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Fig.2.6

Fig.2.6. Low E: Low freq. & high l. High E: High freq. & low l. (most damaging!). (most intense). (most abundant). Radiation from the Sun (Fig 2.7). Not between. Energy. Radiation exists only at these energy levels. Frequency. (2.5) Radiation and Matter. “Particles” of Energy.

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Fig.2.6

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  1. Fig.2.6 Low E: Low freq. & high l High E: High freq. & low l

  2. (most damaging!) (most intense) (most abundant) Radiation from the Sun (Fig 2.7)

  3. Not between Energy Radiation exists only at these energy levels Frequency (2.5) Radiation and Matter “Particles” of Energy Max Planck: Radiation is quantized – exists only at certain energy levels

  4. Einstein: One “step” = photon “bundle of light energy” New way of thinking about light: Light is a particle Has no mass Moves in waves

  5. Planck’s Constant: 6.63 x 10-34 J·s Calculating the Energy of Light: Unit of energy: joule (J) Accelerate a 1 kg mass from 0 to 1 m/s over a distance of 1 m (1 heartbeat) Equation: E=nh

  6. What is the energy of UV light with a frequency of 1.00 x 1015 s-1 E = hn = (6.63 x 10-34 J·s)(1 x 1015 s-1) E = 6.63 x 10-19 J Can also calculate energy from l E = hn = hc (since n = c) l l Compare to radio wave of l 3 x 109 m E = hc =(6.63 x 10-34 J·s)(3.00 x 108 m/s) l 3 x 109 m E = 6.63 x 10-35 J UV has 10 quadrillion times more energy!

  7. What happens when light hits matter? IR – molecules vibrate, matter heats up Visible – excite electrons, chemical reactions can occur (photosynthesis) UV – knock electrons off  charged particles High freq. UV – break covalent bonds (!) (disrupt biol. processes, damage tissues, cancer)

  8. Fig.02.11 l ≤ + Fig. 2.9: Chapman Cycle (Ozone = steady state) l ≤ +

  9. UV Absorption by O2 and O3 Oxygen: 200-242 nm Ozone: 200-320 nm Why does ozone absorb a broader range? It’s more reactive! O O O O O “Bond-and a half” weaker than double bond  Lower energy light can react

  10. Fig. 2.10 DNA Damage

  11. Cause for Concern • Short l = massive DNA cleavage • 280 nm is 100,000X more damaging than 320nm • Ozone conc. has been dropping • More short l light gets thru • More damage to organisms • 1% decrease in O3 = 2% increase in skin cancer

  12. Skin Cancer • Awareness: increased • Treatments: improved • Early detection • Trend: on the rise!

  13. Reasons • Ozone depletion – partly responsible • Geographic location • More people in outdoor activities? • Tanning beds?

  14. Tanning • Cosmetic benefit vs. cancer risk • Cancer can occur after exposure has stopped • Advance ageing process • Highest risk: Fair hair & skin • Winter • Snow-blindness, cataracts from UVB

  15. Other facts • Geographical location – big factor! • Sunblock helps • Not immune! • UVB harms other organisms • Plants • Marine life (phytoplankton) • Ultimate food source for ocean life • Absorb 80% of man-made CO2 • Greenhouse gas

  16. Fig. 2.13

  17. O3 Decline – Our Fault? • Natural fluctuations: • Seasonal variation in UV intensity • Sunspot activity cycles (1-2% effect) • Wind • Random fluctuations

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