Lfnrtec St»t«
Environmental Protection
Agency
AC t'ohution Training Institute
K'sD 2C>
Environmental Research Center
rch Tnengle Park, NC 2771";
Air
450282009
APTl
Course Sl:409
Basic Air Pollution
Meteorology
Student Guidebook
Developed by:
Donald Bullard
Marilyn Peterson
Northrop Services, Inc.
P.O. Box 12313
Research Triangle Park, NC 27709
Under Contract No.
6&-02-3573
EPA Project Officer
R. E. Townsend
United States Environmental Protection Agency
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
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Notice
This is not an official policy and standards document. The opinions and selections
are those of the authors and not necessarily those of the Environmental Protection
Agency. Every attempt has been made to represent the present state of the art as
well as subject areas still under evaluation. Any mention of products or organiza-
tions does not constitute endorsement by the United States Environmental Protec-
tion Agency.
Availability
This document is issued by the Manpower and Technical Information Branch,
Control Programs Development Division, Office of Air Quality Planning and Stan-
dards, USEPA. It was developed for use in training courses presented by the EPA
Air Pollution Training Institute and others receiving contractual or grant support
from the Institute. Other organizations are welcome to use the document.
Copies may be obtained for a fee from
National Audiovisual Center
General Services Administration
Order Section HH
Washington, DC 20409
(301)763-1891
11
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Table of Contents
Page
Lesson 1. Course Introduction . 1-1
Course Description 1-1
Course Goal and Objectives 1-2
Requirements for Successful Completion of this Course 1-2
Materials 1-2
Use of the Guidebook 1-3
Instructions for Completing the Final Examination 1-4
Lesson 2. Heat Balance of the Atmosphere 2-1
Assignment 2-1
Lesson Goal and Objectives 2-1
Supplementary Reading 2-2
Air Pollution Meteorology—Radiation (Script) 2-5
Radiation and Insolation 2-9
Heat Distribution 2-11
Review Exercise 2-13
Lesson 3. Circulation of the Atmosphere 3-1
Assignment 3-1
Lesson Goal and Objectives 3-1
Pressure Systems, Winds, and Circulation (Script) 3-3
The General Circulation 3-15
Review Exercise 3-20
Lesson 4. Frontal Systems 4-1
Assignment 4-1
Lesson Goal and Objectives 4-1
Supplementary Reading 4-2
Anticyclones, Cyclones and Fronts 4-3
Air Masses 4-5
Review Exercise 4-7
Lesson 5. Vertical Motion and Atmospheric Stability 5-1
Assignment 5-1
Lesson Goal and Objectives 5-1
Supplementary Reading 5-2
Principles Related to Vertical Motion 5-3
Review Exercise 5-7
Atmospheric Stability 5-10
Review Exercise 5-15
Stability and Plume Behavior 5-17
Review Exercise 5-20
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Page
Lesson 6. Meteorological Instruments 6-1
Assignment 6-1
Lesson Goal and Objectives 6-1
Supplementary Reading 6-2
Air Pollution Meteorology Instruments (Script) 6-3
Review Exercise 6-16
Lesson 7. Plume Dispersion 7-1
Assignment 7-1
Lesson Goal and Objectives 7-1
Introduction 7-2
Plume Rise 7-3
Review Exercise 7-5
Dispersion Estimates 7-6
Topography 7-9
Review Exercise 7-15
Lesson 8. Introduction to the Guideline on Air Quality Models 8-1
Assignment 8-1
Lesson Goal and Objectives 8-1
Guideline Topics 8-2
Model Categories 8-3
Review Exercise 8-4
Lesson 9. Introduction to Meteorological Requirements
for State Implementation Plans, New Source Review,
and Air Quality Modeling 9-1
Assignment 9-1
Lesson Goal and Objectives 9-1
Section 3: Requirements for Concentration Estimates 9-2
Section 5: Data Requirements 9-5
Review Exercise 9-11
IV
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Lesson 1
Course Introduction
Course Description
This training course is a 25-hour self-instructional course using slide/tape presenta-
tions and reading assignments dealing with basic meteorology, meteorological
effects on air pollution, meteorological instrumentation, air quality modeling, and
regulatory programs requiring meteorology. Course topics include the following:
Solar and terrestrial radiation
Cyclones and anticyclones
Wind speed and direction
Atmospheric circulation
Cold, warm, and occluded fronts
Atmospheric stability
Turbulence
Meteorological instrumentation
Plume rise/effective stack height
Topography
' Air quality models
Regulatory air quality programs
Figure 1-1. Meteorology and pollution diipenion.
1-1
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Course Goal and Objectives
Goal
The goal of this course is to familiarize you with the fundamentals of meteorology,
the atmospheric factors that transport and disperse pollutants, the instruments used
to gather meteorological data necessary for air quality modeling, plume rise and
effective stack height, categories of air quality models, and the regulatory air qual-
ity programs requiring meteorological data.
Objectives
Upon completing this course, you should be able to:
1. describe the effect of solar radiation on the earth-atmosphere system.
2. describe the pressure, wind flow, and vertical motion in cyclones and
anticyclones.
3. list the four factors that govern the motion of the wind.
4. describe the importance of atmospheric circulation.
5. describe warm, cold, and occluded fronts.
6. name the four types of atmospheric stability.
7. describe the importance of turbulence in the atmosphere.
8. recognize meteorological instruments used for air pollution and match an
instrument to the atmospheric factor it senses.
9. briefly define plume rise and effective stack height.
* 10. describe four types of topographical features that influence pollutant
dispersion.
11. list the four categories of air quality models.
12. identify and describe the three regulatory air quality programs requiring
meteorological data.
Requirements for Successful Completion
of this Course
In order to receive 2.5 Continuing Education Units (CEUs) and a certificate of
course completion, you must:
1. take a mail-in final examination.
2. achieve a final examination grade of at least 70%.
Materials
Reading
51:409 Student Guidebook, Basic Air Pollution Meteorology.
1-2
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Audio-Visual
Slide/tape presentations: SI:409-2, SI:409-S, and SI:409-6. These are numbered to
correspond to the lesson numbers they are used with in this text.
Use of the Guidebook
This guidebook directs your progress through the slide/tape presentations and
reading assignments that are listed in the "Materials" section. Each assignment to
be completed will be presented in a sequence that you should follow carefully. Use
this guidebook as a "roadmap" of the course.
Guidebook Contents
This guidebook contains nine lessons consisting of reading, audio-visual, and sug-
gested supplementary materials. The first lesson gives you an overview of the
course. The second lesson has one slide/tape presentation and a reading assignment
that discusses radiation and its effects. The third lesson has one slide/tape presen-
tation and a reading assignment that discusses general circulation and winds. The
next two lessons are reading assignments covering frontal systems, stability, and
turbulence. The sixth lesson has one slide/tape presentation and a reading assign-
ment that discusses meteorological instrumentation. The next three lessons are
reading assignments on plume dispersion and air quality modeling. The reading
material will be self-paced, presented as text with review questions.
Completing the Review Exercise
To complete a review exercise, place a piece of paper across the page covering the
questions below the one you are answering. After answering the question, slide the
paper down to uncover the next question. The answer for the first question will be
given on the right side of the page separated by a line from the second question
(Figure 1-2). All answers to review questions will appear below and to the right of
their respective questions. The answer will be numbered to match the question.
Review Exercise
1. Question loulo
iilli cllo ylloitiili<
2. Questionoli oul
It uliioiiyic o
3. Question > in lot
^**^4J<> nil i cllo yllon
1. Answer
llllO
2. Answer
"li^iill'^
Figure 1-2. Review exercise format.
1-3
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Using the Slide/Tape Presentations
You do not need to follow the script provided in the appropriate lessons as you
view the slide/tape presentation. The script is provided for you to use to review the
content. The audiocassette is designed to automatically advance the slides at the
correct place in the script if your cassette player has a mechanism for synchronizing
audiotape and 35-mm slides.
• To use the slides and audiotape together, advance to the first slide and focus
the image.
• Leave the tray positioned at slide #1.
• Place the cassette in the tape player so that the side marked "Automatic
Advance" will play. The tape recorder will advance the slides for you.
If you do not have equipment that automatically advances the slides, you can
use a 35 -mm slide projector and any cassette player.
• Use the side of the tape marked "Manual Advance."
• Set the slide tray to the focus slide, #1, and advance the slides as you hear a
"beep" (tone) on the tape.
Lesson Content
• Assignments
• Slide/tape presentation: slide number and cassette numbers
• Reading assignment
• Assignment topics
• Lesson guidance
• Lesson goal and objectives
• Script from slide/tape presentation
• Text of lesson
• Review exercise ••
Some supplementary readings will be recommended, but are not required for
course completion.
Instructions for Completing the Final Examination
Contact the Air Pollution Training Institute if you have any questions about the
course or when you are ready to receive a copy of the final examination.
After completing the final exam return it and the answer sheet to the Air Pollu-
tion Training Institute. The final exam grade and course grade will be mailed to
you.
Air Pollution Training Institute
Environmental Research Center
MD20
Research Triangle Park, NC 27711
1-4
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Lesson 2
Heat Balance of the Atmosphere
Assignment
1. View the slide/tape presentation, Radiation, which consists of tape SI:409-2 and
slides 409-2-1 through 409-2-44.
2. Read pages 2-9 through 2-14 of this guidebook! ,•
Assignment Topics
9 Radiation
• Insolation
• Heat distribution
Lesson Guidance
This lesson and the three following it introduce the fundamental concepts of
meteorology—the science of the atmosphere and its phenomena. The atmosphere
acts as a giant cleanser, removing the wastes produced by the cycles of nature.
Since the industrial revolution, the "cleanser" has not been able to keep up with
the production of new industrial waste materials. Because some of these wastes are
hazardous to human health and may produce future climatic changes, the condi-
tions that cause them to spread throughout the atmosphere must be fully
understood. Therefore, basic operations of and components that produce
atmospheric circulation around the earth will be discussed before, in Lesson 5,
their relationship is tied to the atmosphere's vertical temperature structure and to a
discussion of air pollution dispersion.
Lesson Goal and Objectives
Goal
To familiarize you with the source of energy responsible for atmospheric motion,
and with the way the earth and atmosphere combine to balance the energy
received by the earth.
2-1
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Objectives
Upon completing this lesson, you should be able to:
1. identify the source of energy that "drives" atmospheric motion.
2. name the most important heat storage constituent of the atmosphere.
S. describe a chain of events that could possibly lead to thunderstorms.
4. explain the reason for a long-term heat balance in the atmosphere.
5. name an atmospheric phenomenon that transports pollution.
6. list the four factors that govern the amount of insolation received by the
atmosphere.
Supplementary Reading
Any meteorology textbook such as the ones listed under References at the end of
this guidebook.
2-2
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Air Pollution Meteorology-
Radiation
Slide
1.
2.
3.
Script
Selected Visuals*
4.
5.
6. We are all familiar with raging thunderstorms, howling winds,
blinding snowstorms, and hot muggy days.
7. We usually think of these weather patterns in terms of the
rain, wind, cold, or heat they bring.
8. But these weather patterns do more than create the need for
umbrellas, snowsuits,
9. windbreakers, and air conditioners.
10. The winds, rain, and other meteorological conditions they
create can transport, disperse, or trap air pollutants.
11. For example, pollutants can be carried from urban areas with
many factories. . .
12. to rural areas where no factories are in sight for miles.
13. Meteorological conditions help dilute—or disperse—pollutants
in heavily industrialized areas.
Air Pollution Meteorology
Radiation
•illustrations included here, no live shots
2-5
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Slide
Script
Selected Visuals
14. But these conditions can cause air pollution episodes—which
are unhealthy concentrations of pollutants.
15. The weather patterns that can transport, dilute, or trap air
pollution are caused by movement of the atmosphere and,
indirectly, by ocean movement.
16. But what causes atmospheric and oceanic movement??
17. It all starts with the sun. The sun gives off energy—or
radiation—from a surface that is 6000 kelvin. That is
equivalent to more than 10,000 degrees Fahrenheit.
18. If we received all of the sun's radiation, the earth would be so
hot that life as we know it could not exist. The surface of the
earth—and everything on it—would be parched, much like
the surface of Mercury.
19. Luckily, only one^one-billionthTbf the sun's radiation reaches
the tip of the earth's atmosphere.
6.000 K
20. And because the atmosphere acts as a filter,
21. only one':quartei^oftha^ radiation ever reaches us at the
surface of the earth.
22. The earth and its atmosphere then absorb and reradiate this
energy.
2-4
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Slide
Script
Selected Visuals
23. The ability to absorb and reradiate energy is referred to by
scientists as the blackbody principle.
Blackbody
24. The amount of energy radiated by a body is it%albedo.*
Radiated energy is measured in wavelengths.
25. How long the wavelengths are depends on the temperature of
the body that is radiating them. Warmer bodies radiate
shorter wavelengths, and cooler bodies radiate longer
wavelengths. The longer wavelengths are more likely to be
absorbed by our atmosphere. Thus, they are potentially more
useful to us because the earth needs some of that absorbed
heat.
26. Obviously, the sun and the earth have very different
temperatures; so, although they both radiate energy, their
wavelengths are different. The sun radiates very short
wavelengths, and the earth radiates the longer ones.
27. As a matter of fact, even the range of wavelengths radiating
from the earth is always changing as the earth's surface and
atmosphere heat and cool.
< Warm Body Cool Body
•Albedo is actually expressed as a ratio. The fraction of energy radiated
by a body compared to the total insolation received is its albedo.
2-5
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Slide
Script
Selected Visuals
28. Heat is also stored and radiated by the earth's atmosphere.
All of the components of the atmosphere absorb and radiate
heat. The most important of these is water vapor.
29. Waterlvapor stores about six times more heat energy than all
the other atmospheric components combined.
AllOther
Component*
Water Vapor
30. Water vapor holds or stores this heat and then releases it.
Sometimes this heat is released very quickly, in the form of
thunderstorms.
31. But sometimes this heat or energy is stored and transported
long distances before being released as snow, rain, or other
precipitation.
32. For example, water can evaporate over the warm Gulf of
Mexico and be transported all the way to North Dakota before
it condenses and releases heat.
S3. Atmospheric water in the form of vapor and precipitation is
not the only water that transports heat, however. Water in the
oceans also helps maintain the heat balance.
34. Ocean currents take heat from the warm equatorial regions
and transport it to the much colder polar regions hi the north
and south.
2-6
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Slide
Script
Selected Visuals
35. For example, during the summer, the ocean near the equator
is heated to a very warm temperature. A small tropical storm
forms. As the storm drifts westward, it may develop into a
hurricane or typhoon. Ocean currents help guide its path.
And large quantities of heat are transported away from the
equator by the storm.
36.
37.
38.
Since new energy from the sun is also entering the
atmosphere, the earth would overheat if all of this energy
were stored. So, energy must eventually be released back into
space. On the whole, this is what happens. What comes in
eventually goes back out, and a heat balance, called the
radiational balance, is created.
Our atmosphere also uses some of this energy— or heat— so
some of it is stored for a while before it is released. Some heat
is stored for short periods of time, and some is stored for
longer periods. This difference in heat storage both creates
atmospheric movement and helps maintain the relatively
consistent temperatures that support life.
Heat is stored by the earth and everything on it. During the
day, when the sun is shining, the earth and objects on it are
absorbing and storing heat. At night, when the sun isn't
shining, the warmed earth radiates heat back out into space.
Some objects hold heat better than others. This is called
rate at wWch^thjjsnergyjs
reradiated bjick^intojpjace varies. But it is all radiated back
out as useful long-wave radiation. Both the amount of heat
and the rate at which it is radiated play a major role in the
creation of atmospheric movement.
39. We've seen that the sun is the source of energy for
atmospheric and oceanic motions. The earth heats unevenly
and transfers heat from the equator to the poles. The earth
also loses as much radiation as it gains.
2-<7
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Slide
Script
Selected Visuals
40. What all of this heat storage and transfer adds up to is a
balance of energy and a finely tuned system. While things
within the atmosphere are always heating up or cooling down,
the net result is a system that continues to maintain an overall
balance of heat:
41. a balance that allows variation sufficient enough to create
atmospheric and oceanic movement, yet predictable enough to
allow an orderly system of life.
42. Credit: Crew
Radiation
Grapkkx- B«uyH>tei
ttmmttam- luck
43. Credit: Northrop
Lecture development
and production by:
Northrop Services Inc.
under
EPA Contract No. 6842-2374
44. Credit: NET
Northrop
Environmental
Training
2-8
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Radiation and Insolation
The energy expended in the atmospheric processes
was originally derived from the sun. This energy is
transferred by radiation of heat by electromagnetic
waves. The radiation from the sun has its peak
energy transmission infthe visible range (U.4 to O.Tl
rnicrometers^of the electromagnetic spectrum.
However, the sun also releases considerable energy
in the ultraviolet and infrared regions. The
greatest part of the sun's energy is emitted in
wavelengths between 0.1 and 30 migometers^ ,
The amount of radiatioiTreceived on anydate
jp~"
at a location on the earth's surface is calleq[m5o2a
on] Insolation js governed by four factors^
"pthejolarConstant—which depends on:
energy output of the sun
• distance from the earth to the sun
I'; • transp_arency..of the atmosphere
"v) • duration of_the daily^sunlight period
^A* angle at which the sun's noon rays strike the
It- / r—" -- — "~ • .... *
earth.
Solar Constant
The solar constant is the amount of radiation
received at a point in the earth's outer
atmosphere. The "constant" depends on the
distance and position of the earth relative to the
sun; however, the average amount of radiation
received at a given point will not vary significantly.
Since the sun essentially emits a constant radia-
tion, it alone would imply constant weather within
the atmosphere. However, transparency, duration,
and angle are much more important in influencing
the amount of insolation received, which in turn
changes the weather.
Transparency
Transparency of the atmosphere does have an
important bearing upon the amount of insolation
that reaches the earth's surface. As shown in
Figure 2-1, some of the radiation received by the
atmosphere is reflected from the tops of clouds
and from the land and water surfaces of the earth.
Top of atmosphere
Loss: 36%
Gain: 64%
Figure 2-1. Heat balance of the
atmotphere.
2-9
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Thejgmeral reflectivity is
for the
elrth and atmosphere as a wholiu_is.36% for_
tions of cloudiness over the earth.
This reflectivity is greatest in the visible range of
wavelengths.
Some of the gases in the atmosphere (notably
water vapor) also absorb solar radiation. This
reduces the insolation. Water vapor, although
comprising only 5% of the atmosphere, on the
average absorbs about six times as much solar
radiation as all other gases combined. The amount
of radiation received at the earth's surface is
therefore considerably less than that received out-
side the atmosphere. The earth reradiates energy
in proportion to its temperature. Because of the
earth's temperature, the maximum reradiation
occurs in theOnhki-JsJn-the -infrared
gases of the
atmosphere absorb some of this radiation. Because
the atmosphere absorbs much more of the^ter-
restrial radiationearth
"tion) tharTsolar radiation, some of this heat energy
is conserved. This is the^greenKoiue 'effect)
Tiansparen£y~is~aiunction of not only
cloudinesSj, but alsojof latitude. The sun's rays
must pass through a thicker layer of reflecting-
scattering atmosphere at middle and high latitudes
than at tropical latitudes (Figure 2-2). This effect
varies with the seasons, being greatest in winter
when the sun's rays are lowest on the horizon.
Daylight Duration
The duration of daylight also affects the amount
of insolation received. Daylight duration varies
with latitude and the seasons. The longer the
period of sunlight, the greater the total possible
insolation. At the equator, day and night are
always equal. In the polar regions, the daylight
period reaches a maximum of twenty-four hours in
summer and a minimum of zero hours in winter.
Equator
Figure 2-2. Relationship of
transparency to latitude.
2-10
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Angle of Rays
The angle at which the sun's rays strike the earth
varies considerably as the sun "shifts" back and
forth across the equator. A relatively flat surface
perpendicular to an incoming vertical sun ray
receives the largest amount of insolation.
Therefore, areas at which the sun's rays are
oblique receive less insolation because the oblique
rays are spread over a^^Sater^urface area) and
/ _f ^~ -^ ,^— ^llr~T-.'~~"_ -_'_- - ^J—'" "' """-jfc— °^r- , -^
must passlhrougka thickerTayer of reflcctin^and
absorbing atmosphere (Figure 2-3). This same
principle also applies to the daily shift of the sun's
rays. At solar noon the intensity of insolation is
greatest. In the morning and evening hours, when
the sun is at a low angle, the amount of insolation
is small.
Heat Distribution
As seen in this discussion, the world distribution of
insolation is closely related to latitude. Total
annual insolation is greatest at the equator and
decreases regularly toward the poles. Figure 2-4
the earth and atmosphere^ compared to thejqng_
^3ygjaHiaffenJlgayingL±h£atmQSphere. The
amount of insolation received annually at the
equator is about four times that received at either
of the poles. As the rays of the sun shift seasonally
from one hemisphere to the other, the zone of
maximum possible daily insolation moves with
them. For the earth as a whole, the gains in solar
energy equal the losses of earth energy back into
space. However, since the equatorial region does
gain more heat than it loses, and the poles lose
more heat than they gain (as shown in Figure 2-4),
something must happen within the atmosphere to
distribute heat evenly around the earth. Otherwise,
the equatorial regions would continue to heat and
the poles would continue to cool. Therefore, in
order to reach equilibrium, a continuous large-
scale transfer of heat (from low to high latitudes)
is carried out by atmospheric and oceanic
circulations.
Oblique
Figure 2*3. Oblique and vertical
rayi.
600
200-
100
' .1 I I I
IT
•.Surplus
Long wave
radiation
leaving
Short wave
radiation __
absorbed
*V Deficit
v
I
I
I
I III
0 10 20 30 40 50 60 70
Equator Poles
Latitude
rigure 2-4>> Distribution of beat
' latitudinally.
2-11
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Heat transfer from the tropics poleward takes
place throughout the year, but at a much slower
rate in summer than in winter. The reason is that
the temperature difference between low and high
latitudes is considerably smaller in summer than in
winter—only about half as large in the Northern
Hemisphere. As would be expected, the winter
hemisphere has a net energy loss and the summer
hemisphere a net gain. Most of the summertime
gain is stored in the surface layers of land and
ocean, mainly in the ocean.
The atmosphere is often referred to as a giant
"heat engine," driving warm air poleward and
bringing cold air toward the equator. Figure 2-5
depicts the simple heat engine. This diagram has
coordinates of horizontal distance and height (or
pressure). The simple heat engine is based on the
principle that warm fluid moves from a heat
source to a cold source at low pressure, while cold
fluid moves from a cold source to a heat source at
high pressure. At the cold source, the warm mass
loses heat, increases in density, and sinks; the
reverse takes place at the heat source. During
winter in the United States or any other middle-
latitude area, winds from the south make the air
wanner while winds from the north cause the
temperature to fall. The movement of warm air
masses into the polar regions and cold air masses
into the tropics alters the wanning and cooling
trends that would result from radiation alone.
The oceans also play a role in heat exchange.
Warm water flows poleward along the western side
of an ocean basin and cold water flows toward the
equator on the eastern side. At higher latitudes the
east-west position of warm and cold currents in the
ocean reverses, but still the warm water moves to
higher latitudes and the cold water to lower
latitudes. Thus, the oceans contribute to poleward
heat transport, accounting for about 25% of the
total transport in the subtropical and middle
latitudes. Almost all other phenomena of weather
and climate, including atmospheric disturbances
(storms), work together to equalize the heat
Cold source
Warm air
(light)
o
u
3
i/t
2
£
Heat source
Cold air
(heavy)
Horizontal distance
2-5. Sintple heat engine.
2-12
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balance. As Table 2-1 shows, the greatest transfer
of heat is required in the middle latitudes. The
greatest turbulence and storminess is found hi
regions where both horizontal air movement and
air-mass movement are greatest.
Since the analogy of the earth as a heat engine
was realistic in low latitudes, the whole general cir-
culation was once thought to act as a simple heat
engine. Then computations, which were begun in
Austria about 1920 and pursued widely from the
1940s onward, demonstrated that the cyclones and
anticyclones outside the tropics and the waves in
the upper westerlies provided an important means
for exchanging heat between the tropics and the
polar zone. The importance of the disturbances in
the westerlies has been studied compared to the
simple heat engine through laboratory experiments
conducted by Dave Fultz at the University of
Chicago since the late 1940s (Riehl, 1965). This
work has lead to theories about the general cir-
culation of the atmosphere, a much more com-
plicated process than described by the simple heat
engine principle. This general circulation will be
discussed in the next lesson.
Table 2-1. Required heat flux
toward the poles across
latitudes (10" calories
per day).
Latitude
0
10
20
SO
40
50
60
70
80
90
Flux
0
4.05
7.68
10.46
11.12
9.61
6.68
3.41
0.94
0
Review Exercise
1. The source of energy responsible for atmospheric and
oceanic motion is the
2. Which of the following stores more heat energy than
all other atmospheric constituents combined?
a. carbon dioxide
b. acid rain
c. water vapor
d. nitrogen
1. sun
3. How much of the sun's radiation reaches the tip of
the earth's atmosphere?
a. one quarter of it
b. half of it
c. one-millionth of it
d. one-billionth of it
2. c. water vapor
3. d. one-billionth of it
2-13
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4. Since the earth's atmosphere acts as a filter, how
much radiation at the tip of the atmosphere reaches
the surface of the earth?
a. one-quarter of it
b. half of it
c. all of it
d. none of it
5.\The fraction of energy radiated by a body compared
\.Jto the amount of incoming energy is its
a. atmosphere. <(
b. albedo.
c. heat balance.
d. solar constant. , V
4. ^ one-quarter of it
6} What is differential heating?
5. b. albedo.
A heat balance on the earth implies that
a. the cold earth holds all of the heat it receives.
b. the cold poles hold as much heat as the warm
equator radiates.
c. everything on the earth and in the atmosphere
stores, releases, and transfers heat.
d. the earth warms in the winter and cools in the
summer.
6. the ability of some objects
to hold heat better than
others.
8. List the four factors that govern the amount of
insolation received by the earth.
c. everything on the
earth and in the
atmosphere stores,
releases, and transfers
heat.
9. When the air is heavily polluted or clouded,
more/less direct insolation will be received. This is
because of
8. • solar constant
• atmosphere's
transparency
• daily sunlight duration
• sun's angle at noon
10. True or False? Oblique rays produce more heating
per unit area than vertical rays do.
9. less,
absorption of solar radia-
tion by atmospheric gases
10. False
2'-14
-------
Lesson 3
Circulation of the Atmosphere
Assignment
1. View the slide/tape presentation, Pressure Systems, Winds, and Circulation,
which consists of tape SI:409-S and slides 409-3-1 through 409-3-74. This
presentation is an overview of the reading material in this lesson and in
Lesson 4.
2. Read pages 3-15 through 3-20 of this guidebook.
Assignment Topics
• Atmospheric pressure
• Isobars and the pressure gradient
• Factors affecting wind motion
• Pressure systems
Lesson Goal and Objectives
Goal
To familiarize you with the atmosphere's scales of motion, atmospheric pressure,
wind motion, and air masses in the Northern Hemisphere.
Objectives
Upon completing this lesson, you should be able to:
1. define high pressure and low pressure.
2. name three forces that determine wind direction and speed within the earth's
friction layer.
3. describe the way cyclones and anticyclones are created by air movement.
4. name the four scales of motion of the atmosphere and recognize their size
relationship to each other.
3-1
-------
-------
Pressure Systems, Winds,
and Circulation
Slide
1.
Script
Selected Visuals*
Pressure
Systems.
Winds, and
Circulation
2. Everything on the earth absorbs, stores, and then reradiates
the sun's energy. Some parts of the earth heat more readily
than other parts. This is known as differential heating. For
example, in the summertime a plowed field heats quickly and
stores vast amounts of heat. On the other hand, a large lake
does not heat well.
3. Differential heating of the earth affects the air above it. When
the earth is warm, the air immediately above it becomes
warm. This happens because heat always moves to an area of
less heat.
4. This wanning happens because of two principles. jSonduction)
is-the-a^msfeiuafj^ajjhjitjakes place when something touches
a Seated surface. In this case, the air,tguches_the_heated earth
and gains somejpf^ that heat.
O
-r -i -i —
However, a few inches above the earth's surface, \conyection3
takes over;jthe_heat transfer process. Convection is vertical
mixing of air. The warm air near the bottom rises, and as it
rises displaces cooler air. This cooler air descends to within a
few inches of the earth's surface where it is heated. This cycle
continues as long as the earth is warmer than the surrounding
air.
•illustrations included here, no live shots
3-5
-------
Slide
Script
Selected Visuals
6. Picture an imaginary column of air above a warm spot on the
earth. Since warm air holds moisture well, this warm air
above the warm earth is moist, light, and buoyant. In fact, it
is so buoyant that the air in the column rises—much as a
balloon is light and buoyant and rises.
7. Now picture a similar column of air above a cold spot on the
earth. Because the heat is moving toward an area of less heat,
what little heat is in the air is transferred to the cool earth,
leaving the air even cooler than it was.
8. Since cool air does not hold moisture well, this cool air above
the cool earth is dry and fairly heavy. It is not buoyant and
does not rise. In fact, it may even descend.
9. These same two situations can also occur over warm and cold
bodies of water. But wherever they occur, when the air is
warm, light, and buoyant there is low pressure. When the air
is cool, heavy, and not buoyant there is high pressure.
10. The term "pressure" refers to the weight of the air. In other
words, it refers to the amount of force that the air exerts on
the area directly below it.
ll
«--..
(1
I1 1
--«*
1.1
$
11. The air in a low pressure area is light and buoyant, so it
exerts relatively little pressure on the land below it. On the
other hand, the air in a high pressure area is dense and
heavy; therefore, it exerts a lot more pressure on the land
below it. To help you remember which is which, associate the
first letter of the word "low," an "L," with the word "light";
associate the first letter of the word "high," an "H," with the
word "heavy."
12. Suppose two columns of air are each twenty centimeters tall
and of the same diameter. Centimeter-for-centimeter, the high
pressure column is heavier. For example, it might take only
four centimeters of the heavier air to exert as much pressure
as sixteen centimeters of the lighter air.
5-4
-------
Slide
Script
Selected Visuals
IS. If we choose points of equal pressure, one will be near the
bottom of the low pressure column, but the other will be near
the top of the high pressure column.
14. The relative positions of the points of equal pressure are
important. In our imaginary columns, one point is high up in
the column and the other is low in the column. If we connect
these two points of equal pressure with a line, the line is
slanted.
15.
16.
The line shows the steepness— or f»Jt— between points of equal
pressure in the high and low pressure areas. This tilt is
instrumental in the formation of wind.
Wind is created by differences in pressure. Picture, again, the
tilt of the pressure areas. Air flows down this tilted surface—
much like a marble rolls down a hill. The steeper the tilt, the
faster the air flows down it.
17. Of course, air isn't really found in columns. The cool and
warm air found above the earth actually forms "hills" and
"valleys" of high and low pressure. Wherever there-are "hiuV
otfeigJl-pressure, there will bg associated "vallgys" of low
H
18. Just as we could draw a line to connect points of equal
pressure within our imaginary columns of air, we can
represent points of equal pressure in our atmosphere by
drawing the silhouette of these hills and valleys. This, of
course, gives us only a two-dimensional picture.
19. Our atmosphere is actually three-dimensional. If we form a
three-dimensional picture of the hills and valleys of high and
low pressure, every part of the surface represents points of
equal pressure. We can refer to this as a pressure surface.
Equal PTCMUI*
EqiMl Pranura
S-5
-------
Slide
Script
Selected Visuals
20. For example, every point on the surface has equal pressure
exerted on it. Any point below the surface has more pressure
exerted on it, and any point above the surface has less
pressure exerted on it.
21: As we have seen, the pressure surface tilts and air flows
downward along the surface.
22. Generally, a large high pressure area—or hill—is only slightly
tilted near its center, so the air flows relatively slowly there.
We say that the wind is blowing lightly.
23. However, near its associated low pressure area—or valley—the
tilt is steeper, somewhat like a cliff. Here the air flows faster,
and we say that the wind is blowing strongly.
24. We can picture the air flowing down the pressure surface as if
it were air flowing down the side of a hill. It is being pulled
downhill by gravity.
25. As it flows faster, it is affected by other forces in the
atmosphere, and it begins to flow around and down in a
counter-clockwise direction.*
26. When the rotating wind hits the valley floor, it can spiral
downward no further, so it starts spiraUn^jip_the_center of the
valley. We now have the start of a lowjiressure system^
Unlike the low pressure area described earlier, the low
has turning winds and is dynamic. The
27.
"spiraling wind helps create more spiraling wind, which in turn
helps keep it going. Until other factors hi the atmosphere
affect it, the air just keeps on spiraling.
28. The ah- coming out of the center of a low pressure system
cools as it rises and more or less spills over onto the adjacent
high pressure area. As the spilled ah- rotates down and around
the high pressure area, it is referred to as a high pressure
system. Thus the two systems help to perpetuate each other.
*in the Northern Hemisphere. Flow is clockwise in the Southern
Hemisphere.
S-6
-------
Slide
Script
Selected Visuals
29. Where there is a low pressure system, there will always be an
associated high pressure system.
SO. This is, of course, a simplified picture of how wind is created
and how it flows. If the earth were smooth and slick, this
simple picture would be quite accurate. However, the surface
of the earth is neither smooth nor slick; therefore, there is
friction. This friction causes the air flow near the surface to
slow down and change direction.
SI. As we get further and further from the surface, friction
becomes less and less of a factor in wind speed and direction.
And finally, if we get high enough up into the atmosphere,
friction doesn't affect wind at all. This point is called the
planetary boundary layer. The effect of friction is to cause
variations in the speed and direction of the wind created by
the high and low pressure areas.
32. The pressure areas that create wind and their associated
pressure systems are short-lived. They form, stay around for
a while, move to another location, and then dissipate.
S3. Pressure systems do not always form in the same place, and
they are of various sizes.
34. Consequently, the winds associated with them do not always
cover the same area and do not always last for the same
amount of time. The pressure areas and their associated winds
are relatively localized.
5-7
-------
Slide
Script
Selected Visuals
35. But this localized wind is not the only air flow in our
atmosphere. There are very large areas of air circulating in
our atmosphere. Unlike wind, these air flows are not caused
by high- and low-pressure areas.
36. To describe larger air flows, and to compare them to the
winds we have just described, we need some unit of measure
or a scale. Meteorologists use four "scales of motion" to help
describe the relative sizes of these and other Ineteorological
phenomena.
Meteorological
Scale* of Motion
Macracale
Synoptic Scale
MewMcale
Micracalc
37. The smallest of these is thelmicroscale. ttt covers a vertical^
distance of up to 100 meters and a horizontal distance of up
^To kilometers.
Microscale
vertical:
•urface-» ~ 100 m (i km)
horizontal:
lmm-»2km
38. When a meteorologist reports that the winds at the airport are
11 kilometers per hour, he is-describing microscale wind flow.
39. Th
-------
Slide
Script
Selected Visuals
44. The large areas of wind flow we are about to discuss are
macroscale phenomena.
45. These four scales of motion—the microscale, the mesoscale,
the synoptic scale, and the macroscale—can be used to help
describe any meteorological phenomena.
46. We mentioned earlier the very large areas of air circulating in
our atmosphere. We also said that these are macroscale
phenomena. To help you understand the large areas of air
flowing around our planet, pretend that the earth does not
rotate. This will allow us to see what happens to these large
areas of air in the atmosphere without the complications
caused by rotation.
47. If the earth were not rotating, we would see a very predictable
circulation pattern. Cells—or self-contained areas of rotating
air—would extend from the equator to the poles.
48. Since the equator would receive more of the sun's radiation,
the air there would be hotter than the air at the poles. The
air at the equator would be warm, moist, and buoyant, and
the ah* at the poles would be cold, dry, and heavy.
49. The warm, moist air at the equator would result in
thunderstorms. The release of heat during the storms would
cause the air to continue to rise and as it reached the upper
limit of our atmosphere and could rise no further, it would
begin to move toward the polar regions and continue to cool.
Scales of Motion
Mfcracalc
Macmcale \ 7 /
50. In the Northern Hemisphere, the air flow near the surface
would always be out of the north because the cooler air from
the North Pole would return to the equator to be reheated.
S-9
-------
Slide
Script
Selected Visuals
51. But the earth does rotate. And this rotation takes the
relatively simple air flow just described and changes it into a
very complex situation. And it creates an air flow that is, in
general, from west to east.
52. The air flow situation becomes complex because of a factor
called th^gpncjis^ffect] This effect makes all moving objects
appear to turn to the right.
CoriolU Effect
53. Suppose that you're standing on the North Pole. You have a
rifle and you line it up with a specific longitude line.
54. You fire the rifle, and the bullet begins to move stmight
ahead.
55. However, since you are standing on the earth and it is
rotating, you and the earth are rotating toward the left. The
bullet, of course, continues on its straight path.
56. As you and the earth rotate further and further to the left,
the bullet ends up more and more to the right of the original
longitude line. Thus, in terms of your position—since you
don't feel yourself rotating—the bullet seems to be moving to
the right.
5-10
-------
Slide
Script
Selected Visuals
57. In a like manner, from our perspective in the Northern
Hemisphere the atmosphere and ah* flow we described earlier
turn to the right because we are rotating to the left with the
earth. This is the Coriolis effect.
58. As the air flow turns to the right, it divides each of the
hemispheres into three cells.
Coriolis Effect
_
59. Consider the Northern Hemisphere. It has k polar cell; a
. — ->_.__»—- -*\ \~ ---- — ~i ~- _ -— ___ _
, mid^latitude cell, and a tropical cell*
-------
Slide
Script
65. In the last lesson, we looked at the sun's radiation and how it
affects the atmosphere and oceans of the earth.
66. Then in this lesson we've talked about how differential heating
causes pressure surfaces to tilt, and this tilt causes the wind to
start flowing.
Selected Visuals
67. In addition to this localized air flow, there are large masses of
air circulating in our atmosphere.
68. These air masses are affected by the earth's rotation and the
Coriolis effect and become three large air cells in each of the
hemispheres.
69. In general, the flow of air in our atmosphere is from west to
east. This is because of the earth's rotation. But superimposed
_. ~r~' — . r -*^ * *
on this general west-to-east ^ir flow are the localized winds
that blow in variouTctifections.
70. Therefore, predicting the direction and concentration of air
pollutants must be based on long-term studies* using
instruments and methods developed primarily for air pollution
monitoring. These topics will be discussed in following lessons.
71. Credit: Crew
•To make accurate predictions, studies are needed to back up short-term
judgements. These studies are based on actual experiences which are used
as data for air quality models.
l*l««««f« Syvtcm*
S-12
-------
Slide Script Selected Visuals
72. Credit: Northrop
and production by:
Northrop Service* Inc.
under
EPA Contract No. 68-02-2374
73. Credit: NET Northrop
Environmental
Training
S-1S
-------
The General
Circulation
Introduction
The previous lesson discussed the necessity of
having a heat balance in the atmosphere. Heat
was shown to transfer from the warm equatorial
regions to the cold polar regions to maintain this
heat balance. This transfer of heat is the main
cause of atmospheric motion on the earth. The
rotation of the earth modifies this motion but does
not cause it, since the atmosphere essentially
rotates with the earth.
If the earth did not rotate, rising air above the
equator would move poleward, give up some of its
heat, sink, and return toward the equator as a sur-
face current. However, as Figure 3-1 illustrates,
atmospheric circulation, as developed by Palmen,
is based on rotation that causes three major cells
of wind flow in each hemisphere. The rotation
causes a spiral pattern of wind flow from poles to
equator. Winds in the Northern Hemisphere are
deflected to the right; therefore, flow from the
tropics toward the poles becomes more westerly
and flow from the poles toward the equator tends
to become easterly. The result is that most of the
motion is around the earth in zonal patterns, with
less than one-tenth of the motion between the
poles and equator (meridional). In the latitudes of
the westerlies, high speed winds blow from west to
east near the tropopause. The winds, called polar
front jet streams, are extremely forceful. The jet
streams do not remain long in one position, but
meander and are constantly changing position.
This causes changes in the location of the polar
front and perturbations along the front. Migrating
cyclones and anticyclones result. These play an
important part in heat exchange, transferring heat
northward. .1 ^
90 °N
Figure 3-1. General circulation
model.
S-15
-------
Wind
Wind is the basic element in the general circula-
tion of the atmosphere. Wind movements from
small gusts ft> large air masses all contribute to
transport of heat and other conditions of the
atmosphere around the earth. Winds are always
named by the direction from which they blow.
Thus a "north wind" is a wind blowing from the
north toward the south. If a wind vane is allowed
to turn freely, it will always point into the wind.
When wind blows more frequently from one
direction than from any other, the direction is
termed the prevailing wind.
Wind speed increases rapidly with height above
the ground level, as frictional drag decreases.
Wind is commonly not a steady current but is
made up of a succession of gusts, slightly variable
in direction, separated by lulls. Close to the earth,
wind gustiness is caused by irregularities of the sur-
face, which create eddies. Eddies are variations
from the main current of wind flow. Larger
irregularities are caused by convection—or vertical
transport of heat. T,hese and other forms of tur-
bulence contribute to the movement of heat,
moisture, and dust into the air aloft.
Creating Wind
Wind is nothing more than air in motion.
Although the motion is in three dimensions, the
horizontal component is the most useful for deter-
mining wind direction and speed. Three forces
affect the wind: deflection (Coriohj), pressure_g|a^
diem, and frictionT {f5
-------
Coriolis Force
The first force, the Coriolis, is an apparent force.
It occurs because wind flow above the earth has a
tendency to move in a straight path while the
earth rotates underneath. When viewed from the
earth, especially from the poles, the wind will
appear to be deflected to the right of the observer
in the Northern Hemisphere and to the left of the
observer in the Southern Hemisphere (Figure S-2).
This apparent force on the wind seems to
• increase as wind speed increases,
• remain at right angles to wind direction, and
• increase with an increase in latitude (i.e.,
exert more "force" as viewed from the poles
than as viewed from the equator).
The effect of this deflecting force is to make the
wind seem to change direction on earth. Actually,
the earth is moving with respect to the wind.
Pressure Gradient Force
Wind is also caused by nature's attempt to correct
differences in air pressure. Wind will flow from
areas of high pressure to low pressure. Isobars,
connecting points of equal pressure, may follow
straight lines or form rings around the highest or
lowest pressure in a geographic location.
The pressure gradient is the rate and direction
of pressure change. It is represented by a line
drawn at right angles to the isobars as shown in
Figure S-3. Gradyn^arejtegp^whergjsjobars are
The wind will move faster across
steep gradients. Winds are weaker where the
isobars are farther apart because the slope between
them is not as steep; therefore, wind does not
build up as much force.
As we said, wind moves from areas of high to
low pressure, but because of the Coriolis force
(effect of the earth's rotation), wind does not flow
parallel to the pressure gradient.
Figure 3-2. Coriolii (deflecting) force
as teen from each pole.
Steep
Figure S-3. Preuure gradients.
5-17
-------
Friction
Friction, ttoe_thirdLmajp.ii force affecting the
comes into playaMigjoJ^Op^mete^above the
Earth's surface. Above thT friction layer and at
YatifuofergfeliteTthan 20°, the Coriolis forehand
the pressure gradient force are in balance and the
isobars are straight lines. As shown in Figure 3-4,
the balanced forces create a wind that will blow
parallel to the isobars. This is called the
the Northern Hemisphere low
pressures will be to the left of the wind. The
reverse is true in the Southern Hemisphere.
Within the friction layer, the Coriolis force,
pressure gradient force, and friction all exert an
influence on the wind. Isobars are curved or closed
within the friction layer. The Coriolis force and
the pressure gradient force are thrown out of
balance due to fractional drag acting on one of the
forces.
Pressure Systems
When friction reduces the influence of the Coriolis
force on the wind's direction, the resultant wind is
then influenced more by the pressure gradient
force and begins to move from areas of high to low
pressure, as shown in Figure 3-5. The difference
between these two forces is the centripetal
acceleration, or net acceleration, toward the
center. In the Northern Hemisphere the air will
curve counterclockwise. This motion causes the
formation of a cyclone, a pressure system with its
lowest pressure in the center. This system is
represented by closed isobars around the low.
In the case of an anticyclone, the pressure force
accelerating outward must be exceeded by the
Coriolis force, as shown in Figure 3-6. This will
cause the air to accelerate centripetally toward the
center and move in a circular clockwise path in
the Northern Hemisphere. The highest pressure
will be in the center and the winds will blow out
from the center.
<\/
-------
Therefore, as shown in Figure 5-7, the com-
bined effects of pressure gradient force, Coriolis
force, and friction cause airflow in a cyclone to be
convergent, with surface winds flowing obliquely
across the isobars toward the center of the low. In
an anticyclone the circulation is divergent, with
surface winds moving obliquely across the isobars
outward from the center. This is a two-
dimensional representation of pressure. As shown
in the slide program for this lesson, systems are
actually three-dimensional, appearing as adjoining
hills and valleys of air. Pressure systems are
represented on weather maps as illustrated in
Figure 3-8. (Note that a pressure system is
depicted by the isobars forming a circle around
the high or low.) The relationship of cyclones and
anticyclones to weather patterns will be discussed
in the next lesson.
Northern Hemisph
figure 5-7/) Cyclone and anticyclone
circulation.
Figure 5-8.ressure syitems.
-------
Review Exercise
1. Most of the air motion in the atmosphere is zonal, or
the earth, while only one-tenth is merid-
ional, or
2. Palm en's model divides the earth into
cells in each hemisphere.
a. two
b. three
c. four
1. around,
between equator and
poles
3, Since the earth rotates, the Coriolis force makes
the wind appear to in the
Northern Hemisphere.
2. b. three
4. In reality, with respect to the Coriolis force, the wind
follows a straight/curved path while the earth
rotates underneath.
3. turn to the right
5. When air touches the heated earth and in turn
becomes warm, has just occurred.
4. straight
6. The heating process that causes the vertical mixing of
the air above the earth's surface is
a. conduction.
b. convection.
5. conduction
7. Lines that represent points of equal pressure are
called
6. b. convection.
8. The air in a low-pressure area is
a. light and buoyant.
b. light and dense.
c. heavy and buoyant.
d. heavy and not buoyant.
7. isobars
9. The tilt or steepness between isobars is called
the
8. a. light and buoyant.
10. Strong winds are associated with
isobars.
.-spaced
9. pressure gradient
10. closely
-------
Lesson 4
Frontal Systems
^Assignment
Read pages 4-3 through 4-8 of this guidebook.
Assignment Topics
9 Fronts
• Air masses
Lesson Guidance
The graphic representations of frontal zones are greatly simplified. For a more
accurate cross-sectional picture and more information refer to the text by Saucier
given in Supplementary Reading.
Lesson Goal and Objectives
Goal
To familiarize you with the basic characteristics of warm fronts, cold fronts,
occluded fronts, and introduce some of the effects that fronts have on pollution in
the atmosphere.
Objectives
Upon completing this lesson, you should be able to:
1. identify three frontal systems from descriptions or pictures representing each.
2. describe the physical situation of slope, clouds, and precipitation found with
each front.
3. describe the effects of warm and cold fronts on pollution trapping.
4. identify the two properties that define an air mass.
5. recognize, by region of origin and symbol, the six classifications of air masses.
4-1
-------
Supplementary Reading
If more information is needed about frontal systems, the following references are
suggested:
Saucier, W. J. 1955. Principles of Meteorological Analysis. University of Chicago
Press. Pages 134 through 142, S45 through 348.
Slade, D. H. editor. Meteorology and Atomic Energy. 1968. Section 2.34, pages
21 through 24.
4-2
-------
^Anticyclones, Cyclones,
^
nts^-
Migrating areas of high pressure (anticyclones) and
low pressure (cyclones) and the fronts associated
with the latter are responsible for the day-to-day
changes in weather that occur over most of the
mid-latitude regions of the earth. The low pressure
systems in the atmospheric circulation form along
frontal surfaces separating masses of air having
different temperature and moisture characteristics.
The formation of a low pressure system is accom-
panied by the formation of a wave on the front
consisting of a warm front and a cold front, both
moving around the low pressure system in a
counterclockwise motion. This low pressure system
is referred to as a cyclone. The life cycle of a
typical cyclone is shown in Figure 4-1. The
triangles (A) indicate cold fronts and the
semicircles (•) indicate warm fronts. The five
stages depicted here are:
1 . beginning of cyclonic circulation,
2. warm sector well defined between fronts,
3. cold front overtaking warm front,
4. occlusion (merging of two fronts), and
5. dissipation. ^— \ ___ ^^~
.FjourfrontaLpattenw— (^^ q1cclude
-------
When cold and warm fronts merge— the cold
front overtaking the warm front —occludedjamts
form (Figure 4-4). Occluded fronts can be called
cold front or warm front occlusions, as shown in
Figure 4-5, but, in either case, a colder air mass
takes over an air mass that is not as cold.
As either type of occluded front approaches, the
clouds and precipitation resulting from the
occluded front will be similar to those of a warm
front (Figure 4-S). As the front passes, the clouds
and precipitation will resemble those of a cold
front (Figure 4-2). Therefore, it is often impossible
to distinguish between the approach of a warm
front and the approach of an occluded front.
Regions_with a predorninance of o^TudejHronts
JKavsJLgre«de^lj>Ho^^
amounts of precipitation, and small daily
temperature changes.
The last type of front is the datiouxon}. As
the name implies, the air masses^around this front
are not in motion. It will resemble the warm front
in Figure 4-3 and will manifest similar weather
conditions. Figure 4-6 shows how a stationary front
is represented on a map. The abbreviations cP and
mT stand for continental Polar and maritime
Tropical air masses. A stationary front can cause
bad weather conditions that persist for several
days.
Frontal Trapping
Frontal systems are accompanied by inversions.
Inversions occur whenever warm air rises over cold
air and "traps" the cold air beneath. Within these
inversions there is relatively little air motion, or
the air becomes relatively stagnant. (In Lesson 5,
we will discuss the effect of inversions on air pollu-
tion concentrations.) This frontal trapping may
occur with either warm fronts or cold fronts. Since
a warm front is usually slower moving than a cold
front, and since its frontal surface slopes more
gradually, trapping will generally be more
important with a warm front. In addition, the low
level and surface wind speeds ahead of a warm
front— within the trapped sector— will usually be
lower than the wind speeds behind a cold front.
Cold air
Occluded
front
Warm air
front.
Cold front occlusion
Warm
Colder
air
Cold air
Warmfront occlusion
Cold air
Colder air
Figure 4-5. Cott-a«d^warm front
occlusions)
N
mT
tationary front
resented on a map.
4-4
-------
Most warm frontal trapping will occur to the west
through north from a given pollutant source, and
cold frontal trapping will occur to the east through
south of the source.
Air Masses.
Air masses are macroscale phenomena, covering
hundreds of thousands of square miles and extend-
ing upward for thousands and ten thousands of
feet. They are relatively homogeneous volumes of
air that have acquired the characteristics of a cer-
tain world region. The processes of radiation, con-
vection, condensation, and evaporation condition
the air over a period of several days into an air
mass. Air masses develop more commonly in some
regions than in others. These areas of formation
are known ^source region^, and they determine
the classification of the air mass. Air-masses are
classified as maritime or continental according to
origin over ocean orHapd. and ajrc^ic,
principally on thelatitude of
ongnTTTable 4-1 summarizes air masses and their
properties. Fronts generally separate air masses.
Figure 4-7 shows an advancing warm front
between Tropical maritime (mT) and Polar con-
tinental (cP) air masses.
Weather characteristics of an air mass depend
mjwo basic properties: the_vgrticaj_distribution of
emperature and jhe vertical distribution and^
The first property, in addi-
tion to indicating a warm or cold air mass,
indicates the stability of the air mass. Stability
influences the extent of vertical movement of the
air mass in the atmosphere. Stability, an impor-
tant influence on the spread (dispersion) of air
pollution, will be covered in the next lesson.
Moisture is the second basic property in an air
mass. Moisture plays such a significant role in
weather and climate that it is commonly treated
separately from the other constituents of air. In
one or more of its forms, atmospheric moisture is a
factor in humidity, cloudiness, precipitation, and
visibility. Water vapor and clouds affect the
transmission of radiation both to and from the
N
mT
Figure 4-7. Warm front between two
air manes.
4-5
-------
Viable 4-1
ication of air masses.
Name
Arctic
Polar continental*
Polar maritime
Tropical continental
Tropical maritime
Equatorial
Origin
Polar regions
Subpolar continental
areas
Subpolar area and
arctic region
Subtropical high-
pressure land areas
Southern borders of
oceanic subtropical,
high-pressure areas
Equatorial and
tropical seas
Properties
Low temperatures,
low specific but high
summer relative
humidity, the coldest
of the winter air
masses
Low temperatures
(increasing with
southward move-
ment), low humidity,
remaining constant
Low temperatures,
increasing with
movement, higher
humidity
High temperatures,
low moisture content
Moderate high
temperatures, high
relative and specific
humidity
High temperature
and humidity
Symbol
A
cP
mP
cT
mT
E
•The name of an air mass, such as Polar continental, can be reversed to continen-
tal Polar, but the symbol, cP, is the same for either name.
earth's surface. Through the process of evapora-
tion water vapor also conveys latent heat into the
air, giving it a function in the heat exchange (as
well as in the moisture exchange) between the
earth and the atmosphere. Atmospheric water is
gained by evaporation but lost by precipitation.
Only a minute fraction of the earth's water is
stored as clouds and vapor in the atmosphere at
any one time. The net amount at the end of any
given period for a particular region is an algebraic
summation of the amount stored from a previous
period, the gain by evaporation, the gain or loss
by horizontal transport, and the loss by precipita-
tion. This relationship expresses the water balance.
of the atmosphere. Moisture, as it relates to the
stability of the atmosphere, will also be discussed
in the next lesson.
4-6
-------
Review Exercise
i.
fronts separate advancing warm air from
retreating cold air.
a. Warm
b. Cold
c. Occluded
2.
fronts have slopes of from 1:50 to 1:150.
1. a. Warm
a. Warm
b. Cold
c. Occluded
S. Generally,
fronts have a cloud cover and
2. b. Cold
precipitation following the position of the surface
front.
a. warm
b. cold
4. Match the following symbols with the fronts they
denote.
a. ^ b. ,. c. m. d. A * occluded
• warm
• stationary
• cold
3. b. cold
\
5. Precipitation is generally found in advance of a
front.
a. warm
b. occluded
c. stationary
d. warm, occluded, or stationary
4. a. cold
b. warm
c. occluded
d. stationary
6. Fronts generally separate
5. d. warm, occluded, or
stationary
7. Air masses are named by their source regions based on
their origin over or and their
6. air masses
f. land, sea>
latitude
-------
8. List two land based air masses.
9. The uniformity of an air mass is based on two physical
properties. What are they?
8. • continental Polar
• continental Tropical
9. temperature
moisture content
4-8
-------
Lesson 5
Vertical Motion
and Atmospheric Stability
Assignment
Read pages 5-3 through 5-21 in this guidebook.
Assignment Topics
• Principles related to vertical motion
• Stability and instability
• Stability and plume behavior
Lesson Guidance
This lesson includes simplified adiabatic diagrams. Adiabatic diagrams represent
the average conditions in the area surrounding the site of the temperature profile.
When temperature changes with spatial distribution, adiabatic diagrams are
needed for each area.
Lesson Goal and Objectives
Goal
To familiarize you with the vertical temperature structure of the atmosphere and to
introduce its relationship to plume dispersion.
Objectives
Upon completing this lesson, you should be able to:
1. briefly explain the concept of buoyancy.
2. recognize the four major categories of lapse rates.
3. describe unstable conditions.
4. describe stable conditions.
5. define four types of inversions.
6. name five types of plume behavior and relate each to atmospheric conditions.
5-1
-------
Supplementary Reading
If more information is needed about atmospheric stability, the following references
are suggested:
Byers, Horace S. 1957. Meteorology. McGraw-Hill, pages 511 through 519.
Slade, D. H. editor. Meteorology and Atomic Energy. 1968. U.S. Atomic Energy
Commission, Division of Technical Information, Oak Ridge, TN, pages 42
through 45, 66 through 77.
5-2
-------
Introduction
The two previous lessons discussed horizontal
motion of the atmosphere. Vertical motion is
equally important in air pollution meteorology, for
the degree of vertical motion largely determines
how much air is available for pollutant dispersal.
There are a number of basic principles related to
vertical motion that you must be familiar with
before you can understand the mechanics and con-
ditions of vertical motion. These principles are
presented first and are followed by discussions of
instability, stability, and plume behavior.
Principles Related to Vertical
Motion
Parcel
Throughout the lesson we will be discussing a
parcel of air (also referred to as an air mass). This
parcel is a relatively well-defined body of air (a
constant number of molecules) that acts as a
whole. Self-contained, except on its boundaries, it
does not readily mix with the surrounding air.
The exchange of heat between the parcel and its
surroundings is minimal, and the temperature
within the parcel is generally uniform. The air
inside a balloon is an analogy for an air parcel.
Buoyancy Factors
Holding other conditions constant, the tempera-
ture of air (a fluid) increases as atmospheric
pressure increases, and conversely decreases as
pressure decreases. The rate of change in
atmospheric temperature with elevation is the
lapse rate.
An air parcel that becomes warmer than the
surrounding air (for example, by heat radiating
from the earth's surface), begins to expand and
cool. If the cooling does not reduce the parcel's
temperature to that of the surrounding air, then
the parcel has less mass than the cooler surround-
ing air. Therefore, it rises, or is buoyant. As it
5-3
-------
rises, its pressure decreases and, therefore, its
temperature decreases as well. The initial cooling
of a parcel has the opposite effect. In short, warm
air rises and cools, while cool air descends and
warms.
The extent to which a parcel rises or falls
depends on the relationship of its temperature to
that of the surrounding air. As long as the parcel's
temperature is greater, it will rise; as long as it is
cooler, it will descend. When the temperatures of
the parcel and the surrounding air are the same,
the parcel will neither rise nor descend unless
influenced by wind flow.
Lapse Rates
Dry Adiabatic
A parcel of air does not exchange heat across its
boundaries except by eddy diffusion at, its surface.
Therefore, any changes in temperature within the
parcel are caused by increases or decreases of
molecular activity within the parcel. Such changes,
, are due onlyjo the change hi
ressureTThe rate of adiabatic
heating or cooling oT a dry air parcel is 10°C/ 1000m.
This is known as the dry adiabatic rate. Air is ~~
considered dry, in this context, as long as any
water in it remains in a gaseous state.
The dry adiabatic rate is a fixed rate, entirely
independent of ambient air temperature. A
buoyant parcel of dry air, then, will always cool at
the rate of 10°C/1000 m, regardless of its initial
temperature or the temperature of the surrounding
air. You will see later that the dry adiabatic rate is
central to the definition of atmospheric stability.
A simple adiabatic diagram demonstrates the
relationship between elevation and temperature.
(Elevation is also used to imply pressure in more
complicated adiabatic diagrams.) The dry
adiabatic rate is indicated by a broken line, as
shown hi Figure 5-1, beginning at various
temperatures along the horizontal axis. Remember
that the slope of the line remains constant,
regardless of its initial temperature on the
diagram.
z
I
^
B
.0 i
5 i
2
2
\ ' r\ ' r\ ' v. i
XXX*
X X X \
X X X \
X X X \
X X X \
X X X \
X X X \
X X X \
X \ X \
X X X \
_ X X \ J,
» X X X
X X X X
X % X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
i M i \i 1 \ i \
10
20
30
40
Temperature, °C
Figure 5.^ Dry adiabatic rate.
5-4
-------
Wet Adiabatic
A rising parcel of dry air containing water vapor
will continue to cool at the dry adiabatic rate until
it reaches itsfcondensauonTelnTCfarare, or flewl
1 __— - — — *— — - ~~—^J' — — _ 1 ___ - - T - -"
of the
__
pointthe pressure of the water vapor
"gqualTthe saturation vapor pressure of the air,
and some of the water vapor condenses. (Recall
that cooler air holds less water vapor than does
warmer air.) Condensation releases latent heat in
the parcel, and thus the cooling rate of the parcel
slows. This new rate, called the wet adiabatic rate,
is shown in Figure 5-2. Because of differences hi
prevailing humidity, the wet adiabatic rate, unlike
the dry rate, is not the same world- wide. In the
middle latitudes^however, it is assumed to be
approximately (6°C/ 1 OOCTm.
Atmospheric
The actual temperature profile of the_ambien£jir
*&^calfed" tf^^iimospher^Japsejrate. Sometimes
called the prevailing or environmental rate, it is
the result of complex interactions of meteoro-
logical factors, and is usually considered to be a
decrease in temperature with height. It is par-
ticularly important to vertical motion since sur-
rounding air temperature determines the extent to
which a parcel of air rises or falls. As Figure 5-S
shows, the temperature profile can vary con-
siderably with altitude, sometimes changing at a
rate greater than the dry adiabatic rate and
sometimes changing less. When temperature
actually increases with altitude, the atmospheric
rate is negative. In Figure 5-4, this negative lapse
rate occurs at elevations of from 200 to 350
meters. A negative rate is particularly important in
air pollution, because it limits vertical air motion.
w
ill Till
Wet adiabatic
rate
Dry adiabatic
rate
1 t
10 20 30 40
Temperature, °C
Figure 5-2. Wet adiabatic rate.
1
t
5
I I I I
Atmospheric
lapse rate
I I
10
20
30
40
Temperature, °C
Figure 5-3. Atmospheric lapse
rate.
400
•2 200
\\ I \ I
IT
Negative
rate
I II
1 I L
Temperature, °C
Figure 5-4. Negative lapse rate.
5-5
-------
Mixing Height
Remember the analogy of the air parcel as a
balloon. Figure 5-5 shows three ways hi which the
adiabatic rate affects buoyancy. In each situation
assume that the balloon is filled at ground level
with air at 20 °C, then transported manually to a
height of 1 km. The air hi the balloon will expand
and cool to 10°C. Whether the balloon rises or
falls upon release depends on the surrounding air
temperature and density. In situation "A," the
balloon will rise because it remains warmer and
less dense than the surrounding air. In situation
"B," it will sink because it is cooler and more
dense. In situation "C," however, it will not move
at all, because the surrounding air is the same
temperature and density.
t
a
ABC
Temperature, °C
Figure 5-5. Relationship of adiabatic rate to air temperature.
The same principles apply hi real atmospheric
conditions when an air parcel is heated near the
surface and rises, and a cool parcel descends to
take its place. The relationship of the adiabatic
rate and the atmospheric lapse rate should now be
apparent. The latter controls the extent to which a
parcel of air can rise or descend.
5-6
-------
In an adiabatic diagram, as shown in Figure
5-6, the point at which the air parcel's adiabatic
rate intersects the atmospheric lapse rate
(temperature profile) is known as the mixtrg^
height. This is the^LurparceTs maximuniTevel of
ascejidencjsrlh cases where no intersection^ccurs
(when the atmospheric lapse rate is consistently
greater than the adiabatic rate), the mixing height
may extend to the tropopause, the upper boundary
of the lower atmosphere. Tji^airjbelow the mixing
The largeTthe mixing"
layer, the greater the volume of air in which
pollutants can be diluted.
w
5
V
5
I I I
Atmospheric
lapse rate
Mixing
height
Air parcel
with surface
\ temperature
\ of 30°
y
/Ti i
10 20 W 40
Temperature, °C
Figure 5-6. Mixing height.
Review Exercise
1. A relatively well-defined body of air that does not
readily mix with the surrounding air is a(n)
a. air column.
b. air mass.
c. air parcel.
d. hot air balloon.
e. b and c above
2. The temperature of air increases/decreases as
atmospheric pressure increases.
1. e. b and c above
• air mass
• air parcel
3. What two atmospheric factors influence the buoyancy
of an air parcel?
2. increases
4. If the temperature of a parcel of air is cooler than
the surrounding air, it will usually
a. ascend.
b. descend.
c. stay in the same place.
3. temperature and pressure
4. b. descend.
• 5-7
-------
5. The atmospheric, or prevailing, lapse rate
is the
a. rate of pressure change in the atmosphere.
b. rate of wet air vs. pressure change.
c. temperature profile of the atmosphere.
d. rate of frontal system passage.
6. The change in the temperature of an air parcel
due to a change in atmospheric pressure is called
a. advective.
b. adiabatic.
c. slope.
d. prevailing.
5. c. temperature profile of
the atmosphere
7. The dry adiabatic rate is indicated by a
line of constant
6. b. adiabatic.
8. The dry adiabatic rate is
a. 6°C/1000 meters.
b. <1°C/1000 meters.
c. 10°C/1000 meters.
d. 7.5°C/1000 meters.
7. broken, slope
9. True or False? The dry adiabatic rate is fixed,
entirely independent of ambient air temperature.
8. c. 10°C/1000 meters.
10. The dry adiabatic rate becomes the wet adiabatic
rate once it reaches the
9. True
11. At the wet adiabatic rate, the cooling rate of the
air parcel is usually
a. the same as at the dry rate.
b. slower than at the dry rate.
c. faster than at the dry rate.
10. dew point (or condensa-
tion temperature)
12. True or False? The wet adiabatic rate is the same
world-wide. At all latitudes it is 6°C/1000 meters.
11. b. slower than at the dry
rate.
IS. The actual temperature profile of the ambient air
is the lapse rate. /
12. False
14. True or False? The atmospheric lapse rate influences
the extent to which a parcel of air can rise or
descend.
13. atmospheric
14. True
5-8
-------
15. The maximum level to which a parcel of air will
ascend under a given set of conditions is known
as the
a. ascend/descend level.
b. mixing trough.
c. mixing height.
d. mixing layer.
16. The adiabatic lapse rate for a given air parcel will
intersect the atmospheric lapse rate at the
a. mixing trough.
b. moisture rate.
c. mixing height.
d. none of the above
15. c. mixing height.
17. A large mixing layer implies that air pollutants have
a greater/lesser volume of air for dilution.
16. c. mixing height.
17. greater
5-9
-------
Atmospheric Stability
The degree of stability of the atmosphere is deter-
mined by the temperature difference between an
air parcel and the air surrounding it. This dif-
ference can cause the parcel to move vertically;
i.e., it may rise or fall. This movement is
characterized by four basic conditions that
describe the general stability of the atmosphere. In
/JSz£Ze Conditions, this vertical movement is
discouraged, whereas ^unstable conditions the air
parcel tends to move upward~or downward and to
continue that movement. When conditions neither
encourage nor discourage air movement beyond
the rate of adiabatic heating or cooling, they are
When conditions are extremely
Stable , cooleFair jiear tKgLsurfece is
layer ojjyyannejrja.ir jbove it. This condition,
called ajijIjiveTOOrir! allows virtualljTno vertical air
motion^ These conditions ^mTcBrectly ielated~to~
pollutant concentrations in the ambient air.
Unstable Conditions
Remember that an air parcel that begins to rise
will cool at the dry adiabatic rate until it reaches
the dew point. If the_surrounding^atmosphere has
aJapse_ra.tejgeater than the adiabatic jate (cooT^
.ing-at-more than lO^G^^OO-g^t-ihe-rising parcel
will continue to be wanner than the surrounding
air. This is *^u£fia.diabatic rate; As Figure 5-7
shows, the temperature difference actually
increases with height, and buoyancy is enhanced.
As the air mass rises, cooler air moves
underneath. It, in turn, may be heated and begin
to rise. Under such conditions, vertical motion in
both directions is enhanced, and considerable ver-
tical mixing occurs. The degree of instability
depends on the degree of difference between dry
adiabatic and environmental lapse rates. Figure
5-8 shows both slightly unstable and very unstable
conditions.
post commonly develop on
humidity~and IJow~wind speed.
The earth rapidly absorbs heat and transfers some
of it to the surface air layer. There may be one
5-10
§ 1
i
s
I IX I I I I I
Temperature
\ " difference
I I I I I
10
20
30
40
Temperature, °C
Figure 5-7. Enhanced buoyancy
associated with
instability (super-
adiabatic rate).
r\ i i i i i
\ Slightly
unstable
Very
unstable
I 1 I I
10
20
SO
40
Temperature, °C
Figure 5-8. Unstable conditions.
-------
buoyant air mass if the thermal properties of the
surface are uniform, or there may be numerous
parcels if the thermal properties vary.
Another condition that encourages instability is
the cyclone (low-pressure system^whicih is
characterized by rising air, clouds, and
precipitation.
Neutral Conditions
When the environmental lapse rate is the same as
the dry adiabatic rate, the atmosphere is in a
neutral condition (Figure 5-9). Vertical air move-
ment is neither encouraged nor hindered. The
neutral condition is important as the dividing line
between stable and unstable conditions.
i
I I I I I
I I I I
I
10 20 30 40
Temperature, °C
Figure 5-9. Neutral condition.
Stable Conditions
atmospheric lapse ratejsjejs than the
adiabatic rate (cools at less than 10 °CX 1000 m),
the air is stable and resists vertical motion. This is
rate] A rising parcel of warm air in
stableicondltions cools faster than its surroundings.
At some point it reaches the same temperature as
the surroundings and will not rise further. As with
instability, the degree of stability depends on the
difference between the atmospheric and adiabatic
rates (Figure 5-10).
Stable cgndkionsjire^ most likely^ to ocgur when
thjrgjdnittler gl^nQjyind_.on cloudy dayswuh~nb
strong surface heating,and at night. ~
Conditional Stability and Instability
In the previous discussion of stability and
instability, we have assumed the dry adiabatic rate
for a rising air mass. Very often, however, the air
mass reaches thif~dew point and begins to cool
more slowly, at thejetjdiabatic rate. This
change in the rate of cooling may change the con-
ditions of stability. Conditional instability-will ~
occur when the atmosphericJagsejateJs greater,,.
than the wet adiabatic rate but less thanjhe dry
fate. This^s^flltSstrated^h~Tigure 5-11. Stable con-
, ditions occur up to the condensation level and
unstable conditions occur above it. ~
5-11
I
M
I
Very
stable
i I I
10 20 30 40
Temperature, °C
Figure 5-10. Stable conditions.
2
I
i i i i i
Wet adiabatic
'ratc<&8C/km>
Dry adiabatic
ra\««(100C/km)
Environmental
lapse rate
(7"C/km)
I I I
10 20 30 '
Temperature, °C
Figure 5-11. Conditional
instability.
40
-------
Inversions
An inversion occurs when the temperature of the
atmosphere increases with altitude. An example of
the lapse rate for an inversion is depicted in Figure
5-12. In effect, anjnyersipjo_acts as a£^^_
ygdupgs the mixing
the air in the mixing layer is_usually nrirrmr1y_
staiBle^ HigETconcentrations of air pollutants are
often associated with inversions. The four major
types of inversions are caused by different
atmospheric interactions and can persist for dif-
ferent amounts of time.
Radiation
The radiation inversion is the most common form
,of surfacejnyersion and occurs when the earth's
surface cools rapiHly. As the earth cools, so does
the layer of air close to the surface. If_thjs_air_cogls_
to^jeniperature_belaw-that of the^irjtbove, it
becomes very stable, and the layer of warmer air
impedes any vertical motion (Figure 5-13).
Radiation inversions usually occurJn_the late
jiight-anch early morning under clearjkies, when
the cooling effect is greatest. Thte same conditions
that are conducive to nocturnal radiation inver-
sions are also conducive to instability during the
day. Diurnal cycles of daytime instability and
nighttime inversions are relatively common.
Therefore, th^effects of radiation inversions are
often shoriJived^^jbUuiants-tr-afiped by_the-invei>
signs are dispenedj)yjyjigorous vertical mixing
after the inversion breaks down. Figure 5^ 14
illustrates this diurnal cycle.
In some cases, however, the daily warming that
follows a nocturnal radiation inversion may not be
strong enough to erode the inversion layer. For
example, thick fog may accompany the inversion
and reduce the effect of sunlight the next day.
Under the right conditions, several days of radia-
tion inversion, with increasing pollutant concentra-
tions, may result. This situation is most likely to
occur in an enclosed valley, where nocturnal, cool,
downslope air movement can reinforce a radiation
inversion and encourage fog formation.
u
1 ! I
10 20 SO 40
Temperature, °C
Figure 5-12. Temperature
inversion.
Inversion layer
20 °C
12°C
Figure 5-13. Radiation inversion.
I I I I
Daytime
instability
I I I
Nocturnal
inversion
I I I
10 20 30 40
Temperature, °C
Figure 5-14. Diurnal cycle.
5-12
-------
In locations where radiation inversions are com-
mon and tend to be relatively close to the surface,
tall stacks that emit pollutants beyond the inver-
sion layer can help reduce surface-level pollutant
concentrations.
Subsidence
The subsidence inversion (Figure 5-15) is almost
always associated with^anticyclones (high pressure^
jystems). Recall that airinananticyclone~flescends
'and flows outward in a clockwise rotation. As the
air descends, the higher pressure at lower altitudes
compresses and warms it at the dry adiabatic rate.
Often this wanning occurs at a rate faster than the
' atmospheric lapse rate. The inversion layer thus
formed is often elevated^vcral^undjTdjneters
gboWtfie surface—dunng~tHe~dliyrAt night,
Because of lower air cooling, the base of a sub-
sidence inversion often descends, perhaps to the
ground. In fact, the clear, sunny days character-
istic of anticyclones encourage radiation inversions,
so that there may be a surface inversion at night
and an elevated inversion during the day.
Although the mixing layer below the inversion may
vary diurnally, it will never become very deep.'
Su^sid^ncejnyersions, unlike_radiation inver-
sions, Jast a relatively long time. TJus_is_becau§e
they_jare-associated with_both_the-semipennanent
anticyclones centered on each orpan and thf» slow-
moving migratory anticyclones moving-generally
west to east in the United States. When an
anticylone stagnates, pollutants emitted into a
mixing layer cannot be diluted. As a result, over a
period of daysTpollutant concentrations may rise.
TJxe_inost-severe_air pollution episodes in the
ynited_States h^y^pccurred^ither under a stag-
nant migratory anticyclone (New York, Penn-
sylvania) or under the eastern edge of the Pacific
semipermanent anticyclone (Los Angeles).
Subsiding air
Inversion layer
Top
Base
Mixing layer
Figure 5-15. Subsidence inversion.
5-13
-------
Frontal
i— -—^__
Lesson 4 mentioned frontal trapping^ the inversion
that is usually associated withTjotlTeold and warm
fronts. At the leading edge of either front, the
warm air overrides the cold, so that little vertical
motion occurs in the cold air layer closest to the
surface (Figure 5-16). The strength of the inversion
depends on the temperature difference between
the two air masses. Because fronts are moving
horizontally, the effects of the inversion are usually
short-lived, and the lack of vertical motion is often
compensated by the winds associated with the
frontal passage. However, when fronts become sta-
tionary, inversion conditions may be prolonged.
Advecrive
Advective inversions are associated with the
moves over a cold surface, convection cools the air
closest to the surface, causing a surface-based
inversion (Figure 5-17). This inversion is most
likely to occur in winter when warm air passes over
snow cover or extremely cold land.
Another type of advective inversion develops
when warm air is forced over the top of a cooler
air layer. This kind of inversion is common on the
eastern slopes of mountain ranges (Figure 5-18),
where warm air from the west overrides cooler air
on the eastern side of the mountains. Denver often
experiences such inversions. Both kindsjaf advec:
tiyejnversions are vertically^table_but may have
strong^ivinds under the inversion layer.
Inversion layer
Cold air
M
Warm
air
Figure 5-16. Frontal inversion
(cold front).
Warm air
Inversion layer
Cold ground
Figure 5-17. Surface-baaed advec-
tive inversion.
Figure 5-18. Terrain-based advec-
tive inversion.
5-14
-------
Review Exercise
Vertical mixing due to buoyancy is increased when
atmospheric conditions are
a. unstable.
b. neutral.
c. stable.
d. extremely stable.
On cloudy days with no strong surface heating,
atmospheric conditions are likely to be
a. unstable.
b. neutral.
c. stable.
d. extremely stable.
1. a. unstable.
3. Unstable atmospheric conditions most commonly
develop
a. on cloudy days.
b. on sunny days.
c. on cloudy nights.
d. on clear nights.
2. c. stable.
The cyclone, or low pressure system, will generally
encourage
a. unstable conditions.
b. neutral conditions.
c. stable conditions.
d. inversions.
3. b. on sunny days.
4. a. unstable conditions.
5-15
-------
5. This illustration depicts which stability category?
a. stable below 1000 meters
b. conditional stability above 1000 meters
c. neutral from 0 to 2000 meters
d. conditional instability above 2000 meters
2
3
I I I I
Wet adiabatic
rate (6°C/km)
adiabatic
(10°C/km)'
Environmental
lapse rate
(7°C/km)
I I I
10 20 SO
Temperature, °C
40
6. A(n)
acts as a lid on vertical air
movement.
5. d. conditional instability
above 2000 meters
7. When the earth's surface cools rapidly, such as
between late night and early morning under clear
skies, a(n) inversion is likely to occur.
6. inversion
8. When vigorous vertical mixing follows a radiation
inversion, pollutant plumes will
a. be trapped near the surface.
b. be dispersed away from their source.
7. radiation
9. The subsidence inversion is associated with
because it usually forms high above/at
the surface during the day. ' \
8. b. be dispersed away
from their source.
10. A subsidence inversion generally tends to last for a
relatively short/long period of time compared to a
radiation inversion.
9. anticyclones,
high above
11. Surface-based inversions associated with horizontal
air flow, such as when warm air moves over a cold
surface, are called inversions.
a. subsidence
b. frontal
c. advective
d. adiabatic
10. long
11. c. advective
5-16
-------
Stability and Plume Behavior
The degree of atmospheric stability and the
resulting mixing height have a large effect on
pollutant concentrations in the ambient air.
Although the discussion of vertical mixing did not
include a discussion of horizontal air
movement—or wind—you should be aware that
horizontal motion does occur under inversion con-
ditions. Pollutants that cannot be dispersed
upward may be dispersed horizontally by surface
winds.
The combination of vertical air movement and
horizontal air flow influences the behavior of
plumes from point sources (most commonly
industrial stacks). Lesson 7 will discuss plume
dispersion in greater detail. However, this lesson
will describe several kinds of plumes that are
characteristic of different stability conditions.
The looping plume of Figure 5-19 occurs in
highly unstable conditions and results from tur-
bulence caused by the rapid overturning of air.
JVVhile unstable conditions are generally favorable
foT~pollut^nT^ispersionpmonientarily high ground-
Jqv^lxojLrerm-aulms^^nj^^
downward to the surface.
10 20 TO 40
Temperature. °C
figure 5-19/ Looping plume.
5-17
-------
The fanning plume (Figure 5-20) occurs in
stable conditions. The subadiabatic lapse rate
discourages vertical motion without prohibiting
horizontal motibif,~aricrthe plume may extend
downwind from the source for a long distance.
Fanning plumes often occur in the early morning
during a radiation inversion.
I I
I i I
10 20 SO 40
Temperature, °C
Figure 5-20. Fanning plume.
The coning plume (Figure 5-21) is characteristic
of neutral conditions or slightly stable conditions.
It is likely to occur on cloudy days or on sunny
days between the breakup of a radiation inversion
and the development of unstable daytime
conditions.
Obviously a major problem for pollutant disper-
sion is an inversion layer, which acts as a barrier
to vertical mixing. The height of a stack in rela-
tion to the height of the inversion layer may often c
influence ground-level pollutant concentrations /*•
during an inversion.
10 20 SO 40
Temperature, °C
Figure 5-21. Coning plume.
5-18
-------
When conditions are unstable above an inver-
sion (Figure 5-22), the release of a plume above
the inversion results in effective dispersion without
noticeable effects on ground-level concentrations
round the source. This condition is known as
10 20 SO 40
Temperature. °C
Figure 5-22. Lofting plume.
If the plume is released just under an inversion
layer, a serious air pollution situation could
develop. As the ground warms in the morning, air
below the inversion layer becomes unstable. When
the instability reaches the level of the plume that is
still trapped below the inversion layer, the
pollutants can be rapidly transported.down toward
thejppettnd (Figure 5-23). This is known as
ration} Ground-level pollutant concentrations
vcan be very high when fumigation occurs. Suffi-
ciently tall stacks can prevent fumigation in most
cases.
i l l
M I
10 20 SO
Temperature, °C
40 LJ
Fieure 5-2$; Fumigation
** * **
5-19
-------
Thus far you have learned the basic meteoro-
logical conditions and events that influence the
movement and dispersal of air pollutants in the
atmosphere. Lesson 7 explores more fully the
behavior of pollutants around point sources, while
the next lesson discusses the instrumentation used
for meteorological measurement.
Review Exercise
1. The
plume is characteristic of neutral or
slightly stable atmospheric conditions.
a. fanning
b. looping
c. coning
d. lofting
2. What is the name of the plume depicted in this
illustration?
1. c. coning
3. Which plume is represented by this lapse rate and
stack height?
2. looping
I
1
t.. i-' *•* * JfA^- > *./s- . *^L
10
20 50 40
Temperature, *C
5. lofting
5-20
-------
4.
5.
6.
A fanning plume will occur when atmospheric condi-
tions are generally
a. highly unstable.
b. stable.
c. neutral.
The looping plume ran ranse ,. , , ground-
level concentrations of air pollutants.
If a plume is released just under/over an inversion
layer, a serious air pollution situation could develop.
3. lofting
4. b. stable
5. high
7. The plume in this drawing is an example of
a. coning.
b. looping.
c. fumigation.
d. lofting.
6. under
7. c. fumigation.
5-21
-------
-------
Lesson 6
Meteorological Instruments
Assignment
View the slide/tape presentation, Air Pollution Meteorology Instruments, which is
tape 409-6 and slides 409-6-1 through 409-6-77.
Assignment Topics
* Wind speed instruments
• Wind direction instruments
• Temperature instruments
• Instrument siting procedures
Lesson Goal and Objectives .
Goal
To familiarize you with the meteorological instruments that measure and record
the atmospheric variables of wind speed, wind direction, and temperature—
especially those useful for air pollution studies.
Objectives
Upon completing this lesson, you should be able to:
1. associate three meteorological instruments with the atmospheric variables they
measure.
2. recognize a wind speed instrument used for air pollution studies.
3. recognize a wind direction instrument used for air pollution studies.
4. describe the temperature sensor and recording system most useful for air
pollution studies.
5. identify the role of the transducer in an instrument system.
6. describe the location of a temperature gauge on an active stack.
6-1
-------
Supplementary Reading
Pages 6-3 through 6-38 in APTI Course 411 Air Pollution Meteorology-
Student Manual, "Meteorological Instruments" and "Exposure of Instruments"
by Ronald C. Hilfiker describe the instruments used by air pollution
meteorologists as well as provide some background on the development of
instruments.
Wilson, David J. and Dennett D. J. Netterville, "Influence of Downwind High-
Rise Buildings on Stack Design," Air Pollution Meteorology, APCA Reprint
Series, March 1977.
6-2
-------
Air Pollution Meteorology Instruments
Slide
Script
Selected Visuals*
1. No narration
FOCUS
2.
3.
Air Pollution
Meteorology
Instruments
4. In an industrialized society, the chemical makeup of the
atmosphere is constantly changing.
5. Winds, heat, and other natural processes carry air pollutants
from industrialized centers
•
6. to rural farm lands or into urban areas where they become
trapped;
7. or up into the global circulation pattern.
8. Meteorological instruments have been developed that measure
these natural processes.
9. Analyzing meteorological data helps forecast the routes and
destinations of air pollutants,
10. and helps predict the amount of pollutant matter that will
arrive at a new location. People working to solve air pollution
problems can use this data to evaluate applications for
locating new industrial sources and for changing existing
sources.
'illustrations included here, no live shots
6-3
-------
Slide Script
8 fe)
11. For air pollution meteorology studies, windjpeed, wind
direction, andQemperature are the most important
atmospheric variables to measure. They are responsible for the
transport and dispersion of pollutants. To accurately forecast
the fate of pollutants, we need to collect detailed information
about these variables.
12. In the past, many of the instruments used by meteorologists
were not capable of providing this detail.
IS. With increased concern about the impact of air pollutants on
our environment and health, these instruments have been
refined. Let's discuss the different instruments that measure
and record these atmospheric variables. All of these
instruments should, in general, be easy to operate, durable,
accurate, precise, and sensitive.
Selected Visuals
14. Instruments that measure wind speed are
Instruments that measure wind direction are
ind vanes. And,
instruments that measure air temperature arefeermumeters.
Air Pollution InitmmenU
tmm,m,l,
15. Once atmospheric energy is measured, it must be convened to
ener-gyjthat can be recorded so it can be analyzed. A
(transducer)performs this function.
16. Other instruments display information in a readable form.
These are recorders, and they record data continuously,
digitally, or magnetically.
Recorders
6-4
-------
Slide
Script
Selected Visuals
17. Wind speed can be measured by several different instruments
or aerodynamic sensors that fall loosely under the general
tenn/*anonometery"
18.
19.
20.
The most commonly used and preferred wind speed sensors
are "rotating anemometers." They revolve about a shaft that is
positioned either vertically or horizontally, and they come in
two designs: cup and propeller.
These rotating anemometers have several advantages that
make them desirable. First, there is a direct relationship
between cup or propeller rotation, and wind speed. In other
words, as the wind speed increases, the cups or propellers
rotate the movable spindle faster. ____
Second, rotating anemometers can measure a wide range of
wind speeds— from approximately 0.9 meters to 90 meters per
second. "~ — •""
Wind Speed Instruments
Rotating Anemometer*
Rotation oc wind Speed
Wind Speed Range
0.9 to 90
nctcn/Mcond
21. Third, once anemometers are calibrated, they measure
consistently over several years of operation and are unaffected
by changes in temperature, pressure, or humidity. Therefore,
they require little maintenance.
6-5
-------
Slide
Script
Selected Visuak
22. And finally, data can be transmitted accurately to a remote
location and recorded.
23. Previously, propeller and cup anemometers were constructed
to withstand extreme weather conditions and to provide
average information. Currently, their sensitivity is more
important.
24. Sensitivity is determined by the "starting threshold," which is
the wind speed required to start the anemometer turning. Low
starting speeds are possible because newer cups or blades are
made of lightweight aluminum or plastic. The most efficient
cup anemometers have 3 cups rotating around a vertical shaft,
while two or four blades are commonly found on lightweight
propeller anemometers.
25. Blade size can vary from 15 to 45 centimeters. Smaller blades
are used where high winds are likely to occur. Larger blades
are used when lower starting speeds are desired as in areas
where light winds might occur.
Starting Threshold oc Weight
26.
27.
A design consideration common to both propeller and cup
anemometers is the distance constant. It is the amount of
wind that must pass by before the instrument responds to a
certain change in wind speed. A lightweight instrument will
be more responsive than will a heavy one.
A more sensitive instrument will have a smaller distance
constant. This instrument will respond quickly to rapid
changes in wind speed. Therefore, the instrument with a
smaller distance constant is more desirable for air pollution
studies.
Dicta nee
Constant
-------
Slide
Script
Selected Visuals
28. Once the wind speed is measured by a rotating anemometer,
it must be transmitted to a recording device. This is achieved
with a transducer. The transducer converts rotational energy
*••» "35*1 »»
to easily transmittable electrical or mechanical energy.
29. Electrical transducers have a rotating shaft that drives a small
electrical generator. As the cups or propellers turn faster, the
generator's voltage output increases. This output remains
linear throughout the wind speed. Electrical transducers
usually provide a time plot of the wind speed. In other words,
the wind speeds for a certain time period can be recorded.
Electrical
Transducer
30. Anemometers with mechanical transducers are especially
useful when the desired output is total miles of wind passage
rather than a time plot of wind speed.
Mechanical
Transducer
31. Mechanical transducers simply count or accumulate the
number of turns of the cupwheel or propeller. The total
number of turns per unit time depends on the linear
displacement of wind or the "wind run" that occurs.
$2. Data is then transmitted and the output is recorded
continuously by event marker pens on strip charts. Strip chart
recorders respond rapidly to changing electrical or mechanical
outputs to produce a continuous record of instantaneous wind
speed with time. This example shows wind passage recorded
by a mechanical transducer.
racordcdby
•nictl
6-7
-------
Slide
Script
Selected Visuals
S3. Electrical output can also be recorded by data loggers. Data
loggers store instantaneous wind speed information in
computer memory for later use.
Memory Analog Data Storage
1
Do,
300
1 1
34.
35.
In addition to wind speed, another important wind factor
is needed for air pollution studies. This is "wind
direction." Wind direction is measured using a variety of
instruments, including one of the oldest, the "wind vane."
Many variations of the basic design have been marketed.
The flat plate, splayed vane, air foil, and bivane are
names of wind vanes referring to the tail design.
Wind determines the general direction that a pollutant
travels. Typically, a wind vane is mounted asymmetrically and
is free-turning on a vertical axis. It always points into the
wind.
Wind Direction Instruments
36.
37.
38.
As with wind speed instruments, construction material
determines the vane's primary use. Heavy vanes can measure
only average wind direction. Lightweight vanes are much
more sensitive to fine analyses of wind direction and
turbulence. Their tails are made of thin gauge aluminum or
plastic, or molded expanded polystyrene.
Of the wind vanes mentioned, the "bivane" is the most
efficient for air pollution studies. Bivanes swing up and down
as well as from side to side with changing wind direction,
measuring horizontal and vertical wind movements. Bivanes
are made of very light material and use low friction bearings
resulting in an extra-responsive instrument.
As with anemometers, there are important measurements of
wind vane sensitivity. The first is the starting threshold. It is
the minimum wind perpendicular to the tail surface that will
cause the vane to turn.
flat plan •yUy.d airfoil WV»IM
Bivane
p?
••
Ij — •
n
Starting
Threshold
a
Weight
6-8
-------
Slide
Script
Selected Visuals
The distance^onstant, is the length of wind that must pass the
vafieToTit to respond to a 50% change in direction. (Pause).
pnvtout rind SOX cfauu* MX •
40. And, th£damping ratio ip a measure of the vane's mechanical
resistance to moveinentTWind vanes with low ratios of about
0.6_gjye jthe best response to changes in wind direction.
Instruments with ratios higher than _LO underestimate the true
variability of the wind.
Damping Ratio
0.6 excellent
>1.0 undercrtroatc
true
vuUbUlty
41. As with anemometers, the output signal for vanes is produced
by a transducer and may be either mechanical or electrical.
42. The signal relays the wind vane's position to a recording
device. In this case the wind is blowing from the south.
43.
The recording device for a continuous record of wind
direction is the strip chart similar to the chart used for wind
speed. Strip chart recorders display all of the variations in the
positions of the wind vane. These positions are recorded in
degrees from true north.
6-9
-------
Slide
Script
Selected Visuals
44. There is one drawback to using a 360° strip chart. A gap
must be left in the electrical circuit. This gap is always
pointed north. When the wind blows from the north the
recorder pen wanders because the direction just east of north
is on one side of the chart, and the direction just west of north
is on the other side of the chart. The pen will swing from side
to side as the wind fluctuates around north.
45. To avoid the problem caused by the gap in the 360° circuit, a
540 ° chart was designed. Notice the new positions of north,
X ,'east, south, and west on the chart. This chart keeps the pen
trace in the central portion of the chart when wind is blowing
from the north and eliminates the pen's side-to-side swing.
46.
360* Strip Chert
5W Strip Chart
The last instrument discussed in this presentation is the
thermometer or temperature gauge. Thermometers sample
ambient air temperature. Ambient air temperature is one of
the important variables used to determine the large-scale .
stability of the atmosphere at a given location. \
Temperature Instruments
\
47. This information in turn helps predict the concentration and
duration of air pollution for this location.
48. Since a measure of the vertical structure of the atmosphere is
important, thermometers must be mounted at different
heights from the surface throughout the lower atmosphere.
These instruments must have an accurate system to measure
and transmit data.
u
49. The electrical thermometer is accurate and is widely used in
air pollution studies to measure temperature differences
between heights in the atmosphere.
6-10
-------
Slide
Script
Selected Visuals
50. Data from an electrical thermometer can be stored on a
recording device at the instrument or transmitted to any
location to be recorded. One recorder can store the
temperature differences for several thermometers covering an
entire area under study.
Temperature Recorder*
51. Unlike wind instruments, a rapid response rate from
temperature sensors is not desirable. Temperature tends to be
an air mass phenomenon, whereas wind tends to be localized
and can change rapidly.
52. All instruments, including those discussed here, must be sited
or placed correctly to get usable data. An instrument is sited
correctly when it receives accurate data about the area of
interest.
53. In other words, if you want to know the average wind
direction across a particular field, where would you locate a
wind vane—on the barn's roof or under its eaves? The correct
location—on the roof—is probably obvious. However, many
factors influence instrument siting.
P
54. Wind measurements that represent a fairly large geographic
area are often needed. The United States Environmental
Protection Agency has approved guidelines to be followed
when siting instruments.
55. The general rule is that the instrument's accuracy should not
be influenced by outside factors such as buildings, trees,
towers, or pavement.
Instrument
Siting
Guideline for Siting
6-11
-------
Slide
Script
Selected Visuals
56. Wind speed and direction instruments are usually sited
together. Instruments are sited in three general areas: on or
near a surface, on towers, and aloft.
57.
Since air flow around obstructions on the surface is turbulent,
a random location of the instrument would not give accurate
readings. Instruments must be placed above or outside the
turbulent "cavity" area produced by the obstruction.
58. In a field, an instrument should be placed at a distance 10
times the height of the tallest object at the edge of the field.
For example, if a tree is 10 feet tall, the instrument would be
placed 100 feet away from it.
59. For a building standing alone in open terrain, the site should
be one building height above the roof on the upwind side or
at least twice the building height above the roof on the
downwind side. For instruments sited away from a building,
the distance should be one building height away on the
upwind side.
•tad
60. When several buildings are clustered together, as in an urban
situation, the guidelines are no longer so simple. The siting
location depends on the information needed for the study.
The needed information could be about street level winds or
about general urban-wide winds. If uncertainty about siting
arises, then professional advice should be sought.
61. In a valley or on rough terrain, the influence of local effects
such as channeling and trapping on general wind flow
patterns must be determined. Then a decision must be made
whether to sample the local effects, the larger pattern,—or
both—for purposes of the study. Siting procedures for hills
and ridges are as difficult as those for a city since they
produce similar flow patterns.
I
I
v/
6-12
-------
Slide
Script
Selected Visuals
62.
63.
Temperature instruments located near the earth's surface must
be shielded from sources of heat, such as concrete parking lots
and buildings, and out of direct light from the sun.
Otherwise, temperature readings may be too high. Therefore,
thermometers are usually encased in white louvered
containers.
If instruments must be sited on closed stacks or open towers,
the instruments should not be influenced by them.
Instruments should never be located within 2 to 5 stack
diameters of the top of an active stack. A location on top of a
tower above the turbulent cavity will generally give accurate
readings.
flk
p\
64. When locating any instruments on the side of a tower or
stack, they should be placed out on a boom. On a tower they
should be out by one side length. On a stack they should be
out twice the stack diameter.
65. Wind vanes should be put on a boom that faces into the most
frequent wind direction.
66. Wind and temperature instruments are placed in a different
manner. The spacing between instruments is important for
proper readings. Wind sensors are spaced logarithmically
apart because wind speed is approximately logarithmic with
height. Temperature sensors are placed vertically 13 meters or
more apart.
6-1S
-------
Slide
Script
Selected Visuals
67. To obtain pollution information about the general circulation
pattern, instruments are sited aloft in balloons, aircraft, and
rockets. Balloon launchings should be in areas free from
obstructions.
.
68. Instruments on aircraft should be located at least two feet
forward of the wingtips. On helicopters, the forward tip of the
skids is the most accurate location, provided the helicopter is
moving forward fast enough to project downwash behind the
sensor. If recorders are located inside the aircraft, mounting
them in plastic or sponge rubber will reduce vibrations.
69. Most recorders for airborne instruments, however, are
remotely located. If recorders are part of a radar or radio
tracking equipment system, this equipment should be located
on top of a hill with few or no obstructions on the horizon.
70. In summary, correct instrument siting is crucial to obtain
usable data for air pollution studies. Whether to site near the
surface, on stacks or towers, or aloft depends on which
atmospheric phenomena are most useful to the study.
71. Anemometers, vanes, and thermometers as well as other
instruments used to sample atmospheric variables have been
modified for air pollution study purposes. These instruments
are an optimum combination of sensitivity, durability,
accuracy, preciseness, simplicity, and convenience.
72. Air pollution forecasters monitor and record atmospheric
conditions to anticipate pollution buildup and to predict areas
where that buildup is most likely to occur.
73. This information helps air pollution control agencies decide
where to locate new industrial sources and which geographical
areas may be in danger from overpollution.
6-14
-------
Slide
Script
Selected Visuals
74. The next lesson discusses the dispersion of pollutant plumes
through the atmosphere and their effect on the environment.
Coming next...
75. Credit: Crew
Air Pollution Meterotogy
Instruments
Technical Content: Donald BulUrd
Instructional Design: Marilyn Peterson
Graphic*: Betty Huber
Photography/Audio: David Churchill
Narration: Rick Palmer
76. Credit: Northrop
Lecture development
and production by:
Northrop Services Inc.
under
EPA Contract No. 68-02-2374
77. NET
Northrop
Environmental
Training
6-15
-------
Review Exercise
For questions 1 through 3, match the appropriate
meteorological instrument with the atmospheric variable
that it measures.
1. anemometer a. wind direction
2. wind vane b. wind speed
S. thermometer c. temperature
4. From the following meteorological instruments, choose
an anemometer.
a. b. c. d.
1. b. wind speed
2. a. wind direction
S. c. temperature
5. From the following meteorological instruments, choose
a wind vane.
a. b. c. d.
4. c.
6. A transducer is required in an anemometer system to
a. change rotational motion into an electrical signal.
b. record wind information.
c. record the time the instrument is operating.
d. none of the above
5. d.
7. True or False? An aspirated temperature gauge that
uses electrical resistance to measure temperature is
the most useful in air pollution studies.
6. a. change rota-
tional motion into
an electrical signal.
6-16
-------
8. A temperature sensor
a. must always be located next to the wind sensors.
b. should never be mounted directly on stacks.
c. is not necessary for air pollution studies.
d. measures total solar radiation through temperature
readings.
7. True
8. b. should never be
mounted directly on
stacks.
6-17
-------
-------
Lesson 7
Plume Dispersion
Assignment
Read pages 7-1 through 7-16 of this guidebook.
Assignment Topics
• Stack height and plume rise
• Atmospheric dispersion estimates
• Topographical effects on plumes
Lesson Goal and Objectives
Goal
To introduce you to the effects of stack height and plume rise on plume dispersion,
some factors involved in making dispersion estimates, and the influences of
topography on wind flow and plume dispersion.
Objectives
Upon completing this lesson, you should be able to:
1. define plume rise.
2. define effective stack height.
5. state three assumptions necessary for a plume to be Gaussian.
4. recognize two stack and effluent characteristics responsible for plume rise.
5. recognize Briggs' plume rise formula and be able to identify the terms
included in it.
6. recognize the units that stack effluent is expressed in.
7. state the relationship of momentum and buoyancy to plume rise.
8. recognize the statistical distribution and assumptions about it used by Turner
to define plume spread.
9. describe four topographical categories and their effects on the atmosphere.
7-1
-------
Introduction
Smoke and other pollutants, called effluent, enter
the atmosphere in a number of ways as shown in
Figure 7-1. For example, the wind blows dust off
of the ground. When swamps rot, methane is
released. When garbage is burned, foul-smelling
smoke drifts downwind. An operating factory will
emit smoke from its stacks. There are many other
examples of pollutant release.
Figure 7-1. Dispersion mechanisms.
One method of pollution release has received
more attention than any other; that of pollution
released from smoke stacks. Smoke stacks come in
all sizes—from a small pipe on a building's roof to
a giant stack 1500 feet high (Figure 7-2). Their
function is to release pollutants at an elevation
higher than the surface. The object of the release
height is to aid in dispersing the pollutant into the
atmosphere. An accepted fact is that taller stacks
disperse pollutants better than shorter stacks.
Figure 7-2. Effluent release.
7-2
-------
Plume Rise
As you observe smoke from a stack, you will notice
that the smoke usually rises above the top of the
stack (Figure 7-3). The distance that the plume
rises above the stack is called/ume^ rise. It is
^
actually calculated as the distance to the
imaginary centerlinejrf thej>lume rather than to the
upper-orJower edge of thejglume. Plume rise, Ah,
depends on the stack's physical characteristics and
on the effluent's (stack gas) characteristics. For
example, the effluent characteristic of stack gas
temperature in relation to the surrounding air
temperature is more important than the stack
characteristic of height. The difference in
temperature between the stack gas and ambient
air determines plume density, and density affects
plume rise. Therefore, smoke from a short stack
could climb just as high as smoke from a taller
stack.
Momentum and Buoyancy
Stack characteristics are used to determine
momentum, and effluent characteristics are used
to determine buoyancy (Figure 7-4). Momentum of
the effluent is initially provided by the stack. It is
determined by the speed of the effluent as it exits
the stack. As momentum carries the effluent out of
the stack, atmospheric conditions begin to affect
the plume.
The condition of the atmosphere, including the
winds and temperature profile along the path of
the plume, will largely determine the plume's rise
(Figure 7-5). As the plume rises from the stack,
the wind speed across the stack top begins to tilt ...
the pTuxneT Wind^peejjisually^icrejLsesjwith__
continues upward the stronger winds tilt the plume
even farther. This process continues until the
plume may appear to be horizontal to the ground.
The point where the plume looks level may be a
considerable distance downwind from the stack.
Wind speed is important in blowing the plume
over. The stronger the wind, the faster the plume
•-• "— '— •* ..... ,__ : ft_- —— j_-
will tilt over.
-I- Plume nse -.—
fv^^Pr
—^-^^^e^
Figure 7-3. Plume rue.
Momentum
Figure 7-4. Momentum and buoyancy.
Figure 7-5. Wind flow affeca plume
7-S
-------
' \
/" -- "x
(•Pliiinejjjioyancyjjs a function of temperature.
InFigure 7-6, when the effluent's temperature, Tf,
is warmer than the atmosphere's, T., the plume
will be less dense than the surrounding air. In this
case, the density difference between the plume and
air will cause the plume to rise. The greater the
temp^raturejjjfierence, AT, thgvir^>jit_hunyant fhg
'plumerSsTqng^as the temperature of the pollutant
remains warmer than^ffie^atoo^heie^the jjlume
distance downwind
where the pollutant cools to atmospheric
temperature may be quite far from its original
release point.
Buoyancy is taken out of the plume by the same
mechanism that tilts the plume over— the wind. As
shown in Figure 7-7, mixing within the plume
pulls atmospheric air into the plume interior. The
faster the wind speed, the faster this mixing with
outside air takes place. This mixingjs_cjIledL.
wind "robs" the plume of its
buoyancy very quickly so that on windy days the
plume does not climb very high above the stack.
Formulas
Many individuals have studiecl plume rise over the
years. TJie^nQSLXomrnon plume rise formulas are
those 4>£Gary A. BnggS} One of these is included
in Figure 7-8. PIume~rise formulas are to be used
on plumes with temperatures greater than the
ambient air temperature.
x(
Ah=1.6FK tf'xK
Where:
the stack
distance from the source
Figure 7-8. Briggs' plume rise formula.
As we said, plume rise formulas determine the
imaginary centerline of the plume. Plume rise is a
linear measurement expressed usually in feet or
meters (Figure 7-9). The centerline is where the
greatest concentration of pollutant occurs. Several
techniques are used to calculate pollutant concen-
trations away from the centerline. The next section
covers one technique.
7-4
Figure 7-6. Temperature affects
plume buoyancy.
Figure 7-7. Wind speed affects
entrainment.
Plume rise = meters
Figure 7-9. Plume rise formulas deter-
mine plume centerline,
i but not edges.
-------
Review Exercise
1. True or False? Plume rise is the height that pollutants
rise above a stack. This distance, Ah, is to the edges of
the plume.
2. Plume rise from a stack is due to
a. heat and type of pollutant.
b. momentum and buoyancy.
c. the composition of the stack.
d. none of the above
1. False
Plume rise formulas like those developed by
Briggs are to be used on
a. plumes that are colder than the ambient air.
b. plumes that are hotter than the ambient air.
c. plumes that are the same temperature as the
ambient air.
d. none of the above
2. b. momentum and
buoyancy.
4. How are plume rise calculations expressed?
a. grams/second
b. meters/second
c. grams/meter3
d. meters
3. b. plumes that
are hotter than
the ambient air.
5. The momentum term in plume rise equations
generally involves
a. ambient air temperature, wind speed, stack gas
temperature.
b. wind speed, stack gas temperature, stack opening
diameter.
c. stack gas velocity.
d. stack outside radius.
4. d. meters
6. True or False? Buoyancy terms in plume rise
equations always depend on the difference between
stack gas temperature and the ambientjur
temperature.
5. c. stack gas
velocity.
7-5
-------
7. Atmospheric air pulled into the plume interior by
mixing within the plume is called ,__ The
speed with which the process occurs is directly propor-
tional to
6. True
7. entrainment
wind speed.
Dispersion Estimates
The methods suggested by Briggs or any other
plume rise investigator calculate only the
imaginary centerline of a plume. These methods
do not provide any information as to the ground
level concentration estimates of pollutant down-
wind (Figure 7-10). Plume rise determination aids
only in fixing the distance from the ground of the
area of the plume having the largest pollutant con-
centration. D. B. Turner, in his Workbook of
Atmospheric Dispersion Estimates (as well as other
modelers), has used the Gaussian or normal
distribution (Figure 7-11) to identify the variation
of the pollutant concentration away from the
center of the plume. This distribution of
atmospheric variables such as wind speed and
temperature is time averaged and may not be used
for instantaneous "pictures" of the plume. Tune
averages of 10 minutes to one hour are commonly
used. Then, and only then, can the pollutant con-
centration be assumed to be normally distributed
in the plume.
The plume centerline distance from the ground,
called effective stack height, H, is determined by
adding plume rise, Ah, to the physical height of
the stack, h.. Knowing this centerline distance
from the ground allows the calculation of the
amount of pollutant that will reach the ground
(Figure 7-12). This amount of pollutant is deter-
mined from the Gaussian distribution. Concentra-
tions are at maximum at the centerline and
decrease toward the edges of the plume. Graphs
are available that give the appropriate plume
size factors for distances downwind from the
,——•„-
.,-. Centerline
;• Concentration (x) =
jnicrograms per cubic
.meter (/ig/m§)
Figure 7-10. Ground-level concentra-
tion (x) not determined
by plume rise formulas.
-3 -2 -la T -I-Iff + 2 +S
I = mean (maximum concentration)
a-standard deviation symbol
Figure 7-11. Gaussian distribution.
H« effective Rack height
i conceiiu atioo mean
Figure 7-12. Effective stack height.
7-6
-------
U/l /C
JlA 0-3
stack. These graphs (Figure 7-1S) are logarithmic
in scale and consider horizontal and vertical
spreading only. The plume is not allowed to
stretch or thin out in the downwind direction.
The A through F factors are atmospheric stability
indicators. The basic calculation formulas allow
the plume edge to "bounce" off or reflect from the
ground without losing any pollution. In fact, the
material in the plume must be maintained for the
Gaussian distribution to be used.
If only ground-level concentrations underneath
the centerline of the plume are desired, the basic
formula will reduce appropriately and fewer fac-
tors will be required (Figure 7-14). If there is no
smoke stack and the smoke is generated at the
ground, as in a burning garbage dump, then a
simple formula may be used for calculations.
Plume Size Factors
and a1Ljrejunctions ofjymdjspeeJL cloud cover,
and surface heating by the sun. Table 7-1 relates
tKese factor^ to lines on the plume size graphs used
to determine the size of the plume with distance
downwind. Note that A, B, and C refer to daytime
with unstable conditions; D refers to overcast or
neutral conditions at night or during the day.
£ and F refer to nighttime, stable conditions and
are based on amount of cloud cover.
For computation purposes, the Gaussian
distribution simplifies concentration variations
within a plume. Deposition and transformation of
pollutants are ignored by the Gaussian distribution
presented here.
10.000
Distance downwind
(kilometer*)
100
10,000
1.0
Vertical
diipenion
0.1
Distance downwind
(kilometen)
100
Figure 7-13. Plume lize graph* (log
scales).
7-14. Appropriate Gaussian formulas
-------
Table 7-1. Key to stability categories.
Surface wind
Speed (at 10 m)
(m/iec)
<2
2-3
S-5
5-6
>6
Insolation
Strong
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
D
Slight
B
C
C
D
D
Night
£ 4/8 low
cloud*
—
£
D
D
D
£3/8
cloud
—
F
£
D
D
•Thinly overcast
Note: Neutral Class, D, should be assumed for overcast conditions during
day or night.
The Gaussian distribution, as well as plume rise,
depends on the ground being approximately flat
along the path of the plume (Figure 7-15). Uneven
terrain caused by valleys, hills, and mountains will
affect the dispersion of the plume so that the
Gaussian distribution must be modified. These
modifications are exponential and depend on the
earth's topography. Terrain features affect
atmospheric wind flow and stability. The various
categories of topography are discussed in the
following section. For information on the use of
exponents in the Gaussian distribution equation,
you can refer to the EPA User's Guides for specific
air quality models.
Figure 7-15. Flat terrain for Gaussian
distribution.
7-8
-------
Topography
The physical characteristics of the earth's surface
are referred to as terrain features. As shown in
Figure 7-16, these features can be grouped into
four categories: flat, mountain/valley, land/water,
and urban.
Figure 7-16. Topography.
Topographical features affect the atmosphere in
two ways as shown in Figure 7-17: thermally
(through heating) and geometrically (also known
as mechanically). The thermal effect is caused by
differential heating. Objects give off heat at dif-
ferent rates. For example, a grassy area will not
give off as much heat as a cement parking lot.
The geometric effect is caused by different sizes
and shapes of objects. For example, a building
affects wind differently than trees affect it.
Figure 7-17. Topographical effects on
heat and wind flow.
7-9
-------
Flat
Although very little of the earth's surface is com-
pletely flat, some terrain is called flat for
topographical purposes. Included in this category
are oceans, even though they have a surface tex-
ture; and gently rolling features on land (Figure
7-18).
The geometric effect of flat terrain is limited to
the amount of roughness of either natural or man-
made features that are on the ground. Table 7-2
contains some representative roughness lengths.
Note the variation of wind with height over dif-
ferent size elements. These features induce a fric-
tional effect on the wind speed and result in the
well-known wind profile with height (Figure 7-19).
The thermal effect of flat terrain is due to
natural or manmade features. For example, water
does not heat very much but concrete heats excep-
tionally well. The concrete then releases large
amounts of heat back into the air; water does not.
Air rises over heated objects in varying amounts
(Figure 7-20). Rising air is called convection.
Figure 7-18. Flat terrain.
t
+rf
*c
Wind speed—
Figure 7-19. Wind profile.
Figure 7*20. Differential heating.
7-10
-------
Table 7-2. Roughness factors for rarious surfaces.
Type of surface
Fir forest
Citrus orchard
Large city (Tokyo)
Com
*u».i*35 on sec"1
Ui.i-lSScmsec"1
Corn
a..o = 29 cm sec"1
m.o-212 cm sec"1
Wheat
Ui.»s»190 cm sec"1
Uj.r = 384 cm sec"1
Grass
u».o"148 cm sec"1
u». o = 34S cm sec"1
u2. o—622 cm sec"1
Alfalfa brome
uj.» = 260 cm sec"1
uj.j = 625 cm sec"1
Grass
Smooth desert
Dry lake bed
Tarmac
Smooth mud flats
h(cm)
555
335
300
220
60
60-70
15.2
5-6
4
2-3
z.(cm)
283.0
198.0
165.0
127.0
71.5
84.5
74.2
23.3
22.0
15.4
11.4
8.0
2.72
2.45
0.75
0.14
0.32
0.03
0.003
0.002
0.001
Author
Baumgartner (1956)
Kepner et al. (1942)
Yamamoto and Shimanuki
(1964)
Wright and Lemon (1962)
Wright and Lemon (1962)
Penman and Long (1960)
Deacon (1953)
Tanner and Pelton (1960b)
Rider et al. (1963)
Rider (1954)
. Deacon (1953)
Vehrencamp (1951)
Rider et al. (1963)
Deacon (1953)
•The subscript gives the height (in meters) above the ground at which the
wind speed, u, is measured.
7-11
-------
Mountain/ Valley
The second type is mountain/valley terrain. This
combination shown in Figure 7-21 is also called
complex terrain.
All air pollution investigators agree that
atmospheric dispersion in complex terrain areas
can be very different from, and much more com-
plicated than, that over flat ground. The problems
with terrain have been investigated in fluid model-
ing labs and by field experiments.
The geometric effect of mountain/valley terrain
is invariably connected to the size, shape, and
orientation of the features. The numerous com-
binations of mountain/valley arrangements include
a single mountain on flat terrain, a deep valley
between mountains, a valley in flat terrain, or a
mountain range. However, as in Figure 7-22, air
tends to flow up and over an obstacle in its path
with some air trying to find its way around the
sides. If an elevated temperature inversion caps the
higher elevation, then the air must try to find its
way around the sides of the mountain. If the air
flow is blocked, then trapping or recirculation of
the air occurs. At night, hills and mountains
induce downslope wind flow because the air is
cooler at higher elevations. Usually downslope
winds are light. However, under the right condi-
tions, the wind speeds may be in excess of 45
meters per second (100 miles per hour).
The thermal effect of mountain/valley terrain is
also connected to the size, shape, and orientation
of the features. Again, while every combination of
mountain/valley effects cannot be explained, some
generalizations can be illustrated. Moun-
tain/valleys heat unevenly because of the sun's
motion across the sky (Figure 7-23). In the morn-
Light
Daifc
Ught
Figure 7-21. Mountain/valley (com-
plex) terrain.
Figure 7-22. Wind flow over and
around mountains
(geometric effect).
p.m.
Dark
Light
Figure 7-23. Thermal effect in ralley (air rue* when land if lighted).
7-12
-------
ing, one side of a mountain or valley is lit and
heated by the sun. The other side is still dark and
cool. Air rises on the lighted side and descends on
the dark side. At midday both sides are "seen" by
the sun and are heated. The late afternoon situa-
tion is similar to the morning. After dark, the air
drains down into the valley from all higher slopes.
The other heating effect is due to land features.
Tree covered areas will heat less than rocky slopes
or bare ground. A detailed knowledge of specific
terrain areas is important to interpret the complex
terrain's effect.
Land/Water
The third type of terrain is a land/water interface
(Figure 7-24). Partly because of convenience, a
number of large cities are located next to bodies of
water. The land and water not only exhibit dif-
ferent roughness characteristics but different
heating properties. The air flow and thus plume
dispersion and transport can be very difficult to
predict.
The thermal properties of land and water are
radically different. Land and objects on it will
heat and cool at various rates. We have seen the
effects of land's thermal properties above.
However, water heats and cools relatively slowly.
Water temperatures do not vary much from day-
to-day or from week-to-week. Water temperatures
follow the seasonal changes, being delayed by as
much as 60 days. For example, the wannest ocean
temperatures are in early fall, and the coolest
ocean temperatures are in late spring.
As the sun shines on the water surface, evapora-
tion and some warming take place. The thin layer
next to the air cools due to evaporation and mixes
downward, overturning with the small surface
layer that has warmed. This mixing of the layer
dose to the surface keeps the water temperature
relatively constant.
The warmer daytime temperatures over the land
cause the air to become less dense and rise. The
cooler air over the water is drawn inland and
becomes the well-known Seabreeze. At night, the
Figure 7-24. Thermal effect at
land/water interface.
7-13
-------
air over the land cools rapidly, and the air over
the water is wanner. A return flow called the land
breeze is created. The wind speeds in a land
breeze are light; whereas the wind speeds in a
Seabreeze can be quite fast.
As shown in Figure 7-25, the roughness features
of land and water are also different. The water
appears to be quite smooth to the flow of air. As
the wind speed increases, the water surface is
disturbed, and waves form. With waves induced by
strong wind the water surface is no longer as
smooth as it was with a light wind. However, water
is still smoother than most land features. Because
of the change from relatively smooth water to
rougher land, the air flow changes direction. The
amount of direction change depends on the
amount of roughness change.
Urban
Urban areas exhibit all of the characteristics of
flat, mountain/valley, and land/water terrains.
Also urban areas add tremendous amounts of
manmade pollution to the atmosphere.
The thermal effect of the urban area is quite
pronounced (Figure 7-26). Building materials such
as brick, concrete, and macadam absorb and hold
heat efficiently. After the sun goes down, the
urban area continues to exchange heat between
buildings, etc. Heat is transmitted upward to
create a dome over the city. It is called the heat
island effect. The city emits heat all night. Just
Figure 7-25. Mechanical effect at
land/water interface.
Figure 7*26. Thermal and mechanical effect! of due*.
7-14
-------
when the urban area begins to cool, the sun comes
up again. Generally, the city areas never revert to
stable conditions because of the continual heating.
The geometric effect of the urban area is much
like complex terrain. The buildings, separately
and collectively, offer a mountain shape to the air
flow. The higher the buildings in midtown, the
more the air must go up and over. Also, the street
areas channel and direct the flow in intricate ways.
Just as the mountain/valley terrain could not be
accurately predicted, the urban areas defy
accurate description.
Review Exercise
1. True or False? Effective stack height is determined by
adding plume rise to the physical height of the stack.
2. Turner, in the Workbook of Atmospheric Dispersion
Estimates (WADE), uses,a distribution called the
a. geometric
b. weibull
c. Gaussian
d. Poisson
1. True
S. One of the assumptions of the distribution that
Turner uses in his Workbook is that the
a. source continuously emits pollutants.
b. terrain must be log-normally distributed.
c. distribution in the horizontal direction is bimodal.
d. pollutant falls out of the plume immediately after
release from the source.
2. c. Gaussian
For 4 through 6, match the type of atmospheric stability
to the appropriate Pasquill-Gifford stability categories.
4. unstable a. E-F
5. neutral b. A-B-C
6. stable c. D
3. a. source con-
tinuously emits
pollutants.
7-15
-------
The sigma y and sigma z used in the Gaussian
dispersion formulas are defined as
a. atmospheric pressure at points y and z.
b. standard deviations of pollutant concentration in
the horizontal and vertical directions.
c. temperature variations in the y and z directions.
d. none of the above.
4. b
5. c
6. a
8. Which of the following is typical of a pollution
concentration calculation?
a. Q = 75 ng/m*
b. /3=150/d/m3
c. 7= 100 /tg/ms
d. x=100
7. b. standard
deviations of pol-
lutant concentration
in the horizontal
and vertical
directions
9. The four general categories of terrain are:
a. marsh, flat, complex, rolling.
b. flat, mountain/valley, urban, complex.
c. flat, mountain/valley, land/water, rural.
d. flat, mountain/valley, land/water, urban.
8. d. =
/ig/ms
10. What effects do topographical features have
on the atmosphere?
9. d. flat, mountain/
valley, land/water,
urban.
10. thermal,
geometric
7-16
-------
Lesson 8
Introduction to the
Guideline on Air Quality Models
Assignment
Read pages 8-1 through 8-5 of this guidebook.
Assignment Topics
• Regulatory programs
• Air quality model recommendations
• Data requirements
• Model calibration and validation
• Model categories
Lesson Goal and Objectives
Goal
To familiarize you with the Guideline on Air Quality Models, and general
categories of air quality models available.
Objectives
At the end of this lesson, you should be able to:
1. name the three air quality programs that evolved from the 1977 amendments
to the Clean Air Act.
2. name the document that summarizes the essentials of three air quality
programs.
3. choose the reason why the Guideline on Air Quality Models was written.
4. identify the section of the Guideline on Air Quality Models that recommends
specific air quality models.
5. identify the four general categories of air quality models.
8-1
-------
Introduction
Air quality modeling is required by law. Congress mandated the use of modeling in
the 1977 Clean Air Act Amendments. Three air quality programs evolved that
require modeling to estimate the impact of air pollution on the environment. They
are Control Strategy Evaluation, New Source Review, and Prevention of Significant
Deterioration. Each of these programs have supporting documents containing
specific air quality modeling requirements. One document summarizes the essential
points of all three programs. It is the Guideline on Air Quality Modeling,
EPA 450/2-78-027. The Guideline was written to promote consistency among
modelers so that all air quality modeling activities would be based on the same
recommendations.
Guideline Topics
The Guideline has six sections. It covers air quality models including their purpose,
development, use for different regulatory programs, data requirements, and valida-
tion/calibration. Recommended air quality models are summarized in an appen-
dix. Our discussion will begin with Section 3, "Requirements for Concentration
Estimates."
Section 3: Requirements for Concentration Estimates
Section 3 covers Control Strategy Evaluation, New Source Review, and Prevention
of Significant Deterioration. In Control Strategy Evaluation, emission limits should
be based on concentration estimates for the averaging time that results in the most
stringent control requirements. An air quality model (AQM) is used to determine
which averaging time—annual, 24-hour, 8-hour, 3-hour—causes the standards to
be exceeded. For example, if the annual averaging time results in the largest con-
centrations, then it would be chosen for emission control limits.
A new source or major modification of a source that would increase allowable
emissions by 50 tons per year, 500 pounds per day, or 100 pounds per hour should
have an air quality analysis made. An air quality model is used to determine if the
source will cause a violation of a National Ambient Air Quality Standard. Also an
AQM is used if a proposed new source or an addition to an existing source might
make air quality that is already bad, worse.
In the PSD program, ah* quality models should be used in all significant
deterioration evaluations. Allowable increments or these maximum allowable
increases in pollutant concentrations for sulfur dioxide and paniculate matter are
specified in the Clean Air Act Amendments of 1977. A reprint of Section 3 is
included in the next lesson.
8-2
-------
Section 4: Air Quality Models
Section 4 of the Guideline recommends air quality models for a variety of applica-
tions: point and mukisource models for sulfur dioxide (all averaging times), models
for carbon monoxide, models for nitrogen dioxide, and models for special situa-
tions. The air quality models recommended are used in the three programs men-
tioned above.
Section 5: Data Requirements
Section 5 discusses source data, meteorological data, receptor siting and
background air quality as they apply to specific air quality models. Each of these
data bases cannot be considered in isolation. Together, over time, they can provide
valuable information when planning both New Source Reviews and Control
Strategy Evaluations.
Section 6: Model Calibration/Validation
Section 6 discusses the methods for validating or calibrating air quality models.
Any application of an air quality model may have shortcomings that cause
estimated concentrations to be in error. Validation is the process of comparing
observed air quality data with model estimates. Calibration is the process of chang-
ing the model so that the model estimates more closely agree with observed air
quality data. Specific recommendations about calibrating short-term models are
discussed.
Section 7: Appendix
The appendix lists seven models: AQDM, APRAC-1A, CDM, RAM, CRSTER,
TCM, and TEM. It also itemizes seventeen characteristics of each model. The
characteristics enable the model user to select an appropriate model for a specific
application.
Model Categories
Air quality models can be categorized into four general classes: empirical,
numerical, physical, and Gaussian (or distributional) models.
An empirically-derived air quality model is based on the analysis of source data,
meteorological data, and air quality data. Given a set of observations from air
monitoring and meteorological stations, statistical techniques are used to calculate
relationships among variables. Usually, regression and spectral analysis techniques
are used. Empirical models are not applicable beyond the range of conditions
included in the data used in their development and improvement.
A numerical air quality model uses mathematical equations to simulate the
effects of turbulence, chemical transformations, deposition, etc., on air pollution
transport and dispersion. Numerical models attempt to duplicate atmospheric pro-
8-3
-------
cesses. They are appropriate for multisource applications involving reactive
pollutants. Since these models usually require complex equations in their simula-
tions and large computers to solve the complex formulations, they are not generally
recommended for use.
Physical models are used to investigate pollutant dispersion for situations too
complicated to be simulated by mathematical techniques. The wind tunnel and
water tank are structures where realistic mock-ups of situations are tested. One
advantage of physical modeling is that years of field study time can be simulated in
a matter of weeks. Another advantage is that they aid in improving mathematical
models by filling hi knowledge gaps hi current models.
Some examples of diffusion studies using physical modeling are: simulation of
power plant plumes, effects of complex terrain, and effects of roughness on
transport and dispersion of pollutants.
Gaussian models or other models that use the Gaussian distribution for their
basis are among the most widely used ah* quality models. They are generaly con-
sidered to be state-of-the-art techniques for estimating the impact of nonreactive
pollutants (one that is not changed by some process into a different substance).
Although numerical models may be more appropriate than the Gaussian for reac-
tive pollutants, Gaussian are more widely used. Gaussian models also simulate the
effect of chemical and physical processes on pollution transport and dispersion
using simpler algebraic expressions than required for the numerical models. The
air quality models recommended by USEPA for regulatory purposes are all Gaus-
sian models.
Review Exercise
1. Name the three air quality programs that evolved
from the Clean Air Act Amendments of 1977.
The document that summarizes the essentials of the
three air quality programs is the
a. Guideline on Air Quality Programs,
EPA 450/2-78-027.
b. Guideline on Air Quality Program Summaries,
EPA 450/2-78-027.
c. Guidelines on Air Quality Summaries,
EPA 450/2-78-027.
d. Guideline on Air Quality Models,
EPA 450/2-78-027.
• New Source
Review
• Control Strategy
Evaluation
• Prevention of
Significant
Deterioration
8-4
-------
3. What was the reason the USEPA wrote the document
EPA 450/2-78-027?
a. Air quality modeling should be consistently
applied.
b. Directions on how to repair air quality models
weren't available.
c. Directions on how to write an air quality model
weren't available.
d. none of the above
2. d. Guideline on Air
Quality Models,
EPA 450/2-78-027.
4. True or False? The section of EPA 450/2-78-027 that
recommends specific air quality models is Section 4
called "Air Quality Models."
S. a. Air quality
modeling should be
consistently applied.
5. What are the four general categories of air quality
models?
4. True
For each of the following, match the category of air
quality model with its definition.
6. empirical
7. numerical
8. physical
9. Gaussian
a. investigate pollutant dispersion
for complicated situations
through simulation
b. derived from an analysis of
source data, meteorological data,
and air quality data
c. use complex equations to
simulate the effects of tur-
bulence, chemical transforma-
tions, deposition, etc., on pollu-
tant transport and dispersion
d. techniques for estimating the
impact of nonreactive pollutants,
and use simple algebraic expres-
sions for reactive pollutants
5. • empirical
• physical
• numerical
• Gaussian
6. b
7. c
8. a
9. d
8-5
-------
-------
Lesson 9
Introduction to Meteorological
Requirements for State Implementation
Plans, New Source Review, and
Air Quality Modeling
Assignment.
This lesson contains reading from Section S and 5 of the Guideline on Air Quality
Models, EPA 450/2-78-027. These are pages 9-1 through 9-12 in this Guidebook.
Assignment Topics
• Requirements for regulatory programs
• Meteorological data requirements
Lesson Goal and Objectives
Goal
To familiarize you with the meteorological requirements of State Implementation
Plans (SIPs), New Source Review (NSR), and Air Quality Modeling (AQM).
Objectives
At the end of this lesson, you should be able to:
1. identify how meteorology is used in SIPs, NSR, and AQMs.
2. name the concentration estimate most frequently used to specify short-term
emission limits in SIPs.
S. identify the reason "worst case" meteorological conditions are necessary in
regulatory programs.
4. name the analysis used to estimate concentrations in NSR when required.
5. name the four meteorological factors that are required as a minimum to
describe atmospheric transport in SIPs and NSR.
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Introduction
The Clean Air Act Amendments of 1977 require State Implementation Plans, New
Source Review including Prevention of Significant Deterioration (PSD), and air
quality modeling. These regulatory programs require knowledge of the present
pollutant loading of the atmosphere, air quality modeling in given situations, and
progress in cleaning up the atmosphere. Implicit in air pollution programs is a
knowledge of the meteorological climatology of the area in question.
When air quality modeling is required, the specific model used (from a simple
screening tool to a refined analysis) will need meteorological data. The data can
vary from a few factors such as average wind speed and Pasquill-Gifford stability
categories to a mathematical representation of turbulence. Whatever model is
chosen to estimate air quality, the meteorological data quality must match the
quality of the model used. For example, average wind speed used in a simple
model will not be sufficient for a complex model.
The reading assignment for this lesson taken from the Guideline on Air Quality
Models discusses the essentials of SIPs, NSR, PSD, and the data requirements for
air quality modeling.
\ -v
Section 3: Requirements for Concentration Estimates*
Specific air quality standards and increments of pollutant concentrations must be
considered for control strategy evaluations and for new source reviews, including
prevention of significant deterioration. This section specifies general requirements
for concentration estimates and identifies the relationship between emission limits
and air quality standards/increments for these applications.
Control Strategy Evaluations
SIP-related emission limits should be based on concentration estimates for the
averaging time which results in the most stringent control requirements. In all cases
these concentration estimates are assumed to be a sum of the concentration con-
tributed by the source and an appropriate background concentration.
If the annual average air quality standard is exceeded by a greater degree
(percentage) than standards for other averaging times, the annual average is con-
sidered the restrictive standard. In this case the sum of the highest estimated
annual average concentration and the annual average background provides the
concentration which should be used to specify emission limits. However, if a short-
term standard is exceeded by a greater degree and is thus identified as the restric-
tive standard, other considerations are required because the frequency of occur-
rence must also be taken into account.
•Source: EPA 450/2-78-027 Guideline on Air Quality Models.
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Historically, when dispersion model estimates are used to assist in judging
whether short-term NAAQS will be met, and ultimately in specifying appropriate
emission limits, one of three types of concentration estimates is used: (1) the highest
of all estimated concentrations, (2) the second-highest of all estimated concentra-
tions, or (S) the highest of second-highest concentrations estimated for a field of
receptor sites. The highest of second-highest concentrations for a field of receptors
is obtained as follows: (1) frequency distributions of short-term concentrations are
estimated for each site in a field of receptors; (2) the highest estimated concentra-
tion at each receptor is discarded; (S) the highest of the remaining concentration
estimates from the field of receptor sites is identified. Throughout this guideline
that concentration estimate is referred to as the highest, second-highest
concentration.
The first two types of estimates have been applied most often in specifying emis-
sion limits. However, they may be unnecessarily restrictive in many situations. The
third type of estimate is more consistent with the criteria for determining violations
of the NAAQS, which are identified in Guidelines for Interpretation of Air Quality
Standards. That guideline specifies that a violation of a short-term standard occurs
at a site when the standard is exceeded a second time. Thus, emission limits which
are to be based on an averaging time of 24 hours or less should be based on the
highest, second-highest estimated concentration plus a background concentration
which can reasonably be assumed to occur with that concentration. (See the sec-
tion, "Background Air Quality," page 9-9, for a discussion of the factors and
variety of situations that should be considered.)
An estimate of the highest, second-highest concentration which is based on many
well-chosen receptor sites may well reveal previously Unidentified "hot spots." Such
an estimate may provide a more conservative and realistic indication of the poten-
tial for NAAQS violations and of the appropriate emission limits than do actual
measurements at a few monitoring sites. However, if the data available for model-
ing are limited to a short period, or source data are generalized, the estimated
highest, second-highest concentration is unlikely to provide a true indication of the
threat to air quality standards. Thus it is essential that an adequate data base be
available (see Section 5: "Data Requirements" on page 9-5). Data for a time period
of sufficient length should be considered so that there is reasonable certainty that
meteorological conditions associated with the greatest impacts on air quality are
identified. Similarly, detailed source data are required so that the air quality
impact can be assessed for the source conditions likely to result in the greatest
impact.
There are two exceptions to the above requirement to use the highest, second-
highest estimated concentrations. The first situation occurs where monitored air
quality data from specific sites indicate that concentrations greater than those
estimated can occur with little or no impact from the source(s) in question. For the
purpose of specifying emission limits, these measured concentrations should be
ranked ahead of the estimated concentrations in the frequency distribution of con-
centrations at that specific monitoring (receptor) site.
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The second situation occurs where the Regional Administrator identifies inade-
quacies in the data base or the models for a particular application. As a result of
these inadequacies he may determine that there is a lack of confidence in an emis-
sion limit based on the highest, second-highest concentration or that this concen-
tration simply cannot be estimated. In this case, until such time as the necessary
data bases are acquired or analytical techniques are improved, the use of the
highest estimated concentration to determine source impact and to evaluate con-
trol strategies may be justified.
New Source Reviews
Reviews for new sources that require an air quality impact analysis should deter-
mine if the source will (1) cause or exacerbate violations of a NAAQS or (2) cause
air quality deterioration which is greater than allowable increments. For reviews
relative to both the NAAQS and prevention of significant deterioration (PSD), the
air quality impact analysis should generally be limited to the area where the impact
exceeds "significant concentration increments." Such significant increments are
defined in EPA's PSD regulations (40 CFR 52.21) and in EPA's Emission Offset
Ruling (40 CFR Pan 51, Appendix S). In addition, due to the uncertainties of
estimates for large downwind distances, the air quality impact analysis should
generally be limited to a downwind distance of 50 kilometers from the source,
regardless of the above mentioned significant increments. The following subsections
further identify requirements for concentration estimates associated with air quality
standards and with prevention of significant deterioration.
Meeting Air Quality Standards
For each new source or major modification of a source which would increase
allowable emissions by 50 tons per year, 500 pounds per day, or 100 pounds per
hour, an air quality analysis should be performed to determine if the source will
cause or exacerbate a violation of a NAAQS. For such new sources located in an
attainment area, the concentration estimates should meet the same requirements
that are applicable to control strategy evaluations. The determination of whether
or not the source will cause an air quality violation should be based on (1) the
highest estimated concentration for annual averages and (2) the highest, second-
highest estimated concentration for averaging times of 24-hours or less. The most
restrictive standard should be used in all cases to establish the potential for an air
quality violation. Background concentrations should be added in assessing the
source's impact. The two exceptions to the shorter-term averaging times which were
noted in the preceding section also apply here; i.e., monitored data with higher
concentrations and inadequacies in data bases or model.
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Prevention of Significant Deterioration
Air quality models should be used in all significant deterioration evaluations.
Allowable increments for sulfur dioxide and paniculate matter are set forth in the
Clean Air Act Amendments of 1977. These maximum allowable increases in pollu-
tant concentrations may be exceeded once per year, except for the annual incre-
ment. Thus, in significant deterioration evaluations for short-term periods the
highest, second-highest increase in estimated concentrations should be less than or
equal to the permitted increment.
Since the Clean Air Act Amendments express special concern for Class I PSD
areas, any expected impacts for these areas must be considered. Thus, the distance
limitation of 50 kilometers and the significant concentration increments discussed
in the introduction to the Section on "New Source Reviews" do not apply. In addi-
tion, where an exemption to the Class I increments is requested and approved pur-
suant to section 165(d)(2)(D) of the Clean Air Act, the source may cause the Class I
increments to be exceeded on a total of 18 days during any annual period. In this
case, it is necessary to select the hightest estimated concentration in the field of
receptors for each of the S65 days. These 365 values are then ranked and the 19th
highest is used to determine emission limits. However, the highest, second-highest
concentration may not exceed a somewhat higher increment specified in section
Section 5: Data Requirements
It is essential that appropriate source and meteorological data be used with any
recommended model. Such data, and related procedures for estimating these data,
constitute an integral part of the model. It is often overlooked that few of the
variables input to a model are directly measured or routinely available. Submodels
must appropriately convert the available source and meteorological data to a form
that the air quality model can accept. It is also important that a variety of
load/ emissions conditions, and that a wide range of meteorological conditions
based on several years of data, be considered in evaluating control strategies and in
determining source impact for new source reviews, including prevention of signifi-
cant deterioration. In addition, there is a need to judiciously choose receptor sites
and to specify background air quality. This section identifies requirements for these
data bases.
Source Data
Sources of pollutants generally can be classified as point, line and area sources.
Point sources are generally considered to be those that emit a substantial amount
of an air pollutant, e.g., 50 tons per year, from a stack or group of stacks. Line
sources are generally confined to roadways and streets along which there are well-
defined movements of motor vehicles. Area sources include the multitude of minor
sources with individually small emissions that are impractical to consider as
9-5
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separate point or line sources. Area sources are typically treated as a grid network
of square areas, with pollutant emissions distributed uniformly within each grid
square. Descriptions of individual models should be referenced for specific emis-
sions inventory requirements.
For situations involving one or a few point sources the following are minimum
requirements for new source review and control strategy evaluations. Design process
rate or design load conditions must be considered in determining pollutant emis-
sions. Other operating conditions that may result in high pollutant concentrations
should also be identified.* A range of operating conditions, emission rates, and
physical plant characteristics based on the most recently available data, should be
used in the model with the multiple years of meteorological data (see the following
section, "Meteorological Data") to estimate the source impact. The following exam-
ple (power plant) typifies the kind of data on source characteristics and operating
conditions that are required:
1. Plant layout. The connection scheme between boilers and stacks, and the
distance and direction between stacks, building parameters (length, width,
height, location and orientation relative to stacks) for plant structures which
house boilers, control equipment, etc.
2. Stack parameters. For all stacks, the stack height and diameter (meters), and
the temperature (K) and volume flow rate (actual cubic meters per second) or
exit gas velocity (meters per second) for operation at 100 percent, 75 percent
and 50 percent load.
5. Boiler size. For all boilers, the associated megawatts and pounds of steam per
hour, and the design and/or actual fuel consumption rate for 100 percent
load for coal (tons/hour), oil (barrels/hour), and natural gas (thousand cubic
feet/hour).
4. Boiler parameters. For all boilers, the percent excess air used, the boiler type
(e.g., wet bottom, cyclone, etc.), and the type of firing (e.g., pulverized coal,
front firing, etc.).
5. Operating conditions. For all boilers, the type, amount and pollutant contents
of fuel, the total hours of boiler operation and the boiler capacity factor dur-
ing the year, and the percent load for winter and summer peaks.
6. Pollution control equipment parameters. For each boiler served and each
pollutant affected, the type of emission control equipment, the year of its
installation, its design efficiency and mass emission rate, the date of the last
test and the tested efficiency, the number of hours of operation during the
latest year, and the best engineering estimate of its projected efficiency if used
in conjunction with coal combustion; data for any anticipated modifications or
additions.
•Malfunctions which may result in excess emissions are not considered to be a normal operating
condition. They generally should not be considered in determining allowable emissions.
However, if the excess emissions are the result of poor maintenance, careless operation, or other
preventable condition, it may be necessary to consider them in determining source impact.
9-6
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7. Data for new boilers or stacks. For all new boilers and stacks under construc-
tion and for all planned modifications to existing boilers or stacks, the
scheduled date of completion, and the data or best estimates available for
items 1 through 6 above following completion of construction or modification.
Typically for line sources, such as streets and highways, data are required on the
width of the roadway and its center strip, the types and amounts (grams per second
per meter) of pollutant emissions, the number of lanes, the emissions from each
lane and the height of emissions. The location of the ends of the straight roadway
segments must be specified in appropriate grid coordinates. More detailed informa-
tion and data requirements for modeling mobile sources of pollution are provided
in the guideline on indirect sources.
For multi-source urban situations, detailed source data are often impractical to
obtain. In these cases, source data should be based on annual average conditions.
Area source information required are types and amounts of pollutant emissions, the
physical size of the area over which emissions are prorated, representative stack
height for the area, the location of the centroid or the southwest corner of the
source in appropriate grid coordinates. If the model accepts data on area-wide
diurnal variations in emissions, such as those estimated by emissions models which
are based on urban activity levels and other factors, those data should be used.
In cases where the required source data are not available and cannot be
obtained, the data limitation should be identified. Due to the uncertainties
associated with such a limitation the use of the highest estimated concentration to
determine source impact and to evaluate control strategies may be justified until
such time that a better data base becomes available.
For control strategy evaluations the impact of growth on emissions should be
considered for the next 10-20 year period. Increases in emissions due to planned
expansion of the sources considered or planned fuel switches should be identified.
Increases in emissions at each source which may be due to planned expansion of
the sources considered or planned fuel switches should be identified. Increases in
emissions at each source which may be associated with general industrial/commer-
cial/residential expansion in multi-source urban areas should also be considered.
However, for new source reviews, the impact of growth on emissions should
generally be considered for the period prior to the start-up date for the source.*
Such changes in emissions should consider increased area source emissions, changes
in existing point source emissions which were not subject to preconstruction review,
and emissions due to sources with permits to construct, but have not yet started
operation.
*A new source may result in specific and well defined secondary emissions which can be accurately
quantified. Secondary emissions are those resulting from operation of the source, but not directly
emitted by the source, e.g., emissions from shipping at a port terminal. The reviewing authority
should consider such secondary emissions in determining whether the source would cause or con-
tribute to a violation of the NAAQS. However, since EPA's authority to perform indirect source
review relating to parking-type facilities has been restricted by statute, consideration of parking-
type secondary impacts is not required.
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Meteorological Data
For a dispersion model to provide useful and valid results, the meteorological data
used in the model must be representative of the transport and dispersion conditions
in the vicinity of the source that the model is attempting to simulate. The represen-
tativeness of the data is dependent on (1) the proximity of the meteorological
monitoring site to the area under consideration, (2) the complexity of the terrain in
the area, (3) the exposure of the meteorological monitoring site and (4) the period
of time during which the data are collected. The representativeness of the data can
be adversely affected by large distances between the source and receptors of interest
and valley-mountain, land-water, and urban-rural characteristics of the area.
For new source review and control strategy evaluation, the meteorological data
required as a minimum to describe transport and dispersion in the atmosphere are
wind direction, wind speed, atmospheric stability, mixing height or related
indicators of atmospheric turbulence and mixing. Site-specific data are preferable
to data collected off-site. The availability of such meso- and micro-meteorological
data collections permits more detailed meteorological analyses and subsequent
improvement of model estimates. Local universities, industry, pollution control
agencies and consultants may be sources of such data. The parameters typically
required can also be derived from routine measurements by National Weather Ser-
vice stations. The data are available as individual observations and in summarized
form from the National Climatic Center, Asheville, N.C. Descriptions of individual
models should be referred to for specific meteorological data requirements. Many
models require either hourly meteorological data or annual stability wind roses.
- It is preferable for the meteorological data base used with the air quality models
to include several years of data. Such a multi-year data base allows the considera-
tion of variations in meteorological conditions that occur from year to year. The
exact number of years needed to account for such variations in meteorological con-
ditions is uncertain and depends on the climatic extremes in a given area. Gen-
erally five years yields an adequate meteorological data base. However, if long-term
records are not available, it may be necessary to limit the modeling and subsequent
analyses to a single year of meteorological data. The use of one year of data might
also be justified if the climatological representativeness of that data can be
demonstrated. A longer record from a nearby National Weather Service site could
be used to check for representativeness.
The number of National Weather Service stations for which multiple years of
hourly weather data are available is increasing significantly. Several EPA offices
have ordered such data for a large number of stations. It is dear that more
detailed analyses than previously considered for SIP evaluations and new source
review are necessary. Thus, for areas where meteorological conditions are ade-
quately represented by weather stations, the use of multiple years of meteorological
data appears to be viable and justified.
Where representative meteorological observations are not available, the concen-
tration estimates may be limited to consideration of worst case conditions. An
analysis of worst case conditions should be based on reasonable interpretations of
climatological data and should consider such critical plume characteristics as loop-
9-8
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ing, coning, limited mixing, fumigation, aerodynamic downwash and plume
impaction on terrain. Due to the uncertainties of this approach, the use of the
highest estimated concentration to determine source impact and to evaluate control
strategies may be justified until such time that a better base becomes available.
Receptor Sites
A receptor site is a location for which an air pollution concentration is estimated.
The choice of locations for receptor sites significantly affects the evaluation of
source impact and control strategy effectiveness. It is most important to identify the
location where the maximum concentrations occur, both short- and long-term. The
receptors selected must allow sufficient spatial detail and resolution so that the
location of the maximum or highest, second-highest concentration is identified.
The receptor sites in the vicinity of large point sources at which maximum con-
centrations are likely to occur can be identified by (1) estimating concentrations for
a sufficiently dense array of receptors to identify concentration gradients and (2)
subsequently refining the location of the maximum by estimating concentrations
for a finer array of receptors in the general areas of maximum concentrations.
Another technique is to use a simple model such as PTMAX in combination with
joint frequency distributions of wind speed, wind direction and stability to identify
the downwind distance and direction at which the highest concentrations are most
likely to occur.
Background Air Quality
To adequately assess the significance of the air quality impact of a source,
background concentrations must be considered. Background air quality relevant to
a given source includes those pollutant concentrations due to natural sources and
distant, unidentified man-made sources. For example, it is commonly assumed that
the annual mean background concentration of paniculate matter is 50-40 /ig/m3
over much of the Eastern United States. Typically, air quality data are used to
establish background concentrations hi the vicinity of the source under considera-
tion. However, where the source is not isolated, it may be necessary to use a multi-
source model to establish the impact of all other nearby sources during dispersion
conditions conducive to high concentrations.
If the point source is truly isolated and not affected by other readily identified
man-made sources, two options for determining background concentrations from
air quality data are available. The preferable option is to use air quality data col-
lected in the vicinity of the source to determine mean background concentrations
for the averaging times of interest when the point source itself is not impacting on
the monitor. The second option applies when no monitors are located in the
vicinity of the source. In that case, average measured concentrations from a
"regional" site can be used to establish a background concentration.
For the first option it is a relatively straightforward effort to identify an annual
average background from available air quality data. For shorter averaging times,
9-9
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background concentrations are determined by the following procedure. First,
meteorological conditions are identified for the day and similar days when the
highest, second-highest estimated concentration due to the source occurs. Then the
average background concentration on days with similar meteorological conditions is
determined from air quality measurements. The background for each hour is
assumed to be an average of hourly concentrations measured at sites outside of a
90° sector downwind of the source. The 1-hour concentrations are then averaged to
obtain the background concentrations for the averaging time of concern.
If air quality data from a local monitoring network are not available, then
monitored data from a "regional" site may be used for the second option. Such a
site should characterize air quality across a broad area, including that in which the
source is located. The technique of characterizing meteorological conditions and
determining associated background concentrations can then be employed.
If a small number of other identifiable sources are located nearby, the impact of
these sources should be specifically determined. The background concentration due
to natural or distant sources can be determined using procedures already described.
The impact of the nearby sources must be summed for locations where interactions
between the effluents of the point source under consideration and those of nearby
sources can occur. Significant locations include (1) the area of maximum impact of
the point source, (2) the area of maximum impact of nearby sources, and (3) the
area where all sources combine to cause maximum impact. It may be necessary to
identify these locations through a trial and error analysis.
If the point source is located in or near an urban multi-source area, there are
several possibilities for estimating the impact of all other sources. If a comprehen-
sive air monitoring network is available, it may be possible to rely entirely- on the
measured data. It is necessary that the network include monitors judiciously located
so as to measure air quality at the locations of the point source's maximum impact
and locations of the highest concentrations in the area. If the point source is not
yet operating, its calculated impact can be added to these measured concentra-
tions. If the source already exists and is contributing to the measured concentra-
tions, its calculated contribution should be subtracted from the measured values to
estimate the concentration caused by other manmade sources and by background.
If the monitored data are inadequate for such an analysis, then multi-source
models can be used to establish the impact of all other sources. These models
should be used for appropriate pollutants and averaging times to identify concen-
trations at the times and locations of maximum point source impact. The times
and locations of maximum impact due to all other sources must also be identified.
If a model is not available for the appropriate averaging times, statistical tech-
niques can be used with an appropriate model to extrapolate from one averaging
time to another. All statements in this guide regarding the data requirements and
validity of air quality models are applicable to analyses of this type.
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For control strategy evaluations, the impact growth on area-wide emissions and
on concentrations caused by nearby sources should also be considered for the next
10-20 year period. To determine concentrations in future years, existing air quality
should be proportionately adjusted by the anticipated percent change in emissions
in the vicinity of individual monitoring sites. However, for new source reviews,
changes in existing air quality should generally be considered for the period prior
to the start-up date of the source.
Review Exercise
Meteorological data are necessary when a new source
review is required. It is necessary because
a. new source reviews are conducted by the
meteorologist only.
b. the State governor personally reviews every NSR.
c. air quality modeling under NSR uses meteoro-
logical data.
d. none of the above
Short-term emission limits use which concentra-
tion estimate more frequently?
a. third highest
b. second highest
c. highest, second-highest
d. highest
1. c. air quality
modeling under
NSR uses
meteorological
data.
The meteorological condition that will help in com-
puting the highest possible pollution concentration is
called
a. worst case
b. best case
c. most frequent case
d. last case
2. c. highest,
second-highest
4. The analysis used to determine whether a source will
cause violations of NAAQS or cause deterioration
larger than allowable increments is
a. major modification review.
b. air quality impact.
c. significant increment analysis.
d. violation analysis.
3. a. worst case
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5. The four meteorological factors necessary in NSR and
control strategy evaluation are
a. humidity, wind speed, wind direction, stability.
b. precipitation, stability, wind speed, wind direction.
c. solar radiation, stability, mixing, mixing height.
d. wind speed, wind direction, stability, mixing
height.
4. b. air quality
impact.
5. d. wind speed,
wind direction,
stability, mixing
height.
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References
Critchfield, Howard}. 1966. General Climatology. Englewood Cliffs, New Jersey:
Prentice-Hall, Inc.
Donn, William L. 1975. Meteorology. New York: McGraw-Hill Book Company.
Environmental Protection Agency (EPA) 1975. APTI Course 411 Air Pollution
Meteorology—Student Manual (Draft).
Williamson, Samuel J. 1973. Fundamentals of Air Pollution. Reading,
Massachusetts: Addison-Wesley Publishing Company.
Air Pollution Control Association (APCA) Reprint Series. 1977. Air Pollution
Meteorology. Pittsburgh, Pennsylvania.
Trewartha, Glenn T. 1968. An Introduction to Climate. New York: McGraw-Hill
Book Company.
Riehl, Herbert. 1965. Introduction to the Atmosphere. New York: McGraw-Hill
Book Company.
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TECHNICAL REPORT DATA
(Please read Inarucaons on the reverse before completing)
1. REPORT NO. 2.
EPA 450/2-82-009
4. TITLE AND SUBTITLE
APTI Course SI: 409
Basic Air Pollution Meteorology
7. AUTHOR(S)
Donald Bullard and Marilyn Peterson
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Northrop Services, Inc.
P.O. Box 12313
Research Triangle Park, NC 27709
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environnental Protection Agency
Manpower and Technical Information Branch
Air Pollution Training Institute
Research Trianele Park. flC 27711
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
December. 1982
6. PERFORMING ORGANIZATION
8. PERFORMING ORGANIZATION
CODE
REPORT NO
10. PROGRAM ELEMENT NO.
B 18A2C
11. CONTRACT/GRANT NO.
68-02-2374
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Project officer for this guidebook is R. E. Townsend, EPA-ERC, MD 17, RTP,
NC 27711
16. ABSTRACT
This training course is a 25-hour self-instructional course using slide/tape
presentations and reading assignments dealing with basic meteorology, meteor-
ological effects on air pollution, meteorological instrumentation, air quality
modeling, and regulatory programs requiring meteorological data. Course topics
include the following:
Solar and terrestrial radiation
Wind speed and direction
Cyclones and anticyclones
Atmospheric circulation
Cold, warm, and occluded fronts
Atmospheric stability
Turbulence
Meteorological instrumentation
Plume rise and effective stack height
Topography
Air quality models
Regulatory air quality programs
17.
a.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Air Pollution Training
Meteorology
Air Quality Modeling
Plume Dispersion
IS.
D.STRIBUTION STATEMENT Unlimited
Available from National Audio Visual
Center, National Archives and Records
Sprvire. GSA. Order Service HH.
b. IDENTIFIERS/OPEN ENDED TERMS
Training Course
Self-instructional
course with a/v
materials
19. SECURITY CLASS (This Report]
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COS ATI Field/Group
13 B
5 I
68 A
21. NO. OF PAGES
125
22. PRICE
EPA Form 2220-1 (»-73)
Washington, D.C. 20409
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