w
          United States      Office of Air Quality      EPA-450/3-78-110c
          Environmental Protection  Planning and Standards     September 1978
          Agency        Research Triangle Park NC 27711
          Air
&EPA     The Development of
          Mathematical Models for
          the Prediction of
          Anthropogenic Visibility
          Impairment
          Volume
          Case Studies for
          Selected Scenarios

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                                  EPA-450/3/78-llOc
Volume III:  Case Studies for Selected Scenarios


     THE DEVELOPMENT OF MATHEMATICAL MODELS

       FOR THE PREDICTION OF ANTHROPOGENIC

              VISIBILITY IMPAIRMENT
                       by
               Douglas A.  Latimer
      Systems Applications,  Incorporated
         San Rafael,  California   94903
              Contract 68-02-2593


      EPA Project Officer:   Russell  F.  Lee



                  Prepared  for

      U.  S.  ENVIRONMENTAL PROTECTION AGENCY

       Office of Air,  Noise, and Radiation
  Office of Air Quality Planning and Standards
        Research Triangle Park,  NC  27711




                 September  1978

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                                    11
                             DISCLAIMER
     This report has been reviewed by the  Office  of Air Quality Planning
and Standards, U.S.  Environmental  Protection  Agency, and approved for
publication.  Approval does not signify that  the  contents  necessarily
reflect the views and policies of  the U.S.  Environmental Protection
Agency, nor does mention of trade  names or commercial  products consti-
tute endorsement or recommendation for use.

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                                  111
                               CONTENTS



Disclaimer	    ii

List of Illustrations	    iv

List of Tables	    iv

Key to Parametric Studies of Emissions Rates  	     v

Key to Parametric Studies of Plume-Observer Distances,  Sulfate
Formation Rates,  and Background Ozone Concentrations  	     v

   I   Introduction  	       1

  II   Assumed Input Emission and Ambient Conditions  	       4

 III   Interpretation of Visibility Impairment Parameters   ....       8

       A.  Percent Reduction in Visual Range  	       8

       B.  Blue-Red Ratio  	       9

       C.  Plume Contrast  	       9
       D.  Plume Perceptibility Parameter AE  	      10

       E.  Summary	    11

  IV   Effects of Emissions, Atmospheric Stability, and
       Scattering Angle on Plume Visibility Impairment  	      13

   V   Effects of Plume Observer Distance, Background Visual
       Range, and Atmospheric Stability on Plume  Visibility
       Impairment	      26

  VI   Effect of S02-to-Sulfate Conversion Rate or
       Visibility Impairment 	      45

 VII   Effect of N02 Formation Rate Due to Different Background
       Ozone Concentrations on Visibility Impairment  	      62

VIII   A Summary of Typical Visibility Impairment Caused by  Power
       Plants in the Eastern and Western United States  ......      79

  IX   Summary and Conclusions 	  ......  	      gg

REFERENCES .	      90

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                                    IV
                            ILLUSTRATIONS



1     Geometry of Plume,  Observer, and Sun Assumed in Calculations  .  .    7

2     Key to Parameters Used To Characterize Visibility Impairment  .  .   12

3     Calculated Plume  Visibility  Impairment  	   17

4     Effect of Plume-Observer Distance on Calculated
     Visibility Impairment  	   29

5     Effect of Sulfate Formation  on Calculated Plume
     Visibility Impairment	46

6     Effect of Background Ozone on Calculated Plume
     Visibility Impairment  	   63

7     Comparison of Plume Visibility in the Eastern and
     Western United States  	   80
                                 TABLE


1    Input Parameters Used in  Calculations  	    5

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            KEY  TO  PARAMETRIC  STUDIES  OF EMISSION  RATES
                         Scattering
                          Angle
                            45°
                            90°
                           180°
Pasquill
Stability
Category
3(a)
3(b)
3(0
3(d)
3(e)
3(f)
3(g)
3(h)
3(1)
17
18
19
20
21
22
23
24
25
                         Note:  Base conditions are 2250 Mwe power plant,
                              130 km background visual range (average for
                              western United States), 2.5 km plume-
                              observer distance, and 0.04 ppm background
                              ozone concentration. Each figure presents
                              results for four emission rates.
    KEY  TO  PARAMETRIC  STUDIES  OF  PLUME-OBSERVER  DISTANCES,
SULFATE FORMATION  RATES,  AND  BACKGROUND  OZONE CONCENTRATIONS
Parameter Varied
Case

Region
Eastern
United
States





Western
United
States





Background
Visual
Range
(km)
15
•(average)


30
(best)


130
(average)


200
(best)


Power
Plant
Size
(Mwe)
2250

750

2250

750

2250

750

2250

750

Pasquill
Stability
Category
D
E
D
D
D
E
D
E
D
E
0
E
D
E
D
E
Plume-Observer
Distance (2.5,
5, and 10 km)

Figure
4(a)
4(b)
4(c)
4(d)
4(e)
4(f)
4(g)
4(h)
4(i)
4(j)
4(k)
4(1)
4(m)
4(n)
4{o)
4(p)

Page
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
Sulfate
Formation
Rate (0, 0.5,
and 5%/hr)

Figure
5(a)
5(b)
5(c)
5(d)
5(e)
B(f)
5(g)
5(h)
5(1)
5(j)
5(k)
5(1)
5(m)
5(n)
5(0)
5(p)

Page
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
Background
Ozone Concentra-
tion (0, 0.04,
and 0.1 ppm)

Figure
6(a)
6(b)
6(c)
6(d)
6(e)
6(f)
6(9)
6(h)
6(1)
6(j)
6(k)
6(1)
6(m)
6(n)
6(0)
6(p)

Page
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
East-West
Comparison

Figure
7(a)
7(b)
7(c)
7(d)
7(e)
7(f)
7(9)
7(h)
7(a)
7(b)
7(c)
7(d)
7(e)
7(f)
7(g)
7(h)

Page
80
81
82
83
84
85
86
87
80
81
82
83
84
85
86
87
       Note:  Except as indicated otherwise on figures, the base case conditions are 5.0 km plume-observer
            distance, 0.5 percent/hr sulfate formation rate, 0.04 ppm background ozone concentration,
            and 90" scattering angle.

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                           I     INTRODUCTION
     This report presents calculations of visibility impairment caused
by hypothetical coal-fired power plants under different assumed emission,
meteorological, and ambient background conditions.  Calculations were per-
formed using the Gaussian-based plume visibility model developed by Systems
Applications, Incorporated (SAI) for the U.S. Environmental Protection
Agency and described in Volumes I and II of this report.  Graphs are used
to illustrate the impact on calculated visibility impairment of various
typical values of the following input parameters (see keys on page v):

     >  Emission rates.
     >  Atmospheric stability.
     >  Location of the  observer relative  to  the power
        plant and the plume centerline.
     >  Direction of view relative  to the  sun (scattering
        angle).
     >  Ambient background visual  range.
     >  Ambient background ozone concentration.
     >  Sulfate formation rate.

     In the Clean Air Act Amendments of 1977,  Congress  defined  visibility
impairment to include a  reduction in visual range and atmospheric  discolor-
ation.   Four parameters  that  quantify visibility impairment caused by plumes
have been selected for the graphs:

     >  Percent reduction in  visual  range  (from  background).
     >  Blue-red ratio (indicative  of the  plume  coloration relative
        to the background,  clear horizon sky).

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     >  Plume contrast (relative to the background  sky—indicative
        of the relative brightness of the plume).
     >  Plume perceptibility parameter A£ (proportional  to  the
        plume perceptibility as a result of both brightness
        and color differences between the plume and the  background
        sky).

     This document is designed to offer the air quality  analyst  a
quick reference for estimating visibility impairment caused by modern,
large coal-fired power plants controlled to meet EPA's  current New  Source
Performance Standards (NSPS) (Federal Register, 1976).   These standards
require efficient particulate control devices (e.g., electrostatic  precip-
itators, baghouses, or wet scrubbers) for meeting  the 20 percent opacity
requirement.   Meeting the current SCL emission standard* of 1.2  lbs/10
Btu requires  flue gas desulfurization in the case  of high-sulfur, Eastern
coal, but no  scrubbing for many low-sulfur, Western coals.   Meeting the
current 0.7 lbs/10  Btu NO  emission standard requires  modern boiler com-
                          A
bustion design.

     This document is limited to a few emission, meteorological, ond ambient
conditions that are considered typical; therefore,  it is by no means meant
to replace detailed model calculations or measurement programs that are
carried out to identify visibility impairment.  For example, these  calcula-
tions would not be appropriate for estimating the impact caused  by  older
power plants  with inefficient particulate control  equipment. Also, impacts
during stable, light wind conditions would be much larger than those
presented here, which assume  a moderate wind  speed  of 5 m/s (11  mph).
Furthermore,  the impact caused by secondary aerosol—sulfates  and nitrates--
could be  larger than those indicated here if catalytic particulates (e.g.,
iron, manganese) are emitted, if ambient concentrations of reactive species
(e.g., OH«, NH_) are large, or if water droplets (e.g.,  from clouds, fog,
or cooling tower plumes) are present.
* More restrictive emission standards have recently been proposed.

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     The calculations presented here are based on certain assumptions
regarding viewing conditions.  It is assumed that the plume is viewed
on a horizontal line of sight perpendicular to the plume centerline.   If
the plume were viewed down the centerline (e.g., if the observer were
in an airplane or on elevated terrain), or if it were viewed obliquely,
visibility impairment would be greater.  Also, it is assumed that the
viewing background behind the plume is the clear horizon sky.   If a
bright, white cloud or dark terrain feature were behind the plume, the
coloration and perceptibility of the plume would change.  For example,
with a bright, white background, wavelength-dependent light scattering
caused by aerosols contributes to the yellow-brown coloration  similar to
that caused by NO- light absorption.

     Although the vertical diffusion of the plume is eventually limited
to the mixed layer between the ground and the capping, stable layer,  it  is
assumed that Pasquill-Gifford dispersion coefficients correctly describe
the growth of the power plant plume at intermediate distances.  There
is increasing evidence that power plant plumes, due to entrainment during
plume rise, are initially more dilute than are indicated by Pasquill-
Gifford a a 's; and that because of their elevation, plumes diffuse
less rapidly than Pasquill-Gifford a a 's indicate (Carpenter  et al.,  1971;
Husar et al.,  1978; Smith et al., 1978).   Since visibility impairment is
strongly dependent on the vertical thickness of the plume for  horizontal
lines of sight, it is essential  that plume a 's be known as accurately as
possible in order to predict visibility impairment accurately.  Also,  since
plume a a 's at distances greater than 50 km downwi
the calculations presented here are estimates only.
     Finally, the user of this document is cautioned  about interpolating
and extrapolating these results for different conditions.   NO^  formation
in power plant plumes is diffusion-limited,  that is,  it is limited  by  the
rate at which background ozone is entrained  into the  plume.   Consequently
one cannot simply substitute a ratio of these discoloration effects to cor-
respond to light wind cases or to cases involving different emission rates.

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       II   ASSUMED  INPUT  EMISSION  AND AMBIENT CONDITIONS
     Calculations were performed using the plume  visibility model  for
assumed emissions from hypothetical  coal-fired  power  plants consisting
of one and three 750-Mwe units,  assuming EPA's  NSPS are  just met.
Table 1 summarizes the emission  parameters.

     Emission rates of fly ash,  SOp, and NO   were computed from  the
NSPS emission limits of 0.1, 1.2, and 0.7 lbs/106 Btu, respectively;
however, fly ash emissions were  controlled not  by the above mass emission
limit, but by the 20 percent limitation on stack  opacity.  Emission
parameters were calculated for a subbituminous  B  coal with a heating
value of 9600 Btu/lb; if a different coal  were  used,  emission  parameters
would change somewhat.  It was assumed that  the emitted  fly ash  (after
particulate removal) has a mass  median diameter of 1  vim, a geometric
                                               3
standard deviation of 2, and a density of 2  g/cm  .  On the basis of Hie
calculations for this fly ash size distribution,  it was  found  that
99.6 percent efficient particulate control equipment  would be  required
for this particular coal to meet the NSPS 20 percent  stack opacity limit.

     Table 1 also shows the meteorological and  ambient conditions  used  in
the calculations.  A typical (average) wind  speed of  5 m/s  (11 mph) at  plume
level and two stability categories were used:  Pasquill  D  (neutral) and
Pasquill E (slightly stable).  Calculations  were  carried out to  250 km  down-
wind from the source, assuming that uniform  meteorological  conditions per-
sist that long  (14 hours).*  For Pasquill D conditions vertical  mixing  is
eventually limited by the height of the mixed layer:   1500 m (for  the eas-
tern United States) and 2000 m (for the western United States).   For cases
* Power plant plumes have been tracked and measured as far as 300 km down-
  wind (Husar et al., 1978; Smith et al., 1978).

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              TABLE  1.   INPUT PARAMETERS USED IN CALCULATIONS
                 Parameter
Coal-fired power plant emission conditions
  *Number of boilers and stacks
  *Power output
  Flue gas temperature
  Flue gas flow rate per stack
  Fly ash emission rate per 750-Mwe boiler
  Stack opacity
  Fly ash mass median diameter
  Fly ash size distribution geometric
  standard deviation
  S02 emission rate per 750-Mwe unit
  *NOX emission rate per 750-Mwe unit,
  as fto2
Meteorological and ambient conditions
  Wind speed
  *Stability category
  *Background visual  range
  Background Oj concentration
  *Assumed pseudo-first-order sulfate
  formation rate
  Assumed pseudo-first-order nitrate
  formation rate
  Assumed surface deposition velocities

  *Scattering angle
  *Plume-observer distance
                Value
3, [1]
2250, [750] Mwe
250°F = 121°C
1,724,000 acfm = 814 m3/sec
1.15 tons/day = 12.1 g/sec
20%
1.0 urn
2.0

92.15 tons/day = 968 g/sec
53.75, [0] tons/day = 5.64,
[0] g/sec
5.0 m/sec
Pasquill C, D, and E
[Typical—eastern U.S.:  15 km],
[Best—eastern U.S.:  30 km],
Typical--western U.S.:  130 km,
[Best—western U.S. :  200 km]
[0.0], 0.04, [0.12] ppm
[0], 0.5, [5] %/hr

0 %/hr

1  cm/sec for gases,  0.1 cm/sec
for particles
[45°], 90°, [180°]
[2.5],f 5,  [10] km
* Parameters that were varied in the sensitivity analysis.
t A plume-observer distance of 2.5 km was  used as base  value  for  Fiaures
  2(a) through 2(i).
[ ] = Values of parameters when varied from the base  value.

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where vertical mixing is more severely limited,  visibility impairment would
be greater.  Four background visual  ranges were  assumed in the calculations;
they are representative of the typical and best  eastern United States
conditions (15 and 30 km) and the typical  and best western,  nonurban  U.S.
conditions (130 and 200 km).  Background ozone concentrations were varied
from the base case as shown in the table.

     Three sulfate formation rates were assumed  in the calculations,  as
shown.  The 0.5 percent per hour rate is considered to be typical  of  most
nonurban conditions.  The 5 percent per hour value is representative  of
fast gas-to-particle conversion that could occur in polluted areas.   Owing
to the lack of quantitative data on nitrate formation in plumes, a nitrate
formation rate of 0 was assumed; the validity of this assumption is uncer-
tain.  Secondary plume sulfate aerosol is assumed to be in the submicron
range, with a mass median diameter of 0.18 urn, based on power plant plume
measurements near St. Louis (Whitby and Sverdrup, 1978).  Aerosol  in  this
size range is most effective per unit mass in scattering light.

     Several scattering angles were assumed:  For the base case, a scat-
tering angle of 90° and a solar zenith angle of  45° were used for various
observer locations from 1 to 250 km downwind of  the power plant and at
several distances (2.5, 5, and 10 km) from the plume centerline.  Figure 1
illustrates the orientations of the observer, plume, and sun that were
assumed in calculations.  Note that calculated visual impact refers to
specific lines of sight, not to "prevailing visibility."

     The effect of surface deposition on the pollutant mass flux at a given
downwind distance was considered in the calculations.  The surface deposi-
tion velocity was assumed to be 1 cm/sec for gases (e.g., S0? and NO ) and
                                                            £•       /\
0.1 cm/sec for particles (e.g., fly ash and SOT).

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     Ill    INTERPRETATION  OF VISIBILITY IMPAIRMENT PARAMETERS
     Each of the accompanying figures  displays four parameters that charac-
terize visibility impairment:

     >  Percent reduction in visual  range
     >  Blue-red ratio
     >  Plume contrast
     >  AE.

In this section we briefly define  these  parameters and describe what typical
values for them mean using the following qualitative terms:  bright and dark;
yellow, brown, white, and grey discoloration;  imperceptible and perceptible.
More detailed explanations of these  parameters and details concerning the
models used to calculate them are  given  in  Volume I of this report.

A.   PERCENT REDUCTION IN VISUAL RANGE

     Visual  range is defined as the  farthest  distance at which a black
object can be perceived against the  clear  horizon sky.  The percent reduc-
tion in visual range is calculated as  follows:
                                       x 100%
where r  is the visual range for views through  the  plume center and rvo is
the visual range without the plume (ambient background  visual  range).  In
most situations, the percent reduction in visual  range  is directly propor-
tional to the integral of the plume light scattering  and absorption coef-
ficients along the line of sight and is independent of  the  background
visual range.  The percent reduction in visual  range  is indicative of the
"haziness" of objects observed through the plume.   Until it is diffused,

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the plume will affect only a few of the observer's lines of sight;  there-
fore, calculated visual range reduction pertains only to specific lines of
sight through the plume center (perpendicular to the plume center! ine),
not to prevailing visibility.  The magnitude of visual range reduction is
not necessarily related to the perceptibility of the plume or to atmo-
spheric discoloration.  A significant reduction in visual range could
occur without a perceptible plume or atmospheric discoloration.  This
occurrence is illustrated in our subsequent discussion of plume impact
under typical ambient conditions for the eastern United States.

B.   BLUE-RED RATIO

     The blue-red ratio indicates the coloration of the plume relative to
the unaffected background sky.   It is the ratio of the plume light  inten-
sity at the blue end of the visible spectrum (A = 0.4 ym) to that at the
red end (x = 0.7 pm) divided by the same ratio for the background:
                     ,
                       "
A ratio of 1 indicates that the plume is the same color as  the background
sky, though not necessarily of the same brightness.   Ratios greater than 1
indicate bluish discoloration relative to the background, and ratios of
less than 1 indicate yellowish discoloration.  If the background sky is
blue, the plume could be white or grey with a ratio  of less than 1  because
the ratio is a relative discoloration index.  The plume color will  be a
more saturated yellow with decreasing values of this ratio  (<0.9).

C.   PLUME CONTRAST

     Plume contrast is the normalized difference in  light  intensity of the
plume relative to the background:

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                                   10
                        I (0.55 um) - Ib(0.55
                   Cp =        Ib(0.55 ym)

Contrast is evaluated at a wavelength A of 0.55 ym, which is the midpoint
of the visible spectrum where the human eye is most sensitive.   With  no
color shifts (that is, with a blue-red ratio = 1),  a plume will  be  visible
only if it is sufficiently brighter (C  > 0) or darker (C  < 0)  than  the
background sky.   There are no experimental data concerning the  percepti-
bility threshold contrast for plumes.  A threshold  contrast of  0.02 is
used in defining the perceptibility of a dark object against the horizon
sky in the calculation of visual  range; however, it is likely that  the
threshold contrast for plumes is  greater than 0.02  because, in  many cases,
the boundary between a plume and  the background is  not distinct owing to
the nature of plume dilution.  The use of the blue-red ratio in conjunction
with the plume contrast at 0.55 ym is a simple way  of characterizing  plume
color.  When R > 1, the plume is  more blue than the background;  when  R  <  1,
the plume is redder (or more yellow-brown); when R  = 1, with C  (0.55  ym)  > 0,
the plume is a brighter white than the horizon, and with C (0.55 urn)  <  0,
the plume is a darker grey.
 D.    PLUME  PERCEPTIBILITY  PARAMETER AE

      The  final  step  in  the quantification of plume perceptibility is the
 specification of  color  differences—differences both in color and bright-
 ness.   In 1976  the Commission  Internationale de 1'Eclairage (CIE) adopted
 two  color difference  formulae  by which  the perceived magnitude of color
 differences can be calculated.  Color differences are specified by a
 parameter AE, which  is  a function  of the change in light intensity or
 value (AL*) and the  change in  chromaticity (AX,Ay).  AE can be considered
 as  a distance between two  colors  in a color space that is transformed in

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                                    11
such a way that equal distances (AE) between any two colors correspond to
equally perceived color changes.  This suggests that a threshold (AEg) can
be found to determine whether a given color change is perceptible.
                         r
     Since the CIE could not decide between two different proposed  formulae
for AE, both were adopted in 1976 as standard means by which color  differ-
ences can be specified.   These color differences, which are labeled
AE(I_*U*V*) and AE(L*a*b*), are calculated by the plume visibility code.
We have elected to plot AE(L*a*b*).  A AE of greater than 20 indicates a
strong discoloration, AE's between 5 and 20 represent weak discoloration,
and with a AE Isss than  5,  a plume would probably not be perceptible.   It
is currently uncertain as to what the thresholds of perceptibility  are in
terms of values of blue-red ratio, plume contrast, and AE.

E.    SUMMARY

     Figure 2 summarizes these qualitative interpretations of the quantita-
tive specifications of visibility impairment and may be used as  a key  to
Figures 3 through 7.

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1       2       *    6    10      20      40   60   100     ZGO

  Location of Observer Downwind of  Power  Plant  (km)
 FIGURE 2.   KEY TO PARAMETERS USED TO CHARACTERIZE
             VISIBILITY IMPAIRMENT

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                                   13
     IV  EFFECTS  OF EMISSIONS,  ATMOSPHEKll STABILITY, AND
        SCATTERING ANGLE ON  PLUME  VISIBILITY  IMPAIRMENT
     Figures 3(a)  through  3(i), presented at the end of this chapter,
illustrate calculated  plume  visibility impairment resulting from the hypo-
thetical,  three-unit,  2250-Mwe, coal-fired power plant.  For all  of these
plots,  the background  ambient conditions are typical of those in nonurban
areas of the western United  States:  The background visual  range is 130  km,
and the background ozone concentration is 0.04 ppm.  The observer is assumed
to be situated  2.5 km  from the plume centerline, at the indicated downwind
distances.  See the key on page v and Table 1 for base conditions.

     Four  emission/formation scenarios are assumed and illustrated in  each
of these figures:

     (1)  Normal  NOX emissions (at the NSPS limit); 0.5 %/hr
          sulfate  formation  (the base case).
     (2)  Normal  NO emissions; no sulfate formation (equiva-
                   A
          lent  to  the  assumption of no SO^ emissions, or
          complete flue gas  desulfurization).
     (3)  No NO  emissions;  0.5 %/hr sulfate formation
               X
          (equivalent  to complete NO  removal and no S0~
                                   A                  C-
          removal).
     (4)  No NO  emissions;  no sulfate formation (equivalent
               A
          to complete  NO   and SO- control except for fly ash
                       A       t_
          emissions).

Figures 3(a), 3(b), and 3(c) illustrate for a scattering angle of 45°  (a
forward scattering case--sun in front of observer) the visibility impairment
parameters for Pasquill stabilities C, D, and E, respectively.  Figures

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                                    14
3(d), 3(e), and 3(f) show the same plots for a scattering angle of 90°;  and
Figures 3(g), 3(h), and 3(i) show the impact for a scattering angle of 180°
(a backscatter case--sun behind the observer).

     By comparing these nine figures, the following observations can be
made:

     >  Plume visibility impairment is greatest during stable
        atmospheric conditions (Pasquill E).   More stable
        conditions or lighter winds (allowing less dispersion)
        would result in still greater visibility impairment.
     >  The effect of the orientation of the sun relative to
        the observer and plume (scattering angle)  is chiefly
        manifested in the relative brightness of the plume, as
        indicated by plume contrast.   In backscatter, the plume
        is always darker than the background; in forward scatter,
        when NO  is not emitted, the  plume is always brighter
               X
        than the background:  In such a situation, more light
        is scattered toward the observer when the sun is in front
        of the observer (0 < 90°) than when the sun is behind the
        observer (e > 90°).
      >  The impact of fly ash on visual range (see Case No. 4 in
        these figures) is negligible, but is greatest (a 5 percent
        reduction) during stable conditions, 1 km downwind (the
        closest distance considered).
      >  The impact on visual range of sulfate formed in the atmo-
        sphere from S02 emissions (see Case No. 3 in these
        figures) is small, but increases with distance downwind
        and with increasing stability, reaching a maximum of  about
        a 10 percent reduction for stable conditions (Pasquill  E)
        at the farthest distance considered (350 km).
      >  The impact of NOp on visual range is negligible for  the
        plume-observer distance assumed in these calculations

-------
                            15
 (2.5 km).   (This impact on visual range increases with
 increasing  plume-observer distance, as will be shown in
 subsequent  plots.)
 Sulfate aerosol and fly ash (Case Nos. 3 and 4) have almost
 no effect on discoloration, as indicated by the blue-red
 ratio.  However, it should be noted that sulfate plumes
 (Case No. 3) are brighter (whiter) in forward scatter
 and darker  (greyer) in backscatter than the background
 sky.
 NOp formed  in the plume has the most significant effect
 on plume coloration and plume perceptibility, as indi-
 cated by the blue-red ratio and AE.  N02 is the dominant
 colorant, though sulfate contributes slightly, in
 backscatter situations.
 For all scattering angles, sulfate aerosol  will reduce
 somewhat the N0? coloration, as evidenced by blue-red
 ratio, because cf the masking effect of scattered light;
 however, in backscatter only (e = 180°), sulfate contri-
 butes to plume perceptibility,  as evidenced by larger AE
 values, because of its darkening effect (negative plume
 contrasts).
 The location downwind from the  power plant, at which the
maximum discoloration occurs and at which the plume is
most perceptible, varies with the rate of plume dilution.
 During well-mixed conditions [Pasquill C--see Figures
 2(a), 2(d), and 2(g)], a plume  would be most colored
 (blue-red ratio < 0.9) and most likely to be visible
 (AE > 5) at 10 to 15 km downwind.  However, since AE = 5,
 the plume would probably not be noticeable.  During neu-
 tral conditions [Pasquill  D--see Figures 2(b), 2(e), and
 2(h)], maximum plume coloration and perceptibility occurs
 at about 25 km downwind.  The blue-red ratio of about
 0.82 and the AE value of 7 indicate that, at this dis-
 tance, the plume would appear slightly yellowish; however,

-------
                           16
some people might not notice the plume  at  all.   For  stable
conditions [Pasquill  E—see Figures  2(c),  2(f),  and  2(i)],
the maximum discoloration (blue-red  ratio  =  0.78)  occurs
at 40 km downwind and the plume would be perceptible
(AE = 10) to most people as a grey-yellow  haze.   Decreasing
plume coloration at distances beyond the maximum results
from plume dilution.

-------
                                          17
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                             FIGURE  3    (Continued)

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                                    21
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-------
                                   26
            EFFECTS OF  PLUME OBSERVER DISTANCE,  BACKGROUND
              VISUAL RANGE, AND ATMOSPHERIC STABILITY
                   ON PLUME VISIBILITY IMPAIRMENT
     Figures  4(a)  through 4(p), at the end of this chapter,  illustrate
plume visibility  impairment as a function of downwind distance for three
different plume-observer distances (2.5, 5, and 10 km)  for the permuta-
tions of:

     >  Atmospheric  stability  (Pasquill D and E).
     >  Power plant  size (750- and 2250-Mwe).
     >  Background visual range (typical for the eastern
        United States:  15 km;  best for the eastern United
        States:  30 km;  typical for the western United
        States:  130  km; and best for the western United
        States:  200  km).

The base emission and ambient  conditions were selected for  all these
cases:  typical  NSPS emissions; 0.04 ppm background ozone; and 0.5 %/hr
sulfate formation.  (Also see  the  key  on p.  v and Table 1 on p.  5.)

     The effect of increasing  atmospheric stability on visibility impair-
ment is, as previously  mentioned, an increase in both the magnitude of
impairment and the distance downwind at which maximum impairment occurs.
Additional observations based  on Figures 4(a) through 4(p) can be made:

     >  For given emissions and stability, the percent reduction
        in visual range is not affected by the magnitude  of  the
        background visual range.
     >  The percent  reduction  in visual range increases with
        increasing plume-observer  distance for two reasons.
        First, as the plume diffuses,  some of the plume material

-------
                            27
diffuses beyond the observer at a fixed distance from the
plume center!ine and is not within the given line of
sight.  Second, plume NCL will have a greater effect on
visual range when plume discoloration is reduced owing to
plume dispersion.
Since visual range reduction is proportional to plume
sulfate flux, and since SO^-to-SO^ conversion is assumed
to be first-order, the impact on visual range of the
three-unit (2250-Mwe) plant is three times the impact of
the single-unit (750-Mwe) plant.
As the background visual  range decreases and plume-
observer distance increases, the discoloration of the
plume becomes less pronounced because of the masking
effect of light scattered by the background aerosol.  For
typical eastern United States conditions [see, for example,
Figure 4(b)], a plume would not be visible at all since
AE < 5; for typical  western United States conditions [see,
for example, Figure 4(j)], a plume might be faintly visible
as a yellow haze (5 < AE  < 10); however, coloration
decreases with increasing plume-observer distance.
The location downwind from the power plant at which maximum
discoloration occurs increases with increasing stability and
increasing plume-observer distance.
Plume perceptibility and  coloration is more severe in areas
such as the nonurban western United States, where the back-
ground visual range is excellent.   For the conditions inves-
tigated, plumes in the eastern United States would not be
perceptible.
Unlike visual range, plume discoloration and perceptibility
is not proportional  to power plant emissions or size because
NO-to-NOp conversion is not linear and is diffusion-limited.
For example, Figure 4(n)  indicates a maximum plume percepti-
bility AE value of 10 for the 2250-Mwe plant, while Figure 4(p)

-------
                            28
indicates that, under identical  ambient conditions,  the
maximum coloration impact of a 750-Mwe plant corresponds
to a AE of 5, more than one-third the impact of the  three-
unit plant.
Discoloration and plume perceptibility would increase if  a
light wind situation (u < 2 m/sec) occurred, or if the
plume were viewed along the plume axis or obliquely instead
of with the line of sight perpendicular to the plume axis,
as was assumed in these calculations.

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                                     29
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          FIGURE 4.   EFFECT OF  PLUME-OBSERVER DISTANCE
                      ON  CALCULATED VISIBILITY IMPAIRMENT

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                              (3) !0.0 KM
                                                  till
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                i   i   i
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                              10      20      40   60    100
                              DMNMIND OISTRNCE (KM)
                                                               ZOO
    (k)   Hypothetical  750-Mwe Coal-Fired Power Plant;   Typical
          Western  Ambient Conditions with Pasquill  Stability  D
                         FIGURE 4  (Continued)

-------
                                      40
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                                                   60    100
                                                                 200
     (1)  Hypothetical  750-Mwe Coal-Fired Power Plant;   Typical
          Western Ambient Conditions with Pasquill  Stability  E
                         FIGURE 4  (Continued)

-------
                                      41
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                                                 i  i i  i i
                              10       20       40   60    100
                              WMNMINO OrSTRNCE (KM)
                                                                200
    (m)   Hypothetical 2250-Mwe Coal-Fired  Power Plant;  Best
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                        FIGURE 4  (Continued)

-------
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                                                                200
     (n)   Hypothetical  2250-Mwe  Coal -Fired  Power  Plant;  Best
           Western Ambient  Conditions  with Pasquill  Stability E
                        FIGURE 4  (Continued)

-------
                                     43
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                              10      20      40   60
                              DIMNHIND DISTRNCE (KN)
                                                       100
                                                               200
    (o)   Hypothetical  750-Mwe Coal-Fired Power Plant;  Best
          Western  Ambient Conditions with Pasquill Stability D

                       FIGURE 4 (Continued)

-------
                                         44
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                                (21 5.0 KM
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                        i  ill
                                10      20      40   60
                                DfMNMINO DISTANCE (KM)
                                                         100
                                                                 200
      (p)   Hypothetical  750-Mwe  Coal-Fired  Power  Plant;  Best
            Western Ambient  Conditions  with  Pasquill  Stability E
                          FIGURE  4 (Concluded)

-------
                                   45
           VI    EFFECT OF S02-TO-SULFATE CONVERSION  RATE
                        ON VISIBILITY IMPAIRMENT
     Figures  5(a)  through  5(p)  illustrate the effect of the rate of SCL-to-
sulfate conversion on visibility  impairment.  Three rates were evaluated:
5, 0.5, and 0 percent per  hour.*  The most significant effect of fast sulfate
formation (5 percent/hr) is  the dramatic reduction in visual range, partic-
ularly at far downwind distances; for example, the 2250-Mwe power plant would
cause a 25 percent reduction in visual  range as shown in Figure 5(a) at
100 km downwind during ieutral  conditions (Pasquill D), and greater than
a 60 percent reduction, ai shown  in  Figure 5(b), during stable conditions
(Pasquill E).  In  some instances  (particularly for the eastern U.S. cases)
the plume becomes  less perceptible with the assumptions of faster sulfate
formation because  of the color-masking  effect of additional scattered
light; however, in other cases  (notably under the western U.S.  conditions
with good background visual  range),  the larger sulfate concentrations
resulting from fast SOp-to-sulfate conversion will cause a more notice-
able grey plume or haze.
* See key on  p.  v  and  Table  1 on p. 5 for base conditions.

-------
                                    46
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                              (3) 0.0 PERCENT/H8UR
                                       =8=5=
                                        8  3
                              10       20       40
                              OIHNHIND DISTANCE (KH)
                                                  60     100
                                                               200
    (a)   Hypothetical  2250-Mwe  Coal-Fired Power Plant; Typical
          Eastern Ambient  Conditions with Pasquill  Stability D
    FIGURE 5.   EFFECT OF  SULFATE FORMATION ON CALCULATED
                 PLUME VISIBILITY  IMPAIRMENT

-------
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                                        47
                                 SULFflTE FBRHRTIBN FflTE
                                 (1)  5.0 PERCENT/H8UR
                                 (2)  0.5 PERCENT/HHUR
                                 (3)  0.0 PERCENT/H8LIR
                                10       20       40    60
                                DWMMIMD DISTANCE (KM)
                                                           100
                                                                   200
      (b)   Hypothetical  2250-Mwe  Coal  Fired Power Plant;  Typical
            Eastern  Ambient Conditions  with  Pasquill  Stability E
                         FIGURE  5 (Continued)

-------
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                                        48
                                SULFPTE F9RHMTI3H RflTE
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                                (2) 0.5 PERCENT/HBUR
                                (3) 0.0 PERCENT/HBUR
                                10       20       40
                                DIMNUIND DISTANCE (KH»
                                                     60
                                                          100
                                                                  200
      (c)  Hypothetical  750-Mwe  Coal-Fired  Power Plant; Typical
           Eastern  Ambient  Conditions  with  Pasquill  Stability  D
                         FIGURE 5  (Continued)

-------
                                49
                         SULFSTE F8PHRTISN PflTE
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(d)  Hypothetical  750-Mwe Coal-Fired Power Plant;  Typical
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                  FIGURE  5  (Continued)

-------
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-------
                                        51
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                                MMNHINO DISTANCE (KM)
                                                          100
                                                                  EDO
     (f)   Hypothetical  2250-Mwe  Coal-Fired Power Plant;  Best
           Eastern  Ambient  Conditions  with Pasquill  Stability E
                         FIGURE 5  (Continued)

-------
 60.0
                                     52
                               SULFPTE FSRMSTI3N RSTE
                               (1) 5.0 PERCENT/HBIIB
                               (2) 0.5 PERCEHT/H8IIR
                               13) 0.0 PERCENT/HBUB
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                                                    60
                                                          100
                                                                  200
    (g)   Hypothetical  750-Mwe  Coal-Fired  Power Plant;  Best
          Eastern  Ambient  Conditions  with  Pasquill  Stability D
                        FIGURE 5  (Continued)

-------
                                        53
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                                 (1) 5.0 PERCENT.'HSUR

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                                 (3) 0.0 PERCENT/HBUR
                                        i a  a
                                10       20      40
                                DIMNHINO DISTRNCE (KM)
                                                     60
                                                           100
                                                                   200
      (h)   Hypothetical  750-Mwe Coal-Fired  Power Plant;  Best
            Eastern Ambient Conditions  with  Pasquill  Stability  E
                         FIGURE  5 (Continued)

-------
                                       54
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                                MHNHtND DISTANCE (KHJ
                                                    SO
                                                          100
                                                                 200
      (i)  Hypothetical  2250-Mwe  Coal-Fired  Power Plant; Typical
           Western Ambient Conditions  with Pasquill Stability D
                         FIGURE  5 (Continued)

-------
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                                        55
                                SULFflTE F8RMHTISN FRTE
                                (1) 5.0 PERCENT-"HaUR
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                                                          100
                                                                  200
      (j)   Hypothetical  2250-Mwe  Coal-Fired Power Plant;  Typical
            Western  Ambient  Conditions  with  Pasquill  Stability  E
                         FIGURE  5 (Continued)

-------
                                        56
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       (k)   Hypothetical 750-Mwe Coal-Fired Power Plant;  Typical

             Western Ambient Conditions with Pasquill  Stability D
                          FIGURE  5 (Continued)

-------
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                                                                     200
       (1)   Hypothetical  750-Mwe Coal-Fired  Power  Plant; Typical

             Western  Ambient  Conditions  with  Pasquill Stability E
                           FIGURE 5  (Continued)

-------
                                     58
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     (m)  Hypothetical  2250-Mwe Coal-Fired  Power  Plant;  Best
          Western  Ambient Conditions  with Pasquill  Stability  D
                       FIGURE 5  (Continued)

-------
                                        59
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            Western Ambient  Conditions  with Pasquill  Stability E
                          FIGURE 5  (Continued)

-------
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       (o)   Hypothetical  750-Mwe Coal-Fired  Power Plant;  Best

             Western Ambient  Conditions with  Pasquill  Stability  D
                           FIGURE 5  (Continued)

-------
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                                        61
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                                (1) 5.0 PERCENT-'HIIUR
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                                                    60
                                                          100
                                                                  200
      (p)   Hypothetical  750-Mwe Coal-Fired Power  Plant;  Best
            Western Ambient Conditions with Pasquill  Stability E
                         FIGURE 5  (Concluded)

-------
                                   62
      VII    EFFECT OF  N02 FORMATION RATE DUE  TO DIFFERENT
                  BACKGROUND  OZONE  CONCENTRATIONS ON
                         VISIBILITY  IMPAIRMENT
     The effect of different assumptions about the background  ozone concen-
tration, which affects  the  conversion of colorless NO to the red-brown NOp
gas in power plant plumes,  is  illustrated in Figures 6(a)  through  6(p).
Three background ozone  concentrations were evaluated:  0.12, 0.04, and
0.00 ppm.*  An ozone  concentration of 0.04 ppm is typical  of many  nonurban
areas, while 0.12 ppm is  typical of polluted areas where photochemical
reactions among NO and reactive hydrocarbon emissions cause ozone forma-
                  /\
tion.  With no background ozone, only about 10 percent of NO   emissions
                                                          A
are converted to NOp  (resulting from the reaction of NO with Op).  Note
that increased NOp concentrations have almost no effect on the visual
range, but significantly  increase the coloration and the perceptibility
of plumes.  For example,  Figure 6(j) shows that, with a background visual
range of 130 km and an  ozone concentration of 0.12 ppm, the plume  percep-
tibility parameter AE approaches a value of nearly 15.  It should  be
noted, however, that  a  high ozone concentration would not likely coincide
with a high visual range.
* See key on p.  v and Table  1  on  p.  5  for base conditions.

-------
                                      63
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                              10       20      40
                              08MNMIND DISTANCE IKM)
                                                       100
                                                              200
       (a)   Hypothetical  2250-Mwe Coal-Fired  Power Plant; Typical
            Eastern Ambient Conditions  with Pasquill  Stability D
      FIGURE 6.   EFFECT  OF BACKGROUND  OZONE ON  CALCULATED
                   PLUME VISIBILITY IMPAIRMENT

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     (b)   Hypothetical  2250-Mwe Coal-Fired Power Plant; Typical
           Eastern Ambient Conditions with Pasquill  Stability E
                        FIGURE  6 (Continued)

-------
                            65
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                FIGURE  6  (Continued)

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     (d)   Hypothetical  750-Mwe Coal-Fired Power Plant; Typical
           Eastern Ambient Conditions with Pasquill  Stability E
                        FIGURE  6 (Continued)

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                                     67
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                        FIGURE 6  (Continued)

-------
                                         68
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                         FIGURE  6 (Continued)

-------
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-------
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-------
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                        FIGURE  6 (Continued)

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                                   79
     VIII    A SUMMARY  OF TYPICAL VISIBILITY  IMPAIRMENT
               CAUSED BY  POWER PLANTS IN  THE EASTERN
                      AND  WESTERN UNITED STATES
     We have rearranged the plots shown in different  figures to compare on
a single plot the  visibility impairment caused by power  plant plumes under
typical eastern  and western U.S. ambient conditions,  where  background vis-
ual  ranges are poor and excellent, respectively.   Figures 7(a) through 7(h)
compare eastern  and western visibility impacts for the permutations of:

     >  Atmospheric stability (Pasquill D and E).
     >  Power plant size  (750- and 2250-Mwe).
     >  Typical  and best  background visual range.*

These plots indicate  that at the assumed 5 km plume-observer distance the
discoloration of power plant plumes is not likely to  be  perceptible in the
eastern United States, where a typical background visual range is 15 km
(9 miles); but in  the nonurban areas of the western United  States, where a
typical background visual range is 130 km (80 miles), plumes from large
power plants are likely to be perceptible as a yellowish (or possibly brown)
haze.
  See key on p.  v and Table  1 on p. 5 for base conditions.

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                                (I) ERSTERN U.S. IBflOGFflUND VISIBILITY = IS !>"

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                Typical  Visibility with Pasquill  Stability  D
          FIGURE  7.   COMPARISON OF  PLUME  VISIBILITY  IN THE

                       EASTERN  AND WESTERN  UNITED STATES

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                                 (II EASTERN II S  fBflrhC-Reii'ND  "I'IBILITV = 1?

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                  Typical  Visibility  with  Pasquill  Stability E
                                FIGURE 7  (Continued)

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                                      82
                                (1)  EBSTERN II S.  f6flCKn*0l'tJC -I-IPILITY - IS Hi;
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                 Typical  Visibility  with Pasquill  Stability D
                              FIGURE  7 (Continued)

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                                FIGURE  7  (Continued)

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                                FIGURE 7  (Continued)

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                                FIGURE 7  (Concluded)

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                    IX    SUMMARY AND CONCLUSIONS


     We briefly summarize the most  important  conclusions drawn from this
analysis of power plant  plume visibility  impairment as follows:

     >  The most significant reduction  in  visual  range due to
        power plant emissions occurs  because  of  secondary
        aerosol formation (e.g.,  sulfates  and nitrates), par-
        ticularly at large downwind distances more than 100 km
        from the power plant.   For  new  plants, fly ash emis-
        sions must be controlled  so that  stack opacity is no
        greater than 20  percent in  order  to meet NSPS limits
        and, therefore,  fly ash emissions  have a small effect
        on visual range.
     >  Plume discoloration (plume  blight) is of particular
        concern and is caused primarily by N02 formed by reac-
        tions in the atmosphere with  0? and 0~ from NO  emissions.
                                      C-      O       A
        Discoloration will be more  perceptible under clear back-
        ground conditions (a good background  visual range) during
        stable conditions with  high background ozone concentra-
        tions.  In certain circumstances,  fly ash and sulfate will
        contribute somewhat to  discoloration  and plume percep-
        ti bi 1 i ty.
     >  Reductions in visual range  caused by  750- and 2250-Mwe
        coal-fired power plants meeting NSPS  will be small (<  10
        percent) for average ventilation  conditions and SO^-to-
        sulfate conversion rates  of 0.5 percent/hr.
     >  Reductions in visual range  could be significant  (> 25
        percent) when conditions  are  such that sulfate is  rapidly
        formed, during poor plume dispersion  conditions  (e.g., with
        light winds, stable air), or  if the regional effects due
        to  several sources are  considered.

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                            89
Atmospheric discoloration caused by 2250-Mwe coal-fired
power plants will be perceptible as a white, grey,  yellow,
or brown haze, particularly in areas with excellent back-
ground visibility, and during stab'le conditions when plume
dispersion is poor.
Plumes from power plants located in the eastern United
States are not likely to be perceptible because of  the
typically low background visual range; in nonurban  areas
in the western United States, plumes from large coal-fired
power plants will be perceptible at times, even as  far as
100 km downwind.
Visibility impairment will  be greater than indicated here
when plume dilution is poor under stable, light wind condi-
tions, or when plumes are viewed along the plume centerline
or obliquely.  Also, if emission rates and particle size
distributions are different from those assumed  here, visi-
bility impairment will be different.  More detailed analyses
based on appropriate emission, meteorological,  and  ambient
conditions are needed to evaluate fully the visual  impact of
a given source.
We suggest that the user of this document exercise  caution
in applying these results to specific power plant analyses.
These results are idealized cas s for specific  emission,
meteorological, ambient background, and viewing conditions
based on a model  that has not yet been validated.

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                                    90
                              REFERENCES
Carpenter,  S.  B.,  et a^ .  (1971),  "Principal Plume Dispersion Models:  TVA
     Power  Plants,"  J. Air Poll.  Contr. Assoc.. Vol. 21, pp. 491-495.

Federal  Register (1976),  "Regulations  on Standards of Performance for New
     Stationary Sources,"  41(111):   23059.

Husar,  R. B.,  et al.  (1978),  "Sulfur Budget of a Power Plant Plume," Atmos.
     Environ.,  Vol.  12, pp.  549-568.

Smith,  T. B.,  et al.  (1978),  "Transport of S02 in Power Plant Plumes:  Day
     and Night," Atmos. Environ.,  Vol. 12, pp. 605-611.

Whitby,  K.  T.,  and G.  M.  Sverdrup  (1978), "California Aerosols:  Their
     Physical  and  Chemical  Characteristics,"  to be published in the ACHEX
     Hutchinson Memorial  Volume,  Particle Technology Laboratory Publication
     Number 347, University of Minnesota, Minneapolis, Minnesota.

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                                             91
                                  TECHNICAL REPORT DATA
                           fl'lcesc read lii±Lr.• /TITMC' lic/urc c
. REPORT NO.
   EPA-450/3-78-110a,b,c
                             2.
. TITLE AND SUBTITLE
 THE  DEVELOPMENT OF MATHEMATICAL  MODELS FOR THE
 PREDICTION OF ANTHROPOGENIC. VISIBILITY IMPAIRMENT
                                                           3. RECIPIENT'S ACCECSI Off NO.
                                                           6. REPORT DATE
                                                               November 1978
                                                           6. PERFORMING ORGANIZATION CODE
 AUTHORIS)
 D.  A.  Latimer, R. H. Bergstron,  S.  R.  Hayes, M. K.  Liu,
 J.  H.  Seinfeld, G. 2. Whitten,  M.  A.  Wojcik, M. J. Hillye
                                                           8. PERFORMING ORGANIZATION REPORT NO.

                                                               EF78-68A,B,C
 PERFORMING ORGANIZATION NAME AND ADDRESS

    Systems Applications,  Incorporated
    950 Northaate Drive
    San Rafael, California   94903
                                                           IQ. PROGRAM ELEMENT NO.
                                                           11. CONTRACT/GRANT NO.

                                                             EPA 68-03-3947  and  68-02-2593
2. SPONSORING AGENCY NAME AND ADDRESS
  U,  S. Environmental Protection  Agency
  Waterside Mall
  401 M Street, S.W.
  Washington, D.C.  20460	
                                                           13. TYPE OF REPORT AND PERIOD COVERED

                                                           Final  Report:  10/77 to 9/78
                                                           14. SPONSORING AGENCY CODE
                                                            EPA-OPE/OAQPS
5.SUPPLEMENTARY NOTES
6. ABSTRACT

    This report describes a  nine-month study to recommend  and develop models that pre-
 dict the contribution of man-made air pollution to  visibility impairment in federal
 Class I areas.  Two models  were developed.  A near-source plume model based on a
 Gaussian formulation was designed to compute the  impact of a plume on visual range
 and atmospheric coloration.   A regional model was designed to calculate pollutant
 concentrations and visibility impairment resulting  from emissions from multiple
 sources within a region with  a spatial scale of 1000  km and a temporal scale of
 several days.  The objective  of this effort was to  develop models that are useful
 predictive tools for making policy and regulatory decisions, for evaluating the
 impacts of proposed new sources, and for determining  the  amount of emissions reduc-
 tion required from existing sources, as mandated  by the Clean Air Act Amendments
 of 1977.  Volume  I  of this  report contains  thf  main  text;  Volume  II  contains  the
 appendices;  Volume  III  presents case  studies of power plant plume visual impact  for
 a variety of emission,  meteorological, and ambient  background scenarios.
7.
                               KEY WORDS AND DOCUMENT ANALYSIS
                                              b.JOENTIFIERS/OPEN ENDED TERMS  c. COSATI I'icld/Group
                 DESCRIPTORS
 Air quality modeling
 Visual range
 Atmospheric discoloration
 Power plants
IB. DISTRIBUTION STATEMENT
 RELEASE TO PUBLIC
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                                              UNCLASSIFIED
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                                                                                    ill.
                                                                         22. PRICE
                                                                          Vol.  Ill—91
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