5.3: Ultraviolet Radiation Damage

Question 1

What are the effects of UV radiation on organisms?

Answer 1

• Humans: skin cancer
• Green plants: light-harvesting photosynthetic mechanisms are intended for visible radiation, so intense UV-radiation can destroy those mechanisms/processes
• Phytoplankton: start of food chain = ↓ w/ ↑ exposure
• Crops: exposure = ↓ chlorophyll content = ↓ biomass formation = ↓ crop yields

Question 2

What wavelengths of light are absorbed by O2 and O3? How do these wavelengths compare to the spectrum of incoming solar radiation?

Answer 2

• O2 ≈ 125-175 nm (shorter)
• O3 ≈ 175-300 nm
• Ozone = only absorbs 200-300 nm w/in incoming solar radiation spectrum (entire spectrum = 200-700 nm)

Question 3

How does UV light damage molecules? What is the relationship between UV-induced damage of molecules and damage to organisms?

Answer 3

• UV can break bonds of organic molecules and produce reactive fragments
• damage done to living tissue = dependent on wavelength

Question 4

Define absorptivity/extinction coefficient

Answer 4

E = absorptivity = extinction coefficient (length-1)
- Depends on wavelength bc absorption of light by O3 varies by wavelength

Question 5

Which wavelengths of light are most sensitive to changes in the amount of O3? Why?

Answer 5

• O3 changes affect the UV flux most sensitivitly @ shortest wavelengths (where damage to biological molecules = greatest
• Bc % UV light transmitted = ↑ w/ ↓ ozone layer

Question 6

UV-radiation exposure = linked to…

Answer 6

skin cancer & damage green plants & damage to crops

Question 7

UV-B = 280-320 nm =

Answer 7

most damaging (for skin)

Question 8

UV-A = 320-400 nm =

Answer 8

less damaging (for skin) but still damaging (just of less concern)

Question 9

Solar flux = ↓ w/ __ distance from equator

Answer 9

↑

Question 10

Flux @ ground level = depends on ____ bc…

Answer 10

latitude
- sun’s rays = more direct @ ↓ latitude
- O3 = thinner over equator

Question 11

Beer-Lambert Law

Answer 11

How much does a change in the O3 layer affect the amount of UV light reaching earth’s surface? –> Beer-Lambert Law = As thickness of layer increases, fraction of light transmitted through decreases