Earth’s Changing Atmosphere Earth’s atmosphere supports life The Sun supplies the atmosphere’s energy Gases in the atmosphere absorb radiation Human activities affect the atmosphere

Earth’s Atmosphere supports life The atmosphere makes life possible. It is a mixture of gases (primarily nitrogen and oxygen) that surrounds Earth. It keeps Earth warm and transports energy around the planet. Characteristics of the atmosphere. As altitude increases, the density of the air decreases (due to less air particles). Pressure increases as density increases (due to more air particles). There is no definite “top” to the atmosphere, it just gets thinner and thinner… “Outer space” is considered to begin at an altitude of 300 miles. 99% of the atmosphere’s mass is within the first 20 miles.

Earth’s Atmosphere supports life (cont’d) Materials in the atmosphere Mostly gases (78% nitrogen, 21% oxygen, <1% CO2 and other gases) Water (H2O) vapor can be up to 4%... Dust, dirt, pollen, etc. Natural processes modify the atmosphere Cycles Carbon cycle: CO2 and O2 circulate among animals, plants, and atmosphere. Nitrogen cycle: Tiny organisms remove N2 from the air and turn it into nitrites (NO2) and nitrates (NO3) that are used by plants. When these organisms and plants die and decay, the nitrogen is slowly released back into the air. Water cycle: Water moves between surface/life through evaporation/transpiration, condensation, precipitation, run-off, and percolation/infiltration.

Earth’s Atmosphere supports life (cont’d) Sudden changes to atmosphere a. Volcanic eruptions: Add gases and rock ash. May lower temperatures worldwide. b. Forest fires: Carbon in the forest’s composition combines with oxygen in the atmosphere to form CO2. Wood ash also added. c. Dust storms: Eroded soil picked up by strong winds.

The sun supplies the atmosphere’s energy Energy from the Sun heats the Earth’s atmosphere a. Almost ALL energy around you comes from the Sun. b. Most of this energy comes in the form of visible light (one form of electromagnetic radiation). c. 50% absorbed by surface; 20% absorbed by clouds and atmosphere 5% reflected by surface; 25% reflected by clouds and atmosphere d. When solar radiation is absorbed, that object is heated. The atmosphere moves energy by three means of “heat transfer” Radiation: energy transferred by “light” Conduction: energy transferred by “touch” (contact) Convection: energy transferred by “currents” (moving fluid…liquid OR gas)

The sun supplies the atmosphere’s energy (cont’d) The atmosphere has temperature layers a. Troposphere: 0-6 miles; temperature decreases w/altitude (further away from surface) 80% of atmosphere’s mass; almost all weather occurs here b. Stratosphere: 6-31 miles; temperature increases w/altitude (ozone absorbs UV) almost 20% of atmosphere’s mass; clear and dry c. Mesosphere: 31-56 miles; temperature decreases w/altitude (further from strato-) less than 0.1% of atmosphere’s mass; extremely thin air; most meteors burn up d. Thermosphere: 56->> miles; temperature increases w/altitude (gases absorb UV) even though temperature increases, particles are so few that you would freeze

Gases in the atmosphere absorb radiation Gases can absorb AND give off radiation. Atmosphere can absorb, reflect, allow radiation to pass through, or re-emit light. Infrared light is light that is just below red light (in terms of energy) in the visible portion of the EM spectrum. Ultraviolet light is light that is just above violet light (in terms of energy) in the visible portion of the EM spectrum.

Gases in the atmosphere absorb radiation (cont’d) The ozone “layer” protects life from harmful UV radiation. Ozone (O3) absorbs UV radiation, but allows other light to pass through. Ozone “layer” is found throughout the stratosphere. If the ozone were compressed in an actual layer, it would only be 2 to 5 mm thick! Ozone is formed and destroyed by complex natural processes that tend to balance. Montreal Protocol 1987. Ozone could be restored within 50 years. Limits harmful chemicals…especially those containing chlorine. The greenhouse effect keeps Earth warm. Much of the energy (in visible light form) that passes through the atmosphere to Earth is absorbed by the surface and re-emitted as lesser energy infrared light. IR light does not pass as easily BACK through the atmosphere; therefore, the atmosphere helps “hold in” some of this warmth. (average global temperature is about 59 degrees F) The main gases in the atmosphere that inhibit IR light from passing through are carbon dioxide, methane, water vapor, and nitrous oxide.

Human activities affect the atmosphere Human activity can cause air pollution. Air pollution: smoke and other “harmful” materials that are added to the air. Given time, most air pollution either leaves the air or becomes dispersed enough to become less harmful. Pollution is moved around by both global and local winds. Types of pollution Pollutants are classified as either gases or particles. Gas pollutants include carbon monoxide, methane, ozone, sulfur oxides and nitrogen oxides. Some occur naturally, some are human-made. Particulates (tiny particles or droplets) include smoke, dust, dirt, pollen, and tiny particles of salt. Most pollution comes from the burning of fossil fuels (formed from the remains of prehistoric plants and animals). Smog: the combination of smoke and fog.

Human activities affect the atmosphere (cont’d) Effects of Pollution are… short-term health problems (eye, nose, throat, and lung irritations) and long-term health problems (asthma, lung disease, etc.) damage to plants, buildings, outdoor structures due to particulates sticking on them. changing the weather and ultimately rivers, lakes, and oceans. global warming (carbon dioxide has increased 30%, methane?, 10 degrees F?). Controlling pollution. Laws, treaties, agreements to limit output. Awareness and action at the individual and local community levels.