Relative humidity is the measure of water vapor in the air. It is calculated by dividing the actual vapor pressure of the air by the saturation vapor pressure of the air at the same temperature. The result is expressed as a percentage.

The relative humidity of air can be affected by a number of factors, including the temperature of the air, the amount of water vapor in the air, and the air pressure. When the temperature of the air increases, the relative humidity decreases. This is because the saturation vapor pressure of air increases as the temperature increases, so the amount of water vapor in the air must also increase in order to maintain the same relative humidity.

The amount of water vapor in the air can also affect the relative humidity. When the amount of water vapor in the air increases, the relative humidity increases. This is because the saturation vapor pressure of air is constant at a given temperature, so the relative humidity will increase as the amount of water vapor in the air increases.

Finally, the air pressure can also affect the relative humidity. When the air pressure decreases, the relative humidity increases. This is because the saturation vapor pressure of air decreases as the air pressure decreases, so the amount of water vapor in the air must also decrease in order to maintain the same relative humidity.