EPA/AA/TSS/83-7
Technical Report
Determination of a Range
of Concern for Mobile
Source Emissions of
Hydrogen Sulfide
by
Craig A. Harvey
August 1983
NOTICE
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.
U. S. Environmental Protection Agency
Office of Air, Noise and Radiation
Office of Mobile Sources
Emission Control Technology Division
Technical Support Staff
2565 Plymouth Road
Ann Arbor, Michigan 48105
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Summary
This paper describes an effort by the Emission Control
Technology Division of the EPA to establish a suggested range
of concern for hydrogen sulfide (H2S) emissions from mobile
sources. As defined in this report, the lower value of the
range will be the lowest level at which there is some
suggestion of adverse physiological effects, the upper level
of the range of concern is that pollutant concentration above
which the studies show that the pollutant causes so great a
health hazard as to strongly suggest it be avoided. The
region between these suggested limits will be termed the
"ambient air range of concern", indicating the bounds of
uncertainty regarding evidence of adverse physiological
effects caused by exposure to various concentrations of the
pollutant. This range is also put into terms of a vehicle
emission range of concern to show what quantities of
automotive emissions would create ambient concentrations
within the ambient air range of concern.
In light of the action called for in section 202{a)(4) of the
Clean Air Act (CAA)(1)* and due to a concern within industry
*Numbers in parentheses denote references listed at end of
report.
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as to what emission levels will be used as the basis for the
evaluation of current and future technologies, a methodology
was developed prior to this paper for bracketing a range of
concern for various unregulated pollutants (2). This paper
coordinates the efforts from two EPA contracts in order to
use that methodology specifically for an evaluation of
hydrogen sulfide. 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 hydrogen sulfide emission factors
(grams/mile or grams/minute) . In conjunction with this, a
hydrogen sulfide health effects literature search was
conducted by Midwest Research Institute under contract to EPA
to aid in the determination of the final range of concern
(3) . Some of the typical health effects noted were eye and
respiratory tract irritation, dizziness, nausea and headaches
of various degrees, depending on exposure.
The results of the Midwest analysis suggest a range of
concern for ambient hydrogen sulfide concentrations of 0.015
mg/m to 14.0 mg/m . This corresponds to motor vehicle
emission levels of from 5.3-4,900 mg/mile to 479.3-447,300
mg/mile on the road and 0.2-204 mg/min to 1.9-1,770 mg/min
for garages, depending on the type of exposure. Under normal
operating conditions or when a vehicle engine malfunction
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does not cause a rich mixture to occur simultaneously with
high catalyst temperature and low exhaust space velocity, the
resulting H.S emissions are negligible (below the suggested
range of concern for any scenario).
The current average in-use vehicle is estimated to emit 0.03
mg/mile of hydrogen sulfide. This is well below the lower
limit of the lowest moving vehicle scenario range of concern
of 5.3 mg/mile. For moving vehicles the lowest ranges are
those of the roadway tunnel scenarios. For this to result in
ambient H?S concentrations within the suggested range of
concern, it would require most of the vehicles in a tunnel to
be malfunctioning in a way that would cause high H~S
emissions (over 5.3 mg/mi).
During idle and very low speed conditions, as would occur in
residential garages or public parking garages, recent tests
have found no H_S emissions for normal or malfunction
operation. This was true for a range of vehicle emission
control system configurations and operating conditions
including engine/emission control system malfunctions. This
includes a diesel automobile, a non-catalyst gasoline
automobile, two 3-way catalyst equipped automobiles, and two
oxidation catalyst equipped automobiles.
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I. Introduction
This introduction is intended to answer the question of why
H2S is being examined in this report. Emissions from
gasoline-fueled vehicles have been characterized by industry,
government and private researchers for many years. While
Federal motor vehicle regulations have been in effect since
1968 establishing emission standards for HC and CO (1973 for
NOx), there are also a number of unregulated pollutants which
have been and are being characterized to see if they could
represent an unreasonable risk to public health and welfare.
One reason these other pollutants need to be studied is that
it is possible for a new emission control system to increase
an unregulated pollutant while decreasing the regulated
ones. For instance, catalyst equipped vehicles emit
significantly more sulfuric acid than non-catalyst vehicles
(4) .
Hydrogen, sulfide is an unregulated pollutant emission that
has been measured in various concentrations in automotive
emission tests (4,5,6,7). Due to its toxic properties and
its disagreeable rotten-egg odor, tests have been conducted
to measure E^S emissions as a function of driving cycle,
emission control system, and sulfur content of fuel. These
data along with health effects data, as summarized later in
this report, are used to determine the conditions under which
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automotive H2S emissions could possibly be of concern with
respect to public health and welfare.
Barnes and Summers of General Motors reported in 1975 that
three conditions occurring simultaneously favored the
formation of H_S by Pt/Pd oxidation catalysts: (a) rich
air/fuel ratio (i.e., a reducing condition); (b) low exhaust
space velocity; and (c) high catalyst temperature (7). These
conditions rarely occur simultaneously with properly tuned
vehicles. However, malfunctioning vehicles or vehicles with
maladjusted carburetors that run rich may meet these
conditions and emit hydrogen sulfide and carbonyl sulfide*
(COS) .
In the interest of suggesting a range of concern for levels
of t^S in motor vehicle exhausts, Midwest Research
Institute (MRI) under contract to EPA compiled information on
the health effects of hydrogen sulfide at different
concentrations (3) . The results of that work form the basis
for the range of concern suggested later in this report.
*Carbonyl Sulfide has a typical sulfide odor similar to
hydrogen sulfide. A fifty minute exposure to 6,000 ppm
(14,700 mg/m^) can cause death. One rich-malfunctioning
3-way catalyst vehicle tested for COS yielded approximately
20% as much COS as H2S.
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II. General Information on Hydrogen Sulfide
Hydrogen sulfide (H-S) is a colorless gas having an odor of
rotten eggs. It can result in severe toxic effects if
inhaled at concentrations greater than about 200 ppm (260
ing/m ), and various lesser effects at lower concentrations
as detailed in the health effects section.
The gas must be handled carefully because of its toxic
properties (particularly dangerous because it may temporarily
desensitize the olfactory nerves thus making it impossible to
sense its presence), and its explosive tendencies (low
ignition temperature of 260°C and wide flammability range
from 4.3 to 44% by volume in air).
Hydrogen sulfide reacts rapidly with ozone or NC^ to
produce SO-. Any continued presence or accumulation in a
strongly oxidizing atmosphere is unlikely. Hydrogen sulfide
is also subject to photodissociation. Therefore, in the air
hydrogen sulfide is only likely to accumulate at night or in
winter, even if it were emitted in substantial quantity.
The gas results from the decomposition of metal sulfides and
albuminous matter and is found in the areas of mineral
springs, sewers, and in some mines where it is referred to as
"stink damp". Hydrogen sulfide also is a by-product of
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several industrial processes, including synthetic rubber,
viscose rayon, petroleum refining, dyeing, and
leathertreating operations. In the laboratory, H2S usually
is prepared by treating a sulfide with an acid, such as iron
pyrites and HC1, or by heating thioacetamide, CH3C(S)NH2.
In an automotive system, hydrogen sulfide is formed from fuel
sulfur compounds undergoing reactions in a reducing
atmosphere in the catalyst system. These reducing conditions
occur when the fuel/air mixture is rich, such as during a
cold start-up, a high acceleration rate, or at idle
immediately following deceleration from a high speed cruise.
Under these conditions the presence of an oxidation or three
way catalyst tends to increase the formation of hydrogen
sulfide, especially during the last condition above: idle
following deceleration from a high speed.
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III. Legislative 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:
202 (a) (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
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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)
11 (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 enaine 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
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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 was
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
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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) (1) 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 Administrator) , 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 76) in June 1978, to
aid the manufacturers in complying with section 202 (a) (4) .
Manufacturers were 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.
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Another Advisory Circular (AC 76-1) was issued in November of
that year continuing these procedures for 1980 and later
model years. At that time EPA began work to develop and
implement a methodology which would provide a preliminary
assessment of potential mobile source unregulated pollutant
hazards in order to assist the manufacturers in deciding
which, if any, unregulated pollutants are of particular
concern.
Up to this time several preliminary assessments have been
made covering sulfuric acid, hydrogen cyanide, and ammonia.
In each of these cases the preliminary assessment found no
reason for suspecting a public health problem from the
current fleet emissions of these pollutants, and recommended
low levels of monitoring work be done to be sure that new
vehicle/emission control system configurations did not result
in greatly increased emissions.
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IV. 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 explained 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" (2) . 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 effort. 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.
Health effects literature searches have been conducted by MRI
in an attempt to aid EPA in suggesting a range of concern for
various selected pollutants. The upper level of the range
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will be that value above which the studies show that the
pollutant causes so great a health risk as to strongly
suggest that it be avoided. The lower value of the range
will be the lowest level at which there is some suggestion of
adverse physiological effects. The region between these
suggested limits will be termed the "ambient air range of
concern", indicating the bounds of uncertainty regarding
evidence of adverse physiological effects caused by exposure
to various concentrations of hydrogen sulfide. Any
technology whose emissions convert to ambient air
concentrations within the range of concern should 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 above the highest value of
the range should be considered "high risk" with respect to
human health.
For the purpose of this report, this particular methodology
has been used to develop a suggested range of concern
specifically for motor vehicle emissions of hydrogen sulfide.
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V. Vehicle Emissions of Hydrogen Sulfide
Hydrogen sulfide exhaust emissions have been measured for a
variety of vehicle types. The EPA recommended procedure for
this measurement is described in an EPA report entitled,
"Analytical Procedures for Characterizing Unregulated
Pollutant Emissions from Motor Vehicles" (10). This basic
procedure was used to obtain the H2S emission data in this
report. Small amounts of H_S have been measured in the
exhaust of gasoline-fueled vehicles equipped with either
oxidation or three-way catalysts under normal operating
conditions, at levels between 0.0 and 1.5 mg/mile. Under
malfunction conditions, however, these emissions can increase
considerably. A reported emission rate for a malfunctioning
vehicle operating with a 3-way catalyst was as high as 8.2
mg/km or 13.2 mg/mile, for the sulfate emission test (SET)*
driving schedule (11).
Tests were run by EPA-ORD in order to evaluate the impact of
low ambient temperatures on 3-way catalyst-equipped vehicle
emissions during normal operation (12). These studies showed
*Sulfate Emission Test, also known as the Congested Freeway
Driving Schedule (CFDS) , is a driving cycle with a 35 mph
average speed designed to represent driving on congested
freeways.
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Table I
Hydrogen Sulfide Emission Factors9
Number
Vehicle Category of Tests
Light Duty Diesel Vehicles0
Light Duty Diesel Trucks0
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; no air pump
3-way Plus Ox. Cat.; air pump
Light Duty Gasoline Truck6
Non-Catalyst, air pump
Catalyst, no air pump
2
1
0
33
11
35
24
22
23
0
0
Hydrogen
Sulfide
(mg/mi) SET
Schedule
Average
0.0
0.0
0.0
0.00
0.00
0.07
0.01
0.27
0.00
0.00
0.07
Malfunction
Worst Case
Average13
0.0
0.0
0.0
0.00
0.22
3.78
5.94
7.13
5.86
0.22
3.78
Heavy Duty Gasoline Trucksf 0 0.00 0.88
References appendix c of 13, 14, and 15; appendix B of 16; 17.
bAverage of 2 or 3 replicates of worst case test configuration.
°Below minimum limits of detection (FTP) . No data available
on sulfate emission test cycle.
tested, but assumed insignificant due to light duty data.
eSame as Light Duty Gasoline Vehicles.
fDue to a lack of sufficient data, this value is assumed to he
the same as that given for non-catalyst, light duty gasoline
vehicles with air, adjusted for approximate differences in fuel
consumption.
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that H_S emissions for the most part were not significantly
affected by low ambient temperature operation. Of the four
vehicles tested, one (Chevrolet Caprice) showed significant
change due to the low test temperature, and this was mainly
due to the cold-start portion of the test. For this first
portion of the test, the H2S emissions at the lower test
temperature (60°F) were about 20 mg/mile as compared to 0.02
mg/mile at the higher (normal) test temperature (81°F). For
the complete Federal Test Procedure, the maximum observed
H2S emission level was 4.21 mg/mile, which was at 60°F for
the Chevrolet Caprice. Following are descriptions of other
data taken into account in the calculation of fleet average
H^S emissions.
Malfunction Conditions
Average H2S emission factors for various vehicle types were
collected from several available sources. The values
obtained are listed in Table I. These emission factors were
compiled for the SET driving schedule, unmodified mode (i.e.
properly tuned vehicle), as well as for various malfunction
modes (when such data were available). Since the available
data for some technologies list both an unmodified and a
malfunction emission value, the final, average emission
factor was weighted such that the value is 75% of the
unmodified emission rate plus 25% of the malfunction rate.
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This calculation was based on the assumption that 25% of the
vehicle fleet operates in some malfunction mode (i.e., rich
idle, misfire, high oil consumption, etc.) at any given time
(18). Further work may identify a more accurate percentage.
The emissions found for the malfunction mode are especially
important to this effort due to the fact that H2S emissions
tend to increase under malfunction conditions. Maximum
emission levels have been listed below for three vehicle
categories.
Maximum Reported t^S Emission Levels under Malfunction Modes
(Highest Values Reported From Any Source on Any Single Test)
Light Duty
Vehicle Category mg/mile References
non-catalyst SET 0.29 (13, Table C-2)
FTP 0.82 (13, Table C-2)
oxidation catalyst SET 7.82 (13, Table C-12)
FTP 1.21 (13, Table C-150)
3-way catalyst SET 13.24 (11, Table IV -34)
FTP 9.57 (14, Table C-12)
The reported emissions for the 3-way catalyst vehicles under
malfunction conditions are higher than those of the other two
categories, and they are also much higher than any of the
vehicle categories listed in Table I.
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Driving Cycles
The driving cycles used in this report were the Sulfate
Emission Test (SET) and idle testing. The results available
for the Federal Test Procedure (FTP) were generally similar
to SET values, and the Highway Fuel Economy Test (HFET)
results were slightly lower.
It may be more appropriate to choose driving cycles which
would specifically simulate those scenarios under
investigation (enclosed spaces, street canyons, etc.). At
present, however, such data exist only for the garage
scenarios (idle test data) . For the most part the standard
test cycles provide only rough approximations of the driving
that occurs in the different scenarios examined in this
report. It is not known at this point what percent of error
is introduced by using these approximations.
Available I^S idle emissions data were used to estimate
F^S exposures in parking garage situations, and will be
discussed later in this report. One study by GM (5)
investigated idle sulfide emissions as a function of
oxidation catalyst temperature and air/fuel ratio. It was
found that the mixture had to be richer than the correct
setting, and catalyst temperature needed to be above 570°C to
result in any detectable HjS formation (greater than 0.05
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ppm). Obtaining this condition required cruising the car at
96 km/hr (60 mph) for seven minutes (during which no
detectable H2S was emitted) and then decelerating to idle
for the sample collection. This would be more representative
of a situation like a freeway off ramp rather than a cold
start in a garage.
Fleet Average Emissions
Using the average H2S emission factor data presented in
Table I, it is possible to calculate a fleet average emission
factor. The information necessary to make these calculations
is listed in Table II. A fraction of the vehicle miles
traveled (VMT) is listed for each vehicle class. These data
were derived from information presented in the Pedco Report
of 1978 (19) , and the EPA report, "Mobile Source Emission
Factors: For Low Altitude Areas Only" (20). Each vehicle
class VMT fraction is multiplied by the corresponding
emission factor for that class, giving a fraction quantity of
pollutant emitted from a particular vehicle category in
comparison to other vehicle categories in the fleet. The EF
X VMT fractions for each vehicle class are calculated and
then summed to obtain a total fleet average. For hydrogen
sulfide emissions, this value is 0.03 mg/mile. This average
takes into account only those vehicle classes listed in Table
II. Of course, should any of these categories change, so
would the total fleet average.
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It is difficult to predict exactly what percentage of vehicle
categories will make up the entire fleet at any one time.
The most severe case, with respect to any pollutant emission,
would be that case in which the entire vehicle fleet was
comprised of all of the highest emitting technologies. In
order to account for differing proportions of the highest
H-S emitting technologies, Table III was put together.
The emission levels presented in Table III reflect real and
hypothetical situations in which different percentages of the
vehicle fleet consist of the highest emitting technologies.
In reading Table III, it should be noted that it presents not
only different emission control technology percentages, but
also different malfunction percentages. The last entry in
this table, being the worst case examined, tends to overstate
the emissions that could actually occur in the future, since
it is highly unlikely that catalyst-equipped gasoline
vehicles would replace all light and heavy duty diesels.
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Table II
Example Calculation of
Fleet Average Emission Factor - Hydrogen Sulfide
(Sulfate Emission Test Cycle)
1981 Fleet, No Malfunction
Vehicle Class
Light Duty Diesel Vehicles
Light Duty Diesel Trucks
Heavy Duty Diesel Trucks
Fraction3
VMT
0.015
0.002
0.027
Emission
Factor0
(mg/mile)
0.0
0.0
0.0
EF x VMT
Fraction
0
0
0
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
0.147
0.098
0.289
0.261
0.012
pump 0.008
0.096
0.010
0.00
0.00
0.07
0.01
0.27
0.00
0.00
0.07
0.000
0.000
0.020
0.003
0.003
0.000
0.000
0.001
Heavy Duty Gasoline Trucks
0.035
0.00
0.000
Total Fleet Average
0.03 mg/mile
aBased on 1978 data for fraction of VMT as a
vehicle age.
DFrom Table I.
function of
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Table III
Hydrogen Sulfide - Fleet Average Emissions9
SET Driving Schedule, mg/mile
Current (1981) Fleet 0.03
Current (1981) Fleet
With 25% Malfunction 0.75
@ 2.89 mg/mile
100% of Fleet
With 3-Way Catalysts0 0.27
100% of Fleet
With 3-Way Catalysts0 1.99
25% of them Malfunctioning
@ 7.13 mg/mile
aBased on emissions in Table I, and fleet mix from Table II.
^Hypothetical "worst" case situation in which all light and
heavy duty vehicles on the road emit H2S at the highest
light duty rates from Table I.
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VI. Hydrogen Sulfide Ambient Air Concentrations
The H-S emission factor information provided in Tables I
through III can be used in conjunction with the modeling
techniques developed by Southwest Research Institute (SwRI)
(see Reference 2) , in order to calculate the ambient air
concentrations produced by varying levels of H2S vehicle
emissions for different exposure situations. Future work may
identify other scenarios which would also be appropriate for
the assessment of human exposure to exhaust pollutants, but,
for this task, only five exposure scenarios were
investigated: personal garages, parking garages, roadway
tunnels, street canyons, and urban expressways. A typical
and severe case situation was developed for each of these
scenarios. Each situation has been considered separately,
and, therefore, no cumulative effects have been determined at
this point. Reference (2) discusses the reasoning behind
using these specific scenarios as well as the information
used in the determination of the modeling techniques.
Table IV presents ambient air concentrations of hydrogen
sulfide, as a function of vehicle emissions, for seven
ambient situations. These calculations are based on the
relationship of emissions to ambient concentrations for each
scenario as shown graphically in Figure 1. Garage scenarios
are not included in Table IV, but are described in the text
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Table IV
Ambient Air Scenarios
Hydrogen Sulfide Concentrations3,
Current
Fleet
Scenario13
Roadway Tunnel
Typical
Severe
Expressway
Typical
Severe
Close
Proximity
Street Canyon
Typical
Severe
Current
Fleet
25%
Malfunction
Entire
Fleet
3-Way
Catalysts
Entire Fleet
3-Way Catalyst
25% Malfunction
0.03
0.09
0.004
0.02
0.003
0.001
0.01
0.84
2.14
0.09
0.38
0.08
0.03
0.21
0.30
0.77
0.03
0.14
0.03
0.01
0.08
2.23
5.68
0.25
1.01
0.21
0.08
0.56
aBased on fleet average emissions from Table III. Note:
These numbers are ug/nH, not mg/m^.
bFor garage scenarios refer to text and Table V.
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because idle/very low speed emissions of H2S have been
found to be negligible.
Each scenario is intended to represent a specific type of
situation. The typical personal garage situation represents
a 30 second vehicle warm-up time and the severe situation
simulates a five minute vehicle warm-up time. Both of these
cases, of course, take place within a residential garage, and
are intended to correspond to summer and winter conditions,
respectively.
The typical parking garage case simulates an above the
ground, naturally ventilated garage in which it is assumed
that a vehicle spends an equal amount of time on both the
parking level and ramp level. The severe case represents an
underground garage wherein the exposed population is assumed
to be at parking level five (lowest level) . It is also
assumed that this exposure occurs 20 minutes after a major
event in which the parking structure is emptying from an
essentially full condition. The initial concentration of
H2S is assumed to be low (0.001 mg/m ).
In order to more closely assess public exposure to H-S in
garage situations, idle emissions data were collected from a
limited number of vehicles. One study using experimental
three way catalysts of widely varying composition found idle
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H..S emissions ranging from 0.0 - 1.2 mg/minute under
malfunction conditions (11). More recently, six production
vehicles were tested to provide more reliable data regarding
in-use vehicle operation. This testing included a 1970
non-catalyst vehicle, 1978 and 1980 oxidation catalyst
equipped vehicles, 1981 and 1982 three way catalyst equipped
vehicles, and a 1981 diesel vehicle. No ^S emissions were
detected from any of these vehicles during idle or very low
speed testing under normal or malfunction conditions (24).
In light of these findings for production vehicles, there
seems to be no cause for concern regarding hydrogen sulfide
emissions in personal or public garages. However, it should
be noted that these data are from a sampling of only six
vehicles, and in a personal garage, it would only take one
vehicle producing hydrogen sulfide to create a potential
health problem.
Two specific tunnel designs were chosen to estimate the two
roadway tunnel cases. A newly designed, two lane roadway
tunnel, with moderate traffic flow, is used for the typical
condition, while an old design, heavily-traveled roadway
tunnel is used for the severe condition.
The street canyon situations are simulated by examining the
parameters of two street canyons. The most sensitive
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parameter in this model appears to be the number of traffic
lanes within the canyon. The typical condition is calculated
for a two lane street canyon with a traffic load of 800
vehicles per hour and a sidewalk location of the exposed
population. The severe condition is based on a six lane
street canyon with a 2400 vehicles per hour traffic load, and
the exposed population is located inside the vehicles.
Three different cases were considered in order to cover the
possible range of exposures in an expressway situation. 1)
The off road case estimates an exposure involving a close
proximity to the highway (i.e., living or working close to a
heavily-traveled freeway). This case is calculated on a
short term basis for a distance of 50 meters downwind of the
roadway. 2) The typical, on road exposure is based on a four
lane expressway with a traffic load of 1400 vehicles per hour
and a westerly wind (perpendicular to roadway) of 1.0
meter/second. In this situation, the exposed population is
located inside the vehicle. 3) The severe case represents a
heavily-traveled (3600 vehicles/hour), ten lane freeway with
a 1.0 meter/second westerly wind (perpendicular to roadway),
and an in-vehicle location of the exposed population.
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30
VII. Hydrogen Sulfide Health Effects
A literature review on the health effects of hydrogen sulfide
was performed as an input to the determination of a suggested
range of concern for mobile source emissions of this compound
(3,21). The specific health effects that were found included
irritations of the eyes and respiratory tract, dizziness,
nausea and headaches of various degrees depending on the
exposure level and duration. Chronic exposures resulted in
more adverse effects than acute exposures for a given
exposure level.
Although it would be more appropriate to consider exposure
concentrations relative to their corresponding exposure times
for each resulting health effect, this degree of detail was
not feasible with the data available. The determination of
the range of concern was based primarily on acute human
experimental studies, since these were thought to most
closely simulate the exposure situations examined in this
report.
The literature search reveals an epidemiological study (22)
which shows that a chronic exposure concentration as low as
0.05 mg/m caused a 50% higher morbidity rate as well as
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31
headaches, weakness, nausea, and vision problems in a group
of apartment house residents. This exposure, however, was
confounded with hydrocarbon exposure. Also, the control
group was not specified except that they did not use gas heat
(which was the source of H2S and HC) , so there may have
been other variables besides the H2S and HC exposure.
There is also a study done in an occupational exposure
setting involving babies whose nursing mothers worked in a
viscose (rayon) shop. During nursing these babies were
exposed to hydrogen sulfide from the mothers' clothing at
concentrations ranging from 0.028 - 0.055 mg/m . Compared
to babies whose mothers worked in other shops without H-S
exposure, these babies were more poorly developed, vomited
more frequently after feeding, and were more susceptible to
severe infectious diseases (23) .
The TLV* for hydrogen sulfide is 14 mg/m , which is
suggested as the upper limit for the range of concern for
healthy workers and similar people. However, the above data
on babies indicate that they constitute a more susceptible
subgroup. Therefore, 0.03 mg/m could be considered the
upper limit for a range of concern for babies.
*TLV - Threshold Limit Value set by the American Council of
Governmental Industrial Hygienists for 8 hr/day, 40 hr/wk
exposure of healthy workers.
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32
Data concerning less severe exposures indicate that the odor
threshold ranged from 0.0007 to 0.5 mg/m . The level not
affecting eye sensitivity to light was 0.008 to 0.010
mg/m , while light sensitivity-related eye responses were
seen at 0.012 - 0.013 mg/m .
It is not known whether these eye responses, in themselves,
could be considered adverse effects or simply changed
physical parameters. Taking this into account, along with
the higher susceptibility of babies mentioned above, the
suggested lower limit of the range of concern is 0.015
mg/m .
Between the chosen limits of this range, there are a few data
points, some of which show adverse effects and some that do
not. Therefore, this region has been termed the "range of
concern" for hydrogen sulfide concentrations in the ambient
air.
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33
VIII. Determination of the Range of Concern and Conclusions
According to the methodology described earlier in the report,
the lower and upper levels suggested as the health effects
range of concern are compared to the mobile source situations
to calculate a corresponding 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 suggested mobile source range.
of concern for hydrogen sulfide emissions can be estimated
for the different mobile source situations. Table V lists
the vehicle emission factors which correspond to the high
3 3
(14.0 mg/m ) and low (0.015 mg/m ) portions of the range
of concern for hydrogen sulfide. Inspection of this table
shows that the differences among scenarios result in a wide
range of emission factors corresponding to this suggested
ambient air range of concern. More importantly, it shows
that none of the scenarios studied are expected to have
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34
hydrogen sulfide concentrations within, let alone above, the
suggested range of concern.
The findings for - low ambient temperature conditions indicate
a possible large increase in hydrogen sulfide emissions for
certain emission control systems. Considering that this was
found at a relatively mild temperature (60°F) , additional
lower temperature testing may be worthwhile. The severe
personal garage scenario would be the most likely situation
for any problem to show up, since in that situation it would
only take one vehicle emitting 0.2 mg/min. hydrogen sulfide
to enter the range of concern.
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35
Table V
Hydrogen Sulfide
Emission Factors Required to Result in
Exposure Limits for the Ambient Air Range of Concern
Ambient Air
Scenario3
Emission Emission
Factor (mg/mile) Factor (mg/mile)
corresponding corresponding
to a 0.015 to a 14.0
^ exposure mg/m^ exposure
Maximum
Conceivable
Fleet Avg.
Emissions0
(mg/mile)
Street Canyon -
Typical
Expressway -
Typical
Expressway -
Close Proximity
Street Canyon -
Severe
Expressway -
Severe
Roadway Tunnel -
Typical
Roadway Tunnel -
Severe
Personal Garage -
Typical0
Parking Garage -
Typical0
Parking Garage -
Severe0
Personal Garage -
Severe0
479.3
123.0
88.5
44.9
30.3
13.4
5.3
1.9
1.7
0.3
0.2
aln order of increasing mg/m-3
(or Ig/min) emission rate.
DFrom last column of Table III
malfunction.
°Emission factors are given
exposures.
dThe only vehicle to produce a
447,300
114,800
81,900
41,860
28,280
12,460
4,900
1,770
1,588
252
204
concentration
: All 3-way
in mg/minute
ny measurable
1.99
1.99
1.99
1.99
1.99
1.99
1.99
0.00d
0.00d
0.00d
0.00d
for 1 g/mile
catalyst, 25%
for garage
H?S at idle
(1.2 mg/min) was a malfunctioning Volvo with an unusual
experimental catalyst, rather than the standard catalysts
actually used on production vehicles.
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37
References
1) "Clean Air Act as Amended August 1977," Public Law
88-206, 89-272, 89-675, 90-148, 91-604, 92-157, 93-319,
95-95, 95-190.
2) "An Approach for Determining Levels of Concern for
Unregulated Toxic Compounds from Mobile Sources," R.
Garbe, EPA Technical Report No. EPA/AA/CTAB/PA/81-2, July
1981.
3) "Hydrogen Sulfide Health Effects," EPA report no.
EPA-460/3-81-028, by Midwest Research Institute under
contract no. 68-03-2928, EPA Project Officer Robert Garbe.
4) "Emission of Sulfur Bearing Compounds from Motor Vehicle
and Aircraft Engines," EPA report no. EPA-600/9-78-028,
by J, Kawecki, Biospherics Inc., contract no.
68-02-2926, August 1978.
5) "Sulfide Emissions from Catalyst-Equipped Cars," S.
Cadle, P. Malawa, Environmental Science Department,
General Motors Research Laboratories, 1977.
6) "Measurements of Unregulated Emissions from General
Motors' Light Duty Vehicles," S. Cadle, G. Nebel, and R.
Williams, SAE Paper 790694, June 1979.
7) "Hydrogen Sulfide Formation Over Automotive Oxidation
Catalysts," G. Barnes, J. Summers, SAE Paper 750093,
February 1975.
8) Van Nostrand's Scientific Encyclopedia, Fifth Edition, D.
Considine, Ed., 1976, P. 1315.
9) "Characterization of Exhaust Emissions from Passenger
Cars Equipped with Three-way Catalyst Control Systems,"
L. Smith, F. Black, SAE Paper 800822, June 1980,
10) "Analytical Procedures for Characterizing Unregulated
Pollutant Emissions from Motor Vehicles," EPA report no.
600/2-79-017.
11) Final Report for EPA Contract no. 68-03-2485 by Exxon
Research Corp. on Unregulated Emissions from
Malfunctioning 3-way Catalysts on a 1977 Light Duty
Gasoline Vehicle.
12) "Impact of Low Ambient Temperature on 3-way Catalyst Car
Emissions," J. Braddock, SAE Paper 810280, February 1981.
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38
13) "Regulated and Unregulated Emissions from Malfunctioning
Oxidation Catalyst Automobiles," EPA report No.
EPA-460/3-81-003, by Southwest Research Institute,
Contract no. 68-03-2499, January 1980.
14) "Regulated and Unregulated Exhaust Emissions from
Malfunctioning Three-way Catalyst Gasoline Automobiles,"
EPA report no. EPA-460/3-80-004, by Southwest Research
Institute, contract no. 68-03-2588, January 1980.
15) "Regulated and Unregulated Exhaust Emissions from a
Malfunctioning Three-way Catalyst Gasoline Automobile,"
EPA report No. EPA-460/3-80-005, by Charles Urban,
Southwest Research Institute, contract no. 68-03-2692,
January 1980.
16) "Unregulated Exhaust Emissions from Non-Catalyst Baseline
Cars Under Malfunction Conditions," EPA report no.
EPA-460/3-81-020, by Charles Urban, Southwest Research
Institute, contract no. 68-03-2884, May 1981.
17) Nissan submission for the EPA 1981 Status Report, Chapter
II. G., "Unregulated Emissions."
18) "Inspection and Maintenance for 1981 and Later Model Year
Passenger Cars," SAE Paper 810281, D. Hughes, February
1981.
19) "Air Quality Assessment of Particulate Emissions from
Diesel-Powered Vehicles," PEDCo Environmental, Inc., EPA
Contract No. 68-02-2515, Project Officer, J. Manning,
March 1978.
20) "Mobile Source Emission Factors: For Low Altitude Areas
Only," EPA report no. EPA-400/9-78-006, March 1978.
21) "Health Effects of Hydrogen Sulfide, A Literature
Review," Conducted as part of an evaluation of the
health effects of auto emissions from malfunctioning
3-way oxidative catalysts, G. Fairchild, DVM, Biomedical
Research Branch, Clinical Studies Division, U.S. EPA.
22) "Basic Principles for the Determination of Limits of
Allowable Concentrations of H2S in Atmospheric Air," R.
Loginova, in: Limits of Allowable Concentrations of
Atmospheric Pollutants III, V. Riazanov, Ed., 1957.
23) "Establishing Maximum Allowable Concentration of Hydrogen
Sulfide," Atomospheric Air, 3:98-10., L.F. Glebova, 1960.
24) "Unregulated Emissions for Vehicles Operated Under Low
Speed Conditions," Lawrence R. Smith, Southwest Research
Institute, Draft Final Report for EPA Contract No.
68-03-3073 Work Assignment 4, October, 1982.
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