At what level of oxygen has the air quality deteriorated to the point that it threatens life?
The level of oxygen in the Earth's atmosphere is relatively stable and does not typically fluctuate to an extent that threatens life directly. Oxygen concentration in the atmosphere is maintained at approximately 21% by volume, which is considered suitable for supporting human and most animal life. However, air quality can deteriorate due to the presence of pollutants or the reduction of oxygen relative to other gases, which can be harmful to life. For instance, when certain pollutants or contaminants displace the oxygen in the air, it can lead to oxygen deficiency or oxygen depletion, making it difficult for living organisms to breathe properly.
Therefore, the deterioration of air quality and its impact on life is not solely determined by oxygen levels but also depends on the presence of other gases and pollutants. Factors such as the concentration of pollutants like carbon monoxide (which can bind to hemoglobin in the blood, reducing its oxygen-carrying capacity) or the presence of harmful respiratory irritants can pose significant threats to life, even if the oxygen concentration remains relatively constant.