Parts per million (ppm)

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Number of parts of a chemical found in one million parts of a particular gas, liquid or solid mixture. Climate scientists and activists use the term to describe the concentration of pollutants, such as carbon dioxide or methane, in the atmosphere. Many scientists agree that carbon dioxide levels should be at 350 ppm to be considered safe; 2022 levels are about 400 ppm and growing by approximately 2 ppm each year.


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