What is the general trend of water vapor content as altitude increases?

What is the general trend of water vapor content as altitude increases?

• A. Increases with altitude
• B. Decreases with altitude
• C. Remains constant
• D. Varies unpredictably with altitude

Answer: (B)

Water vapor content generally decreases with altitude. As you climb, the air becomes thinner, so there are fewer water molecules per unit volume. The atmosphere also cools with height in the lower layers, and cooler air holds less moisture, which further lowers the amount of water vapor. Since most moisture comes from the surface and can't be supplied efficiently at high elevations, the absolute humidity (and mixing ratio) drops as you go higher, especially in the troposphere where weather happens. Beyond the troposphere, moisture remains scarce, so the overall trend is downward with altitude.

Water vapor content generally decreases with altitude. As you climb, the air becomes thinner, so there are fewer water molecules per unit volume. The atmosphere also cools with height in the lower layers, and cooler air holds less moisture, which further lowers the amount of water vapor. Since most moisture comes from the surface and can't be supplied efficiently at high elevations, the absolute humidity (and mixing ratio) drops as you go higher, especially in the troposphere where weather happens. Beyond the troposphere, moisture remains scarce, so the overall trend is downward with altitude.