15 The AtmosphereC

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Charging Toward Cleaner Air in London

• More than 4000 people in London died during a “killer smog” event in 1952.

• In 2003, London started charging a fee to people who drove into the city during the week.

• Since the program began, traffic congestion in London has decreased by 30%, but there is not a lot of evidence that air quality has improved.

Talk About It What are the pros and cons of a congestion-charging program?

Lesson 15.1 Earth’s Atmosphere

The air we breathe and all the weather we see is contained in the lowest 1% of the Earth’s atmosphere.

15.1: Earth’s AtmosphereKey Vocabulary

•Atmosphere•Relative humidity•Air pressure•Troposphere•Stratosphere•Ozone layer•Mesosphere

•Thermosphere•Radiation•Conduction•Convection•Convection current•Air mass•Front

Properties of the Atmosphere

• Composition: 78% nitrogen, 21% oxygen, and 1% other gases

• Temperature: Varies and location

• Pressure: In general, air pressure decreases with altitude; can bemeasured using abarometer.

Lesson 15.1 Earth’s Atmosphere

Barometer

Relative Humidity• The ratio of water vapor in

air to the maximum amount the same air could contain at the same temperature

• Is affected by temperature and location; in general, warm air holds more water.

• When air cools, water vapor may condense to liquid or to ice. Water vapor can only condense on surfaces, such as a petal or a dust particle.

Lesson 15.1 Earth’s Atmosphere

Frost on leaves

Layers of Atmosphere

Lesson 15.1 Earth’s Atmosphere

• Troposphere: 0–11 km; movement of air, weather

• Stratosphere: 11–50 km; ozone layer, absorbs and scatters UV rays

• Mesosphere: 50–80 km; meteoroids burn up

• Thermosphere: 80+ km; disturbances produce aurora borealis

Did You Know? The stratosphere and mesosphere are cold, but the upper thermosphere can be hotter than 1500°C.

Heat Transfer in

the Troposphere

Lesson 15.1 Earth’s Atmosphere

• Radiation: The transfer of energy through space, such as heat from the sun to Earth’s atmosphere

• Conduction: The transfer of heat directly between two objects that are in contact

• Convection: The transfer of heat by the movement of currents within a fluid (liquid or gas)

Convection Currents

• Warm air is less dense than cool air.

• When air near the surface heats up, it rises; as it rises, it cools and then sinks.

• Rising and sinking fluids generate convection currents.

• Cause wind and heat to move through the atmosphere

Lesson 15.1 Earth’s Atmosphere

Air Masses and Fronts•Air masses: Large bodies of air with similar properties• Fronts: Boundaries between air masses of different properties

Lesson 15.1 Earth’s Atmosphere

Warm front• Boundary along which a mass of warmer,

moister air pushes against a mass of cooler, drier air

• Can produce light precipitation

Cold front • Boundary along which a mass of cooler,

drier air pushes against a mass of warmer, moister air

• Can produce heavy precipitation

Lesson 15.2 Pollution of the Atmosphere

Air pollution is estimated to cause 2 million premature deaths worldwide every year.

15.2: Pollution of the Atmosphere

Key Vocabulary•Air pollution•Emission•Fossil fuel•Primary air pollutant•Secondary air pollutant

•Smog•Temperature inversion•Acid deposition

Sources of Air Pollution

Lesson 15.2 Biomes

• Natural processes: Windblown dust, particles in volcanic eruptions, smoke and soot from fire

• Human sources: Most come directly or indirectly from the burning of fossil fuels.

Did You Know? Humans can increase the hazards of natural air pollution. For example, by removing trees, humans expose soil, which can dry out and add to huge dust storms when picked up by wind.

Dust storm approaching a U.S. farm during the 1930s

Types of Air Pollutants

Lesson 15.2 Pollution of the Atmosphere

• Primary air pollutants: Released directly into the atmosphere; example: soot

• Secondary air pollutants: Formed when primary pollutants react chemically with other substances; example: sulfuric acid

How Air Pollutants Affect Your Health

Lesson 15.2 Pollution of the Atmosphere

• Lung irritation and respiratory illnesses, such as asthma

• Carbon monoxide interferes with body’s ability to use oxygen.

• Trace amounts of some air pollutants, such as benzene or soot, may contribute to cancer.

Smog

Lesson 15.2 Pollution of the Atmosphere

• A mix of air pollutants that forms over cities

• “Smog” is a combination of the words smoke and fog.

• Industrial smog (soot, sulfur, and water vapor) comes from industrial sources.

• Photochemical smog is mostly tropospheric ozone created when primary pollutants from vehicle exhaust react to sunlight.

• Normally, air near Earth’s surface warms and rises, carrying pollutants with it.

• When a layer of warmer air sits over a layer of cooler air, it traps pollution near Earth’s surface.

Temperature Inversions

Lesson 15.2 Pollution of the Atmosphere

Did You Know? A thermal inversion caused London’s “killer smog.”

Acid Deposition

Lesson 15.2 Pollution of the Atmosphere

• Sulfur dioxide and nitrogen oxides can react with water, oxygen, and other chemicals to form acids.

• Acid falls as particles or dissolves in precipitation, lowering the pH of rain and snow.

• Acid deposition harms forest and lakes and damages human structures.

Did You Know? Rainwater is naturally acidic (pH 5.6), but acid precipitation in some parts of the U.S. has a pH as low as 4.

Lesson 15.3 Controlling Air Pollution

Since the Clean Air Act was first enacted in 1963, emissions of the worst pollutants in the U.S. have decreased by 57%.

15.3: Controlling Air PollutionKey Vocabulary

•Clean Air Act•Catalytic converter•Scrubber•Ozone hole•Chlorofluorocarbon (CFC)•Montreal Protocol

The Clean Air Act

Lesson 15.3 Controlling Air Pollution

• First passed in 1963 to protect human and environmental health by improving air quality; has been revised several times

• Limits emissions of pollutants, sets standards for air quality, establishes a legal framework for suing industries that break the rules, and provides funding for pollution control

Major Accomplishments of the Clean Air Act

Lesson 15.3 Controlling Air Pollution

• Catalytic converters, present in all cars since 1975, have reduced vehicle emissions.

• Lead has been phased out of gasoline.

• Industries and power plants have reduced releases of pollutants by using scrubbers, which remove or alter chemicals before they leave factory smokestacks.

Did You Know? The removal of lead from gasoline has led to a 99% reduction in lead emissions since 1973.

The Ozone Hole

Lesson 15.3 Controlling Air Pollution

• Ozone is a pollutant in the troposphere, but in the stratosphere it creates a protective barrier against UV radiation.

• Chemicals called chlorofluorocarbons, which used to be found in everything from aerosol cans to refrigerators, have destroyed ozone, causing an “ozone hole” to form over Antarctica.

• An ozone hole allows more UV radiation to reach Earth’s surface, potentially increasing cases of skin cancer.

Aerosol spray can

Recovery of the Ozone Layer

Lesson 15.3 Controlling Air Pollution

• The Montreal Protocol is an international treaty signed in 1987 that has cut CFC production by 95% since the 1980s.

• Ozone levels in the stratosphere have begun to stabilize, and the ozone hole will likely start to disappear.

Ozone Hole 1979 Ozone Hole 2000