v>EPA
United States
Environmental Protection
Agency
                            Environmental Criteria and
                            Assessment Office
                            Research Triangle Park NC 27711
EPA-600/9-78-015
June 1978
Research and Development
Altitude as a Factor
in Air  Pollution

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                         RESEARCH REPORTING SERIES

         Research reports of the Office of Research and Development, U.S. Environmental
         Protection Agency,  have been grouped into nine series. These nine broad cate-
         gories were established to facilitate further development and application of en-
         vironmental technology  Elimination  of traditional grouping was consciously
         planned to foster technology transfer and a maximum interface in related fields.
         The nine series are
               1    Environmental  Health Effects Research
               2   Environmental  Protection Technology
               3.   Ecological Research
               4   Environmental  Monitoring
               5.   Socioeconomic Environmental Studies
               6   Scientific and Technical Assessment Reports (STAR)
               7   Interagency  Energy-Environment Research and Development
               8.   "Special" Reports
               9.   Miscellaneous Reports
                              EPA REVIEW NOTICE


This report has been reviewed  by the Office of Research and Development. EPA, and approved for
publication.  Mention of trade names or commercial products does not constitute endorsement or
recommendation lor use.
          This document is available to the public through the National Technical Informa-
          tion Service, Springfield, Virginia  22161.

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                                EPA-600/9-78-015
                                July 1978
  ALTITUDE AS A FACTOR IN
         AIR POLLUTION
                  i L   606G4
                            -  -tion

                           „, Kjorn 167Q
ENVIRONMENTAL CRITERIA AND ASSESSMENT OFFICE
    OFFICE OF RESEARCH AND DEVELOPMENT
    U.S. ENVIRONMENTAL PROTECTION AGENCY
 RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711

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                              PREFACE
  This document has been prepared in response to a request by EPA Region VIII.
  The major objective of the document is to provide a state-of-knowledge report on
the differential effects caused by higher altitudes upon air pollution and related
activities. Although preparation of this report has required a review and evaluation of
current scientific knowledge regarding altitude effects on air pollution, the document
does not jconstitute an in-depth scientific review.
  A separate report to Congress is in preparation by Emissions Control Technology
Division (ECTD) at Ann Arbor for release October 1, 1978, in response to the Clean
Air Act Amendments of 1977. In contrast to the economic impact and technological
feasibility for  separate  high altitude standards to be discussed in the report to
Congress, the following document presents a  general overview of altitude effects on
pollution.
  The Agency acknowledges efforts and  contributions  of all  persons who have
participated as authors and reviewers of this document.
                                    in

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                              ABSTRACT
  Air pollution is affected by change in altitude. Cities with surface elevations above
1,500 meters have atmospheric pressures which are approximately fifteen percent
(15%) below pressures at sea level. Consequently, mobile sources designed to operate
at pressures of one atmosphere perform less efficiently at high altitudes and emit
greater amounts  of hydrocarbons and  carbon monoxide than those designed to
operate at the lower atmospheric pressures. The net result is a photochemical smog
problem which is further enhanced by the increased solar radiation of higher altitudes.
  The most significant effect of air pollution at high altitudes is upon human health.
This is due primarily  to the inhalation of carbon monoxide at the reduced oxygen
concentrations of high altitudes. Particularly susceptible is the fetus  exposed to
hypoxia and elevated carboxyhemoglobin  levels. There is  insufficient  evidence to
establish significantly increased ecological  effects at high  altitudes. Reduction in
visibility is being  observed in the vicinity of large metropolitan areas and near large
industrial complexes at high altitudes.
                                      IV

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                            CONTENTS

                                                                    Page
PREFACE	   iii
ABSTRACT	   iv
   I.  SUMMARY	  1-1
  II.  ENVIRONMENTAL RELATIONSHIPS	  2-1
       Effects of Altitude on the Atmosphere	  2-1
        Introduction	  2-1
        General Climatology	  2-1
        Chemical Properties and Phenomena	  2-2
        Effects of Altitude on Aerosol Dynamics	  2-3
       Effects of Altitude on Soil	  2-4
       Effects of Altitude on Water	  2-4
       References 	  2-5
 III.  AIR POLLUTION MONITORING	  3-1
       Introduction	  3-1
       Altitude Effects on Concentrations Measured In PPM	  3-1
       Altitude Effects on Concentrations Reported in Mg/m3	  3-2
       Altitude Effects on Calibration	  3-3
       Altitude Effects on Automated Methods (Analyzers)	  3-3
 IV.  STATIONARY SOURCES	  4-1
       Emissions	  4-1
       Measurements	:	  4-1
       Control Technology for Stationary Sources	  4-1
  V.  MOBILE SOURCES	  5-1
       Introduction	  5-1
       Theory 	  5-1
       Measurements	  5-2
       Emissions	  5-2
       Control Devices	  5-3
       References 	  5-3
 VI.  AIR POLLUTION EFFECTS	  6-1
       Human Health	  6-1
        General Considerations	  6-1
        Hypobaric Pharmacology  - Toxicology	  6-1
        Effects of Carbon Monoxide under Hypobaric Conditions	  6-2
        Effects of Altitude on Carboxyhemoglobin Formation Kinetics	  6-5
        Effects of Altitude and Carbon Monoxide on the Fetus	  6-8
       Ecology	  6-8
       Materials 	  6-9
       Weather, Visibility, and Climate	  6-9
       References	6-10
APPENDIX A 	A-l
APPENDIX B	  B-l

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                                       I.  SUMMARY
  Few air pollution studies have been performed in
which altitude (surface elevation above sea level) and
associated  atmospheric  properties  (pressure,
temperature, density,  solar radiation)  have  been
treated as independent variables. Notable exceptions
are the studies involving the health effects of carbon
monoxide  (CO)  under hypobaric conditions.  The
results of these studies indicate that the effects of CO
exposure and of hypoxia induced by high altitude are
similar and  suggest that when high altitude and CO
exposure are combined, the effects are additive. In
vivo, there is an interaction between these two factors
such that exposure to  one  may induce a physiological
response that influences the response of the body to the
other.
  Significant alterations in alveolar ventilation occur
at high altitudes. This results in higher aero-toxicant
dosage, especially for particulate or gaseous pollutants
produced   in  closed  spaces.   Absorption   and
translocation of aero-toxicants may  be affected by
changes in altitude; however,  experiments have not
been performed to confirm this.
  Very few studies have been performed regarding the
effects of air pollution as a function of altitude on
ecosystems.  The available data  are inconclusive;
however, they suggest that at least certain ecosystem
components may be more sensitive to air pollutants at
altitudes above approximately 2,500 m.
  Emissions from mobile  sources are  directly related
to changes in  atmospheric density, hence changes in
altitude. Other factors being equal, most vehicles will
emit more hydrocarbons and carbon  monoxide and
less  oxides  of nitrogen  as  the altitude increases.
Normally, the amount of hydrocarbons and CO in
diesels will increase with altitude. Changes in fuel-air
mixtures  and  fuel  composition  may  partially
compensate for the change in altitude.
  The efficiency of combustion will normally decrease
with an increase in altitude. This factor, coupled with
lower air viscosity at higher altitudes,  may affect
particulate concentrations in the vicinity of stationary
sources located at higher altitudes. However, the effect
is thought to be small compared to other factors due to
the decrease in atmospheric density.
  Altitude is a  significant  factor  in  ambient  air
pollution   monitoring.  Changes  in  ambient
atmospheric pressure directly affect the volume of air
sampled. Most techniques and devices are designed for
operation at  standard sea level pressure of 760 torr.
Failure to correct for a change in elevation to 1,525 m
(5,000 feet) may result in an error of approximately 15
percent in volume, hence concentration. Historically,
the National Air Surveillance Network (NASN) has
made  no   correction  for  differing  atmospheric
pressures   at  the  various  sites  in  its  network.
Calibration  methods are  affected  by  changes in
altitude and  care must be exercised to minimize this
effect.

  The two most common units of measurement of air
pollutants, micrograms per cubic meter (/ug/m3) and
parts per million (ppm), are both affected by changes
in altitude, but in different ways. Unless volumes of air
sampled  are corrected to  a  reference pressure  and
temperature, the calculated  value of  the mass of
pollutant per unit volume of air sampled will vary with
the altitude of the sampling site. Exposure to identical
parts per million concentration at  differing pressures
does not expose the receptor to identical numbers of
moles of pollutant  per unit volume  of air, since  the
conversion is a function of pressure. The implication of
this altitude effect on pollutant exposure data may not
be widely appreciated.

  Important  properties of  the atmosphere (pressure,
temperature,  density, solar  radiation, wind, stability)
vary  significantly  with  altitude.  These properties,
coupled   with   the  chemistry  of  the  medium,
characterize the behavior of the atmospheric boundary
layer. It is logical to conclude that  the behavior of
pollutants emitted to the atmosphere will be influenced
by variations in altitude. For example, reduction in
visibility  is  being  observed in the vicinity of large
metropolitan areas  and  near  large  industrial
complexes. Also, differences in altitude may account
for  a  portion  of  the variance  observed between
different urban atmospheres. Since altitude is only one
of many variables in a complex system, the question of
significance is one of degree.
                                                 1-1

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                    II.  ENVIRONMENTAL  RELATIONSHIPS
EFFECTS OF ALTITUDE ON THE
ATMOSPHERE

Introduction
  The purpose of this document is to discuss the state
of  knowledge  of the  effects  of altitude (surface
elevation  above  sea   level)  on  the  production,
dispersion, and potential effects of air pollution. There
are four urban  areas in the United States above 1,300
m and with populations greater than 200,000: Denver,
Salt Lake City, Albuquerque, and Colorado Springs.
The  types   and  degree  of  air  pollution vary
considerably across  the United  States. The main
factors causing the differences are source emissions,
chemical reactions in the free atmosphere, meteorology,
and topography. Altitude may also play a  role in
determining the degree of pollution.

  The meteorological and  climatic conditions of a
given  region are related to  its geographical location
and local topography. Location  determines  the
large scale weather influences that dominate a  region,
and topography alters air flow and thermal structure
of the atmosphere which may increase or restrict the
dispersion of air pollutants. Over the western  United
States  and  in  parts  of the eastern United  States,
climates  change rapidly  even  within   very  short
distances  due to the terrain and  the variations in
altitude. A change in all climatic parameters is  related
to changes in altitude. This is true, of course,  for the
free atmosphere as well as for different land elevations.
In general, as the elevation of the land increases above
mean sea level, there  is a  decrease in atmospheric
pressure, a decrease  in temperature, an  increase of
wind  speed  and an increase  of solar radiation. As
altitude increases there is a  complex effect  on  the
distribution   of  cloudiness,  precipitation,  and
pollutants.
  The effects of variations in ambient air temperature,
pressure, solar radiation and wind  speed caused by
increased  altitude on production and dispersion of
either primary or secondary pollutants may be either
direct or indirect.
General Climatology
  The weather at a given place is the sum total of all
meteorological variables, such  as  solar  radiation,
temperature, pressure, wind, precipitation, etc. Each
variable is subject to change with altitude.
  The intensity  of solar radiation  on a horizontal
surface  is generally greater at higher altitudes. This
results primarily  because of the molecular effect of
three attenuators of solar energy: air molecules, water
vapor, and cloudiness. Cloudiness is by far the most
important factor, except in cases of high levels of
particulates,  for  example,  volcanic  eruptions.
Although cloudiness tends to decrease with increasing
altitude, some communities located at high altitudes
with a peculiar meteorological or topographic setting
may  actually receive  relatively  small amounts of
sunshine because of significant cloud cover.
  In  terms  of loss of  ultraviolet radiation  to  the
atmosphere,  one may  consider  total loss from  the
outer limits of the atmosphere  to  sea level  as  100
percent. At 1,525 to 2,500 m (5,000 to 7,675 feet), only 80
percent  of that  loss will have occurred.  Therefore,
locations at  altitudes of 1,500 to 2,500 m will receive
some 20  percent more ultraviolet  radiation than
locations at  sea level. Absorption of solar energy by
water vapor strongly affects the longer wavelength
infrared radiation but does not affect the ultraviolet
radiation. Since water vapor concentrations generally
decrease with increasing altitude, a site at 1,525 m
will usually receive some five percent more total solar
energy than  a sea level locality.
  From  the central  United  States  to the  Rocky
Mountains,  land  elevation generally increases, while
atmospheric  water  vapor and cloudiness decrease.
Consequently, Denver  annually  receives  about  10
percent  more solar  radiation  than St.  Louis  or
Washington D.C., and about  20 percent more than
Chicago. This difference, however, is due to different
latitudes as well  as to the higher altitude in Denver.
  The normal  variation of  solar  radiation  with
altitude may be influenced by air pollutants, while the
intensity of solar radiation received at a given location
                                                 2-1

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may affect  the chemical  behavior  of these  same
pollutants.
  Atmospheric  pressure  normally  decreases
approximately  logarithmically  with  height. At an
altitude of  1,458  m (4,781  feet),  the pressure is
approximately  850  mb  (646 torr),  a  decrease  of
about  15  percent  of the standard  sea level value.
The diurnal variation at  a  given altitude is normally
on the order of one to three percent. It follows, of
course, that comparable decreases in density  occur
with changes in altitude.
  The  average annual temperature depends  to a
considerable degree on the  altitude of a location and
its surrounding terrain.  Higher altitudes generally
have  cooler  summer  temperatures,   and winter
temperatures can  reach very  low  minima. Local
terrain conditions have a marked influence on the cold
season temperatures, frequently resulting in  extreme
temperature differences between stations at the same
altitude. In all seasons, high altitude locations exhibit
a large daily temperature range.
  In the free troposphere,  the wind speed normally
increases  with  increasing  height above  sea  level.
However,   the  correlation  between  higher  land
elevations and higher wind  speed is in part due to the
occurrence of rugged terrain at  higher altitudes. The
dispersion of air pollutants is strongly dependent upon
local wind conditions.
  On the windward side  of mountainous terrain, the
amount of precipitation is considerably increased by
the forced ascent of the air. The leeward slopes, on the
other hand, are in the rain shadow and have much less
precipitation.
  The total precipitation also decreases on each range
as one proceeds through a mountain system to the
leeward side. For example,  more precipitation occurs
over the  western  than over  the   eastern Rocky
Mountains.  The amount of precipitation at  any one
location  is, therefore, dependent in part  upon its
exposure and altitude. Because precipitation is one of
the principal removal mechanisms for air pollutants,
changes  in  altitude may  contribute to significant
pollution effects by this mechanism.

Chemical Properties and Phenomena
  The photochemical reactions  of pollutants to form
smog are a function of several factors. The major ones
are:
    1.  Concentration
    2.  Ultraviolet  Radiation
    3.  Temperature
  All three factors are vitally important to the kinetics
of the reactions.
  The rate of a photochemical reaction is represented
by the general rate equation (1):
             Rate = K [Af[B]n                 (1)
where [A] and [B] represent reactant concentrations,
m and n represent the stoichometry of the reaction,
and  K  is the reaction rate constant. Therefore, a
concentration increase results in a proportional effect
on the rate of the reaction when m and n are unity.
  At higher altitudes, the atmospheric  pressure of the
ambient air is lower  than at low altitudes and this
results in lower partial pressures of oxygen. Unless
adjustments are made to increase air flow in engines,
the lower oxygen content will result in higher emission
rates of unreacted hydrocarbons from vehicular and
industrial  sources,  the  major source  of
photochemically reactive pollutants in urban areas.
  Sunlight  is  necessary to  initiate  ambient
photochemical  reactions.  The  simplified,  general
mechanism for the formation of photochemical smog
is given by the reactions:
       NO2 + hv
        0 + 02
        O3 + hv
        -.*
M
NO + O       (2)
    03
  02 + O*     (3)
   20H
 R + H20
   R02
RO + NO2
       O + H2O        -
       OH + RH       -
        R + O2         -
       RO2 + NO       -
          etc.
  Solar  radiation  is  supplied  to  these  reactive
pollutants  not  only by direct sunlight but also  by
reflection from the  atmosphere and from the earth's
surface. The quantity of light radiation supplied to the
reactive pollutants is dependent on the solar spectral
irradiance incident on the atmosphere, the solar zenith
angle, the nature and amount of scattering, diffusion,
absorption of radiance by the  atmosphere, and the
albedo of the surface under the region of interest. On
the other hand, the proportion of radiation absorbed
by   the  reactive   pollutants  is  dependent  upon
absorption coefficients, concentration  of pollutants,
and effective path lengths. All of these factors must be
considered  when evaluating the effect of light  on
photochemical  reactions. The  mechanism  of
photochemical smog formation  has been discussed by
Demerjian et a/.(l) and  Moortgat and Warneck.(2)
The exact  reaction  mechanisms proceeding from the
primary step of light absorption are not completely
understood. For the above reasons, it is difficult to
make exact statements about the photochemistry of
reactive pollutants even at sea level.
  It is perhaps more convenient to limit the discussion
to the effect of altitude on two properties: wavelength
distribution and intensity. Altitude effects have been
                                                 2-2

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observed for both  of these properties. Most of the
information  available  on  these  effects  has been
determined by use of aircraft at high elevations above a
ground level reference point. Nader (3) reported a 14
percent increase in ultraviolet light intensity between
Los Angeles (350 feet surface elevation) and nearby
Mt.  Wilson (5,700 feet  surface  elevation). These
measurements were made  on a relatively  clear day.
Included in the 14 percent was a 21  to 25  percent
increase in light intensity of wavelength distribution
between 3,050 and 3,450 A, and a 12 to 15  percent
increase in light intensity of wavelength distribution
between  3,450 and 3,950 A.  These  results would
suggest that altitude  significantly effects ultraviolet
light intensity; however, a further evaluation  of these
results is necessary since pollution in Los Angeles may
have   been  partly  responsible  for  the  observed
difference.
  If increasing  altitude  results in  increases  in  the
intensity of light at all wavelengths and the increase is
greatest for the lower wavelength  region, then  the
following effects will be expected:
    1. Increased light intensity at higher altitudes will
       result and, therefore, there will be an increase
       in photochemical activity.
    2. The rate of the primary step for the production
       of  photochemical  smog,  NO2  photolysis,
       will  be  significantly  increased  due  to  the
       increased intensity  of shorter wavelengths of
       light at higher altitudes. The increased lower
       wavelength  light  may  also  have a  great
       effect  on   reactions   of  other  secondary
       pollutants such as the aldehydes and ketones.
  Temperature  is  an important  parameter in  all
chemical reactions. Temperature is a measure of the
kinetic energy  available  to  molecules;  this energy
directly  affects  the  collision  frequency  between
reactant  molecules.   Consequently,  elevated
temperatures  produce higher  collision  frequencies
between molecules resulting in a greater probability of
a reaction occurring. Also, since most  reactions have
an activation  energy, as the temperature  increases,
more   energy is supplied  to  overcome  this energy
barrier, and the  reaction rate increases.
  Within the troposphere, ambient air temperatures
generally decrease with increasing altitude, except in
the case  of temperature  inversion.  However,  an
industrialized city contributes a considerable amount
of heat to its surrounding atmosphere. For this reason
the ambient temperatures  of the atmosphere above
cities at higher altitudes may be higher than above
adjacent non-urban locales. In general, however, the
lower temperatures characteristic of higher altitudes
should   contribute  to  slowing of  photochemical
reactions.
  To conclude,  if  emissions  at  high altitude  are
comparable to those  found at lower altitudes,  the
greater  solar intensity at high altitudes will tend to
increase photochemical smog production, while  the
lower temperatures will tend to decrease it. Due to the
different effects of these parameters and the complex
interactions in  photochemical  reactions, it  is  not
possible to provide a general prediction of the altitude
effect on photochemical smog formation.

Effects of Altitude on Aerosol Dynamics1
  The only mass transport parameters for air that
exhibit  significant dependence on elevation are  air
density  (or   molecular mean-free  path) and
temperature. It is possible that the rates of aerosol
processes such as nucleation, condensation, dry and
wet  deposition,  coagulation,  and  gas-to-aerosol
conversion may  be  different at high elevation with
respect to sea  level. Also, the performance of aerosol
instrumentation  and the deposition  efficiencies  of
aerosols may be a function of elevation.
  The process of heterogeneous nucleation is not yet
completely understood, and it is not possible to state
whether  nucleation  rates  for  the  same  mass
concentration   of nucleating  monomers  would   be
increased or decreased at higher elevations; this rate
also has a complex dependence on other factors, such
as the aerosol size distribution in the  air. The rate of
condensation  is  not  expected to be significantly
different at high elevations since  the half-life  for
molecular  collisions with urban aerosols is on  the
order of one second. Coagulation rates of fine aerosols
are pressure and temperature dependent; for the same
temperature, fine aerosols should coagulate 20 to 40
percent  faster at  high   elevations.   A decrease  in
temperature decreases  the coagulation rate.
  The process  of dry  deposition for  aerosols is  not
completely understood. Generally, the deposition of
aerosols with  diameters greater  than  0.3  /urn  is
discussed in terms  of sedimentation and  impaction.
Settling for aerosols with diameters less than 75 urn at
high elevations during cold periods (242° K) will  be
greater (10 to 20 percent) than at low elevations during
warm (293° K) periods; however, there will be little
difference when the temperatures are equal. Impaction
efficiencies may be on the order of 20 percent greater at
high elevation. Most likely, dry deposition velocities of
coarse particles will be approximately equal for high
   'For a more detailed discussion of this subject, see Appendix A
                                                  2-3

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and low elevations. Dry deposition of aerosols with
diameters less than 0.3 /urn is generally discussed in
terms  of  Brownian   diffusion.  The  fine aerosol
deposition velocities will probably be about the same
for high and low elevations at a temperature of 293° K;
however,  if the temperature is 242° K at the high
elevation site, then the fine aerosol deposition rate will
be lowered by about 20 percent.
  The  performance  of  aerosol samplers  and monitors
calibrated at  lower elevations may be affected when
used at  high  elevations.  The  devices  that will  be
affected  are  those that  size  particles by the air
resistance-to-motion  principle.   Such  devices
include   sedimentation  chambers,  elutriators,
impactors,  cyclones,   diffusion  batteries,  electrical
mobility  analyzers,   etc.  The most  important
parameter to  be considered is the  air viscosity for
devices  sizing aerosols  with diameters greater than
about  0.5 /urn.  The air viscosity is independent of
pressure,  but decreases as  temperature  decreases.
Thus,  elutriators,  impactors,  and  cyclones  are
expected  to  increase  in efficiency. The sizing of
small  particles  by diffusion batteries  depends  on
both  the  viscosity  and  the  molecular  mean-free
path,  and  is   handled in  a  direct  manner  by
recalculating  the  aerosol diffusion  coefficients.
However,  the  electrical  mobility analyzer performance
is  more  complex  due to its additional dependence
on the level of aerosol charging.
  One of the important differences in  high and low
elevations is the  change in lung deposition efficiencies
of aerosols.  Since the air is equilibrated to body
temperature  before passing the pharynx, the air
viscosity is  constant  in the lungs at high and  low
elevation. However, the pressure at high elevation is
decreased, resulting in  an  increase  in the molecular
mean-free  path.  Thus,   the  particle  diffusion
coefficients will be increased. Coarse aerosols will have
about the same deposition efficiencies in lungs at high
and low elevations, but fine particles may be deposited
with  up  to  20 percent greater efficiency at high
elevation.

EFFECTS OF  ALTITUDE ON SOIL
   Soils at higher altitudes in the eastern United States
are basically gray-brown podzolic soils. These are high
in organic  matter, have low  acidity,  and contain
numerous  microorganisms  and  earthworms.  In  the
Rockies  and the other mountains of the West, they
vary  from shallow soils of mountain,  upland,  and
valley to the gray desert types.
   Studies dealing with effects of pollutants on soils at
high altitudes are limited in number. Therefore, it is
necessary to theorize. At high altitudes, radiation and
wind have easier access to the soil and rock surfaces
due to less vegetation. Climatic changes are extremely
important because of the precarious balance of the
soil, its organisms, and the vegetation growing in the
soil. Any pollutants which might bring about a change
in soil  acidity,  to cause vegetational  changes  or
influence mineral cycling, could adversely affect the
soil. Nutrient cycling and the decomposition of leaf
litter is of importance at surface elevations below the
timberline, which includes almost all of the mountains
of the eastern  United States. Therefore,  pollutant
effects  upon these processes can appropriately  be
studied  in  this area.  Witkamp (4) has shown that
bacterial  and  fungal  populations   generally  are
decreased   at  higher   elevations.   Temperature,
particularly, plays an important role in the numbers of
bacteria  and  fungi  that are present  and  in the
respiration rate of soil microorganisms.
  Inman el al. (5) and Abeles et al. (6) have shown that
soil microorganisms have the ability to take up CO and
hydrocarbons   from  auto  exhaust.  Many  other
scientists have shown that hydrocarbons can be readily
metabolized by microorganisms.  However, very few
studies have shown, at any altitude, how the changes in
microbial populations  in the soil influence the soil
itself. There is  a general need for soil studies at  all
altitudes.
  The  Inman et al. study indicates that CO uptake
appears to be dependent upon altitude. The CO uptake
decreases from about  80 Mg/hr  m2  at  sea level  to
approximately 5/ng/ hr m2 at 610 m (2,000 feet). How-
ever, Inman points out that altitude is but one of several
variables involved  in the reactions. Other factors are
temperature,  soil  type,  and  the   types  of
microorganisms.   These  factors  are  difficult  to
separate. A study  is required that uses the same soil
with the same amount and  types of microflora and
microfauna. This  soil could  then be transported to
different land elevations  and the pollutant  uptake
measured. Inman's results show that the maximum CO
uptake occurs at approximately 35°C. If higher land
elevations  have lower temperatures, then  the CO
uptake would be expected to decrease with all  other
variables remaining constant.
EFFECTS OF ALTITUDE ON WATER
   For the purposes of this report, it is assumed that
pollutant-to-water interactions take place mainly via
the following mechanisms:
     1. Pollutant contribution to the atmosphere from
       sea and land masses of water.
                                                  2-4

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    2. Pollutant  removal from the atmosphere by
       scrubbing action of rain and by contact of the
       atmosphere with water masses.
    3. Change of  pollutant  form  due to  chemical
       reaction with water.
  Seiler and Junge (7) and Swinnerton el al. (8) have
stated that the ocean  and rain water are sources of
carbon monoxide. Swinnerton found that rain water,
collected at an altitude of about 1,525 m (5,000 feet),
was supersaturated with carbon monoxide. As yet no
mechanism has been proposed and verified to account
for this phenomenon.
  Organics with low boiling points that are immiscible
with  water [i.e.,  CH2C12,  (CH3-CH2)2-O]  would
evaporate  rapidly into the atmosphere if discharged
into a river, pond, or lake, and this would occur more
rapidly at  higher  altitudes.
  For this reason, pollutant  control  strategies for
industrial   activities  operated  at  altitudes   above
approximately 1,525 m (5,000 feet) should consider the
increased  volatility of organic  waste  discharges to
determine  impact on the atmosphere.
  With regard to 2 and 3 above,  the scrubbing of
pollutants  from  the atmosphere by  water and the
change of pollutant form due to reaction with water
probably would not be significantly different between
1,525 m (5,000 feet) and sea level.

REFERENCES

  1.  Demerjian,  K..  L.  , J.  A. Kerr, and J. G. Calvert. The
    Mechanism  of  Photochemical  Smog  Formation.  Adv.
    Environ. Sci. Technol. 4:1-262, 1974.
  2.  Moortgat,  G. K. and P. Warneck. Relative O('D) Quantum
    Yields in the Near UV Photolysis of Ozone at 298° K.  Z.
    Naturforsch. Teil A 30:835-844, 1975.
  3.  Nader, J. S., (ed.). Pilot Study of Ultraviolet Radiation in Los
    Angeles, October  1965. P.H.S. Publication No. 999-AP-38,
    U. S. Government Printing Office, 1967, pp. 1 - 98.
  4.  Witkamp, M. Microbial Populations of Leaf Litter in Relation
    to Environmental Conditions and Decomposition. Ecology
    44:370-376, 1963.
  5.  Inman, R. E., R. B. Ingersoll, and E. A. Levy. Soil: A Natural
    Sink for Carbon Monoxide. Science / 72:1229-1231, 1971.
  6.  Abeles, F. B., L. E. Craker, L. E. Florrence, and G. R.. Leather.
    Fate of Air Pollutions: Removal of Ethylene, Sulfur •.Dioxide
    and Nitrogen Dioxide by Soil. Science 772:914-916, .1971.
  7.  Seiler, W. and C. Junge. Carbon Monoxide in the Atmosphere.
    J. Geophys. Res. 75:2217-2226, 1970.
  8.  Swinnerton, J.  W ,  R.  A.  Lamontgne, and   V.  J.
    Linnenbom.  Carbon  Monoxide  in  Rain  Water. Science
    / 72:943-944, 1971.
                                                     2-5

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                       III.  AIR  POLLUTION MONITORING
INTRODUCTION
  Gaseous air pollutants such as sulfur dioxide (SO:),
carbon monoxide (CO), ozone (Os), etc., are measured
by determining their concentrations in the ambient air.
Since both these pollutants and the ambient air are
gases, changes in pressure directly affect their volume.
According to Boyles law, if the temperature of a gas is
held constant, the volume occupied by the gas varies
inversely with the pressure (as  pressure increases,
volume decreases). The major effect of altitude on air
pollution monitoring is that volume differences result
from the differences in pressure  that prevail when
monitoring is carried out at different land elevations.
This  pressure  effect  must  be  considered  when
measuring  pollutant  concentrations.  Normal atmo-
spheric  pressure variations at any given sampling
location  have  very  little  effect  on  air  pollutant
measurements. However, when comparing pollutant
concentrations  measured  at  significantly different
altitudes, volume corrections are sometimes necessary
depending on the pollutant concentration units used.
  The two units most  commonly used in reporting
pollutant concentrations are micrograms per cubic
meter (/ug/ m3), a "mass of pollutant per volume of air
sample" measurement, and parts per million (ppm), a
"volume of pollutant  per volume of air  sample"
measurement.  When /*g/m3 units are used, volume
corrections can  be  made  such that  results  can be
reported at a reference pressure (760 torr). When ppm
units are used, volume corrections are not necessary
because the ppm unit is not dependent on pressure
effects.
  The discussion on the following pages will show how
altitude  (pressure)   variation  effects  should  be
considered when reporting air pollutant measurements
expressed  either  as  ppm or ng/m3. Also a  brief
discussion is given on how altitude affects calibration
and air monitoring instruments.

ALTITUDE EFFECTS ON CONCENTRATIONS
MEASURED IN PPM
  The measurement of gaseous air pollutants in ppm
(volume per volume) units  is widely used in the air
pollution scientific community. The use of this unit has
a number of advantages. It is dimensionless  and is
numerically equivalent to such ratios as microliters per
liter, molecules per million molecules, and micromoles
per mole. It is readily understood by non-scientific
people and can be easily changed to "parts per billion"
to eliminate decimal fractions.
  The ppm  unit is  used  primarily in  reporting
pollutant concentrations measured with continuous
analyzers, because it is a ratio of two volumes and is
therefore independent of pressure and temperature.
Both  gases (pollutant  and air sample) closely  follow
the ideal gas law (Boyles law) where volume changes
proportionately  in  response  to  changes in  pressure;
thus, their ratio remains unchanged. This means that
an air pollution analyzer can measure concentrations
in ppm under  conditions of varying pressure without
error due to the resulting changes in volume. This does
not mean, however, that an analyzer can be calibrated
at low altitude and  then carried to a higher altitude
without recalibration.  In this  case the sample air
metering device  would  be affected by  the pressure
change from one altitude to another and recalibration
would be necessary at the new altitude.
  The primary disadvantage of the use of ppm units is
the fact that while the ppm  unit does not vary with
pressure, the mass  of a gaseous  pollutant per unit
volume does vary with pressure. For example, air
containing 1 ppm of a pollutant at a high altitude such
as Denver,  Colorado, will still contain 1 ppm if that air
is brought  down to  sea level. However, the mass per
unit volume of air will increase with the  decreasing
altitude.
  This relationship can be demonstrated as follows:
recall  that  parts  per  million  can  be  defined as
microliters (/nl) of gaseous pollutant per liter of air, or
     _
ppm -
     _ microliter (/il) of gaseous pollutant (g.p.)
      - * - "*-* —
                   liter (1) of air
  If gas behavior is assumed to be ideal, the ppm con-
centration unit can be converted into moles of gaseous
                                                 3-1

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pollutant per liter of air, a unit which is most useful in
considering health effects caused by exposure to air
pollution.
  The derivation of moles of gaseous pollutant per
liter of air from the ppm unit follows:
moles of g.p.
   1 of air    =
1 mole of g.p.
24.45 1 of g.p.
760
     of air
298
 T
1(P1 of g.p.
 Ml of g.p.
                           (5)
where     P = atmospheric  pressure  at  sampling
               site, torr,
           T = temperature  at  sampling site, °K

         760 = standard pressure, torr,

         298 = reference temperature, °K (298° K or
               25° C is used by EPA as more appro-
               priate  to  ambient air  measurement
               conditions than  the  conventional
               273° K orO°C), and

       24.45 = liters of gas/mole, at standard pres-
               sure and reference temperature
         g.p. = gaseous pollutants
 which simplifies to:

     moles of g.p.
       1 of air
         1.604 x  10"8 x  |r
  It is evident from equation 6 that constant parts per
million contain differing numbers of moles per unit
volume of air as pressure (and temperature) changes.
For this reason exposure to identical parts per million
concentration  at differing pressures does not expose
the receptor to identical numbers of moles of pollutant
per  unit  volume  of air.  Although  air pollutant
concentrations reported in ppm units are not directly
affected by altitude differences, the effective mass per
unit volume differences should be considered  when
interpreting data taken from different altitudes. It is
important to note that if concentration results, in ppm,
are to be converted to moles per liter air or to pg/m*,
the pressure at which the sample was  taken must be
known.
measurement methodology  is based  on a  manual
method (i.e., the pararosaniline method for measuring
SO2). In the latter case, samples are generally collected
in liquid absorbing solutions  which are taken  to a
central laboratory for chemical analysis. In this case,
the pollutant  is analyzed  on a weight basis  and,
consequently, results are computed in  ng/m} units,
which can be converted to  ppm units if the pressure
and temperature at which the  sample was taken are
known.
  When air pollutant concentrations are reported in
Ugl m3, the volume of air sampled must be corrected to
a reference pressure and temperature  (temperature
effects  are  not considered  in this  discussion) if the
comparisons of data from different locations are to be
made. If not, the calculation of the mass of a pollutant
per unit volume of air sampled will be  a function of
pressure, and concentrations obtained will vary  with
the altitude of the sampling site.
  For example, consider a situation in which 50 /ug/ m3
of paniculate matter is  measured  without correction
at a  location having an atmospheric pressure of 625
torr (common in Denver). If a cubic meter of that  air is
pressurized to 760 torr (reference conditions), it would
be compressed to  about 80 percent of its  original
volume, and the correct particulate concentration per
cubic meter would be correspondingly higher, as the
following calculation shows:
                                                                  V2 =
                                                       PiVi
                                                        P2
                                   where  V2 =  volume at reference conditions,
                                          P2 =  760 torr,
                                          Vi = 1 m3,
                                          Pi =  625 torr,  and

                                   therefore,                    3
                                             v  -  625 torr  x  1 m  _    .  3.
                                             V2 -  	-,n .	  - 0.82 m
                                                      760 torr


                                   thus, the particulate matter concentration would be
                                                                0.82m
ALTITUDE EFFECTS ON CONCENTRATIONS
REPORTED IN
  The  micrograms  per cubic meter  unit  is  used
primarily for pollutants which are not gases. However,
it is  also  used  for  gaseous pollutants  when the
                                     It is obvious  that volume corrections should be
                                   made when  pollutant concentrations, in terms of
                                   Mg/m3, are compared between locations of different
                                   altitudes.   For  purposes  of  comparison,  all
                                   measurements reported in /zg/m3 should be corrected
                                                 3-2

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to the reference pressure of 760 torr, as specified in the
Code of Federal Regulation, Part 50.3 (40 CFR Part
50.3).
  It should be noted here that historically the EPA
National Air Surveillance Network (NASN) has made no
corrections for the differing atmospheric pressures at
the various  sites in its  network. These corrections
would require measurement, or estimation,  of the
barometric pressure  during sampling at each site.
Pragmatically, for many sites, the elevation correction
would be comparable to  or less than the intrinsic
variability of the earlier monitoring methods.


ALTITUDE EFFECTS ON CALIBRATION
  Dynamic calibration of methods and instruments
for measuring gaseous  air pollutants is commonly
done in one of two ways. The first of these employs a
known amount of a pollutant gas, generated at the alti-
tude of measurement and diluted with pollutant-free
air  to the various concentrations needed for calibra-
tion.  Permeation  tubes and constant flow  ozone
generators are two examples of devices  using this
procedure  to  prepare   calibration  gases.  The
second  calibration method uses  known  mixtures
of the gaseous pollutant in a diluent gas,  contained
in  pressurized  cylinders.  These  cylinders  are
transported to the site of the measurement needed
for  calibration.  Altitude does not generally  affect
either of these procedures.  When  permeation tubes
(or  an ozone generator) are used, the calibration
gas  is prepared at the altitude where it  is  being
used. When  pressurized  cylinders  are  used,  the
concentration  of pollutant  in  the cylinder  is
assayed  in  ppm  units,  which  is  independent   of
pressure.
  When working in units of /ig/ m3 (mass per volume),
a correction must be applied in those calibration pro-
cedures using calibration gases that  have been pre-
pared at one altitude and used at a different altitude.
For example, a cubic meter of a calibration gas that
contains 100 y.g of a pollutant at sea level atmos-
pheric pressure will  expand with  the  decreasing
pressures  at higher altitudes. Thus, a cubic  meter
of the  expanded  gas  is  left with proportionately
less of the 100 ng of pollutant.


ALTITUDE EFFECTS ON AUTOMATED
METHODS (ANALYZERS)
  Most air  pollution  analyzers can  be operated at
almost any surface elevation in the continental United
States. The exceptions are the monitoring systems that
employ hydrogen flames, such as the flame ionization
detector for  hydrocarbons or the flame photometric
detector for SCh. At altitudes in excess of 3,000 m
(10,000 feet),  the  partial pressure of  oxygen is
sufficiently low that an auxiliary oxygen supply may be
necessary to support the combustion of these flames.
  As  stated  above, the main influence of altitude on
measurements is that of pressure, which alters the mass
of a pollutant per unit volume. For example, 1 ppm of
NC>2  measured at 25°C and 760 torr pressure is
equivalent to 1,880 pg of NCh per cubic meter of air;
whereas, 1 ppm of NCh measured at  25° C and 625 torr
pressure is equivalent to 1,546 ^g of NO2 per cubic
meter of air. Since most commercial air monitoring
instruments  record data in ppm, a  knowledge of the
prevailing atmospheric pressure and temperature is
needed in  order to convert correctly ppm readings to
Mg/ m3 at the condition of measurement. It should be
noted  that  factors  given  with the  EPA reference
methods for measuring the criteria pollutants have
been defined such that any properly measured ppm
concentration can  be converted correctly to /ig/m3,
under the  reference conditions of 760 torr and 25°C.
                                                 3-3

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                             IV. STATIONARY SOURCES
EMISSIONS
  There has been no documented evidence to date on
any altitudinal effect on the nature, quantity, or char-
acteristics of emissions from stationary sources. Based
upon current knowledge, one would not expect to see
measurable differences due to altitude, except, perhaps,
with losses by evaporation from dry  cleaning plants
(organic  solvents),  petroleum  products  (volatile
matter),  and  surface-coating  operations.  Altitude
effects  on evaporation  loss from storage  can be ex-
pected  to be minimal.
  In the case  of paniculate matter,  two  competing
factors can be expected to affect the nature and quan-
tity of  atmospheric particles. The two factors are less
complete combustion processes caused  by the lower
atmospheric pressure (less available oxygen) and the
lower air viscosity. The first factor would be expected
to result in more (numerically) and larger particles; the
second factor would be expected to cause more  rapid
fallout of particles, thus resulting in  a smaller  mean
mass diameter. Initial ambient air measurements  at
high altitudes have shown the mean mass diameter  to
be slightly larger than anticipated.

MEASUREMENTS
  One  must  consider  the two  general types  of
measurement systems separately. In the case of optical
(non-contact) methods using a fixed path length, the
lower atmospheric pressure at high altitudes means
fewer molecules are in the optical path  to absorb the
light energy. This factor would be compensated for in
the calibration method. In the instance  of manual
sampling  systems, pressure  may  affect  the gas
solubilities in  collection media. However, variations
due to this effect are not expected to affect reproduci-
bility  of  the   measurement  method.  No  other
measurements are likely  to be  affected  by  slight
changes in pressure.
  Pilot tube velocity measurements should be affected
by   pressure  differences  due  to  altitude.  The
measurements are directly proportional to the density
of the gas, and the primary effect of increased altitude
is a smaller pressure change for a given change in air
stream velocity. In the Denver area, this would result
in a  sensitivity decrease of approximately 15  percent,
but the decrease could be greater at very low velocities.
  Since the measurement systems for particles use
isokinetic sampling techniques and all measurements
are referenced back to standard atmospheric pressure
and temperature, no altitudinal effect is expected.


CONTROL TECHNOLOGY FOR STATIONARY
SOURCES
  For essentially all combustion devices, the mass air
required to produce a given amount of heat release is
essentially constant. Because of the reduction in at-
mospheric pressure  with  increasing altitude, the
volume of air and exhaust gas per unit of energy will
increase  proportionately.  Thus,  most atmospheric
pressure handling equipment must be sized  7 to 15
percent larger at 1,525 m (5,000 feet) land elevation
than at sea level and will cost 5 to 10 percent more.
Such gas  handling equipment includes, for example,
scrubbers,  baghouses,  catalytic reactors, fans, and
compressors. The effect of atmospheric pressure is
insignificant compared to variations that would occur
at any altitude in pollutant concentration, gas  temper-
ature, air dilution rates, and other source parameters.
                                                 4-1

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                                 V.  MOBILE SOURCES
INTRODUCTION
  This section briefly describes the effect of changes in
altitude on regulated emissions from motor vehicles.
Regulated  emissions are  those for which emission
standards apply; these include HC, CO, NOX,  and
particulate. Both exhaust engine emissions and evap-
orative emissions are discussed.
  The  references  included  at  the  end  of  this
section  represent a  selected  few to  provide  an
introduction to the very substantial literature on the
general subject. No attempt has been made to cover all
aspects.


THEORY
  The engine combustion process is affected when the
engine is  forced to operate at differing altitudes.
Increase in altitude results in a decrease in atmospheric
pressure  accompanied  by a decrease in air  density.
These density  changes alter the mass of air available
for the combustion process. Consequently, changes in
altitude create changes in the air-fuel ratio at which the
engine must operate. Because combustion efficiency
and exhaust emissions are a function of air-fuel ratio,
altitude changes, unless compensated or corrected for,
affect both engine performance and emissions. For this
reason, vehicles are often "retuned" when they are to
be operated at higher altitudes.

  Carbureted  engines,   which  are  essentially
volumetric devices,  are  those most susceptible to
altitude change. Since the fuel flow under fixed engine
operating conditions is   only  slightly  affected by
pressure  changes,  the  decreasing density  of  the
inducted air at  increased altitude results in engine
operation with richer mixtures.

  For a carburetor installation undergoing an altitude
change from sea level to 1,525 m (5,000 feet), the result
would be approximately seven percent enrichment of
air-fuel ratio. (1) This would result in decreased power,
decreased  engine efficiency,  and  decreased  NOX
emissions,  and  increased  HC and  CO emissions.
However, proper adjustment of the ignition timing for
vehicles to be operated at high altitudes would reduce
the magnitude of these effects.
  Fuel injected engines behave somewhat differently
when subjected to changes in altitude. Although some
injection systems have been designed to compensate
for  altitude  effects,  numerous  noncompensating
systems are in use which cause a leaning of the air-fuel
ratio  with  increasing  altitude.  These  systems
commonly  utilize  speed-density  control  systems
without back pressure sensing. It has been reported
that a change from sea level to 1,525 m (5,000 feet) of
altitude would result in a 2.1 percent leaning of the air-
fuel  ratio  of  the  mixture   for  noncompensating
injection systems.(l) This leaning would generally tend
to reduce  engine regulated  emissions slightly.
  The  theoretical  effect  of  altitude  changes  on
evaporative emissions should also be  considered.
Evaporative emissions are caused  primarily by  the
venting of  fuel  vapors  from  the  carburetor float
chamber and vehicle fuel tank. These can constitute a
sizable  source  of HC emissions in the absence of
appropriately functioning control devices.
  Low  barometric   pressures  prevalent at  high
altitudes effectively lower the distillation temperature
curve of gasoline causing it to become more volatile at
all temperatures. Gasoline losses increase significantly,
especially  during vehicle hot-soak when temperatures
are elevated following engine shutdown.(2)

  Diurnal  evaporative   losses   show   a  strong
correlation with gasoline Reid  Vapor Pressure, which
for high-altitude  fuels, is  generally lower than  for
low-altitude fuels.(2-4) Although this fact would imply
that  the  altitude  effect  on  volatility  might  be
compensated   for,   in  actuality,  high altitude
evaporative losses are greater according to surveillance
test  data  obtained in the  Los Angeles and  Denver
areas.(5)
  Many   additional  factors   such  as   an
altitude-temperature relationship,  fuel characteristics,
fuel distribution efficiency, injection spray geometry
(diesel), fuel-air  mixing  efficiencies,  etc.,   have a
                                                 5-1

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bearing on engine performance and emissions at high
altitudes.  In the case of diesel engines, a fixed  fuel
injection rate can be maintained over only a moderate
range of altitudes if excessive smoke and deposits are
to be avoided.

MEASUREMENTS
  All  differences  in  recommended  measurement
procedures at high altitudes  are  practical and  not
theoretical. All  certification  measurements  are
corrected  volumetrically to a mass basis at standard
sea  level  temperature  and  pressure.(6)  All
measurements of physical and/or chemical moieties
must be corrected to a common physical base if the
results are to have any comparability. The base must
include an  altitude correction  if it  is  a relevant
parameter.
  All affected measurements currently specified in the
Federal Register include an altitude (i.e., barometric
pressure) correction. Any measurement that does not
include this parameter should be considered  suspect
unless made at sea level and at 25°C.

EMISSIONS
  As   theory   has   predicted,   regulated  exhaust
emissions from  mobile  sources are  quantitatively
affected by altitude. Changes in air-fuel ratio brought
about  by operation at varying  altitudes are largely
responsible for variation in emission rates. When these
emissions are expressed  as  ppm,  data regarding
carbureted vehicles, which comprise the bulk of mobile
source emitters currently in the United States, are most
susceptible to  altitude effects. Those vehicles that are
not specifically designed for high altitude operation
will emit  more hydrocarbons and carbon monoxide
and  less nitrogen oxides with increases  in altitude.
Smoke emitters,  such as  diesel engines, will emit
greater quantities of  visible, carbonaceous material
with  increasing  altitude. The smoke  capacity of a
turbocharged diesel engine almost triples between 183
and 1,830 m (600 and 6,000 feet) and then falls off at
higher altitudes. The same is true of smoke from diesel
locomotives.(7,8)
  Only  limited  information is  available   on  the
functional  relationship  between  emissions  and
altitude.  From the information which is available, it
has been  determined  that a near linear relationship
exists  between HC,  CO,  and  NO*  emissions  and
altitude.  A research paper  published by Volkswagen
(9) contains data on a single vehicle which was tested at
six different altitudes. The linear regressions obtained
using these data are expressed as:
           HC  :  E=  2.95+0.00072 A

           CO  :  £ = 30.33+0.0074 A

           NOX:  E=  2.82-0.00027 A
where E is the emission in grams per kilometer and A is
the altitude in meters. The rates, expressed as a percent
change per 100 m, are 2.5,5.0, and -2.0 percent for HC,
CO,  and  NO,,  respectively. Because of  the  linear
relationship cited above, interpolation may be used to
determine an emission  rate at  a given altitude when
emission rates at both a high and  low altitude are
known. For such a case, the following expression may
be used:

                    EFh - EF,
       EFu = EF, +	 (A. - A,)
                    (Ah - A,)

where  EFu = user emission factor,
       EFi = low altitude emission factor,
       EFh = high altitude emission factor,
        Au = user altitude,
        Ai = low altitude level, and
        AH = high altitude level.

This expression can be readily applied to emission
factor data listed for both high and low altitudes. The
average low altitude is assumed to be about 150 m (500
feet) and  1,677  m (5,500 feet) for the average high
altitude.(lO)
   Evaporative   emissions  from  gasoline powered
vehicles are categorized as either hot-soak losses or
diurnal losses. The hot-soak losses  occur  during the
vehicle's cooling-down period  immediately following
engine  shutdown. Diurnal losses  occur  while the
vehicle is  not  operating and  is  essentially  in
temperature equilibrium with  the environment.
   In an emission surveillance study conducted  on
in-use 1976 model vehicles, data were obtained on
evaporative emissions  in both the Los  Angeles and
Denver areas. The former city  represents the sea level
case, while the latter represents the high altitude case at
about  1,585 m (5,200 feet).  Both hot-soak and diurnal
evaporative losses were determined for 20 different
vehicles using the Sealed  Housing for Evaporative
Determinations  (SHED)  technique.  In both  cases
Denver vehicles were  found to have significantly
higher evaporative emissions. The mean diurnal loss in
Denver was  21.7 g  as compared with 7.8 g in Los
Angeles, and the mean hot-soak  loss in Denver was
 10.5 g versus 5.4 g in  Los  Angeles.  Assuming an
average of 3.3 trips per day and 47.3 km (29.4 miles)
                                                  5-2

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per day, the combined evaporative emission losses are
1.2 g per km (1.9 g per mile) in Denver versus 0.56 g per
km (0.9 g per mile) in Los Angeles.(5)

CONTROL DEVICES
   Control of air-fuel ratio is the key to  any system
which  is   designed  to  compensate  for  altitude
differences  in mobile source emissions. Carburetors
have  been designed with aneroid pressure sensors to
correct for altitude effects. The sensor utilizes feedback
to control the amount of inlet air which will bypass the
carburetor's venturi. Although carburetors of this type
have been on display, none are currently being used to
any extent by the major automobile manufacturers.

   The  three-way catalyst  systems   which  are  in
production utilize the feedback from an oxygen sensor
located in the exhaust gas stream to  control air-fuel
ratio. This is possible because exhaust oxygen level can
be directly related to the engine operating air-fuel
ratio. The system is designed to control air-fuel ratios
within an extremely narrow range in order to achieve
80 percent catalyst efficiency. Control is  within the
range of 0.02 to 0.08 units of air-fuel ratio for most
installations.(l 1) Foreign companies employing three-
way catalysts on their vehicles have used the feedback
system in conjunction with fuel  injection systems.
Domestic companies, on the other hand, have recently
certified  three-way  catalyst  vehicles   that   have
carbureted  systems.  The  only shortcoming that  the
three-way catalyst systems possess with regard to high
altitude operation is the limited range  of response
designed into the system itself.
   Some fuel injection techniques are sophisticated to
the point that control of air-fuel ratio is possible over a
wide range of altitudes. Engines having speed-density
control systems with back-pressure sensors essentially can
compensate for altitude changes. Another fuel injec-
tion approach has been to monitor the mass flow of air
into the engine by using volumetric flowmeters with
pressure and  temperature  sensors. A  microprocessor
with flowmeter and sensor inputs is used  to  calculate
the air flow, and the fuel is metered accordingly.
REFERENCES

 1.  Bolt, J. A., S. P. Bergin, and F. J. Vesper. The Influence of the
    Exhaust Back Pressure of a Piston Engine on Air Consumption
    Performance, and Emissions. SAE Prepr. (730195), 1973.
 2.  Wade,   D.  T.  Factors  Influencing  Vehicle  Evaporative
    Emissions. SAE Trans. 7(5:811-823,  1968.
 3.  Biller W. E., M. Manoff, J.  Sachdev, W. C. Zegel, and D. T.
    Wade.   Mathematical  Expressions Relating  Evaporative
    Emissions from Motor Vehicles Without Evaporative  Loss
    Control. SAE Prepr. (720700), 1972.
 4.  U.S. Department of the Interior, Bureau  of Mines. Motor
    Gasolines, Summer 1974. Petroleum Survey No. 88, 1975.
 5.  Rutherford, J. A. Automobile Exhaust Emission Surveillance-
    Analysis of the  FY  1975 Program, EPA-560/3-77-022,
    USEPA, Ann Arbor, Mich., 1977.
 6.  Control of Air Pollution from New Motor Vehicles and New
    Motor Vehicle Engines. Fed. Regist. 5(5:128, pp.  12652-12664.
 7.  Ephraim, M. Jr. Status Report on Locomotives as Sources of
    Air Pollution. Internatl. Conf. on Transportation and the
    Environment, Part I. SAE, New York,  1972, pp. 9-13.
 8.  Dennis,  J.  W. Turbocharged Diesel Engine Performance at
    Altitudes. SAE Prepr. (710822), 1971.
 9.  Schurmarn, D. and H. Klingenberg.  Considerations on a
    Measuring Program to Investigate the Influence of the Ambient
    Air Conditioning on Vehicle Exhaust  Emissions. Research
    Report No.  MT-F5-77/13, Volkswagenwerk, A6, 1977.
10.  Compilation of Air Pollution Emission Factors. Third Edition,
    AP-42,  USEPA,  Research Triangle  Park, N.C.,  1977,
    pp. 3.1.1.-1 to 3.3.3.-2.
11.  Sittig,  M.   Automotive Pollution  Control Catalysts and
    Devices. Noyes Data Corporation,  Park Ridge, New Jersey,
    1977, pp. 195-214.
                                                    5-3

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                           VI.  AIR  POLLUTION  EFFECTS
HUMAN HEALTH
General Considerations
  Alterations of drug and toxic effects in man at high
altitudes may  be anticipated because of significant
physiological alterations occurring at altitudes greater
than  2,290 m  (7,500 feet). These  physiological
alterations  and most overt symptoms, including the
syndrome of mountain sickness, result almost entirely
from anoxia due to the diminishing oxygen content of
the rarified atmosphere.
  In addition, significantly lowered total atmospheric
pressure can result in higher concentrations of toxic
gases or fumes when the emission occurs  in enclosed
spaces.
  For these reasons, and especially since the advent of
the Space Age, a wealth of information on the effect of
hypobaric  environments on drug and toxic  actions
might be presumed to exist. In fact, the  opposite is
true.
  A  literature  search of  more  than   500,000
publications in relevant subject areas uncovered very
few publications dealing directly with the differential
effects on human health caused by exposure to air
pollutants at high altitudes. This statement does not
include  work  on carbon  monoxide,  which  will be
treated  separately in this report. Nor does it include
high altitude problems of gas/vapor anesthetics which
are well understood  and  predictable.  There is  a
reduction of potency and duration of actions due to
lowered partial pressure in all but completely closed
systems. It  may be that implications from these kinds
of observations account for the lack of experimental
interest  in the influence of hypobaric environments on
the  effects  of other  volatile  noxious  agents  or
paniculate   pollutants. Experts  in  oxygen-related
physiology  or aero-toxicants generally agree that there
is   a  great lack  of  knowledge  in this   area  of
pharmacology and toxicology.
Hypobaric Pharmacology-Toxicology
  Despite the shortage of information, it is possible
to make some predictions based on pharmacological
principles,  gas  physics,  and  well-documented
physiological obeservations on man's  response and
adaptation to high altitudes.
  If it  is true that  no  significant  physiological
alterations occur much below 2,290 m (7,500 feet), it is
obvious that the following discussion will apply only to
a very small fraction of the American population.
Perhaps that is the reason why, with the exception of
teaching the  principles of anesthetics, the  medical
schools   at  Denver  and  Salt  Lake City  teach
pharmacology and toxicology much  the same  as
elsewhere.
  In unenclosed spaces in free equilibrium with the
atmosphere, partial pressures of  gaseous  pollutants
decrease  with  increasing  altitude.  This  results  in
decreased alveolar  partial  pressure which reduces
systemic  absorption.  There probably  is little
altitudinal effect on local injury potential. Responses
to particulate pollutants would not be affected by the
lower atmospheric density.
  In enclosed spaces at high altitudes, a given quantity
of pollutant initially will reach a higher concentraion
in higher partial pressure relative to oxygen than is
reached at sea level; however, the absolute  alveolar
partial  pressure  may  or  may  not  be  increased.
Absorption as well as local injury potential may  be
increased.
  Significant alterations in alveolar ventilation occur
at high altitudes. There is an invariable increase in this
parameter, the maximum of which is a function of the
particular altitude. This maximum is reached within
100 hours for new arrivals at high altitudes. Prolonged
stay at these levels results in very gradual decline (over
years), but even natives have a higher ventilation rate
at rest.  This results in higher aero-toxicant dosage,
especially for particulates  and  gaseous  pollutants
produced in enclosed  spaces.
  Effects of altitude on absorption of aero-toxicants
can be summarized as follows:
     1. Increased blood flow seen most prominently
       after acute introduction to high altitude and
       also  in  the early  stages  of adaptation will
                                                 6-1

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       promote  increased  absorption of  soluble
       aero-toxicants.
     2. Increased alveolar diffusing capacity in natives
       and adapted sojourners  will  have similar
       effects.
     3. Reduced  partial  pressures  of  gaseous
       pollutants will decrease absorption.
  Effects  of high altitude on physiological fate  of
absorbed toxicants include the following:
     1. Due to increased blood  flow, there will  be
       increased  absorption  by  peripheral tissues of
       aero-toxicants initially absorbed by the lungs.
     2. The  decreased  plasma  volumes  cause
       increased  plasma  concentration of dissolved
       toxicants  which will also increase absorption
       by peripheral tissues.
     3. Reduced pressure gradients across membranes
       will decrease translocation.
     4. A redistribution of blood flow away from the
       skin occurs at high altitude, an effect which
       may favor translocation of toxicants to vital
       organs.
  While  no specific  information  is  available  on
altitudinal alterations in metabolism of aero-toxicants,
Merritt  and  Medina (1)  showed  that  hexobarbital
sleeping  time  decreased  in  mice  which  had  been
acclimatized to  a hypobaric  atmosphere.  A  similar
decrease  was shown  for zoxazolamine paralysis  time.
In both instances  increased hepatic microsomal enzyme
activity could be demonstrated, resulting in more rapid
declines of blood levels of these drugs.
  No definite trends can be deduced from sketchy
discussions in the literature.  (1-6) When renal  blood
flow decreases,  there  appears  to be  an increased
filtration rate. A tendency towards dehydration at high
altitudes  implies that  excretion  is diminished and
blood and tissue levels of soluble toxicants or  active
metabolites are prolonged.
  An  interesting  example,   experimentally
investigated, is the tenfold increase of amphetamine
toxicity in mice and rats  under hypobaric conditions
(acute and acclimatized).  This was found to be due to
increased brain levels of catecholamines.
  Other  examples  of hypobaric effects  cited  by
Medina  and Merritt (6), are increased  toxicity of
digitalis in cats, of strychnine in rats and of reserpine in
mice.
 Effects of Carbon Monoxide Under Hypobaric
 Conditions2
   The effects of CO exposure and of hypoxia induced
 by high altitudes are similar. Much experimental data
suggest that when high altitudes and CO exposures are
combined, the effects are additive. In vivo, there is an
interaction between the two factors such that exposure
to one may induce  a physiological  response that
influences the response of the body to the other. For
example, Forbes et al. (7) have shown that during light
activity their subjects  had an increased rate  of CO
uptake at an altitude of 4,880 m (16,000 feet) compared
to that at sea level, becasue of the hyperventilation that
results from the decreased partial pressure of oxygen
(P02).  When the ventilation rate was corrected to its
value at sea level, the rate of uptake of CO decreased to
a value within 10 percent of the sea level value.

  Although the effects of hypoxia and CO appear to
be additive at very high altitudes,  individually they
produce  different physiological  responses. This is
because they have different effects on blood PO2,on the
affinity of Oz for blood hemoglobin, on the extent of
oxyhemoglobin  (O2Hb)   saturation,   and  on
ventilation.  The  presence  of  carboxyhemoglobin
(COHb)  increases the  affinity  of  the  remaining
hemoglobin  for  O2, but  lowers  the total  O2Hb
satuaration. The ventilation rate appears to be influ-
enced by receptors in the carotid and aortic bodies that
are responsive to  blood  P02, and PCo2- (8)  Hypoxia
results in  a  lowering  of the   P02  and  increased
ventilation ensues; in CO exposure, the P02apparently
does  not change sufficiently  to  induce  increased
ventilation.
   Several different  physiological and  psychomotor
tests have been used to determine the effects of altitude
with and without CO. Pitts et al. (9)  have observed the
physiological responses to exercise when blood COHb
levels were increased by 6 percent and 13 percent in a
group of 10 men at simulated altitudes: 0; 2,130; 3,050;
and 4,575 m (sea level; 7,000; 10,000; and 15,000 feet).
The parameters measured were pulse rate, respiratory
rate,  and minute  ventilation. A  previous study had
indicated that in subjects at rest, the pulse showed no
change with  atmospheric  pressure  down to that
corresponding to an altitude of 5,000 m (16,500 feet).
After  regulated  exercise at  atmospheric  pressures
corresponding to altitudes from sea level up to 6,360 m
(21,000 feet), however, it showed a steep, almost linear
increase. Of the  parameters  measured in both these
studies, mean pulse rate during exercise and for the five
minutes  immediately following exercise showed the
closest correlation with blood COHb and ambient Po2.
At sea level, an  increase of  13 percent  in  COHb
increased the mean exercise pulse rate from 105 to 112
and the recovery pulse rate from 91  to 98. An increase
  :For a more detailed discussion of this subject, see Appendix B
                                                   6-2

-------
of six percent COHb produced a significantly higher
exercise pulse rate compared to that produced by
simulated  increase in altitude alone. Pitts calculated
that for every one percent increase in blood COHb in
normal subjects, up to 13 percent COHb, the increase
in exercise pulse rate is equal to that which would be
produced  by  a  100-m (335-foot)  rise  in altitude
throughout the range of 2,130 to 3,050  m (7,000 to
10,000 feet). It is likely that some of the subjects were
smokers, since the group mean control COHb level
ranged from 2.88 to 3.64  percent on different days.
Since the smokers would have been preconditioned in
part to the effects  of CO, their responses to additional
small quantities of CO might be expected to be lower
than those of nonsmokers. This could have masked the
additive effect of CO and hypoxia. A more recent
study indicated that cigarette smokers may be partially
adapted to carbon monoxide. (10)
  Another study compared the effects of CO exposure
and altitude. (11) Eight healthy male subjects were
divided randomly into two groups of four each; each
group followed a different daily schedule. The subjects
were   briefly   exposed   daily  for  10  days  to
concentrations of five percent CO (57,500 mg/m3 or
50,000 ppm) at four-hour intervals between the hours
of 7 a.m. and 11 p.m. The doses were sufficient to give
an average COHb level of 15 percent, although values
ranging between 5 and 25 percent were recorded.  A
variety of circulatory, ventilatory, and renal function
tests  were  performed  during  the course  of the
experiment.  The  same  experimental  protocol was
carried out on the same eight subjects after they spent
10 days at a simulated altitude of 3,430 m(l 1,225 feet).
This condition gave roughly a degree  of hypoxemia
equilalent to that given by 15 percent COHb. The data
obtained from the two studies are compared in Table 1.
Of  great  significance  are  the  circulatory  and
ventilatory responses  to the two types of hypoxic
conditions. As expected, CO hypoxemia shifted the
O2Hb dissociation curve to the left;  whereas, high
altitude caused a shift to the right, the latter occurring
during the first 24 hours. At increased simulated alti-
tude, both the cardiac output and the ventilatory rate
increased with the first 24 hours; whereas, CO had no
consistent effect on these parameters.
  The lowered arterial P02 at simulated high altitude
most likely stimulated the chemoreceptors in the aortic
and  carotid  bodies, with  the  resultant regulatory
changes in ventilation.  Mills and Edwards (12) have
shown that these chemoreceptors are also stimulated
during  CO inhalation.  These  investigators have
suggested  that the lack of ventilatory response during
CO hypoxemia is  a result of depression of respiratory
centers in the central nervous system. The effects of the
two types of hypoxemia at  the cellular level can  be
estimated by comparing the  P02 of the mixed venous
blood under both circumstances,  since this reflects
tissue P02. The data in Table 1 show that the average
P02 of mixed venous blood in CO hypoxemia is lower
than in hypoxic (high altitude) hypoxemia.  In both
types  of hypoxemia, a lowered tissue P02 is expected;
as indicated by the mixed venous P02, this was more
pronounced in CO  hypoxemia under the conditions
observed. At increased simulated altitude, the shift of
the O2Hb curve to the right and the circulatory and
ventilatory  responses  compensate for most of  the
associated tissue hypoxia during the first 24 hours.
Such  regulatory mechanisms do  not appear to  be
stimulated  by CO hypoxemia,   and  hence, CO
hypoxemia  may  be considered to  be more of a
physiological  burden  than  comparable  levels  of
hypoxia hypoxemia.
   In a study released by the National Asthma Center,
the effects of low-level carbon monoxide exposure at
1,610 m  (5,300 feet)  for healthy young men was
reported. (13)  For COHb levels ranging from 0.96 to
1.15 percent, the effects of CO on exercise performance
are similar to,  but not greater than, effects at sea level.
  Other studies on  the combined  effects of CO and
altitude have used psychomotor tests. Variable results
have  been  reported,  but  some  of these may  be
explained by the use of different tests and others by the
lack of  proper controls. The flicker fusion frequency
(FFF) and  the critical flicker  fusion (CFF), often
employed in these studies, have recently been criticized
because of their lack of reliability.  (14)

  McFarland  et  al (15) have used the  increased
threshold of visual perception as an index of the effect
of both  CO and high altitude. It is pertinent to note at
this point that McFarland  et al.  found  that visual
perception was impaired in a single subject who had a
COHb  level of about five percent  at  sea level. This is
equivalent to the impairment associated with low Po2
at an altitude  of 2,130  m (7,000 feet).

  In another  experiment, a  group  of four  trained
subjects was used to study the time course of recovery
from CO and altitude. (16) Data from a single subject
suggest  that it takes longer to recover from  a given
COHb level than from an equivalent lowering of P02
due to altitude. The difference could not be accounted
for wholly by the presence of COHb. It is possible that
the compensatory mechanisms normally activated by
lowered P02 were not activated when CO caused the
drop  in O2Hb saturation. Alternatively,  it  is also
possible that CO exerts a specific toxic effect on the
                                                6-3

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             TABLE 1. AVERAGE DATA FOR EIGHT SUBJECTS (DIVIDED INTO TWO GROUPS OF FOUR)
                        TO COMPARE EFFECTS OF CO AND SIMULATED HIGH ALTITUDES
                                ON VARIOUS PHYSIOLOGICAL PARAMETERS (11)
           Test
                                          Effect of 15% COHb
                                                                                    Effect of 3,420 m simulated
                                                                                           altitude
O:Hb saturation curve
Affinity of Hb for Ch
Mixed venous oxygen
  tension, by estimation
Shift to left
Increased (within 12 hr)
10 to 20% decrease throughout exposure
  period
Shift to right
Decreased (within 24 hr)
20% increase on first day, 10% decrease on
  second day,  return to normal for rest of
  experimental period
Ventilation
  VESTPDa - rest
           - work
  VEBTPSb - rest
           - work
  Respiratory rate - rest
                  -  work
 No change
 Slight increase on first day
 No change
 No systematic change

 No change
 No change
15 to 20% decrease
Slight decrease
30% increase
35% increase on first day, 50% increase by
  tenth day
15 to 35% increase
15 to 35% increase
Circulation
  Paco2' - rest
  Pycoj" - rest
  Cardiac output
Almost unchanged
Almost unchanged
Group 1 increased 27% on first day, followed
  by return to normal; no change in Group 2
Continuous decrease from 90 to 75% of control
Continuous decrease from 90 to 75% of control
Group 1 increased 35 to 45% for the entire
  10-day period Group 2 increased 25% by
  fourth day and returned to normal by end
  of stay
 Mixed venous-arterial
  CO2 difference, by day,


          - work
Group 2 showed no change
Group 1 increased 20% on third and fifth
  days, no other changes noted
Group 1 decreased 15 to 20% for the entire
  10-day period; Group 2 decreased on
  fourth day only
15 to 25% increase for the entire 10-day
  period
Renal function
  Glomerular
    filtration
Renal plasma flow
Diuresis


Serum lipids
   (cholesterol)
Hematocrit
Reticulocyte count
50% increase on first day, return to normal
  on second day, remain within 20% of
  control for rest of experimental period

40% increase on first day, return close to
  pre-exposure value on second day,
  remain < 15% below control value for rest
  of experimental period
Increase of 400 to 500 ml


No significant  change for first 4 days; 6%
  increase in last 2 days (p<0 05)
No change
Threefold increase on third day; nearly
  fourfold increase by sixth day
Very slight decrease but close to control
  value
Very slight decrease, but close to control
  value
Increase to more than twice control by
  sixth  day

6 to 9% increase in first 2 days
Very slight increase (43.5 to 47)
Twofold increase on third day; nearly
  threefold by ninth day
  'VESTPD (I/mm) - ventilation at 0°C, 760 torr, dry
  "VEBTPS (I/mm) - ventilation at body temperature and ambient pressure saturated with water vapor
  'P.tn, - alveolar carbon dioxide tension
  dPyco1 - mixed venous carbon dioxide tension
                                                       6-4

-------
central nervous system that is unrelated to the COHb
level.
  In  both studies just  described,  the investigators
imply that the subjects exhibited similar responses, but
they  do   not  supply  supporting  data.  Other
investigators have commented on the great variability
in response between subjects when  similar tests have
been used.
  Lilienthal et al. (17)  produced an impairment  in
FFF in five subjects at simulated altitudes of 3,050 to
3,650 m (10,000 to  12,000  feet).  Exposure to CO
(COHb increases of five to  nine percent) combined
with decreased atmospheric pressure equivalent to  an
altitude of 1,525 to  1,830 m (5,000  to  6,000  feet)
effected an impairment  in FFF, although neither  of
these stresses alone affected the FFF. The data indicate
that an increase  in the COHb level of 8 to 10 percent
above resting values caused the tolerance for altitude
altitude to be lowered by 1,220 m (4,000 feet) or more.
  It should be noted that impairment in FFF is not
necessarily consistent with a given COHb percentage.
For example, at simulated pressure equivalent to 1,525
m (5,000 feet), one subject showed a depressed FFF at
8.7 percent COHb; yet, in another  experiment at the
same pressuie, his FFF remained  constant at  10.5
percent COHb.  There  is  a  possibility that COHb
determinations in this  experiment were inaccurate.
The subjects' resting COHb levels varied from 1.0 to 3.5
percent, indicating that there were smokers  in the
group. Since smokers may have higher hemoglobin
values than nonsmokers (18), the assumed hemoglobin
value used in this experiment may not be valid.
  By contrast, Vollmer et al. (19) have found that the
effects of  CO and high  altitude  hypoxia are not
additive. Twenty subjects were used  to study the effect
of CO and high altitude hypoxia [3,050 to 4,575  m
(10,000 and 15,000 feet)] on FFF, body sway, and size
of the red  visual field all during light activity. There
was a significant impairment at simulated increased
altitude, compared with performance at sea level, with
and without exposure to CO. There was no significant
difference  between the mean  test  scores during
hypoxia alone and the mean test scores following
administration of CO. The increases in COHb were
from 9 to  19 percent, with a final COHb ranging from
12 to 22 percent.  This suggests that  the resting COHb
was three  percent, and indicates that some of the
subjects were smokers. Vollmer suggests that at 4,575
m (15,000 feet), any additional burden imposed by the
presence of small amounts of COHb is masked by
hypoxia compensatory mechanisms. Alternatively, he
considers that it is possible that 9 to  19 percent COHb
does not impose an important  additional stress. At
hypoxia corresponding  to 4,750  m  (15,500 feet),
however, 4 of 17 subjects collapsed after being exposed
to CO. The  tests  used in this study appear to be
inadequate for predicting  a  serious cardiovascular
reaction; nor can their sensitivity be ranked very high.
  Most of the above studies  were conducted before
1950. In 1966,  Denison  (20) demonstrated the significant
effect hypoxia alone has on complex reaction times at a
simulated altitude of 1,525 m (5,000 feet) during light
work. At 1,525 m (5,000 feet), 8 of 10 subjects showed
slower reaction times than 9 of 10 matched controls (p
< 0.05). This effect of hypoxia was observed only
during  the early  stages  of  learning the  complex
experimental  task.  Once the task had been learned, a
simulated  altitude up to 2,440 m (8,000 feet) had no
effect.  The effect  of small amounts of CO on the
learning of a new task at increased altitude remains to
be determined.

Effects of Altitude on Carboxyhemoglobin Formation
Kinetics
  Coburn, Forster, and Kane (21) published a detailed
theoretical analysis of the  physiology and  variables
that determine blood  carboxyhemoglobin values  in
man. Some of these  are schematically depicted  in
Figure 1.


  The basic relationship  they describe is:

     A [COHb], - VcoB - PICO
                             = e (-tA/VbB) = e"
    A [COHb]0 - VcoB - PICO

Defining terms:
[COHb]o = carboxyhemoglobin concentration
           at t = o units: ml CO/ml blood
      e.g. : 1 g of Hb combines stoichiometrically
           with 1.34 ml of CO or 02. Assuming
           15 g% Hb: 0.5% COHb = (0.005)
           (1.34) (.15) = .005 ml CO/ml blood

[COHb]t  = carboxyhemoglobin concentration at
           t = minutes exposure
     e.g.  : 2.5% COHb = (0.025)  (1.34) (.15) =
           .005 ml CO/ml blood
       A  = PC02/M[02Hb]
           PC02 = pulmonary capillary O2 tension at
                  sea level this ss 100 torr
              M = relative affinity of Hb for CO and
                  02
         [OjHb] = oxyhemoglobin  in  ml   O2/ml
                  blood assuming 100% saturation
                  of arterial blood
                                                 6-5

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  AMBIENT
     PCO   A
 ALVEOLAR

    PCO
                  EXOGENOUS
ENDOGENOUS
HEMOGLOBIN
CATABOLISM
OTHER HEME
                    0.3 ml/hr
                    0.1 ml/hr
                                     CARBON MONOXIDE STORES
                                     HEMOGLOBIN
                                         8ml
                                      MYO-
                                      GLOBIN
                                     . 1.5ml
                                                       OTHER
                                                         < 0.5 ml
                                                                      0.2%/hr
                                                               METABOLISM
                                                                                 CO
 Figure 1. Diagrammatic summary of current concepts regarding variables that influence body CO stores. (22)
      e.g.   : [ChHb] = (1.34) (.15) = .201 m!O2/
             ml blood
      B =    1      PL
            DL    VA
       DL  = pulmonary diffusing capacity for
                 ss 30 ml/min/torr
       PL  = sum of partial pressures of alveo-
             lar  gases excluding water Vapor
             (47  torr at 37° C)
           ~ 760 -47 = 713 torr
       VA  = alveolar ventilation
           =£4200 ml/min at rest
     Vb = blood volume as 5,500 ml for 70
          kilo man
    PICO = Partial pressure of CO in inspired
          air
       k = Boltzmann's Constant
               PicpxlO6
ppm     - Barometric pressure
    Vco = rate of endogeneous CO production.
          This is related to heme metabolism
          which can vary considerably, as a
          function of red blood cell life span.
                                          Any factor reducing RBC survival
                                          elevates Vco. A reasonable average
                                          value for healthy adults = 0.007 ml/min.
                             The most useful rearrangements of the basic relation-
                             ship are:
                                           e" [A(COHb)0 - VcoB]
                                     PICO =
                                                   ek - 1
                                                           VcoB - A(COHb),
                             whereby, exposure level needed to produce a given
                             change in COHb over a given time can be calculated:
                                 [COHb], =
                                                                       ICQ
e" [A(COHb)o - VcoB-Pico]
           A

                 I" VcoB + P

                 L      A
                              whereby, COHb resulting from a given exposure level
                              for a given duration of exposure can be calculated.
                                Careful  comparison of these relationships  with
                              available human exposure data confirms the general
                              validity of using a theoretical  model to solve the
                              complicated problem of predicting COHb levels under
                              a variety of experimental and clinical conditions.
                                            6-6

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  Figure 2  shows a  comparison of carboxyhemo-
globin levels predicted  by three  empirical formulas
and the theoretical model. During the first few hours
of exposure, the formulas of Hanks (23) and Forbes
(7, 24) agree very well with the model. Stewart's (25,
26) formula gives results  which are  higher than the
others from the beginning  and this difference  is
accentuated with time. Forbes' linear relationship is
only  applicable to about the first four  hours of
exposure. In order to examine the behavior of these
formulas with  long  exposure  times, the curves in
Figure 3 were calculated. The inapplicability of both
Forbes' and Stewart's formulas to long exposure times
is  dramatized.   Results  with  Hanks'  formula are
virtually  indistinguishable  from  those  of the
theoretical model for the first 10 hours, and with both
models COHb levels come into equilibrium at about the
same time with relatively little separation between the
two  asymptotes.  Figure 4 shows the comparison of
COHb  equilibrium  values  for  arbitrarily  chosen
exposures  calculated  from  the formula  of the
California State Board of Public Health (22) and from
the theoretical model. The points lie very close to the
45 degree line of identity.
JD

8
a*
            I    I    I    I    I    I    I
            I    I    I    I    I    I    I    I   I
                                                10
                      EXPOSURE, hours

    Figure 2, Comparison of CHOb levels predicted by
    three empirical formulas and a theoretical model.
  It  seems,  therefore,  that  the   California
mathematical  formula  agrees very  closely  with
available   data when  those  data  are  properly
interpreted. In addition,  of course, the theoretical
model allows computer simulation of CO exposure
kinetics with the ability to vary a large number of input
parameters. Great care must be exercised, however, in
choosing appropriate and internally consistent values
for these parameters as well as interpreting the results
of modeling  in a context  that  is physiologically
reasonable.
  The formula of  Coburn et at. (21) becomes much
more versatile and general if the alveolar air equation
 o
 o
                    30  40  50  60  70  80  90  100
                       EXPOSURE, hours
    Figure 3. Comparison of COHb levels predicted by
    three empirical formulas and a theoretical model
    over long exposure times.
and certain empirical relationships between altitude
and physiological variables (27) are included.
  The alveolar equation is:
      PA02  = FI02 (BP-47) - PAC02 [F102 +  1 - FI02]

where PA02   = alveolar oxygen tension (torr),
      FIO    = fraction of oxygen in inspired i
      BP    = barometric pressure (torr),
                                                                                                  R
O
O
13

12

11

10

 9

 8

 7

 6

 5

 4

 3

 2

 1

 0
                                                                   IT   I  \  I  T  I   I   I   I   T
           I   I   I  I  I   I   I   I   I   I   I   I   I
                               8  9  10 11  12  13  14
                     % COHb (Theoretical)
  Figure 4. Comparison of equilibrium values calculated
  by the California State Department of Health's formula
  and the theoretical model.
                                                 6-7

-------
     PACOJ = alveolar COi tension (torr), and
         R = respiratory exchange ratio =
             Vco/Vo2.
  With a negligible alveolar to arterial 02 gradient,
pulmonary capillary Oi tension approximately equals
alveolar  02  tension.  The alveolar  air  equation,
therefore, can be used in the definition of factor A in
the Coburn formula.
  Simulation  of  the  effect  of  altitude  can be
accomplished   with   the following  empirical
relationship:
                           r»
                       -(-
             P = 760 e
                          7924
where    P = atmospheric pressure (torr)
         a = altitude above sea level in meters.
  The calculated atmospheric pressure at altitude can
thus be substituted for actual measured pressure in the
alveolar air equation and in the conversion from ppm
CO  to PICO. It is important to remember that the
conversion from mass to volume units in  aerometry
also involves atmospheric pressure. Thus,  the details
of instrument calibration must be known before one
can decide whether or not it is appropriate to include
an atmospheric pressure correction factor in calcu-
lating Plco from mass units.
            % RHb = 2.76 e
                            2133
where  %  RHb is  reduced hemoglobin formed as a
result  of exposure to altitude. This must be added
to the %  RHb present  in a given individual at sea
level   and  also   taken   into  consideration  when
calculating factor A in the Coburn equation.
  Permutt  and Farhi  (28)  have  emphasized  the
importance  of considering the effect of CO exposure
on  tissue  oxygenation,  and this  effect can  also  be
calculated from known physiological variables. Thus,
reliable mathematical modeling of the effect of CO
exposure on tissue oxygenation is possible.

Effects of Altitude and  Carbon Monoxide on the
Fetus

  It has been stated that the fetus under unpolluted sea
level conditions lives at Po comparable to the summit
of Mt. Everest. (29) If this is the case, then decreases in
fetal blood oxygen content, such as caused by four to
five percent COHb, if prolonged, may cause brain
damage  and  mental   retardation.  (30-32)  The
implications of these studies are great, particularly in
the  case  of the  expectant mother  living  at  high
altitudes who is exposed tg moderately high levels of
CO from auto exhaust or smoking.
ECOLOGY
  From an ecological standpoint, a number of effects
of altitude on air pollution should be considered. The
pollutant conditions  most frequently associated with
altitude are confinement or  entrapment within an
inversion layer. The impact on the plant environment,
thus,  may  be accentuated  either because  of an
exposure of longer duration or a buildup of pollutant
concentrations.
  Within  the first  few hundred  feet  above  the
earth's  surface  the  atmospheric  composition  is
influenced  be vegetation.  Plants growing at  high-
er altitudes are  susceptible to the same pollutants
as plants  at lower levels.  The pollutants  reaching
the vegetation at higher altitudes  are the result of
advection   from  air  pollution sources  at   lower
levels.  Ozone  transport  from Los   Angeles  has
been shown  to  be  the cause  of  death of Jeffrey
(Pinus  Jeffreyi)  and  Ponderosa  (P. ponderosa)
pines in the San Bernardino and the  Sierra Nevada
Mountains.  (33-36)  Transport of  sulfur dioxide
could  also  cause  vegetational  injury  at  high
altitudes.
  Vegetational injury from both sulfur dioxide and
ozone is dependent on  pollutant entry into the leaves
through the stomata. Environmental conditions, such
as water  stress, can result in closed stomata and
protection  from injury. (5) The vegetation of high
altitude areas with low rainfall would probably be less
susceptible to injury.  Plant  life may also  remove
pollutants  from the atmosphere  by presenting  a
barrier to particulates and curtailing their dispersion,
or by adsorbing them. The latter  processes may be
important in scavenging pollutant  gases or in sound
absorption  where  noise   is  excessive.  Pollutants
removed via these mechanisms may be deposited into
the soil. Although dependent on edaphic factors, such
deposition does not usually enrich the soil.
  Altitude, as defined in this report, relates primarily
to ecosystems or their components located on plateaus
or in mountainous regions at  land elevations from
1,525 m (5,000 feet) up to at least 3,050 m (10,000 feet)
or more. At these  land elevations the  distribution of
biotic communities is complicated due to the diversity
of physical conditions and due to the many species
unique to mountain biomes. (37) Growing conditions
for plants in the mountains become increasingly less
favorable with increasing land elevation. (34) Because
of the indigenous nature and lack of diversity of
species, any pollutant stress may trigger exaggerated
changes in these intricately balanced systems.
                                                  6-8

-------
  For example, solar insolation increases (38) and the
light spectrum changes with increased altitudes. "The
alpine environment  is more severe  than the  arctic
during the growing season...and higher ultraviolet
radiation adds  to  this severity."  (39)  Biological
ecosystem  components at higher  land  elevations,
although receiving more ultraviolet radiation than
those at  sea level, have adapted to such  conditions.
(38,40,41) Pirschle (42) studied plants from high land
elevations in controlled chambers under varying light
conditions. Those from alpine areas subjected  to
ultraviolet  irradiation,  although inhibited in  their
elongation, suffered no other damage, while test plants
from sea level were killed. The amplitude of ultraviolet
radiation is tempered by ozone concentrations.
  Biological aerosols, suspensions of microorganisms
in the air, and aeroallergens are ubiquitous in nature.
The altitudes at which these organisms may exist or
may concentrate and yet remain viable are shown in
Figure 5. (43) Most show seasonal fluctuations, while
some may occur at specific times only. Most exhibit
extreme  dispersion which is beneficial in maintaining
the species since they are important parts of some of
our ecosystems. On the other hand, undesirable species
may become established in distant locations following
aerosol transport or may act detrimentally in spreading
disease  or  allergenic  episodes  within  man's
environment. (44-45)
  Temperature  inversions  limit  normal upward
migration of microorganisms from the earth's surface,
resulting in large microorganismal populations  below
the inversion.(46) Such confinement of disease-causing
or  allergenic microorganisms can  result  in episodic
responses in the local human population.

MATERIALS
  No known research has been published in which the
influence of elevation on air pollution  damage  to
materials has been studied.
  Several studies (47-56) concerning textile materials,
however, have shown that  the  presence  of sunlight
produces a synergistic damage effect (i.e., the overall
damage  produced is  greater than  the sum of the
damage  effects  produced by sunlight and certain
pollutants  individually).   From  a theoretical
standpoint, therefore, it is reasonable to assume that
because of increased ultraviolet  radiation at higher
altitudes, reaction  rates  between  pollutants  and
materials would  further accelerate. Of  course the
deteriorating action of sunlight alone, which for some
materials is much more severe than that of pollutants
alone, would also increase and could conceivably have
greater significance at higher altitudes.
  UJ
  Q
  D
       30
       27
       24
       21
       18
       15
       12
'Note: It is not known what effects
       pollutant intermixing    	
      will have on such aerosols.
         10"
  10'6  io'5
                          10
ID'1
10''
                      CONC., jug/g air

  Figure 5. Concentration of aerosols with altitude. (43)

  The  lack of  research precludes any  definitive
conclusions. However, a hypothetical conclusion is
that  for  a given level of air pollution, damage  to
materials is probably greater (to an unknown extent)
at higher than  at  lower altitudes because of the
potentiating effect of the more intense insolation.


WEATHER, VISIBILITY, AND CLIMATE
  In Chapter II,  the impact of the increase in altitude
on  weather parameters  was discussed.  It  is now
appropriate to describe the effects of the variations of
weather factors on air pollution.
  The  greater amount of solar radiation experienced
at higher altitudes  has  the  effect  of enhancing the
formation  of  secondary  pollutants  such   as
photochemical  smog.   The  greater amount   of
ultraviolet radiation  combined with  increases  in
automobile  traffic  may  account for the increased
photochemical smog  noted at  major metropolitan
areas in  the Rockies. The greater  amount of solar
                                                 6-9

-------
radiation available also has the effect of enhancing the
occurrence of convective air currents near the ground,
thereby  promoting  a well-developed mixing  layer
daily. For example, at Denver throughout the year,
the mean afternoon mixing heights vary from about
915 m (3,000 feet) above ground level in January to
about  3,340 m (11,000  feet) in July. These  mixing
height characteristics  for  Denver are typical of the
mountain and high land elevation areas of the West
and exceed the mean mixing heights experienced by
the rest of the nation.
  Similarly, the  loss of  infrared  radiation  by the
earth's surface at night is enhanced at high altitudes.
Under clear skies the temperature profile  at night is
drastically changed by the rapid radiational cooling of
the ground and the subsequent cooling of the layers of
air near  the  surface.  This  creates  an  inversion.
According to Hosier, (57)  the occurrence of low-level
inversions is greatest in  the Appalachian and Rocky
Mountain chains. Low-level inversions are present 30
to 50 percent of all hours in these areas. Under an
inversion  the   atmosphere  is  stable,  vertical
interchange of air is inhibited, and pollutants tend to
remain near the ground.
   In the warm season of the year, with much ground
heating, temperatures normally decrease rapidly with
increasing height  at high altitudes, but  in  winter,
especially when  the  ground is covered  by  snow,
temperature inversions  near the earth's surface are
frequent  and persistent.  Therefore, vertical dispersion
is favored during  the summer  and limited during
winter. Atmospheric  conditions favoring pollution
episodes  occur in the winter in the Rocky Mountains
and Great Basin areas of  the western United States.
  The rising air currents  on the windward slopes of the
mountains tend to disperse pollution through deep
layers.  Also  the  high  frequency of "precipitation,
brought about by the forced ascent of air particularly
at high altitudes in the coastal ranges, tends to wash
out pollutants in the air mass. Snow is more efficient in
washing   out  pollution  than   rain.  Washout  of
pollutants, and damage  to  surface receptors, may
occur if the concentration  of pollutants in the air mass
is high. Moreover, the pollution may find its way into
lakes and streams and contribute to the contamination
of  these  waters.  Acidic particulate species may
adversely affect not only lakes and streams, but also
soil conditions in some  areas.
   In general, the visibility within air masses over the
higher altitudes in the western United States remains
good. However, in the vicinity of large metropolitan
areas and near large power plant complexes, reduction
in visibility is being  observed. The major visibility
problems at  the present time occur  where large
metropolitan  areas,  with a  multitude of  pollutant
sources,  are  located  in topographical depressions
which favor the occurrence of low wind speeds and
stable air near the earth's surface. The high frequency
of stagnating air masses in the late fall and winter favors
the   occurrence  of  air  pollution   episodes   in
metropolitan areas such as Denver. (58-61)


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                                                           6-12

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                                         APPENDIX  A
EFFECTS OF ALTITUDE ON
AEROSOL DYNAMICS
  The atmospheric aerosol processes of interest that
might be affected by high altitude are: nucleation, con-
densation, dry and wet deposition, coagulation, and
gas-to-aerosol conversion.  Aerosol instrumentation
response and performance might be changed for de-
vices  calibrated at sea level and  used at high land
elevations.  Also, aerosol  lung deposition efficiencies
at high  altitudes might  be changed with respect to
those at sea level. Modification of the rates of these
processes,  instrumentation performance, and lung
deposition  efficiencies will be  discussed. However,
variations  in source  emission  characteristics as a
function of altitude will not be addressed here, nor will
the performance  of  industrial  devices for primary
aerosol control (such as electrostatic precipitators and
wet scrubbers).
  The important  mass transport  parameters for air
that change with altitude and that might be expected
to influence  aerosol dynamics  are:  air density  (or
molecular mean-free path), air viscosity, the accelera-
tion due to gravity, and temperature. The change in
density, molecular mean-free path, and viscosity for
increasing  altitude  is  shown  in  Table A-l.  The
viscosity is essentially constant down to pressures
below 0.3 kg m~2(0.02 torr). Also, over the contiguous
48 states, the acceleration due to gravity varies within
the range of 9,790 to 9,809 m  sec"2,  which for  our
purposes can be considered constant. Thus, the only
mass  transport  parameters  for  air  exhibiting
significant   dependence  on   altitude  are  density
(molecular mean-free path) and temperature.

Processes
  Since an exact theory for nucleation is lacking for
heterogeneous mixtures,  an  equation  for  the
production rate of critical nuclei in the atmosphere as
a function of the collision frequency, temperature, and
the Gibbs free energy of adsorption cannot be stated.
The  heterogeneous  nucleation   rate per unit   of
substrate surface area decreases as pressure decreases.
However, the dependence of the rate on temperature
and the Gibbs free energy may be more important and
could result in increases or decreases at high altitude
cities compared to  sea level for  the  same  mass
concentration  of nucleating  monomers.  The rate of
condensation  of  low-vapor  pressure  gases  onto
existing aerosols (4) can be described by
          F =
               4?rR2

                   D
                    1 + cX/R
  where F  =  mass flux per unit area to a spherical
             particle,
          =  mass flux to a spherical particle of
             radius R,
        R  =  radius of sphere,
                          TABLE A-1. MASS TRANSPORT PARAMETERS (T = 293° K)
Elevation, meters
Sea level
1,524 m
3,048 m
(5,000 ft)
(10,000ft)
Standard
Pressure, kg
10.33
8.56
7.07
(760
(630
(520
m'1

torr)
torr)
torr)
Density
242" K
1.56
1.30
1.06
'. kg m'1
293° K
1.29
1.07
0.88
Molecular Mean-
Free Path' nm
242° K
54.0
64.8
79.2
293° K
65.3
78.8
95.4
Viscosity '
242° K
1.54
1.54
1.54
, kg m"' sec"'
293° K
1
1
1
.81
.81
.81
 'From ret 1   "From ref 2   'From ret. 3
                                                 A-l

-------
        D  = gaseous diffusion coefficient of
             condensing specie,
         c  = constant («* 1.5),
         X  = molecular mean-free path,
       n,.  = concentration of condensing specie far
             from the particle's surface, and
        n,  - concentration of condensing specie at
             the particle's surface.
The ratio of fluxes at sea level and at 1,524 m has been
calculated for T = 20° C (293° K), assuming that the
mass  concentrations of the condensing specie are
equal. The ratios are presented in Table  A-2 for var-
ious aerosol diameters.

           TABLE A-2. RATIO OF FLUXES
                (T= 20° C [293° K])
                                                     For polydisperse systems,

                                                            dn(ri,r2,t)/dt = -K(n,r2)n(ri,t)n(r2,t),

                                                     where K(ri,r2,) is the coagulation constant for particles
                                                     of radius r, with particles of radius rj, and is a function
                                                     of the mean thermal speeds, concentration gradient
                                                     thicknesses, and particle diffusion coefficients. With
                                                     the  formula  given  by  Fuchs (5),  the  ratio  of
                                                     coagulation coefficients for various combinations of
                                                     atmospheric  pressure and  temperature  can  be
                                                     calculated, as shown in Table A-3.
                                                                     TABLE A-3. RATIO OF
                                                                COAGULATION COEFFICIENTS
                                                     Diameters,
                   O.pVO.02
                                                                                              0.02^ 0.2
Diameter, ^m :
0(1,524 m)a
 (sea level)"
0.01
1.00
0.1
1.00
1
1.17
KAb
Kcl
KAb
"A T = 293° K, / = 0.065 ^m, ,
1.03
0.92
i = 1.81 kg m "
1.36
0.97
•sec" '
1.20
0.97

 'Pressure = 8.56 kg rrfj   "Pressure = 10 33 km rrf2

  The half-life for molecular collisions with urban
aerosols is on the order of a second; thus, condensa-
tion rates would be expected to be approximately the
same  for sea level and high altitude cities for T = 20° C
(293° K).  Lowering the  temperature (at constant
pressure)  from  20°C (293°K) to  -31°C  (242°K)
reduces the gaseous diffusion coefficient by about 30
percent, but  also significantly lowers  the vapor
pressure (ns) of the condensing species. The two effects
act in opposition and for various species the rate may
be  increased or decreased.  Because the half-life for
collisions is so short, the change in the condensation
rate due  to  pressure and  temperature changes is
probably  not significant,  although a decrease in the
condensation rate may  cause  an  increase  in  the
nucleation rate. For both sea level and high altitudes, a
lowering of the temperature  depresses the equilibrium
vapor pressure  and  may result  in  large shifts of
condensible vapors from the gas phase to aerosols.
   The process of coagulation changes the atmospheric
aerosol size distribution. The decrease in the aerosol
number concentration can be expressed by the basic
equation

                   dn/dt  =  -K0n2

for a monodisperse aerosol, where

         n = aerosol number concentration, and
        Ko = coagulation constant (monodisperse).
 •B- T = 293° K, / = 0.079 (im, ^ = 1 81 kg m " 'sec" '
 'C T = 242° K, / = 0.065 i*m. ju = 1 54 kg m ' 'sec  '

  At high altitude as compared to low altitude at the
same  temperature, the  coagulation  rates  for  fine
aerosols will be faster, perhaps by as much as 20 to 40
percent.  However,  when the temperature  at  high
altitude is low (-31°C), the rates are essentially the
same.
  The process of atmospheric dry deposition is not
completely understood. However, in general terms,
the deposition of aerosols with diameters greater than
about 0.3 nm is explained in terms  of sedimentation
and impaction. For  sedimentation, the terminal fall
velocity for viscous and non-viscous flow is (5)
              v _
                s
                                                                             (PP -p.)g]
                                                                              3p,Co J
  where V, = terminal fall velocity,
        R = radius,
        PP = density of particle,
        p, = density of air,
         g = acceleration due to gravity, and
       CD = drag coefficient.

 Usually, for atmospheric aerosols, the particle density
 (pp) is in  the range 1 to 2.5 g/cm3, which is large in
 comparison to the air density (0.00129 g/cm3 at sea
 level). Thus, in the above equation, the  term (pp-pa)
                                                  A-2

-------
can be replaced by pp for atmospheric applications.
For viscous flow, the drag coefficient is

                   CD =  24/Re

 where Re = particle Reynolds number
           = 2VR/H/i|,
        V = fall velocity, and
        77 = air viscosity.
Therefore, the terminal settling for viscous flow is
                       R
               v-=   I
which is independent of the air density. The values for
viscosity (17) and acceleration due to gravity (g) are
constant  for  changes  in  pressure,  causing  the
sedimentation rates for viscous flow to be the same for
sea level and high altitude sites (assuming constant
temperature). Sedimentation in nonviscous flow must
also be considered since the atmosphere is in turbulent
motion. The  drag coefficient  for non-viscous flow
must  account for the air inertia terms in the equations
of motion, making it more complex. For a force of Ig
on the particle, the above equation can be written as
             CDRe2 = 32
Davies' (6) empirical expression (not shown) for the
Reynolds number as a function of CoRe2 was used to
calculate the settling velocities for non-viscous flow at
sea level  and  1,524 m  at  a temperature  of  20° C
(293° K); the particle's density was  taken to be 2.5
kg/ m3. The ratios of settling velocity are in Table A-4.
The  settling velocity for particles with a geometric
diameter of lOOfxm is  approximately  four percent
greater at an altitude of 1,524 m than at sea level for the
same temperature;  for smaller diameters, the ratio
decreases to a limit of unity. The settling velocity at
      TABLE A-4. NON-VISCOUS FLOW SETTLING
                 VELOCITY RATIOS
              (T = 293°K, p, = 2.5 kg m"3)
Diameter, ^m :
V. (1,524m)'
V. (sea level)"
V, (sea level)',
cm sec"'
: 1
1.00
'• 0.007

25
1.0
4.6

50
1.02
17.3

75
1.03
34.3

100
1.04
54.7

1,524 m for a pressure of 8.56 kg m 2 and a temperature
of -32° C (241.6° K) has been calculated and its ratio to
the settling velocity at sea level for a pressure of 10.33
kg m"2 and a temperature of 20° C (293 °K) is given in
Table 5.
     TABLE A-5. NON-VISCOUS PLOW SETTLING
          VELOCITY RATIOS (p, = 2.5 kg rrf3)
Diameter, /im
V. (1,524 m)'
V, (sea level)"
1      25      50.      75.    100

1.3      1.2      1.2      1.1     1.0
  •Pressure = 8.56 kg m~!, p. = 107 kg m"!
  'Pressure = 10.33 kg m"1, A = 1.29 Kg rtr1
  •Pressure = 8.56 kg nf2, p. = 1 29 kg m"1, T = 242°K, M = 1.54 kg rrf' sec"1
  "Pressure = 10.33 kg m"1, p. = 1.29 kg rrf', T = 293° K, v. = 1.81 kg m"' secM
Settling for aerosols with diameters less than 75 pm at
high altitudes during cold periods will be greater (10 to
20 percent) than at low altitudes during warm periods,
but at equal temperatures there is very little difference.
   Impaction is also an  important  dry deposition
process for aerosols with diameters in the range 0.3 to
100 /*m. Impaction of aerosols onto environmental
surfaces can be thought of as a function of the stop
distance, which  is the path length traversed by  a
particle that is in motion and is diverted into still air.
The stop distance, L, is expressed as (5)
                     2V0r2 pp
                        9rj
where Vo = initial velocity of the particle upon entering
still air  zone.  Simplistically, one can  visualize the
aerosol to  be in turbulent motion in the atmosphere
and directed toward an environmental object that has
a thin viscous sublayer (thickness = X)  of air at its
surface. If the aerosol has a stop distance (L)  that is
greater than X, it will be impacted; if not, it will likely
be swept away  by the turbulent  air. In the  above
equation, the  viscosity  is  independent of pressure;
thus,the stop distance for high altitude and sea  level is
constant for particles with the same radii, density, and
initial velocity.  However, the thickness, X,  of the
viscous  sublayer  (5)   is  approximately inversely
proportional to the fluid Reynolds number (Rer) as
                 X« Ref"' oc p,'1.
Thus, the ratio of thickness of the viscous sublayer for
1,524 m  to sea level is
         X (1,524 m)   ^   p.   (l,S24m)''
         X (sea level)   ~   p,   (sea level)
                       «   1.20
The  particle efficiency of penetration through the
viscous sublayer is inversely proportional to X; thus,
the dry deposition flux due to impaction is expected to
be approximately 20 percent less  at an  elevation of
1,524  m with  respect  to  sea level   at  constant
temperature  20°C  (293°K).  However,   for   a
                                                 A-3

-------
temperature of-31 °C (242° K) at an altitude of 1,524 m
and for a temperature of 20° C (293 ° K) at sea level, the
ratio becomes unity; there should be no difference in
the dry deposition flux due to impaction. It is difficult
to resolve the contributions of settling and impaction
to dry deposition  of aerosols  in  size range  0.3<
diameter  <  100 yum. Most likely, dry deposition
velocities  at high  altitudes  and sea  level will be
approximately the same for particles in the range 0.3 <
diameter < lOOyum.
  Settling and impaction are generally thought to be
unimportant for the dry deposition of atmospheric
aerosols with  diameters less than approximately 0.3
nm. The dry deposition of these fine aerosols can be
visualized  as  follows:  the  fine  aerosols  are  in a
turbulent  eddy that moves toward an environmental
object  that has a variable  thin viscous sublayer
(thickness =5) of air at its surface. The fine aerosols are
transported to the edge of the laminar layer, and may
be deposited  only  by diffusing  across the viscous
sublayer. The dry deposition flux of fine aerosol to the
surface is (5)

          N-D-f-
            = D (ns-ns) (6
   where N = flux of aerosol to the surface,
          n{ = aerosol concentration at the edge of
              the viscous sublayer of thickness,*,
          ns = aerosol concentration at a distance of
              one molecular mean-free path of air
              from the surface of the environmental
              object, and
          D = particle's Brownian diffusion
              coefficient.
   Since, ns = O, the equation for the flux becomes
          N = Dns/8.
This equation must be integrated over  the size distri-
bution to  account for the dependence of the diffusion
coefficient on the particle radius. Both the diffusion
coefficient and thickness of the viscous sublayer vary
with altitude. The diffusion coefficient, D, is
          D =kTB
          B = [1 +  Ap+Qpexpt-br/O^TTTjr)-'

where     k = Boltzmann's constant
          T = temperature, °K
          B = particle mobility
          A = 1.246
          / = molecular mean-free path of air
          Q = 0.42
          b = 0.87
The diffusion coefficient is independent of the density
of the aerosol, but dependent on changes in T, /, and M-
The ratios for diffusion coefficient for an altitude of
1,524 m and sea level are shown in Table A-6.
  Since the viscous  sublayer is inversely proportional
to the air density, the ratio of drv deposition for fine
aerosols   is shown  in Table  A-7.   Thus,   for  a
temperature of 20°C (293°K)  at upper altitude and at
sea level, the dry deposition rate of fine aerosol would
be about the same. However, if the temperature at the
higher altitude  is  242° K,   then  the fine aerosol
deposition rate will  be about 20 percent lower than at
sea level.
  Wet deposition of gases and aerosols is difficult to
compare for high and low altitudes,  since in-cloud
scavenging (rainout and snowout) and below-cloud
scavenging (washout) are complex phenomena. The
removal  efficiencies  depend  strongly on  such
parameters  as  the  raindrop  or snowflake  size
distribution, collision efficiencies, electrical charge,
crystal  type, shape, fall speed,  etc.  Since  these
processes  are   still  not  completely   understood,
speculations regarding differences related to altitude
will not be made.
Aerosol Instrumentation
  The performance of aerosol samplers and monitors
calibrated at lower altitudes may be affected when
                                TABLE A-6. RATIO OF DIFFUSION COEFFICIENT
Diameter, /*m :
D (1,524 m)1
D (sea level)'
D (1,524 m)c
0 (sea level)"
D (sea level)" ;
cm2sec
0.005
1.20
0.73
2.08x10"'
0,01
1.20
0.74
5.28 x 10"1
0.05
1.20
0.81
2.37 x 10~5
0.1
1.13
0.87
6.85 x 10"'
0.5
1.05
0.96
6.26 x 10'7
 •T = 293'K /« 78.8 nm, p = 1.81 kg m ' sec '
 'T = 293°K / = 85.3 nm, p = 1.81 kg m'1 sec '
 T = 293CK / * 64.8 nm, p = 1 54 kg m"' sec'1
                                                  A-4

-------
TABLE A-7. RATIO OF FINE AEROSOL FLUX
Diameter, prn
N (1.524 m)'
N (sea level)"
N (1.524 m)c
N (sea level)"
0.005
1.00
0.73
0.01
1.00
0.74
0.05
0.98
0.81
0.1
0.94
0.87
0.5
0.87
0.96
 •T = 293°K, ft = 1.07kgrrT'
 1 = 293"^ p. = 129 kg rrT!
 T = 242* K, p. = 1.30 kg m"J
used at high altitudes. The devices that will be affected
are those whose principle employs the resistance of the
air to the motion of the aerosol particles being sized.
Such   devices  include:  sedimentation  chambers,
horizontal and vertical elutriators, impactors, virtual
impactors, cyclones,  diffusion  batteries, electrical
mobility analyzers, etc. The parameters that  can be
expected to modify the performance are viscosity (due
to temperature differences) and the mean-free path of
air. Sedimentation chambers  and horizontal  and
vertical elutriators are not  now commonly used for
determining atmospheric size  distributions  or for
aerosol classification; however,  they are of historic
interest.  Their  performance  depends  on  the
sedimentation velocity and  air flow  profile  (for
elutriators). The changes in sedimentation velocity as
a function of altitude can be treated directly and has
been  discussed above. The flow profile within the
elutriator can be thought of as a function of the fluid
Reynolds number
                  Ref = ptvL/ ft
where    L = characteristic dimension of conduit.
          v = average fluid velocity.
If the dimension, L, is constant, for a  constant
velocity, v, the  Reynolds  number depends  on air
density  and viscosity; however, difference between
the Reynolds number for high and low altitudes and
various temperatures  is expected to be  less than 10
percent. Thus, significant changes in performance due
to modification of the flow profile are not expected.
   Cascade impactor is probably the most commonly
used  research device  for aerosol classification.  The
efficiency of an impaction stage depends on the Stokes
number (7),
                Stk  = CppVd2/18ML
where    C   = Cunningham slip correction  factor,
          v   = average velocity of air in jet, and
          L   = diameter (or width) of jet.
A  stage is usually characterized by experimentally
determining the diameter (dso) for which 50 percent of
the particles  are  impacted. (For  round jets,  dso
corresponds to Stk = 0.2.) For aerosols with diameter
                      greater than 0.2 /tin, C does not change significantly
                      with altitude (pressure and temperature) to  be of
                      concern.  However,  the  viscosity  is  temperature-
                      dependent and  a change from 20° C (293° K) to -31°C
                      (242° K)  will lower  the  dso values by  about eight
                      percent for a constant volume flowrate. Also, it can be
                      expected  that  the  cut point diameter for virtual
                      impactors  should  exhibit  a  similar  temperature
                      dependence. The  dependence of flow profiles on the
                      fluid Reynolds number (which probably varies  less
                      than 10 percent) is not expected to be important with
                      regard to performance.
                        There is not yet an exact theory for the operation of
                      cyclones.  Fuchs  (5) has  made  an estimate  of  the
                      efficiency (E) of cyclones, considering turbulent flow:
                                    E  =  1 - exp (-7rvrs/2h)
                      where    v  = average flow velocity,
                               s  = number of turns of spiral,
                               h  = width of inlet, and
                               T  - relaxation time
                                  = 2 r2pp/9M.

                        Although the equation cannot be considered to be
                      exact, it should be suitable for deducing the influence
                      of altitude factors on the performance of cyclones.  For
                      a constant volume flow rate, the only parameter that
                      needs to be considered  is the viscosity. Since viscosity
                      is  independent  of pressure,  only  temperature
                      variations are imporatant. From the above equation,
                      it is estimated that a cyclone with a 50 percent efficiency
                      for particles with a 4-jum diameter, operated at 20° C
                      (293° K),  will have  an efficiency of 56 percent if
                      operated at -31°C (242°K) with the same volume flow
                      rate (uncorrected). However, if the cyclone is operated
                      at  constant  air  mass  flow rate,  its efficiency is
                      estimated to be 63 percent at -3I°C  (242° K) for 4/im
                      diameter particles at 1,524 m, compared to 50 percent
                      at sea level.
                        The determination of aerosol size distributions for
                      particles with a diameter less than 0.2 /um has been
                      performed with diffusion batteries (5). The technique
                      is based on a measurement of the decrease in aerosol
                      number concentration  as a function of length of the
                  A-5

-------
capillary conduit; the depletion of aerosol results from
diffusion deposition on the conduit walls. Thus, the
technique is dependent  upon the aerosol  diffusion
coefficient,  which  is  a function  of pressure and
temperature. The correction can be made to the
diffusion coefficient  as described above in the section
on dry deposition.
  Electrical  mobility analyzers are coming into
frequent use for aerosol size measurement of particles
with diameters less than 0.5 /zm. There are two sources
of possible performance modification for this device:
the aerosol charging section and the aerosol drift tube.
Usually, the charging section is operated with a constant
corona current to yield an ion density*charging time
(Not) product of 106. The  degree of aerosol charging
(number of particles charged and charge distribution)
depends on the ion mobility, which is proportional to
the  molecular   mean-free  path.  An   instrument
calibrated at sea level and operated at constant corona
current at an altitude of 1,524 m will have its (Not)
decreased by 20 percent, due to the 20 percent increase
in ion  mobility. The effect on  aerosol  charging is
nonlinear,  and the charge distribution on aerosol is
very sensitive for small (Not) values of 106 or less. If a
(Not) value  of  107  (at  sea level) is employed, the
modification of charge distribution is less, but greater
multiple charging occurs,  lowering the resolution of
the instrument. In the drift tube, sizing is inferred from
the quantity of charged aerosol that passes through the
tube as a function of applied electrical field. Thus, the
aerosol removal is a function of electrical mobility, Z:
                    Z  =  qB,
where    q  = number of electrons on particle, and
          B  = aerosol mechanical mobility (given in
              discussion above  on dry deposition/
              diffusion).
B has a dependence  on both the molecular mean-free
path and viscosity. The  value  of B at a constant
termperature, 20° C (293° K),  will  increase  by 20
percent  for 0.005 Mm  and  5  percent  for 0.5 pm
diameter particles in going from sea level to 1,524 m.
However, if the temperature is -31°C (242°K) at 1,524
m, B is  depressed with respect  to values at sea level
20°C  (293°K).  The  performance  of the  mobility
analyzer is expected  to  be sensitive  to altitude
parameters,  but  due  to the  complexity  of  the
calculations, no degree of deviation from performance
at sea level is anticipated.
  Aspiration inlets for  aerosol  sampling are known
to have a variable efficiency for coarse particles (5).
The performance of inlets at  this time cannot be
described exactly, but the same aerosol properties that
govern dry depostion of fine  and coarse aerosol are
expected to govern inlet performance. It is expected
that inlet performance at sea  level and at 1,524 m is
unity for particles with diameters less than 1 /*m. The
change in stop distance is used to estimate the change
in performance at high  and low altitudes.  Since  the
stop  distance is dependent upon  the viscosity,  but
independent  of air density,  one would expect  the
coarse particle performance of  inlets to  depend only
upon temperature. A lowering of the temperature from
20° C  (293° K)   to  -31° C (242° K)  increases  the
stop  distance  by about 20 percent, which  implies
qualitatively  that the efficiency  of an aspiration inlet
will decrease as temperature  decreases.  Generally, it
would be  expected that the efficiency  of the high
volume sampler would be unity for fine aerosols at
high  and low altitudes, but its efficiency (less than
unity) for coarse  aerosol would  be decreased  as
temperature  decreased.
   It should be recognized that certain devices (such as
most single particle light-scattering instruments) that
do not measure a resistance-to-motion parameter have
the same calibration at  both  high  and low altitudes.
Care must be taken with nephelometric measurements
in removing  the air scatter, which is a function of air
density.  Condensation  nuclei  counters  would  be
expected to have a slightly lower counting efficiency at
higher  altitudes,  due  to the decreased  thermal
conductivity of air at lower pressures.


REFERENCES
  1. Fairbridge, R.  W (ed.). The Encyclopedia  of Atmospheric
    Sciences and Astrogeology. Encyclopedia of Earth Sciences
    Series, Vol. II. Van Nostrand Reinhold Publishing Corp., New
    York, 1967.
  2. Weast, R. C. Handbook of Chemistry and Physics,  57th
    Edition. CRC Press, Cleveland, 1976.
  3. Bretsznajder, S. Prediction of Transport and Other Physical
    Properties  of Fluids. Pergamon; Press, New  York,  1971.
  4. Hidy, G. M. and J. R. Brock. The  Dynamics  of Aerocollodial
    Systems. Pergamon Press, New York, 1970.
  5. Fuchs, N.  A.The Mechanisms of Aerosols. Pergamon Press,
    New York, 1964.
  6. Strauss, W. Industrial Gas Cleaning. Pergamon Press,  New
    York, 1966.
  7. Friedlander, S. K. Smoke, Dust and  Haze. John Wiley and
    Sons, New York, 1977, pp. 162-164.
                                                   A-6

-------
                                        APPENDIX B
OTHER SYSTEMS - HIGH ALTITUDES
  Precise data on the potential scope of the problems
due to carbon monoxide for high altitude residents
and  visitors are  not  available. Approximately 2.2
million people live at  altitudes above 1,524 m in the
United States. These figures do not present a complete
picture of potential numbers of individuals who may
be subjected to carbon monoxide at these altitudes
because the tourist population in these areas is high in
both summer and winter. Furthermore, proper tuning
of automobiles for high altitude travel is uncommon
and the influx of visitors with cars that emit carbon
monoxide and other contaminants may prove to be an
important factor  in raising pollution exposure to an
unacceptable point.
  Ambient air standards set at sea  level  are  not
applicable for high altitude sites. The United States
Environmental Protection Agency's (EPA)  primary
standards are expressed in milligrams per cubic meter
of air.  At  1,540  m,  each  cubic  meter contains
approximately 18 percent less air than at sea level.
Therefore,  allowable concentrations  of  carbon
monoxide in air in a city like Denver will be 22 percent
higher than at sea level (i.e., a 10-mg/m3 maximal
permissible 8-hour average is equivalent to 10 mg/m3
at sea level but 11.8 mg/m3 at Denver's altitude).
  Carbon monoxide  exposure may aggravate the
oxygen  deficiency  at  high  altitudes.  When  high
altitude and carbon monoxide exposure are combined
(Table B-l), the  effects are apparently  additive. It
should be noted that each of these, decreased Po2 in the
air   and  increased carboxyhemoglobin,   produce
different  physiologic responses. They have different
effects on blood  Po2,  on the affinity of oxygen for
hemoglobin,  on  the extent  of  oxyhemoglobin
saturation (carbon  monoxide hypoxemia shifts the
oxyhemoglobin dissociation  curve to the left, and a
decrease  in PAo2 shifts  it  to  the  right),  and on
ventilatory drive.
  The most supportive information on the  additive
nature of CO hypoxia and hypoxic hypoxia originates
from psychophysiologic studies, and even these are
not as persuasive as one would desire. Blackmore (1)
analyzed the cause of aircraft accidents in Britain and
    TABLE B-1. APPROXIMATE PHYSIOLOGICALLY
      EQUIVALENT ALTITUDES AT EQUILIBRIUM
            WITH AMBIENT CO LEVELS
Ambient
CO Concentration
mg/m1

0
28.6
57.3
114.5
ppm

0
25
50
100
Actual Altitude (meters)
0 (sea level)
1.524
3,048
(Physiologically Equivalent Altitudes with COHb)
0 (sea level)
1,829
3,048
3,749
1,524
2,530
3,658
4,663
3,048
3,962
4,694
5,486
found   that  carboxyhemoglobin  levels  provided
valuable information relative to altitude and  CO
sources.  The relatively high  levels found could be
attributed to equipment failure, smoking, and fires.
No  data are available on the effects of  carbon
monoxide on native inhabitants of high altitude or on
the reactions of these natives when they are suddenly
removed to sea level and possible high ambient carbon
monoxide concentrations.
  McFarland et al. (2) showed that changes in visual
threshold occurred with carboxyhemoglobin as low as
five percent or a simulated altitude of approximately
2,425 m. Halperin et al. (3) further noted that recovery
from the detrimental effects on visual function lagged
behind the elimination of carbon monoxide. However,
the data given were sparse and the variability among
the few subjects and the day-to-day variation were not
given. Vollmer et  al. (4) studied the effects of carbon
monoxide at simulated altitudes of 3,070 and 4,555 m
and  reported that there were no additive effects of
carbon monoxide and altitude. They suggested that
the effects of carbon monoxide were masked by some
compensatory mechanisms. The data  presented were
not convincing. Lilienthal and Fugitt (5) indicated that
the combination of altitude (1,540 m) and a five to nine
percent carboxyhemoglobin induced a  decrease in
flicker  fusion frequency, although neither one alone
had an effect. They also reported that the presence of
8 to 10 percent carboxyhemoglobin  was effective in
reducing altitude tolerance by some 1,215 m. Forbes et
al. (6) found that, during light activity at an altitude of
4,875 m,  carbon  monoxide uptake  was increased,
probably owing to the hyperventilation caused by the
respiratory stimulus of decreased Po2 • Evidence that
                                                B-l

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CO  elimination was  similiar at  sea level  and  at
altitudes  up to  10,000 m was obtained  by several
investigators. (7,8)  Increased ambient temperatures
up to 35°C and hard physical work increased the rate
of elimination. (4) Pitts and Pace (9) stated that every
one percent increase in carboxyhemoglobin (up to 13
percent) was equivalent to a 109-m rise in altitude if
the subjects were at altitudes of 2,100 to 3,070 m. Their
observations were based on changes in the heart rate
response to work.  Subjects who may  have been
smokers were not identified.
  Two groups of investigators  have presented data
comparing  the physiologic responses of subjects  to
altitude and carbon monoxide where the hypoxemia
due   to   altitude   and  the  presence   of
carboxyhemoglobin were approximately equivalent.
In one  study,  (10)  the carboxyhemoglobin varied
around 12 percent (although the mode of presentation
of carbon monoxide was such that carboxyhemoglobin
ranged  from 5  to  20  percent  during  the carbon
monoxide  exposures)  and the  altitude  study was
conducted at 3,977 m. The second study (8) compared
responses   of  altitudes   of  4,000   m   and  a
carboxyhemoglobin  content of 20 percent. In both
these  studies,  carboxyhemoglobin content  was  in
excess  of  that  anticipated for  typical  ambient
pollution. However, it was suggested that the effects
attributable to carbon monoxide and to altitude were
equivalent.
  It was recommended on theoretical grounds that the
ambient   carbon   monoxide  in tunnels  being
constructed at 3,859 m should not  exceed 29 mg/m3.
(11)   The  maximal  aerobic  capacity  is  reduced
approximately 20 percent in individuals exposed to an
altitu ie of 3,085 m..Weiser et al. (12) reported that
max Vo2 was significantly impaired in subjects living
at 1,700 m when their COHb levels were five percent.
However, this decrement is similar to that seen in sea
level  residents.  No data  are available  for higher
altitudes. Brewer et al (13)  conducted  a study  on
residents of Leadville, Colorado (3,085 m). The mean
COHb level in smokers at this altitude was higher than
that of smokers at sea level. This increased degree of
hypoxemia may have contributed to the elevated red
cell  mass  observed, since individuals who stopped
smoking demonstrated a reduction in their  red cell
mass.
   The most important information regarding carbon
monoxide exposures and altitudes, the preciseness of
their potentially additive  effects., has  not received
much attention, and what little information there is
has been obtained by assuming simple additive effects.
(14) It has not been verified by direct experiments.
  Recently reported  epidemiological data indicate a
correlation between complaints of cardiorespiratory
problems and ambient CO levels in Denver residents.
The results suggest there is a threshold effect at levels
lower than had been previously suggested. (15, 16).

REFERENCES
 1.  Blackmore, D. J. Aircraft Accident Toxicology: U.K. Exper-
    ience 1967-1972. Aerosp. Med. 45:987-994, 1974.
 2.  McFarland, R. A., F. J. W. Roughton, M. H. Halperin, and
    J. I. Niven. The Effects of Carbon Monoxide and Altitude on
    Visual Thresholds. J. Aviat. Med. 75:381-394, 1944.
 3.  Halperin, M. H., R. A. McFarland, J. I. Niven, and F. J. W.
    Roughton. The  Time Course  of the Effects  of  Carbon
    Monoxide on Visual Thresholds. J. Physiol. (London) 146:583-
    593, 1959.
 4.  Vollmer, E. P., B G. King, J. E. Birren, and M. B. Fisher.
    The Effects of Carbon Monoxide on Three Types of Perform-
    ance at Simulated Altitudes of 10,000 and 15,000 Feet. J. Exp.
    Psychol. 56:244-251,  1946.
 5.  Lilienthal, J. L., Jr. and C. H. Fugitt. The Effect of Low
    Concentrations of Carboxyhemoglobin  on  the "Altitude
    Tolerance" of Man. Am. J. Physiol. /45:359-364, 1946.
 6.  Forbes, W. H., F. Sargent, and F. J. W. Roughton. The Rate of
    Carbon Monoxide Uptake by Normal Men. Am. J.  Physiol.
    /
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