The maximum amount of water vapour that air can hold is determined by its capacity to absorb and retain moisture.

Factors Affecting Water Vapour Capacity

The key factor influencing how much water vapour air can hold is its air temperature. This relationship can be explained as follows:

• Warmer air molecules possess more kinetic energy, allowing them to move faster and spread further apart. This increased space and energy enable them to accommodate a larger number of water vapour molecules before reaching saturation.
• Conversely, colder air molecules have less energy, move slower, and are closer together. This reduces the air's capacity to hold water vapour.

Understanding Saturation Point

The air temperature dictates the saturation point, which is the maximum concentration of water vapour the air can hold at a given temperature and pressure. When air reaches its saturation point, it cannot hold any more water vapour, and processes like condensation may occur.

Option Analysis

• Air Temperature: Directly determines the maximum water vapour capacity.
• Dew Point Temperature: Is the temperature at which saturation occurs, a consequence of the air's moisture content and temperature, not the primary determinant of capacity.
• Humidity: Measures the *current* amount of water vapour in the air relative to its maximum capacity, not the capacity itself.
• Evaporation: Is the process of water turning into vapour, which adds water vapour to the air, but it doesn't define the air's maximum holding capacity.

Therefore, the maximum amount of water vapour air can hold is fundamentally dependent on air temperature.