This one is courtesy of our friends at the American Chemistry Council
A part-per-million can be thought of as:
- A credit card lying in the middle of a football field
- One step, on a 568–mile (914 km) walk
- One minute, in a two-year span
A part-per-billion can be thought of as:
- One thousand times smaller than that credit card on the football field
- One heartbeat in 27 years for an average male (70 heartbeats per minute)