How much oxygen and carbon dioxide is there in the air we breath? Does it change with the seasons? Does it change with the location on our planet? I thought the average oxygen level was approximately 20.95 percent by volume? Do you have anymore exact numbers? Also, I thought ambient carbon dioxide levels were approximately 360-400 ppm. Do you have an exact average?Both vary in space and time, but the variability of oxygen is much smaller than that of CO2. Your value for the oxygen concentration is close to the "US Standard Atmosphere" value of 20.9476%. Current CO2 concentrations are about 370 parts per million by volume, and show significant seasonal variations associated with biospheric processes and spatial variations related to emissions and sinks. The long-term increase in CO2 due to fossil fuel use is thought to be contributing to a small, but perceptible, decline in O2. For more information about the changes in atmospheric oxygen, I refer you to an article by Wallace Broecker on the web at http://www.columbia.edu/cu/21stC/issue-2.1/broecker.htm. Information about CO2, including data and graphs showing the strong seasonal cycle and the upward trend, are available from the NOAA Climate Monitoring and Diagnostics Lab. Dian Seidel |
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