Atmosphere a heat engine driven by solar radiation. Light from the sun ultimate source of energy. Atmospheric Structure is not uniform in Temperature or Pressure.
Pressure also decreases with altitude.
Air less dense at higher altitudes, therefore lower P's. The Earth's radiation balance is determined by how much solar radiation reaches the atmosphere and how much escapes back to space. Latitude changes are due to the curvature of the Earth. Less light reaches the latitudes above the equator. This is due to winds which are due to convection in the atmosphere.