Why is the air pressure greater in sunny days than in rainy days and greater in winter than in summer?

Atmospheric pressure is related to the density of air, and the density of water vapor is less than that of air (mainly nitrogen and oxygen). When there is more water vapor in the air, the air pressure becomes lower.

Winter is dry and cold (cold air density is higher than hot air), air density is higher than summer, and water vapor content is lower than summer, so the air pressure in winter is higher than summer; The water vapor content in the air on sunny days is much less than that on cloudy days, so the air pressure is higher than that on cloudy days.