atmospheric

Just like atmospheric pressure is created by the weight of air molecules pressing down on each other, pressure exists in the subsurface of the Earth from the weight of the soil and rock above.

We can remove excess nitrogen using this same method to further lower our atmospheric pressure.

So, the oil inside the pipe is pressurized (usually around 14 times normal atmospheric pressure or over 200 PSI) to ensure that no bubbles can form.

Basically the molecules of the bulk substance push against the air more strongly than atmospheric pressure, lowering the energy barrier for molecules to peel off the solid and change states to a gas.

It works just like when you turn a cup upside down before putting it under water, except in this case the cup is much bigger, and the pressures inside can be much higher than normal atmospheric air pressure.