At a depth of 30 meters/99 feet, how much denser is the air you breathe compared to the surface air?

At a depth of 30 meters (99 feet) underwater, the pressure increases significantly due to the weight of the water above. For every 10 meters of seawater, pressure increases by about one atmosphere (or approximately 14.7 psi), resulting in a total pressure at 30 meters that is about four times greater than at the surface.

Since the air you breathe is primarily nitrogen and oxygen, its density increases with pressure. At sea level, air has a certain density, and as the pressure increases under water, the gases compress, leading to an increase in density. This means that the air you breathe at 30 meters will be significantly denser than air at the surface.

The correct understanding is that at a depth of 30 meters, the total pressure is about four atmospheres (one atmosphere from the surface plus three additional atmospheres due to the water pressure). Consequently, the density of the air becomes four times greater as well, making the correct answer indicative of this increased density at that depth.