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 1997 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 designated nonattainment for PM10, ozone, and carbon monoxide. 

Two of these pollutants - 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 expeditious rate of 

reduction towards the state air quality standards. The overall control strategy is designed 

so that efforts to achieve the standard for one criteria pollutant do not cause unnecessary 

deterioration of another. A three-step modeling process was originally crafted in the 

1989 AQMP to develop the control strategy. The three-step process began with an 

analysis of future nitrogen dioxide air quality, followed by PM10 air quality, and lastly, 

future ozone air quality. Subsequent attainment of the nitrogen dioxide standard in 1995 

reduced the number of steps in the modeling process to two: analysis of future PM10 air 

quality followed by the future 1-hour ozone air quality. Air quality analyses under the 

2003 AQMP are performed in keeping with this two-step modeling approach. 

However, future efforts to achieve the PM2.5 and 8-hour average ozone standards 

deserve consideration in the selection of the overall air quality standards. 

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

of the PM10/ozone strategy. A photochemical grid model is used to project regional 

future carbon monoxide (CO) air quality. An additional “hot-spot” analysis is required 

to assess impacts at intersections. Both analyses are performed in the 2003 AQMP to 

update the 1997 Revision of the Carbon Monoxide Attainment Demonstration (CO 

Plan). It is important to note that the Basin did not exceed the federal 8-hour average 

carbon monoxide standard in 2001 and exceeded the standard only once in 2002. Thus, 

the Basin has met the criteria for attainment of the federal 8-hour average carbon 

monoxide standard. The 2003 CO Plan will serve as a replacement for the 1997 CO 

Plan that lapsed in 2000 and will provide the basis for a future maintenance plan for the 

Basin pending submission of a petition for redesignation of attainment status. 

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 ozone 

air quality projections for the Coachella Valley are presented in Chapter 8 and in 

Appendix V. 
Final 2003 AQMP 

5 - 2

MODELING 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.

In the 1997 AQMP a combination of different modeling techniques (receptor and 

photochemical grid models) were 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 were compared to a modified 

emissions rollback method (performed on a component-by-component basis) to provide 

assurance that the modeling techniques are giving directionally appropriate conclusions. 

Of the modeling methodologies evaluated for the 1997 AQMP, a photochemical grid 

model application using the Urban Airshed Model with a flexible chemistry mechanism 

(UAM-FCM) coupled with an empirical linear chemistry module (LC) proved to be the 

most promising means to calculate annual average PM10 concentrations (excluding the 

secondary organic component). The UAM/LC methodology built upon the particle-incell (PIC) dispersion model approach used by the District since 1989 to examine annual 

primary particulates, ammonium, secondary sulfate and nitrate concentrations. 

UAM/LC model performance was evaluated for 1995 against speciated particulate data 

acquired from the PM10 Technical Enhancement Program (PTEP). (A detailed 

description of the PTEP monitoring program is provided in Appendix V of the 1997 

AQMP. Receptor modeling using the Chemical Mass Balance (CMB) model with 

enhanced source profiles to estimate secondary organic particulate formation completed 

the model simulation package to estimate the primary and secondary PM10 components. 

A second methodology that coupled the UAM-FCM with a full gas phase and aerosol 

chemistry mechanism, the UAM-AERO model, was evaluated for potential episodic 

PM10 prediction. While this methodology showed promise, the data resources required 

for the episodic model application were extensive for extended application. Since the 

1997 AQMP, efforts have been made to modify the UAM/LC to incorporate full gas 

phase chemistry with the empirical aerosol mechanism for long-term (LT) for annual 

applications. The resulting UAMAERO-LT was also extended to incorporate PM2.5 air 

quality prediction capability. 

The newly developed UAMAERO-LT model is a simplified version of the UAM-AERO 

model. The detailed thermodynamic routine (ISOROPIA) of the UAM-AERO model 

was replaced with the parameterized inorganic gas/aerosol partitioning module. The 

secondary organic aerosol formation scheme was replaced with a condensed version of 

the Carnegie Melon University secondary organic aerosol module. The CMU module 
Chapter 5 Future Air Quality

5 - 3 

treats organic products as semi-volatile species and employs an equilibrium approach to 

the gas/aerosol partitioning of these species. In addition, the detailed particle-sizing 

scheme used in the UAM-AERO model was also replaced by an observation-based, two 

size (fine and coarse) particle-sizing scheme for secondary aerosols. UAMAERO-LT 

utilizes a full Carbon Bond IV gas-phase chemical mechanism and simulates the 

formation of particulate nitrate, sulfate, ammonium, organic carbon, elemental carbon 

and other primary particles. 

For the 2003 AQMP, UAMAERO-LT model was used to simulate 1995 meteorological 

and air quality data to determine Basin annual average PM10 and PM2.5 concentrations. 

Model performance was evaluated against speciated particulate PTEP (PM10 and 

PM2.5) air quality data as well as Source Selective Inlet (SSI) High-Vol PM10 data 

measured at the District’s air monitoring network from 1995. The future year attainment 

demonstration was analyzed for 2006, the target set by the federal CAA. Additional 

PM2.5 model simulations are provided for 2010 to scope the potential reductions needed 

to meet the new fine particulate standards. 

The UAMAERO-LT simulations incorporated several changes in model applications 

compared to the UAM/LC analyses. The vertical structure was increased to 5 layers 

(compared with the 2-layer analysis of UAM/LC). The temperature structure aloft was 

also modified to reflect a more comprehensive field of daily, diurnal mixing heights. 

Finally, the simulations benefited from enhancements made to the emissions inventory 

including updated ammonia emissions, improved specification of primary road and 

fugitive dust emissions and better allocation of those emissions through GIS land use 

mapping. 

While UAMAERO-LT is the desired tool to simulate Basin annual average PM10 and 

PM2.5 concentrations, the model is not run with detailed, temperature-corrected dayspecific emissions. As a consequence, the annual model simulations are not suited for 

projecting maximum 24-hour average PM10 and PM2.5 concentrations. Speciated linear 

rollback is used to simulate peak 24-hour average concentrations at five key PTEP 

monitoring locations having detailed profiles of particulate components for the days 

when the 1995 Basin maximum concentrations were observed. 

The following section summarizes the PM10 modeling approach conducted in 

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

AQMP Modeling Approach

The 2003 AQMP annual average PM10 modeling employs a deterministic approach to 

demonstrate attainment of the PM10 in 2006. UAMAERO-LT simulations were 

conducted for the 1995 base year meteorology and emissions to determine model 

performance when compared to the speciated ambient PM10 and PM2.5 monitoring 

data. Performance comparisons were conducted for the ammonium, nitrates, sulfates, 
Final 2003 AQMP 

5 - 4

secondary organic matter, elemental carbon, primary and total particulate mass for five 

PTEP monitoring sites (Los Angeles, Anaheim, Diamond Bar, Rubidoux, and Fontana). 

Additional performance comparisons are conducted for the SSI particulate mass at 19 

District sites that routinely measured SSI Hi-Vol data to demonstrate the 

representativeness of the modeling simulation throughout the modeling domain. 

UAMAERO-LT is used in combination with emissions projections to determine PM10

air quality for the 2006 future-year baseline and controlled scenario. A weight of 

evidence demonstration is provided in Appendix V to address future year PM10

predictions at "hot spot" grids, where the particulate emissions have significant 

uncertainty. A supplemental PM2.5 simulation is provided for the 2010 future-year 

control scenario to quantify the extent of additional emissions reduction needed to meet 

the PM2.5 beyond that date. The results of the 2010 PM2.5 concentrations are presented 

in Chapter 10. 

All future-year PM10 air quality projections are compared to the 1995 concentrations. 

The 1995 Basin maximum annual average PM10 concentration was equivalent to the 

1995 design value (69 μg/m3 for 1993-1995). The 2001 PM10 design value for the 

South Coast Air Basin is approximately 6 percent lower than that of 1995 at 65 μg/m3 

(averaged for 1999-2001). 

Linear rollback on particulate component species is used to assess future year 24-hour 

maximum PM10 concentrations at the five PTEP monitoring sites. Observed 24-hour 

average maximum PM10 for 1995 are used to anchor the rollback calculation for future 

year impacts. For Rubidoux, the 1995 second maximum PM10 concentration (206 

μg/m3) observed in 1995 is used for the analysis since the peak 24-hour average (219 

μg/m3) occurred during a “Santa Ana” high wind day. The peak concentration, (April 9, 

1995), has not been tagged as a natural event in the AIRS data set since the policy did 

not take effect until 1997. It is useful to note that the 24-hour PM10 standard has been 

exceeded on only 16 days since 1995 with 10 of those days being high wind events. In 

addition, since 1997, only high wind events have caused the 24-hour standard to be 

exceeded. 

Projected controlled emissions for 2006 and 2010 are used to determine future 24-hour 

maximum PM10 at the five key monitoring stations. Detailed discussions of all 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. In the 1997 AQMP, UAM, the 

photochemical model at that time recommended by the U.S. EPA guidance (40 CFR Part 

51, Appendix W), was used with the CB-IV chemistry package for the Basin ozone 

attainment demonstration and supporting analyses. UAM is an urban scale, threedimensional, grid-type, numerical simulation model. It is designed for computing ozone 
Chapter 5 Future Air Quality

5 - 5 

concentrations under short-term, episodic conditions lasting one to three days. On April 

15, 2003, the final revisions to Appendix W were published in the Federal Register. 

Revised Appendix W removed UAM as the sole recommended model by EPA for ozone 

analysis, and in its place did not name a successor. Revised Appendix W promotes the 

use of models employing state-of-the-art advances in science. 

For the 2003 AQMP, UAM with the Carbon Bond IV (CB-IV) chemistry is used to 

demonstrate future year (2010) attainment of the 1-hour federal ozone standard. 

Experience gained in implementing UAM and interpreting the impacts of the simulation 

results in prior AQMPs provides the current application with a large measure of 

confidence. This is demonstrated both in the model’s ability to simulate peak ozone 

concentrations for a new historical meteorological episode (discussed later) and in the 

capacity of the model to estimate observed Basin maximum ozone concentrations for 

2002, as a "mid-course" evaluation. Performance statistics and model inputs are 

discussed extensively in Appendix V. 

Regardless, while UAM has been selected as the primary modeling tool for the 2003 

AQMP, the California Photochemical Grid Model (CALGRID) [Yamartino, et. Al, 

1989) using SAPRC99 chemistry was also evaluated for its potential to simulate base 

and future year ozone to demonstrate Basin attainment of the federal one hour standard. 

CALGRID is a regional scale, three dimensional, grid type model that embodies several 

enhancements in layer structure, advection and dispersion schemes not found in UAM. 

CALGRID has been used for selected ozone attainment demonstrations nationwide and 

has been used in ozone analyses in other countries. The SAPRC99 chemistry reflects the 

state of the science in chemical mechanisms with its enhanced treatment of reactivity 

and interaction of additional chemical species. An expert panel of air quality researchers 

was convened to review the 2003 AQMP modeling efforts. Their general 

recommendation supported the transition to the CALGRID/SAPRC99 modeling system. 

A discussion of the CALGRID/SAPRC99 modeling system and its performance is 

provided as attachment A-7 to Appendix V. In general, model performance for error and 

bias is good, however, the model was unable to simulate peak base year ozone 

concentrations (approximately 12 percent lower than observations) using the same 

emissions as the UAM. It was assumed that the tendency to under predict in the base 

year would carry through to future year simulations and result in the underestimation of 

emission reductions needed to meet the federal standard. (The CALGRID 2010 

simulations are presented as part of a technical report in Attachment-7 of Appendix V. 

When the CALGRID projected 2010 ozone concentrations for the two control options 

are scaled for under prediction in the base year, the adjusted predicted ozone carrying 

capacity is essentially equivalent to the UAM ozone projections. As a consequence, the 

carrying capacity would not change). 

Like CALGRID/SAPRC99, the Comprehensive Air Quality Model with Extensions 

(CAMx) [Environ, 2002], with SAPRC99 chemistry, was also evaluated as a possible 

modeling tool for the AQMP attainment demonstration; however it also was unable to 
Final 2003 AQMP 

5 - 6

simulate base year peak ozone concentrations. (CAMx with CB-IV chemistry is being 

run in a low reactivity mode to support of the carbon monoxide attainment 

demonstration to take advantage of its layer structure meteorological and dispersion 

advection schemes). As a consequence, UAM was used for the 2003 AQMP regional 

ozone simulations. However, based on the expert review panel recommendations, the 

District is committed toward using the CALGRID/SAPRC99 modeling system in the 

future. 

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

meteorological episodes. Only one episode was modeled for the 1989 AQMP. For the 

1991 AQMP, three ozone meteorological episodes were used to predict future air 

quality; two meteorological episodes during the 1987 Southern California Air Quality 

Study (SCAQS) (Lawson, 1990) were used to complement the single episode from the 

1989 AQMP. For the 1994 AQMP, two additional SCAQS episodes were added to the 

analysis and for the 1997 AQMP, the first modeling episode developed for the 1989 

AQMP (the June 5-7, 1985 episode) was removed from further use since such 

meteorological conditions rarely occur in the Basin. 

The Southern California Ozone Study (SCOS97) [Jackson, et.al., 1998, Doislager, 1998, 

among others] measured ozone, precursor and meteorological data for several episode 

periods during the summer and fall of 1997. The monitoring program took place 

approximately one and a half years after the implementation of California Phase-II fuel 

reformulation. The goal of SCOS97 was to provide comprehensive air quality and 

meteorological data for the purpose of evaluating state of the art meteorological and air 

quality models for use in attainment demonstrations. While intensive field monitoring 

during SCOS97 captured several ozone meteorological episodes including a weekend 

episode, the period beginning August 3-7, 1997 produced the Basin second maximum 

concentration (0.188 ppm). This meteorological episode has been selected for the 

current attainment demonstration. One additional candidate episode was considered for 

the attainment demonstration, (July 16, 1998), however, when evaluated using statistical 

ranking, the July 1998 episode, like the June 1985 episode, was determined to be rare 

event ranked at the 99.9th percentile of the episode distribution with an expected 

frequency of less than once four years. 

The current form of the federal ozone air quality standard allows for the standard to be 

exceeded once per year to account for these rare meteorological events. As such, a peak 

ozone concentration due to meteorological conditions in the June 1985 or July 1998 

episodes would not be accounted for in the current form of the standard. In addition, 

EPA modeling guidelines recommend that meteorological episodes used for attainment 

demonstration is no older than ten years. The August 1997 SCOS97 episode satisfies 

these criteria. 

Table 5-1 lists the primary meteorological episode (August 1997) used for ozone air 

quality analysis including the peak measured ozone concentrations in the South Coast 

Air Basin, the Mojave Desert Air Basin and the Coachella Valley portion of the Salton 
Chapter 5 Future Air Quality

5 - 7 

Sea Air Basin. One additional SCAQS episode (August 1987) is carried forward from 

the 1997 AQMP to provide continuity between AQMP attainment demonstrations. The 

August 1997 episode is comprised of "Type-1" high potential, meteorological days 

categorized by the classification system used in previous attainment demonstration 

(Appendix V-P, 1989 AQMP). While it is desirable to have meteorological episodes 

from several categories, the "Type-1" meteorology has accounted for 52 percent of all 

days exceeding the federal 1-hour standard, averaged from 1996-2002. With the 

continuing trend of reduced precursor emissions it is expected that the percentage of 

days exceeding the standard having "Type-1" meteorology will increase and eventually 

become the sole path to high ozone concentrations in the Basin. Nonetheless, UAM 

future air quality projections are included for the August 1987 SCAQS episode that 

features days in meteorological categories other than "Type-1." 

TABLE 5-1 

Ozone Meteorological Episodes Used for the Ozone Attainment Demonstration 

 Peak Concentration Peak (pphm) 

Episode South Coast Mojave 

Desert 

Salton Sea. - 

Coachella Valley 

Introduced in the 

August 26-28, 1987 29 13 16 1991 AQMP 

August 3-7, 1997 19 14 16 2003 AQMP 

The baseline performance evaluation of the 1987 meteorological episode is provided in 

the 1994 AQMP. A comprehensive description of the UAM modeling system 

including, air quality and meteorological inputs and the performance evaluation using 

the 1997 August SCOS episode for the base and future year simulations is provided in 

Appendix V. 

Carbon Monoxide 

The CAA requires the use of an area wide model to describe the accumulation of 

emissions over several hours and kilometers within the region. CAMx, a fixed layer, 

regional simulation model, is used for the area wide analysis. CAL3QHC, a roadway 

intersection model, is used to calculate carbon monoxide concentrations near the 

intersection. CAMx and CAL3QHC were both simulated for a new meteorological 

modeling episode, October 31-November 1, 1997, during the SCOS97 monitoring 

program. The SCOS97 episode replaces the December 1989 episode and ranks second 

in observed peak carbon monoxide concentrations (17.0 ppm 8-hour average) in the post 

Phase II fuel reformulation period (1996 - 2002). 

Previous carbon monoxide attainment demonstrations were submitted to the U.S. EPA in 

1992, 1994 and 1997 to bring the Basin into attainment with the federal standard in 

2000. In 2000, the CO standard was exceeded in the Basin on three days, leaving the 
Final 2003 AQMP 

5 - 8

Basin in non-attainment status. At that time, a request to EPA for an extension of the 

attainment date to 2002 was planned to be included in the 2000 revision to the AQMP. 

However delays in the availability of newer on-road mobile emissions estimates 

(EMFAC2002) forced a postponement of the plan submittal until 2003. As a 

consequence, the carbon monoxide attainment demonstration provided in the 1997 

AQMP has lapsed. 

To meet this void, the 2003 AQMP contains a revised CO Plan that jointly uses ambient 

monitoring data and modeling results for 2002 and emissions projections for future years 

to provide a weight of evidence demonstration that will replace the prior submittals. The 

CAMx and CAL3QHC modeling results are used to demonstrate the progress made 

towards attaining the federal 8-hour air quality standard for carbon monoxide in the year 

2002. The 2002 observed carbon monoxide concentrations, coupled with the 2002 

modeled air quality and the EMFAC2002 projected seven percent annual carbon 

monoxide emissions reductions for the Basin serve as a weight of evidence 

demonstration of compliance to the federal standard. 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 

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)]. As indicated in Chapter 1, the District has formally requested 

U.S. EPA to grant the five-year extension. Figure 5-1 depicts future annual average 

PM10 air quality projections at five PM10 monitoring sites having comprehensive 

particulate species characterization compared to federal and state annual PM10 

standards, respectively. Shown in the figure are the estimated baseline conditions for the 

years 1995, 2006 and 2010, along with projections for 2006, and 2010 with control 

measures in place. All sites will attain the federal annual standard by the year 2006. 

None of the sites will meet the recently revised state annual PM10 standard (20 μg/m3

based on a geometric average) by 2010. 
Chapter 5 Future Air Quality

5 - 9 

The projections for the 24-hour state and federal standards are shown in Figure 5-2. 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

) by 2006. With respect to the state 24-hour 

standard (50 μg/m3

), none of the sites will be in attainment by 2010. 

Ozone 

As an 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, two meteorological episodes 

August 3-7, 1997 and August 26-28, 1987 are used in the ozone attainment 

demonstration. 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 2003 AQMP control strategy at the 

appropriate level for the year modeled. 

0

50

100

Central

LA

Anaheim Diamond

Bar

Fontana Rubidoux

Concentration (ug/m3)

1995-Baseline 2006-Baseline

2006-Controlled 2010-Baseline

2010-Controlled Option-1

FIGURE 5-1 

Annual Arithmetic Average PM10 Concentrations 

Federal

Standard 

50 μg/m3
Final 2003 AQMP 

5 - 10

0

150

300

Central LA Anaheim Diamond Bar Fontana Rubidoux

Concentration (ug/m3)

1995-Baseline 2006-Controlled 2010-Controlled

FIGURE 5-2 

Maximum 24-Hour PM10 Concentrations 

Table 5-2 shows the total VOC and NOx emissions in the Basin and projected maximum 

1-hour average ozone concentrations for August 5th and 6th, the most restrictive days of 

the 1997 episode and August 27th and 28th, the most restrictive days of the 1987 episode. 

The emissions presented in Table 5-2 are episode-specific and therefore differ from the 

planning inventories reported in Chapter 3. Baseline emissions and the predicted Basin 

maximum ozone concentrations are presented for 2002, 2007 and 2010. The 2002 

baseline ozone simulation provides a "mid-course" evaluation of model performance. 

The predicted 1-hour maximum concentrations simulated for the two meteorological 

episodes compare well with the 2002 annual basin maximum concentration (169 ppb) 

that was observed on a day having statistically similar meteorological conditions to the 

August 5, 1997 episode. 

Baseline predictions for 2007 serve a dual capacity: The 2007 simulation is required to 

assess transport to the Mojave Desert Air Basin and is directly used in the Coachella 

Valley portion of the Salton Sea Air Basin ozone attainment demonstration. (The 

Coachella Valley Plan and ozone attainment demonstration is discussed further in 

Chapter 8. Impacts to the Mojave Desert Air Basin are discussed in Appendix V). In 

addition, the 2007 simulation serves and a second "mid-course" evaluation of the 

modeling in response to expected reductions in VOC and NOx. 

Federal 

Standard 

150 μg/m3
Chapter 5 Future Air Quality

5 - 11 

TABLE 5-2 

Basin Precursor Emissions and UAM-Predicted Ozone Concentrations 

Peak Ozone 

concentration 

(ppb) 

Peak Ozone 

concentration 

(ppb) 

Precursor Emissions

(Tons Per Day) 

Aug 5th Aug 6th Aug 27th Aug 28th

Year/Scenario 

VOC NOx 1997 1997 1987 1987 

1997 Historical Year 1262 1283 199 193 143 173 

2002 Baseline 919 1075 162* 168* 127* 153* 

2007 Baseline 710 892 146 153 116 139 

2010 Baseline 671 764 153 148 120 136 

* Predicted peak ozone concentrations for August 5th, 1997 and August 28th, 1987 meteorological episodes for 

2002 baseline emissions are provided as "mid-course" estimations of model performance The modeled 

concentrations are compared to an observed 2002 Basin maximum ozone concentration of 169 ppb which 

occurred under similar meteorological conditions. 

Figure 5-3 depicts the predicted baseline basinwide maximum ozone without further 

AQMP measures for the two meteorological episodes modeled. As shown, basinwide 

peak ozone concentrations are on the order of 140 - 150 ppb from 2002 to 2010, 

regardless of the meteorological episode simulated. 

0

50

100

150

200

250

1997 2002 2007 2010

Concentration (ppb)

Aug. 5, 1997 Aug. 6, 1997

Aug. 27,1987 Aug. 28, 1987

FIGURE 5-3 

Baseline Basinwide 1-Hour Maximum Ozone Concentrations 

Federal 

Standard 

(124 ppb) 
Final 2003 AQMP 

5 - 12

Control Strategy Impacts

Two options for controlled emissions are presented in Table 5-3 reflecting differing 

penetrations of NOx and VOC controls by the year 2010. Option-1 presents the 

District's proposed control strategy needed to attain the federal 1-hour standard. Option1 holds NOx emissions held at the 1997/99 SIP levels. This low NOx plan is designed to 

ensure progress towards lowering Basin PM2.5 concentrations. 

A secondary backstop control strategy that demonstrates attainment using the same air 

quality model, atmospheric chemistry, and episodes, but utilizes a different mix of VOC 

and NOx reductions was also simulated. This strategy assumes no additional NOx or 

VOC emission reduction measures from sources under federal jurisdiction. Under this 

scenario, the NOx emissions target would be adjusted to cover the loss of federal 

reductions, while the VOC target would stay the same for ozone attainment in 2010. 

The effect of using the primary (Option-1) and backstop (Option-2) control strategies on 

the mix of VOC and NOx reductions that result in attainment are shown in Table 5-3. 

Figure 5-4 shows the predicted Basin-wide maximum ozone for the two meteorological 

episodes for 2010, with the two proposed emission control strategies in place. The 

results indicate that both proposed control strategies 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 98 and 124 ppb. 

Figure 5-5 shows the predicted Basin-wide 8-hour average maximum ozone for the two 

meteorological episodes for 2010, with the two proposed emission control strategies in 

place. The results indicate that neither both proposed control strategies will bring the 

entire Basin into compliance with the federal ozone standard (80 ppb) by the year 2010. 

The impact of the two strategies is discussed further in Chapter 10. 

TABLE 5-3 

Precursor Emissions and Model-Predicted Ozone Concentrations 

Peak Ozone 

concentration 

(ppb) 

Peak Ozone 

concentration 

(ppb) 

Precursor* 

Emissions 

 (Tons Per Day) 

Aug 5th Aug 6th Aug 27th Aug 28th

Scenario 

VOC NOx 1997 1997 1987 1987 

Controlled Emissions: 

Option-1 

313 541 123 120 98 111 

Controlled Emissions 

Option-2 

314 619 123 124 98 112 

* Day specific emissions for August 5, 1997 
Chapter 5 Future Air Quality

5 - 13 

The spatial distribution of maximum ozone concentrations for the 1997 historical year is 

shown in Figure 5-6. Future year ozone air quality projections for 2010 with and 

without implementation of all control measures are presented in Figures 5-7 through 5-9. 

Figure 5-8 depicts the spatial distribution of maximum predicted ozone for control 

scenario Option-1 while Option-2 is presented in Figure 5-9. 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. 

0

20

40

60

80

100

120

140

Option-1 Option-2

Concentration (ppb)

Aug. 5, 1997 Aug. 6, 1997

Aug. 27, 1987 Aug. 28, 1987

FIGURE 5-4 

2010 Basinwide Maximum 1-Hour Average Ozone Concentrations: 

District Proposed Emissions Control Scenario: Option-1, and 

Backstop Emissions Control Scenario: Option-2 

Federal 

Standard 

(125 ppb)
Final 2003 AQMP 

5 - 14

0

20

40

60

80

100

120

Option-1 Option-2

Concentration (ppb)

Aug. 5, 1997 Aug. 6, 1997

Aug. 27, 1987 Aug. 28, 1987

FIGURE 5-5 

2010 Basinwide Maximum 8-Hour Average Ozone Concentration: 

District Proposed Emissions Control Scenario: Option-1, and 

Backstop Emissions Control Scenario: Option-2 

Federal 

Standard

Federal 

Standard 

(85 ppb) 
Chapter 5 Future Air Quality

5 - 15 

FIGURE 5-6 

Model-Predicted Maximum Hourly Ozone Concentrations in 1997 
Final 2003 AQMP 

5 - 16

FIGURE 5-7 

Model-Predicted Maximum Hourly Ozone Concentrations 

 in 2010 (with rules adopted as of September 2002) 
Chapter 5 Future Air Quality

5 - 17 

FIGURE 5-8 

Model-Predicted Maximum Hourly Ozone Concentrations in 2010: Control Option-1 
Final 2003 AQMP 

5 - 18

FIGURE 5-9 

Model-Predicted Maximum Hourly Ozone Concentrations in 2010: Control Option-2 

Carbon Monoxide 

As discussed earlier, based on carbon monoxide air quality monitoring conducted during 

2001 and 2002, the South Coast Air Basin has technically met the federal carbon 

monoxide criteria for attainment. The predicted 2002 maximum 8-hour average CO 

concentrations coupled with the projected trend of reduced on-road carbon monoxide 

emissions serve as a replacement for 1997 CO Plan and provides the basis for a CO 

maintenance plan. 

The carbon monoxide air quality projections are based on CAMx and CAL3QHC 

simulations analysis for the fall meteorological episode. The October 31-November 1, 

1997 episode recorded maximum 1-hour and 8-hour average carbon monoxide 

concentrations of 19.0 ppm and 17.0 ppm, respectively. These were the highest recorded 

values in the Basin since 1996. Table 5-4 summarizes the carbon monoxide emissions 
Chapter 5 Future Air Quality

5 - 19 

and predicted concentrations for 1997 and 2002. (All control measures implemented 

through October, 2002 are included in the baseline emissions). The 2002 predicted 8-

hour average maximum concentration closely matches the maximum observed carbon 

monoxide concentration measured at Lynwood in 2002 (10.1 ppm on January 8th). 

However, the concentration exceeds the federal and state levels by a marginal amount. 

Figure 5-10 depicts the trend of EMFAC2002 projected carbon monoxide emissions for 

1997 through 2005. On-road CO emissions from vehicles that are the primary 

contributors to urban carbon monoxide episodes are projected to decrease by an average 

of seven percent per year in 2003 through 2006. Total CO emissions reductions for all 

categories are projected to be reduced approximately 6 percent per year through 2006. 

Using liner rollback, the base on the projected reduction in CO emissions, the predicted 

carbon monoxide maximum 8-hour concentration is expected to be reduced to below the 

federal standard of 9.4 ppm in 2003 and below the California standard of 9.0 ppm in 

2004. The continued reductions in carbon monoxide emissions are expected to maintain 

the attainment of the federal 8-hour standard demonstrated through observations in 2001 

and 2002. 

TABLE 5-4 

Carbon Monoxide Emissions and Model-Predicted Concentrations 

Year/Scenario CO-Planning 

Inventory 

(tons/day) 

8-hr Maximum

Concentration 

(ppm) 

1-hr Maximum

Concentration 

(ppm) 

1997 Baseline 6460 14.9 16.7 

2002 Baseline 4835 9.9 10.8 

2003 Predicted 4527 9.1 9.9 

2004 Predicted 4278 8.4 9.2 

2005 Predicted 4029 7.8 8.5 

State 1-hr CO standard = 20 ppm 

State 8-hr CO standard = 9.0 ppm 

Federal 8-hr CO standard = 9.5 ppm 
Final 2003 AQMP 

5 - 20

0

1000

2000

3000

4000

5000

6000

1997 1998 1999 2000 2001 2002 2003 2004 2005

(TPD)

FIGURE 5-10 

EMFAC2002 Projected On-Road Carbon Monoxide Emissions for 1997 Through 2005 

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 to approximately 7.9 miles in the year 2010. 

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

visibility would improve to over 9 miles at Rubidoux 

SUMMARY AND CONCLUSIONS 

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

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

for the years 2002, 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 - 21 

FIGURE 5-11 

Annual Average Daytime Visibility Projections at Rubidoux 

0

100

200

PM10 (An. Avg.) Ozone (1-Hour) CO

Percent of Standard

Historic Base 2002 Baseline

2003 Baseline 2006 Baseline

2006 Control 2010 Baseline

2010 Option-1/Option-2

FIGURE 5-12 

Projection of Future Air Quality in the Basin in Comparison 

with the Most Stringent Federal Standards 

0

2

4

6

8

10

1986 2006 2010

Visibility (Miles)

Baseline Control
Final 2003 AQMP 

5 - 22

0

100

200

300

400

PM10 (An. Avg.) Ozone (1-Hour) CO

Percent of Standard

Historic Base 2002 Baseline

2003 Baseline 2006 Baseline

2006 Control 2010 Baseline

2010 Option-1/Option-2

FIGURE 5-13 

Projection of Future Air Quality in the Basin in Comparison with 

Most Stringent California State Standards 

Table 5-5 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 - 23 

TABLE 5-5 

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 125 ppb 2010 

 CAAQS 1-hour 90 ppb beyond 2010 

 

PM10 NAAQS Annual 50 ug/m3 2006 

 NAAQS 24-hour 150 ug/m3 2000 

 CAAQS Annual 20 ug/m3 beyond 2010 

 CAAQS 24-hour 50 ug/m3 beyond 2010 

 

CO NAAQS 8-hour 9 ppm Achieved*

 NAAQS 1-hour 35 ppm Achieved*

 CAAQS 8-hour 9 ppm 2004 

 CAAQS 1-hour 20 ppm Achieved 

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

2002, the Basin achieved the 8-hour CO air quality standard. The Basin is still 

considered nonattainment until a petition for redesignation is submitted by the state and is 

approved by EPA.

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 that 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 2003 AQMP 

5 - 24

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 multi-component 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 that 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, PM10, and ozone. 

VOC and oxides of nitrogen are used for ozone. PM10 additionally requires reductions of 

sulfur oxides and directly emitted PM10. Carbon monoxide is based solely on carbon 

monoxide emissions. Table 5-6 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., 2003 for carbon monoxide, 2006 

for PM10, and 2010 for ozone Option-1 and Option-2). 

Comments were raised during the public review period for the plan regarding the various 

combinations of carrying capacity for the ozone attainment demonstration. More 

specifically the question posed was what maximum NOx loading and its corresponding 

VOC level as a carrying capacity could the Basin tolerate while (1) attaining the ozone 

standard in 2010 and (2) attaining the PM10 standard in 2006 and maintaining that 

standard in 2010. Staff conducted a series of ozone and particulate matter simulations to 

generate isopleths of predicted concentration as a function of NOx and VOC emissions 

to attempt to answer the question. The results of the analysis indicate that the carrying 

capacity provided in Control Option-2 represents the approximate upper bound for NOx 

emissions to achieve the ozone standard. 

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 Option-1 2003 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 - 25 

TABLE 5-6 

Emissions Carrying Capacity Estimations for the South Coast Air Basin (tons/day) based on 

the Planning Inventory 

a) Carbon Monoxide Attainment Strategy to meet NAAQS (2003) 

Emission Category CO 

Point 47 

Area 323 

On-Road 3088 

Off-Road 1040 

Overall Control Strategy 4497 

b) PM10 Attainment Strategy to meet NAAQS (2006) 

Emission Category VOC NOx SOx PM10

Point 65 48 16 13 

Area 216 46 1 238 

On-Road 252 549 5 19 

Off-Road 139 291 36 21 

Overall Control Strategy 673 935 57 291 

c) Ozone Attainment Strategy to meet NAAQS (2010) Option-1 

Emission Category VOC NOx

Point 67 50 

Area 113 33 

On-Road 65 256 

Off-Road 65 190 

Overall Control Strategy 310 529 

d) Ozone Attainment Strategy to meet NAAQS (2010) Option-2 

Emission Category VOC NOx

Point 67 50 

Area 113 33 

On-Road 66 270 

Off-Road 67 244 

Overall Control Strategy 313 597 
Final 2003 AQMP 

5 - 26

0

200

400

600

800

1000

1200

1400

1997 2002 2006 2010

Year

Tons Per Day

Point Sources Area Source

On-Road Mobile Off-Road Mobile

FIGURE 5-14 

VOC Emissions - Baseline Scenario 

0

200

400

600

800

1000

1200

1400

1997 2002 2006 2010

Year

Tons Per Day

Point Sources Area Source

On-Road Mobile Off-Road Mobile

FIGURE 5-15 

VOC Emissions - Under 2003 AQMP: Option-1* 

* Under Option-2, the VOC emissions are maintained at the same level. 
Chapter 5 Future Air Quality

5 - 27 

0

200

400

600

800

1000

1200

1400

1997 2002 2006 2010

Year

Tons Per Day

Point Sources Area Source

On-Road Mobile Off-Road Mobile

FIGURE 5-16 

NOx Emissions - Baseline Scenario 

0

200

400

600

800

1000

1200

1400

1997 2002 2006 2010

Year

Tons Per Day

Point Sources Area Source

On-Road Mobile Off-Road Mobile

FIGURE 5-17 

NOx Emissions - Under 2003 AQMP: Option-1* 

* Under Option-2, NOx emissions would be raised by 68 tons per day.