Ch. 23 The AtmosphereCh. 23 The Atmosphere

Ch. 23.1 Characteristics of the Ch. 23.1 Characteristics of the AtmosphereAtmosphere

Composition of the AtmosphereComposition of the Atmosphere

Most abundant elements—nitrogen, oxygen, Most abundant elements—nitrogen, oxygen, and argon.and argon.

Most abundant compounds—carbon dioxide Most abundant compounds—carbon dioxide and water vapor.and water vapor.

Water vapor is added through evaporation and Water vapor is added through evaporation and transpiration, and removed through transpiration, and removed through condensation and precipitation. Its condensation and precipitation. Its concentration varies from 4% to less than 1%.concentration varies from 4% to less than 1%.

OzoneOzone—a form of oxygen (O—a form of oxygen (O33 instead of O instead of O22) )

that exists in the upper atmosphere—important that exists in the upper atmosphere—important because it absorbs harmful ultraviolet rays.because it absorbs harmful ultraviolet rays.

Ozone can be destroyed by human pollutants Ozone can be destroyed by human pollutants such as chlorofluorocarbons (CFC’s).such as chlorofluorocarbons (CFC’s).

Also present is Also present is atmospheric dustatmospheric dust—suspended —suspended mineral particles from the land and salt mineral particles from the land and salt crystals from the ocean.crystals from the ocean.

78% Nitrogen78% Nitrogen 21% Oxygen21% Oxygen 0.9% Argon0.9% Argon 0.1% other (including 0.1% other (including carbon dioxidecarbon dioxide))

Oxygen in the AtmosphereOxygen in the Atmosphere

Oxygen is both removed and replaced in the Oxygen is both removed and replaced in the atmosphere at a constant rate, so the atmosphere at a constant rate, so the percentage of oxygen remains in a state of percentage of oxygen remains in a state of balance.balance.

Removed by: animals, bacteria, plants, Removed by: animals, bacteria, plants, burning of fuels and forests, and the burning of fuels and forests, and the weathering of rocks.weathering of rocks.

Replaced by: land and ocean plants through Replaced by: land and ocean plants through photosynthesis.photosynthesis.

Nitrogen in the AtmosphereNitrogen in the Atmosphere

The The nitrogen cyclenitrogen cycle maintains a constant maintains a constant amount of nitrogen in the atmosphere.amount of nitrogen in the atmosphere.

Nitrogen moves from the air, to the soil, to Nitrogen moves from the air, to the soil, to plants and animals, and again back to the air.plants and animals, and again back to the air.

Nitrogen-fixing bacteria convert atmospheric Nitrogen-fixing bacteria convert atmospheric nitrogen into useful nitrogen compounds taken nitrogen into useful nitrogen compounds taken up by plants, which are then eaten by animals.up by plants, which are then eaten by animals.

Denitrifying bacteria release nitrogen back to Denitrifying bacteria release nitrogen back to the air when plants and animals decay or the air when plants and animals decay or excrete waste.excrete waste.

Atmospheric PressureAtmospheric Pressure

Atmosphere is held by Earth’s gravity.Atmosphere is held by Earth’s gravity. 99% of atmosphere’s mass is within 32 km of 99% of atmosphere’s mass is within 32 km of

the surface.the surface. Remainder extends upwards towards space for Remainder extends upwards towards space for

hundreds of kilometers, getting thinner with hundreds of kilometers, getting thinner with increasing altitude.increasing altitude.

Weight of the atmosphere presses on the Weight of the atmosphere presses on the surface.surface.

A column of air one square inch at its base, at A column of air one square inch at its base, at sea level, and extending upward to the upper sea level, and extending upward to the upper edge of the atmosphere, weighs 14.7 pounds.edge of the atmosphere, weighs 14.7 pounds.

Force of the air on the surface can be Force of the air on the surface can be expressed in newtons (101,325 N).expressed in newtons (101,325 N).

Atmospheric pressureAtmospheric pressure is the ratio of the force is the ratio of the force of the air to the area of the surface on which it of the air to the area of the surface on which it presses.presses.

Atm. press. Atm. press. decreasesdecreases with increasing altitude. with increasing altitude.

Mercurial BarometerMercurial Barometer

BarometersBarometers are instruments that measure are instruments that measure atmospheric pressure.atmospheric pressure.

In a mercurial barometer, the atmospheric In a mercurial barometer, the atmospheric pressure presses on a bowl of mercury and pressure presses on a bowl of mercury and forces it up a tube.forces it up a tube.

At sea level, mercury would be forced up the At sea level, mercury would be forced up the tube to an average height of 760 mm.tube to an average height of 760 mm.

Aneroid BarometerAneroid Barometer

AneriodAneriod—without liquid.—without liquid. Contains sealed metal container at a vacuum.Contains sealed metal container at a vacuum. Sides of container flex inwards or outwards Sides of container flex inwards or outwards

depending on air pressure.depending on air pressure. Pointer attached to container. It moves along a Pointer attached to container. It moves along a

scale, and indicates the atmospheric pressure.scale, and indicates the atmospheric pressure.

Layers of the AtmosphereLayers of the Atmosphere

Pressure gradually decreases with increasing Pressure gradually decreases with increasing altitude, but altitude, but temperaturetemperature shows shows distinct distinct differencesdifferences with increasing altitude. with increasing altitude.

Temp. differences are due to the way solar Temp. differences are due to the way solar energy is absorbed as it moves downward energy is absorbed as it moves downward through the atmosphere.through the atmosphere.

Four distinct layers based on temperature Four distinct layers based on temperature differences.differences.

The TroposphereThe Troposphere

Layer closest to the earth, in which nearly all Layer closest to the earth, in which nearly all weather occurs.weather occurs.

Almost all water vapor and carbon dioxide Almost all water vapor and carbon dioxide found in the troposphere.found in the troposphere.

Temp. decreases with increasing altitude, due Temp. decreases with increasing altitude, due to increasing distance from earth’s surface to increasing distance from earth’s surface (and distance from the warming effect of (and distance from the warming effect of sunlight absorbed by earth’s surface). sunlight absorbed by earth’s surface).

Rate of temperature decrease is about 6.5Rate of temperature decrease is about 6.5° C ° C per km.per km.

The StratosphereThe Stratosphere

Extends upward from the troposphere to a Extends upward from the troposphere to a height of about 50 km.height of about 50 km.

Contains most of the ozone in the atmosphere Contains most of the ozone in the atmosphere (the ozone layer(the ozone layer))..

About -60About -60°° C at its base, but temp. begins C at its base, but temp. begins rising in upper stratosphere as altitude rising in upper stratosphere as altitude increases…due to direct absorption of solar increases…due to direct absorption of solar energy by ozone.energy by ozone.

The MesosphereThe Mesosphere

Layer above the stratosphere, extending to an Layer above the stratosphere, extending to an altitude of about 80 km.altitude of about 80 km.

Temperature decrease as altitude increases…Temperature decrease as altitude increases…the coldest layer, dropping to about -90the coldest layer, dropping to about -90° C.° C.

Very thin air, but thick enough to burn up most Very thin air, but thick enough to burn up most meteors.meteors.

The ThermosphereThe Thermosphere

Layer above the mesosphere. Temperature Layer above the mesosphere. Temperature increases steadily with altitude, due to increases steadily with altitude, due to absorption of short wavelength solar energy by absorption of short wavelength solar energy by oxygen and nitrogen.oxygen and nitrogen.

Although very high temperatures Although very high temperatures (over 2000(over 2000°C recorded), air is so thin and its °C recorded), air is so thin and its molecules so far apart that little heat is molecules so far apart that little heat is transferred.transferred.

Upper boundary of thermosphere not Upper boundary of thermosphere not accurately determined.accurately determined.

The IonosphereThe Ionosphere

Within lower region of thermosphere (80 – Within lower region of thermosphere (80 – 550 km).550 km).

Solar rays strip electrons from gas molecules, Solar rays strip electrons from gas molecules, forming ions and free electrons.forming ions and free electrons.

There are four layers of the ionosphere.There are four layers of the ionosphere. Free electrons can reflect radio waves back to Free electrons can reflect radio waves back to

earth.earth.

The ExosphereThe Exosphere

Region of atmosphere where it blends into the Region of atmosphere where it blends into the vacuum of interplanetary space.vacuum of interplanetary space.

Extends thousands of km above the surface.Extends thousands of km above the surface.

Air PollutionAir Pollution

Substances in the atmosphere harmful to Substances in the atmosphere harmful to people, animals, plants, or property.people, animals, plants, or property.

Results mainly from the burning of fossil Results mainly from the burning of fossil fuels.fuels.

Gases from fossil fuels combine with water to Gases from fossil fuels combine with water to form form acid rainacid rain, which kills plants and fish., which kills plants and fish.

Sometimes, Sometimes, cold air becomes trapped under cold air becomes trapped under warm airwarm air…this condition is a …this condition is a temperature temperature inversioninversion. The air is unable to disperse, and . The air is unable to disperse, and pollutants build up (common in Los Angeles).pollutants build up (common in Los Angeles).

The result is The result is smogsmog (smoke and fog). (smoke and fog).