GEO 125

Physical Geography

Composition of the Atmosphere

Uniform gases (also known as constant or nonvariable gases because their amount in the modern atmosphere is fixed)

  • Nitrogen (79% of all atmospheric gas molecules)
  • Oxygen (20% of all atmospheric gas molecules)
  • Other minor uniform gases include argon, helium, krypton

The Uniform gases play no role in affecting weather and climate but are of extreme importance to the completion of natural cycles that sustain life on the earth

Variable gases (also known as the nonconstant or nonuniform gases because their amounts fluctuate over time and space) are derived from both natural sources and are also present in the atmosphere as the result of pollution. They modify both weather and climate and can impact human health and cause property damage

  • Water vapor (measured as humidity; a key component in the hydrologic cycle; and directly impacts humans in terms of sensible heat)
  • Carbon monoxide (natural sources include volcanic eruptions, associated with mobile sources of pollution; and number one atmospheric pollutant by weight)
  • Carbon dioxide (natural sources associated with volcanic eruptions, decay of plants, and forest fires; as a pollutant associated with generation of electricity, disposal of solid wastes by burning, and other industrial processes; carbon dioxide is the major greenhouse gas and controls world temperatures
  • Sulfur dioxide (naturally associated with volcanic eruptions and wildfires in coniferous forests; as a pollutant is is associated with the burning of fossil fuels; as a pollutant it causes the greatest impact on human health and is a key contributor to acid rain)
  • Nitrogen oxides (naturally associated with volcanic eruptions; as a pollutant it is associated with certain industrial processes and as an output from mobile sources of pollution; a prime component of photochemical smog)
  • Ozone (a form of oxygen, can be formed by lightning or other intense electrical discharges into the atmosphere or as a by-product from the emissions of mobile sources of pollution; near the ground surface ozone is considered to be a primary pollutant and is a prime component of photochemical smog)
  • Chloroflurocarbons (CFCs) (manmade chemical that is used for many purposes including, enters the atmosphere from several small sources, chemically inert but will react with ultraviolet light, leading chemical associated with ozone depletion; CFSs are also considered to be a greenhouse gas)

Particulate matter in the atmosphere (also known as suspended solids) can be derived from both natural sources or associated with ar pollution.

  • Natural sources of particulate matter include the eruption of composite volcanoes, forest fires, dust storms, ocean spray; plants, and meteor impacts
  • Sources of particulate matter associate with atmospheric pollution include heavy industry, burning (solid waste disposal, agricultural burning; or home heating), exotic vegetation oil fires, and as result of nuclear winter

Importance of particulate matter in the atmosphere

  • High amounts input into the atmosphere by volcanic eruptions can cause short term cooling
  • The hydrologic cycle could not be completed without particulate matter in the atmosphere to act as condensation nuclei
  • Increased levels of particulate matter in the atmosphere, associated with either natural sources or as a result of pollution, have been associated with increased levels of precipitation
  • Scattering of light in the atmosphere by particulate matter causes sky to be blue and sunrises and sunsets to be red or orange
  • As a pollutant, particulate matter is the second most important pollutant to impact human health

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