Some Examples of Important Small Amounts:
He wasn't driving drunk, he just had a trace of blood alcohol; 800 ppm (0.08%) is the limit (PDF) in all 50 U.S. states, and limits are lower in most other countries.
Don't worry about your iron deficiency; iron is only 4.4 ppm of your body's atoms.
Ireland isn't important; it's only 660 ppm (0.066%) of the world population.
That ibuprofen pill can't do you any good; it's only 3 ppm of your body weight (200 mg in a 60 kg person).
The Earth is insignificant; it's only 3 ppm of the mass of the solar system.
Your children can drink that water; it only contains a trace of arsenic (0.01 ppm is the WHO and U.S. EPA limit).
Ozone is only a trace gas: 0.1 ppm is the exposure limit established by the U.S. National Institute for Occupational Safety and Health. The World Health Organization (WHO) recommends an ozone limit (PDF) of 0.051 ppm.
A few parts per million of ink can turn a bucket of water blue. The color is caused by the absorption of the yellow/red colors from sunlight, leaving the blue. Twice as much ink causes a much stronger color, even though the total amount is still only a trace relative to water.
