(b) Explain why the stratosphere, which is about 35 km thick, has a smaller total mass than the troposphere, which is about 12 km thick.

Verified step by step guidance

1. insert step 1> The troposphere is the lowest layer of Earth's atmosphere and contains approximately 75% of the atmosphere's total mass. This is because it is denser and contains more air molecules per unit volume due to the gravitational pull being stronger closer to Earth's surface.
2. insert step 2> The stratosphere, located above the troposphere, extends from about 12 km to 47 km above Earth's surface. Although it is thicker than the troposphere, it contains less mass.
3. insert step 3> The reason for the smaller total mass of the stratosphere is that air density decreases with altitude. As you move higher in the atmosphere, the air becomes less dense, meaning there are fewer air molecules in a given volume.
4. insert step 4> The stratosphere's lower density is due to the decrease in atmospheric pressure with altitude. As you ascend, the weight of the air above decreases, leading to a reduction in pressure and density.
5. insert step 5> Therefore, even though the stratosphere is thicker in terms of vertical distance, its lower density results in a smaller total mass compared to the denser, albeit thinner, troposphere.

Key Concepts

Atmospheric Layers

The atmosphere is divided into layers based on temperature gradients, with the troposphere being the lowest layer where weather occurs, extending up to about 12 km. Above it lies the stratosphere, which extends from 12 km to about 50 km. Each layer has distinct characteristics, including temperature and composition, affecting their mass and density.

Density and Pressure

Density is defined as mass per unit volume, and it varies with altitude in the atmosphere. The troposphere contains a higher concentration of air molecules due to greater pressure at lower altitudes, resulting in higher density. In contrast, the stratosphere, being higher and less dense, has fewer air molecules, contributing to its smaller total mass despite its greater thickness.

Temperature Variation

Temperature plays a crucial role in atmospheric structure. In the troposphere, temperature decreases with altitude, leading to more air being compressed and thus a higher mass. Conversely, in the stratosphere, temperature increases with altitude due to the absorption of ultraviolet radiation by ozone, which reduces the density of air and results in a lower total mass despite its greater height.