How is ionization of a volume of air measured?

Ionization of a volume of air is measured primarily in Roentgens or Coulomb per kilogram. Roentgen is a unit that quantifies the amount of ionization produced in air by X-rays or gamma rays, specifically reflecting the ion pairs created in one cubic centimeter of air. The Coulomb per kilogram (C/kg) is a more modern SI unit that accounts for the charge of ions produced when radiation interacts with air.

The connection between these units lies in their representation of the same physical phenomenon—ionization due to radiation exposure. The Roentgen unit is historically significant and is still used in many circumstances, while the Coulomb per kilogram provides a more precise, fundamental measurement in accordance with contemporary scientific standards.

Other units, such as Gray or Sievert, focus on absorbed dose and biological effects, respectively, while Rad or rem serve similar purposes in older terminology. Decibels and watts pertain to entirely different areas, such as sound intensity and electrical power, and are not applicable to ionization measurement.