Chemistry of the Atmosphere Notes

The atmosphere consists primarily of:
Nitrogen (N₂)
Oxygen (O₂)
Trace amounts of Argon, Carbon dioxide, Neon, and other gases.
Approximately 5.3 x 10^18 kg total mass (water not included due to variability).

Closest to Earth's surface (7-18 km above the equator)
Contains 80% of the atmosphere's mass; where weather occurs (rain, lightning, hurricanes).
Temperature decreases with altitude.
Most active region – where all the dramatic events
of weather (rain, lightning, hurricanes) occur.
Thinnest layer of the atmosphere (10 km )

19-50 km above the equator.
Composition: Nitrogen, Oxygen, and contains Ozone (O₃).
Temperature increases with altitude due to UV radiation reactions creating ozone to protect Earth from harmful UV rays.
One of the products of this reaction sequence is
ozone (O3), which serves to prevent harmful UV
rays from reaching Earth’s surface.

50-400 km above the equator.
Temperature rises with altitude due to solar energetic particles.
Ionized particles reflect radio waves back to Earth.
In reverse, these processes liberate the equivalent
amount of energy, mostly heat

~400 km to ~10,000 km above the equator.
Outermost layer; separates atmosphere from outer space.
This layer separates the rest of the atmosphere from outer space – 10,000 km thick
There is a lot of empty space in between of very spread-out hydrogen and helium gases
Very low density of gases (Hydrogen and Helium); extremely cold with virtually no breathable air.

Nitrogen Fixation: the conversion of molecular nitrogen into nitrogen compounds such as nitrates
Atmospheric Nitrogen Fixation:
- Reaction:
- 2NO (g) + O₂ (g) → 2NO₂ (g)
- 2NO₂ (g) + H₂O (l) → HNO₂ (aq) + HNO₃ (aq)
- ▪ Nitric acid is converted to nitrate salts in
  the soil.
  ▪ These nutrients are taken up by plants,
  which in turn are ingested by animals.
  ▪ Animals use the nutrients from plants to
  make proteins and other essential
  biomolecules.
  ▪ Denitrification reverses nitrogen fixation to
  complete the cycle.
  ▪ For example, anaerobic organisms
  decompose animal wastes as well as dead
  plants and animals to produce free
  molecular nitrogen from nitrates.
Industrial Fixation:
- N₂ (g) + 3H₂ (g) → 2NH₃ (g)

Denitrification: Returns nitrogen to atmosphere, involving anaerobic organisms decomposing waste.
Key components: Ammonium, Nitrites, Nitrates, Nitrous Oxide (NO), and their transformation in ecosystems.

Oxygen cycles through various forms and processes, heavily tied to photosynthesis and respiration.
The cycle is complicated because oxygen takes so many different chemical forms
Atmospheric oxygen is removed through respiration and various industrial processes (mostly combustion), which produces CO2.
Photosynthesis is the major mechanism by which molecular oxygen is regenerated from CO2 and water.
Processes:
Removal of atmospheric O₂ through respiration & industrial processes, producing CO₂.

Result from solar flares and particle collisions with Earth's atmosphere, creating stunning light shows.
Spectacular celestial light shows as a result of ejection of myriad electrons and protons in space during solar flares or violent eruptions on the surface of the sun.
Types of Auroras:
Aurora Borealis (Northern Hemisphere)
Aurora Australis (Southern Hemisphere)
Emission of light due to excited atmospheric molecules transitioning back to ground states, emitting photons at various wavelengths (e.g., Green at 558 nm, Red at 630-636 nm).
The excited molecules and ions return to the ground state with the
emission of light.
▪ An excited oxygen atom emits photons at wavelengths of 558 nm
(green) and between 630 and 636 nm (red).
▪ The blue and violet colors often observed
in auroras result from the transition in the
ionized nitrogen molecule. The
wavelengths for this transition fall between
391 and 470 nm.