The astronauts had removed all air pressure from the spacecraft.

VOA: special.2009.06.24

NOAA scientists say Katrina's air pressure was very low.

VOA: special.2010.08.24

The second is the low barometric air pressure.

VOA: special.2010.06.30

Bigger livestock herds are putting greater pressure on land resources and disrupting some ecosystems and the animals generate significant amounts of water and air pollution, including methane, a climate-changing greenhouse gas.

VOA: standard.2010.02.22