Question

What is the average presence of carbon dioxide in percentage in a given volume of air?

Answer 1

The average concentration of carbon dioxide (CO₂) in today’s dry outdoor air is about 420 – 430 parts per million by volume (ppm), which is roughly 0.042 – 0.043% of the air by volume (convert ppm to percent by dividing by 10,000: e.g., 425 ppm = 425/10,000 = 0.0425%). NOAA’s global analysis gives a 2024 global average near 422.8 ppm, Mauna Loa’s 2024 annual average was about 424.6 ppm, and monthly/seasonal peaks in 2025 have exceeded 430 ppm, all equivalent to about 0.042 – 0.043% by volume.