EPA/AA/CTAB/PA/82-7
Technical Report
Determination of a Range
of Concern for Mobile
Source Emissions of
Hydrogen Sulfide
by
Craig A. Harvey
January, 1982
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 Source Air Pollution Control
Emission Control Technology Division
Control Technology Assessment and Characterization Branch
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 range of concern for hydrogen sulfide (l^S)
emissions from mobile sources. 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 as to what emission levels will be used as the basis for the
evaluation of current and future technologies, a methodology was developed
in order to bracket a range of concern for various unregulated pol-
lutants^). This paper coordinates the efforts from two EPA contracts in
order to use this 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). In conjunc-
tion 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. This search
provides adequate evidence to support the chosen limits of the range.
The results of this analysis provide a range of concern for ambient hydrogen
sulfide concentrations of 0.03 mg/m^ to 14.0 mg/m^. This corresponds to
motor vehicle emission levels of from 10.5-4,900 mg/mile to 958.5-447,300
mg/mile on the road and 0.04-204 mg/min to 3.8-1,770 mg/min for garages,
depending on the type of scenario chosen to represent public exposure.
Under non-malfunction conditons or when the malfunction does not cause a
rich mixture, high catalyst temperature and low exhaust space velocity, the
resulting I^S emissions are negligible (below the range of concern for any
scenario).
The current estimated vehicle fleet emission factor for hydrogen sulfide,
0.34 mg/mile, is well below the lowest moving vehicle scenario range of
concern of 10.5 mg/mile. For moving vehicles the controlling (lowest)
ranges are those of the roadway tunnel scenarios. For this to result in
ambient I^S concentrations within the range of concern, it would require
most of the vehicles to be malfunctioning in a way that would cause high
H2S emissions (over 10.5 mg/mi).
Under certain malfunction conditions, idling catalyst-equipped vehicles can
emit H2S at approximately 1.0 mg/minute. In personal or parking garage
scenarios this would result in I^S concentrations within the range of con-
cern for severe situations. For this to present a possible problem in a
parking garage scenario, a large percentage (50%) of the cars would have to
be malfunctioning in this manner. However, for a severe case personal
garage scenario, it would only take the one vehicle malfunctioning in this
manner to cause a chronic repetitive exposure of the driver to a level of
HoS within the range of concern. Therefore, closer scrutiny of idle H2S
emissions is recommended to determine if production vehicle/catalyst systems
could yield l^S levels as high as those reported here (which were from
experimental catalysts).
* Numbers in parentheses denote references listed at end of report.
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I. Introduction
Emissions from gasoline engine vehicles have been characterized by industry,
government and private researchers for many years. While federal motor
vehicle regulations have been in effect since 1968 for HC, CO and NOx, there
are a number of unregulated pollutants which 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 can
emit significantly more sulfuric acid than non-catalyst vehicles (4).
Hydrogen sulfide is an unregulated pollutant emission that has been found in
various concentrations in some automotive emission tests (4,5,6,7). Due to
its toxic properties and its disagreeable rotten-egg odor, tests have been
conducted to characterize H2& emissions as a function of driving cycle,
emission control system, and sulfur content of fuel. The results of these
tests along with health effects test data, as summarized later in this
report, are used to determine the conditions under which automotive t^S
emissions could be of concern with respect to health and welfare.
Barnes and Summers of General Motors reported in 1975 that three conditions
favored the formation of H2S by Pt/Pd oxidation catalysts: (1) rich
air/fuel ratio (i.e., a reducing condition); (2) low exhaust space
velocity; and (3) high catalyst temperature. 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 H2& and COS. It should be noted that the
reducing conditions that favor sulfide formation do not favor sulfate
formation.
In the interest of establishing a range of concern for levels of H2S in
motor vehicle exhausts, Midwest Research Institute (MRI) compiled
information on the health effects of hydrogen sulfide at different
concentrations^). The results of that work form the basis for the range of
concern determined later in this report.
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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).
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(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
manufacturers in complying with section 202 (a)(4). Manufacturers were
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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.
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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 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",
indicating scattered data points providing evidence of adverse physiological
effects caused by exposure to various concentrations of hydrogen sulfide.
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
hydrogen sulfide.
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IV. General Information
Hydrogen sulfide (t^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 (280 mg/m^), and various lesser effects at lower
concentrations as detailed in the health effects section.
The gas must be handled carefully because of (1) its toxic properties
(particularly dangerous because it may temporarily desensitize the olfactory
nerves thus making it impossible to sense its presence), and (2) its ex-
plosive tendencies (low ignition temperature of 260 °C and wide flammability
range from 4.3 to 44% by volume in air).
Fluorine, chlorine, bromine and iodine react chemically with H2S to form the
corresponding halogen acid. Metal sulfides of varying solubilities are formed
when H2& is passed into solutions of the heavy metals, such as Ag, Pb, Cu,
and Mn. This reaction is responsible for the tarnishing of Ag and is the
basis for the separation of these metals in classical wet qualitative
analytical methods. Hydrogen sulfide also reacts with many organic com-
pounds .
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." ^S also is a by-product of several
industrial processes, including synthetic rubber, viscose rayon, petroleum
refining, dyeing, and leather-treating 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> Three processes are used
industrially to produce H2S in large quantities:
(1) treating a sulfide with an acid,
2NaHS + H2S04 -» 2H2S
(2) reacting sulfur with an alkali,
4S + 2NaOH + 2H20 -
(3) directly reacting sulfur with hydrogen,
S + H2 -» H2S.
Large quantities of by-product ^S usually are converted into elemental
sulfur or ^804.
Industrial uses for ^S incude (1) the preparation of sulfides, such as
sodium sulfide and sodium hydrosulfide, (2) the production of sulfur-bearing
organic compounds, such as thiophenes, mercaptans, and organic sulfides, (3)
the removal of Cu, Cd, and Ti from spent catalysts where the gas acts to form
a precipitate, (4) the formulation of extreme-pressure lubricants, and (5) the
preparation of rare-earth phosphors used in color TV tubes(8) .
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In an automotive system, hydrogen sulfide is formed by the reduction of fuel
sulfur as it passes through the exhaust system. Three-way catalyst systems
oxidize the hydrocarbons and carbon monoxide to carbon dioxide and water, as
do conventional oxidation catalysts; however, at the same time they reduce
NOx to nitrogen. This reduction process provides a pathway for the
formation of other reduced exhaust species such as ammonia, cyanide, organic
amines, hydrogen sulfide and organic sulfides that would not be expected in
significant quantities from conventional oxidation catalysts(9).
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V. Emission Factors
H2S 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 is what
was used to obtain all the H2& emission factors in this report. Small
amounts of H2S 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 mal-
function conditions, however, these emission rates can increase consider-
ably. 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 car emissions (12). These studies
showed that H2S emissions for the most part were not significantly
affected by subambient temperature operation. Of the four vehicles tested,
only 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 FTP, the maximum
observed H2S emission rate was 4.21 mg/mile, which was at 60 °F for the
vehicle mentioned above .
Average l^S emission factors for various vehicle types were collected from
several available spurces. The values obtained are listed in Table I.
These emission factors were compiled for the SET driving schedule, un-
modified mode (i.e. properly tuned), 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. This
calculation was based on the assumption that 25% of the vehicle fleet
operates in the malfunction mode (i.e., rich idle, misfire, high oil
consumption, etc.) at any given time (18). Further work may identify a more
accurate percentage.
*Also known as the Congested Freeway Driving Schedule (CFDS), which is a
driving cycle with a 35 mph average speed designed to represent driving on
congested freeways.
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The emission factors obtained 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 rates have been
listed below for three vehicle categories.
Maximum Reported H2S Emission Rates under Malfunction Modes
(Highest Values Reported From Any Source on Any Single Test)
Vehicle Category mg/mile
non-catalyst SET 0
FTP .08
oxidation catalyst SET 6.9
FTP 1.1
3-way catalyst SET 13.2
FTP 9.0
The reported emission factor for the 3-way catalyst vehicles under mal-
function conditions is higher than those of the other two categories, and it
is also much higher than any of the vehicle categories listed in Table I.
The driving cycles considered in this report were the Federal Test Procedure
(FTP), the Sulfate Emission Test (SET), and idle testing. The results
available for the Highway Fuel Economy Test were similar to SET values, but
were usually 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, data do not exist to permit use of
this approach for H2S. It is not known at this point what percent of
error is introduced by using emission factors from the standard test cycles.
Available t^S idle emissions data were used to estimate I^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 H2S formation
(greater than 0.05 ppm). Obtaining this condition required cruising the car
at 96 km/hr 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.
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
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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 totaled and then averaged to obtain a total fleet average. For
hydrogen sulfide emissions, this value is 0.34 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.
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 I^S emitting
technologies, Table III was devised. The emission factor values presented
here reflect hypothetical situations in which 25, 50, 75, and 100 percent of
the vehicle fleet is comprised of the highest emitting technologies. The
compiled emission factors listed in Table III will become an important tool
in comparing vehicle emissions to the range(s) of concern. In subsequent
steps, these values will be used to calculate ambient concentrations of
H2& for various fleet mixes of emission control technologies.
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VI. Hydrogen Sulfide Health Effects
A literature review on the health effects of hydrogen sulfide was performed
as an input to the determination of a range of concern for mobile source
emissions of this compound(3,21 ). A summary of this literature search is
included as an Appendix to this report.
As indicated in the methodology, in order to focus the health effects liter-
ature review, a preliminary range of ambient levels was selected to bracket
the region of uncertainty with respect to hydrogen sulfide health effects.
This range was determined to be 0.15 mg/m^ - 14.0 mg/m^ for l^S. The
lower end of this range was selected to approximate the lowest level at
which adverse physiological effects could be detected. The preponderance of
the evidence has shown little or no health effects at levels of hydrogen
sulfide below this, although upon investigation a few instances of adverse
reactions were found with chronic exposures as low as 0.05 mg/nH in adults
and 0.03 mg/nH in babies.
The upper level of the preliminary range was chosen to be the threshold
limit value (TLV) recommended by the ACGIH as 14 mg/m^ (9). Above this
level several studies had shown an adverse reaction in healthy subjects
which could be harmful under repeated exposure.
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. More
details of the relationship between health effects and exposures are in-
cluded in Section VIII, "Determination of the Range of Concern."
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VII. Hydrogen Sulfide Ambient Air Concentrations
The I^S emission factor information provided in Table I through III can be
used in conjunction wth 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 H^S vehicle emis-
sions for different exposure situations. Future work may identify other
scenarios which would also be appropriate for the assessment of human ex-
posure 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 de-
termination of the modeling techniques.
Table IV presents ambient air concentrations of hydrogen sulfide, as a
function of vehicle emission rates, for eleven ambient situations. The
vehicle emission rates correspond to those emission factors which were cal-
culated for the various combinations of fleet categories found in Table
III. This information will later be used to develop a plot which graphi-
cally represents the relationship between the emission factors for various
scenarios and ambient air concentrations.
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 essentially full. The initial concentration of H2S is
assumed to be low ( 0.001 mg/m^).
In order to more closely assess public exposure to I^S in a garage situ-
ation, idle emissions data were averaged from a limited number of sources.
Although there was deviation depending on catalyst composition and type of
malfunction, the available idle data indicate that vehicles with 3-way
catalysts, operating in the malfunction mode can emit t^S at rates ranging
as high as 0.5 - 1.2 mg/rain. For calculation purposes a rate of 1.0 mg/min.
will be assumed.
In a worst case situation, where 100% of the vehicle fleet consists of auto-
mobiles with 3-way catalysts, operating in the malfunction mode, the H2S
ambient air concentrations for each of the garage situations would be as
listed below. This, of course, might be a reasonable case for a personal
garage situation in which a person starts his vehicle, equipped with a 3-way
catalyst presently operating in the malfunction mode, in an enclosed garage.
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H?S Ambient Air Concentrations,
Emission Personal Garage Parking Garage
Fleet Make Up Factor Typical Severe Typical Severe
100% 3W 1 mg/min. 0.008 0.067 0.009 0.056
Since these values more accurately reflect the I^S vehicle emissions in an
actual garage situation, they should be used in the identification of those
scenarios which may be of most concern to public health, with respect to ex-
posure to H2S. Due to limited data, idle emission values can only be
evaluated for vehicles with 3-way catalysts (operating in the malfunction
mode). In the future, when more idle data have been collected, it may be
possible to evaluate other categories which would contribute to the vehicle
fleet make up.
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 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. The off road case estimates an ex-
posure 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. 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. 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 popu-
lation.
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VIII. Determination of the Range of Concern
The range of concern for hydrogen sulfide emissions from automobiles is de-
termined 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 IV) . Using the preliminary
range (0.15 mg/m3 - 14 mg/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 an epidemiological study (22) which shows that
a chronic exposure concentration as low as 0.05 mg/m3 caused a 50% higher
morbidity rate as well as headaches, weakness, nausea, and vision problems
in a group of apartment house residents.
There is also a study done in an occupational exposure setting involving the
babies of nursing mothers who 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/m3. Compared to
babies whose mothers worked in other shops without H2S exposure, these
babies were more poorly developed, vomited more after feeding, and were more
susceptible to severe infectious diseases.
Since the nature of the exposure to automobile generated t^S will not
likely be comparable to the above exposure in that the exposure will more
likely be of an acute or short term chronic nature (several hours per day
repeatedly as a maximum) , the upper level of the range of concern should be
set at 14 mg/m3. This exposure level corresponds to the TLV for hydrogen
sulfide as set by the ACGIH for 8 hr. per day/40 hr. per week exposure to
healthy workers.
Data concerning less severe exposures indicate that the minimum odor
threshold was 0.005 mg/m . The level not affecting eye sensitivity to
light was 0.008 to 0.010 mg/m3, while light sensitivity-related eye
responses were seen at 0.012 - 0.013 mg/m . Since 0.03 mg/m^ is the
lowest level at which any indications of adverse health effects were found,
this is the recommended lower limit of the range of concern.
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. This range can now be used in conjunction with the
emission factor data to graphically present the conversion of hydrogen
sulfide emissions to ambient air concentrations.
Once the literature search was completed and the appropriate information was
tabulated for hydrogen sulfide, a table was prepared compiling all the
information for the animal and human studies (3). These tables list the
studies according to the exposure concentration of hydrogen sulfide. Using
this health effects information along with the emission factor data pre-
sented in Table IV, graphs were composed representing the relationship
between ambient air concentrations, emission factors, and the various types
of public exposure situations (see Figures 2-6).
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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 hydrogen
sulfide can be estimated for the different mobile source situations. Table
V lists the vehicle emission factors which correspond to the high (14.0
mg/m^) and low (0.03 mg/m^) portions of the range of concern for hydro-
gen sulfide. Inspection of this table shows that the scenarios result in a
wide range of emission factors corresponding to the health effects range of
concern of 0.03 mg/nH to 14.0 mg/m^.
-------
-18-
Conclusions - Hydrogen Sulfide
1. The range of concern for ambient hydrogen sulfide concentrations is 0.03
- 14.0 mg/m^.
2. This range of concern corresponds to motor vehicle emission rates
ranging from 10.5 - 4,900 mg/mi to 958.5-447,300 mg/mile depending on
the scenario of interest.
3 At higher concentrations (above 0.05 mg/m^) the possible health ef-
fects range from minor eye and respiratory tract irritation to dizzi-
ness, nausea and headaches depending on degree of exposure and sus-
ceptibility.
4. With respect to the moving vehicle scenarios the controlling (lowest)
ranges are those of the roadway tunnel scenarios. Some malfunctioning
catalyst-equipped vehicles could emit t^S at a level within, but not
above, the range of concern for severe or typical tunnel scenarios. For
this to result in ambient l^S concentrations within the range of
concern, it would require most of the vehicles to be malfunctioning in a
way that would cause high t^S emissions (over 10.5 mg/mi).
5. The current estimated vehicle fleet emission factor for hydrogen
sulfide, 0.34 mg/mile, is well below the lowest moving vehicle scenario
range of concern of mg/mile.
6. Under certain malfunction conditions, idling catalyst-equipped vehicles
can emit I^S at approximately 1.0 mg/minute. In personal or parking
garage scenarios this would result in l^S concentrations within the
range of concern for severe situations. For this to present a possible
problem in a parking garage scenario, a large percentage (50%) of the
cars would have to be malfunctioning in this manner.
However, for a severe case personal garage scenario, it would only take
the one vehicle malfunctioning in this manner to cause a chronic
repetitive exposure of the driver to a level of t^S within the range
of concern. Therefore, closer scrutiny of idle t^S emissions is
recommended to determine if production vehicle/catalyst systems could
yield H2S levels as high as those reported here (which were from
experimental catalysts).
7. Under non-malfunction conditions or when the malfunction does not cause
a rich mixture, high catalyst temperature and low exhaust space
velocity, the resulting I^S emissions are negligible (below the range
of concern for any scenario).
-------
-19-
Table I
Hydrogen Sulfide Emission Factors®
Vehicle Category Hydrogen Sulfide (mg/mi) SET
Schedule Average
Light Duty Diesel Vehicles 0.0*
Light Duty Diesel Trucks 0.0*
Heavy Duty Diesel Trucks 0.0**
Light Duty Gasoline Vehicles
Non Catalyst; no air pump 0.00
Non Catalyst; air pump 0.02
Oxidation Catalyst; no air pump 0.31
Oxidation Catalyst; air pump 0.87
3-way Catalyst; no air pump 1.02
3-way Plus Oxidation Catalyst; air pump 0.44
Light Duty Gasoline Truck
Non Catalyst, air pump 0.02
Catalyst, no air pump 0.31
Heavy Duty Gasoline Trucks 0.08***
6References 13,14,15,16,17
* Below minimum limits of detection. (FTP)
** Not tested, but assumed insignificant due to light duty data.
***Due to a lack of sufficient data, this value is assumed to be the same as
that given for non-catalyst, light duty gasoline vehicles, adjusted for
approximate differences in fuel consumption.
-------
Table II
Fleet Average Emission Factors -Hydrogen Sulfide
(Sulfate Emission Test Cycle)
Vehicle Class
Light Duty Diesel Vehicles
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)
0.0
0.0
0.0
0.00
0.02
0.31
0.87
1.02
0.44
0.02
0.31
EF x VMT
Fraction
0
0
0
0.000
0.002
0.090
0.027
0.012
0.004
0.002
0.003
Heavy Duty Gasoline Trucks
0.035
0.08
0.003
Total Fleet Average
0.34 mg/mile
-------
-21-
Table III
Hydrogen Sulfide Emission Factor - Compiled
Fleet Category mg/mile
Fleet Average (FA) 0.34
75% FA + 25% OC* 1.2
50% FA + 50% OC 2.1
25% FA + 75% OC 2.9
100% OC 3.8
75% FA + 25% OC/3W+air* 1.7
50% FA + 50% OC/3W+air 3.1
25% FA + 75% OC/3W-air 4.5
100% 3W 5.9
1
' * I
75% FA + 25% 3W*** 2.0
50% FA + 50% 3W 3.7
25% FA + 75% 3W 5.4
100% 3W 7.1
* Light Duty Gasoline Vehicles, without air pump, with oxidation catalyst
under worst-case malfunction conditions.
** Light Duty Gasoline Vehicles, with air pump, with either oxidation
catalyst or three-way catalyst under worst-case malfunction conditions.
*** Light Duty Gasoline Vehicles, without air pump, with three-way catalyst
under worst case malfunction conditions.
NOTE; The malfunction emissions for this analysis are not the single one
test results reported earlier. They are the average results from several
test programs, the average being taken for those malfunctions producing the
highest H2S value.
-------
Table IV
Ambient Air Scenarios
Hydrogen Sulflde Concentrations
Enclosed Spaces
Street Canyon
Expressway
Fleet E
Make F
up n
Fleet Average
75% FA**
+25% OC***
50% FA
+50%OC
25% FA
+75% OC
100% OC
75% FA
+25%OC/3w+air@
50% FA
+50% OC 3W*air
+75% OC/3W+air
100% OC/3VH-air
75% FA
+25% 3W1
50% FA
+50% 3W
25% FA
+75% 3W
100% 3W
[mission Personal Garage*
'actor
ig/mlle typical severe
0.34
1.2
2.1
2.9
3.8
1.7
3.1
4.5
5.9
2.0
3.7
5.4
7.1
Parking Garage* Roadway
typical severe typical
.0004
.0013
.0024
.0033
.0043
.0019
.0035
.0051
.0066
.0023
- .0042
.0061
.0080
Tunnel
severe
.0010
.0034
.0060
.0083
.011
.0049
.0089
.013
.017
.057
.011
.015
.020
typical severe
(2)
(2)
.0001
.0001
.0001
.0001
.0001
.0001
.0002
.0001
.0001
.0002
.0002
.0001
.0004 •
.0007
.0010
.0013
.0006
.0010
.0015
.0020
.0007
.0012
.0018
.0024
on road on road
off road typical severe
.0001
.0002
.0004
.0005
.0006
.0003
.0005
.0008
.0010
.0003
.0006
.0009
.0012
(2)
.0001
.0003
.0004
.0005
.0002
.0004
.0005
.0007
.0002
.0005
.0007
.0009
.0002
.0006
.0010
.0025
.0033
.0015
.0027
.0039
.0051
.0017
.0032
.0045
.0062
** FA = fleet average.
*** OC - Light Duty Gasoline Vehicles - Oxidation Catalyst without air pump, worst case malfunction.
@ OC/3VH-air = Light Duty Gasoline Vehicles - Three-way + Oxidation Catalyst with air pump.
1 3W " Light Duty Gasoline Vehicles - Three-way Catalyst without air pump, worst case malfunction.
2 = Less than 0.00005
I
to
N)
I
-------
-23-
Table V
Hydrogen Sulfide
Emission Factors Required to Result in
Exposure Limits for the Ambient Mr Range of Concern
Ambient Air Scenario* Emission Factor (mg/mile) Emission Factor (mg/mile)
corresponding to a corresponding to a
0.03 mg/m^ exposure 14.0 mg/m^ exposure
Street Canyon - Typical 958.5 447,300
Expressway - Typical 246.0 114,800
Expressway - Close Proximity 177.0 81,900
Street Canyon - Severe 89.7 41,860
Expressway - Severe 60.6 28,280
Roadway Tunnel - Typical 26.7 12,460
Roadway Tunnel - Severe 10.5 4,900
Personal Garage - Typical** 3.8 1,770
Parking Garage - Typical** 3.4 1,588
Parking Garage - Severe** 0.5 252
Personal Garage - Severe** 0.4 204
* In order of increasing mg/m^ concentration for 1 g/mile (or Ig/min)
emission rate (excluding garage situations).
** Emission factors are given in rag/minute for garage exposures.
-------
Figure 1
Pollutant Concentrations va Emission Factors
I
-3-
Cv)
I
1*
i
4)
1
0
•rf
Jl
o
*»
E
0
0)
o
I.
0
•rf
E
v>
a
M
<
t~
z
UJ
m
<
1000 -
950 J
900 .
850 .
800 .
750 .
700 .
650 .
600 .
550 .
500 .
'
450 .
400 .
350 .
300 .
250 .
200 .
150 .
100 .
50 .
cal)
EMISSION FACTOR
-------
-25-
FIGURE2
PERSONAL PARKING GARAGE
c
o
E
O
••••.
I
E
O
o
o
UJ
i—»
DQ
EMISSION FACTOR (milliqrajaa/raile)
-------
-26-
FIGURE 3
PARKING GARAGE
c.
o
B
o
•t*'
o
o
O
O
C33
EMISSION FACTOR (milli3ram0/mile)
-------
-27-
FIGURE 4
ROADWAY TUNNEL
W 53
•—• •—•
EMISSION FACTOR (mi
-------
-28-
FIGURE 5
STREET CANYON
S H3 g
,_4 w—*
-------
-29-
953..
TUB..
o
4*
0
B
O
•«-•
1
0
o
c.
o
az
m..
a 23..
CQ
FIGURE e
EXPRESSWAY
KJ
£2
eg tn csa i
£5 O»S trt e
w—• •—« «—• w
EMISSION FACTOR
-------
-30-
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.
13) "Regulated and Unregulated Emissions from Malfunctioning Oxidation
Catalyst Automobiles," EPA report No. EPA-460/3-81-003, by Southwest
Research Institute, Contact 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.
-------
-31-
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., "Un-
regulated 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 mal-
functioning 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 Concen-
trations of H2S in Atmospheric Air," R. Loginova, in: Limits of Allow-
able Concentrations of Atmospheric Pollutants III, V. Riazanov, Ed.,
1957.
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-32-
TABLE S-2. SUMMARY OF HUMAN EXPERIMENTAL EXPOSURE TO H2S
Level
(mg/m3)
Exposure Table
Effects
3,499-
8,165
1,420-
4,700
994-
1,988
284-
568
0.20-
0.96
0.08-
0.50
0.27
0.15
0.1
0.031-
0.09
0.012-
0.03
Acute IV-1 Eye, nose, and mouth irritations, leading
to congestion and secretion. Higher ex-
posures also caused dizziness, trembling,
numbness, and heart palpitations. After-
wards, swollen and light-sensitive eyes,
headache, fatigue, diarrhea, and bladder
tenesraus lasting from several hours to a
day.
Acute IV-1 Irritation of eyes, nose, throat, and
trachea, leading to tearing, swelling, and
catarrh. Symptoms increased with increas-
ing time and concentration. Sometimes irri-
tation and headache continued for several
hours after exposure stopped.
Acute IV-1 Weak irritation of the eyes and throat at
the lower levels. At the highest level,
bronchitis, rhinitis, and heavy conjunc-
tivitis lasted up to 4 d.
Acute IV-1 No signs of irritation, as determined by
cursory observation and subjective reaction.
Acute IV-1 All people in the test group detected the
odor.
Acute IV-1 Range of odor thresholds within a group.
Acute IV-1 Range of odor thresholds within a group.
Acute IV-1 Threshold of objectionability (not odor).
Acute IV-1 Most people in the test group detected the
odor.
Acute IV-1 • Some of the people in the test group de-
tected the odor.
Acute IV-1 Range of odor thresholds within a group.
(continued)
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-33-
TABLE S-2. (concluded)
Level
(mg/m3)
0.012
0.026
0.012-
0.013
(2 studies)
0.010
(2 studies)
0.005-
0.009
Exposure
Acute
Acute
Acute
Acute
Table Effects
IV- 1 Odor was not detected.
IV- 1 Increased light sensitivity- related eye
responses .
IV-1 One study found significantly increased
light sensitivity-related eye responses.
The other study did not.
IV-1 Range of "calculated" odor thresholds
within several groups.
0.008
0.00067
Acute IV-1 No effect on the ability of the eye to
adapt to darkness.
Acute IV-1 Lowest concentration at which all subjects
recognized the odor.
-------
-34-
TABLE S-3. SUMMARY OF OCCUPATIONAL AND EPIDEMIOLOGICAL EXPOSURES TO H2S
Level
(mg/m3)
Exposure
time Table
Effects
S 28.4-
> 852
(and low
concns. of
HCN, S02,
CS2, hydro-
carbons)
326.6
40-185
•v 142
Acute" V-l
13.7-
36.6
15-35
28.4
(often ex-
ceeded)
7.1-14.2
.(and S02 and
lower ali-
phatic com-
pounds)
7.1-14.2
(and S02)
< 14.2
20 min V-l
Acute,
repeated
5-15 y
V-l
V-l
V-l
"Acute" V-l
V-l
V-l
V-l
V-l
Fatigue, dizziness, unconsciousness with or
without respiratory failure. Rapid recovery
(0.5 h) except for some nervous symptoms
possibly lasting up to 1.5 mo.
Unconsciousness, cramping, slow and shallow
breathing, and low blood pressure. Fully
recovered in 6 mo.
Within several hours, many signs of eye,
nose, and throat irriation. Wide variation
in individual responses.
Within several hours, many signs of eye
irritation. A wide variation in individual
response, light cases recovering in a few
hours, and severe cases in a week.
Eye irritation of varying severity, lasting
from several hours to days. Some individuals
had repeated episodes.
Nausea, weakness, and pain in the chest.
Complete recovery within a week, no sequelae.
Fatigue, loss of appetite, irritability,
headache, loss .of memory, itching, and irri-
tation of the eyes and respiratory tract.
Respiratory, gastroenteric, eye, and skin
irritation.
Dermal symptoms suggestive of an allergic-
type response. Some lung damage.
Weakness, nausea, dizziness, headache,
nervousness, and occasional unconsciousness.
(continued)
-------
-35-
TABLE S-3. (concluded)
Level
(mg/m3)
Exposure
time
Table
Effects
0-9.94
0.03-
0.43
0.005-
0.300
0.028-
0.055
3 d V-l Occasional slight and irregular changes in
serum Fe and transferrin levels and in
fractions of urinary sulfates.
29 d . V-2 Mild symptoms of nausea, vomiting, headache,
shortness of breath, burning eyes, respira-
tory tract irritation, gastrointestinal
complaints, and disturbed sleep.
Chronic V-2 Headache, weakness, nausea, vision problems,
and higher general morbidity rates in those
households with ^ 0.05 rag H2S/m3.
Chronic V- 1 Babies were poorly developed, underweight,
listless, anemic, dyspeptic, and more sus-
ceptible to infectious diseases.
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