Stratospheric Ozone Depletion (module 5)

Question 1

Describe the structure and thermal patterns of Earth’s atmosphere, and explain where the ozone layer is located

Answer 1

• composed of several sub-layers that differ in density, gas composition, and temperature
• Troposphere (we live here, earth’s surface up to 20km, temp decreases with altitude due to cooling effect) - mount Everest
• Stratosphere (50km, temp increases with altitude due to absorption of UV radiation)
• Mesosphere (85km, temp decreases with altitude) - meteors
• Thermosphere (690km, temp increases a lot due to absorption of high energy solar radiation) - shuttle
• Exosphere (10000km)
• 90% of ozone found in stratosphere (30-35 km above Earth’s surface) (comprised almost entirely of nitrogen and oxygen, high concentration of ozone)

Question 2

Describe the role of the stratospheric ozone in the atmosphere

Answer 2

• UV radiation absorption when intact (50% of UV-A, 90% of UV-B, and all of UV-C coming from the sun)
• Protection of Life
• Prevention of DNA damage
• Climate regulation

Question 3

Explain how the ‘hole’ in the ozone layer was first discovered, and recognize how ongoing research monitors ozone levels

Answer 3

• Significant decline in stratospheric ozone levels over Antarctica - Dobson spectrophotometer
• Depletion was due to man made chemicals (CFC’s)
  Monitor: satellite observations, Dobson spectrophotometer

Question 4

Explain the three conditions needed to enable ozone destruction

Answer 4

• UV radiation
• Extremely low temperatures
• A surface on which the ozone destruction process can occur (polar stratospheric clouds)

Question 5

Describe the basic chemistry of how stratospheric ozone is created and destroyed

Answer 5

• When high energy UV radiation from the sun breaks apart molecular oxygen
• Oxygen atom them combines with an oxygen molecule producing a new molecule with three atoms of oxygen (ozone)
  Destroyed - ozone absorption of UV radiation
• oxygen atom produced reacts with another ozone molecule to form two oxygen molecules

Question 6

Identify the control variable and planetary boundary for stratospheric ozone depletion

Answer 6

Stratospheric ozone concentration (DU)
- <5% reduction from preindustrial level of 290 DU
- Only transgressed over Antarctica in southern hemisphere spring (200 DU)

Question 7

State the main goal of the Montreal Protocol as well as why it was amended over time, and describe some of its outcomes

Answer 7

• Plan developed to phase out CFC’s
• Individual governments developed their own policies for reduction of CFC’s
• amended to account for new ozone-depleting substances
• advancements in alternative technologies
• outcomes: reduction in ozone-depleting substances
• protection of human health (skin cancer cases avoided)
• environmental benefits (reducing UV radiation, minimizing damage to plants)

Question 8

Reflect on the factors that made the Montreal Protocol an environmental policy success story

Answer 8

• Global collaboration
• Timely action
• Scientific consensus

Question 9

Explain why ozone depletion is most prevalent over Antarctica in Southern Hemisphere spring

Answer 9

• unique atmospheric and climate conditions
• strong stable polar vortex
• low temperatures which lead to formation of polar stratospheric clouds