Ions are small particles that take on an electrical charge.
In nature we tend to find between a few hundred to a few thousand of these ions per cubic centimeter. The small particles that take on this charge are either negatively charged, positively charged or neutral. In a cubic centimeter of air out over a grass field, we find the ratio is almost balanced between negative ions and positive ions. In other words we are breathing quantities of electricity. Positive ions are known to make asthma victims worse.