EPA/AA/CTAB/PA/81-2
An Approach for Determining Levels of Concern for
Unregulated Toxic Compounds
from Mobile Sources
by
Robert J. Garbe
July, 1981
Technical Reports do not necessarily represent final EPA decisions or
positions. They are intended to present technical analysis of issues using
data which are currently available. The purpose in the release of such
reports is to facilitate the exchange of technical information and to inform
the public of technical developments which may form the basis for a final EPA
decision, position or regulatory action.
Control Technology Assessment and Characterization Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, Mi. 48105
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EPA/AA/CTAB/PA/81-2
An Approach for Determining Levels of Concern for
Unregulated Toxic Compounds
from Mobile Sources
by
Robert J. Garbe
July, 1981
Technical Reports do not necessarily represent final EPA decisions or
positions. They are intended to present technical analysis of issues using
data which are currently available. The purpose in the release of such
reports is to facilitate the exchange of technical information and to inform
the public of technical developments which may form the basis for a final EPA
decision, position or regulatory action.
Control Technology Assessment and Characterization Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, Mi. 48105
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Introduction
This report presents an approach for determining ranges of concern for vehicle
emissions of toxic unregulated pollutants. The information used in deriving
this approach was generated either in-house at EPA or under EPA contract to
Midwest Research Institute in Kansas City, Missouri; and/or Southwest Research
Institute in San Antonio, Texas.
This work represents an EPA technical effort designed as one input that may
bear on EPA policy with respect to implementation of section 202(a)(4) of the
Clean Air Act amendments of 1977. As such, this report does not represent
EPA policy at this time. This report will also be of interest to parties
outside EPA, such as the automobile manufacturers, who are involved with
deciding whether unregulated pollutants from motor vehicles constitute a
public health hazard. This approach, outlined in the subsequent sections of
this report, has four separate parts, the last of which is a summary of the
previous three. An example of how the approach works is presented for a
sample mobile source pollutant; sulfuric acid
The range of compounds which are expected to be assessed by this approach are
those compounds which have non-zero "thresholds" (e.g. not genotoxic)
associated with them. This approach is not intended for the evaluation of
mutagenic, teratogenic, and/or carcinogenic effects of substances emitted from
mobile sources, but may be used to evaluate the non-genotoxic health aspects
of a substance which may have other harmful effects also.
It is important to point out that this approach is not intended to be a
rigorous examination of all the issues and variables surrounding any
hazardous pollutant question. Such an effort would require an extensive
program similar to the procedures used to determine and support the NAAQS
process. The intent of this approach is to identify and prioritize hazardous
pollutants that are emitted from mobile sources so that research by EPA and
the automobile manufacturers can focus on those emission products of
significant concern. If one pollutant, for example, is shown to fall within
a potential problem range, then additional work can be initiated to determine
in more detail the hazards of that pollutant.
The first step in determining the range of concern for a pollutant involves
compiling a list of emission factors £f_ the various motor vehicle categories.
These categories are assigned to as many discrete subsets of the mobile
source population as are necessary to characterize the current and future
mobile source fleet.
The second step is to review the relevent health effects literature on the
pollutant of interest. The basic review would involve selecting valid health
effects studies on a particular unregulated pollutant which fall within a
range of exposure concentrations suspected to be of concern to human health.
The lowest value of this range would represent the lowest concentration at
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which negative physiological effects* can be detected. The highest value
would represent that level above which the hazards are so well defined as to
encourage regulation. A simplified means of approaching the upper level would
be to use a Threshold Limit Value (TLV) as the basis from which to estimate
the range of concern. The TLV can be adjusted for exposure time and safety
margin and subsequently can be used to estimate the range of concern.
The third step is to use an appropriate set of pollutant dispersion scenarios
to convert emission factors to concentrations that people may be exposed to.
Both worst case and average cases for a number of situations are evaluated.
The fourth step will combine the results of_ the previous three steps and
determine ranges of concern for unregulated pollutants from mobile sources.
Background
The Clean Air Act (CAA) was amended in August 1977 to include section 202
(a)(4) and 206 (a)(3) dealing with the emissions of hazardous pollutants from
vehicles produced after 1978. The specific language of the statute is:
202 (a)(4)
"(4)(A) Effective with respect to vehicles and engines
manufactured after model year 1978, no emission control device,
system, or element of design shall be used in a new motor
vehicle or new motor vehicle engine for purposes of complying
with standards prescribed under this subsection if such device,
system, or element of design will cause or contribute to an
unreasonable risk to public health, welfare, or safety in its
operation or function.
(B) In determining whether an unreasonable risk exists under
subparagraph (A), the Administrator shall consider, among other
factors, (i) whether and to what extent the use of any device,
system, or element of design causes, increases, reduces, or
eliminates emissions of any unregulated pollutants; (ii)
available methods for reducing or eliminating any risk to public
health, welfare, or safety whch may be associated with the use
of such devices, systems, or elements of design which may be
used to conform to standards prescribed under this subsection
without causing or contributing to such unreasonable risk. The
Administrator shall include in the consideration required by
this paragraph all relevant information developed pursuant to
section 214."
*It is recognized that controversy exists as to what a negative physiological
effect is in relation to regulatory action pursuant to protecting the public
health. Since this approach attempts to separate clear health problem
emissions from non health problem emissions, it is prudent to be conservative
in selecting the lowest level of the range.
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206 (a) (3)
"(3) (A) A certificate of conformity may be issued under this
section only if the Administrator determines that the
manufacturer (or in the case of a vehicle or engine for import,
any person) has established to the satisfaction of the
Adminstrator that any emission control device, system, or
element of design installed on, or incorporated in, such vehicle
or engine conforms to applicable requirements of section
202(a)(4).
(B) The Administrator may conduct such tests and may require
the manufacturer (or any such person) to conduct such tests and
provide such information as is necessary to carry out
subparagraph (A) of this paragraph. Such requirements shall
include a requirement for prompt reporting of the emission of
any unregulated pollutant from a system, device or element of
design if such pollutant was not emitted, or was emitted in
significantly lesser amounts, from the vehicle or engine without
the use of the system, device, or element of design."
In response to these 1977 CAA requirements EPA began a program to modify the
existing procedures dealing with hazardous compounds or conditions. The
existing sections pertaining to the hazardous pollutant areas were contained
in 40CFR 86.078 subsection 5(b) as follows:
"Any system installed on or incorporated in a new motor vehicle
(or new motor vehicle engine) to enable such vehicle (or engine)
to conform to standards imposed by this subpart:
(i) Shall not in its operation or function cause the
emission into the ambient air of any noxious or toxic
substance that would not be emitted in the operation of
such vehicle (or engine) without such system, except as
specifically permitted by regulation; and
(ii) Shall not in its operation, function, or malfunction
result in any unsafe condition endangering the motor
vehicle, its occupants, or persons, or property in close
proximity to the vehicle.
(2) Every manufacturer of new motor vehicles (or new motor
vehicle engines) subject to any of the standards imposed by
this subpart shall, prior to taking any of the action
specified in section 203 (a)(l) of the Act, test or cause
to be tested motor vehicles (or motor vehicle engines) in
accordance with good engineering practice to ascertain that
such test vehicles (or test engines) will meet the
requirements of this section for the useful life of the
vehicle (or engine)."
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Furthermore 40 CFR 86.078-23(d), which deals with data required as a
precondition for certification, states the following:
d) "A statement that the vehicles (engines) for which
certification is requested conform to the requirements in
86.078-5(b) and that the descriptions of tests performed to
ascertain compliance with the general standards in
86.078-5(b) and the data derived from such tests are
available to the Adminstrator upon request."
In past years, the manufacturers simply submitted the required statement but
not the data on which it was based.
As a first attempt at bringing attention to and developing procedures for the
implementation of section 202(a)(4), a working draft Advisory Circular was
sent to the manufacturers for constructive comment on October 18, 1978. As a
result of the input received from the manufacturers and other interested
parties, EPA has proceeded to refine the approach to implementation of section
202(a)(4) of the Clean Air Act. EPA had issued Advisory Circular (AC) 76 (on
June 28, 1978) requiring the manufacturers to continue to provide statements
to the effect that the new model vehicles certified to be in compliance with
the vehicle emission standards would not contribute to an unreasonable risk to
public health. On November 30, 1978, EPA issued AC 76-1 which continued the
procedures set forth in AC 76 for the 1980 and later model years.
In addition to the aforementioned activities, EPA has been developing and
documenting measurement methodologies for the automobile industry to use in
investigating unregulated pollutants from mobile sources. Two reports on
unregulated pollutant measurement methods have been produced and widely
distributed among auto manufacturers (1,2)*. Also, EPA has produced an
initial data base on unregulated pollutants under a variety of conditions from
vehicles utilizing different emission control systems (3,4,5).
Methodology
The following sections will discuss the methodology developed for determining
a range of concern for toxic unregulated pollutants from mobile sources. It
should be reemphasized that this is an approach to this problem but not the
only approach. It is felt that this methodology provides a valid procedure
that is neither too complex nor too simple for the problem. It is also felt
that this methodology could be used for a wide range of unregulated compounds
and yield acceptable results.** Figure 1 is provided to illustrate the way
this approach is structured.
* Numbers in parentheses refer to references
which are listed at the end of this report.
** We invite comments from interested parties
on this approach to implementing one part
of section 202(a)(4) of the Clean Air Act.
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Figure 1
Flow Diagram - Toxic Pollutant Range of Concern
Preliminary
Estimated
Range
of
Concern
Substance
of
Concern. .
Identifled
II
Hcalch Effects
. Literature
Search
Mobile Source
Emission ['actors
(determined or
estimated)
III
Dispersion
Models Re-lacing
Emission Factors
To Health. Effects
"No Problem"
Implies Low Level
of Effort
Monitoring
"Concern"
Implies Voluntary
Action by
Industry
IV
Range of
Concern
Emission Level
"Determined
Emission Control
Systems of
Concern
Identified
. (If
"Danger"
Implies
Re&ulat Lon
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Emission Factors
An essential part of the information for this methodology is accurate vehicle
emission factors. An emission factor may be determined from the available
literature and is the mass per unit distance or unit time of a pollutant which
is emitted from a particular vehicle type over a certain driving cycle or
mode. A complete listing of vehicle emission factors for the pollutant of
interest is needed for the full range of vehicle types and driving schedules
that contribute to the fleet emissions of the pollutant. Since most of the
exposure situations (to be discussed later) involve highway situations or city
street canyons, emission factors are needed on the vehicle types which may be
present in these locations. Therefore, emission factor information will be
needed for the categories listed in Table I. This list is not intended to be
all-inclusive and the groupings may change from specific pollutant case to
specific pollutant case depending on the information available and the
information needed.
Table I
Emission Factor Categories
I. Heavy Duty Vehicles (HDV)
A. Gasoline-Fueled Heavy Duty Trucks (HDT-G)
B. Diesel-Fueled Heavy Duty Trucks (HDT-D)
II. Light Duty Vehicles (LDV)
A. Gasoline-Fueled Light Duty Vehicles (LDV-G)
B. Diesel -Fueled Light Duty Vehicles (LDV-D)
III. Light Duty Trucks (LOT)
A. Gasoline-Fueled Light Duty Trucks (LDT-G)
B. Diesel-Fueled Light Duty Trucks (LDT-D)
IV. Motorcycles
V. Others
In general, under each classification, an entry for the emission factor of
the unregulated pollutant under study is needed, if it is appropriate.
Sometimes certain emission factors are not needed. For example, if the
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unregulated pollutant had to do with tetraethyl lead or motor mix and/or its
combustion products, an emission factor for those vehicles that use Diesel
fuel would not be necessary,since Diesel fuel does not contain lead.
On the other hand, subclassifications more detailed than those shown in Table
1, may be needed, if the emissions of the unregulated pollutant are not
adequately described by that level of detail. For example, for sulfuric acid
emissions the presence or absence of an oxidation catalyst and the details of
the air injection system are known to influence the emission factor
significantly, so some more detailed subclassification is necessary.
The "Other" category is for gas turbine-powered vehicles or electric or hybrid
vehicles, etc, a catch-all category of unusual and/or potentially
problematical power-plants or vehicles which might emit the unregulated
pollutant of interest.
Unregulated pollutant emission factors are frequently a function of the
vehicle and engine type, emission control system design, vehicle driving
schedule, vehicle condition (e.g. malfunction), vehicle mileage and other
variables. The combination of these factors provide a fleet average emission
factor. However, simplifying assumptions can be made for a given pollutant so
that the combination of these factors can be reduced to a workable calculation.
The fleet average emission factor for the unregulated pollutant of interest
should be calculated for a variety of vehicle fleet situations. Two primary
sources of information used to determine fleet average emission factors are
the Pedco report (6) and the EPA publication "Mobile Source Emission Factors:
For Low Altitude Areas Only" (7). This information can be used to determine
fleet emission factors for use in the ambient concentration models. Examples
of these procedures can be found in the sulfuric acid example in later
sections of this report.
The information contained in the Pedco report allows the determination of
weighting factors for the different major categories of vehicles in Table 1.
The information contained in the EPA mobile source emission factors report
allows for a further demarkation of the weighting factors to include different
emission control system designs. Both of these references aid in calculating
a fleet average emission factor.
When one vehicle category is of particular interest, such as the 3-way plus
oxidation catalyst light duty vehicle in the sulfuric acid example, the fleet
emission factors should be calculated for various percentages of this vehicle
category. Using values of 25%, 50%, 75% and 100% of the vehicle category
comprising the entire vehicle fleet will allow the effects of the specific
vehicle/control system type to be estimated.
In most cases it will be desirable to compare the emissions and corresponding
air quality of a specific vehicle category to the ranges of concern for an
unregulated pollutant. Thus, the above method of determining fleet emission
factors will probably be most desirable. However, other suitable methods of
making this determination are also possible using different references and
averaging schemes. This method has been picked because of the author's
familiarity with the cited references and the simplicity of application.
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II Health Effects
A health effects literature review is necessary to determine a range of
concern for a particular pollutant. Health effects information at low levels
of exposure are quite important for this assessment, especially since the
health effects at these levels are not always as easily detected, or readily
apparent. Also, chronic exposure at low levels, such as exposure to a low
concentration of pollutant for 1-2 hours per day, 5 days a week for a
significant portion of the subject's life, are very important due to the fact
that this is the type of exposure which most people will be encountering in
their day to day activities. Of particular interest, of course, is that
health effects information involving human subjects. Complete and appropriate
information on these lower levels is a very desirable element in the
determination of a range of concern for mobile source emissions. The lowest
level of the range of concern can be defined as the lowest concentration of
the pollutant at which adverse physiological effects are detectable. This
definition provides a useful and workable concept for later calculations
involving vehicle emissions, but does not adequately address the actual
causative factors relating to hazardous pollutants. Other concepts which are
of critical importance in the ultimate determination of a pollutant hazard are
exposure and dose or effective dose. Exposure can be defined as that
parameter resulting from the calculation of concentration multiplied by time.
Dose is defined as some fraction of the exposure which is presented to the
critical organ or subpart of the organism of interest. However, in order to
provide a reasonable workable methodology, only concentration and occasionally
exposure information will be used. It is recognized that if a potential
concern is determined by this methodology then a more detailed assessment
involving dose determination may need to be done. In general, this type of
terminology is used in conjunction with experiments involving various doses of
the chemical of interest. Below the lowest level of the range there should be
no evidence, from the available literature, which would lead to the belief
that there is a hazard to human health. The highest value of the range, on
the other hand, can be defined as the concentration above which studies show
hazards so well defined as to encourage regulation. Both the highest and
lowest levels of the range are not static quantities and may vary depending on
the interpretation of the health effects data and results from new tests.
Each, however, provide important information on the estimation of the levels
which may be hazardous to humans.
The literature search, that will result in a set of relevant citations on the
pollutant of interest, comprises the first step in the health effects review.
A thorough computer assisted search using the computer data bases TOXLINE and
TOXBACK as well as a manual journal search is usually appropriate to uncover
most of the health effects data on a given pollutant. An example of this type
of search is contained in Appendix II.
Prior to the evaluation of the literature search information, a preliminary
range of pollutant level concern with respect to public exposure should be
established that will bracket the range of concern. The selection of a
preliminary range of concern allows a closer focus on the literature review,
eliminating from primary consideration those studies which provide health
effects data due to very high concentration exposures. To simplify this
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calculation, the upper value of the range will be the Threshold Limit Value
(TLV) as listed by the ACGIH, if available and appropriate. The lower value
of the range should represent the lowest concentration suspected to cause
health effects. This lower value can be determined from the available
literature. In the event that such a level cannot readily be determined, the
lower level will be estimated according to the guidelines provided for
hazardous pollutants from multimedia sources (MEGs)(8).
The studies obtained during the literature search and document acquisition
should be reviewed and rated as to their scientific merit and suitability for
further use. The studies which are rated as being of high quality and which
are suitable for use in range of concern determinations should be used to
develop a concise set of tables listing the results of all related studies.*
These tables are ultimately used to sort out the data prior to a decision on a
range of concern.
The whole process of the health effect literature review can be considered as
an effort to narrow, or validate, the preliminary range of exposure
concentration suspected to be of concern which was determined at the start of
the process. The detailed information may allow the higher and lower values
of this range to be changed such that the differences between the high and low
become smaller.
Once the appropriate information has been tabulated, a large table will be
prepared compiling, separately, all the information for the animal and human
studies. These studies will be arranged in numerical order from highest to
lowest concentration, noting especially the exposure time, and will later be
used in conjunction with the ambient air scenarios to graphically represent
the conversion from an ambient air concentration range of concern to an
emission factor range of concern.
In the event that health effects information is not readily available for a
particular pollutant at low concentrations, but a TLV has been established for
that same pollutant, an equation using the TLV can be used to compute ambient
air concentrations for various exposure times (8). This equation is
represented below.
Rating of the scientific studies should be performed by a competent,
professional in the particular field of study (i.e. epidemiologist,
toxicologist, pharmacologist). The rating process may vary but should
include the evaluation of several aspects of each study such as the
number of animal subjects in each test group, the suitability of the
control groups used, comparison with historical controls and
experimental results, suitability of analytical/pathological methods,
etc. Peer reviews and judgements of independent experts are expected to
be helpful when available.
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TLV
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TLV 4£
int 100 x e
where TLVint = Threshold Limit Value based intercept
TLV = Threshold Limit Value
100 = a safety factor (this value may vary
but for the purpose of this paper is
chosen to be 100)
40 = hours worked per week (assuming 8 hours
per day, 5 days per week)
ex = exposure time per week (in hours) corresponding
to scenario X
It is desirable to have a full and complete literature search, but this is not
always possible. The TLV-based approach is one that is not far from being a
last resort. The TLV-based approach is also somewhat conservative as the
following table indicates, as far as carbon monoxide (CO) goes.
Table II
Example of the TLV - Based Method
CO TLV 50 ppm (10)
CO value based on daily
8 hr exposure (50/100) x (40/40) 0.5 ppm
8 hr NAAQS for CO 9.0 ppm
CO value based on
daily 1 hr exposure (50/100) x (40/5) 4.0 ppm
1 hr NAAQS for CO 35 ppm
It can be seen that the TLV-based -method predicts lower values than those of
the NAAQS, at least for CO.
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III Concentrations To Which People Might Be Exposed
In order to relate the health effects information gathered in the health
effects literature review to vehicle emission rates, a set of models must be
chosen to represent situations of appreciable mobile source pollutant
concentrations with significant public exposure. This involves the
application of pollutant dispersion modeling techniques to estimate the
concentrations of mobile source pollutants. Since toxic (non carcinogenic)
pollutants are of primary interest in this report, special emphasis has been
given to those models and situations which may reflect short-term scenarios to
which the public is exposed.
In relating the public exposure of a mobile source pollutant to known health
effects information, the most important parameter is the dose which the public
receives. However, a pollutant dose determination for the general public is a
very difficult parameter to measure, and there is expected to be considerable
variation in the parameter throughout the population. Therefore, for the
purposes of this approach, the exposure time of the general populace to the
pollutant of interest in most cases will be assumed to be of approximately 1-2
hours per day, probably on each day of a 5 day work week. This overall
exposure time may be spread among one or more of the scenarios listed below.
This assumption is made to keep this approach simple with the intent that if
the resulting analysis shows that a significant potential problem may exist,
then a more detailed analysis of both the health effects and the exposure or
dose may be desired.
Public exposure to mobile source pollutants occur in a variety of situations
from potential short-term, high concentration events involving personal
garages, parking garages or other enclosed spaces, to long-term low
concentration events in an area wide scenario. For non genotoxic pollutants,
the most relevant situations to be concerned about with respect to public
health would appear to be high concentration short-term situations (acute
exposures). This is not to imply that chronic effects of these pollutants are
not of concern, but rather that these chronic situations require data from
long term health studies, of which very few have been done. This report will
be concerned with short-term high concentration exposures. These acute
exposures are probably repeated often, perhaps five or more times in each week
so that a chronic exposure to a repeated acute dose may be the most relevant
exposure regimen. However, it is expected that little, if any, health effects
data will be available for these conditions and that the most closely related
health data will be used as a comparison to the mobile source case. The
scenarios which should be used in this assessment are listed in Table III.
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Table III - Exposure Scenarios
I. Enclosed Space
A. Single Family Garage
B. Parking Garage
C. Roadway Tunnel
II. Street Canyons
III. Expressway
A. On Expressway
B. Beside Expressway
IV. Localized Area Sources
A. Parking Lots, Airports
These scenarios may vary in the maximum concentrations of mobile source
pollutants but each scenario has the potential for elevated concentrations
under certain conditions which may lead to a public health hazard. For each of
the scenarios listed above, it is possible to select an infinite number of
input variables to determine the results. Among the variables which may have
strong effects on the results are meteorological variables such as windspeed
and atmospheric stability, model parameters such as the mixing factor, as well
as physical parameters such as number of lanes per highway, number of
vehicles, fleet composition, emission factors, and building height. Within
this myriad of choices we selected two collections of variables for each
scenario to represent an "average" and a "severe" situation with respect to
the particular scenario. Each average and severe situation was chosen to
represent a "real world" situation. A more detailed discussion of the
situations listed above, along with the the models and conditions chosen, can
be found in Appendix I.
Enclosed Space Models
The enclosed space scenarios which we have chosen to model include private
residential garages, parking garages, and roadway tunnels. Each situation
will be estimated using some form of Turk's equation (see Appendix I).
Residential Garage
The example conducted for the residential garage involves two situations, one
with an operator entering the garage, opening the garage door, starting the
car, warming the car up for 30 seconds, and driving out of the garage. This
situation results, for example, in a garage concentration of 58 ppm CO in the
case of an emission rate of 7 grams/min. CO. The second situation involves the
previous condition followed by a 5 minute period of idle, with the garage
door open, before the car is driven out. In this case, the CO has increased
from 58 ppm to 280 ppm. The equations and charts in Appendix I can be used to
perform similar calculations for other pollutants.
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Parking Garage
The parking garage scenario is being estimated by the use of two separate
parking structures. An underground parking structure (Los Angeles Music
Center) is being used to simulate a severe case while an above ground parking
structure (San Antonio, Texas) is being used to simulate an average or typical
case for this scenario.
The ambient air concentrations for the parking garage scenarios were
calculated using the following equations;
1. For contribution of initial concentration in garage
G! = C0 exp (-% FV2 t/V)
2. For contribution of pollutant concentration in incoming
ventilation air
C2 - C± [ 1 - exp (-R-J. FV2 t/V)]
3. For contribution of vehicles within the garage
ng
C3 = RiFv3 [1 - exp (-Ri FV3 t/V)]
4. The total ambient concentration is:
C = GI + C2 + 03
where:
C = nominal pollutant concentration, ug/m^
Co = initial pollutant concentration at time, t = o, ug/rn^
GI = contribution of initial pollutant concentration, ug/m^
C2 = contribution of ventilation air, ug/m^
63 = contribution of pollutant source, ug/m^
Ci = concentration of pollutant in ventilation air, ug/m^
Fv = effective ventilation factor, dimensionless
n - number of vehicles or emission sources, dimensionless
q = pollutant source rate of emission, g/min
R^ = ventilation rate, ft^/min
t = time, minutes
V = volume,
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In the severe case, the exposed population is assumed to be located at level 5
of the parking structure and is leaving the structure after a major event, 20
minutes after the garage started to empty. Then, for an emission factor (EF)
of 1 g/min of pollutant, and an initial concentration assumed to be 1 mg/m3
the following factors pertain to this severe case.
Severe case parking garage (1 g/min EF)
Level 5 9,600 ug/m3 for Ig/min EF (ramp intake)
46,100 ug/m3 for Ig/min EF
Ramp 5 to 4 14,900 ug/m3 for Ig/min EF
Ramp 4 to 3 12,300 ug/m3 for Ig/min EF
Ramp 3 to street 10,100 ug/m3 for Ig/min EF
As in all these situations, the emission factor (EF) is a direct multiplier so
that pollutant concentrations can be directly factored up from the base
level. To illustrate this severe case, CO can be used. If an emission rate
of 7 g/min is used for both ramp and level areas then the following numbers
are generated.
Level 5 9,600 x 7 g/min = 67,200 ug/m3 (Ramp air)
46,100 x 7 g/min = 322,700 ug/m3
Total Level 5 = 389,900 ug/m3
or 339 ppm
Ramp 5 to 4 14900 x 7 = 90 ppm
Ramp 4 to 3 12300 x 7 = 75 ppm
Ramp 3 to street 10100 x 7 = 61 ppm
This example illustrates the substantial build up of mobile source pollutants
which may occur in an underground, mechanically-ventilated garage during a
high vehicle use period.
The typical case provides factors for an above ground, naturally ventilated
parking structure in San Antonio, Texas. For a 1 g/min emission rate these
factors are:
Typical Parking Garage Scenario
Parking level 3,900 ug/m3 for 1 g/min EF
Ramp Room 13,750 ug/m3 for 1 g/min EF
To illustrate this example for CO, assuming a 0 ppm inlet air concentration,
the concentrations corresponding to a 7 g/min emission rate are:
Parking level 7 x 3900 = 24 ppm
Ramp Room 7 x 13750 = 84 ppm
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Roadway Tunnel
The average and severe roadway tunnel situations have been simulated by use of
two separate roadway tunnels. The severe case has been selected as the
Baltimore Harbor tunnel, which is a long, heavily used tunnel with a somewhat
aged ventilation design. The typical case is a Minnesota highway tunnel.
Details on these two tunnels and on the modelling methods used for the tunnel
scenario can be found in Appendix I. The multiplicative factors for these
situations are:
Tunnel Scenarios (1 g/mile emission rate)
Typical - 1123 ug/m3 for 1 g/mile EF
Severe - 2856 ug/m3 for 1 g/mile EF
Street Canyon
The street canyon situation will be simulated by a form of an equation
developed by researchers at SRI, Int'l. and is represented by the general
equation below.
Cv
7 x 106 QL
(U + 0.5) (S + 2)
where: Cy = ambient concentration resulting from the
vehicles in the street canyon, ug/m
QL = vehicle emission rate, g/sec m
U = rooftop wind speed m/sec
S = slant distance from exhaust to receptor, m
7 = empirical correlation factor
10^ = units conversion, grams to ug
0.5 = empirical wind correction, m/sec
2 - empirical slant distance correction, m
The general form of this equation has been indirectly verified by wind tunnel
tests. Several situations have been worked out for the street canyon
scenario. The example situations model a street canyon in San Antonio and
Houston, Texas with specific physical characteristics. This example, using a
unity emission factor of 1 g/mile results in the pollutant concentrations
listed in Table IV.
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-17-
Table IV
Street Canyon Ambient Air Concentration
Concentration from Vehicle ug/m^
Average Case Sidewalk 31.3
In Vehicle 114.1
Severe Case Sidewalk 97.5
In Vehicle 334.8
Since the emission factor in this equation is a direct multiplier, the
concentration of any pollutant can be scaled up by multiplying the emission
factor by a specific entry in Table iy.
Expressways
Expressway related exposure to mobile source pollutants can occur in
essentially two ways: either by being in close proximity to the expressway
(living and working close) or by being on the expressway as a commuter. These
two situations call for different approaches to modeling. The close proximity
case can be estimated by using one of the available line source dispersion
models. This report will make use of the G.M. model developed by Chock. The
close proximity expressway example uses an existing Houston, Texas freeway
and obtains an ambient concentration vs distance from the roadway for a unity
emission factor. Details on this can be found in Appendix I. The commuter
case will be handled by use of the EPA Point, Area and Line model ("PAL")
which can input both point and line source. The approach used can best be
described as a relative motion procedure viewing each vehicle as a point
source upwind of the commuter.
The close proximity expressway situation can be considered to be a severe case
simulation. A typical case is not provided here because the ambient air
concentrations resulting from this situation are very low compared to the
other scenarios and thus only the severe case assumptions provide data that is
useful in making up the various pollutant concentration profiles. The short
term factors are calculated for a rush hour time period (one hour average)
with an average traffic density of 3780 vehicles/hour. The factors that
result from this expressway model treatment are listed below.
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-18-
Table V
Close Proximity Expressway Situation (1 g/mile EF)
Distance downwind
from road edge, Ambient Concentration
meters Short Term ug/m^ Long Term*
1 397.0 61.0
5 368.0 55.0
10 334.0 48.0
25 248.0 35.0
50 171.0 27.0
100 105.0 14.0
500 26.3 4.0
1000 13.6 1.6
* The long term case has been developed using
a long term average of observed values for
CO along the Houston freeway. The values
were corrected for emission factor in
deriving the table above.
The on-expressway (commuter) scenario is simulated using a typical and severe
case. This scenario used a specifically designed computer program, called
ONEX, to calculate ambient concentrations of pollutants in the vicinity of the
vehicles on the expressway. The typical exposure case used a San Antonio
expressway running north and south during the peak rush hour. A 4 lane
segment of this freeway with an average daily traffic of 30,000 vehicles per
day was used in the simulation.
Table VI presents the multiplicative factors for the typical expressway
situation using a range of wind directions and speeds. The range of these
values (61 to 124 mg/nP) is fairly close considering the large range of wind
speeds used (1.0 to 6.0 mph).
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-19-
TABLE VI AMBIENT CONCENTRATION FOR RECEPTOR ON EXPRESSWAY
TYPICAL EXPRESSWAY EXPOSURE SITUATION
1 g/mile EF
Outside downwind lane
Wind Direction Wind Speed Ambient Concentration
Degrees Relative m/sec (mph)
357.5 1.0 (2.2) 120
355.0 1.0 (2.2) 120
340.0 1.0 (2.2) 122
315.0 1.0 (2.2) 124
270.0 1.0 (2.2) 122
357.5 2.0 (4.5) 114
355.0 2.0 (4.5) 113
340.0 2.0 (4.5) 109
315.0 2.0 (4.5) 103
270.0 2.0 (4.5) 95
357.5 3.0 (6.7) 109
355.0 3.0 (6.7) 107
340.0 3.0 (6.7) 99
315.0 3.0 (6.7) 85
270.0 3.0 (6.7) 77
357.5 6.0 (13.4) 96
355,5 6.0 (13.4) 92
340.0 6.0 (13.4) 75
315.0 6.0 (13.4) 61
270.0 6.0 (13.4) 72
The severe exposure case used the Santa Monica freeway in Los Angeles. A 10
lane portion of this highway with a 200,000 vehicle/day traffic load was used
in the simulation. Table VII presents the multiplicative factors for the
severe situation.
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-20-
TABLE VII,
AMBIENT CONCENTRATION FOR RECEPTOR ON EXPRESSWAY
SEVERE EXPRESSWAY EXPOSURE SITUATION
1 g/mile EF
Wind Direction
Degrees Relative
357.5
355.0
340.0
315.0
270.0
357.5
355.0
340.0
315.0
270.0
357.5
355.0
340.0
315.0
270.0
357.5
355.0
340.0
315.0
270.0
Area Wide Sources
Wind Speed
m/sec (mph)
1.0 (2.2)
1.0 (2.2)
1.0 (2.2)
1.0 (2.2)
1.0 (2.2)
2.0 (4.5)
2.0 (4.5)
2.0 (4.5)
2.0 (4.5)
2.0 (4.5)
3.0 (6.7)
3.0 (6.7)
3.0 (6.7)
3.0 (6.7)
3.0 (6.7)
6.0 (13.4)
6.0 (13.4)
6.0 (13.4)
6.0 (13.4)
6.0 (13.4)
Outside downwind lane
Ambient Concentration
ug/m3
454
467
494
506
495
453
458 .
428
400
369
444
435
375
327
285
399
366
275
200
148
Parking lots are an exposure scenario which may also involve large populations
of people in close proximity to mobile sources. However, EPA studies (see
Appendix I) have not shown appreciable levels in parking lots, although
several measurements have shown levels up to 50 ppm CO where the parking lot
enters the street. Normally, the levels were 20 ppm or less for CO even
during peak use of a sports stadium parking lot where the intermittent use is
important. Thus, it appears that parking lots do not produce as high a level
of automotive pollutants as do the other scenarios. Because of the difficulty
which was encountered in locating suitable models and applying them, no case
was developed for this scenario.
IV Range of Concern Determination
Using the compiled information from the previous sections of this report, it
is possible to convert the health effects data to corresponding mobile source
emission factors for the various ambient air scenarios.
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-21-
Figure 2_ represents graphically the output of the mathematical models used to
simulate the different scenarios used in this report. An inspection of this
plot (Fig. 2) reveals that, for any specific ambient air concentration of
pollutant, a large number of vehicle emission factors, one for each scenario,
can be selected. However, if an ambient air concentration is intended to
represent a lower or upper level of health effects concern, then an additional
variable is important, and that variable is exposure time. The health effects
data used to project or estimate a range of concern in the ambient air always
has a specific exposure time associated with it, which relates back to the
actual dose the organism receives when the adverse health parameters are
measured. When comparing these health data to mobile source emission
scenarios it is important to remain consistent regarding the exposure time.
However, in practice it has been determined that very few if any health
effects data have exposure times and exposure schedules similar to the actual
human exposure to mobile source pollutants. Another confounding factor
related to this exposure time issue is that the exposure time and exposure
schedule of a specific individual in the population would be spread out among
a number of the mobile source scenarios in any given day. As an example from
Appendix I, consider the hypothetical exposure pattern of a typical suburban
commuter.
Suburban Commuter Exposure (Weekday)
1) Starts car in garage 5 minutes -personal garage scenario
2) Expressway to work 20 minutes -Expressway scenario
3) Tunnel on trip 5 minutes -Tunnel scenario
4) Central Business district on trip 10 minutes -Street canyon scenario
5) Evening reversal of above
It can be seen from this example that this one individual experiences several
types of automotive pollutant exposure in his/her work day.
In order to provide, in this methodology, a workable approach to estimate the
levels of unregulated pollutants that may constitute a human hazard it has
proven necessary to assume a standard exposure time and schedule and then try
to fit the available health data into this regimen. Thus, for the purposes
of this methodology the exposure time of the general population is assumed to
be 1-2 hours/day, 5-7 day/week throughout the year. It is felt that this
type of exposure is similar to what most populations are affected by in their
normal activities. In most cases, health effects data resulting from
exposures of this type will not be available, necessitating the use of
judgement in arriving at the ranges of concern for mobile source pollutants.
It should be emphasized at this point that this methodology is intended to
provide an initial conservative assessment of the potential hazardous levels
of unregulated pollutants from mobile sources. If a significant hazard
appears possible, then it may be prudent to perform additional health and
exposure studies to more concretely identify the potential hazard to exposed
humans.
In addition to exposure time, other issues may be important to the overall
evaluation of a mobile source pollutant. One such issue is atmospheric
reactivity of a pollutant after it is emitted, which may decrease or increase
the exposure of the population to mobile source pollutants. When information
-------
• Figure 2
Pollutant Concentrations vs Emission Factors
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1000
950 .
900 .
850 .
800 .
750 .
700 .
650 .
600 .
550 .
500 .
450 .
400 .
350 .
300 .
250 .
200 .
150 .
100 .
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-------
-23-
on the reactivity of a pollutant is available, it can be used to modify the
emission factors by an appropriate amount. However, in most cases this
information is not expected to be readily available and should not be
considered necessary for the use of this methodology.
After the ambient air range of concern is identified using the appropriate
health effects data and utilizing the assumptions on exposure time stated
previously, then this range of concern can be converted to vehicle emission
factors for the various mobile source exposure scenarios. The result of this
exercise should be a table (illustrated fully in the example provided later
in the report as Table XII) compiling, in effect, a range of concern for each
scenario and situation. In certain cases, the use of both the high and low
levels of the range of health effects may be inappropriate, such as when a
severe situation (e.g. Severe Expressway) is compared to the low level of the
range of concern, if the low level were derived using long term exposure
data, and the severe situation were derived using parameters (e.g.
meteorology) that would only occur infrequently.
An examination of this table of ambient concentrations will reveal that one
scenario will be dominant in that it will have the lowest emission factor
range of concern. However, if this scenario is an inappropriate measure of
the potential levels of human health hazard for the specific pollutant of
interest, or if other scenarios are of specific interest, then other portions
of the exposure table will also be important.
Initially, the derivation of the emission range of concern for a specific
scenario will apply to the average emissions of that pollutant for the entire
vehicle fleet, except for the residential garage situation. However, in most
cases, it will be desirable to compare specific vehicle/ emission control
technology combinations to this range. Obviously, if a high emitting
technology, with respect to a particular pollutant (compared to the other
technologies) has a maximum emission rate below the lowest level of the
range, then that technology poses no concern relative to that pollutant.
However, if a specific emission control technology has an emission factor
which falls within the range of concern for a specific scenario, then some
question will exist with respect to that technology and it will, therefore,
be subject to closer scrutiny. The overall evaluation will take into
consideration additional factors which include the fleet average emissions of
the pollutant and the maximum percentage of that technology which can be
expected in the future. Any technology which has an emission factor above
the highest level of the range will be considered as potentially hazardous
with respect to that pollutant.
Summary and Conclusions
This methodology has been designed to be a valid and workable approach toward
estimating whether emissions of an unregulated pollutant are a potential
hazard to public health. The effort of trying to maintain a simple approach
has resulted in the necessity of using several simplifying assumptions to
avoid complexities inappropriate to the nature of this methodology. If a
potential problem is uncovered by this methodology for an unregulated
pollutant, then a more detailed investigation of that specific pollutant can
be undertaken to provide a more complete evaluation of the hazard. The more
-------
-24-
important simplifying assumptions are that pollutants are non-reactive
within the time frames considered, short term exposures are most relevant
and health effects data can be used to estimate the effects of mobile
sources on public health.
To illustrate the way that this methodology works, the last section of this
report provides an example of one pollutant, sulfuric acid.
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-25-
Sulfuric Acid Example
This section is presented as an illustration of the way in which major
portions of this approach are intended to work. Sulfuric acid has been chosen
as the example pollutant for the approach because there is a large amount of
existing data on it, both in the health effects and emission factors area.
In spite of this apparent depth of information and data, no range of concern
for mobile source emissions has ever been estimated or established for this
compound.
Sulfuric Acid Emission Factors
Emission factors for sulfuric acid were collected from a number of available
sources and are listed in Table VIII. These emission factors have been
compiled at this time only for the Congested Freeway Driving Schedule. This
particular driving schedule is most applicable to the expressway exposure
situation, but may still have utility for the street canyon situation. The
emission factors for the enclosed space conditions, which would best be
derived from an idle or slow speed schedule, will be the subject of further
work to identify concrete emission factors for these situations.
While this example is concerned with sulfuric acid only, the emission factors
reported here generally are measurements of aqueous soluble sulfates. In most
cases, the predominant soluble sulfate species in mobile source exhaust is
sulfuric acid (10). However, other sulfates such as ammonium sulfate could be
present. For the purposes of this example, it is assumed that the mobile
source emission factors represent 100 percent sulfuric acid.
These emission factors can be combined to calculate fleet average emission
factors for the vehicle fleet by using available information on vehicle miles
traveled (VMT) for the different vehicle classes. For simplicity in this
example the VMT fractions will be derived from information in the Pedco report
(6) for calendar year 1980 and Mobile Source Emission Factors: For Low
Altitude Areas Only (7). In future assessments, other references may be used
to perform these calculations. Table IX provides a breakdown of the vehicle
class VMT's and the fleet average emission factor for sulfuric acid.
Obviously this particular set of calculations does not represent any specific
fleet emission factor. Depending on the make up of the vehicle fleet at any
point in place or time that is of interest, the fleet emission factor will
differ. The most severe case could be considered to be the scenario where
high sulfuric acid emitting technology is the predominant member of the
vehicle fleet. To address this possibility, and the possible presence
-------
-26-
TABLE VIII
Sulfuric Acid Emission Factors*
Vehicle Category
Light Duty Diesel Vehicles
w catalyst
w trap Oxidizers
Light Duty Diesel Trucks
Heavy Duty Diesel Trucks
Light Duty Gasoline Vehicles
Non Catalyst; no air pump
Non Catalyst; air pump
Oxidation Catalyst; no air pump
Oxidation Catalyst; air-pump
3-way Catalyst
3-way Plus Oxidation Catalyst; air pump
Light Duty Truck
Non Catalyst
Catalyst, no air pump
Heavy Duty Gasoline Vehicles
Sulfuric Acid (mg/mile)**
Avg
9
100
100
16
100
0.2
1.0
10
20
4
30
1.0
20
4
Based on congested Freeway Driving
Schedule and 0.030 wt % Sulfur for
gasoline and 0.2 wt % for Diesel fuel.
These emission factors may change with
other fuel sulfur levels or test
cycles.
** Reference 9-14.
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-27-
TABLE IX
Fleet Average Emission Factors - Sulfurlc Acid*
Vehicle Class
Light Duty Diesel Automobiles
Light Duty Diesel Trucks
Heavy Duty Diesel Trucks
Light Duty Gasoline Vehicles
Non Cat.; no air pump
Non Cat . ; air pump
Ox . Cat . ; no air pump
Ox. Cat.; air pump
3-way Cat . ; no air pump
3-way Plus Ox. Cat.; air
Light Duty Gasoline Trucks
Non Catalyst
Catalyst
Heavy Duty Gasoline Trucks
Total Fleet Average
Fraction
VMT
0.015
0.002
0.027
0.147
0.098
0.289
0.261
0.012
pump 0.008
0.096
0.010
0.035
Sulfuric Acid
Emission Factor
(mg/mile)
9.0
16.0
100.0
0.2
1.0
10.0
20.0
4.0
30.0
1.0
20.0
4.0
11.8 mg/mile
EFxVMT
Fraction
0.135
0.032
2.700
0.029
0.098
2.890
5.220
0.048
0.240
0.096
0.200
0.140
*These calculations were based on available information from the reference
listed above (7,8) and in Table 1. Buses, which may be a significant source
of sulfuric acid emissions under certain conditions, are not included in these
fleet averages.
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-28-
of future technology, the fleet average emission factor can be modified to
reflect different proportions of these higher emitting technologies. As a
worst case, a vehicle fleet consisting of 100 percent of the highest emitting
technology could be calculated.
Table VIII also presents emission factors for vehicle/emission control
categories which are expected to be the highest emitters of sulfuric acid
under a variety of conditions. Obviously, it is these technologies, on an
individual basis, that might be expected to constitute the most likely source
of an unreasonable risk to public health. Since most of these technologies
are not yet in common use except on an experimental basis, the potential risk
can be considered to be a future concern. To establish bounds on the
potential risk from sulfuric acid that these technologies present, they will
be considered in a number of hypothetical calculations to comprise 25, 50, 75
and 100 percent of the total vehicle miles traveled.
By using the fleet average emission factors in Table IX and the hypothetical
calculations listed above, a list of emission factors can be calculated to
use in subsequent steps. This list is presented in Table X.
Sulfuric Acid Health Effects
A literature review on the health effects of sulfuric acid was performed as an
input to the determination of a range of concern for mobile source emissions
of this compound. At the present time only a preliminary draft of this
literature is available and further information may modify the conclusions.
The preliminary draft of the literature search is included as Appendix II to
this report.
As indicated in the methodology, in order to focus the health effects
literature review, a preliminary range of ambient levels has been selected to
bracket the region of uncertainty with respect to sulfuric acid health
effects. This range has been determined to be 10 ug/m^ - 1000 ug/m-^ for
sulfuric acid. The lower end of this range has been selected to approximate
the lowest level at which adverse physiological effects can be detected. The
preponderance of the evidence has shown little or no health effects at levels
of sulfuric acid below this, although there are some indications that
sensitive subgroups of asthmatics may show some reaction to these levels of
sulfuric acid. To as great an extent as possible, this lower level also takes
into account the interactions of various pollutants such as S02 and
H2S04.
The upper level of the range is chosen to be the TLV recommended by NIOSH and
the ACGIH as 1000 mg/m^ (9). Above this level several studies have shown
an adverse reaction in healthy subjects which may be harmful under repeated
exposures.
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-29-
Table X
Sulfuric Acid Emission Factors - Compiled
Fleet Category mg/mile@
Fleet Average (FA) 12
FA + 25% 3W +OC* 17
FA + 50% 3W+OC 22
FA + 75% 3W+OC 26
100% 3W-OC 30
FA + 25% D+C** 34
FA + 50% D+C 56
FA + 75% D+C 75
100% Diesel Cat. 100
FA + 25% D+To*** 34
FA + 50% D+To 56
FA + 75% D+To 75
100% D+To 100
@Normalized to the Congested Freeway Driving Schedule
* Light Duty Gasoline Vehicle - Three way + Oxidation Catalyst with air pump
** Light Duty Diesel Vehicle - Catalyst equipped
*** Light Duty Diesel Vehicle - Trap-oxidizer equipped
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-30-
Sulfuric Acid Ambient Air Concentrations
By using modeling techniques in conjunction with sulfuric acid emission
factors, ambient concentrations can be determined that should bracket the
range of possible sulfuric acid emission concentrations from mobile sources.
This matrix of ambient concentrations (Table XI) is composed of five
scenarios, out of thousands possible, and was chosen at this time as one
example of the exposure ranges. More work is currently being done to more
concretely specify the most appropriate scenarios to use and thus the
scenarios may change in future efforts of this kind. The information in Table
XI is depicted graphically in Figure 2.
As indicated above, the range of exposures to the general public can be
estimated by considering a limited number of specific scenarios. The
scenarios selected are all expected to be dominantly influenced by mobile
source emissions. Personal garages, parking garages, roadway tunnels, street
canyons, and urban expressways have been selected to bracket the range of
sulfuric acid concentrations from mobile sources that influence short term
health effects in the exposed population. Each scenario is developed as both
severe and average exposure situations calculated by the use of existing
ambient air modeling techniques. No attempt has been made to determine the
cumulative effects of these situations on general public health. Appendix I
contains a detailed explanation of the rationale for choosing the specific
situations and parameters which lead to the numerical results presented here.
Table XI presents the ambient air concentration of sulfuric acid for eleven
ambient situations as a function of vehicle emission rates. Two personal-
garage situations are presented, one (average or typical) using a 30 second
vehicle warmup time and the other (severe) using a five minute vehicle warmup
time. These two situations are intended to simulate summer and winter
conditions, respectively.
The two parking garage situations simulate average and severe conditions, with
an above ground, naturally ventilated garage for the former and an underground
garage for the latter. The average parking garage case is calculated assuming
an exit time in which the vehicle spends equal time on the parking level and
the ramp level. The severe parking garage is calculated assuming that the
exposure takes place 20 minutes after a major sporting event finishes, wherein
the exposed population is at parking level 5. The initial concentration of
sulfuric acid in this garage is assumed to be low (1 mg/m^).
The roadway tunnel situations used two different specific tunnels to estimate
an average and severe condition. A new design, two lane roadway tunnel with
moderate traffic flow is used for average conditions, while an old design,
heavily used roadway tunnel is used for severe conditions.
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-31-
The two street canyon situations are simulated by examining the parameters of
two street canyons. The most sensitive parameter in this model appears to be
the number of traffic lanes in the canyon. The severe condition is calculated
for a six lane street canyon with a 2400 vehicle/hr traffic load and with the
exposed population located inside of the vehicle. The typical condition is
calculated for a two lane canyon with 800 vehicles/hr of traffic and a
sidewalk location of the exposed population.
The expressway situations require three specific estimations to cover the
range of possible concentrations. One highway condition tends to estimate an
exposure involving a close proximity to the highway such as would be gotten by
living or working close to a heavily travelled freeway. This case is
calculated on a short term basis for a distance of 50 meters downwind of the
roadway. The other two expressway situations simulate a commuter (located in
the vehicle) exposure, with the average case using a four lane, medium use
1400 vehicle/hour) and a westerly wind at 1.0 meters/sec and the severe case
using a ten lane, heavily travelled (3600 vehicles/hr) freeway with a 1.0
meter/sec westerly wind.
Determination of the Range of Concern
The range of concern for sulfuric acid emissions from automobiles is
determined using the outputs from the previous three areas, emission factors,
health effects and exposure estimation (the emission factors and exposure
estimates have already been combined in Table XI). Using the preliminary range
(10 ug/m3 - 1000 ug/m3) as a stepping stone for this effort, along with
the guidelines explained earlier in the methodology section of this report, an
upper and lower value can be determined for the final range of concern.
The literature search reveals a human study which shows that an acute exposure
concentration as low as 66.0 ug/m3 caused significant differences in
lung function parameters in 3 out of 18 subjects tested (Gardner et. al.
1976). The evidence provided in the literature also shows that no
physiological effects were detected for exposure concentrations below 66.0
ug/m3. Since, at this time, there is no available information definitely
concluding that there are adverse physiological effects at concentrations of
sulfuric acid below 66.0 ug/m3, this value will be chosen as the lower value
in the range of concern.
The upper value of the range will remain at 1000 ug/m3 as was set for the
preliminary range of concern. This TLV for sulfuric acid is the time-weighted
average concentration for a normal 8-hour workday or 40-hour workweek, to
which nearly all workers may be repeatedly exposed, day after day, without
adverse effects. The evidence of adverse health effects above this level
would be sufficient to support regulatory action.
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-32-
Between the chosen limits of this range, there are scattered data points
providing evidence of adverse physiological effects caused by exposure to
various concentrations of sulfuric acid. Therefore, this region has been
termed the "range of concern" for sulfuric acid concentrations in the ambient
air. This range can now be used in conjunction with the emission factor data
to graphically present the conversion of sulfuric acid emissions to ambient
air concentrations.
Once the literature search was completed and the appropriate information was
tabulated for sulfuric acid, a large table was prepared compiling all the
information for the animal and human studies (see Appendix 111). These tables
list the studies according to the exposure concentration of sulfuric acid
(highest to lowest concentration). Using this health effects information
along with the emission factor data presented in Table XI, graphs were
composed representing the relationship between ambient air concentrations,
emissions factors, and the various types of public exposure situations (see
Figure 2-7).
According to the methodology described earlier in the report, the lower and
upper levels which comprise the health effects range of concern are compared
to the mobile source situations to calculate the emission factor range of
concern. The chief element of comparability between the health effects range
and the ambient situations is exposure time. Most of the mobile source
situations simulate short term exposures (durations of an hour or less per
day) perhaps repeated several times per week over an extended period. The
average exposure situations appear more likely to be repeated often, while
the severe exposure conditions would likely only occur on infrequent
occasions.
With the above information, the mobile source range of concern for sulfuric
acid can be estimated for the different mobile source situations. Table XI
lists the vehicle emission factors which correspond to the high (1000 ug/m3)
and low (66 ug/m3) portions of the range of concern for sulfuric acid.
Inspection of this table shows that the scenarios result in a variety of
ambient concentrations corresponding to the health effects range of concern of
66 ug/m3 to 1000 ug/m3.
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-34-
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PARKING GARAGE
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EMISSION FACTOR (milligrame/milo)
-------
-35- -
FIGURE 5
ROADWAY TUNNEL
CCSftStfe*
EMISSION FACTOR (milli9ram8/milo)
-------
-36-
I 553
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520
453
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FIGURE 6
STREET CANYON
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EMISSION FACTOR
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EMISSION FACTOR (milli3ram9/mile)
-------
-38-
TABLE XI
Emission Factors Required to Result in
Two Different Ambient Sulfuric Acid Levels***
Ambient Situation* Emission Factor Emission Factor
mg/mile for rag/mile for
66 ug/m3 1000 ug/m3
exposure exposure
Street Canyon - Typical 1540 23077
Expressway - Typical 619 9375
Expressway - Close Proximity 388 5882
Street Canyon - Severe 165 2500
Expressway - Severe 132 2000
Personal Garage - Typical**
Parking Garage - Typical**
Roadway Tunnel - Typical 59 822
Roadway Tunnel - Severe 22 350
Parking Garage - Severe**
Personal Garage - Severe**
* In order of increasing ug/m3 concentration for 1 g/mile
(or 1 g/min) emission rate.
** These situations were not evaluated for sulfuric acid because of an
inadequate data base- for emission factors under idle and low speed
conditions.
*** If the severe roadway tunnel situation is of primary interest then a fleet
emission factor of 22 mg/mile over an appropriate driving schedule will be
enough to put the ambient concentration within the range of concern.
However, if expressway operation is of primary interest, then emission
factors of up to 132 mg/mile would yield ambient concentrations below the
range of concern even for severe conditions.
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Summary and Conclusions - Sulfurlc Acid
1) The range of concern for sulfuric acid emissions from motor vehicles
varies from 22-350 mg/mile to 1540-23077 mg/mile depending on the scenario
and situation of interest.
2) The lowest level of this range (22 mg/mile) is based on an ambient air
concentration of 66 ug/m^ for a severe roadway tunnel situation.
3) No vehicle emission factors from the garage scenarios were considered in
calculating the range of concern. More data is probably needed on
emissions of sulfuric acid from light duty vehicles under idle and slow
speed conditions to evaluate the effects of the garage situations on the
sulfuric acid range of concern.
4) The roadway tunnel scenario appears to be a controlling factor in this
methodology for the sulfuric acid case. There is some doubt whether this
scenario identifies a potential mobile source problem or a potential
roadway tunnel ventilation problem. If a potential problem were
identified resulting from roadway tunnel exposures to mobile source
pollutants, then it is possible that the most appropriate solution would
be to increase tunnel ventilation rather than to reduce the vehicle
emissions.
5) This preliminary example of sulfuric acid has not considered a specific
margin of safety. It is possible that the inclusion of the roadway tunnel
scenario as the controlling factor in the range of concern consitutes a
margin of safety in view of conclusion 4 above, but no specific factor has
been calculated.
6) The current vehicle fleet emission factor for sulfuric acid is 12
mg/mile, which is well below the lowest of the ranges of concern for
sulfuric acid.
7) With respect to specific vehicle emission control designs, and referring
to Table IV, it appears that the emission control design/ vehicle
categories that have emission factors most often appearing within the
ranges of concern are Heavy Duty Trucks and Light Duty Diesel vehicles
with trap-oxidizers (100 mg/mile).
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References
(1) Analytical Procedures for Characterizing Unregulated Pollutants
Emissions from Motor Vehicles, EPA Report No. 600/2-79-017.
(2) Analytical Procedures for Characterizing Unregulated Emissions from
Vehicles Using Middle Distillate Fuels, EPA Report No. 600/2-80-068.
(3) Regulated and Unregulated Exhaust Emissions from Malfunctioning Non
Catalyst and Oxidation Catalyst Gasoline Automobiles, EPA Report No.
460/3-80-003.
(4) Regulated and Unregulated Exhaust Emissions from Malfunctioning
Three-way Catalyst Gasoline Automobiles, EPA Report No. 460/3-80-004.
(5) Regulated and Unregulated Exhaust Emissions from a Malfunctioning
Three-way Catalyst Gasoline Automobile, EPA Report No. 460-/3-80-005.
(6) Air Quality Assessment of Particulate Emissions from Diesel-Powered
Vehicles, Pedco Environmental, Inc., March 1978.
(7) Mobile Source Emission Factors: For Low Altitude Areas Only, March
1978, EPA Report No. 400/9-78-006
(8) Multimedia Environmental Goals for Environmental Assessment Volume 1,
EPA Report No. 700/7-77-136a.
(9) Emission of Sulfur-Bearing Compounds from Motor Vehicle and Aircraft
Engines, EPA Report No. 600/9-78-028.
(10) Regulated and Unregulated Emissions from Malfunctioning Automobiles, SAE
Paper 790606.
(11) Emissions from Light and Heavy Duty Engines, EPA Report No.
460/3-79-007.
(12) Exhaust Emissions from Malfunctioning Three-Way Catalyst-Equipped
Automobiles, SAE Paper 800511.
(13) Light Duty Diesel Catalysts, EPA Report No. 460/3-80-002.
(14) Automobile Sulfate Emissions - A Baseline Study, SAE Paper 770166.
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