CFC Chlorofluorocarbon Properties & Environmental Impact 5 — Questions and Answers
Question 1: Polar stratospheric clouds (PSCs) accelerate ozone depletion over Antarctica primarily by:
- Blocking UV radiation from reaching the ozone layer
- Providing surfaces for heterogeneous chemical reactions that activate chlorine (Correct answer)
- Absorbing CFCs before they reach the ozone layer
- Increasing temperatures that speed up ozone reactions
Correct answer: Providing surfaces for heterogeneous chemical reactions that activate chlorine
PSC ice crystal surfaces catalyze reactions that convert reservoir chlorine compounds (like HCl and ClONO₂) into active Cl₂ gas, which rapidly destroys ozone when spring sunlight arrives.
Question 2: The term 'ozone hole' technically refers to:
- A permanent absence of ozone above Antarctica
- A region where stratospheric ozone falls below 220 Dobson Units (Correct answer)
- Any area with less ozone than the equatorial average
- Destruction of all ozone in a localized column
Correct answer: A region where stratospheric ozone falls below 220 Dobson Units
Scientists define the Antarctic ozone hole as the region where total column ozone drops below 220 Dobson Units (DU), which is substantially lower than the pre-depletion baseline of ~300 DU.
Question 3: R-113 (CFC-113) was primarily used as a(n):
- Refrigerant in domestic freezers
- Solvent for cleaning electronic circuit boards (Correct answer)
- Blowing agent for polystyrene foam
- Aerosol propellant in medical inhalers
Correct answer: Solvent for cleaning electronic circuit boards
CFC-113 (trichlorotrifluoroethane) was extensively used as a precision cleaning solvent in electronics manufacturing due to its excellent solvency and non-flammability.
Question 4: What does a Dobson Unit (DU) measure in relation to ozone?
- The concentration of ozone at a specific altitude
- The total column amount of ozone compressed to standard temperature and pressure (Correct answer)
- The rate of ozone depletion per year
- The thickness of the stratospheric layer in kilometers
Correct answer: The total column amount of ozone compressed to standard temperature and pressure
One Dobson Unit represents a layer of pure ozone 0.01 mm thick at standard temperature and pressure; the total atmospheric ozone column is measured by summing ozone at all altitudes.
Question 5: Which international agreement strengthened the Montreal Protocol by accelerating CFC phase-out schedules for developed nations?
- Kyoto Protocol (1997)
- Copenhagen Amendment (1992) (Correct answer)
- Paris Agreement (2015)
- Vienna Convention (1985)
Correct answer: Copenhagen Amendment (1992)
The Copenhagen Amendment of 1992 significantly accelerated CFC phase-out deadlines, moving the complete production ban in developed countries from 2000 to January 1, 1996.
Question 6: What is the approximate ODP of HCFC-22 (R-22) compared to CFC-11's reference value of 1.0?
- 0.005
- 0.055 (Correct answer)
- 0.5
- 0.9
Correct answer: 0.055
R-22 has an ODP of approximately 0.055, roughly 18 times less damaging than CFC-11, due to its hydrogen atom enabling tropospheric degradation before much of it reaches the stratosphere.
Question 7: Which health effect is most directly linked to increased UV-B radiation resulting from stratospheric ozone depletion?
- Increased rates of melanoma and non-melanoma skin cancers (Correct answer)
- Higher incidence of lung cancer from UV absorption
- Increased cardiovascular disease from UV-induced inflammation
- More frequent cataracts from UV-A radiation exposure
Correct answer: Increased rates of melanoma and non-melanoma skin cancers
UV-B radiation is strongly linked to both melanoma and non-melanoma skin cancers; each 1% decrease in stratospheric ozone is estimated to increase UV-B by about 2% and skin cancer rates by roughly 2-4%.
CFC Chlorofluorocarbon Properties & Environmental Impact 5
Polar stratospheric clouds (PSCs) accelerate ozone depletion over Antarctica primarily by: