The Earth’s Atmosphere Part 1: Atmospheric Science

Overview The atmosphere, when scaled to the size of an apple, is no thicker than the skin on an apple. The atmosphere is a gas. The atmosphere is a fluid – acts as a fluid There is a surface but no “top” – the atmosphere gradually thins out with increasing altitude Air is a mixture of different gases and particles, each with its own physical properties. Facts: Top surface extends up to 620 miles above the Earth’s surface Mass =  5.1480 × 1018 kg Average surface temp = 15^C

Composition of the Atmosphere permanent gases N2 = 78.08% O2 = 20.95% Ar = 0.9% variable gases H2O = Variable 0-4% (average 1%) trace gases Minor (ppm): Argon (Ar) - 9340; Carbon Dioxide (CO2) - 400 Neon (Ne) - 18.18; Helium (He) - 5.24; CH4 - 1.7 Krypton (Kr) - 1.14; Hydrogen (H2) - 0.55 Aerosols Dust Sea-spray Microbes Suspended particles Cloud Condensation Nuclei (CCN)

Composition of the Atmosphere Carbon dioxide 390 ppm (by mass) and counting… Natural and anthropogenic sources/sinks Influential greenhouse gas (GHG) CO2 is neither the strongest atmospheric GHG pound-for-pound nor molecule-for-molecule… Why the fuss? CO2 is a product of the reaction that allows modern civilization to exist: combustion and the utilization of non-renewable fossil fuels.

Composition of the Atmosphere Ozone, CFCs and NOx Ozone (O3) shields the surface from UV rays produced by reaction with NOx and sunlight near the surface CFC’s (Chlorofluorocarbons) destroy stratospheric ozone chlorine is a catalyst: it destroys one O3 molecule and then is free to find another Ozone at high altitudes (stratosphere) is “good”; ozone at low altitudes (troposphere) is “bad.”

The “dry atmosphere”: 78% N2, 21% O2, 1% Ar N2 is primordial – it’s been part of the atmosphere as long as there’s been an atmosphere O2 has been rising from none at all about 2.2 Gya (billion) – comes from photosynthesis Ar40/Ar36 tells us that the atmosphere has been outgassed from volcanoes

Composition of the Atmosphere The Hydrological Cycle - Review