Although the atmosphere is a mixture of many gases, it behaves much as if it were a single ideal gas. At constant pressure, the absolute temperature and density of an ideal gas are inversely proportional. At constant density, the pressure and absolute temperature of an ideal gas are directly proportional. The constant of proportionality, R, varies depending on the specific gas. If air is heated within a closed container, air pressure inside the container will rise following Charles's 2nd law.
Air density is variable within the atmosphere.
Therefore, when the air is heated, air pressure decreases as a result of reduction in air density. This is because molecular weight of water is less than average molecular weight of dry air. Cold, dry air produce higher surface pressure than do warm, humid air. Warm, dry air produces higher surface pressure than equally warm, but more humid air. Divergence at surface results from sinking, downward air motion decreasing air density and air pressure at surface.