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

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

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

Fig.2.6

High E: High freq. & low Low E: Low freq. & high

Page 2: Fig.2.6 High E: High freq. & low  Low E: Low freq. & high

Radiation from the Sun (Fig 2.7)

(most intense) (most abundant)

(most damaging!)

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(2.5) Radiation and Matter

“Particles” of Energy

Max Planck:Radiation is quantized – exists only at certain energy levels

Frequency

Energy

Radiation exists onlyat these energy levels

Not between

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Einstein: One “step” = photon“bundle of light energy”

New way of thinking about light:Light is a particleHas no massMoves in waves

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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=h

Planck’s Constant: 6.63 x 10-34 J·s

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What is the energy of UV light with a frequency of 1.00 x 1015 s-1

E = h = (6.63 x 10-34 J·s)(1 x 1015 s-1)

E = 6.63 x 10-19 J

Compare to radio wave of 3 x 109 m

E = hc = (6.63 x 10-34 J·s)(3.00 x 108 m/s) 3 x 109 m

E = 6.63 x 10-35 J

Can also calculate energy from

E = hhc (since = c)

UV has 10 quadrillion times more energy!

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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)

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Page 9: Fig.2.6 High E: High freq. & low  Low E: Low freq. & high

Fig.02.11≤

+

+

Fig. 2.9:Chapman Cycle

(Ozone = steady state)

Page 10: Fig.2.6 High E: High freq. & low  Low E: Low freq. & high

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

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Fig. 2.10

DNADamage

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Cause for Concern

• Short = massive DNA cleavage

• 280 nm is 100,000X more damaging than 320nm

• Ozone conc. has been dropping More short light gets thru More damage to organisms

1% decrease in O3 = 2% increase in skin cancer

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Skin Cancer

• Awareness: increased

• Treatments: improved– Early detection

• Trend: on the rise!

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Page 15: Fig.2.6 High E: High freq. & low  Low E: Low freq. & high

Reasons

• Ozone depletion – partly responsible

• Geographic location

• More people in outdoor activities?

• Tanning beds?

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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

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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

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Fig. 2.13

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O3 Decline – Our Fault?

• Natural fluctuations:

– Seasonal variation in UV intensity

– Sunspot activity cycles (1-2% effect)

– Wind

– Random fluctuations