6.2 Stratospheric Ozone Flashcards
how are ozone molecules formed?
solar ultraviolet radiation breaks apart one oxygen molecule (O2) to produce two oxygen atoms (2 O)
each of these highly reactive atoms combines with an oxygen molecule to produce an ozone molecule (O3).
these reactions occur continually whenever solar ultraviolet radiation is present in the stratosphere. As a result, the largest ozone production occurs in the tropical stratosphere
why is stratospheric ozone a dynamic equilibrium?
ozone is constantly being created and destroyed
seasonal changes in stratospheric ozone in polar regions
winter in Southern hemisphere = air over Antarctica is cut off from rest of atmosphere by circumpolar winds (block warm air from entering Antarctica)
- temperatures get extremely cold = formation of clouds of ice particles
- ice particles offers surfaces on which chemical reactions can take place, involving chlorine compounds present in the stratosphere as a result of human activities
- Reactions release chlorine atoms
- in the presence of sunlight (UV atoms) in spring -> chlorine atoms destroy ozone in a series of chemical reactions
→ hole in ozone increases in spring
- in summer, the ice clouds evaporate, chlorine converted into other compounds (i.e. chlorine nitrate), ozone hole diminishes
Ozone-depleting substances (ODS) examples
- Chlorofluorocarbons (CFCs or freons) - propellants in spray cans, foam, refrigerants
- Hydrochlorofluorocarbons (HCFCs) - replacements for CFCs
- Halon - fire extinguishers
- Methyl bromide - pesticides
- Nitrogen oxides - bacterial breakdown of nitrites and nitrates in the soil, supersonic aircraft
how is ozone depleted by CFCs?
1) UV radiation breaks off a chlorine atom from a CFC molecule.
2) The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone.
3) The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO).
4) The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2).
effects of ultraviolet radiation on human health
exposure to UV-B=
- eye damage: temporary blindness (acute), cataracts -> eventually blindess (chronic)
- mutations during cell division, sunburn and in the long term, skin cancers
- immune system can be damaged
effects of ultraviolet radiation on biological productivity
- damage to photosynthetic organisms
- ! phytoplankton (form the basis of aquatic food webs)
- decreases rate of photosynthesis
Altering Human Activity to reduce ozone depletion
- Replace gas-blown plastics
- Replace the old fridge with the existing “greenfreeze” technology which does not deplete the ozone
- Non-propellant alternatives -> no need for aerosols
Regulating and reducing pollutants to reduce ozone depletion
- Recover and recycle CFCs from refrigerators and AC units
- legislate to return fridges to manufacturer and coolants
- capture CFCs from scrap products to prevent harm from entering atmosphere
Cleanup and Restoration to reduce ozone depletion
- Add ozone to or remove chlorine from stratosphere
UNEP
- United Nations Environmental Programme
- provide information to countries and public on disadvantages of pollution
- created initial Montreal Protocol on Substances that Deplete the Ozone layer 1987
Identify issues that still persist with ozone-depleting substances
- illegal market for ODSs continues and requires consistent monitoring
- in many low income countries, there is still a significant demand for CFCs as reliance on equipment using these chemicals remains high
what are reasons for the illegal trade of ODSs?
- ODS substitutes are often costlier than CFCs
- updating equipment to enable use of alternative chemicals is generally expensive
- the lifetime of CFC-containing equipment is often long
- penalties in many countries for ODS smuggling is small
magnitude of illegal ODS trade is between 7000-14000 tonnes of CFCs annually
montreal procotol successes
- by end of 2002: industrialised coutnries reduced ODS consumption by more than 99%
- provided an incentive for countries to find alternatives
- provided funding and technical support to developing countries
Vienna Convention
- 1985
- protection of Ozone Layer
- aimed to protect human health and the environment against adverse effects resulting from human activities which modified or were likely to modify the ozone layer
what are CFCs being replaced with?
hydrochlorofluorocarbons (HCFCs)
- greenhouse gases
- global warming potential less than CFCs
montreal protocol full name
montreal protocol on substances that deplete the ozone layer
montreal protocol failures
- cfcs have long lifespans, thus the effect is not completely seen
- an illegal trade of ODSs persists
- penalities in many countries (LEDC) for ODS sumggling remains small
- some countries slow to comply at first
montreal protocol aims
Protect the ozone layer by phasing out the production and consumption of ODS
how many countries signed the montreal protocol and when
24 countries 1987 ->
now 197 countries
why can most ODS’s be referred to as stable compounds?
they persist in atmopshere for decades as they travel upwards to stratopshere
what type of UV is harmful to humans?
UV-B
