EPA/AA/TSS/83-7
                      Technical Report
                  Determination of a Range
                    of Concern for  Mobile
                     Source Emissions of
                      Hydrogen Sulfide
                             by

                       Craig A.  Harvey




                         August  1983


                            NOTICE

Technical  Reports  do  not  necessarily  represent  final  EPA
decisions  or  positions.    They   are  intended   to   present
technical analysis  of  issues using  data  which are  currently
available.  The purpose  in  the  release of such reports  is  to
facilitate  the  exchange  of  technical  information  and  to
inform  the  public  of  technical developments  which may  form
the basis  for a  final EPA decision,  position or  regulatory
action.
            U. S. Environmental Protection Agency
              Office of Air, Noise and Radiation
                  Office of Mobile Sources
             Emission Control Technology Division
                   Technical Support  Staff
                     2565 Plymouth Road
                  Ann Arbor, Michigan  48105

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Summary



This  paper  describes  an  effort  by  the  Emission  Control

Technology Division of the EPA to establish  a  suggested  range

of concern  for  hydrogen sulfide  (H2S)  emissions  from  mobile

sources.  As defined  in  this report,  the  lower value of  the

range  will  be   the   lowest   level  at  which  there  is  some

suggestion of adverse physiological effects,  the  upper  level

of the  range of  concern  is that  pollutant  concentration  above

which  the  studies  show that  the  pollutant causes so  great  a

health  hazard  as  to  strongly   suggest  it  be  avoided.   The

region  between   these suggested  limits  will   be  termed  the

"ambient  air range   of  concern",  indicating   the  bounds  of

uncertainty  regarding   evidence   of   adverse  physiological

effects caused  by  exposure  to  various concentrations of  the

pollutant.   This range is also  put  into  terms of  a  vehicle

emission   range  of   concern  to   show   what   quantities   of

automotive   emissions  would create   ambient   concentrations

within  the ambient air range of concern.



In light of  the  action called for in  section 202{a)(4)  of  the

Clean Air Act (CAA)(1)* and  due to  a concern within  industry
*Numbers  in parentheses  denote  references  listed  at  end  of
report.

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as to what emission  levels  will be used as the  basis  for  the



evaluation of current  and  future technologies,  a  methodology



was developed prior  to this paper  for  bracketing  a  range  of



concern  for  various  unregulated pollutants  (2).  This  paper



coordinates  the  efforts from  two  EPA  contracts  in order  to



use  that  methodology  specifically  for   an   evaluation   of



hydrogen   sulfide.    Mathematical   models  were   previously



designed  for various  exposure  scenarios   (such  as  enclosed



spaces,  expressways,  and  street canyons)  and  were   used  to



calculate  the  ambient  air   concentrations   resulting  from



various  mobile  source  hydrogen   sulfide  emission  factors



(grams/mile  or  grams/minute) .   In conjunction  with  this,  a



hydrogen   sulfide   health  effects  literature   search   was



conducted by Midwest Research  Institute under  contract to  EPA



to  aid  in the  determination  of the  final range  of  concern



(3) .  Some of  the  typical  health  effects  noted were  eye  and



respiratory  tract  irritation,  dizziness,  nausea and headaches



of various degrees, depending on exposure.








The  results   of  the  Midwest   analysis suggest  a  range  of



concern  for  ambient  hydrogen  sulfide concentrations  of 0.015



mg/m   to  14.0  mg/m .   This   corresponds  to  motor  vehicle



emission  levels  of  from 5.3-4,900  mg/mile to  479.3-447,300



mg/mile  on  the road  and 0.2-204  mg/min  to 1.9-1,770 mg/min



for garages,  depending on the  type  of  exposure.   Under normal



operating  conditions  or  when  a  vehicle   engine  malfunction

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does not  cause a  rich  mixture to  occur simultaneously  with



high catalyst temperature and low exhaust space  velocity,  the



resulting H.S  emissions are  negligible  (below  the  suggested



range of concern for any scenario).







The current average  in-use  vehicle  is estimated  to  emit  0.03



mg/mile of  hydrogen sulfide.   This is  well  below  the  lower



limit of  the  lowest  moving  vehicle scenario  range  of concern



of  5.3  mg/mile.  For moving vehicles the  lowest  ranges  are



those of  the roadway tunnel  scenarios.   For  this to result in



ambient  H?S  concentrations  within the  suggested  range  of



concern,  it would require most  of the  vehicles  in a tunnel to



be  malfunctioning  in  a   way  that   would   cause   high   H~S



emissions (over 5.3 mg/mi).







During  idle and very  low  speed conditions,  as would occur in



residential garages  or  public  parking garages,  recent  tests



have  found  no  H_S  emissions  for   normal   or  malfunction



operation.  This  was true  for a   range  of   vehicle emission



control   system  configurations   and   operating   conditions



including engine/emission control   system malfunctions.   This



includes  a   diesel  automobile,   a  non-catalyst   gasoline



automobile,  two 3-way catalyst equipped  automobiles,  and  two



oxidation catalyst equipped  automobiles.

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I.  Introduction







This  introduction  is  intended to  answer  the question  of  why



H2S   is  being  examined  in   this   report.    Emissions  from



gasoline-fueled vehicles have  been  characterized  by industry,



government  and private  researchers  for  many  years.   While



Federal motor  vehicle regulations  have  been in  effect since



1968  establishing emission  standards  for  HC and  CO (1973  for



NOx), there are also  a number  of  unregulated pollutants which



have  been  and are  being  characterized to  see if  they could



represent an  unreasonable  risk to  public health  and welfare.



One reason  these  other pollutants need to be  studied  is that



it  is possible for  a  new emission  control  system to increase



an  unregulated   pollutant   while  decreasing  the  regulated



ones.    For   instance,   catalyst   equipped   vehicles  emit



significantly  more  sulfuric  acid  than  non-catalyst vehicles



(4) .







Hydrogen,  sulfide  is  an  unregulated  pollutant emission that



has  been measured  in  various  concentrations  in   automotive



emission  tests (4,5,6,7).   Due   to  its  toxic  properties  and



its disagreeable  rotten-egg odor,  tests  have  been conducted



to  measure E^S  emissions  as a  function  of  driving  cycle,



emission control  system,  and  sulfur  content of  fuel.   These



data  along  with health effects  data, as summarized later  in



this  report, are  used to determine  the conditions under which

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automotive H2S  emissions could  possibly be  of concern  with

respect to public health and welfare.



Barnes and  Summers of  General  Motors  reported  in  1975  that

three   conditions  occurring   simultaneously   favored   the

formation  of  H_S  by   Pt/Pd  oxidation  catalysts:   (a)  rich

air/fuel  ratio  (i.e.,  a reducing condition);  (b)  low exhaust

space velocity; and (c)  high catalyst temperature  (7).   These

conditions  rarely  occur  simultaneously  with  properly  tuned

vehicles.  However, malfunctioning  vehicles  or  vehicles  with

maladjusted   carburetors  that   run   rich   may   meet   these

conditions and emit  hydrogen  sulfide  and  carbonyl sulfide*

(COS) .



In  the  interest of suggesting a  range of  concern for  levels

of   t^S   in  motor   vehicle    exhausts,    Midwest   Research

Institute  (MRI) under  contract to EPA compiled information on

the   health    effects   of   hydrogen   sulfide   at   different

concentrations  (3) .  The results  of  that work  form  the basis

for  the range  of  concern suggested  later in  this report.
*Carbonyl  Sulfide  has  a  typical   sulfide   odor   similar  to
hydrogen  sulfide.   A  fifty  minute  exposure   to   6,000  ppm
(14,700  mg/m^)  can  cause  death.    One  rich-malfunctioning
3-way  catalyst vehicle  tested for  COS  yielded approximately
20% as much COS as H2S.

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II. General Information on Hydrogen Sulfide







Hydrogen sulfide  (H-S)  is a colorless  gas having an  odor  of



rotten  eggs.    It can  result   in  severe  toxic  effects  if



inhaled  at concentrations  greater than  about  200  ppm  (260



ing/m ),  and  various  lesser effects  at  lower  concentrations



as detailed in the health effects section.







The  gas  must  be handled  carefully   because  of  its  toxic



properties (particularly  dangerous  because it may temporarily



desensitize the olfactory nerves  thus  making  it impossible  to



sense  its  presence),  and  its  explosive  tendencies  (low



ignition  temperature of  260°C  and wide  flammability  range



from 4.3 to 44% by volume in air).







Hydrogen   sulfide  reacts  rapidly  with   ozone   or   NC^  to



produce  SO-.   Any continued  presence  or  accumulation  in  a



strongly oxidizing atmosphere  is  unlikely.   Hydrogen  sulfide



is also  subject  to photodissociation.   Therefore,  in  the air



hydrogen sulfide  is  only  likely  to accumulate  at  night or  in



winter, even if it were emitted in substantial quantity.







The gas  results  from the  decomposition of  metal  sulfides and



albuminous  matter and  is  found   in   the  areas  of  mineral



springs, sewers, and  in some mines  where  it is  referred to  as



"stink  damp".   Hydrogen  sulfide   also  is  a  by-product  of

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                              8




several  industrial  processes,  including  synthetic  rubber,



viscose    rayon,    petroleum    refining,     dyeing,     and



leathertreating  operations.   In the  laboratory, H2S  usually



is prepared by  treating  a  sulfide  with an acid, such  as  iron



pyrites and HC1, or by heating thioacetamide,  CH3C(S)NH2.







In an automotive system, hydrogen sulfide  is  formed  from  fuel



sulfur   compounds    undergoing  reactions    in   a   reducing



atmosphere in the catalyst  system.   These reducing  conditions



occur  when  the  fuel/air  mixture  is  rich, such as during  a



cold   start-up,  a  high   acceleration   rate,   or  at   idle



immediately following  deceleration  from a high  speed  cruise.



Under these conditions  the  presence of an  oxidation or  three



way  catalyst   tends  to  increase  the  formation of  hydrogen



sulfide,  especially  during  the  last  condition above:  idle



following deceleration from a high speed.

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III. Legislative Background







When  the Clean  Air  Act  was  amended   in  August  1977,  the



additions  included  sections  202(a) (4)  and  206 (a) (3)  which



deal  with mobile  source  emissions  of  hazardous  pollutants



from vehicles manufactured after 1978.   These  sections are as



stated below:







202 (a) (4)







    "(A)   Effective  with  respect  to  vehicles  and  engines



    manufactured  after  model year  1978, no  emission control



    device,  system or element  of  design shall  be used  in a



    new  motor  vehicle  or   new   motor   vehicle  engine  for



    purposes  of  complying  with   standards  prescribed  under



    this  subsection  if  such device,  system,  or  element of



    design will  cause or  contribute  to an  unreasonable  risk



    to public  health,  welfare,  or  safety in  its operation or



    function.








    (B)   In   determining  whether an  unreasonable  risk exists



    under subparagraph  (A),  the Administrator shall  consider,



    among other  factors,  (i) whether  and to  what extent the



    use  of  any device,  system,  or element of design causes,



    increases,   reduces,   or  eliminates  emissions   of  any



    unregulated   pollutants;    (ii)   available   methods   for

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                             10




    reducing  or  eliminating  any  risk   to   public   health,



    welfare, or safety  which may  be  associated with  the  use



    of such devices, systems, or elements  of design which  may



    be used to conform  to  standards  prescribed  under  this



    subsection  without  causing   or   contributing   to   such



    unreasonable  risk.   The  Administrator shall  include  in



    the consideration required by  this  paragraph  all  relevant



    information developed pursuant to  section 214."
206 (a) (3)
    11 (A)  A certificate of conformity may  be  issued under this



    section  only   if  the  Administrator   determines  that  the



    manufacturer  (or  in  the case of  a vehicle or  engine  for



    import,  any  person)  has  established  to  the  satisfaction



    of the  Administrator  that any  emission  control  device,



    system,   or   element    of  design   installed   on,   or



    incorporated  in,  such  vehicle  or   enaine  conforms  to



    applicable requirements of section 202(a)(4).








    (B)   The  Administrator  may  conduct   such  tests  and  may



    require  the manufacturer  (or  any such person)  to  conduct



    such  tests  and provide such  information  as  is  necessary



    to carry out  subparagraph (A)  of  this  paragraph.   Such



    requirements  shall  include  a   requirement   for   prompt



    reporting of  the  emission of  any unregulated  pollutant

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                             11




    from  a  system  device  or  element  of  design  if  such



    pollutant   was   not   emitted,   or   was   emitted   in



    significantly lesser amounts,  from the vehicle  or  engine



    without  the use  of the   system,  device,  or  element  of



    design."







Prior   to   these   amendments,   EPA's   guidance   to   the



manufacturers regarding  hazardous  unregulated  pollutants  was



contained  in  the  Code  of  Federal  Regulations,  Title  40,



section 86.078-5b.   This subsection is stated as follows:







    "Any  system installed  on  or  incorporated in  a  new motor



    vehicle  (or new  motor vehicle engine)  to enable   such



    vehicle  (or engine) to  conform  to  standards  imposed  by



    this subpart:







          (i) Shall not  in  its  operation  or  function cause the



         emissions  into the  ambient  air  of  any   noxious  or



         toxic  substance  that  would  not  be  emitted  in  the



         operation of  such vehicle (or  engine) without such



         system,   except   as   specifically   permitted   by



         regulation;  and







          (ii)   Shall  not  in   its  operation,   function,   or



         malfunction   result   in   any   unsafe    condition



         endangering  the  motor  vehicle,   its  occupants,  or

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                             12
         persons,   or   property  in  close  proximity  to  the
         vehicle.

         (2)  Every manufacturer of new motor vehicles  (or  new
         motor  vehicle  engines)   subject    to  any  of  the
         standards  imposed  by  this  subpart  shall,  prior  to
         taking any  of  the  action  specified  in  section  203
         (a) (1) of the Act,  test  or  cause to be  tested motor
         vehicles   (or  motor  vehicle  engines)  in  accordance
         with  good engineering  practice to  ascertain  that
         such  test  vehicles  (or  test  engines)  will meet  the
         requirements  of  this  section for the  useful  life of
         the vehicle (or engine)."

Before certification  can be granted for new motor  vehicles,
manufacturers  are  required  to  submit a  statement,  as  well as
data   (if   requested   by   the   Administrator)  ,   which  will
ascertain  that  the  technology  for which  certification  is
requested  complies with  the standards  set  forth  in   section
86.078-5(b).   This statement is made in  section 86.078-23 (d) .

The EPA  issued an Advisory Circular  (AC  76)  in June 1978, to
aid the  manufacturers in  complying  with section  202   (a)  (4)  .
Manufacturers  were asked  to   continue   providing  statements
showing  that  their technologies  did comply with  the   vehicle
emission  standards  and   also  will  not  contribute   to  an
unreasonable risk to public health.

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                              13
Another Advisory Circular  (AC 76-1) was  issued  in November of
that  year  continuing  these  procedures  for  1980  and  later
model  years.   At  that  time  EPA  began  work  to develop  and
implement  a methodology which  would provide   a  preliminary
assessment  of  potential  mobile  source  unregulated  pollutant
hazards  in  order   to  assist  the  manufacturers in  deciding
which,  if  any,  unregulated  pollutants  are   of  particular
concern.

Up  to  this  time  several preliminary  assessments  have   been
made  covering  sulfuric  acid,  hydrogen cyanide,  and ammonia.
In  each of  these  cases  the  preliminary assessment  found no
reason  for  suspecting   a  public  health   problem  from  the
current  fleet  emissions  of these  pollutants,  and recommended
low  levels of  monitoring work  be  done  to  be  sure  that new
vehicle/emission control system  configurations did not result
in greatly  increased emissions.

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                              14




IV. Methodology Overview







Along with the previously mentioned  activities,  EPA,  with the



input  from  several   interested   parties,   has   developed  a



methodology  which  is  one  possible  approach  to  implementing



section 202  (a)(4) of  the CAA.   This approach  is explained in



detail in EPA  report  number  EPA/AA/CTAB/PA/81-2,  "An Approach



for  Determining  Levels  of  Concern  for  Unregulated  Toxic



Compounds from Mobile  Sources"  (2) .   Only a brief  summary of



this method will be presented in this report.







Under  contract to EPA,  Southwest Research  Institute  (SwRI),



and Midwest  Research  Institute  (MRI), have  provided valuable



information  for  this  effort.    SwRI developed  or  modified



mathematical models for  predicting ambient air concentrations



of  mobile   source  pollutants   for   a   variety  of  exposure



situations  including  enclosed  spaces,   street   canyons,  and



expressways.   Once   vehicle   emission   factors  for   various



vehicle  categories  have  been  determined   for   a  particular



pollutant,   these  models  can   then  be  used   to   calculate



corresponding  ambient  air  values  for both  severe and  typical



exposure situations for each scenario.







Health effects literature searches have  been conducted by MRI



in an  attempt  to  aid  EPA  in  suggesting  a range of concern for



various  selected  pollutants.   The  upper  level   of  the range

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                             15
will  be  that  value  above  which the  studies  show  that  the
pollutant  causes  so  great  a  health  risk  as  to  strongly
suggest  that  it  be  avoided.  The  lower value  of the  range
will be  the lowest level at  which there  is  some suggestion of
adverse  physiological  effects.    The  region  between  these
suggested  limits  will be  termed  the  "ambient  air  range  of
concern",  indicating  the  bounds  of  uncertainty  regarding
evidence of adverse  physiological effects caused  by  exposure
to   various   concentrations  of   hydrogen   sulfide.    Any
technology   whose   emissions    convert    to   ambient   air
concentrations within the  range  of concern  should be  subject
to  closer  scrutiny.    Technologies  with   emission   levels
falling  below  the lowest  level  of  the range  will constitute
"no  problem",   implying  a  low  level of  effort  monitoring.
Technologies with  emission levels above the  highest  value of
the range  should  be  considered  "high risk"  with  respect to
human health.

For the  purpose of this  report, this particular  methodology
has  been  used  to  develop  a  suggested  range  of  concern
specifically for motor vehicle emissions of hydrogen sulfide.

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                              16


V.  Vehicle Emissions of Hydrogen Sulfide



Hydrogen sulfide  exhaust emissions have  been  measured  for  a

variety of  vehicle  types.   The EPA recommended  procedure for

this  measurement  is  described  in an EPA  report  entitled,

"Analytical   Procedures    for    Characterizing    Unregulated

Pollutant  Emissions  from  Motor  Vehicles"  (10).  This  basic

procedure  was  used  to  obtain the H2S  emission  data  in this

report.   Small  amounts of  H_S  have  been  measured  in  the

exhaust  of  gasoline-fueled  vehicles  equipped  with  either

oxidation  or   three-way   catalysts   under   normal  operating

conditions,  at levels  between  0.0  and  1.5  mg/mile.   Under

malfunction conditions,  however,  these emissions can increase

considerably.   A  reported  emission rate  for  a  malfunctioning

vehicle operating  with a  3-way  catalyst was  as high as 8.2

mg/km  or  13.2  mg/mile,  for  the  sulfate  emission  test  (SET)*

driving schedule  (11).



Tests  were  run  by EPA-ORD  in order to  evaluate  the  impact of

low  ambient  temperatures  on  3-way catalyst-equipped  vehicle

emissions during normal operation  (12).  These studies showed
*Sulfate Emission  Test,  also known  as the Congested  Freeway
Driving  Schedule   (CFDS) ,   is  a  driving  cycle  with  a  35  mph
average  speed  designed   to  represent  driving  on  congested
freeways.

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                              17

                           Table I

              Hydrogen  Sulfide Emission Factors9


Number
Vehicle Category of Tests
Light Duty Diesel Vehicles0
Light Duty Diesel Trucks0
Heavy Duty Diesel Trucks^
Light Duty Gasoline Vehicles
Non-Catalyst; no air pump
Non-Catalyst; air pump
Oxidation Catalyst; no air pump
Oxidation Catalyst; air pump
3-way Catalyst; no air pump
3-way Plus Ox. Cat.; air pump
Light Duty Gasoline Truck6
Non-Catalyst, air pump
Catalyst, no air pump
2
1
0

33
11
35
24
22
23

0
0
Hydrogen
Sulfide
(mg/mi) SET
Schedule
Average
0.0
0.0
0.0

0.00
0.00
0.07
0.01
0.27
0.00

0.00
0.07
Malfunction
Worst Case
Average13
0.0
0.0
0.0

0.00
0.22
3.78
5.94
7.13
5.86

0.22
3.78
Heavy Duty Gasoline Trucksf        0         0.00        0.88
References appendix c of 13, 14, and 15; appendix B of 16; 17.

bAverage of 2 or 3 replicates of worst case test configuration.

°Below  minimum  limits  of detection  (FTP) .    No  data  available
on sulfate emission test cycle.
     tested, but assumed insignificant due to light duty data.

eSame as Light Duty Gasoline Vehicles.

fDue to  a  lack of sufficient data,  this  value is assumed  to  he
the  same as  that  given  for  non-catalyst,  light duty  gasoline
vehicles with  air,  adjusted for approximate differences  in fuel
consumption.

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                             18




that H_S  emissions  for the  most  part were  not  significantly



affected by  low ambient temperature  operation.   Of  the  four



vehicles  tested,  one  (Chevrolet  Caprice)  showed  significant



change due  to  the low  test  temperature,  and this  was  mainly



due to  the  cold-start  portion  of the  test.   For  this  first



portion  of  the  test,   the  H2S emissions  at  the   lower  test



temperature  (60°F) were about  20  mg/mile as  compared to  0.02



mg/mile at  the  higher   (normal) test  temperature  (81°F).   For



the complete Federal  Test  Procedure,   the  maximum  observed



H2S emission  level  was 4.21 mg/mile, which  was  at  60°F  for



the Chevrolet  Caprice.  Following  are  descriptions  of  other



data taken  into account in  the calculation of  fleet average



H^S emissions.








Malfunction Conditions








Average H2S  emission factors  for  various  vehicle  types  were



collected   from  several   available   sources.    The  values



obtained are  listed  in Table I.  These  emission  factors  were



compiled for  the  SET driving schedule,  unmodified  mode (i.e.



properly tuned  vehicle),  as well  as  for  various  malfunction



modes  (when  such  data  were  available).   Since  the  available



data  for  some  technologies  list both  an  unmodified  and  a



malfunction  emission   value,   the   final,   average  emission



factor  was  weighted  such   that  the  value  is  75%  of  the



unmodified  emission  rate  plus  25%  of the malfunction  rate.

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                              19

This calculation was based  on the assumption that 25%  of  the

vehicle fleet  operates  in  some  malfunction  mode  (i.e.,  rich

idle, misfire, high oil  consumption,  etc.)  at any given  time

(18).  Further work may identify a more accurate percentage.



The emissions  found  for  the  malfunction mode  are  especially

important to  this  effort due  to  the  fact that  H2S  emissions

tend  to  increase  under  malfunction  conditions.    Maximum

emission  levels  have  been listed  below for   three  vehicle

categories.



Maximum Reported t^S Emission Levels under Malfunction Modes

 (Highest Values Reported From Any Source on Any Single Test)
    Light Duty
    Vehicle Category       mg/mile         References

    non-catalyst           SET  0.29       (13, Table C-2)
                           FTP  0.82       (13, Table C-2)
    oxidation catalyst     SET  7.82       (13, Table C-12)
                           FTP  1.21       (13, Table C-150)
    3-way catalyst         SET 13.24       (11, Table IV  -34)
                           FTP  9.57       (14, Table C-12)
The reported  emissions  for the  3-way  catalyst vehicles under

malfunction conditions are higher  than those  of the other two

categories,  and they are  also  much  higher  than  any  of  the

vehicle categories listed in Table I.

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                             20
Driving Cycles

The  driving  cycles  used  in  this  report  were  the  Sulfate
Emission Test  (SET)  and idle testing.  The  results available
for  the  Federal Test Procedure  (FTP)  were  generally  similar
to  SET  values,  and  the  Highway  Fuel  Economy  Test  (HFET)
results were slightly lower.

It  may be  more appropriate  to choose  driving  cycles  which
would    specifically   simulate    those    scenarios    under
investigation  (enclosed spaces,  street  canyons,  etc.).   At
present,  however,   such  data  exist  only   for   the  garage
scenarios  (idle  test data) .  For  the most  part  the standard
test cycles  provide  only rough approximations  of the driving
that  occurs  in  the different   scenarios  examined  in  this
report.  It  is  not known at this point what  percent of error
is  introduced by using  these approximations.

Available  I^S  idle   emissions  data were  used  to  estimate
F^S  exposures  in parking  garage   situations,   and  will  be
discussed   later   in  this   report.   One   study   by  GM   (5)
investigated   idle  sulfide  emissions   as  a   function   of
oxidation  catalyst  temperature  and air/fuel  ratio.   It  was
found  that  the  mixture had to  be richer  than   the  correct
setting, and  catalyst temperature  needed  to  be  above 570°C to
result  in   any  detectable   HjS  formation  (greater  than  0.05

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                             21




ppm).   Obtaining  this  condition  required cruising the  car  at



96  km/hr   (60  mph)   for  seven  minutes   (during   which  no



detectable  H2S  was  emitted)  and  then  decelerating to  idle



for the sample collection.  This would  be  more representative



of a  situation like  a freeway off  ramp  rather  than  a  cold



start in a garage.







Fleet Average Emissions







Using  the  average  H2S   emission  factor  data  presented  in



Table I,  it  is possible  to calculate a  fleet average emission



factor.  The  information  necessary  to make these calculations



is  listed  in Table  II.   A  fraction  of  the vehicle  miles



traveled  (VMT) is listed for each vehicle  class.   These data



were  derived from  information presented in  the  Pedco  Report



of  1978  (19) , and  the  EPA report,  "Mobile  Source Emission



Factors:  For Low Altitude  Areas  Only"  (20).   Each vehicle



class   VMT   fraction  is  multiplied   by   the  corresponding



emission  factor for  that  class, giving  a fraction quantity of



pollutant  emitted   from  a  particular  vehicle  category  in



comparison  to other vehicle  categories  in  the  fleet.  The EF



X  VMT  fractions  for  each  vehicle  class  are  calculated and



then  summed  to obtain a total  fleet average.   For hydrogen



sulfide emissions,  this  value is  0.03  mg/mile.   This average



takes into  account  only  those  vehicle classes listed in Table



II.   Of course,   should   any  of  these  categories change,  so



would the total fleet  average.

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                             22




It is difficult to predict exactly what percentage  of  vehicle



categories will  make up  the entire  fleet at  any  one  time.



The most severe case, with respect to any  pollutant emission,



would  be  that  case  in  which  the  entire vehicle  fleet  was



comprised of  all of  the highest  emitting technologies.   In



order  to  account  for  differing  proportions   of  the  highest



H-S emitting technologies, Table III was put  together.







The emission  levels  presented in  Table III  reflect real  and



hypothetical situations in which different percentages of  the



vehicle fleet  consist  of  the  highest  emitting  technologies.



In reading Table III, it  should be  noted  that  it  presents  not



only  different  emission  control  technology  percentages,  but



also  different  malfunction  percentages.   The  last entry  in



this table, being the worst  case examined, tends  to overstate



the emissions that could  actually  occur in the  future,  since



it   is  highly  unlikely  that   catalyst-equipped  gasoline



vehicles would replace all light and heavy duty diesels.

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23
Table II
Example Calculation of
Fleet Average Emission Factor - Hydrogen Sulfide
(Sulfate Emission Test Cycle)
1981 Fleet, No Malfunction
Vehicle Class
Light Duty Diesel Vehicles
Light Duty Diesel Trucks
Heavy Duty Diesel Trucks
Fraction3
VMT
0.015
0.002
0.027
Emission
Factor0
(mg/mile)
0.0
0.0
0.0
EF x VMT
Fraction
0
0
0
Light Duty Gasoline Vehicles
Non Cat.; no air pump
Non Cat.; air pump
Ox Cat.; no air pump
Ox Cat. ; air pump
3-way Cat.; no air pump
3-way plus Ox Cat.; air
Light Duty Gasoline Trucks
Non Catalyst
Catalyst
0.147
0.098
0.289
0.261
0.012
pump 0.008

0.096
0.010
0.00
0.00
0.07
0.01
0.27
0.00

0.00
0.07
0.000
0.000
0.020
0.003
0.003
0.000

0.000
0.001
Heavy Duty Gasoline Trucks
0.035
0.00
0.000
Total Fleet Average
                                                    0.03 mg/mile
aBased  on 1978  data  for   fraction  of  VMT  as  a
vehicle age.
DFrom Table I.
                    function  of

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                             24

                          Table III
         Hydrogen Sulfide -  Fleet Average  Emissions9
                SET Driving  Schedule,  mg/mile
       Current (1981)  Fleet                    0.03

       Current (1981)  Fleet
       With 25% Malfunction                    0.75
           @ 2.89 mg/mile

       100% of Fleet
       With 3-Way Catalysts0                   0.27

       100% of Fleet
       With 3-Way Catalysts0                   1.99
       25% of them Malfunctioning
       @ 7.13 mg/mile
aBased on emissions in Table I, and fleet mix from Table II.

^Hypothetical "worst"  case  situation in  which  all  light  and
heavy  duty  vehicles  on  the   road  emit  H2S at  the  highest
light duty rates from Table I.

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                             25




VI. Hydrogen Sulfide Ambient Air Concentrations







The  H-S  emission   factor  information  provided  in  Tables  I



through  III can  be  used  in  conjunction  with  the  modeling



techniques  developed  by  Southwest  Research  Institute  (SwRI)



(see  Reference 2) ,  in  order   to  calculate  the ambient  air



concentrations  produced  by varying   levels  of  H2S  vehicle



emissions for  different  exposure  situations.   Future work may



identify  other  scenarios which would  also  be appropriate for



the  assessment of  human exposure to  exhaust  pollutants,  but,



for   this   task,   only   five   exposure   scenarios   were



investigated:   personal  garages,  parking  garages,  roadway



tunnels,  street canyons,  and   urban  expressways.   A  typical



and  severe  case  situation was  developed  for  each of  these



scenarios.   Each   situation has  been  considered separately,



and,  therefore, no  cumulative  effects have  been determined at



this  point.   Reference   (2)  discusses  the  reasoning  behind



using  these specific  scenarios  as   well  as   the information



used  in the determination of the modeling techniques.







Table  IV  presents  ambient air  concentrations  of  hydrogen



sulfide,  as   a  function  of  vehicle  emissions,   for  seven



ambient  situations.   These calculations  are   based  on  the



relationship of emissions to ambient concentrations for  each



scenario  as shown graphically  in Figure  1.  Garage scenarios



are  not included  in Table  IV,  but  are described  in the  text

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                             26
                          Table IV
                    Ambient Air Scenarios
           Hydrogen Sulfide Concentrations3,
                 Current
                  Fleet
Scenario13

Roadway Tunnel
  Typical
  Severe

Expressway
  Typical
  Severe
  Close
   Proximity

Street Canyon
  Typical
  Severe
         Current
          Fleet
           25%
       Malfunction
           Entire
           Fleet
           3-Way
         Catalysts
       Entire Fleet
       3-Way Catalyst
       25% Malfunction
0.03
0.09
0.004
0.02

0.003
0.001
0.01
0.84
2.14
0.09
0.38

0.08
0.03
0.21
0.30
0.77
0.03
0.14

0.03
0.01
0.08
2.23
5.68
0.25
1.01
0.21
0.08
0.56
aBased  on  fleet  average  emissions  from Table  III.   Note:
These numbers are ug/nH, not mg/m^.
bFor garage scenarios refer to text and Table V.

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                             27




because  idle/very  low  speed   emissions  of  H2S  have  been



found to be negligible.







Each  scenario  is  intended  to   represent a  specific type  of



situation.  The  typical  personal garage  situation  represents



a  30  second vehicle  warm-up  time  and  the severe  situation



simulates a five  minute  vehicle warm-up time.  Both of these



cases, of course,  take place within a  residential garage,  and



are intended  to  correspond to  summer  and  winter conditions,



respectively.







The  typical  parking  garage  case  simulates  an  above  the



ground,  naturally ventilated  garage  in  which it  is  assumed



that  a  vehicle spends  an equal  amount  of  time  on  both  the



parking  level  and ramp level.   The severe  case  represents an



underground garage wherein  the exposed  population  is assumed



to  be at  parking  level five   (lowest  level) .    It is  also



assumed  that  this  exposure  occurs  20 minutes after a major



event  in which   the  parking   structure  is  emptying from  an



essentially  full  condition.    The  initial  concentration  of



H2S is assumed to  be low  (0.001 mg/m ).







In  order to more closely  assess public  exposure  to  H-S  in



garage situations,  idle  emissions data  were collected  from a



limited  number of vehicles.    One  study  using  experimental



three way catalysts of widely  varying composition  found idle

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                             28




H..S  emissions   ranging   from   0.0  -   1.2   mg/minute   under



malfunction conditions  (11).  More  recently, six  production



vehicles were  tested  to  provide more  reliable data regarding



in-use  vehicle  operation.    This  testing  included  a  1970



non-catalyst   vehicle,   1978  and  1980   oxidation  catalyst



equipped vehicles,  1981  and  1982  three  way  catalyst equipped



vehicles, and  a 1981 diesel vehicle.   No ^S emissions were



detected from  any  of these  vehicles  during  idle or  very low



speed testing under normal or malfunction conditions  (24).







In  light of  these  findings  for  production vehicles,   there



seems to  be no  cause  for concern regarding  hydrogen sulfide



emissions in  personal  or public garages.  However, it should



be  noted that  these data are  from  a  sampling  of  only six



vehicles, and  in a  personal garage,   it would only  take one



vehicle  producing  hydrogen  sulfide   to create  a  potential



health problem.








Two  specific  tunnel designs were  chosen to  estimate the two



roadway  tunnel  cases.   A newly  designed,  two   lane roadway



tunnel,   with  moderate traffic  flow,  is used  for  the typical



condition,  while  an  old  design,  heavily-traveled  roadway



tunnel is used for the severe condition.







The  street  canyon situations are  simulated  by  examining the



parameters  of   two  street   canyons.   The   most  sensitive

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                             29




parameter in  this  model appears to  be the number  of traffic



lanes within the canyon.  The  typical  condition  is calculated



for  a  two  lane street  canyon  with  a  traffic  load of  800



vehicles  per  hour  and  a sidewalk  location  of  the  exposed



population.    The  severe  condition  is based  on  a  six  lane



street canyon with a 2400 vehicles  per hour  traffic load, and



the exposed population is located inside the vehicles.







Three different  cases  were considered in order  to cover the



possible  range  of  exposures in  an  expressway  situation.   1)



The  off  road case estimates  an exposure  involving  a  close



proximity to  the highway (i.e.,  living or working  close  to a



heavily-traveled  freeway).    This   case  is  calculated  on  a



short term  basis for  a distance of  50 meters  downwind of the



roadway.  2) The typical, on road  exposure  is  based on a four



lane expressway with a  traffic load of 1400  vehicles per hour



and  a  westerly   wind   (perpendicular  to   roadway)  of  1.0



meter/second.   In  this  situation,  the exposed  population  is



located inside  the vehicle.   3)  The severe  case represents a



heavily-traveled (3600  vehicles/hour), ten  lane freeway with



a  1.0 meter/second westerly wind  (perpendicular to  roadway),



and an in-vehicle  location of  the exposed population.

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                             30




VII. Hydrogen Sulfide Health Effects







A literature review on the  health  effects  of  hydrogen sulfide



was performed as an input to the  determination  of  a suggested



range of concern for mobile source emissions  of this compound



(3,21).  The specific health effects  that  were  found included



irritations  of   the  eyes  and   respiratory tract,  dizziness,



nausea  and  headaches  of  various  degrees depending on  the



exposure  level  and duration.   Chronic exposures  resulted in



more  adverse  effects   than   acute  exposures   for  a  given



exposure level.







Although  it would  be  more  appropriate to consider exposure



concentrations relative  to  their  corresponding  exposure times



for  each  resulting health  effect, this degree  of  detail was



not  feasible with the data available.  The  determination of



the  range  of  concern  was  based  primarily  on acute  human



experimental  studies,   since   these   were  thought  to  most



closely  simulate  the  exposure  situations examined  in   this



report.








The  literature  search reveals an  epidemiological  study  (22)



which  shows that a chronic exposure concentration  as  low as



0.05  mg/m   caused  a 50%  higher  morbidity  rate  as  well as

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                             31

headaches, weakness,  nausea,  and vision  problems  in a  group

of apartment  house  residents.   This  exposure,  however,  was

confounded  with  hydrocarbon  exposure.   Also,   the  control

group was not specified except that  they  did  not  use gas heat

(which  was  the  source of  H2S  and  HC) ,  so  there  may  have

been other variables besides the H2S and HC exposure.



There  is  also   a   study  done   in  an  occupational  exposure

setting  involving  babies whose  nursing  mothers  worked  in  a

viscose   (rayon)  shop.   During  nursing  these  babies  were

exposed  to  hydrogen  sulfide  from  the  mothers'  clothing  at

concentrations  ranging from  0.028   -  0.055  mg/m  .   Compared

to  babies whose mothers  worked  in other  shops without H-S

exposure,  these babies  were more  poorly  developed,  vomited

more  frequently after feeding,  and  were more  susceptible  to

severe infectious diseases  (23) .
The  TLV*   for   hydrogen  sulfide  is   14   mg/m ,   which  is

suggested  as  the  upper  limit  for  the  range of  concern for

healthy workers  and  similar people.   However,  the  above data

on  babies   indicate  that they  constitute a  more susceptible

subgroup.   Therefore,  0.03  mg/m  could be  considered  the

upper limit for a range of concern for babies.
*TLV  -  Threshold Limit Value  set  by the  American  Council of
Governmental  Industrial  Hygienists  for  8  hr/day,  40  hr/wk
exposure of healthy workers.

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                             32




Data concerning  less  severe  exposures indicate that  the  odor



threshold  ranged from 0.0007  to  0.5 mg/m .   The level  not



affecting  eye   sensitivity  to  light  was   0.008  to  0.010



mg/m ,  while  light   sensitivity-related  eye  responses  were



seen at 0.012 - 0.013 mg/m .







It  is  not known whether  these eye  responses,  in themselves,



could  be  considered  adverse  effects  or   simply   changed



physical  parameters.   Taking  this  into  account,  along  with



the  higher  susceptibility  of babies  mentioned  above,  the



suggested  lower  limit  of  the  range  of  concern   is  0.015



mg/m .







Between the chosen limits  of this  range,  there are a few data



points, some  of which show  adverse  effects and  some that do



not.   Therefore, this region  has  been  termed the  "range of



concern"  for  hydrogen sulfide concentrations in  the ambient



air.

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                             33




VIII. Determination of the Range of Concern and Conclusions







According to the methodology described earlier  in  the report,



the  lower  and upper  levels  suggested as  the  health  effects



range of concern are compared  to  the  mobile  source situations



to  calculate  a   corresponding  emission  factor   range   of



concern.   The chief   element   of  comparability  between  the



health  effects range  and  the  ambient situations  is  exposure



time.   Most  of the  mobile  source situations  simulate  short



term exposures (durations  of an hour  or  less  per  day)  perhaps



repeated several times per week over  an  extended  period.  The



average exposure situations appear more  likely  to  be repeated



often, while the severe exposure  conditions  would  likely only



occur on infrequent occasions.







With the above information,  the suggested  mobile  source range.



of  concern  for hydrogen  sulfide  emissions  can be  estimated



for  the different mobile source  situations.   Table V  lists



the  vehicle  emission  factors   which  correspond  to   the  high


           3                        3
(14.0  mg/m )  and  low  (0.015   mg/m )  portions of  the  range



of  concern  for hydrogen  sulfide.  Inspection  of this  table



shows  that  the  differences among  scenarios  result  in  a wide



range  of  emission  factors  corresponding  to   this  suggested



ambient air  range  of  concern.   More  importantly,   it  shows



that  none  of  the  scenarios  studied are  expected  to  have

-------
                             34




hydrogen sulfide concentrations  within,  let alone  above,  the



suggested range of  concern.







The findings  for - low ambient temperature  conditions  indicate



a possible  large  increase in  hydrogen sulfide emissions  for



certain emission control  systems.   Considering that  this  was



found  at  a  relatively  mild  temperature   (60°F)  ,  additional



lower  temperature   testing   may  be  worthwhile.   The  severe



personal garage  scenario would  be  the most  likely situation



for any problem  to  show up,  since in  that  situation  it would



only take  one vehicle  emitting  0.2  mg/min.  hydrogen sulfide



to enter the range  of concern.

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                              35
                           Table V
                       Hydrogen  Sulfide
            Emission Factors  Required to Result in
     Exposure Limits for  the  Ambient Air Range  of  Concern
Ambient Air
Scenario3
   Emission         Emission
Factor (mg/mile) Factor (mg/mile)
corresponding     corresponding
  to a 0.015       to a 14.0
    ^ exposure   mg/m^ exposure
  Maximum
Conceivable
 Fleet Avg.
Emissions0
(mg/mile)
Street Canyon -
Typical
Expressway -
Typical
Expressway -
Close Proximity
Street Canyon -
Severe
Expressway -
Severe
Roadway Tunnel -
Typical
Roadway Tunnel -
Severe
Personal Garage -
Typical0
Parking Garage -
Typical0
Parking Garage -
Severe0
Personal Garage -
Severe0
479.3
123.0
88.5
44.9
30.3
13.4
5.3
1.9
1.7
0.3
0.2
aln order of increasing mg/m-3
(or Ig/min) emission rate.
DFrom last column of Table III
malfunction.
°Emission factors are given
exposures.
dThe only vehicle to produce a
447,300
114,800
81,900
41,860
28,280
12,460
4,900
1,770
1,588
252
204
concentration
: All 3-way
in mg/minute
ny measurable
1.99
1.99
1.99
1.99
1.99
1.99
1.99
0.00d
0.00d
0.00d
0.00d
for 1 g/mile
catalyst, 25%
for garage
H?S at idle
(1.2  mg/min)   was  a  malfunctioning  Volvo  with  an  unusual
experimental  catalyst,   rather  than  the  standard  catalysts
actually used on production vehicles.

-------
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-------
                             37

                         References

1)   "Clean  Air  Act  as  Amended  August  1977,"   Public   Law
    88-206,  89-272,  89-675,  90-148,  91-604,  92-157,  93-319,
    95-95, 95-190.

2)   "An  Approach  for  Determining  Levels  of  Concern   for
    Unregulated  Toxic  Compounds  from  Mobile   Sources,"   R.
    Garbe, EPA Technical Report  No.  EPA/AA/CTAB/PA/81-2, July
    1981.

3)   "Hydrogen  Sulfide  Health   Effects,"    EPA   report   no.
    EPA-460/3-81-028,  by   Midwest  Research  Institute  under
    contract no.  68-03-2928,  EPA Project Officer  Robert Garbe.

4)   "Emission of Sulfur Bearing Compounds   from Motor  Vehicle
    and  Aircraft  Engines," EPA report  no.  EPA-600/9-78-028,
    by   J,    Kawecki,   Biospherics    Inc.,    contract   no.
    68-02-2926, August 1978.

5)   "Sulfide  Emissions   from   Catalyst-Equipped  Cars,"   S.
    Cadle,  P.   Malawa,   Environmental  Science   Department,
    General Motors Research Laboratories, 1977.

6)   "Measurements   of   Unregulated  Emissions   from  General
    Motors'  Light Duty Vehicles,"  S. Cadle, G. Nebel,  and R.
    Williams, SAE Paper 790694, June 1979.

7)   "Hydrogen  Sulfide  Formation  Over  Automotive  Oxidation
    Catalysts,"  G.   Barnes,  J.   Summers,   SAE  Paper  750093,
    February 1975.

8)   Van  Nostrand's  Scientific  Encyclopedia, Fifth  Edition, D.
    Considine, Ed., 1976,  P.  1315.

9)   "Characterization  of  Exhaust  Emissions  from  Passenger
    Cars  Equipped  with Three-way Catalyst Control  Systems,"
    L. Smith, F. Black, SAE Paper 800822, June 1980,

10) "Analytical  Procedures  for  Characterizing  Unregulated
    Pollutant Emissions from Motor Vehicles," EPA report  no.
    600/2-79-017.

11) Final  Report for  EPA Contract  no.  68-03-2485  by  Exxon
    Research    Corp.   on   Unregulated    Emissions    from
    Malfunctioning  3-way  Catalysts  on  a  1977  Light  Duty
    Gasoline Vehicle.

12) "Impact of  Low  Ambient Temperature  on  3-way Catalyst  Car
    Emissions," J. Braddock,  SAE Paper 810280, February 1981.

-------
                             38

13)  "Regulated and  Unregulated  Emissions from  Malfunctioning
    Oxidation   Catalyst   Automobiles,"   EPA   report    No.
    EPA-460/3-81-003,    by   Southwest   Research    Institute,
    Contract no.  68-03-2499,  January 1980.

14)  "Regulated   and  Unregulated   Exhaust   Emissions   from
    Malfunctioning  Three-way  Catalyst Gasoline  Automobiles,"
    EPA  report  no.  EPA-460/3-80-004, by  Southwest  Research
    Institute, contract no.  68-03-2588,  January 1980.

15)  "Regulated  and  Unregulated  Exhaust  Emissions   from  a
    Malfunctioning  Three-way Catalyst  Gasoline  Automobile,"
    EPA  report   No.   EPA-460/3-80-005,   by   Charles   Urban,
    Southwest  Research   Institute,  contract  no.  68-03-2692,
    January 1980.

16)  "Unregulated Exhaust  Emissions  from  Non-Catalyst  Baseline
    Cars  Under   Malfunction  Conditions,"   EPA   report   no.
    EPA-460/3-81-020,   by Charles   Urban,  Southwest  Research
    Institute, contract no.  68-03-2884,  May 1981.

17)  Nissan submission for the EPA 1981  Status  Report,  Chapter
    II. G., "Unregulated Emissions."

18)  "Inspection and Maintenance for 1981 and  Later Model  Year
    Passenger Cars,"  SAE Paper  810281,  D.  Hughes,  February
    1981.

19)  "Air  Quality  Assessment of  Particulate  Emissions  from
    Diesel-Powered  Vehicles," PEDCo Environmental,   Inc., EPA
    Contract  No.  68-02-2515,  Project  Officer,  J.  Manning,
    March 1978.

20)  "Mobile Source  Emission  Factors:  For   Low Altitude Areas
    Only,"  EPA report no. EPA-400/9-78-006, March 1978.

21)  "Health   Effects   of  Hydrogen  Sulfide,   A   Literature
    Review,"   Conducted  as   part   of an  evaluation  of  the
    health  effects  of   auto  emissions  from  malfunctioning
    3-way  oxidative catalysts,  G.  Fairchild,  DVM, Biomedical
    Research Branch, Clinical Studies Division, U.S. EPA.

22)  "Basic  Principles  for   the  Determination  of  Limits  of
    Allowable Concentrations  of  H2S  in  Atmospheric Air,"  R.
    Loginova,  in:  Limits   of   Allowable   Concentrations  of
    Atmospheric  Pollutants III,  V.  Riazanov, Ed., 1957.

23)  "Establishing Maximum Allowable Concentration  of  Hydrogen
    Sulfide," Atomospheric Air,  3:98-10., L.F. Glebova, 1960.

24)  "Unregulated  Emissions   for  Vehicles Operated Under  Low
    Speed Conditions,"  Lawrence  R.  Smith,  Southwest  Research
    Institute,  Draft  Final  Report  for   EPA  Contract   No.
    68-03-3073 Work Assignment 4, October,  1982.

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