Why does atmospheric pressure decrease when the amount of water vapor in the air increases ?

Why does atmospheric pressure decrease when the amount of water vapor in the air increases ?
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Answer :

As water vapor is lighter than air, the pressure in the atmosphere decreases as the amount of water vapor in the air increases. During cooking, water vapor is seen rising upwards. This indicates that the concentration of water vapor is lower than that of air. For this reason, when the amount of water vapor in the air increases, the average density of air decreases. So as the amount of water vapor in the air increases, the pressure decreases.
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