What processes change/affect the percentage of gases in air?

Question

mainly oxygen and nitrogen is what im focusing on,

I already know photosynthesis and respiration, but what others?

Answer 1

Fires.

Answer 2

Temperature is probably the biggest effect, since the equilibrium mixing ratio of water is a function of temperature.  Higher temperatures lead to more water vapor (if you are over an ocean, which is true for 65% of the planet, roughly), which will decrease the mixing ratios of nitrogen and oxygen.