What you need to know in 9.1 - 9.

4
1. All about the CFCs and their replacements. Even though HCFC and HFCs do not emit free chlorine radical, they are still highly
potent GHGs that will increase global temperature. HCFCs have a GWP of about 70-2000 over a period of 100 years. Leaking
refrigerator gas unit have contributed to the rise in HCFC levels during past 30 years.
2. Stratospheric ozone blocks sun’s UV-B and UV-C radiations. These are high-energy radiations that cause DNA mutations.
Accumulation of such mutations can lead to melanoma over one’s lifetime. Ozone that is formed near the ground in the
troposphere as a result of emission of NO2 by gasoline cars and photochemical oxidants is extremely harmful for humans and
plants. ‘Ozone in low-zone is bad’.
3. Due to global warming, coastal areas are flooded more often causing property damage and financial loss. The US northeast
coast and Gulf of Mexico (if they are still calling it this), specifically Texas and Louisiana are few of the worst affected areas.
Growing human population causes more people to live everywhere including the flooded coastal areas increasing financial loss
due to property damage.
4. You need to know the specific set of chemical reactions that lead to ozone depletion by the CFCs. find them in the slides and
do additional research when needed.
5. Ozone is depleted naturally as well. Antarctic spring melt causes the formation of polar stratospheric clouds (PSC) over
Antarctica. These are clouds made of water and nitric acid and can only be formed at temperatures reaching -100 degrees.
They are wave clouds and can induce gravity waves in the lower stratosphere. In presence of PSC, chlorine nitrate and
hydrochloric acid react to give off free chlorine which depletes ozone just like it does when released by CFCs.
6. Montreal protocol (1987) issued a global ban on the use of CFCs in refrigeration and aerosols. The phasing out needed some
time. Alternatives include HFC and HCFC. neither contains chlorine, the culprit in ozone depletion. A better alternative is HFO
which is better than HFC because it contains C-C double bonds that are unstable and breaks down easily reducing the GWP
because the compound breaks down on it own.
What you need to know in 9.1 - 9.4
1. The greenhouse effect : slide 18 and 21 describes it in details. You should be able to describe it in as much details as
you see in the slides.
2. However, also remember that life would not be possible on earth without the greenhouse effect.
3. Which type of surfaces absorb more solar radiation (lower albedo). Urban surfaces (concrete, asphalt - darker color)
always have lower albedo than natural ground.
4. Snow is white, so has a high albedo and polar regions receive indirect sunlight, so our planet has the polar ice caps.
Global warming is causing the ice caps and glaciers to melt revealing the dark colored igneous soil underneath.
These have lower albedo because of color, absorbs solar radiation, ice melts faster - proceeds like a positive feedback
cycle depleting the ice caps at a faster rate. Once the rock/sol layer underneath is exposed, the ice sheets reduce in
area dramatically.
5. Major GHGs in the atmosphere are CO2, CH4, nitrous oxides and CFCs. carbon dioxide remains in the atmosphere for
100s of years. CFCs can remain in the atmosphere for 1000s of years. Methane is relatively short-lived but has a high
GWP (read details in the slide 23). Methane is released from multiple sources including anaerobic decomposition and
thawing of permafrost either seasonally or due to global warming. You need to know all the sources listed for the
above mentioned gases. Water vapor is also a GHG but it is promptly circulated by the water cycle naturally, so it is
not a concern.
6. You need to know all the effects of increased GHGs in slide 28. You should be able to explain the how and why of -
thermal expansion of the ocean, increase in range of tropical pathogens, saltwater intrusion, refugee influx inland,
thermohaline values off balance in oceans.
7. Species that depend on the Arctic tundra ecosystems like polar bear, penguins and reindeers are facing population
decline because of melting ice sheets from last Pleistocene. Yes, you need to know the name of the geologic era
when the glaciers were formed.
 9.1 & 9.2 - Stratospheric
Ozone Depletion
and
Reducing Ozone Depletion
9.1 - Objective/EKs/Skill
 9.1 and 9.2
1. Ozone is depleted by CFCs. Used to be in refrigerators (high heat capacity), aerosol
sprays (as propellant).
2. Very stable, slowly rise to great altitudes in atmosphere. Reaches stratosphere where
photons are high energy.
3. CFCs break only in sunlight, otherwise very stable. Release chlorine radical. Free
chlorine breaks O3 and combines with one oxygen atom. This chlorine monoxide reacts
with another O atom to regenerate a chlorine radical. Thus, the cycle feeds itself.
4. Ozone depleting gases : methyl bromide, carbon tetrachloride,
dichlorodifluoromethane.
5. The ozone depletion was detected in Antarctica. Appears every year during spring
(October). Sun rises after long antarctic winter and starts breaking down the CFCs.
6. Montreal protocol : 1987 - global collaboration for sustainable development.
7. Phase out CFCs. Use alternatives. HCFCs, HFCs, HFOs (hydrofluoroolefins).
8. HFOs have C=C double bond which is unstable.
 Stratospheric Ozone & Life on Earth
⛰Ozone in the stratosphere absorbs UV-C and
much of UV-B radiation
● Without ozone layer, life on land would not be
possible since UV-B & C radiation causes
significant tissue damage & mutates DNA
● Human health benefits of stratospheric ozone:
○ Prevention of skin cancer & cataracts
○ UV-B & C mutate DNA (skin cancer) & cause
oxidative stress in eyes (cataracts)
⛰Remember: tropospheric = respi. Irritant, damaging
to plant tissue & precursor to photochemical smog
 Most chemicals, when released into the atmosphere get rapidly broken down
into smaller, harmless components by reactions in the lower atmosphere. The
CFCs however, are so stable and unreactive that they survive to reach the
highest levels of the atmosphere, and become globally distributed in the
stratosphere.

At these high altitudes, the intensity

It is the atomic chlorine that does the
of ultraviolet radiation is so great that
damage, since it can react with ozone
even the stable CFCs are split apart to
(O3) to form oxygen.
release a chlorine atom.

Effects on Ozone
 How Ozone Absorbs UV-B & UV-C
⛰UV-C breaks O2 into two free oxygen atoms (2 O)
● When a free oxygen atom from this

2
rxn combines with an O2 molecule,
ozone (O3) is formed 1
O2 1
O2 1
+ 2 O3

2
+ O2 1
● UV-C also reverses the rxn by breaking ozone (O3) O3
into O2 and O, which can then bond with another 2
free O to form O2 1: formation
● Continued formation & break down of O3 in 2: breakdown
stratosphere absorbs all UV-C & much UV-B
radiation (protecting org. on earth)
 Anthropogenic Ozone Depletion
One single Cl atom
⛰CFCs (chlorofluorocarbons) are a primary
persists in atm. for
anthropogenic (human) cause of O3 breakdown
50-100 years and can
● Used as refrigerant chemicals and destroy up to 100,000
propellants in aerosol containers (hair F ozone molecules
spray, febreeze, etc.) C O
O23
Cl Cl
Cl
Cl
O
Cl O23
Cl
● UV radiation causes free chlorine atom to
O2
separate from CFCs
● Highly electroneg. chlorine atom bonds to one of the oxygen atoms of ozone (O3) converting it
into oxygen (O2) and releasing chlorine monoxide.
● ClO reacts with another oxygen atom to form chlorine and diatomic oxygen, thus
regenerating the chlorine. One single chlorine atom can be reused about 100,000 times to
destroy equal number of ozone molecules.
Anthropogenic Ozone Depletion

F
O23
C O
Cl Cl
Cl
Cl
O
Cl O23
Cl

O2
 Natural Ozone Depletion

⛰Antarctica spring melt forms polar stratospheric

clouds (PSC)
● Clouds made of water & nitric acid (HNO3) that
can only form in consistent -1000 F temp. range
found above antarctica
 Natural Ozone Depletion

● In presence of PSCs, chlorine nitrate (ClONO2)

and hydrochloric acid (HCl) react & give off Cl2
○ Cl2 is photolyzed (broken by sun) into 2 free
Cl atoms
 Natural Ozone Depletion

⛰Remember what Cl atoms from CFCs do to ozone

(break O3 down into O2 over and over)

9.2 - Objective/EKs/Skill
 9.2 - Reducing Ozone Depletion
⛰Main way to reduce anthropogenic O3 depletion is
phasing out & replacing CFCs
● Montreal Protocol (‘87) was a global agreement
to phase CFCs out of production in refrigerators,
aerosols and other uses
● Replaced with HCFCs (CFCs with hydrogen added)
● HCFCs still deplete O3 and act as GHGs, but to a lesser
degree than CFCs
● Not a permanent solution, but a temporary transition
option (phase out in dev. Nations after 2020, developing
nations have until 2030)
*Replacement for HCFCs is HFCs (still GHGs, but not O3 depleting since
they don’t contain Cl)
**Replacements for HFCs are HFOs (just HFCs with C-C
double bonds that shorten atm. Lifetime & GWP)
Practice FRQs
9.1 & 9.2
Describe how stratospheric ozone
protects organisms on earth from UV
radiation. Describe how CFCs deplete
stratospheric ozone.

Explain how the Montreal Protocol

decreased ozone depletion.
9.3
The Greenhouse
Effect
Objectives/Eks/Skill
The greenhouse effect
➔ Some of the sun’s rays that pass through the atmosphere get reflected back. But
loses energy and wavelength increases - IR radiation = hot.
➔ If there are GHGs around, they absorb these IR and don’t let these reflect back to
outer space. These are gases, so absorbs and radiates in all directions (gas
molecules move everywhere). GHGs go nowhere, just keep moving within
atmosphere.
➔ More GHGs, more heat radiated everywhere = global warming
➔ Without natural CO2 and ensuing greenhouse effect, earth’s temperature will be well
below freezing. No life possible.
➔ Carbon dioxide, methane, nitrous oxides, CFC/HCFC/HFCs. Water vapor too, but does
not make a significant change.
➔ Burning FFs, agriculture, refrigerants, sprays
➔ New concept - GWP = global warming potential : how long does it stay + how well
does it absorb IR
➔
 Solar Radiation
⛰Not all incoming solar radiation reaches earth’s
surface
● 26% reflected back into space by clouds & atm.

● 19% absorbed by atm. & clouds & radiated

out into space & down to earth
● The rest reaches earth’s surface where it
can be absorbed or reflected (depending on
the albedo of the surface it strikes)

● Darker, lower albedo surfaces absorb

sunlight & release infrared radiation
(which we feel as warmth)
● Lighter, higher albedo surfaces reflect
sunlight, directly back out into space,
or into clouds/GHGs that absorb it
 The greenhouse Effect
⛰Gases in earth’s atmosphere trap heat from the
sun & radiate it back down to earth
● Without greenhouse effect, earth would be too
cold to support life
How it works:
● Solar radiation (photons) strike earth’s surface,
heating it

● Earth’s surface releases infrared radiation

● Greenhouse gases absorb infrared

radiation & radiate it both out into space
and back toward earth
● Portion coming back to earth is the
“greenhouse effect”
 Greenhouse Gases & Sources
⛰Most important Greenhouse Gases (GHGs) are:
● CO2 - FF comb, decomposition, deforestation

● Methane (CH4) - natural gas extraction &

combustion, animal farming, anaerobic decomp.
(especially permafrost thaw) N2O CFCs

● Nitrous oxide (N2O) - agricultural soils

(denitrification of nitrate, especially in
overwatered, over fertilized soils)

● CFCs/HCFCs/HFCs - refrigerants, blowing

agents in aerosol products

*Water vapor (H2O) - evaporation & transpiration from plants

*Technically a GHG by definition, but doesn’t drive atm. temp
change (other way around - temp. Controls atm. H2O vapor level)
 Global Warming Potential (GWP)
⛰Measure of how much a given molecule of gas can contribute to the
warming of the atmosphere over a 100 year period, relative to CO2

⛰Based on 2 factors:
1) Residence time: how long molecule stays in the atmosphere
2) Infrared absorption: how well the gas absorbs & radiates Infrared radiation (IR)
1
CO2 has a GWP of 1 (all other gases are measured in relation to CO2)

23 - 84 Methane (CH4) remains in atm. around 12 yrs, absorbs more IR than CO2

N2O remains in atm. around 115 yrs, absorbs much more IR than CO2
1,600 -
300
13,000

CFCs remain in atm 50-500 yrs, absorb much, much, much more IR than CO2
The solid arrows and the dashed arrows indicate the
direction of solar radiation and infrared radiation,
respectively, which flow to and from Earth, the atmosphere,
and space. The numbers express units, in relative terms, of
the total incoming solar or outgoing infrared energy.
How many units of energy are absorbed by Earth's surface?
 Practice FRQ 9.3
Explain how greenhouse gases in the
atmosphere contribute to the heating of
earth’s climate.
Identify a greenhouse gas that has a GWP
greater than 1. Explain why this
greenhouse gas has a higher GWP than 1.
9.4
Increase in
Greenhouse Gases
Objective/EKs/Skill
 Increase in GHGs
1. Thermal expansion of water = swelling oceans
2. Increase in GHGs raise the global temperature, so the ice sheets that have
been there since Pleistocene are melting. The ice melt is flowing into the
oceans causing sea level to rise.
3. Melting ice comes from poles and glaciers.
4. Environmental effects : salt concentration imbalance in coastal ecosystems
(estuaries, mangroves); loss of habitat for arctic tundra animals (polar
bears); evaporative loss deprives organisms of water; loss of biodiversity
5. Impact on humans : increased flooding (financial loss); saltwater intrusion
in wells; refugee influx inland
6. Diseases : insect vectors active only near tropics can now survive far up
north. New disease outbreaks in previously colder climates. Dengue,
chikungunya, malaria
7. Newer populations are at risk who don’t have natural immunity against
these diseases. Sickle cell disease in Africa and malaria.
Why Sea Level Is Rising
● Water molecules move slightly further apart when they’re

�� heated and layers of molecules slide past each other in groups

giving it fluidity.
Thermal ● This increased motion in water molecules when warm is
Expansion increasing sea levels.

● Increased greenhouse gases lead to a warmer climate &

more melting of ice sheets (at the poles and glaciers)
🧊🌊
● This water flows into the ocean and leads to sea level rise. Melting Polar &
Added volume of water comes in from glacier-melt. Glacial Ice
Why Sea Level Is Rising
 Env. Impacts of Sea Level Rise
🏔 Flooding of coastal ecosystems like estuaries (mangroves, salt marshes)
● Loss of species that depend on arctic and tundra ecosystems (polar bears, penguins, reindeer)
● Loss of thaw-freeze cycle that glaciers go through, depriving surrounding ecosystems and
human communities of water source
 Env. Impacts of Sea Level Rise

Human Impacts
🏔 Relocation of coastal human populations
● Increase in flood frequency = higher insurance
and repair costs, lost property
● Saltwater intrusion (salt water pushing into
ground water & contaminating wells)

● Refugees forced to move inland

Disease Vectors

🦟
● Living organisms (usually mosquitoes, ticks, fleas) that can
transmit diseases from human to human or animal to human

Vectors ● Ex: malaria, Zika, West Nile, dengue fever, cholera

● Warmer temperatures allow insect-transmitted diseases to

spread to parts of the world previously too cold
🌡🗺
● As the insect vectors expand their range further from Expanded
equators, toward poles, new human pops. are at risk Range
Current Aedes aegypti range 🦟
Vector for dengue fever, Zika virus, yellow fever
Projected Aedes aegypti range 🦟
Vector for dengue fever, Zika virus, yellow fever
 Practice FRQ 9.4

Identify a region where

malaria rates may increase
by the year 2050.

Explain how climate

change may contribute to
this increase in malaria in
this region.