As the PH scale decreases or increases, how does this affect the acidity?

When pH decreases acidity increases,

and if pH increases  acidity decreases.

Explanation:

1 2 3 4 5 6 7(neutral) 8 9 10

acidic                          basic

So, when pH decreases acidity increases,

and if pH increases  acidity decreases.

hope you got the answer

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.