Good questions, but difficult to answer, as there are many variables, and the changes we see with psi are mostly temperature dependent.

Ideally the "amount" of air in the tire doesn't change unless you change it or you have a leaking tire. The "amount" of air is not volume, or psi, but rather the number of air molecules. The space (volume) these molecules occupy is restricted by the tire volume. The psi varies with temperature, and to a much lesser degree external pressure (barametric pressure).

Now, I know you just want the "skinny" and just give you a straightforward answer. But I really can't.

I can make a guess, but first you have define for me your: "On a day like this." What is the day like (and don't tell me that it's the SOS, or "I'm in a pretty good mood today")