The balance in oxygen level is maintained by

Atmospheric oxygen stays balanced through photosynthesis releasing oxygen and respiration consuming it in a continuous cycle.

Industrial gas emissions add pollutants rather than regulating the natural oxygen balance.

Ozone forming in the upper atmosphere shields against ultraviolet rays but does not govern surface oxygen levels.

Photochemical smog is a pollution product and degrades air quality rather than balancing oxygen.

Green plants and photosynthetic organisms release oxygen while all living cells return carbon dioxide during respiration.

Oceanic phytoplankton contribute roughly half of the planet's oxygen production.