What Are Negative Ions?

Air may look empty, but it contains molecules, tiny particles and electrical charges. Negative ions are part of this invisible world.

Start with an electron

An ion is an atom or molecule with an electrical charge. A negative ion has gained an electron; a positive ion has lost one. Here, “negative” describes the charge. It does not mean harmful or undesirable.

Why are they called air ions?

In the atmosphere, charged molecules can gather other molecules around them to form small clusters. Scientists study these clusters, their composition and how they move in an electric field. Air ions are continually formed and lost, so the air around us is a changing system.

They are already part of our environment

Natural ionization comes from sources including cosmic radiation and radioactive decay. Ions may recombine with opposite charges or attach to airborne particles. Their concentration therefore changes with the surroundings.

A useful distinction

An air ion and a dust particle are different things, although a particle can carry charge. Understanding this distinction makes the next step—how ionization technology works—much easier to follow.