14.2 – NOTES Solar Radiation

The Earth’s atmosphere is needed for several reasons Midday sun would fry eggs on rock UV rays would burn skin Nights would be cold enough to freeze CO2 into a solid, in the form of dry ice Sun’s radiant energy and atmospheric gases make an hospitable climate The atmosphere acts as a reservoir/storage unit for oxygen and carbon dioxide It also protects us from harmful radiation and moderates temperature

B.1 The Electromagnetic Spectrum and Solar Radiation Sun’s energy is a result of nuclear fusion   Fusion is combining 2 small nuclei into 1 larger nucleus The reaction is extremely exothermic (releases a lot of energy)

Electromagnetic radiation Energy liberated through fusion in the sun is transmitted to earth as electromagnetic radiation   Electromagnetic spectrum Shows wavelengths and frequencies of various wave types, but all waves have the same speed Type of ER represents a particular wavelength and frequency Radio, micro, infrared, visible light, UV, x-rays, gamma rays, cosmic rays

Made of photons Small packets of light that travel as waves   Photons transfer energy as they collide/interact with matter

Electromagnetic radiation travels as wave Do not require a medium to travel through- can move through a vacuum as well as air   They oscillate, therefore have Frequency- f – the number of waves that pass a given point per second, unit is Hertz (Hz) Hertz – 1/s or s-1 Wavelength- l - distance between the top of two successive waves C= l * f C = speed of light = 3 x 108 m/s – all electromagnetic radiation moves at this speed l = wavelength (m) F = frequency (1/s)

Solar radiation The radiant energy given off by the sun is spread over a large portion of the spectrum The majority of the radiation falls in three regions   45% in IR region 46% in visible region 9% in UV region

Infrared radiation (IR) Frequencies slightly lower than visible red light, and wavelength is slightly longer   Causes certain bonded atoms to vibrate more energetically, which increase the object’s temperature Most is absorbed by CO2 and H2O in the atmosphere This was demonstrated by Tyndall in 1860s This process reradiates energy back into the atmosphere, where it is retained and helps to warm the atmosphere

Visible radiation More than 90% reaches the surface on a clear day   Can energize electrons in some bonds Interacts with electrons is chlorophyll molecules, which provides the energy needed for photosynthesis

Ultraviolet radiation The most harmful radiation given off by the sun   Three separate categories UV-A Longest wavelength, lowest energy Longer than 320 nm Most absorbed by ozone layer Effects: tanning, sunburn, DNA damage, skin cancer

UV-B 280-320 nm   Most absorbed by stratospheric ozone layer Effects: sunburns, skin cancer, DNA damage

UV-C Most energetic of the three UV types   Blocked by the ozone layer Wavelengths shorter than 280 nm Have enough energy to break covalent bonds Used to sterilize materials because it can kill bacteria and destroy viruses Effects: DNA and tissue damage, kills bacteria and viruses

Humans need some UV radiation to produce vitamin D