What is the primary component of air, by volume?

The primary component of air, by volume, is nitrogen. It constitutes about 78% of the Earth's atmosphere, making it the most abundant gas present. Nitrogen plays a critical role in maintaining life on Earth by acting as a buffer and diluent for oxygen, which comprises approximately 21% of air. This balance is essential for many biological processes, including respiration and combustion.

The presence of nitrogen in the atmosphere is also vital for other environmental processes, such as the nitrogen cycle, which is important for plant growth and soil health. Understanding the composition of air is fundamental in fields like respiratory therapy and environmental science, as it affects how gases behave, their effects on human health, and the functioning of various systems in nature and in medical applications.