CFC Chlorofluorocarbon Properties & Environmental Impact 4 — Questions and Answers
Question 1: What UV radiation wavelength range (nm) is most effectively absorbed by stratospheric ozone, protecting life on Earth?
- UV-A: 315–400 nm
- UV-B: 280–315 nm (Correct answer)
- UV-C: 100–280 nm
- Visible: 400–700 nm
Correct answer: UV-B: 280–315 nm
Stratospheric ozone primarily absorbs UV-B radiation (280–315 nm), which is the range most damaging to DNA, skin cells, and marine ecosystems.
Question 2: The Halogen numbering system for refrigerants: what does the digit in the 'tens' place of a three-digit refrigerant number indicate?
- Number of chlorine atoms
- Number of hydrogen atoms plus one
- Number of carbon atoms minus one (Correct answer)
- Number of fluorine atoms
Correct answer: Number of carbon atoms minus one
In the ASHRAE refrigerant numbering system, the tens digit equals the number of carbon atoms minus one; for single-carbon molecules (methane-based), this digit is 0.
Question 3: Which greenhouse gas metric compares the warming impact of a CFC relative to CO₂ over a 100-year period?
- Ozone Depletion Potential (ODP)
- Global Warming Potential (GWP) (Correct answer)
- Total Equivalent Warming Impact (TEWI)
- Atmospheric Radiative Forcing (ARF)
Correct answer: Global Warming Potential (GWP)
Global Warming Potential (GWP) quantifies how much heat a greenhouse gas traps over 100 years relative to CO₂, which is assigned a GWP of 1.
Question 4: R-114 (CFC-114) was commonly used in which specific application before its phase-out?
- Automobile air conditioning
- Centrifugal chillers for large building cooling (Correct answer)
- Domestic refrigerators
- Aerosol propellants in hairspray
Correct answer: Centrifugal chillers for large building cooling
R-114 (dichlorotetrafluoroethane) was used in centrifugal chillers for large commercial and industrial cooling applications due to its low pressure operating characteristics.
Question 5: What is the primary reason CFC molecules are so stable in the lower atmosphere (troposphere)?
- They react quickly with water vapor
- They lack C-H bonds and are resistant to hydroxyl radical attack (Correct answer)
- They dissolve readily in rainwater
- They are heavier than air and sink to the ground
Correct answer: They lack C-H bonds and are resistant to hydroxyl radical attack
CFCs lack hydrogen atoms, so the hydroxyl (OH) radical—which breaks down most organic compounds in the troposphere—cannot attack them, allowing CFCs to persist and migrate to the stratosphere.
Question 6: According to EPA regulations, what is the maximum allowable leak rate for commercial refrigeration equipment with a charge over 50 lbs before repair is required?
- 10% per year
- 20% per year (Correct answer)
- 30% per year
- 50% per year
Correct answer: 20% per year
Under EPA Section 608 regulations, commercial refrigeration equipment with charges over 50 lbs must be repaired if the annual leak rate exceeds 20% of the system charge.
Question 7: Which physical property causes CFCs to migrate upward from the troposphere to the stratosphere despite being denser than air?
- Electrical charge attraction
- Atmospheric mixing and diffusion over decades (Correct answer)
- Active chemical reactions that propel them upward
- Thermal convection currents in the stratosphere
Correct answer: Atmospheric mixing and diffusion over decades
Although CFCs are denser than air, they are transported to the stratosphere through atmospheric mixing, turbulence, and slow diffusion over many years rather than density-driven settling.
CFC Chlorofluorocarbon Properties & Environmental Impact 4
What UV radiation wavelength range (nm) is most effectively absorbed by stratospheric ozone, protecting life on Earth?