Final answer:
The percentage of phosphorus in the atmosphere is insignificant and not typically measured. Phosphorus has a very slow environmental cycle, mainly occurring in the earth's crust and within living organisms, and has a long residence time in the ocean before it cycles back to land.
Step-by-step explanation:
The percentage of phosphorus in the atmosphere is extremely low, so much so that it's not commonly referred to as a standard component of atmospheric gases. The atmosphere at Earth's surface mainly consists of around 78% nitrogen (N₂), 21% oxygen (O₂), and 1% argon (Ar), with traces of water vapor (H₂O), carbon dioxide (CO₂), and other gases.
Phosphorus cycles very slowly through the environment and is primarily found in the earth's crust and in living organisms, not in the atmosphere. It is also exchanged between phosphate dissolved in the ocean and marine ecosystems, with an oceanic residence time for the average phosphate ion ranging from 20,000 to 100,000 years. This cycle is much slower than that of many other elements, such as carbon, which has increased from 280 to around 410 parts per million by volume (ppmv) in the atmosphere due to human activities
For context, while the concentration of carbon dioxide has increased significantly, leading to a concentration that is approximately 0.04% of the atmosphere, phosphorus does not have a measureable presence in the atmosphere, remaining an essential but non-gaseous nutrient that moves slowly from the land to ocean ecosystems and back again.