Which layer of the atmosphere is closest to the Earth's surface?

The troposphere is the layer of the atmosphere that is closest to the Earth's surface. It extends from the ground up to about 8 to 15 kilometers in altitude, depending on geographic location and weather conditions. This layer is where nearly all weather phenomena occur, including clouds, precipitation, and storms, as it contains the majority of the atmosphere's mass and water vapor. Because of its proximity to the Earth's surface, the troposphere is characterized by a decrease in temperature with increasing altitude.

Other layers, such as the stratosphere, mesosphere, and thermosphere, are situated above the troposphere. The stratosphere contains the ozone layer, which absorbs and scatters ultraviolet solar radiation. The mesosphere is further above that, where temperatures again decrease with altitude, while the thermosphere is characterized by extremely high temperatures and is where the ionosphere is located, impacting radio communications and GPS systems. Understanding the structure of the atmosphere, particularly the troposphere's role in weather and climate, is essential in the study of air pollution and its effects on human and environmental health.