Answer:
Parts per billion (ppb) is a unit of measurement used to express very low concentrations of a substance. It is equivalent to one part of a substance per billion parts of a whole, or one microgram per liter (μg/L) in the case of a liquid solution. For example, if a water sample contains 1 ppb of a certain chemical, it means that there is one microgram of that chemical per liter of water. It is often used in environmental monitoring to measure the levels of pollutants in air, water, and soil.
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