Ppm

PPM    (parts per million)

One part per million (ppm) denotes one part per 1,000,000 parts, one part in 106, 1/1,000,000 * 100% = 0.0001% (or 1% = 10,000 ppm), and a value of 1 × 10−6. This is equivalent to one drop of water diluted into 50 liters or about 32 seconds out of a Terran year.