1. Intro and GHG

Question 1

List examples of how energy is derived from the sun.

Answer 1

• Solar uses sun’s light directly.
• Biomass uses photosynthesis, sunlight to sugar.
• Wind caused by sun heating planet, movement of air.
• Waves generated by wind passing over oceans.
• Rainfall from solar evaporation causes HE power.

Question 2

List exceptions where energy is not derived by sun.

Answer 2

• Nuclear is radioactive decay of matter.
• Geothermal is gravitational potential of Earth’s creation.
• Tidal is largely driven by the moon.

Question 3

Define direct and indirect radiation.

Answer 3

• Direct Radiation is when light from the sun does not interact with the atmosphere, direct incident on Earth, casts a shadow.
• Indirect Radiation is when sun’s light is scattered in the atmosphere.

Question 4

Outline the three major types of scattering.

Answer 4

1. Mie Scattering - Same WL as light.
2. Geometric Scattering - WL larger than light.
3. Rayleigh Scattering - WL very small.

Question 5

Outline the absorption process.

Answer 5

• Specific WL that can be absorbed by a material is dependent on the material’s electronic energy levels.
• When light is absorbed, the material absorbs a photon, which is subsequently destroyed. This energy release excites an electron to a higher energy level.
• This excitation process only occurs if there is an energy level present for the electron to be raised to.
• Electron usually relaxes back to ground state, releasing a phonon, generating heat.
• Spontaneous emission of a photon may occur, when energy is emitted as light.

Question 6

Outline the greenhouse effect.

Answer 6

• Sun radiates UV, visible light and IR to the planet. UV is largely absorbed and reflected back to space by O2/O3.
• IR radiation is largely absorbed by H20.
• Visible light passes through the atmosphere, and is absorbed by the Earth’ surface. This visible light is emitted by the Earth at a longer wavelength, IR radiation.
• Some of this IR radiation is then absorbed by H2O. However, there are some gaps in the atmosphere’s absorption/scattering spectrum that allows the IR to escape.
• GHGs are an issue because they close these gaps in the spectrum. They will absorb this IR radiation, and emit it back to Earth, the net result is global warming.
• GHGs let visible light through and refuse to let the IR leave, this is the greenhouse effect.