Transcript Stratospheric Ozone

Stratospheric Ozone
• Stratosphere is about
10,000 m to 49,000 m
• Temperatures about 50oC until 30,000 m
and then increase to
about 23oC. Increase
due to absorption of
UV by ozone/oxygen.
• Ozone protects earth
surface from UV rays.
Ozone Formation/Destruction in
the Stratosphere
Ozone Depletion
• World-wide
monitoring shows
stratospheric ozone
decreasing for more
than two decades.
• Since the 1970s, an
ozone hole has
formed over
Antarctica in which
up to 60 % of the total
ozone is depleted.
• Depletion of ozone
primarily due to
ChloroFluoroCarbons
(CFCs)
What are CFCs
• CFCs are commonly
used as refrigerants,
solvents, and foam
blowing agents.
• The most common
CFCs are CFC-11,
CFC-12, CFC-113,
CFC-114, and CFC115.
CFC Production
• Freon 11 is
fluorodichloromethane
and has a structure of
CCl3F
• Carbon tetrachloride,
methyl bromide and
methyl chloroform and
other halons also
destroy the ozone layer
CFC production in US
• HCFC (hydrogenated
CFCs) are more reactive
in troposphere and so less
destructive to ozone layer
• Brominated compounds
also more reactive in
troposphere but Br is 40
times more efficient at
destroying ozone than
chlorine.
How do CFCs affect ozone?
• CFCs - unreactive in the
troposphere and move
unchanged to stratosphere
• Short-wave UV light in
stratosphere breaks down
CFCs and chlorine is
released
• Much of the chlorine
reacts to form HCl or
other compounds that do
not react with ozone
 Cl + O3  ClO + O2
 ClO + O  Cl + O2
 ClO + ClO  Cl2O2  Cl2
+ O2
 Cl2 can photodissociate to
form more chlorine atoms
“A single chlorine atom can destroy as many as
100,000 ozone molecules during residence in
stratosphere”
Ozone Depleting Potential
All CFCs are not created equal
• The ozone depleting potential (ODP) is the ratio of
the impact on ozone of a chemical compared to the
impact of a similar mass of CFC-11. Thus, the
ODP of CFC-11 is defined to be 1.0. HFCs have
zero ODP because they do not contain chlorine.
• Other CFCs and HCFCs have ODPs that range
from 0.01 to 1.0. The halons have ODPs ranging
up to 10. Carbon tetrachloride has an ODP of 1.2,
and methyl chloroform's ODP is 0.11.
CFC characteristics
Compound
CFC-11
(CCl3F)
Lifetime ODP
(years)
45
1
GWP-2
CAS No.
4600
75-69-4
100
1
10600
75-71-8
85
0.8
6000
76-13-1
300
1
9800
76-14-2
1700
0.6
10300
76-15-3
Trichlorofluoromethane
CFC-12
(CCl2F2)
Dichlorodifluoromethane
CFC-113
(C2Cl3F3)
Trichlorotrifluoroethane
CFC-114
(C2Cl2F4)
Dichlorotetrafluoroethane
CFC-115
(C2ClF5)
Monochloropentafluor
ethane
Ozone Depletion Means
• Increase in UV radiation
(UVB)
• UVB has been linked to
skin cancer, cataracts,
damage to crops, damage
to marine organisms (like
reefs), damage to plastics
• Picture shows squamous
cell carcinoma in elderly
patient
Skin cancer is definitely related
to UV/sunlight exposure
• Basal cell carcinoma
• Malignant melanoma
Montreal Protocol
• 1989 Global Treaty to
protect ozone layer
• Currently 140 countries
are parties
• Timetable to reduce and
end production and
consumption of 8 major
halocarbons
• Many governments
committed to early phase
outs
Global Climate Change
• Earth’s temperature balance between solar
radiation input and
reflection and reradiation
of energy from earth back
into space.
• Atmospheric gases trap
some outgoing energy,
retaining heat - The
Greenhouse Effect
Solar energy blocked by atmospheric sulfates
(radiating force in watts per square meter)
What are greenhouse gases?
• Carbon dioxide –
burning of fossil fuels,
wood products.
• Methane – production
of coal, gas and oil.
Decomposition of
wastes at landfills.
Raising livestock.
• Nitrous oxide –
industrial and
agricultural activites.
• CFCs, HFCs, sulfur
hexafluoride –
generated in industrial
processes.
• Water vapor, ozone.
Global Warming Potential
(GWP)
Global Warming Potential: a number that refers to the amount
of global warming caused by a substance
The GWP is the ratio of the warming caused by a
substance to the warming caused by a similar mass of carbon
dioxide. Thus, the GWP of CO2 is defined to be 1.0 . Methane
is 21. Nitrous Oxide (N2O) is 310. CFC-12 has a GWP of
8,500, while CFC-11 has a GWP of 5,000. Various HCFCs
and HFCs have GWPs ranging from 93 to 12,100. SF6 is
23,900. Water, a substitute in numerous end-uses, has a GWP
of 0.
GHG Emissions from various sources in the US
Methane emissions in US
CFC Emissions in US
Nitrous oxide emission in US
Percentage of total energy consumed in US as
fossil fuels, renewables and nuclear.
Effects of climate change
• Ecosystem decline
such as Everglades,
coral reefs
• Flooding/desertific
ation
• Human health
issues
• Agricultural
impacts
Change in ecological systems
Increases in precipitation and extreme weather
events can lead to flooding
Health Issues
• Warmer climates in temperate
zones can mean that tropical
and subtropical diseases can
enlarge their range.
• Infectious diseases like
cholera more likely in warm
climates.
• Hotter temperatures increase
deaths as it aggravates
cardiovascular and
respiratory problems.
Human populations at risk
Severe shifts in agriculture
due to extreme weather,
extended droughts and
flooding. For example,
glaciers have disappeared
in Northern India, severely
affecting the region where
farmers rely on melting of
glaciers for irrigation.