Ion density

From Glossary of Meteorology

ion density

(Or ion concentration.) In atmospheric electricity, the number of ions per unit volume of a given sample of air; more particularly, the number of ions of given type (positive small ion, negative small ion, positive large ion, etc.) per unit volume of air.

Wait, C. R., and W. D. Parkinson 1951. Compendium of Meteorology. 124–125.