Problem 10 - Chemistry: The Central Science

Question

(a) How are the boundaries between the regions of the atmosphere determined? (b) Explain why the stratosphere, which is more than 20 miles thick, has a smaller total mass than the troposphere, which is less than 10 miles thick.

Step-by-Step Solution

Answer

The boundaries between the regions of the atmosphere are determined by distinct changes in temperature. The troposphere is the lowest atmospheric layer containing most of the atmosphere's mass. The stratosphere is the second layer and is thicker than the troposphere. Despite this, the stratosphere has less mass as air density decreases with altitude, making the air in the stratosphere less compressed and less dense than in the troposphere.

Step 1: (Understanding the Atmosphere Layers)

The atmosphere is composed of several layers with distinct properties and boundaries. Each layer has specific characteristics like temperature, pressure, and chemical composition, which differ from the ones above or below it. These atmospheric layers, from the Earth's surface to the outermost region, are: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Step 2: (Determining the Boundaries)

The boundaries between the regions of the atmosphere are determined by distinct changes in the temperature profile. The change in temperature acts as a barrier and defines the start and end of an atmospheric layer. For example, the boundary between the troposphere and the stratosphere is called the tropopause, which is where the temperature starts to increase instead of decreasing with altitude.

Step 3: (Characteristics of the Troposphere and Stratosphere)

The troposphere is the lowest atmospheric layer, it ranges from the Earth's surface to an altitude of about 7 to 10 miles. This is the layer where we experience weather phenomena, and it contains most of the atmosphere's mass. On the other hand, the stratosphere is the second atmospheric layer, situated above the troposphere, and it ranges from about 10 to 31 miles in altitude. Its most distinctive feature is the presence of the ozone layer, which absorbs UV radiation and causes an increase in temperature within the stratosphere.

Step 4: (Explaining the difference in mass between the Troposphere and Stratosphere)

Although the stratosphere is thicker than the troposphere, it has a smaller total mass. The explanation for this can be found in the relationship between atmospheric pressure and altitude. In the troposphere, the air pressure and density decrease exponentially with altitude, making this section of the atmosphere denser than the other layers. On the other hand, as one goes higher in altitude, air particles are less compressed, causing a decrease in air pressure and density. The air density in the stratosphere is significantly lower than in the troposphere since it is farther from the Earth's surface. Consequently, despite the stratosphere being thicker than the troposphere, it has less mass due to its lower air density.