What is ppb and ppm?

Ozone is measured by the concentration of ozone within the air, and units are recorded in parts per billion (ppb). For example, one ppb is the equivalent of one drop in one billion drops of water or about one drop of water in a swimming pool. Another unit of measurement for some of the air quality standards is parts per million (ppm), and one ppm is the equivalent of about one cup of water in a swimming pool. One ppm is equivalent to 1,000 ppb.