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Fig. 4.1
Gas Volume
Nitrogen (N2) 780,840 ppmv[1] (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 393.65 ppmv (0.039365%)
Neon (Ne) 18.18 ppmv (0.001818%)
Methane (CH4) 1.77 ppmv (0.000177%)
Helium (He) 5.24 ppmv (0.000524%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.3 ppmv (0.00003%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)
Xenon (Xe) 0.09 ppmv (0.000009%)
Ozone (O3) 0.0 to 0.07 ppmv (0 to 0.000007%)[2]
Nitrogen dioxide (NO2) 0.02 ppmv (0.000002%)
Iodine (I2) 0.01 ppmv (0.000001%)
Ammonia (NH3) trace
Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface

Different gases have different absorption properties, and so interact differently with various wavelengths of radiation. Radiation of a given wavelength may pass almost unimpeded through relatively thick layers of one gas, but be almost totally absorbed by even small amounts of another gas. This is the source of the greenhouse effect: the composition of the atmosphere directly affects how much radiation (and of which wavelengths) is able to escape to space. Recall that the wavelength of the energy radiated by an object depends on its absolute

  1. “ppmv” stands for “parts per million by volume.”
  2. Ozone composition varies significantly by vertical distance from the surface of the Earth, latitude, and time of year. Most ozone is concentrated in the lower-to-mid stratosphere (20-35 km above the surface of the Earth), and there is generally less ozone near the equator and more toward the poles. Ozone concentration is at its highest during the spring months (March-May and September-November for the Northern and Southern hemispheres, respectively).