Which factor positively relates to air's capacity to hold water vapor?

The factor that positively relates to air's capacity to hold water vapor is temperature. As temperature increases, the ability of air to hold moisture also increases. This phenomenon occurs because warmer air has more energy, allowing it to accommodate more water vapor molecules before it becomes saturated. The relationship between temperature and water vapor holding capacity is often illustrated by the concept of the saturation vapor pressure, which increases exponentially with warmer temperatures.

In contrast, while humidity denotes the amount of water vapor present in the air, it does not indicate the air's capacity to hold more water vapor. Pressure plays a role in various atmospheric processes but does not directly determine the water-holding capacity of air either. Wind speed can influence the distribution of moisture but does not inherently affect the saturation level of water vapor in the air. Thus, temperature is the key factor in determining how much water vapor the air can hold.