Altitude Effects on Compressor Performance - Tech Talk 89
Manufacturers give performance ratings on blowers/compressors at standard temperature and pressure (STP), which is 68°F (20°C) at sea level. This is important because air (and all other gases) expands and contracts significantly at higher and lower temperatures and pressures. For instance, a one cubic foot balloon at sea level will expand to about 1.2 cubic feet at 5,000 feet (1,500 meters) altitude. Taken 33 feet below sea level, it will compress to 0.5 cubic feet.
When an air compressor is operated at altitude, it takes in less air because the air up there is less dense. It must turn more revolutions to move the same amount of air it does at sea level.
When selecting a blower/compressor for use at altitude, a general rule of thumb is to reduce its expected output (both volume and pressure) by 4 percent for each 1,000 feet (300 meters) of altitude above sea level.