6.2 Stratospheric Ozone

Question 1

how are ozone molecules formed?

Answer 1

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

Question 2

why is stratospheric ozone a dynamic equilibrium?

Answer 2

ozone is constantly being created and destroyed

Question 3

seasonal changes in stratospheric ozone in polar regions

Answer 3

• cold temps in winter allow formation of clouds of ice particles : polar stratospheric clouds
• 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

Question 4

Ozone-depleting substances (ODS) examples

Answer 4

• 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

Question 5

how is ozone depleted by CFCs?

Answer 5

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).

Question 6

effects of ultraviolet radiation on human health

Answer 6

exposure to UV-B=

• eye damage (catarcas)
• mutations during cell division, sunburn and in the long term, skin cancers
• immune system can be damaged

Question 7

effects of ultraviolet radiation on biological productivity

Answer 7

• damage to photosynthetic organisms
• ! phytoplankton (form the basis of aquatic food webs)
• decreases rate of photosynthesis
• mutations

Question 8

​Altering Human Activity to reduce ozone depletion

Answer 8

• Replace gas-blown plastics
• Replace the old fridge with the existing “greenfreeze” technology which does not deplete the ozone
• Non-propellant alternatives

Question 9

Regulating and reducing pollutants to reduce ozone depletion

Answer 9

• 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

Question 10

Cleanup and Restoration to reduce ozone depletion

Answer 10

• Add ozone to or remove chlorine from stratosphere

Question 11

UNEP

Answer 11

• United Nations Environmental Programme
• provide information to countries and public on disadvantages of pollution

Question 12

Identify issues that still persist with ozone-depleting substances

Answer 12

• 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

Question 13

what are reasons for the illegal trade of ODSs?

Answer 13

• 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

Question 14

montreal procotol successes

Answer 14

• by end of 2002: industrialised coutnries reduced ODS consumption by 99%
• raised awareness of effect of ODS on environment
• provided an incentive for countries to find alternatives

Question 15

Vienna Convention

Answer 15

• 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

Question 16

what are CFCs being replaced with?

Answer 16

hydrochlorofluorocarbons (HCFCs)
- greenhouse gases
- global warming potential less than CFCs

Question 17

montreal protocol full name

Answer 17

montreal protocol on substances that deplete the ozone layer

Question 18

montreal protocol failures

Answer 18

• 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
  • ODS substitutes are often costlier than CFCs

Question 19

montreal protocol aims

Answer 19

Protect the ozone layer by phasing out the production and consumption of ODS

Question 20

how many countries signed the montreal protocol and when

Answer 20

197 countries in 1987