The phrase "oxygen concentrations" refers to how much oxygen is present in a given area or substance. It is a measurement of the amount of oxygen compared to other gases or molecules around it. Full definition
Areas with a lot of trees have a higher oxygen concentration in the environment, and therefore it's easier to breathe and relax. (wellnessmama.com)
At the same time, the increase in temperature, reduced oxygen concentration and adjustment of the tidal cycle produced no significant effect. (sciencedaily.com)
Their iron content also promotes immunity by raising oxygen concentration in the blood. (insteading.com)