EP A/AA/CTAB/P A/81-21
The Determination of a Range
of Concern for Mobile
Source Emissions of
Sulfuric Acid
by
Craig A. Harvey
and
Robert J. Garbe
August, 1981
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analyses 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, Michigan 48105
-------
Summary
This paper describes an effort by the Emission Control Technology Division
of the EPA to establish a range of concern for sulfuric acid (H«SO,)
emissions, from mobile sources. In light of the action called for in section
202(a)(4) of the Clean Air Act (CAA) and due to a concern within industry as
to what emission levels will be used as the basis for the evaluation of cur-
rent and future technologies, a methodology was developed in order to
bracket a range of concern for various unregulated pollutants. This paper
coordinates the efforts from two EPA contracts in order to use this meth-
odology specifically for an evaluation of sulfuric acid. Mathematical
models were previously designed for various exposure scenarios (such as
enclosed spaces, expressways, and street canyons) and were used to calculate
the ambient air concentrations resulting from various mobile source sulfuric
acid emission factors (grams/mile). In conjunction with this, a sulfuric
acid health effects literature search was conducted to aid in the
determination of the final range of concern. This search provides adequate
evidence to support the chosen limits of the range.
The results of this analysis provides a range of concern for sulfuric acid
emissions from motor vehicles of from 22-350 mg/mile to 1540-23077 mg/mile
depending on the type of scenario chosen to represent public exposure. The
available emission factor data indicate that 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. The specific emisson
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).
-------
-3-
I. Introduction
It was discovered in late 1972 that catalyst equipped vehicles operating on
unleaded fuel had substantially higher particulate emissions than
non-catalyst vehicles operating on unleaded fuel(l)*. Analysis of the
particulate samples taken from catalyst cars showed mostly hydrated sulfuric
acid to be present(2). Analysis of particulate samples collected from
non-catalyst vehicles have also shown sulfate but at much lower levels(l,2,).
The results of four subsequent studies of motor vehicle sulfate emission^
were compiled by EPA for the report to Congress called for in the Clean Air
Act Section 403G as amended August 1977. Some of the major conclusions from
this were:
1) Oxidation catalyst-equipped passenger vehicles emit significantly
more sulfate (sulfuric acid) than either production or prototype
gasoline-fueled passenger vehicles without catalysts.
2) Laboratory-maintained production vehicles exhibit higher sulfate
emissions than do consumer-owned production vehicles. Deterioration or
alteration of the emission control system(s) of consumer-owned/maintained
vehicles increases regulated gaseous emissions (i.e., HC, CO, and NOx) and
decreases sulfate emissions from these vehicles.
3) Diesel trucks exhibit the highest measured vehicular sulfate
emission rate, 50 mg/mile.
Health effects research on sulfuric acid has been conducted including in
vitro, in vivo, and human epidemiology studies. Since sulfuric acid
contained in an aerosol is particulate matter, its toxicity depends to some
extent on its deposition and retention in the respiratory tract. The acid
is considerably more potent than sulfur dioxide in exerting physiological
*Numbers in parentheses designate references listed at end of report.
-------
-4-
effects; for example, one study showed that sulfuric acid more than tripled
the increase in pulmonary flow resistance caused by an equimolar amount of
so2.
In the interest of establishing a range of concern for levels of H9SO,
in motor vehicle exhausts, Midwest Research Institute (MRI) was contracted
by EPA to compile information on the health effects of sulfuric acid at
different concentrations^). The results of that work form the basis for
the range of concern determined later in this report.
II. Background
When the Clean Air Act was amended in August 1977, the additions included
sections 202(a)(4) and 206(a)(3) which deal with mobile source emissions of
hazardous pollutants from vehicles manufactured after 1978. These sections
are as stated below:
"(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 sub-
section 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 sub-
paragraph (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 un-
regulated pollutants; (ii) available methods for reducing or eliminating
any risk to public health, welfare, or safety which 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."
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 Administrator 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).
-------
-5-
(b) The Administrator may conduct such tests and may require the manu-
facturer (or any such person) to conduct such tests and provide such
information as is necessary to carry out subparagraph (A) of this para-
graph. 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."
Prior to these amendments, EPA's guidance to the manufacturers regarding
hazardous unregulated pollutants were contained in the Code of Federal
Regulations, Title 40, section 86.078-5b. This subsection is stated 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
emissions 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)."
Before certification can be granted for new motor vehicles, manufacturers are
required to submit a statement, as well as data (if requested by the Adminis-
trator), which will ascertain that the technology for which certification is
requested complies with the standards set forth in section 86.078-5(b). This
statement is made in section 86.078-23(d).
The EPA issued an Advisory Circular (AC) (4) in June 1978, to aid the
a/
manufacturers in complying with section 202 (a)(4). Manufacturers were
-------
-6-
asked to continue providing statements showing that their technologies did
comply with the vehicle emission standards and also will not contribute to an
unreasonable risk to public health. Another Advisory Circular (5) was issued
in November of that year continuing these procedures for 1980 and later model
years.
III. Methodology Overview
Along with the previously mentioned activities, EPA, with the input from
several interested parties, has developed a methodology which is one possible
approach to implementing section 202 (a)(4) of the CAA. This approach is ex-
plained in detail in EPA report number EPA/AA/CTAB/PA/81-2, "An Approach for
Determining Levels of Concern for Unregulated Toxic Compounds from Mobile
Sources" (6). Only a brief summary of this method will be presented in this
report.
Under contract to EPA, Southwest Research Institute (SwRI), and Midwest
Research Institute (MRI), have provided valuable information for this ef-
fort. SwRI developed or modified mathematical models for predicting ambient
air concentrations of mobile source pollutants for a variety of exposure
situations including enclosed spaces, street canyons, and expressways. Once
vehicle emission factors for various vehicle categories have been determined
for a particular pollutant, these models can then be used to calculate
corresponding ambient air values for both severe and typical exposure
situations for each scenario. A plot of ambient air concentrations vs.
emission factors can then be designed for use in further steps of this
methodology.
Health effects literature searches have been and are being conducted by MRI in
an attempt to aid EPA in the determination of a range of concern for various
selected pollutants. With adequate information, the limits for this range can
be chosen. The upper level of the range will be that value above which the
studies show that the pollutant causes so great a hazard to human health as to
require formal rulemaking action. The lower value of the range will be the
lowest level at which there is evidence of adverse physiological effects. The
region between these limits will be termed the "ambient air range of concern",
-------
-7-
indicating scattered data points providing evidence of adverse physiological
effects caused by exposure to various concentrations of sulfuric acid. Using
the ambient air vs emission factor plot developed earlier, any technology
emitting a concentration of a pollutant (when converted to ambient air
concentrations) falling within the range of concern will be subject to closer
scrutiny. Technologies with emission levels falling below the lowest level of
the range will constitute "no problem", implying a low level of effort
monitoring. Technologies with emission levels which fall above the highest
value of the range will be considered "dangerous" with respect to human health
and, therefore, this will imply a necessity for regulation.
For the purpose of this report, this particular methodology has been used to
develop a range of concern specifically for motor vehicle emissions of
sulfuric acid.
IV. General Information
Sulfuric acid (H2SO,) is a colorless, odorless, extremely corrosive, oily
liquid, sometimes called oil of vitriol. Concentrated sulfuric acid has a
very strong affinity for water. It is sometimes used as a drying agent and
can be used to dehydrate (chemically remove water from) many compounds, e.g.,
carbohydrates. It reacts with the sugar sucrose, C,?H,,,,0,,, removing
eleven molecules of water, H^O, from each molecule of sucrose and leaving a
brittle spongy black mass of carbon and diluted sulfuric acid. The acid
reacts similarly with skin, cellulose, and other plant and animal matter.
When the concentrated acid mixes with water, large amounts of heat are
released.
Sulfuric acid is one of the most important industrial chemicals. More of it
'is made each year than is made of any other manufactured chemical; nearly 30
million tons of it were produced in the United States in 1970. It has widely
varied uses and plays some part in the production of nearly all manufactured
goods. The major use of sulfuric acid is in the production of fertilizers
e.g., superphosphate of lime and ammonium sulfate. It is widely used in the
manufacture of chemicals, e.g, in making hydrochloric acid, nitric acid,
sulfate salts, synthetic detergents, dyes and pigments, explosives, and
drugs. It is used in petroleum refining to wash impurities out of gasoline
-------
-8-
and other refinery products. Sulfuric acid is used in processing metals,
e.g., in pickling (cleaning) iron and steel before plating them with tin or
zinc. Rayon is made with sulfuric acid. It serves as the electrolyte in the
lead-acid storage battery commonly used in motor vehicles (acid for this use,
containing about 33% H-SO, and with specific gravity about 1.25 is often
called battery acid).
There are two major processes (lead chamber and contact) for production of
sulfuric acid, and it is available commerically in a number of grades and
concentrations. The lead chamber process, the older of the two processes, is
used to produce much of the acid used to make fertilizers; it produces a
relatively dilute acid (62%-78% H2SO,). The contact process produces a
purer, more concentrated acid but requires purer raw materials and the use of
expensive catalysts. In both processes sulfur dioxide is oxidized and
dissolved in water(7).
Sulfuric acid from motor vehicles occurs via two basic processes, both of
which begin with some of the sulfur in the fuel oxidizing to sulfur dioxide
(SO ) during combustion. After this, in vehicles equipped with oxidation
catalysts, some of the S02 is further oxidized by the catalyst to sulfur
trioxide (SO,) which can then combine with water to form sulfuric acid. The
other route by which sulfuric acid is formed is the photochemical oxidation of
exhaust sulfur oxides to sulfuric acid and sulfate by natural processes in the
atmosphere(8).
Typical ambient public exposure to sulfuric acid is due to inhalation of
suspended sulfuric acid particles from a variety of sources such as
fossil-fueled industrial facilities. It can come from stationary sources,
electric power plants or motor vehicles. Overall automotive sulfuric acid
emissions are generally low (2%) in comparison to stationary sources, but it
is possible that high localized concentrations could occur under certain high
volume traffic conditions.
When sulfuric acid in the form of a suspended aerosol is inhaled, it acts as
an irritant to the respiratory tract. At lower exposures (less than 1.0
o
mg/m ; and smaller particle sizes (less than 2 urn) the effects include
slight respiratory irritation and significant changes in mucociliary
-------
-9-
clearance. With larger particles or higher exposures the irritation
increases, making deep breathing difficult for some and increasing light
sensitivity(3,9).
V. Emission Factors
Emission factors for sulfuric acid were collected from a number of available
sources and are listed in Table I. 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 report, 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
(11) for calendar year 1980 and Mobile Source Emission Factors: For Low
Altitude Areas Only (12). In future assessments, other references may be
used to perform these calculations. Table II 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
-------
-10-
TABLE I
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, 10, 14, 15, 16, 17.
-------
-11-
TABLE II
Fleet Average Emission Factors - Sulfuric 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 pump
Light Duty Gasoline Trucks
Non Catalyst
Catalyst
Fraction
VMT
0.015
0.002
0.027
0.147
0.098
0.289
0.261
0.012
0.008
0.096
0.010
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
EFxVMT
Fraction
0.135
0.032
2.700
0.029
0.098
2.890
5.220
0.048
0.240
0.096
0.200
Heavy Duty Gasoline Trucks
0.035
4.0
0.140
Total Fleet Average Sulfuric Acid
11.8 mg/mile
*These calculations were based on available information from the reference
listed above (12, 13) 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.
-------
-12-
Table III
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% IM-C 56
FA + 75% EHC 75
100% Diesel Cat. 100
FA + 25% D+To*** . 34
FA + 50% D+To 56
FA + 75% IH-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
-------
-13-
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 I 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 II 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 III.
VI. 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. This 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
3 3
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
-------
-14-
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 S00 and
H2S04.
The upper level of the range is chosen to be the TLV recommended by NIOSH and
2
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.
VII. 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.
The range of exposures of the general public to motor vehicle exhaust
emissions 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. Figure one depicts graphically the ambient air
concentrations vs motor vehicle emission factors for the eleven specific
situations discussed below.
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.
-------
Figure 1
Pollutant Concentrations vs Emission Factors
^
0
E
0
•H
jQ
3
0
N
0
E
0
0)
o
L
0
J
K.
<
Z
UJ
»— «
m
<
1000
950 .
900 .
850 .
800 .
750 .
700 .
650 .
600 .
550 .
500 .
450 .
400 .
350 .
300 .
250 .
200 .
150 .
100 .
50 .
ical)
OC. OQEYER/t*
EMISSION FACTOR
-------
-16-
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
3
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.
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.
VIII. 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,
-------
-17-
health effects and exposure estimation (the emission factors and exposure
estimates have already been combined in Table IV). Using the preliminary range
3 3
(10 ug/m - 1000 ug/m ) 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
o
concentration as low as 66.0 ug/m 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/m . Since, at this time, there is no available information definitely
concluding that there are adverse physiological effects at concentrations of
3
sulfuric acid below 66.0 ug/m , 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/m 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.
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.
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 III). 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 IV, graphs were
-------
-18-
TABLE IV
Emission Factors Required to Result in
Two Different Ambient Sulfuric Acid Levels**
Ambient Situation* Emission Factor Emission Factor
mg/mile for mg/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.
-------
-19-
composed representing the relationship between ambient air concentrations,
emissions factors, and the various types of public exposure situations (see
Figure 2-6).
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 IV
lists the vehicle emission factors which correspond to the high (1000 ug/m )
and low (66 ug/m ) 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.
IX. Conclusions - Sulfuric 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
3
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
-------
-20-
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 constitutes 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 I, 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).
-------
-21-
FIGURE 2
PERSONAL PARKING GARAGE
c
o
*>
o
1
1
o
O7
O
O
EMISSION FACTOR (milli3ram8/mile)
-------
-22-
FIGURE 3
PARKING GARAGE
0>
-§
o
oe
CO
EMISSION FACTOR (milli3rane/mile)
-------
-23-
FIGURE 4
ROADVAY TUNNEL
73.,
tceera/j.
EMISSION FACTOR (milligrame/milo)
-------
-24-
75B
o
•«"«
-O
m
o
3
or
258
FIGURE 5
STREET CANYON
typical
/u »
EMISSION FACTOR (milligrame/mile)
-------
-25-
758
7BB
o
4>
g
O
•**
1
-------
-26-
References
(1) "Characterization of Particulates and Other Non-regulated Emissions from
Mobile Sources and the Effects of Exhaust Emission Control Devices on
these Emissions," James E. Gentel, Otto J. Manary, and Joseph C. Valenta,
Final Report EPA Contract EHS 70-101 with Dow Chemical Co., March 1973.
(2) "Sulfuric Acid Aerosol Emissions from Catalyst-Equipped Engines," William
Pierson, Robert H. Hammerle, and Joseph T. Kummer, SAE Paper 740287,
February 1974; SAE Transactions 83, 1233 (1975).
(3) "Sulfuric Acid Health Effects," Midwest Research Institute Report for EPA
Contract No. 68-03=2928, 1981.
(4) U.S. EPA Advisory Circular 76, June, 1978.
(5) U.S. EPA Advisory Circular 76-1, November, 1978.
(6) "An Approach for Determining Levels of Concern for Unregulated Toxic
Compounds from Mobile Sources," Robert J. Garbe, U.S. EPA,
EPA/AA/CTAB/PA/80-2, July, 1981.
(7) The New Columbia Encyclopedia, Columbia University Press, New York, 1975,
page 2649.
(8) "Sulfate Emissions from Catalyst-Equipped Automobiles," Charles R.
Begeman, Marvin W. Jackson, George J. Nebel, G.M. Research Laboratories,
SAE Paper 741060, October, 1974.
(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) "Air Quality Assessment of Particulate Emissions from Diesel-Powered
Vehicles," Pedco Environmental, Inc., March, 1978.
-------
-27-
(12) "Mobile Source Emission Factors: For Low Altitude Areas Only," EPA
Report No. 400/9-78-006, March,1978.
(13) Multimedia Environmental Goals for Environmental Assessment Volume 1,
EPA Report No. 700/7-77-136a.
(14) "Emissions from Light and Heavy Duty Engines," EPA Report No.
460/3-79-007.
(15) "Exhaust Emissions from Malfunctioning Three-Way Catalyst-Equipped
Automobiles," SAE Paper 800511.
(16) "Light Duty Diesel Catalysts," EPA Report No. 460/3-80-002.
(17) "Automobile Sulfate Emissions - A Baseline Study," SAE Paper 770166.
------- |