Earth's atmosphere is a complex system of layers, each with unique properties. From the troposphere where we live to the exosphere at the edge of space, these layers play crucial roles in protecting life and regulating our climate.

Understanding the atmosphere's structure helps us grasp weather patterns, ozone depletion, and climate change. The ozone layer in the stratosphere shields us from harmful UV rays, while the troposphere is where most weather happens.

Atmospheric Layers and Characteristics

Layers of Earth's atmosphere

• Troposphere
  • Lowest layer extends from Earth's surface to an average altitude of 12 km (7.5 miles)
  • Contains 75-80% of the atmosphere's mass and nearly all water vapor and aerosols
• Stratosphere
  • Layer above the troposphere extends from the tropopause to an altitude of about 50 km (31 miles)
  • Contains the ozone layer which absorbs harmful UV radiation from the sun
• Mesosphere
  • Layer above the stratosphere extends from the stratopause to an altitude of about 85 km (53 miles)
  • Coldest layer where temperatures can drop to -90°C (-130°F) at the mesopause
• Thermosphere
  • Layer above the mesosphere extends from the mesopause to an altitude between 500-1,000 km (311-621 miles)
  • Auroras (northern and southern lights) occur in this layer due to charged particles from the sun
• Exosphere
  • Outermost layer extends from the thermopause to an altitude of about 10,000 km (6,200 miles)
  • Transitional zone between Earth's atmosphere and outer space

Characteristics of atmospheric layers

• Troposphere
  • Temperature decreases with altitude at an average lapse rate of 6.5°C/km (3.6°F/1,000 ft)
  • Pressure and density decrease rapidly with altitude
  • Contains almost all atmospheric water vapor and is where most weather phenomena occur (clouds, precipitation)
• Stratosphere
  • Temperature increases with altitude due to ozone absorbing UV radiation
  • Pressure continues decreasing with altitude but more slowly than in the troposphere
  • Very dry and stable layer with little vertical mixing
• Mesosphere
  • Temperature decreases with altitude reaching the coldest point at the mesopause
  • Pressure continues decreasing and is about 1/1000th of sea level pressure at the top
  • Noctilucent clouds can form at the top of this layer during summer at high latitudes
• Thermosphere
  • Temperature increases significantly with altitude and can reach up to 2,000°C (3,632°F)
  • Air density is very low but individual gas molecules can reach high speeds
  • Highly variable temperatures due to solar activity and the diurnal cycle
• Exosphere
  • Extremely thin layer with negligible atmospheric pressure
  • Hydrogen and helium are the main components and can escape into space
  • Satellites (ISS) and the aurora (northern lights) occur in this layer

Function of atmospheric boundaries

• Tropopause
  • Boundary between the troposphere and stratosphere around 12 km (7.5 miles) altitude
  • Marked by abrupt change in lapse rate from positive (troposphere) to negative (stratosphere)
  • Acts as a "lid" that limits the vertical rise of air from the troposphere, controlling weather
• Stratopause
  • Boundary between the stratosphere and mesosphere around 50 km (31 miles) altitude
  • Marked by a reversal in lapse rate from negative (stratosphere) to positive (mesosphere)
  • Separates the stable stratosphere from the turbulent mesosphere

Ozone layer in stratosphere

• Ozone layer
  • Region of naturally high ozone ($O_3$) concentrations within the stratosphere
  • Located roughly 20-30 km (12-19 miles) above Earth's surface
• UV protection
  • Ozone absorbs harmful solar ultraviolet (UV) radiation, especially UV-B and UV-C wavelengths
  • Protects life on Earth's surface from DNA damage and higher skin cancer risk
• Stratospheric temperature inversion
  • Ozone absorbing UV radiation causes the unusual temperature increase with altitude
  • Creates a stable layer with limited vertical mixing between the troposphere and stratosphere
• Anthropogenic ozone depletion
  • Chlorofluorocarbons (CFCs) and other manufactured chemicals can deplete ozone
  • Ozone holes (severe depletion) can develop over polar regions during late winter/early spring