However, 
Chapter 5 Future Air Quality

5 - 15

information on on-road mobile vehicle travel patterns are not readily available. As a 

sensitivity analysis, typical weekend traffic patterns (by hour) were used to create an 

hourly emissions pattern for a weekend day and a Friday traffic pattern was used to 

create a typical Friday early afternoon commute traffic pattern. In addition, an 

assumption that 50 percent of the heavy-duty truck emissions do not occur on weekends 

was made to represent less commercial activity on weekends. The estimated weekend 

inventory was used as the emissions for the third day of the air quality simulation and the 

Friday inventory was used as the second day’s emissions. The results of the sensitivity 

analysis show that the federal air quality standard is still attained with the 1997 AQMP 

control strategy. Further work is needed to fully quantify the weekend episode 

phenomena. In addition, the field measurement program proposed for summer 1997 will 

provide additional information on weekend effects for future AQMP revisions.

FIGURE 5-8

Model-Predicted Maximum Hourly Ozone Concentrations 

in the South Coast Air Basin in 1987
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(a) Baseline (with rules adopted as of September 1996)

(b) Controlled (with implementation of proposed control measures)

FIGURE 5-9

Model-Predicted Maximum Hourly Ozone Concentrations

in the South Coast Air Basin in 2000
Chapter 5 Future Air Quality

5 - 17

(a) Baseline (with rules adopted as of September 1996)

(b) Controlled (with implementation of proposed control measures)

FIGURE 5-10

Model-Predicted Maximum Hourly Ozone Concentrations

in the South Coast Air Basin in 2010
FINAL 1997 AQMP

5 - 18

Carbon Monoxide

As discussed earlier, future carbon monoxide air quality projections are based on a UAM 

analysis. A carbon monoxide meteorological episode for 1989 was chosen for modeling 

as part of the 1993 Federal Attainment Plan for Carbon Monoxide. This Plan uses the 

same December 6-7, 1989 episode with a recorded 1-hr carbon monoxide concentration 

of 31 ppm and an 8-hr concentration of 21.8 ppm. These were the highest recorded 

values over the most recent years. Table 5-3 summarizes the carbon monoxide 

projections by 2000 with implementation of short- and intermediate-term control 

measures. Attainment of both the federal and state carbon monoxide air quality 

standards is projected in 2000 without any additional controls.

TABLE 5-3

Carbon Monoxide Emissions and Model-Predicted Concentrations

Episode-Specific 8-hr Maximum 1-hr Maximum

Year/Scenario Emissions Concentration Concentration

(tons/day) (ppm) (ppm)

1989 Baseline 9140 22.1 26.1

2000 Baseline 4511 7.7 10.7

2000 Control 4349 7.4 10.3

State 1-hr CO standard = 20 ppm

State 8-hr CO standard = 9.0 ppm

Federal 8-hr CO standard = 9 ppm

Visibility

The results of the visibility analysis for Rubidoux are illustrated in Figure 5-11. Without 

the proposed AQMP control measures, annual average visibility is projected to improve 

at Rubidoux from the current average of 6 miles to 7 miles in the year 2010.

With the implementation of all proposed emission controls for 2010, the annual average 

visibility would improve to about 11 miles at Rubidoux.

SUMMARY AND CONCLUSIONS

Figure 5-12 shows the model-predicted regional peak concentrations for the four 

nonattainment criteria pollutants, as percentages of the most stringent federal standard, 

for the years 2000, 2006, and 2010, (with and without further emission controls). Figure 

5-13 shows similar information related to the most stringent California state standards.
Chapter 5 Future Air Quality

5 - 19

0

2

4

6

8

10

12

1986 2000 2006 2010

Year

Visibility (miles)

Baseline Control

CAL 

STD

FIGURE 5-11

Annual Average Daytime Visibility Projections at Rubidoux

0

50

100

150

200

250

NO2 PM10 Ozone CO

Pollutant

Percent of Standard

Historical Baseline (Design Value) 2000 Baseline

2006 Baseline 2010 Baseline

2000 Control 2006 Control

2010 Control

FED

STD

FIGURE 5-12

Projection of Future Air Quality in the Basin in Comparison 

with the Most Stringent Federal Standards
FINAL 1997 AQMP

5 - 20

0

50

100

150

200

250

300

350

400

450

NO2 PM10 Ozone CO

Pollutant

Percent of Standard

Historical Baseline 2000 Baseline 2006 Baseline

2010 Baseline 2000 Control 2006 Control

2010 Control

CAL

STD

FIGURE 5-13

Projection of Future Air Quality in the Basin in Comparison with

Most Stringent California State Standards

Table 5-4 summarizes the expected year for attainment of the various federal and state 

standards for the four pollutants analyzed. As shown, the Basin will be in compliance 

with federal and state standards for all pollutants except the state ozone and PM10

standards by the year 2010. 
Chapter 5 Future Air Quality

5 - 21

TABLE 5-4

Expected Year of Compliance with State and Federal

Standards for the Four Criteria Pollutants

Concentration Expected

Pollutant Standard Level Compliance Year

Ozone NAAQS 1-hour 12 pphm 2010

CAAQS 1-hour 9 pphm beyond 2010

PM10 NAAQS Annual 50 ug/m32006

NAAQS 24-hour 150 ug/m32000

CAAQS Annual 30 ug/m3beyond 2010

CAAQS 24-hour 50 ug/m3beyond 2010

CO NAAQS 8-hour 9 ppm 2000

NAAQS 1-hour 35 ppm 1990*

CAAQS 8-hour 9 ppm 2000

CAAQS 1-hour 20 ppm Achieved

NO2 NAAQS annual 5.34 pphm Achieved

CAAQS 1-hour 25 pphm Achieved

* The Basin has been achieving the federal 1-hour CO air quality standard since 1990. However,

the Basin is still considered nonattainment until the 8-hour CO air quality standard is achieved.

BASIN EMISSIONS CARRYING CAPACITY (EMISSIONS BUDGET)

The District is required to separately identify the emission reductions and corresponding 

type and degree of implementation measures required to meet federal and state ambient 

air quality standards. Section 40463(b) of the California State Health and Safety Code 

specifies that, with the active participation of the Southern California Association of 

Governments, a South Coast Air Basin emission carrying capacity for each state and 

federal ambient air quality standard shall be established by the South Coast District 

Board for each formal review of the Plan and shall be updated to reflect new data and 

modeling results.

A carrying capacity is defined as the maximum level of emissions which enable the 

attainment and maintenance of an ambient air quality standard for a pollutant. Emission 

carrying capacity for state standards shall not be a part of the State Implementation Plan 

requirements of the Clean Air Act for the South Coast Air Basin.
FINAL 1997 AQMP

5 - 22

Emission carrying capacity as defined in the Health and Safety Code is an overly 

simplistic measure of the Basinwide allowable emission levels for specific ambient air 

quality standards. It is highly dependent on the spatial and temporal pattern of the 

emissions. Because of the multicomponent nature of PM10, carrying capacity for the 

contributing emittants can vary significantly. For ozone and secondary PM10

components, the carrying capacity is a non-linear function among their precursors.

The federal Clean Air Act requires that plans contain an emissions budget which 

represents the remaining emissions levels that achieve the applicable attainment deadline. 

Based on the modeling results, a set of carrying capacities can be defined corresponding 

to federal and state ambient air quality standards for carbon monoxide, nitrogen dioxide, 

PM10, and ozone. VOC and oxides of nitrogen are used for ozone. Table 5-5 shows the 

emissions carrying capacities for the Basin to meet federal air quality standards. These 

estimates are based on emission patterns estimated for each of the federal attainment 

years (i.e., 2000 for carbon monoxide, 2006 for PM10, and 2010 for ozone).

PROJECTED EMISSION TRENDS THROUGH 2010

Figures 5-14 through 5-17 show the projected emission trends for both NOx and VOC 

through the year 2010. Depicted are scenarios for the baseline cases (e.g., no further 

rules), and for the controlled cases (with the 1997 AQMP Measures). Categories are 

described slightly different than most emission inventory summaries in that permitted 

sources (e.g., those emission sources which are permitted with the District) are 

specifically delineated. These figures show that emission levels continue to decrease 

through the year 2010, especially for the controlled case, when attainment with the 

federal ozone standard is expected. For VOCs, emissions are initially dominated by 

mobile sources, but in the later periods area sources will become a more dominant 

fraction. For NOx emissions, mobile sources are expected to be the dominant source 

through the entire period.
Chapter 5 Future Air Quality

5 - 23

TABLE 5-5

Emissions Carrying Capacity Estimations1

for the South Coast Air Basin (tons/day)

a) Carbon Monoxide Attainment Strategy (2000)

Emission Category CO

Stationary 294

On-Road 3125

Off-Road 1549

Overall Control Strategy 4968

to meet NAAQS

b) PM10 Attainment Strategy (2006)

Emission Category VOC NOx SOx PM10

Stationary 341 96 13 271

On-Road 187 350 16 14

Off-Road 95 189 37 16

Overall Control Strategy 623 635 66 301

to meet NAAQS

c) Ozone Attainment Strategy (2010)

Emission Category VOC NOx

Stationary 268 88

On-Road 81 278

Off-Road 64 164

Overall Control Strategy 413 530

to meet NAAQS

1

 Values rounded to the nearest integer.
FINAL 1997 AQMP

5 - 24

0

200

400

600

800

1000

1200

1400

1993 1997 2000 2006 2010

Year

Emissions (Tons/Day)

On-Road Off-Road Permitted Facilities Area Attainment

Attainment

FIGURE 5-14

VOC Emissions - Baseline Scenario

0

200

400

600

800

1000

1200

1400

1993 1997 2000 2006 2010

Year

Emissions (Tons/Day)

On-Road Off-Road Permitted Facilities Area Attainment

Attainment

FIGURE 5-15

VOC Emissions - Under 1997 AQMP
Chapter 5 Future Air Quality

5 - 25

0

200

400

600

800

1000

1200

1400

1993 1997 2000 2006 2010

Year

Emissions (Tons/Day)

On-Road Off-Road Permitted Facilities Area Attainment

Attainment

FIGURE 5-16

NOx Emissions - Baseline Scenario

0

200

400

600

800

1000

1200

1993 1997 2000 2006 2010

Year

Emissions (Tons/Day)

On-Road Off-Road Permitted Facilities Area Attainment

Attainment

FIGURE 5-17

NOx Emissions - Under 1997 AQMP