chemistry of water and atmosphere

Atmosphere

• The word "atmosphere" comes from the Greek words atmos (steam) and sphaira (sphere)
• The atmosphere is a layer of gases that surrounds a planet.
• The gravity of the planet holds the atmosphere in place.

Atmospheric Chemistry

• Studies the chemical composition of the atmosphere
• How matter interacts in the atmosphere
• The impact of humans and living things on the atmosphere

Related Fields to Atmospheric Chemistry

• Environmental Chemistry
• Physics
• Meteorology
• Computer Modeling
• Oceanography
• Geology
• Volcanology
• Engineering

Parts of the Atmosphere

• Troposphere:

  • Height: 6-20 km
  • Weather and climate occur here
  • Temperature decreases with height
  • Most living things live here
  • Most human activities occur here

• Stratosphere:

  • Height: 11-50 km
  • Very dry air
  • Temperature increases with height
  • Commercial jets and weather balloons fly here
  • Polar stratospheric clouds (nacreous clouds) are found here

• Mesosphere:

  • Height: 50-85 km
  • Very dry, similar to the stratosphere
  • Temperature decreases with height
  • Earth's coldest temperatures occur here (-90°C)
  • Difficult to study due to the lack of data

• Thermosphere:

  • Height: 80-800 km
  • Temperature increases with height
  • Absorbs X-rays and UV radiation
  • Satellites orbit here

• Ionosphere:

  • Part of the thermosphere (90 km to 500-1000 km high)
  • Upper thermosphere
    • Temperature in the upper thermosphere ranges from 500°C to 2000°C+
    • 200°C at daytime
    • 500°C at nighttime

• Exosphere:

  • Height: >10000 km
  • Outermost layer
  • Very few molecules, thin
  • Boundary between Earth and outer space

History of the Atmosphere

• 4.7 billion years ago, gases from volcanic activity formed the early atmosphere.
• As the Earth cooled, water condensed, and microorganisms developed.
• Photosynthesis (by plants) began to convert carbon dioxide into oxygen

Today's Atmosphere

• 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, other gases total of 0.17%

Nitrogen Cycle

• Atmospheric nitrogen is converted into usable forms for plants and other living things through various processes like lightning and bacteria
• Nitrogen-fixing bacteria in legume root nodules and soil bacteria convert atmospheric nitrogen into ammonia.
• This ammonia is then converted to nitrites and nitrates (nitrification) for plant use.
• Decomposers (bacteria and fungi) release ammonia back into the soil, completing the cycle.

Oxygen Cycle

• Plants take in carbon dioxide during photosynthesis and release oxygen as a byproduct
• Animals breathe in oxygen and release carbon dioxide

Photochemical Reactions in the Atmosphere

• Initiated by light absorption from the sun
• Photoionization: solar radiation ejects electrons from molecules
• Photodissociation: photons bombard molecules, breaking them down

Ozone in the Atmosphere

• Ozone (O3): found in the stratosphere, layer between 11 and 50 km
• Absorbs UV-C and UV-B, thus protecting life on Earth

Ozone Depletion

• Ozone depletion is the thinning of the ozone layer
• Chlorofluorocarbons (CFCs) are the primary culprits

Acid Rain

• Acid rain is caused by sulfuric and nitric acid
• Sulfur dioxide and nitrogen oxides react with water in the atmosphere

Dry Deposition

• Process where gases and dust particles become acidic

Wet Deposition

• Acidic substances fall to the ground mixed in rain, snow, fog, or hail

Measuring Acid Rain

• pH scale is used to measure acidity
• pH 0-6 is acidic, pH 7 is neutral, pH 8-14 is alkaline

Chemistry of Water

• Water covers 71% of Earth's surface
• 97% is saltwater, 3% is freshwater
• Freshwater sources include glaciers, surface water, and groundwater

Properties of Water

• Polarity: uneven distribution of electron density
  • Water molecules attract each other
• Hydrogen Bonding: strong attractions between water molecules due to their polarity
• Cohesion: water molecules stick to each other
  • High surface tension
• Adhesion: water molecules stick to other materials
  • Capillary action
• Density: Solid water (ice) is less dense than liquid water
• Heat Capacity: Water can absorb a large amount of heat without a significant change in temperature
  • Evaporative cooling
• Universal Solvent: Water readily dissolves many substances due to its polarity

Dissolved Oxygen

• Gaseous oxygen (O2) dissolved in water
• Direct absorption from the atmosphere
• Byproduct of photosynthesis

Importance of DO (Dissolved Oxygen)

• Aquatic life uses DO for respiration
• Photosynthesis also requires dissolved oxygen

Eutrophication

• Excessive richness of nutrients in water
• Causes algal blooms, oxygen depletion
• Harmful to aquatic life

Types of Water

• Freshwater vs. Saltwater

Ocean Water

• 97% of Earth's water is saltwater
• Main components: 55% chloride, 31% sodium
• Other components: magnesium, sulfur, calcium

Desalinization

• Process of removing salt and minerals from water to produce potable water