Why is the air pressure higher on sunny days than on cloudy days?

The main reason why the air pressure is higher on sunny days than on cloudy days is related to the water vapor content in the atmosphere. On cloudy days, the air humidity is high and contains more water vapor, which leads to the decrease of air density, thus reducing the air pressure. On the contrary, on sunny days, the air is dry, the water vapor content is less and the air density is relatively high, so the air pressure is higher. Air pressure is the pressure of the atmosphere on the unit area, that is, it is numerically equal to the gravity of the vertical air column extending upward to the upper limit of the atmosphere, which reflects the pressure of the atmosphere on the earth's surface. It is an important parameter in meteorology. The units of air pressure are Pascal, kilopascal, hectopascal, bar and centimeter mercury. The pressure level is influenced by many factors, including altitude, land and ocean distribution, temperature and vertical airflow.