Let’s say Mars gets terraformed with all the bells and whistles. Oceans worth of added water and an oxygen/nitrogen atmosphere with more or less 1 standard atmosphere pressure at “sea level.” Since the gravity of Mars is substantially lower than Earth, to get that same pressure, the atmosphere will have to be substantially heavier in order to provide the same pressure, and thus be properly breathable. And that heavier atmosphere will be necessarily thicker… not denser, but extended much further out into space: “scale height.” With about 3/8 the gravity, it seems you’d need 8/3 the mass of air per unit area to get the same pressure.
I’ve little doubt that numerous people have run the math on what all would be needed and what all would be the result. Anybody know of examples of such results? What would be the temp and pressure at various altitudes for such an atmosphere? What the lowest stable satellite orbit would be? How tall and how high clouds could get? How freakin’ high the birds would fly?