Summary Study notes for a 7 in IB ESS Topic 6: Atmospheric Systems
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IB Environmental Systems and Societies SL
Institución
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ATMOSPHERIC SYSTEMS, Topic 6
6.1 INTRODUCTION
Dynamic system, affected by human and other organisms activities that impact atmospheric
composition which in turn affects humans and other organisms activities.
Influences on climate:
- Abiotic factors: temperature and precipitation (measured directly and indirectly by
proxy, atmospheric gas concentration in bubbles trapped in ice…)
- Biotic factors: plants and animals (fossilized animals…)
Before plants could photosynthesize there was no free oxygen.
- Early Carboniferous period (350MYA), 20°C, carbon dioxide at 1500ppm (million)
- Carboniferous period (300MYA), 12°C, carbon dioxide at 350ppm
- Today, 15°C, carbon dioxide 400ppm
Greenhouse Effect: natural and necessary phenomenon maintaining suitable
temperatures for living systems. Caused by gases in the atmosphere reducing heat losses
by radiation back into space. They trap energy reflected from the Earth and radiate it back
to its surface.
Incoming solar radiation is made up by ultraviolet light, visible light and infrared heat. About
50% is absorbed scattered or reflected by the atmosphere and clouds. Of the 55% reaching
the Earth’s surface 4% is reflected back and 51% absorbed (photosynthesis, heat ground
and seas, evaporation…).
Greenhouse gases (GHGs): carbon dioxide, water vapour and methane (only molecules
with two or more bonds joining the atoms can absorb and re-emit energy in this way).
If there were none of these, Earth’s temperature would fall drastically each night.
6.2 STRATOSPHERIC OZONE
Ozone (O3): found in the stratosphere where it blocks ultraviolet radiation protecting life
(good), and troposphere (bad, photochemical smog). The highest concentration is found
between 20 and 40km (15 to 20km at poles) and is a very thin layer of about 1-10ppm ozone.
The ozone layer is in dynamic equilibrium since ozone is continuously made from oxygen
atoms and continuously converted back to oxygen (atoms & molecules); both during
formation and destruction UV radiation is absorbed. This allows life to exist on Earth.
UV-C radiation is the most dangerous carrying the most energy and 99% of it is blocked.
About 50% of UV-B radiation is blocked. UV-A radiation is almost harmless, passes through.
Benefits of UV radiation Risks of UV radiation
Stimulates Vitamin D production in animals Genetic mutation and effects of health.
(deficiency causes rickets in child bones Cataract formation in eyes.
when lacking calcium). Skin cancers.
Treat psoriasis and vitiligo (skin diseases). Suppression of the immune system.
Sterilizers as it kills pathogenic bacteria. Damage to photosynthetic organisms and
Air and water purifier. their consumers (both phytoplankton and
zooplankton that feed on them).
, Ozone hole: Since the 1950s scientists studying the stratosphere above Antarctica noticed
the amount of ozone decreasing between September and October and increasing again in
November. Despite this annual cycle, the hole is growing, in the last 30 years the minimum
thickness decreased and recovery time extended. Other areas like the artic began showing
similar conditions. The findings were confirmed by NASA satellite pictures.
Ozone Depleting Substances (ODS)
- Chlorofluorocarbons (CFCs): used as propellants in spray cans, plastic foam
expanders and refrigerants. Release chlorine atoms that react with ozone destroying
it and react with oxygen atoms preventing ozone formation, therefore a single chlorine
atom can destroy many molecules of ozone in a chain reaction with positive feedback.
- Hydrochlorofluorocarbons (HCFCs): used to replace CFCs. They too release chlorine
but have a shorter lifetime, stronger greenhouse gases
- Halogens: used as fire extinguishers. Release bromine atoms
- Methyl bromide: used as pesticide. Release bromine atoms
- Nitrogen oxides: originated from bacterial breakdown of nitrites and nitrates in the soil
(natural). Used in high-flying supersonic aircraft (anthropogenic). They are converted
to NO, which reacts with ozone.
Reducing ODS presence
A. Altering human activity: replace gas-blown plastics, replace CFCs with other
propellants (CO2, propane or air), replace aerosols with pump action sprays, replace
methyl bromide pesticides (many of these are greenhouse gases)
B. Regulating and reducing: recover and recycle CFCs from refrigerators and AC units,
legislate to have fridges returned to the manufacturer and coolants removed/stored.
Capture CFCs from scrap car air conditioner units
C. Clean up and restoration: add ozone or remove chlorine from stratosphere
International Agreements and Actions against CFCs
Before the general public boycotted products containing CFCs changing to ozone-friendly
spray, then forbidden by law and now are hardly produced anymore.
United Nations Environmental Programme: forges international agreements, evaluates
effectiveness of the agreements, gives information to states, organization and public.
Timeline in CFC reduction
1970s: ozone depleting properties of CFCs were discovered, USA and Sweden banned non-
fundamental uses and concerns continued for the 1980s
1985: British Antarctic Survey reports the ozone hole
1987: Montreal Protocol (30+ countries agree to halve CFC emission by 2000)
1990: London Amendment to toughen MP (MEDCs eliminate CFC by 2000, LEDCs by 2010)
1992: further measured to accelerated the phasing out of ODS
1995: Nobel Prize for Chemistry to Molina, Sherwood Rowland and Crutzen for their work
on solving the ozone depleting issue
2006: NASA and NOAA record the Antarctic ozone hole as the largest ever measured.
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