The Atmosphere

Characteristics of the Atmosphere Atmosphere – a mixture of gases that surrounds a planet, such as Earth. The atmosphere is made up a mixture of chemical elements and compounds that we call air. The atmosphere protects Earth’s surface from the radiation of the sun and regulates Earth’s temperature.

Composition of the Atmosphere

The Nitrogen Cycle

Nitrogen Cycle Nitrogen makes up about 78% of Earth’s atmosphere. Nitrogen in the atmosphere is maintained through the nitrogen cycle. In its normal state, nitrogen is not available to plants and animals. However, nitrogen-fixing bacteria remove the nitrogen from the air and chemically change into nitrogen compounds that are vital to the growth of all plants. Animals eat the plants and the nitrogen eventually returns to the soil as waste or the decay of dead organisms.

Oxygen in the Atmosphere Oxygen makes up about 21% of Earth’s atmosphere. Animals, bacteria, and plants remove oxygen from the atmosphere for their life processes. How is oxygen replenished? Land and ocean plants produce large quantities of oxygen during photosynthesis. During photosynthesis, plants use sunlight, water, and carbon dioxide to produce their food, and they release oxygen as a byproduct. The oxygen content of Earth’s atmosphere remains at about 21%.

Water Vapor in the Atmosphere As water evaporates for bodies of water, it enters air as the invisible gas called water vapor. Transpiration – water vapor released by plants and animals. Water vapor is removed from the atmosphere by condensation and evaporation. Dry air has less than 1% water vapor; moist air may contain as much as 45 water vapor.

Ozone Ozone is an important component of the atmosphere. The oxygen we breathe has two oxygen atoms, but ozone has three oxygen atoms. Ozone forms in the upper atmosphere and absorbs the harmful ultraviolet radiation from the sun. Without this ozone layer, living organisms would be severely damaged by the UV rays. Particulates – tiny solid particles in the atmosphere that are the result of volcanic dust, ash from fires, microscopic organisms, plant pollen, and minerals lifted by wind.

Atmospheric Pressure Atmospheric Pressure – the force per unit area that is exerted on a surface by the weight of the atmosphere. Gravity holds the gases of the atmosphere near Earth’s surface. So, the air molecules are compressed together and exert a force on Earth’s surface. Because the pull of gravity is not as strong at higher altitudes, the air molecules are farther apart and exert less pressure on each other at higher altitudes. Thus, atmospheric pressure decreases as altitude increases.

Measuring Atmospheric Pressure Meteorologists use three units for atmospheric pressure: atmospheres (atm), millimeters or inches of mercury, and millibars (mb). Standard of atmospheric pressure, or 1 atm, is equal to 760 mm of mercury, or 1000 millibars. So, 1 atm=760 mm of mercury = 1000 mb The average atmospheric pressure at sea level is 1 atm. Meteorologists use barometers to measure atmospheric pressure.

Barometers Mercurial barometer – atmospheric pressure presses on the liquid mercury in a well at the base of the barometer. The greater the atmospheric pressure, the higher the mercury rises. Aneroid barometer – a sealed metal container forms a partial vacuum. Changes in atmospheric pressure cause the sides of the container to bend inward or bulge out. These changes move a pointer on a scale. How do weather changes affect atmospheric pressure?

Layers of the atmosphere

1.Troposphere – the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases; the part of the atmosphere where weather conditions exist. 2.Stratosphere – the layer of the atmosphere that lies between the troposphere and mesosphere; contains the ozone layer. 3.Mesosphere – the coldest layer of the atmosphere, in which temperature decreases as altitude increases. 4.Thermosphere – the uppermost layer of the atmosphere; temperature increases as altitude increases. Includes the ionosphere where auroras occur.

Auroras In the ionosphere, solar radiation that is absorbed by atmospheric gases causes the atoms of gas molecules to lose electrons and to produce ions and free electrons. These interactions between solar radiation and the ionosphere lead to the phenomena known as auroras.

Quiz Identify the layer of the atmosphere in which weather conditions occur. Atmospheric pressure is measured with _____________. The atmosphere is composed of …?

Solar Energy and the Atmosphere Earth’s atmosphere is heated by the transfer of solar energy from the sun. All the energy that the Earth receives from the sun travel through space as radiation. Radiation includes all forms of energy that travel through space as waves. For example, visible light is the form of radiation that human eyes can detect. Radiation travels through space at very high speeds – 300,000 km/s. The various types of radiation differ in the length of their waves.

Electromagnetic spectrum Electromagnetic spectrum – all of the frequencies or wavelengths of electromagnetic radiation. The wavelengths of ultraviolet rays, x-rays, and gamma rays are shorter than those of visible light. The waves that make up all forms of radiation are called electromagnetic waves.

The atmosphere and solar radiation As solar radiation passes through the atmosphere, the atmosphere affects the radiation in several ways: The upper atmosphere absorbs almost all of the radiation that has a wavelength shorter than that of visible light. The thermosphere and mesosphere absorb the x-rays, gamma rays, and ultraviolet rays. The stratosphere absorbs most of the ultraviolet rays to form ozone. Most of the infrared radiation is absorbed by carbon dioxide, water vapor, and other complex molecules in the troposphere.

Scattering Clouds, dust, water droplets, and gas molecules cause solar radiation to scatter in the atmosphere. This deflection causes the rays to travel out in all directions without changing their wavelengths. As a result of scattering, sunlight that reaches Earth’s surface comes from all directions. Scattering makes the sky appear blue and makes the sun appear red at sunrise and sunset.

Reflection When solar energy reaches Earth’s surface, the surface either absorbs or reflects the energy. The amount reflected or absorbed depends on the characteristics of the surface. Can you think of surfaces that might reflect energy? What surfaces would better absorb energy? Albedo – the fraction of solar radiation that is reflected off the surface of an object.

Absorption and Infrared Energy Solar radiation that is not reflected is absorbed by rocks, soil, water, and other surface materials. These materials are heated by the radiation’s short-wavelength infrared rays and visible light. The absorption of thermal energy from the ground heats the lower atmosphere and keeps Earth’s surface warm. Sometimes, warm air near the Earth’s surface bends light to create a mirage.

Greenhouse Effect Greenhouse effect – the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation.