EPA/AA/CTAB/PA/81-20
Determination of a Range
of Concern for Mobile
Source Emissions of
Ammonia
by
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
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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 ammonia (NH-) emissions
from mobile sources. In accordance with 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 current 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 methodology specifically
for an evaluation of NH_. Mathematical models were previously designed or
adjusted 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 NH, emission factors.
In conjunction with this, an NH health effects literature search was
conducted to aid in the determination of the final range of concern. This
search provides adequate evidence to support the chosen limits of the range.
The results of this analysis provide a range of concern for NH emissions
from motor vehicles of from 1260 mg/mile - 6302 mg/mile to 85,714 - 428,571
mg/minute or from 56 mg/minute - 268 mg/minute to 4811 mg/minute - 22788
mg/minute depending on the type of scenario chosen to represent public
exposure.
The emission levels discussed above are based on the direct impact of NH.,
on human health. Ammonia as an N0_ precursor and participant in subse-
quent photochemical reactions was not considered in the derivation of the
limits discussed above. Ammonia emissions may become a photochemical
oxidant concern before they become a directly emitted health hazard.
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I. Introduction
As the vehicle emission standards have become more stringent, many
automobile manufacturers developed new technologies aimed at reducing these
emissions. In the early 1970's, the three-way catalytic converter was
designed to reduce nitrogen oxides to molecular nitrogen. This new
development raised some questions as to the potential for new tailpipe
contaminants which might be produced by this system. One pollutant of
concern was ammonia (NH_). While raw (untreated) automobile exhaust
contains some NH_, the three-way catalyst can produce much greater
quantitites than present in the raw exhaust.
During the time period around 1976, Volvo and Saab were certifying 3-way
catalyst systems for use in California in 1977. Due to the possibility of
significant emissions of various potentially harmful substances from 3-way
catalyst systems, the Environmental Protection Agency (EPA), as well as
other concerned organizations, began to investigate the possible hazards of
NH^ emissions from mobile sources. Among these efforts was an EPA
contract with Exxon Research and Engineering Company, which investigated the
effects of catalyst composition on the emissions of various unregulated
pollutants (1)*. It was found that rhodium (Rh) - containing 3-way
catalysts tended to give significantly higher levels of NH~ than did
platinum or platinum-palladium catalysts. In-house EPA tests also verified
this conclusion (2). Exxon and other investigators also showed that
three-way catalyst equipped vehicles operating under rich malfunction
conditions emitted greater quantities of NH_ than under normal operating
conditions (1) (2).
Of particular interest to EPA at that time (1976-1978) with respect to
automobile emission of NH., were exposure situations which could be
considered to be "worst case" conditions wherein a combination of high
vehicle emissions rates of NH», adverse metorology, and sensitive
populations coexisted at the same time and place. These early assessements
*Numbers in parentheses indicate references at the end of the paper.
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of ammonia concluded that even under adverse or "worst case" conditions
ammonia emissions from three-way catalyst automobiles would not represent a
public health hazard. The assessments were based on a mean ammonia
3
concentration at the roadway of 0.15 mg/m (0.22 ppm) and on an enclosed
3
garage concentration of 13 mg/m (19 ppm). The garage assessement was
based on the simultaneous presence of CO in the garage at a concentration of
3
3.9 g/m (5,700 ppm) which would constitute a much greater health hazard
than NH-.
While the reports mentioned previously did conclude that NH~ from vehicles
probably did not constitute a health hazard over and above that hazard posed
by CO, no level of concern for NH_ 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 NH, and their health effects. This information
would aid in the determination of levels or ranges of concern for NH-
emissions from motor vehicles.
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-
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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).
(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
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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); Ref. (3) in June 1978, to aid the
manufacturers in complying with section 202 (a)(4). Manufacturers were
asked to continue providing statements showing that their technologies did
comply with the vehicle emission standards and also will not contribute to an
unreasonable risk to public health. Another Advisory Circular was issued in
November of that year continuing these procedures for 1980 and later model
years (4).
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" (5). 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
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corresponding ambient air values for both severe and typical exposure
situations for each scenario.
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
available 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
NH, . Using the ambient air versus 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. Figure one graphically illustrates the logical flow of this
pollutant assessment methodology.
For the purpose of this report, this particular methodology has been used to
develop a range of concern specifically for motor vehicle emissions of NH_.
IV. General Information
Ammonia is a colorless, corrosive, and weakly alkaline gas with a distinctive
pungent odor. This substance is known to be a respiratory and eye irritant
but in large doses it may also be related to other various health problems
such as chronic bronchitis, dyspnea (both associated with lung impairment),
and decreased blood pressure. Although the basic pattern after exposure to
NH_ is irritative damage followed by a recovery period, some deaths have
been reported (See Attachment I).
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Figure 1
Flow Diagram - Toxic Pollutant Range of Concern
Preliminary
Estimated
Range
of
Concern
Substance
of
Concern
Identified
II
Health Effects
. Literature
Search
Mobile Source
Emission Factors
(determined or
estimated)
III
Dispersion
Models Relating
Emission Factors
To Health Effects
IV
Range of
Concern
Emission Level
"Determined
Enission Control
Systems of
Concern
Identified
"No Problen"
Icplies Low Level
of Effort
Monitoring
"Concern"
Inplies Voluntary
Action by
Industry
"Danger"
Implies
Regulation
-8-
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NH_ was originally obtained as a by-product from the production of
manufactured gas by the destructive distillation of coal. In later years,
however, it was learned that NH_ could be made by the direct combination of
nitrogen (N-) and hydrogen (H_) in the presence of a catalyst and at high
temperature and pressure. This is commonly known as the Haber process.
NH» is used in the production of a fertilizers and many other industrial
organic synthetics, as well as in the preparation of numerous inorganic
ammonium compounds, as an ingredient in cleaning and bleaching compounds, as a
refrigerant, as an agent for the saponification of fats and oils, as an
etching compound for metals (particularly aluminum), as a source of inert
atmospheres for heat-treating and surface-hardening of metals, as an
explosive, and as disinfectants and deodorants.
Another source of NH» exposure is cigarette smoke which is frequently an
additional and confounding factor in many human health effects studies.
Apparently, the amount of NH~ in cigarette smoke varies with the type of
tobacco and the investigator (See Attachment I). The ammonium ion is a normal
constituent of body fluids, and it has been discussed that the human breath
contains NH, in measurable, yet varying amounts.
It has been theorized that the variation in the ammonia levels in expired air
between oral and nasal exhalation, which has been attributed to production of
NH, by oral bacteria may be a greater NH, "exposure" than other low level
chronic exposures such as automobiles.
V. Emission Factors
NH, exhaust emissions have been measured for a variety of vehicle types.
The recommended procedure for this measurement is listed in two EPA reports
entitled, "Analytical Procedures for Characterizing Unregulated Pollutant
Emissions from Motor Vehicles" and "Analytical Procedures for Characterizing
Unregulated Emissions from Vehicles Using Middle-Distillate Fuels" (6, 7).
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Small amounts of NH~ have been measured in gasoline-fueled vehicle exhaust,
under normal operating conditions, at levels around 8.0 mg/mile. Under mal-
function conditions, however, these emission rates can increase considerably.
A reported emission rate for a malfunctioning vehicle equipped with a 3-way
catalyst was as high as 518 mg/mile for the FTP driving schedule.
Average NH_ 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 used in this report will be 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 (8). 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 NH~ 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 26.2
oxidation catalyst 90.6
3-way catalyst 518.0
The reported maximum emission factor for the 3-way catalyst vehicle, which was
obtained under malfunction conditions, is considerably higher than that of the
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other two categories. This value is also much higher than any of the vehicle
categories listed in Table I.
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 NH_
emission data for this particular driving cycle, in comparison to other
driving schedules. It may be more appropriate to chose driving cycles which
would most closely simulate those scenarios under sufficient investigation
(enclosed spaces, street canyons, etc.). At present, however, data do not
exist to permit use of this approach for NH« • The percent of error which is
introduced by using the FTP emission factor is not known at this point.
Available NH- idle emissions data were used to estimate NH« exposures in
parking garage situations, and will be discussed later in this report.
Using the average HCN emission factor data presented in Table I, it is pos-
sible to calculate a fleet average emission factor. The data necessary to
make these calculations are 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 (9), and the
EPA report, Mobile Source Emission Factors: For Low Altitude Areas Only (10).
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 NH« emissions, this value is
15.6 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 NH., emitting technologies,
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TABLE I
Ammonia Emission Factors@
Vehicle Category Ammonia (mg/mi)
Average
Light Duty Diesel Vehicles 13.1
Light Duty Diesel Trucks 6.1
Heavy Duty Diesel Trucks 52.4*
Light Duty Gasoline Vehicles
Non Catalyst; no air pump 8.2
Non Catalyst; air pump 5.1
Oxidation Catalyst; no air pump 18.7
Oxidation Catalyst; air pump 11.2
3-way Catalyst; no air pump 123.0
3-way Plus Oxidation Catalyst; air pump 69.9
Light Duty Gasoline Truck
Non Catalyst 8.2**
Catalyst, no air pump 18.7***
Heavy Duty Gasoline Trucks 32.8**
(? References 11, 12, 13, 14
* Due to a lack of sufficient data, this value is assumed to be the same as
that given for light duty Diesel vehicles adjusted for approximate
differences in fuel consumption.
** 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, adjusted for approximate differences in fuel consumption.
*** 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.
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Table II
Fleet Average Emission Factors -Ammonia*
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
Heavy Duty Gasoline Trucks
Total Fleet Average
Fraction
VMT
0.015
0.002
0.027
0.147
0.098
0.289
0.261
0.012
0.008
0.096
0.010
0.035
Emission Factor
(mg/mile)
13.1
13.1
52.4
8.2
5.1
18.7
11.2
123.0
69.9
8.2
18.7
32.8
EF x VMT
Fraction
0.019
0.02
1.41
1.20
0.50
5.40
2.92
1.47
0.55
0.78
0.18
1.15
15.6
* References 9, 10, 11, 12, 13, 14
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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 technologies. In
this case these three technologies include the three-way 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
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 air concentrations of NH- for various automobile fleet
mixes of emission control technologies.
VI. Ammonia Health Effects
Midwest Research Institute (MRI), under contract to EPA, conducted a liter-
ature search of the health effects related to NH_ , the results of which
are contained in a report which is included as Attachment I to this paper.
The purpose of this literature search was to aid in the determination of a
range of concern for NH_ by providing supporting evidence for those levels
at which adverse physiological effects have been detected from exposure to
various concentrations of NH_. 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
physiologial effects from exposure to NH~ can be detected. Below this
limit, the available literature shows little or no health effects.
The upper limit 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 NH as to imply a necessity for regulation. The values
selected for NH- and the rationale for chosing them are discussed in
section VIII.
VII. Ammonia Ambient Air Concentrations
The NH- emission factor information provided in Table I through III, can
be used in conjunction with the modeling techniques developed by Southwest
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Table III
Ammonia Emission Factors - Compiled
Fleet Category
Fleet Average (FA)
75% FA + 25% OC*
50% FA + 50% OC
25% FA + 75% OC
100% OC
mg/mile
16
30
43
57
70
75% FA + 25% 3W**
50% FA + 50% 3W
25% FA + 75% 3W
100% 3W
43
70
96
123
75% FA + 25% 3W***
50% FA + 50% 3W
25% FA + 75% 3W
100% 3W
142
267
393
518
* Light Duty Gasoline Vehicles - Three-way plus oxidation catalyst with
air pump.
** Light Duty Gasoline Vehicle - Three-way Catalyst without air pump.
*** Light Duty Gasoline Vehicles - Three-way Catalyst under malfunction
condition - Maximum Emission Rate.
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Research Institute (SwRI), in order to calculate the ambient air
concentrations produced by varying levels of NH., vehicle emissions for
different exposure situations. Future work may identify other scenarios
which would also be appropriate for the assessment of human exposure to
exhaust pollutants, but, for this task, only five exposure scenarios were
investigated: personal garages, parking garages, roadway tunnels, street
canyons, and urban expressways. A typical and severe case situation was
developed for each of these scenarios. Each situation has been considered
separately, and, therefore, no cumulative effects have been determined at
this point. Appendix II discusses the reasoning behind using these specific
scenarios as well as the information used in the determination of the
modeling techniques. Figures 1-5 presents the exposure situations in a
graphical manner.
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 NH- is
3
assumed to be low (1 ug/m ).
In order to more closely assess public exposure to NH_ in a garage
situation, idle emissions data were averaged from a limited amount of data
(15).
Idle data were readily available for only one vehicle (a 1977 Volvo 3-way
prototype) tested at two laboratories. These emission factors average out
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. FIGURE 1
PERSONAL PARKING GARAGE
LO
LO
LO
LO
Ki
ci H3
en co
Cr"yrvC" r
«-_f4_. -~
EMISSION FACTOR
-17-
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en
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CQ
FIGURE 2
PARKING GARAGE
s w 53
EMISSION FACTOR
-18-
LO
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•~4
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OS
FIGURE 3
RQAWAY. TUNNEL
C.CCCTS/.-J.
EMISSION FACTOR (nilUjrcao/nsilo)
-19-
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952.
752.
c
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E
O
J3
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m
o
0
558
529
458
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S 258.
FIGURE 4
EXPRESSWAY
EMISSION FACTOR (ail!icrcr,o/nilo)
-V
-20-
-------
959.
752
783
658
o
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-5
o
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O
In
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558
522
458
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FIGURE 5
STREET CANYON
EMISSION FACTOR (millisrcn9/nilo)
-21-
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to be approximately 7 mg/min. This value appears to be relatively
independent of vehicle operation condition, being constant under normal or
malfunction conditions. This data point will be used to estimate the garage
concentrations of ammonia, but it should be kept in mind that the lack of
definitive data on these conditions make any of the resulting calculations
subject to some doubt until more information on idle emissions for various
vehicle emission control technologies.
In a worst case situation, where 100% of the vehicle fleet consists of
autompbiles with 3-way catalysts, the NH, 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 in an enclosed garage.
NH3 Ambient Air Concentration mg/m^
Emission Personal Garage Parking Garage
Fleet Make Up Factor Typical Severe Typical Severe
100% 3W 7 mg/min. 0.06 OT4T 0.06 6T39~
As mentioned previously, due to limited data, idle emission values can only be
evaluated for vehicles with 3-way catalysts. 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. The exposed population is
located on the sidewalk.
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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 100 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 NH- 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 NH_ exhaust emissions.
Health effects information on ammonia, as mentioned previously and as
contained in detail in Attachment I, indicate that ammonia is chiefly an
irritant gas particularly of the mucous membrances of the eye and respiratory
tract. Recovery from nonfatal ammonia exposure is usually complete.
Documentation of adverse physiological effects due to NH exposure at low
levels is poor, making the selection of a concrete range of concern
difficult. Table IV (table IV-1 in Attachment II) is an excerpt from the MR!
NH_ report which represents a collection of the human, dose-response data.
^ ^
The ACGIH has given a value of 18 mg/m as a time-weighted-average TLV for
ammonia in order to prevent worker discomfort and lost work efficiency. This
level seems appropriate as the high level of the range of concern for the
general public exposure to automobile exhaust. The lower level of the range
of concern is selected as 3.6 mg/m which is the odor threshold according to
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Table IV
Summary Of Human Experimental Exposure to NH3
Level of
Exposure
(mg/m3)
360-403.2
(several
studies)
180-344
144
96.5-106
(several
studies)
50-79.2
(several
studies)
18-72
Exposure
Time
Acute
Acute
Acute
Acute
Acute
Repeated
51.8-57.6
(several
studies)
36
(several
studies)
36
33.7
Acute
Acute
Repeated
Acute
Effects
Blood pressure decreased; NH3 in the
blood increased; rapdily reversible
changes in lung functions; lacrimation but
no coughing; widely varied subjective
responses.
Changes in lung functions at rest and during
exercise; changes in exercise cardiac
frequency.
Lung function and slight cardiac changes.
Signifcant lung function and cardiac
changes, at rest and exercise; some strong
irritation of eyes, nose, mouth or throat,
though others were relatively unaffected.
Slight lung function changes in some,
reduced cardiac frequency changes in some,
definite eye and throat irritation in some,
though others relatively unaffected.
Occasional mild irritation; increased Forced
Expiratory Volume @1 sec (FEV^) but not
other respiratory or blood pressure
parameters; apparent adaptation in the
ability to withstand brief excursions to 144
mg/m3.
Slight decrease in lung functions; definite
eye and slight throat irritation at the
higher level; slight irritation of some at
the lower level; odor detected.
No lung function changes; slight to
moderate irritation in some; odor
detected.
No significant changes in lung function,
blood pressure, rate of irritation or
neurological response.
Lowest concentration at which 4/4 detected
the odor.
23
Acute
9/10 detected the odor; no irritation.
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Table IV, cont.
21.6
13
10
6.1
2.2
0.45-1.0
0.32-0.76
0.32-0.65
Acute Faint Irritation in some; odor detected.
Acute Increased NH3 levels in blood and urine,;
decreased 02 consumption; no EKG changes;
rapid recovery.
Repeated Some changes in lung functions, heart
rhythm, and odor sensitivity.
Repeated No change in lung functions or heart rhythm;
changes in odor sensitivity.
Acute Tendency to decreased 02 consumption;
insignificant EKG changes; rapid recovery.
Repeated Decreases in some lung functions and camphor
odor theshold.
Acute Range of thresholds of NlTj perception for
22 people.
Repeated The upper range changed cerebral cortical
activity; 0.32 mg/m^ was the subthreshold
level.
Repeated Upper levels decreased eye sensitivity to
light; 0.32 mg/m-^ was the subthreshold
value for eye sensitivity.
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consensus opinion. Below this level several studies have shown physiological
3
effects, such as decreased eye sensitivity to light (about 0.5-0.7 mg/m ) or
changed cerebral cortical activity (0.76 mg/m ) but rapid recovery was
observed. It is not clearly known whether these measurements represent
adverse physiological effects on just changed physiological parameters.
Therefore, it is felt that a 3.6 mg/m level of NH, provided ample public
safety when compared to the spectrum of NH_ toxicity which seems moderate
and reversible in non lethal exposures.
3 3
To contrast the 3.6 mg/m - 18 mg/m range of concern for ammonia to other
levels of ammonia, it can be observed that the average baseline level of
3
ammonia in urban air is about 0.014 mg/m , and that the average level of
ammonia in a healthy persons expired air may range from 0.1 - 1.5 mg/m for
nonsmokers and 0.4 - 1.93 mg/m for smokers. There is also a marked
difference in the level of ammonia between nasal or oral breathers because of
bacteria present in the mouth.
3 3
Between the chosen limits of the range (i.e. 3.6 mg/m to 18.0 mg/m ),
there are scattered data points providing evidence of adverse physiological
effects caused by exposure to various concentrations of ammonia.
According to the methodology which has been used to establish a range of
concern for non-zero threshold pollutants, the boundary limits of the ambient
3
air range, of concern (mg/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 V and VI.
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Table V
Emission Factors Required to Result in
Exposure Limits for the Ambient Air Range of Concern
Ambient Air Scenario*
Street Canyon - Typical
Expressway - Close Proximity
Expressway - Typical
Street Canyon - Severe
Expressway - Severe
Roadway Tunnel - Typical
Roadway Tunnel - Severe
Personal Garage - Typical**
Parking Garage - Typical**
Parking Garage - Severe**
Personal Garage - Severe**
Emission Factor (mg/mile)
corresponding to a
360 mg/w~ exposure
85,714
34,285
29,032
12,765
7114
3205
1260 mg/mile
Emission Factor mg/mile
corresponding to an
18.0 mg/m^ exposure
428,571
171,428
145,169
63,829
428,571
16,028
6302 mg/mile
**
In order of increasing ug/nP concentration for 1 g/mile (or Ig/min)
emission rate (excluding garage situations).
These situations are based on emission rates in grams/minute, and are
evaluated in Table VII.
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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 mg/mile
corresponding to a corresponding to an
3.8 mg/m-* exposure 18.0 mg/m^ exposure
Parking Garage - Typical 4811 22788
Personal Garage - Typical 974 4615
Parking Garage - Severe 82 390
Personal Garage - Severe 56 268
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Conclusions - Ammonia
Several conclusions could be drawn from the information provided in this
report. These conclusions are listed below.
(1) Table V and VI identifies a range of concern in motor vehicle emission
units (mg/mile) for each ambient exposure situation simulated. These
ranges vary from 1,260 - 6,302 mg/mile to 85,714 - 428,571 mg/mile for the
moving vehicle situations (roadway tunnel, street canyons and expressways)
and from 56 - 268 rag/minute to 4811 - 22788 mg/minute 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 current estimated vehicle fleet emission factor for hydrogen cyanide
of 16 mg/mile is well below the lowest moving vehicle situation range of
concern of 1,260 - 6,302 mg/mile.
(4) The current estimate emission rate for an idling vehicle (7 mg/minute) is
well below the lowest stationary vehicle situation range of concern of 56
- 268 mg/minute.
(5) The highest emission rate reported for ammonia (518 mg/mile) is far below
the lowest level of the range of conern (1,260 mg/mile).
(6) Not enough information is presently available to determine whether ammonia
is hazardous to human health at levels below average odor threshold of 3.6
mg/m . Since there are some indications of physiological changes at
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lower levels of exposure, but no indications of adverse effects, future
research may be needed if a closer resolution of the low level health ef-
fects of ammonia is desired.
As more information becomes available on long term, low level exposures
to NH_, a lower level for the range of concern can be more accurately
chosen. At this point, however, it was necessary to make some assumptions in
order to asses a range of exposure concentrations for ammonia, 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 ammonia.
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References
(1) 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.
(2) Ronald L. Bradow, Fred D. Stump, U.S. EPA, "Unregulated Emissions from
Three-way Catalyst Cars", SAE Paper 770369, February - March, 1977.
(3) U.S. EPA Advisory Circular 76, June, 1978.
(4) U.S. EPA Advisory Circular 76-1, November, 1978.
(5) Robert J. Garbe, U.S. EPA, "An Approach for Determining Levels of
Concern for Unregulated Toxic Compounds from Mobile Sources",
EPA/AA/CTAB/PA/81-2, July, 1981.
(6) "Analytical Procedure for Characterizing Unregulated Pollutant Emissions
from Motor Vehicles", U.S. EPA, Environmental Sciences Research Labora-
tory, Report EPA-600-2-79-018, February, 1979.
(7) "Analytical Procedure for Characterizing Unregulated Emissions from
Vehicles Using Middle - Distillate Fuels", U.S. EPA Office of Research
and Development, Environmental Sciences Research Lab., Report
EPA-600-2/80-068, April, 1980.
(8) David W. Hughes, U.S. EPA, "Inspection and Maintenance for 1981 and
Later Model Year Passenger Cars", SAE Paper 810281, February, 1981.
(9) "Air Quality Assessment of Particulate Emissions from Diesel Powered
Vehicles", Pedco Environmental, Inc., March, 1978.
(10) Mobile Source Emission Factors: For Low Altitude Areas Only, EPA Report
No. 400/9-78-006, March, 1978.
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(11) 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.
(12) Lawrence R. Smith, Southwest Research Institute, Frank M. Black, U.S.
EPA, "Characterization of Exhaust Emissions from Passenger Car Equipped
with Three-way Catalyst Control Systems", SAE Paper 800822, June, 1980.
(13) C.M. Urban, Southwest Research Insitute, and R.J. Garbe, U.S. EPA,
"Exhaust Emissions from Malfunctioning Three-way Catalyst-Equipped
Automobiles", SAE Paper 800511, February, 1980.
(14) C.M. Urban, Southwest Research Insitute, "Unregulated Exhaust Emissions
from Non-Catalyst Baseline Cars Under Malfunction Conditions", May, 1981.
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