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Figure 11.3 The ozone layer blocks harmful ultraviolet rays from reaching Earth's surface. Ozone concentration is highest at about 20 km above Earth's surface, in the ozone layer.

Ozone concentration (1012 molecules/cm3)

Figure 11.3 The ozone layer blocks harmful ultraviolet rays from reaching Earth's surface. Ozone concentration is highest at about 20 km above Earth's surface, in the ozone layer.

Ozone concentration (1012 molecules/cm3)

Atmospheric Layers

The atmosphere is classified into five different layers, as shown in Table 11.1 and Figure 11.4. These layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer differs in composition and temperature profile.

Troposphere The layer closest to Earth's surface, the troposphere, contains most of the mass of the atmosphere. Weather occurs in the troposphere. In the troposphere, air temperature decreases as altitude increases. The altitude at which the temperature stops decreasing is called the tropopause. The height of the tropopause varies from about 16 km above Earth's surface in the tropics to about 9 km above it at the poles. Temperatures at the tropopause can be as low as -60°C.

Stratosphere Above the tropopause is the stratosphere, a layer in which the air temperature mainly increases with altitude and contains the ozone layer. In the lower stratosphere below the ozone layer, the temperature stays constant with altitude. However, starting at the bottom of the ozone layer, the temperature in the stratosphere increases as altitude increases. This heating is caused by ozone molecules, which absorb ultraviolet radiation from the Sun. At the stratopause, air temperature stops increasing with altitude. The stratopause is about 48 km above Earth's surface. About 99.9 percent of the mass of Earth's atmosphere is below the stratopause.

Mesosphere Above the stratopause is the mesosphere, which is about 50 km to 100 km above Earth's surface. In the mesosphere, air temperature decreases with altitude, as shown in Figure 11.4. This temperature decrease occurs because very little solar radiation is absorbed in this layer. The top of the mesosphere, where temperatures stop decreasing with altitude, is called the mesopause.

Thermosphere The thermosphere is the layer between about 100 km and 500 km above Earth's surface. In this layer, the extremely low density of air causes the temperature to rise. This will be discussed further in Section 11.2. Temperatures in this layer can be more than 1000°C. The ionosphere, which is made of electrically charged particles, is part of the thermosphere.

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Table 11.1

Interactive Table To explore

Components of the Atmosphere more about layers of the atmosphere, visit glencoe.com.

Atmospheric Layer

Components

Troposphere

layer closest to Earth's surface, ends at the tropopause

Stratosphere

layer above the troposphere, contains the ozone layer, and ends at the stratopause

Mesosphere

layer above the stratosphere, ends at the mesopause

Thermosphere

layer above the mesosphere, absorbs solar radiation

Exosphere

outermost layer of Earth's atmosphere, transitional space between Earth's atmosphere and outer space

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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