Chapter 15: The Atmosphere

Lesson 1: Earth’s Atmosphere

Properties of the Atmosphere Properties of the atmosphere include its composition, relative humidity, temperature, and air pressure. The atmosphere is the thin layer of gases that surrounds Earth. We live at the bottom of the atmosphere, which provides us with oxygen, protects us from the most harmful rays in sunlight, and transports and recycles water.

Composition of the Atmosphere The atmosphere consists of roughly 78% nitrogen gas and 21% oxygen gas. Nitrogen gas occurs as a molecule with the chemical formula N2. The most common form of oxygen in the atmosphere occurs as a molecule having the chemical formula O2. During combustion, oxygen combines chemically with a fuel and produces carbon dioxide and water. Air also contains water – solid, liquid, and gas – that has a chemical formula of H2O

In general, warm air can hold more water vapor than cooler air. Relative Humidity Relative humidity is the ratio of water vapor the air contains to the maximum amount it could have at that temperature. In general, warm air can hold more water vapor than cooler air. Water vapor becomes liquid water or ice through the process of condensation Dew, frost, and clouds are the result of condensation During the formation of clouds, water vapor condenses on tiny particles in the air such as salt crystals, smoke and dust.

Air temperature varies from place to place, and from time to time. The sun’s rays strike some areas more directly than others

A barometer is an instrument that measures air pressure Air pressure, or atmospheric pressure, is the force exerted by air on the area below it. A barometer is an instrument that measures air pressure In a mercury barometer air pressure pushes a column of mercury upward in a tube An aneroid barometer has a metal chamber whose walls bend inward when air pressure is high and bend outward when air pressure is low. In general, the lower the altitude the higher the air pressure

Layers of the Atmosphere The main layers of the atmosphere are the troposphere, stratosphere, mesosphere, and thermosphere.

The troposphere The lowest layer of the atmosphere, directly above the ground Contains the oxygen we need to live The movement of air within the troposphere is largely responsible for Earth’s weather. Almost all clouds are found here Contains three quarters of the atmosphere’s mass Averages about 11 kilometers in height The higher the air is above Earth, the cooler it becomes A layer at the top acts like a cap

Layer of the atmosphere above the troposphere The stratosphere Layer of the atmosphere above the troposphere Extends 11-50 kilometers above sea level Gases do not mix much The highest part is warmer than the lower levels Ozone is concentrated in a portion of the stratosphere called the ozone layer. Ozone gas absorbs and scatters the sun’s UV rays Protects organisms from harmful UV rays A pollutant if present in the troposphere

The mesosphere Layer above the stratosphere Extends 50-80 kilometers above sea level Temperatures decrease with altitude Air pressure is extremely low

The thermosphere The top layer Begins about 80 kilometers above Earth’s surface and extends upward into space. Air is very thin Temperature is very high Disturbances produce the northern lights

The Troposphere and Weather Processes that affect weather in the troposphere include heat transfer and the interaction of air masses. Weather refers to atmospheric conditions over short time periods, typically hours or days, and within relatively small areas. Climate describes the pattern of atmospheric conditions in large geographic regions over long periods. Energy from the sun heats the atmosphere.

Radiation is the transfer of energy through space Heat travels from the sun to Earth’s atmosphere by radiation No direct contact between the heat source and the object being heated

Conduction is the transfer of heat directly between two objects that are in contact with one another. Occurs when molecules collide and energy is transferred from one molecule to another Occurs between Earth’s surface and the molecules in the air

Sinking cool air and rising warm air form convection currents. Convection is the transfer of heat by the movement of currents within a fluid. Cooler air is denser than warmer air and sinks to the surface of Earth where it picks up heat and begins to rise. Sinking cool air and rising warm air form convection currents. Cause winds and move heat through the troposphere

A large body of air is called an air mass Properties such as temperature, pressure, and humidity are similar throughout

The boundary between air masses that differ in temperature and moisture is called a front. A warm front is a boundary along which a mass of warmer, moister air pushes against a mass of cooler, drier air. Warm air rises above the cool air mass and then cools Can result in clouds and light rain

A cold front is the boundary along which a colder, drier air mass pushes against a warmer, moister air mass. Cold air tends to wedge beneath the warmer air May result in clouds, heavy precipitation, and sudden weather changes

Lesson 2: Pollution of the Atmosphere

Sources of Air Pollution Air pollution can be caused by natural processes and human activities Air pollution is the release of damaging materials into the atmosphere The substances that are released are called emissions Dust storms, volcanic eruptions, and forest fires are examples of natural processes that produce air pollution.

Air pollution can come from point sources or nonpoint sources. Most air pollution comes, directly or indirectly, from the combustion of fossil fuels. Fossil fuels are carbon-containing fuels that formed from the remains of living things.

Primary air pollutants are pollutants released directly into the troposphere Ex: soot and carbon monoxide Secondary air pollutants are pollutants produced when primary air pollutants react chemically with other substances Ex: tropospheric ozone and sulfuric acid

How Air Pollutants Affect Your Health Air pollutants can damage the respiratory system, interfere with the body’s uptake of oxygen, and cause cancer Air pollutants irritate people’s air passages and lungs Asthma, bronchitis, and emphysema have all been linked to air pollutants Carbon monoxide interferes with your body’s ability to deliver oxygen to cells Can cause headaches, tiredness, nausea, heart damage, and can be fatal. Trace amounts of some air pollutants, such as soot and benzene, may contribute to cancer.

Smog and Temperature Inversions Temperature inversions may trap smog close to the surface of Earth, preventing the pollutants from dispersing. Smog is an unhealthy mixture of air pollutants that may form over cities and nearby areas.

Industrial Smog Produced when soot combines with sulfur compounds and water droplets in air Government regulations have decreased this type of smog in developed nations

Main source is the exhaust of cars and trucks Photochemical Smog A thick, brownish haze that forms when sunlight acts on certain air pollutants, such as nitrogen oxides and hydrocarbons Tropospheric ozone is the most abundant pollutant in photochemical smog Can damage living tissue Main source is the exhaust of cars and trucks

Temperature Inversions In the troposphere, air temperature usually decreases as altitude increases. A temperature inversion, or thermal inversion, is the condition in the troposphere in which a layer of cooler air is located beneath a layer of warmer air Since cold air has a greater density, the air at Earth’s surface does not rise and mix with the air higher up. Keeps air pollutants from going away

Acid Deposition Acid deposition results when products of combustion combine with water, oxygen, and other substances in the atmosphere. Water vapor containing acids that falls to the ground as rain, snow, sleet or hail is called acid deposition. Normal precipitation is slightly acidic (pH 5.6) and acid precipitation has a lower pH Main sources include sulfur dioxide and nitrogen oxides that are produced through the burning of fossil fuels Can harm ecosystems and structures that humans have built

Possible effects: Lowering the pH of a lake Killing trees Releasing harmful chemicals in the soil Erode stone surfaces Increase acidity of drinking water

Lesson 3: Controlling Air Pollution

The Clean Air Act The Clean Air Act has provisions that have reduced air pollution in the United States. First passed in 1963 and then revised in 1970 and 1990 Goal is to protect and improve the quality of air in order to safeguard human health and the environment

Limits emissions of pollutants by motor vehicles and industries Provisions: Limits emissions of pollutants by motor vehicles and industries Sets standards for air quality Limits the concentration of specific air pollutants Lets people sue industries that break the rules Sets aside funds for research into pollution control

Reduction in Air Pollutants Cars and trucks now cause less pollution The EPA sets nationwide standards governing air pollutants and air quality Reduction in Air Pollutants Cars and trucks now cause less pollution A catalytic converter is a device in a motor vehicle that reduces the amount of air pollutants in emissions Today, gasoline contains almost no lead Industries and power plants use scrubbers A scrubber removes pollutants or changes them chemically before they leave factory smokestacks.

Ozone: A Success Story Nations have taken steps to deal with the problem of ozone loss in the stratosphere. The term ozone hole refers to the area of lowered ozone concentration over Antarctica that occurs every year from August until October. By 1985, the level of ozone was 40-60% lower than it had been 10 years before

In 1974, scientists Sherwood Rowland and Mario Molina suggested that chlorofluorocarbons could cause ozone depletion. Chlorofluorocarbons (CFCs) are a family of chemical compounds containing chlorine, fluorine, and carbon Manufactured in large amounts and used in refrigerators and aerosol spray cans. CFCs were rising into the stratosphere and then releasing chlorine atoms that react with ozone, destroying the ozone molecules.

The Montreal Protocol is a treaty that limits the production of chlorofluorocarbons signed in 1987 by multiple nations. Evidence indicates that the ozone layer is beginning to recover – in the last few years the concentrations of stratospheric ozone have stabilized.