Why does the air pressure change with the seasons?

Gas expands with heat and contracts with cold. In hot weather, the gap between molecules is large and the air pressure is low. Because the temperature is low and the atmosphere is concentrated near the ground, the air pressure is high. Atmospheric pressure usually has two meanings: one refers to atmospheric pressure, which is also the most general statement; The second refers to the oxygen concentration, which is a common saying.

"The atmospheric pressure in winter is higher than that in summer, and the atmospheric pressure in sunny days is higher than that in rainy days" usually refers to the level of oxygen concentration. Winter is dry and cold, the air density is higher than that in summer, and the water vapor content is lower than that in summer, thus making the oxygen concentration higher than that in summer. The water vapor content in sunny days is much lower than that in cloudy days, so the relative oxygen concentration is higher.

It should be mentioned that the statement of atmospheric pressure here is reasonable. It is cold in winter, with small molecular spacing and high density. When there is more water vapor on cloudy days, the relative air density is smaller. However, the comparison of air pressure between winter and summer, sunny and cloudy days is usually based on human feelings, not academics. People's feeling of air pressure is determined by oxygen concentration, so it is more appropriate to discuss it here with oxygen concentration.