(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.

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.