Why is the air pressure low in cloudy weather? Why is the air pressure low in summer?

Atmospheric pressure usually has two meanings: one refers to atmospheric pressure, which is also the most common term; the other refers to oxygen concentration, which is a common term in common saying.

The poster mentioned that "the air pressure is low in cloudy weather; the air pressure is low in summer" usually refers to the level of oxygen concentration. Winter is dry and cold, the air density is greater than in summer, and the water vapor content is less than in summer, so the oxygen concentration is higher than in summer. The water vapor content in the air on a sunny day is much less than that on a cloudy day, and the relative oxygen concentration is higher.

It should be mentioned that it makes sense to use the term atmospheric pressure here. When winter is cold, the distance between air molecules is small and the density is high; when there is more water vapor on cloudy days, the relative density of air is small. However, the comparison of air pressure between winter and summer, sunny days and cloudy days is usually based on human feeling, not academic. People's feelings about the level of air pressure are determined by the oxygen concentration, so it is more appropriate to discuss the level of oxygen concentration here.

As for feeling stuffy when the air pressure is low, it is a physiological reaction caused by insufficient oxygen supply caused by low atmospheric oxygen concentration.

To sum up, cloudy days have lower air pressure than sunny days, and summer has lower air pressure than winter.