The concentration of water vapor in the atmosphere is most pronounced in the lower layers, specifically in the troposphere. This is the part of the atmosphere that extends from the Earth’s surface up to about 8 to 15 kilometers high, depending on geographic location and weather conditions.
The reason for the higher concentration of water vapor in the troposphere is primarily due to its proximity to the Earth’s surface, where water evaporation occurs from oceans, lakes, rivers, and even soil. Warmer air can hold more moisture, which is why areas with higher temperatures tend to have greater humidity levels.
Furthermore, as you move higher into the atmosphere, particularly into the stratosphere and above, the air becomes cooler and drier. The processes of condensation and precipitation play a significant role in depleting water vapor in these upper layers, resulting in much lower concentrations compared to the troposphere.