EP A/AA/CTAB/PA/81-13
The Determination of a Range
of Concern for Mobile
Source Emissions of
Hydrogen Cyanide
by
Colleen L. DeMeyer
and
Robert J. Garbe
August, 1981
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analyses of
issues using data which are currently available. The purpose in
the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical
developments which may form the basis for a final EPA decision,
position or regulatory action.
Control Technology Assessment and Characterization Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, Michigan 48105
-------
-2-
Summary
This paper describes an effort by the Emission Control Technology Division
of the EPA to establish a range of concern for hydrogen cyanide (HCN) emis-
sions from mobile sources. In light of the action called for in section
202(a)(4) of the Clean Air Act (CAA) and due to a concern within industry as
to what emission levels will be used as the basis for the evaluation of cur-
rent and future technologies, a methodology was developed in order to
bracket a range of concern for various unregulated pollutants. This paper
coordinates the efforts from two EPA contracts in order to use this meth-
odology specifically for an evaluation of HCN. 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 HCN emission factors
(grams/mile). In conjunction with this, an HCN health effects literature
search was conducted to aid in the determination of the final • range of con-
cern. This search provides adequate evidence to support the chosen limits
of the range.
!
The results of this analysis provides a range of concern for HCN emissions
from motor vehicles of from 38-3850 mg/mile to 2619-261,904 mg/mile or from
1.6-164 ing/minute to 13.9-1392 mg/minute depending on the type of scenario
chosen to represent public exposure. The available emission factor data
indicate that HCN emissions are not likely to present a problem to public
health. Vehicles equipped with a 3-way catalyst operating under malfunction
modes or low ambient temperatures may, however, make a greater contribution
to any potential huaan exposure problem due to the increased emissions of
HCN under these conditions.
-------
-3-
I. Introduction
Bell Laboratories, in 1975, released the results of an experiment, which
they had conducted, showing that HCN was formed by passing a mixture of
nitrogen oxide (NO), carbon monoxide (CO), hydrogen (H9), and varying
amounts of water and sulfur dioxide (S0«) over a heated platinum catalyst
bed. The same study also showed that the addition of water and S09,
typical of what would be expected in actual automobile exhaust, greatly
supressed HCN production. Although the Bell work was done on a laboratory
bench basis, not on cars, catalysts on engines, or even real automobile
exhaust, the data were interpreted as meaning that catalyst-equipped cars
may emit HCN. While there was some reason to question the significance of
this experiment, as far as mobile sources are concerned (such as the sulfur
content of gasoline and the water in exhaust), tne data did suggest that
further investigation was warranted(1)*.
The Environmental Protection Agency, in early 1976, found that vehicles
using a 3-way catalyst could produce HCN under rich malfunction modes.
Also, at this time, Volvo and Saab were certifying 3-way catalyst systems
for use in California in 1977. Due to the possibility of significant emis-
sions of various potentially harmful substances from 3-way catalyst systems,
EPA requested information from the manufacturers and began a series of tests
in an attempt to estimate the hazards of HCN from mobile sources. Tests
were conducted by several organizations in order to support this effort.
Under contract to EPA, Exxon Research and Engineering Company investigated
the effects of catalyst composition on HCN exhaust emissions (2). It was
found that rhodium (Rh) containing 3-way catalysts tended to give
significantly higher levels of HCN than did platinum or platinum-palladium
catalysts. In-house EPA tests also verified this conclusion (3).
* Numbers in parentheses indicate references at the end of the paper,
-------
-4-
Of particular interest to EPA, with respect to HCN emissions, was the
exposure situation which would be considered as a "worst case", such as
levels of HCN that could occur in parking garages and on heavily-traveled
roadways. After calculations were made, it was found that, in a closed
environment situation, such as a parking garage, an upper bound of 5 ppm HCN
could result from a maximum raw exhaust level of 10 ppm. At this level of
HCN, the calculated level of CO would be as high as 6500 ppm. Because of
this high CO value, it was concluded that the adverse health effects of CO
would overshadow possible adverse health effects of HCN (by more than two
orders of magnitude). Admittedly, this type of analysis could be
characterized as the "HCN pot calling the CO kettle black" since an
evaluation of HCN's effects was not made. With respect to the highway
3
exposure situation, the "worst case" would result in a 1.1 ppm (1.2 mg/m )
HCN level, a level which was not considered to have unacceptable health
effects associated with it.
In 1978, the Office of Research and Development of EPA was asked once again
to review the work which the Environmental Sciences Research Laboratory
(EPA) had done earlier. They concluded that the information that they had
reported earlier was still accurate, and that the HCN emission values
presented did not constitute an unreasonable health hazard to the public
(A,5).
While the reports mentioned previously did conclude that HCN from vehicles
probably did not constitute a health hazard over and above that hazard posed
by CO, no level of concern for HCN had been definitively determined. As a
part of the Emission Control Technology Division's overall responsibility
for the characterization of unregulated pollutants from mobile sources, an
effort was started under contract with Southwest Research Institute (SwRI),
and Midwest Research Insitute (MRI), to gather more information concerning
various pollutants such as HCN and its health effects, to aid in the
determination of levels or ranges of concern for HCN emissions from motor
vehicles.
-------
-5-
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 incorporatred in, such
vehicle or engine conforms to applicable requirements of section
202(a)(4).
(b) The Administrator may conduct such tests and may require the 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:
-------
-6-
"Any system installed on or incorporated in a new motor vehicle
(or new motor veiiicie 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 vould not be emitted in the operation of
such vehicle (or engine) without such system, except as
specifically penritted 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 requiements 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) (6) 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 esission standards and also will not contribute to an
unreasonable risk to public health. Another Advisory Circular (7) was issued
in November of that year continuing these procedures for 1980 and later model
years.
III. Methodology Overview
Along with the previously mentioned activities, EPA, with the input from
several interested parties, has developed a methodology which is one possible
approach to implementing section 202 (a)(4) of the CAA. This approach is ex-
-------
-7-
plained in detail in EPA report number EPA/AA/CTAB/PA/81-2, "An Approach.for
Eetermining Levels of Concern for Unregulated Toxic Compounds from Mobile
Sources" (8). Only a brief summary of this method will be presented in this
report.
i
Under contract to EPA, Southwest Research Institute (SwRI), and Midwest
Easearch 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
Tenicle 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
nernodology.
Health effects literature searches have been and are being conducted by MRI in
an. attempt to aid EPA in the determination of a range of concern for various
selected pollutants. With adequate information, the limits for this range can
be chosen. The upper level of the range will -be that value above which the
studies show that the pollutant causes so great a hazard to human health as to
require formal rulemaking action. The lower value of the range will be the
lovest 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 HCN. 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.
Tscanologies with emission levels falling below the lowest level of the range
v^ii 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,
rr.erefore, this will imply a necessity for regulation.
-------
-8-
For the purpose of this report, this particular methodology has been used to
develop a range of concern specifically for motor vehicle emissions of HCN.
IV. General Information
Hydrogen cyanide (HCN) is a flammable, toxic, and colorless liquid at room
temperature which has the characteristic odor of bitter almonds. Other common
synonyms used for this compound include hydrocyanic acid, prussic acid, and
fornonitrile. HCN is a very potent and fast acting poison which attacks the
respiratory system by combining with the iron complex in the blood, stopping
the oxidation processes in the tissue cells, and causing death by asphyxiation.
In fact, in the past, HCN was one of the gases which was used for capital
punishment executions.
Early symptoms of exposure to HCN may include weakness, headache, confusion,
nausea, vomiting, and intially increased respiratory rate and depth. In later
stages, breathing becomes slow, to the point of gasping. Acute poisoning at
high levels of HCN produces almost immediate collapse and cessation of respi-
ration. Chronic exposure can cause enlargement of the thyroid or goiter.
Hunians are exposed to cyanide through various pathways such as diet and ciga-
rettes, as well as occupational exposure (firefighters, jewelry plating oper-
ations, galvanizing shops, etc.). The common measure of cyanide exposure is
the concentration of the cyanide metabolite thiocyanate in the urine or
blood. This measurement can be misleading if the diet contains foods such as
cherries, almonds, lima beans, and/or cabbage, which release thiocyanate or
isocyanate in the body. Cyanide residues on food, due to fumigation, may also
add to these concentrations.
Cigarettes can also contribute to the amount of hydrogen cyanide measured in
the body. A two-pack-per-day smoking habit might contribute as much as 22 mg
t
HCN to the daily intake (9-see also Appendix II).
Many occupational studies have not taken into consideration the contribution
of diet or smoking to cyanide exposure. Each of these could be as important
as occupational exposure to the urinary excretion of thiocyanate.
-------
-9-
T'oree of the processes by which HCN is commercially produced consist of
reacting methane, ammonia, and air over a platinum catalyst (1000-2000°C),
reacting nitric oxide and gasoline (1400 C), and by reacting hydrocarbons,
p-rr-onia, and oxygen (600-1500 C). Although HCN can be produced by various
other methods, it is reactions of this type which may be responsible for
nobile source HCN exhaust emissions.
The following reaction equations represent the possible pathways by which HCN
can. be formed during engine combustion and catalytic conversion of the exhaust
gas (10).
1) CH4* + NH3 + 3/2 02 >• HCN + 3 H20
2) 2 CO + NH3 >• HCN + HZ + C02
3) 2 CO + 3H2 + 2 NO +- 2 HCN + 2 H,^ + 02
4) CH4 + NH_ >- HCN + 3 H
2
5) 1/3 C.H. + NH, *- HCN + 7/3 H
J O J
6) CO + NH3 - +~ HCN + H20
7) CH4 + NO - »- HCN + H20 + 1/2
8) 2 C + H2 -i- N2 - *- 2 HCN
9) CH + 2 KO - *- 2 HCN + H0 + 1/2
10) C2H2 + 2 NO *- 2 HCN +
xKot only CH4 but all saturated and unsaturated hydrocarbons, radicals, and
cracKing products.
-------
-10-
Considering, however, the equilibrium constant and kinetics for each of these
reactions (in general, less HCN is formed by increased temperature), only
reaction equations 1, 5, 7, 9 and 10 are significant for HCN formation during
the engine combustion and catalytic conversion processes. These reactions can
be further affected by factors such as catalyst poisoning, or the presence o"f
water vapor.
V. Emission Factors
HCN exhaust emissions have been measured for a variety of vehicle types. The
reconmended procedure for this measurement is listed in two EPA reports en-
titled, "Analytical Procedures for Characterizing Unregulated Pollutant Emis-
sions from Motor Vehicles" (11) and "Analytical Procedures for Characterizing
Unregulated Emissions from Vehicles Using Middle-Distillate Fuels" (12). Ap-
parently, this method has some cyanogen (C_N-) interference. Cyanogen is
a flammable, toxic, and colorless gas at room temperature and like HCN has the
characteristic odor of bitter almonds. Its physiological effect on living
tissue is also similar to that of HCN. Attempts to analyze HCN and cyanogen
separately have been unsuccessful and, therefore, cyanogen is included in all
reported HCN emission factor values although it may not be specifically
mentioned as such.
Small amounts of HCN have been measured in gasoline-fueled vehicle exhaust,
under normal operating conditions, at levels around 1.0 mg/mile. Under mal-
function conditions, however, these emission rates can increase considerably.
A reported emission rate for a malfunctioning vehicle operating with a 3-way
catalyst was as high as 112 mg/km or 179 mg/mile, for the FTP driving
schedule(13).
Tests were run by EPA in order to evaluate the impact of low ambient tempera-
tures on 3-way catalyst-equipped car emissions. These studies showed that HCN
emissions also increased significantly during subambient temperature oper-
r'
ation. One of the test vehicles, on the average, emitted 1.02 mg/mile of HCN
at 78°F, while at 58°F, the same car emitted 22.53 mg/mile of HCN (over the
FTP driving schedule). The maximum observed HCN emission rate for all tests
was obtained at 61°F and was 38.02 mg/mile (14).
-------
-11-
Average HCN 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 Federal Test Procedure (FTP) driving
schedule, unmodified mode, as well as for various malfunction modes (when such
data were available). Since the available data for some technologies list
both an unmodified FTP and a malfunction emission value, the final, average
emission factor was weighted such that the value is 75% of the unmodified FTP
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
(15). Further work may identify a more accurate percentage.
The emission factors obtained for the malfunction mode are especially im-
portant to this effort due to the fact that HCN emissions tend to increase
under malfunction conditions. Maximum emission rates have been listed below
for three vehicle categories.
Maximum Reported HCN Emission Rates Under Malfunction Modes
Vehicle Category mg/mile
non-catalyst 11.2
oxidation catalyst 9.6
3-way catalyst 179.2
The reported emission factor for the 3-way catalyst vehicle, which was
obtained under malfunction conditions, is considerably higher than that of the
other two categories. This value is also much higher than any of the vehicle
categories listed in Table I, excluding Heavy Duty Gasoline Vehicles.
For the purpose of this report, only emission factors for the FTP driving
cycle were considered, rather than values, or a combination of values,
corresponding to various other cycles. This is due to the abundance of HCN
emission data for this particular driving cycle, in conparison to other
-------
-12-
TABLE I
Hydrogen Cyanide Emission Factors@
Vehicle Category Hydrogen Cyanide (mg/mi) FTP Schedule
Average
Light Duty Diesel Vehicles 3.2
Light Duty Diesel Trucks 3.2*
Heavy Duty Diesel Trucks 22.4
Light Duty Gasoline Vehicles
Non Catalyst; no air pump 4.5
Non Catalyst; air pump : 4.5**
Oxidation Catalyst; no air pump 2.4
Oxidation Catalyst; air pump 0.9
3-way Catalyst; no air pump 16.0
3-way Plus Oxidation Catalyst; air pump 24.7
Light Duty Truck
Non Catalyst 4.5**
Catalyst, no air pump 2.4***
Heavy Duty Gasoline Vehicles 224.O1
@References 13, 16, 17, 18, 19
* Due to a lack of sufficient data, this value is assumed to be the same as
that given for Light Duty Diesel Vehicles.
** 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, without an air
pump.
*** Due to a lack of sufficient data, this value is assumed to be the same as
that given for light duty gasoline vehicles with oxidation catalyst and no
air pump.
1 This value was derived from the emission factor test data from two heavy
duty gasoline trucks operated over the 1983 HD transient cycle (see
reference 19). Due to the questionability of this high emission factor
value, its validity is suspect until more data become available such that
tnis value can be verified.
-------
-13-
driving schedules. It may be more appropriate to chose driving cycles which
would nost closely simulate those scenarios under investigation (enclosed
spaces, street canyons, etc.). At present, however, data do.not exist to
permit use of this approach for HCN. The percent of error which is
introduced by using the FTP emission factor is not known at this point.
Available HCN idle emissions data were used to estimate HCN exposures in
parking garage situations, and will be discussed later in this report.
i
Using the average HCN emission factor data presented in Table I, it is pos-
sible 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
(20), and the EPA report, Mobile Source Emission Factors: For Low Altitude
Areas Only (21). 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
HCN emissions, this value is 11.4 mg/mile. This average takes into account
only tnose 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 HCN 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 one of the three highest emitting
techologies. In this case, excluding heavy duty gasoline trucks, these
three technologies include the three-way plus oxidation catalyst without air
pump, three-way plus oxidation catalsyt with air pump, and a three-way
catalyst under malfunction conditions. The compiled emission factors listed
-------
-14-
Table II
Fleet Average Emission Factors - Hydrogen Cyanide*
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)
3.2
3.2
22.4
4.5
4.5
2.4
0.9
16.0
24.7
4.5
2.4
EF x VMT
Fraction
0.048
0.006
0.605
0.662
t
0.441
0.694
0.235
0.192
0.198
0.432
0.024
Heavy Duty Gasoline Trucks 0.035
224.0
7.840
Total Fleet Average'
11.4 mg/mile
21
-------
-15- <
Table III
Hydrogen Cyanide Emission Factor - Compiled
Fleet Category ing/mile
Fleet Average (FA) 11
75% FA + 25% 3W* 12
50% FA + 50% 3W 14
25% FA + 75% 3W 15
100% 3W 16
75% FA 4- 25% 3W+OC** 15
50% FA + 50% 3W+OC 18
25% FA + 75% 3WK)C 22
100% 3W+OC 25
75% FA + 25% 3W*** 53
50% FA + 53% 3W 95
25% FA + 75% 3W 137
100% 3W 179
* Light Duty Gasoline Vehicles - Three-way Cataly.'t without air pump
** Light Duty Gasoline Vehicles - Three-way + Oxidation Catalyst with air pump
*** Light Duty Gasoline Vehicles - Three-way Catalyst under malfunction condi-
tion
-------
-16-
in Table III will become an Important tool in comparing vehicle emisions to
the range(s) of concern. In subsequent steps, these values will be used to
calculate ambient air concentrations of HCN for various fleet mixes of
emission control technologies.
VI. Hydrogen Cyanide Health Effects
Midwest Research Institute (MRI), under contract to EPA, conducted a liter-
ature search of the health effects related to HCN, the results of which are
contained in a. report which is included as Appendix II to this paper.
The purpose of this literature search was to aid in the determination of a
range of concern for HCN by providing supporting evidence for those levels at
which adverse physiological effects have been detected from exposure to
various concentrations of HCN. These scattered data points will be bracketed
in order to set a final "range of concern". The lower value of this range
will be selected to approximate the lowest level at which adverse physiologi-
cal effects from exposure to HCN can be detected. Below this limit, the
available literature shows little or no health effects, although some more
sensitive subgroups of the population (asthmatics, etc.) may be affected by
these levels.
The upper linit of the range is chosen to be that value above which the
studies show such an adverse reaction in the exposed population from exposure
to HCN, as to imply a necessity for regulation. The values selected for HCN
and the rationale for chosing them are discussed in section VIII.
VII. Hydrogen Cyanide Ambient Air Concentrations
The HCN emission factor information provided in Table I through III, can be
used in conjunction with the modeling techniques developed by Southwest
Research Institute (SwRI) (see Appendix I), in order to calculate the ambient
air concentrations produced by varying levels of HCN vehicle emissions for
different exposure situations. Future work may identify other scenarios
-------
-17-
which would also be appropriate for the assessment of human exposure to
exhaust pollutants, but, for this task, only five exposure scenarios were in-
vestigated: 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. Appendix I 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 cyanide, as a
function of vehicle emission rates, for eleven ambient situations. The
vehicle emission rates correspond to those emission factors which were
calculated for the various combinations of fleet categories found in Table
III. This information will later be used to develop a plot which graphically
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 HCN is assumed to be low
(1/ig/m3).
In order to more closely assess public exposure to HCN in a garage situation,
idle emissions data were averaged from a limited number of sources (22, 23,
24, 25).
-------
Table IV
Ambient Air Scenario!
Hydrogen Cyanide Concentration* /ug/m
Fleet
Make
«p
FU-et Average
751 FA**
4251 3W«**
50* VA
450'OW
25X VA
4?5» 3W
1001 W
75* FA
42 51 3U40CI3
501 VA
450: 3W40C
251 VA
4751 3W»OC
1001 3W40C
75: VA
425. 3W1
501 IA
4 sot w
«7U IW
100 1 IW
Emission
Factor
rag/mile
11
12
14
15
16
15
18
22
25
53
95
U7
179
2590
Enclosed Spaces
Street Canyon
Expressway
Personal Garage* Parking Garage* Roadway Tunnel
typical severe typical severe typical
12
13
16
17
IB
17
20
25
28
60
107
IV.
201
2910
severe
31
34
40
43
46
43
57
63
71
151
171
I'M
5U
'390
typical severe
.47 4.4
51 48
.60 5 6
.64 6.0
.68 6.4
.64 6.0
76 7 I
.93 8.7
1. 1 9.9
2.2 21
4.0 311
3 II ,4
7.6 71
110 1030
on road
off road typical
I B 1.3
21 15
2.4 1.7
2 6 1.8
2.7 2.0
2.6 1 8
31 22
3.8 2.7
4.3 3.1
9.1 6.5
11 U
n \i
31 22
450 320
on rood
seven-
5.4
5 9
6.9
7.4
7.9
7.4
8.9
10.9
12
26"
47
6H
89
1290
* These values ar* based on emission rates In grams/minute, and are discussed In detail In the body of the report.
** FA » Meet average.
*** JW • Light DMty Gasoline Vehicles-Three-way Catalyst without air pump.
() 3WtQC - Light Duty Gasoline Vehicles-Three-way 4 Oxidation Catalyst with air pump.
1 3W » Lit,ht Duty Gasoline VehlcUs'Three-way Catalyst under malfunction condition.
-------
-19-
Although there was some deviation, the available idle data appear to indicate
that vehicles with 3-way catalysts, operating in the malfunction mode, emit
HCN at a rate of approximately 1 mg/min.
In a worst case situation, where 100% of the vehicle fleet consists of
automobiles with 3-way catalysts, operating in the malfunction mode, the HCN
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 and presently operating in the malfunction mode, in an enclosed
garage.
HCN Ambient Air Concentrations ug/rn-^
Emission Personal Garage Parking Garage
Fleet Make Up Factor Typical Severe Typical Severe
100% 3W 1 mg/min. 7.9 67 8.8 5177
Since these values more accurately reflect the HCN 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
exposure to HCN. 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 road-
way 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 of the vehicle.
-------
-20-
Three different cases were considered in order to cover the possible range of
exposures in an expressway situation. 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. The typical, on road ex-
posure 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 meters/second.
In this situation, the exposed population is located inside of 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 population.
VIII. Determination of the Range of Concern
All of the information gathered up to this point is necessary input for the
determination of a range of concern for HCN emissions from mobile sources.
The health effects information will help to identify the limits of the range,
while the emission factor data, along with the modeling techniques, will aid
in the conversion of emission rates to ambient air concentrations so that it
might be possible to focus upon the potential risks to public health (if any)
from exposure to HCN exhaust emissions.
3 3
The upper value of the range has been chosen to be 11 mg/m (11000 ug/m )
(ambient air concentration). This level is the Threshold Limit Value (TLV)
for hydrogen cyanide, which stands for the time-weighted average concentration
for a normal 8-hour workday or 40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without adverse effects. The
evidence of adverse health effects above this level would be sufficient to
support regulatory action.
The literature search does not reveal any one study in particular which sup-
ports a specific level' which can be considered as the lowest level at which
adverse physiological effects can be detected. In fact, very few of the
-------
-21-
studies are even appropriate for comparison with long-term, low-level exposure
situations, as would be typical of human exposure to automobile exhaust. Due
to a lack of supportive information at very low levels of exposure to HCN, the
lower level of the range is, therefore, more difficult to determine.
Table V (Table IV-1 in Appendix II) is an excerpt from the MRI draft HCN
report, which represents a collection of the human, acute dose-response data
(MRI states that this information is usually generalized from the literature
without original source attribution). This table indicates that 0.2 - 5.5
3 3
mg/m (or 200-5500 ug/m )is considered to be the odor threshold level.
Although this level does appear to have an effect on sensory perception, it
cannot be definitely concluded that it would also cause any adverse
physiological effects. The odor threshold might actually be considered a
problem for those people who do not like the smell (i.e. welfare effects).
The table also labels 0.11 - 0.99 mg/m (or 110-990 ug/m3) as the no
effect level. There is not, however, enough concrete evidence in the
literature search to support this statement.
The HCN health effects literature review emphasizes that there is a very steep
dose-response curve in many of the animal experiments. For example, twice the
no-observed-effect level can be lethal. Due to.this type of response, it has
been determined that a reasonable safety factor should be applied to the TLV
in order to set a lower level for the range of concern. This approach is
assumed to be suitable until more information concerning low level exposure to
HCN is made available. The safety factor for this case has-been chosen to be
100 (26), therefore, setting the lower level of the range at 0.11 mg/m ,
(110 ug/m ) a concentration below which there is no available information
definitely concluding that there are adverse physiological effects from
exposure to HCN.
3 3
Between the chosen limits of the range (i.e. 110 ug/m to 11000 ug/m ),
there are scattered data points providing evidence of adverse physiological
effects caused by exposure to various concentrations of hydrogen cyanide.
-------
-22-
Table V
HUMAN DOSE-RESPONSE DATA AS GENERALIZED IN THE
LITERATURE3
Dose of HCN
mg/m
22,000
7,000-12,000
5,000
3,750
3,600
2,500
1,000
550
400
300
ppm
20,000
6,360-
10,900
4,500
3,410
3,410
2,270
909
500
364
270
Response
Even though breathing is through a gas
mask, vertigo, weakness, and
tachycardia occur after 8-10 min.
Loss of work capacity for 2-3 d.
Level dangerous, after 5 min even though
a gas mask is used because of skin
penetration.
Safe for 1 min.
Safe for 1.5 min.
Safe for 30 min with a gas mask.
Safe for 2 min.
Safe for an experienced, fumigator
indefinitely.
No serious consequences after 1
min exposure
Tolerable for 1.5 min without vertigo.
Immediately fatal.* Lazarev (1971
[2-0144] stated that this concentra-
tion is tolerable for 2 min without
headache. Lazarev (1956) [2-0145]
stated a person at rest would with-
stand this concentration for 2 min
without dizziness.
200 180 Fatal after 10 min.
150 .'' 140 Fatal after 0.5 h.
t
120-150 110-135 Fatal after 0.5-1 h.
*This statement in this reference does not seem to be consistent with the
statement in other references for this HCN level.
(continued)
-------
-23-
Table V (concluded)
Dose of HCN
ppm Response
110 100 Fatal in 1 h. '
50-60 45-54 Tolerated for 0.5-1 h without immediate
or late effects
0.4-50 0.4-45 Headache, vertigo, nausea, regurgi-
ation, heartburn, general weakness
sensation of pressure in the epi-
gastric region, sweating of the
hands, instability of the autonomic
nervous system, decrease in vascular
tone, slowing of blood circulation.
20-50 18-45 Headache, nausea, vomitting, and tachy-
cardia after several hours.
20-^0 18-36 Slight symptoms (headache) after
several hours.
5-20 4.5-18 Headache and vertigo.
11 10 Threshold limit value (ACGIH, 1979)
0.2-5.5 0.2-5.0 Odor threshold
0.11-0.99 0.1-0.9 No effect13
Aghoramurthy and Mehta (1977), Dudley et al. (1942), Einhorn
(1975), Flury and Zernik (1931), Henderson and Haggard (1943),
Hamilton and Hardy (1949), Lazarev (1971) [most levels 300
, McNamara (1976).
Attributed to Lazarev by Czechoslovak Committee of MAC (Wills et al.,
1976)
-------
-24-
Therefore, this region has been termed the "range of concern" for HCN
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 cyanide emissions to ambient air concentrations.
Once the literature search was completed and the appropriate information was
tabulated for HCN, a large table was prepared compiling all the information
for the animal studies (see Appendix III). This table lists the studies
according to the exposure concentration of HCN (highest to lowest concen-
tration). Using the health effects information along with the emission factor
data, graphs were composed representing the relationship between ambient air
concentrations, emission factors, and the various types of public exposure
situations (Figure 1-5).
According to the methodology which will be used to establish a range of
concern for non-zero threshold pollutants, the boundary limits of the ambient
air range of concern (ug/m ) are compared to the mobile source exposure
scenarios in order to calculate the range of concern in vehicle emission
factor units (mg/mi). Exposure time is the main element of comparison between
the ambient air range and the mobile source exposure situations. Most of the
exposure situations represent short term exposures (duration of an hour or
less per day) perhaps repeated several times per week. The typical exposure
situations are likely to be repeated often, while the severe exposure
situations are more likely to occur on an infrequent basis.
With all of the collected information, a mobile source emission factor range
of concern for hydrogen cyanide can be estimated for each scenario and
situation as listed table VI and VII.
-------
-25-
C
o
^>
o
E
o
O
o>
o
o
FIGURE 1
PERSONAL PARKING GARAGE
LO
LO
LT9 C53 LTJ
EMISSION FACTOR (nul!iqrcT.o/rin)
*J
-------
c.
o
.*>
o
E
-5
u
o
E
O
o
o
DC
CQ
-26-
FIGURE 2
PARKING GARAGE
LT5
Rl
era
tru
CO
EMISSION FACTOR
-------
IGZfl
958
-27-
858
8C3
758
TO
E
O
O7
O
O
558
458
483
358
UJ
»—»
CO
158
58
8
FIGURE 3
ROADWAY TUNNEL
LTJ
OJ
LO
LTJ
Rl
ess
LTJ
S3
CO
in
t\j
CTJ
evs
EMISSION rCTGR Gr.illi3rcao/pilo)
-------
-28-
958.
753.
c
o
Jj
o
E
o
•*4
_0
o
E
O
o
o
OS.
LU
559
5S3
458
4B3
S 253.
_ 158
FIGURE 4
EXPRESSWAY
EMISSION FACT:?. G
-------
-29-
ica
953
752
7B3
658
c
o
4>
o
E
-S
o
e
o
o
u
558
523
458
UJ
t—«
m
FIGURE 5
STREET CANYON
EMISSION FACTOR Cmilli
gpcne
/milo)
-------
-30-
Table VI
Emission Factors Required to Result In
Exposure Limits for the Ambient Air Range of Concern
Ambient Air Scenario* Emission Factor (mg/mile) Emission Factor
corresponding to a corresponding to an
3 3
110 ug/m exposure 11,000 ug/m exposure
Street Canyon - Typical
Expressway - Close Proximity
Expressway - Typical
Street Canyon - Severe
Expressway - Severe
Roadway Tunnel - Typical
Roadway Tunnel - Severe
2619
1047
887
390
217
98
38
261,904
104,761
88,709
39,007
21,739
9,800
3,850
* In order of increasing ug/m^ concentration for 1 g/mile (or Ig/min)
emission rate (excluding garage situations).
-------
-31-
Table VII
Emission Factors Required to Result in
Exposure Limits for the Ambient Air Range of Concern ,
Ambient Air Scenario Emission Factor (mg/min. ) Emission Factor
corresponding to a corresponding to an
3 3
110 ug/m exposure 11,000 ug/m exposure
Personal Garage
Parking Garage
Parking Garage
- Typical
- Typical
- Severe
13.9
28.2
2.4
1392
2820
239
Personal Garage - Severe 1.6 164
-------
-32-
IX. Conclusions - Hydrogen Cyanide
Several conclusions could be drawn from the information provided in this
report. These conclusions are listed below.
1) Table VI and VII indentifies a range of concern for each ambient ex-
posure situation simulated. These ranges vary from 38 - 3850 to 2619 -
261,904 mg/mile for the moving vehicle situations (roadway tunnel,
street canyons and expressways) and from 1.6 - 164 to 13.9 - 1392 mg/min
for the stationary vehicle situations (personal and parking garages).
2) With respect to the moving vehicle situations the controlling (lowest)
range is derived using the severe roadway tunnel situation. There is
some question as to whether this scenario identifies a potential mobile
source pollutant exposure problem. In other words, if the roadway
tunnel scenario is identified as a potential problem with respect to a
particular motor vehicle pollutant, then it is possible that the most
appropriate solution would be to increase tunnel ventilation rather than
to reduce vehicle emissions.
3) The hydrogen cyanide range of concern uses a safety factor of 100 in the
determination of a lower level. In view of conclusion 5, it is possible
that the inclusion of the roadway tunnel scenario (which seems to be the
controlling factor) in the range of concern constitutes an additional
margin of safety, but no specific factor has been calculated.
4) The current (estimated) vehicle fleet emission factor for hydrogen
cyanide of 11 mg/mile or 1 g/min for 3 way catalysts equipped vehicles
at idle, is well below the 38-3850 mg/miles or 1.6 - 164 mg/min range of
concern for hydrogen cyanide emissions.
8) Specific emission control technologies or vehicle categories which
^
appear to have emission factors that fall within the range of concern
(referring to Table I) are heavy duty gasoline vehicles and mal-
functioning 3-way catalyst vehicles.
-------
-33-
As more information becomes available on long term, low level exposures
to HCN, a lower level for the range of concern can be more accurately
chosen. At this point, however, it was necessary to .make some as-
sumptions in order to assess a range of exposure concentrations for
hydrogen cyanide, which may be of concern to public health., This range
is intended to aid in the development of future technologies for mobile
sources by providing a basis for exhaust emissions of hydrogen cyanide.
-------
-34-
References
1. Eric 0. Stork, Deputy Assistant Administrator for Mobile Source Air Pol-
lution Control, John Moran, Staff Assistant for Office of Research and
Development, U.S. EPA, "Hydrogen Cyanide from Catalyst Cars", MSAPC
Alert Bulletin, May, 1975.
2. M.H. Keirns, E.L. Holt, Exxon Research and Engineering Company,
"Hydrogen Cyanide Emissions from Three-Way Catalyst Prototypes Under
Malfunctioning Conditions", SAE Paper 780201, February - March, 1978.
3. Ronald L. Bradow, Fred D. Stump, U.S. EPA, "Unregulated Emissions from
Three-Way Catalyst Cars", SAE Paper 770369, February - March, 1977.
4. Internal U.S. EPA memorandum from Delbert S. Barth, Deputy Assistant
Administrator for Health and Ecological Effects, to Michael P. Walsh,
Acting Deputy Assistant Adminstration for Mobile Source Air Pollution
Control, "Response to Memorandum on the Health Effects of Hydrogen
Cyanide and Carbon Monoxide from Motor Vehicles", July 24, 1978.
5. Internal U.S. EPA memorandum from Delbert S. Barth, Acting Deputy
Assistant Administrator for Health and Ecological Effects to Eric 0.
Stork, Deputy Assistant Administrator for Mobile Source Air Pollution
Control, "Health Assessment of Automotive Emissions", September 7, 1976.
6. U.S. EPA Advisory Circular 76, June, 1978.
7. U.S. EPA Advisory Circular 76-1, November, 1978.
8. Robert J. Garbe, U.S. EPA, "An Approach for Determining Levels of
Concern for Unregulated Toxic Compounds from Mobile Sources",
i
EPA/AA/CTAB/PA/80-2, July, 1981.
-------
-35-
9. K.D. Brunnemann, L. Yu, D. Hoffman, "Gas Chromatographic Determination of
Hydrogen Cyanide and Cyanogen in Tobacco Smoke", Journal of Analytical
Toxicology 1:38-42, 1977.
10. "HCN Exhaust Gas Emissions of Gasoline Engines", Volkswagenwerk AG
Research and Development, Research Report No. MT-F5-77/8, April 15, 1977.
11. "Analytical Procedures for Characterizing Unregulated Pollutant Emissions
from Motor Vehicles", U.S. EPA, Environmental Sciences Research
Laboratory, EPA-600-2-79-017, February, 1979.
12. "Analytical Procedures for Characterizing Unregulated Emissions from
Vehicles Using Middle-Distillate Fuels", U.S. EPA Office of Research and
Development, Environmental Sciences Research Lab, EPA-600-2/80-068, April,
1980.
13. C.M. Urban, Southwest Research Institute, and R.J. Garbe, U.S. EPA,
"Exhaust Emissions from Malfunctioning Three-Way Catalyst-Equipped
Automobiles", SAE Paper 800511, February, 1980.
14. James N. Braddock, U.S. EPA, "Impact of Low Ambient Temperature on 3-Way
Catalyst Car Emissions", SAE Paper 810280, February, 1981.
15. David W. Hughes, U.S. EPA, "Inspection and Maintenance for 1981 and Later
Model Year Passenger Cars", SAE Paper 810281, February, 1981.
15. C.M. Urban, Southwest Research Institute, and R.J. Garbe, U. S. EPA,
"Regulated and Unregulated Exhaust Emissions from Malfunctioning
Automobiles", SAE Paper 790696, June, 1979.
17. S.H. Cadle, G.J. Nebel, R.L. Williams, "Measurements of Unregulated
Emissions from General Motor's Light-Duty Vehicles", SAE Paper 790694,
June, 1979.
-------
-36-
18. Harry E. Dietzmann, Mary Ann Parness, Southwest Research Institute, and
Ronald L. Bradow, U.S. EPA, "Emissions From Trucks by Chassis Version of
1983 Transient Procedure", SAE Paper 801371, October, 1980. -
19. Harry E, Dietzmann, Mary Ann Parness, Southwest Research Institute, and
Ronald L. Bradow, U.S. EPA, "Emissions From Gasoline and Diesel Delivery
Trucks by Chassis Transient Cycle", American Society of Mechanical
Engineers Paper No. 81-DGP-6, January, 1981.
20. "Air Quality Assessment of Particulate Emissions from Diesel Powered
Vehicles", Pedco Environmental, Inc., March, 1978.
21. Mobile Source Emission Factors: For Low Altitude Areas Only, EPA Report
No. 400/9-78-006, March, 1978.
22. Hydrogen Cyanide Emissions from a Three-Way Catalsyt Prototype, U.S. EPA,
Emission Control Technology Division, EPA-460/3-77-023, December, 1977.
23. Internal U.S. EPA Memorandum from Dr. Ronald L. Bradow, Chief of Mobile
Source Emissions Research Branch, to Mr. James Marzen, Acting Director of
Certification Division, "HCN Testing of VW Manufactured Automobiles",
September 15, 1976.
24. Internal U.S. EPA memorandum from Dr. Ronald L. Bradow, Chief of Mobile
Source Emissions Research Branch, to Mr. James Marzen, Acting Director of
Certification Division, "HCN Testing - Mercedes Automobiles", October 22,
1976.
25. Internal U.S. EPA memorandum from Dr. Ronald L. Bradow, Chief of Mobile
Source Emissions Research Branch, to Mr. James Marzen, Director of
Certification Division, "HCN Testing - Rolls Royce Automobiles", October
26, 1976.
-------
-37-
26. George Su, Kathryn A. Wurzel, Michigan Department of Natural Resources, "A
Regulatory Framework for Setting Air Emissions Limits for Noncriteria
Pollutants", Journal of the Air Pollution Control Association, February,
1981.
27. A Review of Hydrogen Cyanide as a Possible Public Health Hazard, U.S. EPA,
Health Effects Research Laboratory, Cincinnati, Ohio, July 15, 1976.
28. Melvin N. Ingalls, Southwest Research Institute, and Robert J. Garbe, U.S.
EPA, "Estimating Mobile Source Pollutants in Microscale Exposure
Situations", March, 1981.
------- |