The Earth and Its Atmosphere: Chemical composition and vertical structure

1. The Earth and Its Atmosphere: Chemical composition and vertical structure

2. RECAP • Definition of an atmosphere: the gas surrounding a planet/satellite/comet/… • Origin of the atmosphere. Three stages: • I - gravitational capture of the gasses in the proto planetary nebula of the Sun (mainly H2, He); • II- outgassing of the planet (volcanoes, geysers,…); formation of an ocean (perhaps?);material from meteorites and comets; • III – evolution of the atmosphere due to the presence of life and human activity. • The early atmosphere of the Earth is very different from the atmosphere today! • We learn about the formation and the evolution of the Earth’s atmosphere from the Earth’s geological records and by studying other planets. • The role of the atmosphere: protection from UV and cosmic rays, shields us from meteorites, decreases the day/night temperature variations…

3. Planets in the Solar System • Definition of a planet: a celestial body which • is in orbit around the sun • has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape • has cleared the neighborhood around its orbit • Pluto disqualified since orbit overlaps with Neptune's.

4. The Gainesville Solar Walk • Along NW 8th Ave from 34th St. to 22nd St. • Alachua Astronomy Club (AAC) says • It is the AAC's judgement that Pluto is here to stay and any future modifications of the Solar Walk should be additions or improvements(Approved by the AAC Board, 2006 Sept. 5) • Future enhancement: additional benches, an asteroid rock garden, nighttime lighting, enhanced landscaping

5. Origin of the atmospheres

6. The Terrestrial Planets 1 0.39 0.72 1.5 39.4 1 0.055 0.815 0.1 0.0025 1 0.38 0.95 0.53 0.176 5.5 5.43 5.24 3.94 2 9.78 3.62 8.57 3.7 0.3 23.4 0 2.7 25 62 1 0.24 0.6 1.88 247 24 1407 5832 24.6 153 Mercury Venus Earth Mars Pluto Distance AU. 260 -235 Mass ME. 480 T=15 C Radius RE. -60 Density. -110 Gravity. -190 Obliquity Orbital period. Rotationalperiod -225 -215 Main components - N2, O2 CO2 CH4 CO2

7. The Giant Planets 1 5.2 9.5 19.2 30 1 318 94.5 14.5 17 1 11 9.5 4 3.9 5.5 1.31 0.69 1.29 1.64 9.78 22.9 9 8.7 11 23.4 3 27 98 30 1 11.9 29.5 84 165 24 10 10 18 19 Earth Jupiter Saturn Uranus Neptune Distance AU Mass ME Radius RE Density Gravity Obliquity Orbital period Rotationalperiod Main components N2, O2 H2, He H2, He H2,He,CH4 H2, He

8. Neptune’s atmosphere: 80% H, 19% He, 1% CH4

9. Sample test questions • Since the turn of this century, CO2 in the atmosphere has: a. been increasing in concentration b. been decreasing in concentration c. remained at about the same concentration from year to year d. disappeared entirely • The earth's first atmosphere was composed primarily of: a. carbon dioxide and water vapor b. hydrogen and helium c. oxygen and water vapor d. argon and nitrogen

10. The Earth’s Atmospheric Composition Today Nitrogen (N2) 78.08% Oxygen (O2) 20.95% Permanent gasses Argon (Ar) 0.93% Nobel gasses (Ne, He, H2, Xe) <0.003% Water vapor (H2O) 0-4 % Carbon dioxide (CO2) 0.037 % Methane (CH4) 1.7 ppm Nitrous Oxide (N2O) 0.3 ppm Variable gasses Ozone (O3) 0.04 ppm Particles (dust …) <0.15 ppm 1%=1/100 1ppm=1/1000,000 Chlorofluorocarbons (CFCs) 0.0002 ppm

12. Important gas components OUT IN • Nitrogen: N2 • Input: decaying plant and animal products • Output: biological processes (soil bacteria, plankton) • Oxygen: O2 • Input: photosynthesis; • Output: decay of organic matter, production of oxides, breading (CO2). • Water vapor: H2O • Input: evaporation • Output: condensation • A highly variable greenhouse gas, not visible, results in large latent heat.

13. Carbon dioxide: CO2 • Input: plant decay, exhalation, fossil fuels, deforestation. • Output: photosynthesis, dissolves in the ocean • Greenhouse gas, steadily increases with time. CO2 • Ozone: O3 • O3 in the stratosphere (25 km) shields the UV light; • At the ground level it results in photochemical smog. • Dust, aerosols and pollutants: also can have a greenhouse effect

14. Mass,Weight, Density, Pressure • Mass M: • property of matter, • SI unit: kg. Other units: 1kg=1000 g, 1 lb=450 g • Weight : • a force, has a magnitude and direction (vector). • weight = mass x gravity g(Earth)= 9.78 m/s2 • SI unit: kg m/s2 -> N g(Mars)= 3.7 m/s2 • Density r: • mass per unit volume: density = mass / volume • SI unit: kg/m3, Other: g/cm3 • Pressure p: • p= force/area • SI units: Pa=N/m2, Other: 1bar=100 Pa

15. Atmospheric pressure Atmospheric pressure and density decrease with altitude exponentially!!!

16. Vertical Structure of the Earth’s Atmosphere 99.9% 90%

17. Atmospheric layers(according to the temperature) • Troposphere: • The temperature T decreases with height about 6.5 K/km. • Well mixed as a result of turbulence and convection; • Weather phenomena • Tropopause: • isothermal (T constant) • located 8-15 km above the ground. • Stratosphere: • Increasing temperature; • O3 layer at 25 km altitude; • The atmosphere is very stable. • Stratopause: T=const • Mesosphere: • T is decreasing: effective cooling through IR emission. • Mesopause: the coldest region on Earth. • Thermosphere: fast T increase. Diffusive separation of gasses.

18. Atmospheric layers • Mixing: • Homosphere: • well mixed, • the chemical composition is constant. • Heterosphere: • no turbulence and mixing, • diffusive separation of gasses • Ionization: • Ionosphere: part of the atmospheric gas is ionized through photo ionization or impact ionization.