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Air Pollution, Climate Change
and Ozone Depletion
Core Case Study
Blowing in the Wind:
A Story of Connections
 Wind connects most life
on earth.
 Keeps tropics from being
unbearably hot.
 Prevents rest of world
from freezing.
Figure 5-1
CLIMATE: A BRIEF
INTRODUCTION
 Weather is a local area’s short-term physical
conditions such as temperature and
precipitation.
 Climate is a region’s average weather
conditions over a long time.
 Latitude and elevation help determine climate.
Climate
Climate is the average weather
conditions that occur in a place
over a period of years.
The two most important factors
are temperature and precipitation.
Solar Energy and Global Air
Circulation: Distributing Heat
 Global air
circulation is
affected by the
uneven heating of
the earth’s surface
by solar energy,
seasonal changes
in temperature and
precipitation.
Figure 5-3
Air Pressure
Definition
Air pressure is pressure exerted by
the weight of Earth’s atmosphere.
At sea level it is equal to 14.69
pounds per square inch.
A barometer is used to measure
atmospheric pressure.
Air Pressure
Pressure Gradient
 Changes from high to
low. On a map there is
an arrow to show this.
A higher pressure
gradient means
stronger winds (the
isobars on a weather
map would be drawn
closer together).
Wind
Cause
 Wind is caused by the pressure
gradient force. High pressure means
more air, and low pressure means less
air. The air moves from high to low,
causing wind.
Wind
The Coriolis Effect
 Forces in the
atmosphere,
created by the
rotation of the
Earth on its axis,
that deflect winds
to the right in the
N. Hemisphere and
to the left in the
S.Hemisphere.
Convection Cells: with No spin
Wind
Coriolis Effect
 Global air
circulation is
affected by the
rotation of the
earth on its
axis.
Figure 5-4
Wind
Friction
 A combination of the pressure gradient
force and the coriolis effect. Friction at
the Earth’s surface causes winds to
turn a little. Friction runs parallel to
the isobar.
Wind
Upper Level Flow
 There is little friction up in the upper
troposphere, driving surface features.
Ex. during big thunderstorms, the
wind in the upper level will tell which
way the thunderstorm will move.
Wind
Cyclones
 (called hurricanes in the Atlantic
and typhoons in the Pacific)
 Violent storms that form over
warm ocean waters and can pass
over coastal land.
 Giant, rotating storms with
winds of at least 74 mph. The
most powerful ones have wind
velocities greater than 155 mph.
Air Masses and Winds
Polar vs. Tropical
 The atmosphere has three prevailing winds.
 Prevailing winds that blow from the North or South
Pole are called Polar Easterlies.
 Winds that blow in the middle lattitudes (between
3o and 60 degrees) are called the Westerlies
 Tropical winds that blow toward the equator are
called Trade Winds.
Prevailing Winds
Air Masses and Storms
Continental vs. Maritime
 Continental fronts are generally cool
and dry, whereas maritime (ocean)
fronts are generally warm and moist.
When these two air masses converge,
the result is usually rain.
Convection Currents
 Global air
circulation is
affected by the
properties of air
water, and land.
Figure 5-5
Convection Cells
 Heat and moisture
are distributed over
the earth’s surface
by vertical
currents, which
form six giant
convection cells at
different latitudes.
Figure 5-6
Circulation Patterns
Hadley Cells
 Warm moist air rises at the equator. Rain
 As air rises, it spreads out north & south, then cools and
sinks at 30 degrees. Dry
 This is why most of the world’s deserts are found at 30
degrees.
 These are called the horse latitudes (3o degrees) because
early settlers would get stuck here in their boats & couldn’t
move. They would finally throw their horses overboard to
lighten the load & get moving again.
 Trade Winds blow towards equator
Circulation Patterns
Ferrell Cells
 Warm air rises at about 60 degrees. Rain
 and sinks at around 30 degrees, dry, both north and
south.
 Westerlies. Predominant winds in US
Circulation Patterns
Polar Cells
 Air rises at about 60
degrees. Rain
 floats north, and
sinks at around 90
degrees, both north
and south. Dry
 Easterlies
Circulation Patterns
Circulation Patterns
Convection Cells
 Ocean water transfers heat to the atmosphere,
especially near the hot equator. (Trade winds)
 This creates convection cells that transport heat
and water from one area to another.
 The resulting convection cells circulate air, heat,
and moisture both vertically and from place-toplace in the troposphere, leading to different
climates & patterns of vegetation.
Sea, Land, Valley, & Mountain
Breezes
 Sea - ocean-to-land breezes that occur during the
day.
 Land - land-to-ocean breezes that occur at night.
 Valley - the wind blows from the plains into a
valley between two mountains, the wind must
divert into a smaller area. This causes high winds
to form through the valleys.
 Mountain - Cool air coming from the top of the
mountain sinks down on the eastern slope,
causing increased winds on the mountain.
Topography and Local Climate:
Land Matters
 Interactions between land and oceans and disruptions of
airflows by mountains and cities affect local climates.
Figure 5-8
Ocean Currents:
Distributing Heat and Nutrients
 Ocean currents influence climate by distributing heat
from place to place and mixing and distributing
nutrients.
Ocean Currents:
Distributing Heat and Nutrients
 Ocean currents influence climate by
distributing heat from place to place and
mixing and distributing nutrients.
Earth’s Current Climate Zones
Figure 5-2
Weather
Weather is the condition in the
atmosphere at a given place and
time.
Weather includes temperature,
atmospheric pressure,
precipitation, cloudiness,
humidity, and wind.
Local Weather
 Weather is a local area’s short-term physical conditions such as
temperature and precipitation.
 A weather front marks the boundary between two air-masses at
different densities.
 A front is about 100-200 km wide and slopes where warm and
cool air masses collide.
Cold front
Warm front
Weather
Warm & Cold Fronts
 Warm Front - The boundary between an
advancing warm air mass and the cooler one it is
replacing. Because warm air is less dense than
cool air, an advancing warm front will rise up over
a mass of cool air.
 The leading edge of an advancing air mass of cold
air. Because cool air is more dense than warm air,
an advancing cold front stays close to the ground
and wedges underneath less dense, warmer air. A
cold front produces rapidly moving, towering
clouds called thunderheads.
Weather
Stationary & Occluded
Front
 A stationary front is a
transitional zone between
two nearly stationary air
masses of different
density.
 An occluded front is the air
front established when a
cold front occludes
(prevents the passage of) a
warm front.
Seasons
 The Earth’s 23.5 degree incline on its axis remains
the same as it travels around the sun. As the earth
spins around the sun the seasons change.
Earth-Sun-Moon
Earth’s axis has a 23.5° tilt. This tilt always
faces the same way, resulting in seasonal changes
in sunlight and weather.
Solar year: the journey
around the sun takes
365.2425 days.
Earth day: the Earth spins on its
axis with respect to the stars once
every 23h 56 min 4.09s (one
sidereal day). The solar day,
where the sun returns to its
zenith, is exactly 24 hours.
Lunar month: the time between successive
full moons is 29.5 days, but the moons orbit
around the Earth takes 27.3 days. Because
the moon spins on its own axis once every
27.3 days, the same side of the moon always
faces the Earth.
All images: NASA
Orbital Cycles

Three long term cycles that the Earth goes through as it orbits the Sun are:
Axial tilt: the axis of the Earth varies from 21.5° to 24.5°.
Orbital eccentricity: Earth’s orbit varies from almost circular to elliptical.
Precession: the movement of the axes in space causes them to describe a cone.
All images: NASA
Axial Tilt
 The tilt of the Earth’s axis ranges between 21.5° and 24.5°.
 This can have severe effects on the climate.
An axis tilt of 21.5o
allows more heating near
the poles leading to a
less extreme temperature
gradient from pole to
equator.
When tilted at 24.5o the
variation between winter
and summer temperatures
is much more
pronounced.
Eccentricity

When the Earth’s orbit is almost circular (as it is
now), both summers and winters are relatively mild.

This can trigger ice sheet build up as summer is not
warm enough to melt winter snow.
‣
When Earth’s orbit is more elliptical,
summers (as shown here) in the northern
hemisphere can be relatively cold while
winters are relatively warm.
The opposite occurs in the southern
hemisphere
All images: NASA
Precession

Precession alters the orbital position of the summer and winter solstices.
Around 13,000 years ago the southern hemisphere’s summer occurred in June.
Orbital Cycles
 The changes in the tilting
of the Earth’s axis,
combined with
precession and
eccentricity can cause
variations in the amount
of solar radiation
reaching the Earth’s
surface.
 This can trigger the onset
and recession of ice ages.
Formation
of the Atmosphere

Most of the Earth’s early atmosphere
was lost due to the vigorous solar wind
from the early Sun.

Continuous volcanic eruptions built a
new atmosphere of:
water vapor
carbon dioxide
nitrogen
methane
The Atmosphere
 The mixture of gases known as
air, protects life on Earth by
absorbing ultraviolet radiation
and reducing temperature
extremes between day and
night.
 The atmosphere is not static.
Interactions involving the
amount of sunlight, the spin of
the planet and tilt of the Earth’s
axis cause ever changing
atmospheric conditions.
Weather occurs in the troposphere. Gaseous water molecules
held together by intermolecular forces cause the formation of
clouds.
The auroras occur in the thermosphere and are caused by
interactions between the Earth’s atmosphere and charged
particles streaming from the Sun.
The Earth’s Atmosphere
STRUCTURE AND
SCIENCE
 The atmosphere
consists of several
layers with different
temperatures,
pressures, and
compositions.
STRUCTURE AND SCIENCE
 The atmosphere’s innermost layer
(troposphere) is made up mostly of
nitrogen and oxygen, with smaller
amounts of water vapor and CO2.
 Ozone in the atmosphere’s second layer
(stratosphere) filters out most of the
sun’s UV radiation that is harmful to us
and most other species.
The Atmosphere
 Earth's atmosphere contains roughly:
78% nitrogen
20.95% oxygen
0.93% argon
0.038% carbon
dioxide
Trace gases
The Earth’s atmosphere (where pressure becomes negligible)
is over 140 km thick. Compared to the bulk of the planet, this is
an extremely thin barrier between the hospitable and the
inhospitable.
1% water vapour
All images: NASA
Troposphere
 75% of mass of atmosphere
 0 to 11 miles in altitude
 78% nitrogen, 21% oxygen
 Location of Earth’s weather
 Temperature decreases
with altitude until the next
layer is reached, where
there is a sudden rise in
temperature
Stratosphere
 11 miles to 30 miles in altitude, calm
 Temperature increases with altitude
 Contains 1000x the ozone of the rest of
the atmosphere; ozone forms in an
equilibrium reaction when oxygen is
converted to O3 by lightning and/or
sunlight
 99% of ultraviolet radiation (especially
UV-B) is absorbed by the stratosphere
Mesosphere & Thermosphere
 Mesosphere
 30 to 50 miles in
altitude
 Temperature
decreases with
increasing
altitude
 Thermosphere
 50 to 75 miles in
altitude
 Temperature
increases with
increasing
altitude
 Very high
temperatures
Composition of the Atmosphere
 Components –Nitrogen 78%, Oxygen
21%, .93% argon, & .038% carbon
 Layers – troposphere, stratosphere,
mesosphere, thermosphere, exosphere
(extends from 310 miles to
interplanetary space)
Heat Transfer
 Conduction
 Warm air holds more moisture than cold air.
During conduction, heat & moisture from the
ocean or land moves into the atmosphere.
 Ex. cold air moving over warm water (like a
lake), forming steam fog.
 Radiation
 Radiation drives weather. Heat from the
sun warms the earth, which radiates the
heat back into the atmosphere.
Natural Greenhouse Effect
 Some of the solar energy is trapped by molecules of
greenhouse gases (water vapor, carbon dioxide,
methane). Otherwise earth would be much colder
Global Warming
 Considerable scientific evidence and
climate models indicate that large
inputs of greenhouse gases from
anthropogenic activities into the
troposphere can enhance the natural
greenhouse effect and change the
earth’s climate in your lifetime.