EPA-450/3-75-074
October 1975
COMPARISON
OF FOUR METHODOLOGIES
TO PROJECT EMISSIONS
FOR THE ST. LOUIS
METROPOLITAN AREA
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-75-074
COMPARISON
TO PROJECT EMISS:
THE ST. LOUIS
by
Booz-Allen and Hamilton
4733 Bethesda Avenue
Bethesda, Maryland
Contract No. 68-02-1005
EPA Project Officer: Charles C. Masser
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
, Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
October 1975
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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - as supplies permit - from the
Air Pollution Technical Information Center, Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a
fee, from the National Technical Information Service, 5285 Port Royal
Road, Springfield, Virginia 22161.
This report was furnished to the Environmental Protection Agency by
Booz-Allen and Hamilton, Bethesda, Maryland, in fulfillment of Contract
No.68-02-1005. The contents of this report are reproduced herein
as received from-Booz-Allen and Hamilton. The opinions, findings,
and conclusions expressed are those of the author and not necessarily
those of the Environmental Protection Agency. Mention of company
or product names is not to be considered as an endorsement by the
Environmental Protection Agency.
Publication No. EPA-450/3-75-074
11
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TABLE OF CONTENTS
I. INTRODUCTION
Page
Number
II. SUMMARY OF PROJECTION METHODOLOGIES 5
1. The Regional Emission Projection
System (REPS) 5
2. The Plan Revision Management
System (PRMS) 9
3. The Attainment Study 13
4. The Trial Air Duality Maintenance
Plan (AQMP) 19
III. COMPARISON AND INTERPRETATION OF NUMERICAL
PROJECTION RESULTS 28
1. Numerical Comparison of Projection Data 28
2. Analysis of TSP and SOX Emissions 34
3. Analysis of HC and CO Emissions 41
4. Conclusions 45
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I. INTRODUCTION
This report presents a comparison of four alternate
methodologies which were used to project air pollution
emissions for the metropolitan St. Louis area. Two of the
four methodologies also forecast expected ambient air
quality levels. The purpose of the study was to:
Summarize the structure and nature of each projec-
tion methodology
Compare the numerical projection results
Discuss the relative advantages of each method-
odology.
Two of the four projection methodologies were devel-
oped as general purpose emission projection models which
may be applied to other geographic areas. These models ares
The Regional Emission Projection System (REPS).*
This system is an operational computer program
which is an element of the EPA's Aerometric and
Emissions Reporting System (AEROS).
The Plan Revision Management System (PRMS). This
system includes two elements:
Guidelines for developing projections of
emissions and air quality for a given AQCR
which can be expected from enforcement of
SIP regulations.t
A computer analysis of these projections and
pollutant concentration monitoring data to
* Booz, Allen and Hamilton Inc., The Regional Emission
Projection System, Summary Report, February 1975.
t Research Triangle Institute, Manual for Analysis of
State Implementation Plan Progress, March 1974
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determine if adequate progress toward meet-
ing the objectives of the SIP is being made.*
The methodology contained in the guidelines for
projecting emissions as applied to the St. Louis
AQCR, was analysed in this study.
The other two projection techniques were developed as
elements of specific studies of air pollution in St. Louis.
These two studies are:
Attainment of National Air Quality Standards for
ty_
the
Carbon Monoxide and Oxidants in the St. Louis
AQCR.fEmissions and air quality were projected
in this study to determine whether national
ambient air quality standards would be attained
after implementation of various proposed emission
control strategies. This methodology is referred
to in this report as the "Attainment Study."
St. Louis Trial Air Quality Maintenance Plan.*
The development of the trial AQMP also involved
projecting emissions and air quality. This
methodology is referred to in this report as the
"Trial AQMP."
Comparison of these four methodologies is not a
straightforward task for a number of reasons. As mentioned
previously, REPS and PRMS are general purpose models,
while the Attainment Study and the Trial AQMP were special-
ized studies for St. Louis. Thus, the structure of the
latter two methodologies was oriented specifically to
the mix of source categories and other factors unique to
St. Louis. The direct comparability of numerical results
is further complicated because each study did not consider
the same:
Pollutants: A minimum of two and a maximum of
five pollutants were considered.
* U.S. Environmental Protection Agency, The Plan Revision
Management System, Summary Report (draft), October 1974.
t PEDCo - Environmental Specialists, Inc., March 1974.
$ Planning Environment International, December 1974.
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Geographic area: One study included the St.
Louis Air Quality Maintenance Area (AQMA), the
others the St. Louis interstate Air Quality
Control Region (AQCR). The St. Louis AQMA is a
subregion of the St. Louis AQCR.
Base year for which a local emission inventory
was established.
Projection years for which forecasts were
developed.
In addition, the input data .from which emission in-
ventories, growth factors and the effect of control regu-
lations were developed were not identical for all four
studies. The preceding factors should be considered
when using the numerical comparison as a basis for com-
paring the actual projection methodologies. The key
features of each methodology are summarized in Figure 1.
The remainder of this report contains the following
sections:
A summary of each projection methodology, in-
cluding identification of data sources consulted
and inherent assumptions
A comparison and interpretation of the numerical
projection results.
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FIGURE 1
Key Features of the
Projection Methodologies
Projection Methodology
Geographic Region
Pollutants Considered
Base Year
Projection Years
Emission Projections
Air Quality Projections
Publication Date of
Reference Report
Any AQCR or
the nation
HC
CO
TSP
sox
NOX
1974*
1980*
Yes
No
May 1975
Any geographic
region
HC
CO
TSP
sox
1970f
Continuous to
I977 in semi-
annual incre-
ments^
Yes
No (proce-
dures given but
not numerical
results)
March 1974
St. Louis
AQCR
HC
CO
1972
1975
1977
1980
Yes
Yes
March 1974
St. Louis AQMA
HC
CO
TSP
sox
Various years
adjusted to 1975
1980
1985
Yes
Yes
December 1974
Base year and projection year for REPS are the option of the system user. The base year may be
1974 or any subsequent year; projections may be developed for any year between the base year
and 2000.
The PRMS methodology may be applied to any base year and projection period.
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II. SUMMARY OF PROJECTION METHODOLOGIES
1. THE REGIONAL EMISSION PROJECTION SYSTEM (REPS)
The Regional Emission Projection System is a computer-
ized air pollution emissions projection model, for use at
the AQCR level, to project annual emissions. It combines
exogenous national and regional economic forecasts with
point and area source emission inventories for Air Quality
Control Regions (AQCRs) to project air pollution emissions
levels for all five criteria pollutants on an annual basis.
REPS can be used to project emissions for any of 243 Air
Quality Control Regions (AQCRs) and for the nation as a
whole.* The base year to which all growth is referenced
is 1974 or any subsequent year, and projections may be
made for any year between the base year and the year 2000.
At the present time REPS does not have the capability to
produce projections of air quality.
The projection methodology involves the following
major steps:
Determine regional growth factors for future
years which reflect the expected change (posi-
tive or negative) in pollution-producing activity.
Growth factors are determined from regional eco-
nomic and demographic forecasts.
Project present regional emission inventories
to future years using these growth factors.
The base year emission inventories are those of
the National Emissions Data System (NEDS).
Adjust the emission projections to include the
effects of present and future control regula-
tions. These include existing regulations from
NEDS, and promulgated Federal standards (incor-
porated automatically by REPS) and state or local
regulations (supplied by the user).
The methodology is described in more detail below.
REPS does not consider the four AQCRs which include U.S
territories because regional economic projections were
not available for them.
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There are two primary sources for the economic and
demographic forecast data used in REPS: EPA developed
national economic growth projections, and Department of
Commerce regional activity projections. National economic
growth projections are taken from a standard output of the
SEAS system,* and include total gross output for each of
284 economic sectors and subsectors. For each region, the
relative share of the SEAS national output forecasts is
established using the OBERS economic projections t for
AQCRs, which contain regional forecasts of population and
employment, in addition to projections of regional earn-
ings for 28 industrial sectors. Since 55 of the SEAS
economic sectors produce air pollution, combining the
SEAS and OBERS projections produces 55 different industrial
growth factors. Four demographic and commercial growth
factors are computed from OBERS data above, resulting in a
total of 59 different REPS growth factors.
The SEAS and OBERS projections have been supplemented
in REPS by a- special analysis of growth and relocation
trends for five industries which are among the heaviest
industrial polluters. These critical industries are elec-
tric power generation, steel, chemicals, pulp manufactur-
ing and petroleum refining. The output of this analysis
is a file of data on new plants expected to become opera-
tional in the future. For each plant, the SCC code, the
AQCR, the projected startup year and the plant capacity
are given. These data may be input to the program at the
user's option.
In REPS emissions are projected on an individual
source basis by applying these growth factors to base year
emissions as reported by NEDS, and adjusting the projec-
tions to include the effect of emission controls required
for each source in the projection year. The specific
method for projecting emissions depends on the emission
source category:
Strategic Environmental Assessment System, an econometric
and emission forecasting model developed by the Office of
Research and Development, Environmental Protection Agency,
Washington, D.C.
Regional Economic Activity in the U.S., 1972 OBERS Pro-
jections, developed by the U.S. Departments of Commerce
and Agriculture for. the U.S. Water Resources Council.
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Industrial process. Base year emissions for
each point source are first converted to uncon-
trolled emissions using the base year control
efficiencies given in NEDS. Growth factors for
each process category (such as primary metals,
petroleum refining, etc.) are applied to project
future uncontrolled emissions, which are then
reduced to comply with control regulations for
the projection year.
Fuel combustion. Base year emissions for each
point source are converted to fuel use and Btu
demand. Growth factors for each customer cate-
gory are used to project the Btu demand for each
category. The projected Btu demand is then
apportioned to the fuels expected to be used for
that customer category in the projection year.
This approach produces growth factors for each
fuel within each customer category. These growth
factors are applied to emissions for each point
source, and projected emissions are reduced to
comply with control regulations.
Solid waste disposal. This category is treated
in the same way as fuel combustion, except that
the amount of solid waste burned, rather than
the Btu demand, is determined for each customer
category in the base year and projection year,
and the projected tonnage is allocated to dis-
posal methods in the same way that future fuel
mix is used to allocate the projected Btu demand.
The REPS system includes the effect of control regu-
lations in two ways. First, if any point source has been
granted a control variance which will have expired by the
projection year, projected emissions are reduced to the
level allowable under those regulations. Data concerning
current regulations are taken from the NEDS point source
inventory. Second, Federal New Source Performance Stan-
dards which govern new and retrofit industrial equipment
are included in the REPS system. At the user's option,
standards already promulgated in the Federal Register are
input, as well as proposed standards which are likely to
be promulgated in the future. The proposed standards were
supplied by the Emission Standards and Engineering Division
of the EPA's Office of Air Quality Planning and Standards.
The effect of New Source Performance Standards on future
emissions is determined in the REPS system by estimating
the portion of projected activity which will involve
equipment or facilities governed by these standards.
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The procedure for projecting area source emissions is
to compute future area source emissions for each record in
the NEDS area source inventory for the AQCR. One NEDS area
source data record ordinarily contains a summary of source
activity for a given county or similar jurisdiction.
In general, future area source fuel combustion is
estimated by projecting the Btu demand for each customer
category and allocating that demand to the fuel mix for
the projection year. Future levels of area source solid
waste disposal are estimated by projecting the future level
of solid waste disposal for each customer category, and
distributing that amount among the various methods of dis-
posal. This method is similar to the procedure used to
project point source fuel combustion and solid waste dis-
posal described previously. Transportation emissions are
projected by applying a different growth factor to each of
the following transportation categories:
Highway vehicles
Off-highway vehicles (diesel)
Off-highway vehicles (gasoline)
Rail locomotives
Vessels (recreational)
Vessels (commercial)
Aircraft (civil and commercial)
Aircraft (military).
The REPS system does not include emission controls
for any area source category except gasoline highway
vehicles. Regulations affecting emissions from these
vehicles will have the ultimate effect of lowering the
emission factors (emissions per mile travelled) appropriate
for future years. REPS computes weighted highway vehicle
emission factors which reflect these regulations. These
weighted emission factors are a function of:
The nationwide average vehicle age distribution
Nationwide average travel for vehicles of each
age groxip
Speed correction factors corresponding to
vehicle-mile data from NEDS
Test emission factors for a given model year
and vehicle age.
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The method for computing weighted emission factors, as well
as data of the first three types given above, is given in
AP-42. The test emission factors were taken from AP-42,
Supplement Number 5 (draft), and include inherently the
effect of deterioration of control devices.
2. THE PLAN REVISION MANAGEMENT SYSTEM (PRMS)
This system was designed to monitor progress of an
AQCR in satisfying the requirements of an SIP. The system
considers TSP, CO, S0x and HC pollution, and includes two
elements:
Guidelines for developing projections of emis-
sions and air quality for a given AQCR which can
be expected from enforcement of SIP regulations
A computer analysis of these projections,
together with air quality monitoring data, to
determine if adequate progress toward meeting
the objectives of the SIP is being made.
The guidelines for projecting emissions and air
quality specify three types of input data for the AQCR
under study:
Air quality data (SAROAD)
Emissions data (NEDS)
Enforcement and compliance information (CDS).
From this information, a projected air quality curve may
be developed for the AQCR. As additional ambient air
quality data are submitted, they will be entered into the
SAROAD system. PRMS will analyze these data by comparing
them to the projected air quality values to determine if
adequate progress has been made. In each case where mea-
sured levels exceed projected levels, (allowing for
statistical variation), the region will be identified as
having a "potential deficiency." Since many factors
influence air quality measurements, it is not possible to
state conclusively that a deficiency resulted from an
inadequate SIP. Therefore, after a deficiency is identi-
fied, a review should follow to assure that the deficiency
was not the result of invalid air quality data or unusual
meteorological conditions. Thus PRMS will identify "poten-
tial deficiencies" at monitoring sites within the AQCR and
will indicate the need for further review.
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Guidelines for developing the air quality projections
which are input to the PRMS computer program are contained
in the Manual for Analysis of State Implementation Plan
Progress. This report contains specific instruct ons for-
the manual calculation of projected emissions and projected
air quality for the four pollutants mentioned previously
(TSP, CO, SOX and HC). Two parallel procedures are given
for developing these projections: a detailed (quantita-
tive) method and a simplified (qualitative) method. The
quantitative methodology given in the manual has been
analyzed for this project.
The quantitative method in general involves projecting
emissions for a selected number of point sources on an
individual source basis, and for the remaining point
sources and all area sources on an aggregated source basis.
The base year used for the St. Louis AQCR was 1970; pro-
jections were made in semi-annual increments to 1977.
The general projection method used for point sources
for each of the four pollutants considered was as follows:
Identify the individual point sources which
account for 90% of the point source emissions.
Project emissions for each of these sources
using:
Allowable emissions and compliance dates
for the point source from NEDS
Applicable local emission regulations
A growth factor for the emission source
category in which the source is included.
Project emissions for the remaining sources by
aggregating emissions for each source category
and applying the appropriate growth factor for
that category. Projected emissions for SOX
and HC calculated in this manner were reduced to
reflect emission controls as follows:
SOX: same percent reduction as used for
the individually calculated point sources
HC: reduce emissions by 40%.
c-
No reduction was applied to CO and TSP emissions.
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The rank order listings of pollutants for the
St. Louis AQCR were used to determine what specific sources
are covered in the sources accounting for 90 percent of the
point source emissions, the level to which calculations
were made for St. Louis. For particulate matter the sources
so identified included fuel combustion, primary metals,
and mineral products; for SOX: fuel combustion, primary
metals, mineral products, and petroleum processing; for
hydrocarbons: fuel combustion/ chemical manufacturing,
petroleum processing, surface coating, and petroleum stor-
age; for carbon monoxide: fuel combustion, chemical manu-
facturing, and petroleum processing. Based on an analysis
of the composition and distribution of the point sources
accounting for 90 percent of the hydrocarbon emissions,
and the proportion of hydrocarbon emissions contributed by
point sources (less than 25 percent of total HC emissions),
it was determined that the calculations could be reduced
to the 80 percent group without significant reduction in
precision. Performing individual source calculations for
only the major sources in this manner simplified the pro-
jections considerably, since 154 of 1,048 point sources
accounted for 90% of the TSP, SOX and CO emissions, and
80% of the HC emissions.
The projection method used for area sources was as
follows:
Aggregate emissions for each area source cate-
gory from all jurisdictions in the AQCR.
Identify applicable local regulations which will
effectively reduce projected area source emis-
sions. The regulations which were used in the
emission projections affected the following
source categories and pollutants:
Coal combustion: TSP, SOX
- On-site incineration and open burning: all
pollutants
Land vehicles (1976 compliance to Federal
standards): all pollutants.
Apply appropriate growth factors and control
regulations to the geographically-aggregated
area source emissions to estimate future
emissions.
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Growth factors were calculated for each major category
of point and area sources. The source categories were:
Fuel combustion — residential
Fuel combustion — power plants
Fuel combustion — other
Industrial process
Solid waste disposal — residential
Solid waste disposal — other
Transportation .— land vehicles
Transportation — other
Miscellaneous.
The source of this information was the OBERS projections
with two exceptions. The growth factor for power plants
was developed from published FPC data on new plants or
modifications to existing plants. The other exception was
land vehicle transportation where growth was included in
adjusted transportation emission reduction curves from the
Federal Motor Vehicle Emission Control Program (FMVCP).
The industrial process growth factor was computed by
first determining the growth factors for the primary
industries in the AQCR: fluid crackers, stone quarries,
mineral products, primary metal, process fuel, chemical
manufacturing, and food and agriculture. A composite
growth factor for all industrial processes was then deter-
mined by weighting these growth factors by the number of
plants in each growth category. This composite growth
factor was then applied to all industrial processes with-
in the St. Louis AQCR.
Growth factors were calculated for each half-year
period between 1970 and 1975 by determining a five year
growth factor from the OBERS projections for those years.
These growth percentages are applied in equal increments
over the five-year period from the second half of 1970
through the first half of 1975. It was assumed that
through the use of the new source review procedures there
will be no increase in emissions or air quality beyond the
scheduled attainment date. The rationale for this assump-
tion is that if emissions from a new source are determined
to cause a violation of the national standards, then the
construction of that source would be prohibited and the
air quality would remain within the national standards.
The PRMS documentation recommends using a proportional
model to relate projected air quality to projected emis-
sions. However, no numerical air quality projections were
included in the PRMS references consulted for this study.
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3. THE ATTAINMENT STUDY
The purpose of the Attainment Study was to determine
whether national air ambient quality standards for carbon
monoxide and photo-chemical oxidants would be attained in
the St. Louis AQCR in the near future following implementa-
tion of various control strategies. The approach followed
in this project involved:
Establishing and gridding an emission inventory
for the base year (1972) for the AQCR.
Projecting the base year emission inventory to
future years based on expected'regional growth.
Projection years of 1975, 1977 and 1980 were
selected.
Developing a set of feasible control strategies.
Predicting pollutant concentrations for proposed
strategies based on the projected emission
inventory.
This approach is described in more detail below.
For the purpose of developing the base year emission
inventory, sources were divided into four major categories.
These were point sources (except power plants), power
plants, gasoline highway vehicles, and non-automotive area
sources (including diesel vehicles, non-highway mobile
sources and stationary area sources). Since existing
emission data were considered to be current and accurate
for 1972, that year was taken as the base year upon which
the emission projections were based. The sources consulted
for data to establish the base year inventory and to develop
the emission projections are discussed below for each of
these source categories.
(1) Gasoline Highway Vehicles
This category includes light and heavy duty
gasoline powered vehicles. Emissions from heavy duty
diesel powered vehicles were included in non-automotive
area source emissions, since they comprised only 0.3
percent of the total motor vehicles in the Missouri
portion of the St. Louis AQCR. This proportion was
estimated to be valid for the entire AQCR.
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The calculation method used to determine
emissions from gasoline highway vehicles is outlined
in AP-42. For this method emissions are calculated
from weighted emission factors and annual vehicle
miles traveled, both of which are time dependent.
Weighted emission factors were computed from:
The vehicle age distribution
Average travel for vehicles of each age group
Vehicle miles traveled as a function of average
speed
Low mileage test emission factors
Speed correction factors
Average deterioration factors.
The midyear age distribution of motor vehicles
in the St. Louis AQCR was obtained from automobile
and truck registrations in the Missouri portion of
the St. Louis AQCR. Region-wide registrations were
assumed to be the same. Local registration figures
were used because they represent the actual vehicle
age distribution more accurately than do nationwide
figures. The St. Louis vehicle age distribution
showed a significantly newer car population than the
national average. The newer the car population, the
greater the number of controlled vehicles, and hence
the lower the emissions. Nationwide averages for the
annual distance driven by vehicles of a given age
were used because no local data were available. The
emission factors used in calculating the automotive
emissions reflected the relaxed 1975 standards,
promulgated by the EPA Administrator on April 11, 1973.
The 1972 average daily vehicle-miles traveled by
road function (interstate, principal artery, etc.)
were taken from county travel tables and related in-
formation provided by the Mi ssouri State Highway
Department and the Illinois Department of Transporta-
tion. The average daily distance traveled in subse-
quent years was calculated from growth rates taken
from transportation forecasts published in 1972 by
the Illinois Department of Transportation and the
East-West Gateway Coordinating Council. The annual
growth rates were calculated on the assumption that
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1972-1980 growth will occur at a steady rate. Annual
travel figures were calculated by multiplying daily
travel by 365.
In general, CO and HC emissions decrease as
vehicle speed increases. Average vehicle speeds by
road function were obtained from a 1970 highway net-
work survey. These data included average vehicle
speeds for each of six road functions for each county
in the AQCR. Low mileage test emission factors were
taken from AP-42 (April 1973 edition). Factors
reflecting relaxed 1975 standards supplied by EPA
were substituted for the 1975 factors published in
AP-42. National average deterioration factors and
speed correction factors appropriate for the average
speeds of road types in the AQCR were also taken from
AP-42.
(2) Non-Automotive Area Sources
Non-automotive area source emissions for the
base year were the sum of all the area source emis-
sions reported by NEDS, except for light- and heavy-
duty gasoline vehicles. The NEDS printout that was
used listed emissions (area and point) by jurisdiction
in the St. Louis AQCR, with emissions as of August 28,
1973. The area source emissions reported in NEDS
were emissions calculated to exist under 1973 state
and local regulations. The non-automotive area source
emission categories were residential and commercial/
institutional heating, area source solid waste dis-
posal by combustion, off-highway gasoline usage, all
diesel usage, aircraft, vessels, and gasoline market-
ing and solvent evaporation from architectural
painting and dry cleaning.
The emissions from these sources were calculated
by obtaining the total area source emissions from the
NEDS printout and subtracting from that total, the
emissions (also from the NEDS printout) of light- and
heavy-duty gasoline-powered vehicles. Non-automotive
area source emissions were calculated for 1975, 1977
and 1980 by assuming the changes in emissions were
equal to relative changes in population. For the
St. Louis AQCR, the population growth rate, from 1967
through 1980, is 1.3 percent per year.
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(3) Power Plants
The 1972 emissions from steam-electric utilities
in the St. Louis AQCR were obtained from NEDS. In
calculating emissions for subsequent years, Union
Electric Company predicted a growth rate of 7 percent
per year for their facilities. Illinois Power Com-
pany estimated their annual growth rate at 10 percent,
The growth rate of other (i.e., relatively small)
utilities was assumed to equal the growth rate of
miscellaneous manufacturing as reported by OBERS.
Percent increases in emissions were assumed to
equal the growth rate percentage for electricity
generation since no nuclear power facilities are
planned for the region before 1980.
(4) Point Sources (Except Power Plants)
These sources were divided into two categories.
Major sources were those which emitted more than
one hundred tons per year in 1972. Three other point
sources which emitted less than 100 tons per year
were included nonetheless, since they were initially
identified as major sources. Minor sources were
those which emitted less than 100 tons per year.
These sources were not individually identified and
were treated as one aggregate source.
Major non-utility stationary sources. The pri-
mary source of 1972 emission data for the major
non-utility stationary sources in Missouri was
the NEDS data bank for the St. Louis AQCR, as
corrected by the City of St. Louis Division of
Air Pollution Control. The 1972 emission data
for the major sources in Illinois were provided
by the Illinois Environmental Protection Agency.
Emissions from these major sources were projected
for 1975, 1977 and 1980. This was done by assum-
ing that the rate of increase in emissions for
each major source was equal to the growth rate
of the respective industry. Growth indices for
the major point sources were obtained from OBERS
(June 1970). These indices were used in project-
ing future emissions after taking into account
reductions anticipated in the States' Implementa-
tion Plans.
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No further reductions in HC and CO emissions
were expected to be required for non-utility
stationary sources in Missouri. Therefore, the
1975, 1977 and 1980 projected emissions for
Missouri sources were calculated from the 1972
emissions and the appropriate industry growth
rate with two exceptions. The City of St. Louis
Division of Air Pollution Control indicated that
emissions from the city's municipal incinerators
will decrease 3.2 percent per year. The other
exception was based on data provided by the
Monsanto Industrial Chemicals Company, which
indicated that the company would operate sub-
stantially under capacity in 1975. Consequently
the estimated 1975 CO emissions for Monsanto-
Queeny were based on this information; the 1977
and 1980 emissions were then projected based on
the chemical industry growth rate while using
1975 as a base year.
For non-utility stationary sources in Illinois,
the anticipated reductions by 1975 due to the
Illinois EPA's regulations were 85 percent for
HC and 82 percent for CO. Therefore, before
calculating the projected emissions based on
growth rates, the 1972 allowable emissions were
calculated by reducing 1972 HC and CO emissions
by 85 percent and 82 percent respectively. The
1975, 1977 and 1980 projected emissions were
then calculated by applying the appropriate
industry growth rate to the 1972 calculated
allowable emissions.
Minor Non-Utility Stationary Sources. The NEDS
point source printout for the St. Louis AQCR was
used to determine the total emissions from all
sources which emitted less than 100 tons per year
in 1972. This was done by tabulating the emis-
sions from each point source which contributed
ten or more tons per year. These emissions were
then totaled for all plants which individually
emitted less than 100 tons per year. The result
was the total emissions from all other (less than
100 short tons per year) non-utility stationary
sources. Emissions from these sources for 1975,
1977 and 1980 were projected using the growth
rate of miscellaneous manufacturing.
-17-
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Because the baseline and projected emission inventories
are used to estimate AQMA pollutant concentration levels,
emission sources were gridded or spatially distributed
within the urban-in-fact area. These gridding procedures
are described below.
Point Sources. Coordinates for all power plant
and major non-utility point sources were avail-
able and were used to locate each source
geographically.
Non-Automotive Area Source Emissions. It was
assumed that non-automotive area source emis-
sions are at a constant level throughout each
jurisdiction in the AQCR. Thus, each grid was
assigned emissions according to grid area rela-
tive to the jurisdiction area. Total jurisdic-
tion area was determined by summing all the grids.
Automotive Emissions. Automotive emissions were
calculated for each of the four jurisdictions in
the gridded area. For this purpose, exhaust
emission factors were calculated for each sepa-
rate jurisdiction, based on the speed data found
in the 1970 highway network study. Automotive
emissions were distributed among the grids in
proportion to the relative traffic densities of
each grid as determined from the highway net-
work study. Since this study did not include
100% of the traffic, it was used solely for
proportioning purposes.
Air quality projections were developed from the
emission forecasts. The APRAC-1A urban diffusion model
was used to estimate reductions in maximum CO levels that
would occur by implementing two proposed control strategies.
The APRAC-1A diffusion model for carbon monozide was
developed by Stanford Research Institute to simulate CO
concentrations that result primarily from multiple line
sources distributed over an urban area. Diffusion calcu-
lations are made for sources that fall within angular
sectors that extend upwind from each specified receptor
point. Each cone-shaped area is divided into segments
spaced at increasing intervals away from the receptor
point. The segments, which are at different locations for.
each change in wind direction or receptor point, may be
thought of as overlaying a fixed traffic network for the
urban area.
-18-
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For receptor points in the region for which 1972 CO
sampling data were available, the ratios of concentrations
predicted by the model for 1975/1977 and 1972 were used
as the basis for proportional changes in the 1972 measured
maximum levels. This procedure eliminated the effect of
most of the sensitive inputs to the model, such as speci-
fication of most adverse meteorological conditions and
description of the location of the receptor site relative
to the nearest street, and made the changes in CO concen-
trations almost entirely dependent on differences in the
traffic and emission rate input data. In effect, this
procedure is similar to a proportional reduction model in
which the emissions are weighted according to their prox-
imity to the receptor. At receptor sites where no
measured air quality data were available, concentrations
predicted by the diffusion model had to be used directly.
Thus, these reported values are subject to much larger
errors.
Expected ground level concentrations of non-methane
hydrocarbons were calculated using the Gifford-Hanna model.
This model assumes that the emissions from an urban area
are represented by a uniform grid of area sources. A
further assumption is made that the emission density of
each grid is constant with time and that the grid-to-grid
variability in emission densities is not large. The cross-
wind component of diffusion is neglected and the vertical
component is assumed to be Gaussian.
The area source emission density grid includes motor
vehicle exhaust emissions and evaporative losses, evapo-
rative losses from gasoline marketing and other area
sources of hydrocarbon emissions. In addition there are
28 point sources for which 1972 hydrocarbon emissions
exceeded 100 tons per year. The emissions from these
point sources are treated as area sources in this applica-
tion of the Gifford-Hanna technique.
4. THE TRIAL AIR QUALITY MAINTENANCE PLAN (AQMP)
The goal of the Trial AQMP study was two-fold: the
development of a preliminary Air Quality Maintenance Plan and
a critique of the EPA guidelines for the preparation of Air
Quality Maintenance Plans. Because the project was a demon-
stration exercise and did not result in an official AQMP, and
because time and resources were restricted, it was neces-
sary to make certain compromises in data collection and
-19-
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analysis. Three steps were involved in developing the
trial AQMP:
Perform a detailed analysis of existing and pro-
jected emissions and air quality
Select and evaluate an air quality maintenance
strategy
Determine the jurisdictional cooperation and
coordination necessary to implement the AQMP.
The present analysis considers the first step, the
estimation of existing and projected emissions and air
quality. This effort included projecting emissions and
air quality for TSP, SOX/ HC, and CO for the St. Louis
AQMA (a subregion of the St. Louis AQCR) for the years
1980 and 1985. The following narrative describes the
projection methodology in more detail.
Existing inventory data in the St. Louis Air Quality
Maintenance Area were found to vary both in the year-of-
record for a particular source type and in completeness
of information. To overcome the variation in year-of-
record, existing inventories were projected to 1975 for
each pollutant. This procedure aligns all emissions data
to a baseline year and assumes that all sources will be in
compliance with existing emission control regulations by
1975. To eliminate discontinuities in information, exist-
ing information was supplemented by special analyses to
provide complete baseline emission data.
The information used in the development of the base-
line emission inventory was extracted from the following
sources:
State Implementation Plans of Illinois and
Missouri
NEDS
Local transportation studies, utility statistics
and related data
The Attainment Study
Bureau of Economic Analysis statistics.
-20-
-------
The special analyses undertaken were:
Emissions from primary point sources after com-
pliance to existing regulations
Point and area source spatial distribution (for
TSP and SOX only)
Subcorridor-VMT emission analysis (for CO and HC
only).*
Once the complete data baseline was established,
emissions were projected for four source categories: point
sources (except power plants), power plants, stationary
area sources and mobile sources. The specific sources
consulted for base year emission data, and the projection
methodology applied to each source category is discussed
in the following sections.
(1) Point Sources (Except Power Plants)
Point source emissions data were broken down
into primary sources (greater than 100 tons per year)
and non-primary sources for each pollutant. For the
primary point sources for TSP and SOX, summaries of
source emissions at compliance,.prepared by the
Illinois Environmental Protection Agency and the
Missouri Air Conservation Commission, were used. For
the non-primary source emissions, the emissions were
assumed to be uncontrolled (except as stated in the
SIP) and were taken from NEDS. The CO and HC 1975
point source emissions were taken from the Attainment
Study (as corrected by Illinois EPA).
The preferred method for projecting point source
emissions for 1980 and 1985 was to obtain growth rates
for each company, power plant, and institution that
represents a primary point source. The OBERS projec-
tions were used for non-primary point sources and in
cases where actual growth rates could not be obtained
for a primary point source. Accordingly, a survey
was conducted of the primary point sources to gather
This study was an analysis of transportation plans
and related data concerning the traffic corridors,
subcorridors and highway links in the metropolitan
area, in order to develop projections of highway
vehicle emissions.
-21-
-------
information on growth rates, productivity increase
estimates, and expected increases in capacity.
Responses were received from approximately 35 percent
of the sources contacted. Once the baseline point
source inventory and the growth factors for all the
sources were developed, the 1980 and 1985 emissions
were generated by multiplying the baseline emissions
by the annually compounded growth factors.
(2) Power Plants
Individual plant data were provided by Union
Electric Company, Illinois Power Company, Missouri
Air Conservation Commission, and the Illinois Environ-
mental Protection Agency. Compliance schedules, con-
trol equipment, stack emissions, and growth factors
were applied by MACC and IEPA to the power plants data
to generate an inventory of controlled emissions in
1975. To project power plant emissions for 1980 and
1985, the growth factors and the scheduled changes
in new and old plants were applied to 1975 baseline
controlled emissions.
(3) Stationary Area Sources
Area source emissions data for 1970, 1972, and
1974 were gathered and projected to 1975 by applying
the percent emission control as required by the State
Implementation Plan and growth factors for each area
source.
The method used for projecting area source emis-
sions for 1980 and 1985 was to obtain growth rates
from OBERS growth statistics and local estimates.
Projections were generated by individual area source
category (residential, industrial, and commercial)
and summarized to give total area source emissions
for each pollutant.
(4) Mobile Sources
Mobile source emissions were divided into two
categories: highway and off-highway vehicles. High-
way vehicles include both light- and heavy-duty
vehicles; off-highway vehicles include railroads,
vessels, aircraft, and other vehicles not operated on
roads.
-22-
-------
For off-highway vehicles, mobile source emissions
data were gathered from NEDS and the Missouri and
Illinois State Implementation Plans. Off-highway
emissions were projected using a three percent average
growth rate, which parallels the national average.
This growth rate was applied to the four pollutants.
For highway vehicles, mobile source emissions
data were obtained from the Attainment Study for the
baseline year of 1975. Highway emissions for TSP and
SOX were projected by applying TSP and SOX emissions
factors to projected annual vehicle miles of travel
(VMT). Highway emissions for CO and HC for 1980 were
taken from the Attainment Study for the Air Quality
Control Region and extrapolated to reflect the Air
Quality Maintenance Area. The projected 1985 emis-
sions were calculated from the special analysis (Sub-
corridor VMT Emissions Analysis) for the St. Louis
urban-in-fact area by interpolating the 1970 and 1995
traffic network data for each subcorridor and link
type and extrapolating to reflect the entire Air
Quality Maintenance Area. The distribution of VMT
and emissions by subcorridor and link type was calcu-
lated in this analysis.
Projections of air quality for 1975, 1980, and 1985
were developed for the St. Louis AQMA based on projected
emission levels. The techniques used to model air quality
varied for each of the four pollutants considered, so each
pollutant is discussed separately.
Total Suspended Particulates. The projection of
annual concentrations for TSP was accomplished
through application of statistical relationships
between TSP emissions density and concentration.*
The relationship may be expressed as a curve
(where 1964 TSP concentration samples are plotted
against emissions densities for various land areas
larger than 20 square miles).
The projection method required the summary of
emissions from all sources within selected sub-
areas (36 square miles or greater) of the
St. Louis AQMA and the determination of emission
U.S. Department of Health, Education, and Welfare,
Interstate Air^ Pollution Study: Phase II Project
Report/ December 1966.
-23-
-------
density values by division of total emissions
for each subarea by area size. Estimated annual
concentration were then found from the curve
and recorded at the center of each selected sub-
area in the AQMA. Isopleths were drawn, based
on concentrations at subarea centers, which dis-
play the mean annual TSP concentration distribu-
tion in the St. Louis AQMA. Background concen-
tration was estimated at 40 micrograms per cubic
meter.
Sulfur Dioxide. The projection of air quality
concentrations for S02 was accomplished by apply-
ing two air quality diffusion models: Miller-
Holzworth for the St. Louis central urban area
and the Wood River refinery complex, and Pasquill-
Gifford plume dispersion for four significant
point sources.
These two projection methods required calculation
of concentrations from given equations. The
Miller-Holzworth equation calculates annual
average areawide concentrations of SO2 from
emissions density, mixing depth, urban size, and
mean annual wind speed. The Pasquill-Gifford
plume dispersion calculates a maximum 24-hour
average concentration of S02 from wind speed,
plume rise, emissions rate, stack parameters,
meteorological stability, and assumes a Gaussian
plume.
Carbon Monoxide. The APRAC-1A Diffusion Model
was used to project carbon monoxide concentrations
from projected emissions. Estimates of 8-hour CO
concentrations were calculated for 1975 at nine
selected receptor sites. CO concentrations in
1980 and 1985 at these receptors were extrapolated
from the 1975 estimates using the following pro-
cedure :
Assume worst case meteorological conditions
do not vary
Assume concentrations of CO are directly
proportional to emissions of CO under con-
stant worst-case meteorological conditions
-24-
-------
Calculate 1975, 1980, and 1985 CO emissions
in the vicinity of the selected nine recep-
tors using the subcorridor VMT analysis
Calculate the change in emissions in the
vicinity of each receptor from 1975 to 1980,
and 1980 to 1985.
Apply the corresponding percent change in
emissions to the 1975 concentration at each
receptor to obtain 1980 and 1985 concen-
trations.
This procedure is equivalent to a "roll-forward"
type of calculation using the results of cali-
brated diffusion model to represent baseline air
quality.
Photochemical Oxidants. A statistical relation-
ship between percent reduction in hydrocarbon
emissions and maximum one-hour photochemical
oxidant concentrations was published in the
Federal Register.* This relationship was used
to convert the emission projections to expected
maximum oxidant concentrations.
The EPA has defined oxidants as an areawide
problem. Consequently projected emissions from
the entire AQMA were used to determine the per-
cent emission reductions from the air quality
baseline year of 1972 to 1975, 1980 and 1985.
The 1972 second highest 1-hour concentration was
used as the baseline for oxidants.
Figure 2 contains a summary of all four emission pro-
jection methodologies. For each general emission source
category (power plants, other point sources, highway
Federal Register 40CFR51, Regulations on Preparation
of Implementation Plans, Appendix J.
-25-
-------
vehicles and other area sources), the data sources consulted
for
Base year emissions
Growth forecasts
Applicable emission control regulations
are given for each projection methodology. For a complete
description of a given methodology, consult the references
cited previously in the summary of that methodology.
-26-
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FIGURE 1
Summary of Emission Projection
Methodologies*
Emission
Source
Category
POINT SOURCES
(POWER PLANTS)
o Base year emissions
• Growth
• Pollution
abatement
POINT SOURCES ,'EXC.
POWER PLANTS)
3 Base year emissions
• Growth
• Pollution
abatement
HIGHWAY VEHICLES
» Base year emissions
o Growth
» Pollution
abatement
AREA SOURCES (EXC.
HIGHWAY VEHICLES)
o Base year emissions
• Growth
o Pollution
abatement
PROJECTION METHODOLOGY
REPS
NEDS
FPC
NEDS (allowable
emissions) and
Federal regulations
NEDS
OBERS/SEAS
(industry-specific
growth applied to
individual sources)
NEDS (allowable
emissions) and
Federal regulations
NEDS
OBERS
Weighted emission
factors (AP-42
method-revised)
NEDS
OBERS
None
PRMS
NEDS
FPC
SIP, compliance
by 1977 and NEDS
(allowable emissions)
NEDS
OBERS
(industry -aggregated
growth applied to
individual sources)
SIP, compliance
by 1977 and NEDS
(allowable emissions)
NEDS
FMVCP (includes
growth)
FMVCP (includes
change in emission
factors)
NEDS
OBERS and local
growth data
Local regulations,
compliance by 1975
Attainment
Study
NEDS
Utility-supplied
and OBERS
None
NEDS, as
corrected by
local air pollution
agencies
OBERS
(industry -specific
growth applied
to plant emissions)
Local air pollu-
tion agencies
Local traffic data
Local transporta-
tion studies
Weighted emission
factors (AP-42
method)
NEDS
OBERS and local
growth data
None
Trial AQMP
NEDS
Local
FPC
Local air pollution
agencies
Major: local air
pollution agencies
Minor: NEDS
Plant survey and
OBERS (industry-
and plant-specific
growth applied to
plant emissions)
SIP. compliance by
1975 (major sources)
Local traffic data
Local transportation
studies
Weighted emission
factors (AP-42
method)
NEDS ami SIP
OBERS and local
growth data
SIP. compliance
by 1975
"See text for complete description and definition of terminology.
-27-
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III. COMPARISON AND INTERPRETATION OF
NUMERICAL PROJECTION RESULTS
1. NUMERICAL COMPARISON OF PROJECTION DATA
The numerical projection results for REPS, the Trial
AQMP and the Attainment Study are presented in Tables 1-3
respectively. Emission projections are given for:
Power plants
Other point sources (excluding power plants)
Highway vehicles (excluding diesel vehicles for
REPS and the Attainment Study, including diesel
vehicles for the Trial AQMP)
Other area sources (excluding highway vehicles).
For the Trial AQMP and the Attainment Study, these cate-
gories are consistent with the format and level of detail
for which emission projection data were published in the
cited references. The output of REPS was given in the
NEDS National Emission Report (NER) format, which pro-
vides substantially more source category detail than is
shown in Table 1. The REPS data were aggregated to that
format to facilitate the comparison.
The PRMS output projections are given in a different
source category format:
Fuel combustion
Industrial process
Solid waste
Transportation
Miscellaneous.
These data are given in Table 4. In order to facilitate
numerical comparisons with the other methodologies, the
PRMS data for 1975 were reorganized into comparable source
categories. This was done by using 1972 NEDS inventory
data to disaggregate the emissions of the PRMS categories;
these data were then reaggregated into the categories used
by the other methodologies. The redistributed PRMS data
are given in Table 5.
-28-
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Table 1
Emission Projections:
(Tons per year)
1975
REPS
1980
Source Category
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Total Suspended Particulates
48,884
64,554
8,372
31,838
153,648
12,186
29,708
7,200
38,341
87,435
Sulfur Dioxide
1,026,000
1,289,813
3,360
41,792
1,289,813
611,504
201,694
2,201
50,418
865,823
Carbon Monoxide
Power Plants 6,540
Other Point Sources 161,533
Highway Vehicles 663,459
Other Area Sources 69,172
Total 900,704
6,380
150,410
383,259
72,411
612,460
Hydrocarbons
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
2,182
79,747
112,544
46,407
240,880
1,860
81,447
39,563
49,207
172,077
NOTES: "Other point sources" are all point sources except
power plants
"Highway vehicles" include gasoline and diesel highway
vehicles
"Other area sources" are all area sources except
gasoline and diesel highway vehicles.
-29-
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Table 2
Emission Projections: Trial AQMP
(Tons per Year)
1975
1980
1985
Source Category
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
.Total Suspended Particulates
20,348
50,329
8,383
22,602
101,662
34,064
57,972
9,622
24,632
126,290
34,863
71,617
10,823
28,465
145,768
Sulfur Dioxide
577,190
194,046
2,065
43,779
797,080
864,748
204,013
2,371
48,712
1,119,844
873,000
218,452
2,666
54,935
1,149,053
1,641
46,821
476,242
60,699
585,403
Carbon Monoxide
1,641
50,870
241,459
64,537
358,507
Hydrocarbons
1,700
59,734
146,070
70,658
278,162
1,191
40,208
82,502
41,606
165,507
1,395
50,330
39,217
45,157
136,009
1,666
55,009
25,956
50,446
133,085
NOTES: "Other point sources" are all point sources except
power plants
"Highway vehicles" include gasoline and diesel highway
vehicles
"Other area sources" are all area sources except
gasoline and diesel highway vehicles.
-30-
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Table 3
Emission Projections: The Attainment Study
(Tons per Year)
1972
1975
1977
1980
Source Category
Carbon Monoxide
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
7,238
102,300
632,610
83,930
826,100
9,240
42,240
502,260
87,010
641,300
10,824
44,660
386,430
89,320
531,300
13,838
48,290
254,650
92,840
409,200
Total
Hydrocarbons
3,278
53,460
113,410
43,890
214,500
4,224
38,390
87,010
45,540
174,900
4,829
41,800
60,720
46,640
154,000
6,204
46,860
41,360
48,400
143,000
NOTES: "Other point sources" are all point sources except power
plants
"Highway vehicles" include only gasoline vehicles
"Other area sources" are all area sources except gasoline
highway vehicles.
-31-
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Table 4
Emission Projections: PRMS
(1000 Tons per Year)
1972
1975
1977
Source Category
Fuel Combustion
Process and Incineration
Transportation
Other*
Total
Fuel Combustion
Process and Incineration
Transportation
Other*
Total
Total Suspended Particulates
95
34
10
139"
575
120
10
705
90
28
10
128
Sulfur Dioxide
400
70
10
480
90
28
10
128
400
70
10
480
Fuel Combustion 20
Process and Incineration 230
Transportation 960
Other* 2_
Total 1,210
Fuel Combustion 15
Process and Incineration 60
Transportation 190
Other* 55
Total 320
Carbon Monoxide
20
90
820
930
Hydrocarbons
15
60
175
42
292
20
90
680
790
15
60
145
50
270
Primarily area sources.
-32-
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Table 5
Emission Projections: PRMS
(Modified Source Category Format)
(1000 Tons per Year)
1972
1975
1977
Source Category
Total Suspended Particulates
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
50 48 48
53 46 46
666
30 28 28
139 128 128
Sulfur Dioxide
517 360 360
155 94 94
555
28 21 21
705 480 480
Carbon Monoxide
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
888
231 91 91
922 787 653
49 44 38
Total 1,210 930 790
Hydrocarbons
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
3 3
63 63
167 154
87 72
Total 320 292
3
63
128
76
270
-33-
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Total emissions as a function of time, as projected
by the four methodologies, are illustrated in Figure 3-6.
These four figures give the projections for TSP, SOX, HC
and CO respectively. Numerical comparison of air quality
projections was not attempted because only the Trial AQMP
and the Attainment Study addressed air quality projections,
and the Attainment Study considered only two pollutants.
It can be seen from Figures 3-6 that the emission pro-
jection curves for TSP and SOX resemble each other and the
curves for HC and CO resemble each other. The TSP and
SOX emission projections are similar because for both
pollutants:
The major sources are stationary industrial
point sources
Future emissions are determined by the rate of
compliance of stationary sources to emission
standards and their expected growth
Each methodology applied similar forecasting
techniques to TSP and SOX emissions.
The HC and CO emission projections resemble each other
because for both pollutants:
The major source is highway vehicles (specifically
gasoline vehicles)
Future emissions are determined by the rate at
which late-model vehicles, equipped with more
stringent control devices, gradually replace
older vehicles, and expected changes in vehicle
travel characteristics
Each methodology applied similar forecasting
techniques to HC and CO emissions.
Consequently, in the following discussion the numerical
results of the TSP and SOX projections will be discussed
concurrently, followed by a concurrent discussion of the
HC and CO projections.
2. ANALYSIS OF TSP AND SOx EMISSIONS
A valid comparison of numerical projection results
may be done only for the same period in time. The base
year for both REPS and the Trial AQMP is 1975. The PRMS
study preceded these, starting in 1970; 1975 is PRMS
-34-
-------
A - REPS
D - PRMS
O - TRIAL AQMP
2
O
I-
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O
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H
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1970
80
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YEAR
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UJ
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1-
8
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1300-
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O-TRIAL AQMP
£ - ATTAINMENT STUDY
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1970
71
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73
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76
YEAR
—I—
•77
78
-------
1300.
1200-
1100-
1000-
A- REPS
O-PRMS
O-TRIAL AQMP
• - ATTAINMENT STUDY
I
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1970
71
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77
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YEAR
-------
projection year. This makes a direct comparison involv-
ing PRMS difficult because emission inventories, growth
estimates and abatement regulations (especially for point
sources) evolved significantly during that period. In
addition, in the PRMS study it was assumed that emissions
would remain constant between 1975 and 1977 because the
necessary stationary source regulations would be promul-
gated and enforced. Consequently, the comparison, while
including PRMS to some extent, focuses on the other two
methodologies.
The key characteristics of Figure 3 and 4 are that
between 1975 and 1980:
REPS forecasts a net decrease for both pollutants
The Trial AQMP forecasts a net increase for both
pollutants
The REPS projections are higher than those of the
Trial AQMP in 1975 but lower by 1980 (the curves
intersect).
These differences are attributable primarily to variation
in year of record of the baseline emission inventory, and
assumptions concerning the timing of compliance of sta-
tionary sources to emission regulations. These considera-
tions are discussed in more detail below.
Emissions for 1975 by source category, as given in
Tabels 1, 2 and 5, are as follows:
1975 TSP Emissions, 1000 TPY
Source REPS Trial AQMP PRMS
Power Plants 49 20 48
Other Point Sources 65 5JD 46
Total (Point Sources) 114 71 94
Highway Vehicles 8 8 10
Other Area 32 23_ 24
Total Emissions 154 102 128
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Source
Power Plants
Other Point Sources
Total (Point Sources
Highway Vehicles
Other Area
Total Emissions
1975 SOX Emissions, 1000 TPY
REPS Trial AQMP
1026 865
219 204
454
10
16
480
Total 1975 TSP and SOX emissions are highest for REPS.
PRMS emissions are about the same or lower than REPS for
all source categories. Since REPS used the NEDS inven-
tory as of early 1975 for a baseline inventory, the NEDS
inventory from which PRMS baseline emissions were taken
in 1970 has been enlarged substantially since 1970.
This discrepancy is more significant for SOX emissions,
where the point source PRMS emissions are less than half
those of REPS.
The Trial AQMP emissions are also less than REPS for
both TSP and SOX. The largest emission categories are
power plant and other point sources. The 1975 point source
inventory was estimated in the Trial AQMP by projecting the
emission inventory to 1975 from previous years and assuming
that all sources would comply with SIP regulations by 1975.
Since the REPS projections indicate that many sources were
not in compliance by early 1975, the Trial AQMP, by assum-
ing compliance, probably underestimated the actual 1975
emission inventory.
In addition, large point sources may be located out-
side the AQMA but inside the AQCR (the Trial AQMP con-
sidered the AQMA, which is smaller than the AQCR). It could
not be determined from the available data whether this in
fact is the case.
There is a marked difference in the trend of TSP
emissions as projected by REPS (decreasing emissions) and
the Trial AQMP (increasing emissions):
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TSP Emissions* (1000 TPY)
REPS
Source
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
154
Trial
1975
20
50
8
23
102
AQMP
1980
34
58
10
25
126
NOTE: Totals may differ due to rounding.
Emissions from mobile and other area sources, as
reported by both systems, do not change substantially,
although the absolute levels are slightly different.
Point source emissions do change, however; the Trial
AQMP forecasts moderate increases, while REPS forecasts
significant decreases. The REPS decreases occur because
the emission abatement required by the point source
specific compliance schedules in the current NEDS file for
the 1975-1980 period more than offsets projected growth
in activity. On the other hand, the Trial AQMP did not
expect any additional stationary source abatement during
that period, so emissions increase because of projected
industrial growth.
3.
ANALYSIS OF HC AND CO EMISSIONS
Estimates of 1975 and 1980 highway vehicle emissions
were developed for the AQCR in the Attainment Study; the
Trial AQMP used these estimates directly after adjusting
the data to reflect the AQMA boundaries. This is evident
from Figures 5 and 6 in which HC and CO vehicle emissions
forecast by the Trial AQMP are almost uniformly 5 percent
less than those of the Attainment Study. This is consistent
with the fact that in 1972 the AQMA recorded 4.8 percent
fewer VMT than the AQCR. Consequently the Trial AQMP data
are not included in the comparison.
From Tables 1 and 2.
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The most distinguishing characteristic of Figures 5
and 6 is that all the emission projection curves for both
HC and CO decrease with time with roughly the same slope.
This indicates that all the methodologies account for
more stringent vehicle emission controls in an equivalent
manner. The vertical separation between curves indicates
that base year vehicle travel characteristics (VMT and
average speed) were not identical. The reasons for this
are discussed below. . -
Emissions for 1975 by source category as given in
Tabels 1, 3 and 5 are as follows:
1975 HC Emissions* (1000 TPY)
Source REPS Attainment Study PRMS,
Power Plants 24 3
Other Point Sources 80 38 63
Total (Point Sources) 82 42 ! 66
Highway Vehicles . 113 87 154
Other Area Sources 46 46 72
Total (Area Sources) 159 133 226
Total Emissions 241 175 292
1975 CO Emissions* (1000 TPY)
Source REPS Attainment Study PRMS
Power Plants 798
Other Point Sources 162 42 91
Highway Vehicles 663 502 787
Other Area Sources 69 87 44
Total Emissions 901 641 930
Totals may differ due to rounding.
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The two most important source categories for HC
emissions are highway vehicles and (to a lesser extent)
non-utility point sources. PRMS reports the highest 1975
HC emissions because of a comparatively high estimate for
vehicle emissions; non-utility point source emissions for
PRMS are actually lower than REPS. In the PRMS system,
1970 emissions for highway vehicles were taken from NEDS,
and net emissions were calculated using the Federal Motor
Vehicle Control Program (FMVCP) data.* The use of this
approach, which is relatively simple when compared to the
more sophisticated methods used by the other projection
systems, may have caused the higher emission estimates.
REPS reported higher HC emissions than the Attain-
ment Study in 1975, for both non-utility sources and high-
way vehicles. The non-utility point source emissions may
be higher for the same reasons that TSP and SOX emissions
for REPS were also higher than those of the Attainment
Study: there may be large point sources outside the
AQMA but within the AQCR, and full SIP compliance by 1975
is postulated.
For all the studies, 1975 highway emissions are a
function of VMT, average speed and weighted emission
factors; the latter are computed from vehicle age and
model year distributions and deterioration of control
devices. Average speed and VMT for the Attainment Study
were taken from a 1972 highway network study and projected
to 1975; these data may not have been incorporated into
the NEDS inventory used by REPS.. Weighted emission
factors used by the Attainment Study used local vehicle
distributions while REPS used national distributions.
These factors would be sufficient to account for the
differences in 1975 highway emissions.
HC and CO emissions are expected to decrease during
the period 1975-1980 according to both REPS and the
Attainment Study:
In the PRMS method, expected emissions are forecast
as a simple fraction of 1970 emissions; FMVCP data are
used to compute these fractions which include the
effects of expected growth and weighted automobile
emission factors reflecting relaxed 1975 standards.
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HC Emissions* (1000 TPY)
REPS
Attainment Study
Source
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
1975
2
80
113
46
241
1980
2
81
40
11
172
1975
4
38
87
ii
175
1980
6
47
41
48
143
Source
Power Plants
Other Point Sources
Highway Vehicles
Other Area Sources
Total
CO Emissions* (100.0 TPY)
REPS Attainment Study
1975 1980 1975 1980
7 6 9 14
162 150 42 48
663 383 502 255
69 72 87 93
901 612 641 409
These decreases are caused by decreased highway vehicle
emissions, since all the other source categories remain
relatively unchanged. The rate of decrease for both HC
and CO emissions is about the same for both systems;
slight differences may be the result of different fore-
casts of:
The weighted emission factors appropriate for
projection years
Travel characteristics (VMT and average speed)
V.
Totals may differ due to rounding.
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While both REPS and the Attainment Study calculate
emission factors for projection years using AP-42 data,
REPS uses parameters which were updated after publication
of the Attainment Study. On the other hand, the travel
forecasts of the Attainment Study are based on county-
specific growth factors derived from two local transporta-
tion studies, while the REPS travel forecasts are based on
population projections. These differences could easily
account for the slight differences in projected emissions.
4. CONCLUSIONS
The summary and comparison of projection methodologies
applied to St. Louis has identified a number of considera-
tions which are important for projecting emissions for
any geographic area. First of all, future emissions
ordinarily are forecast based on these three types of data:
Base year emissions (stationary sources) and
transportation activity (mobile sources).
Emission projections are only as accurate as the
inventories on which they are based. Care should
be taken that the inventories are up-to-date
and include all major sources. "Unconventional"
sources like fugitive dust which in the past
were often ignored, are in many areas significant
pollution sources.
Estimates of industrial, demographic and trans-
portation growth. In addition to forecasting
growth for existing sources, new sources entering
or leaving the region must be identified.
Emission abatement regulations and compliance to
these regulations. In St. Louis, as in many
other regions,tKe effect of point source
emission abatement regulations more than offsets
expected growth.
Each of the methodologies reviewed had certain advan-
tages and disadvantages. The following capabilities, which
are important for any projection methodology, were inherent
in at least one of the methodologies under study:
Stationary source emissions should be estimated
on an individual point source basis. This is
critical because individual sources often have
unique emission rates and compliance schedules.
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Emission projections in REPS and PRMS are developed
on an individual source basis, while in the Attain-
ment Study and the Trial AQMP, emissions are forecast
on a plant basis. For the latter approach plant-
wide averages for growth and extent of control must
be estimated for the various process and fuel com-
bustion point sources within each plant.
A computerized methodology greatly facilitates
individual source calculations, and allows alter-
native forecast scenarios to be evaluated quickly
and efficiently. REPS is a computerized model;
in addition to containing complete "default sce-
nario" data, REPS has extensive capability for
override of these default data with more accurate
local information concerning emission rates,
growth and compliance schedules for existing and
proposed stationary sources.
All point and area sources must be identified by
legislative jurisdiction. Computerized systems
should be able to access all source data for each
jurisdiction, in order to apply emission regula-
tions for each jurisdiction to the appropriate
sources. PRMS, the Attainment Study and the
Trial AQMP considered all emission sources by
jurisdiction. Although only NEDS information
and Federal New Source Performance Standards
were input to the REPS projections presented in
this report, the effect of other local emission
control regulations may be input to REPS by the
system user.
Local information and studies, such as plant
survey data and detailed transportation studies,
increase the accuracy of emissions (and air
quality) forecasts. Plant surveys identify
specific growth and expansion plans, compliance
schedules and process changes. Transportation
studies and forecasts define average speed,
mileage and other traffic characteristics which
have a significant effect on emission and air
quality estimates. Both the Attainment Study
and the Trial AQMP utilized plant surveys and
detailed transportation forecasts.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-75-074
3. RECIPIENT'S ACCESSI OIV NO.
4. TITLE AND SUBTITLE
Comparison of Four Methodologies to Project ;
Emissions for the St. Louis Metropolitan Area
6. PERFORMING ORGANIZATION CODE
5. REPORT DATE
October
1975
7. AUTHOR(S)
T. J. Consroe
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Booz, Allen & Hamilton Inc.
4733 Bethesda Avenue
Bethesda, Maryland 20014
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-1005
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency
Office of Air and Water Management
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes a comparison of four alternate methodol-
ogies which were used to project air pollution emissions for the
metropolitan St. Louis area. Two of the four methodologies also
forecast expected ambient air quality levels. The purpose of the
study was to:
Summarize the structure and nature of each projection
methodology
Compare the numerical projection results
Discuss the relative advantages of each methodology.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Emission Projections
Emissions
Pollutants
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
13. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
46
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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