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 dioxide,
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
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.
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 Cp and Cb are the future year and baseline oxides of nitrogen
(NOx) concentrations, respectively, Qp and Qb are 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.
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. 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 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 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, 33 12 15 1994 AQMP
1987
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 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.
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
1hour nitrogen dioxide concentrations are projected from the baseline
maximum 1hour concentrations using linear rollback. The predicted
maximum 1hour nitrogen dioxide concentrations for the future-year
baseline conditions with and without controls are shown in Figure
5-2.
FIGURE 5-1
Annual Average NO2 Concentration Projections
FIGURE 5-2
Maximum 1-Hour NO2 Concentration Projections
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 1hour 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.
FIGURE 5-3
Annual Arithmetic Average PM10 Concentrations
FIGURE 5-4
Annual Geometric Average PM10 Concentrations
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 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 off-road 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.
FIGURE 5-6
Baseline Basinwide Maximum Ozone Concentrations
FIGURE 5-7
Basinwide Maximum Ozone Concentration with Proposed Emissions
Controls
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 on-road 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, 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
(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
(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
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.
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.
FIGURE 5-11
Annual Average Daytime Visibility Projections at Rubidoux
FIGURE 5-12
Projection of Future Air Quality in the Basin in Comparison
with the Most Stringent Federal Standards
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.
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/m3 2006
NAAQS 24-hour 150 ug/m3 2000
CAAQS Annual 30 ug/m3 beyond 2010
CAAQS 24-hour 50 ug/m3 beyond 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.
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.
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).
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.
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
to meet NAAQS
|
|
4968
|
|
|
|
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
to meet NAAQS
|
623
|
635
|
66
|
301
|
|
c) Ozone Attainment Strategy (2010)
|
|
Emission Category
|
VOC
|
|
NOx
|
|
|
Stationary
|
268
|
|
88
|
|
|
On-Road
|
81
|
|
278
|
|
|
Off-Road
|
64
|
|
164
|
|
|
Overall Control Strategy
to meet NAAQS
|
413
|
|
530
|
1 Values rounded to the nearest integer.
FIGURE 5-14
VOC Emissions - Baseline Scenario
FIGURE 5-15
VOC Emissions - Under 1997 AQMP
FIGURE 5-16
NOx Emissions - Baseline Scenario
FIGURE 5-17
NOx Emissions - Under 1997 AQMP
|
