Figure 1.4

Air density, pressure, and height. Air density and pressure are greatest near sea level, where air molecules are most tightly compressed. At higher altitudes, air molecules are less compressed, so air has lower density and lower pressure. If a 1-cubic-meter (1 m3) box (inset diagrams) were filled with air at sea level and another one higher in the atmosphere, the air in the sea-level box would have a higher molecular density and more air pressure.