Will PCB oxidize in hot weather?

No matter how high the temperature is, there is generally no oxygen.

You mean the PCB without solder mask? If it is not treated, it can be left there for a day or two. It soon turned black, and it was hard to find the disconnection.

I usually paint a layer of rosin alcohol solution on the board after I make it myself, and the alcohol volatilizes dry rosin on it, which can be placed for a long time and contribute to the welding effect.