Why does atmospheric pressure vary with altitude?

At sea level the atmospheric pressure is 1013-1023 hPa at 15 degree. Every ~ 8 meter 1 hPa will reduce. read more

Thanks for the A2A. The other answerers have covered the fine points pretty well. Inversely proportional, less mass of air atop you, etc. From a chemical engineering standpoint, compare it to hydrostatic pressure. read more

Atmospheric pressure reduces with altitude for two reasons - both related to gravity. The gravitational attraction(*) between the earth and air molecules is greater for those molecules nearer to earth than those further away - they have more weight - dragging them closer together and increasing the pressure (force per unit area) between them. read more