# Is the air we breathe ionized?

Is the air we breathe ionized? I am reading a book that says that the air we breathe is ionized but from what I have read so far, it is only the air in the upper atmosphere that is ionized.

• Nearly every gas is ionized to some degree; the question is, how small does the ionization fraction have to be before you call it negligible? – probably_someone Mar 20 '18 at 20:17

A quick search tell us that outdoor air typically has 100 to 1000 ions per cubic centimeter, both positive and negative. That's roughly 1 ion per $10^{19}$ molecules.