Negative ions in the natural environment

Negative ions are generally created by:

(1) Photoelectric effect by solar rays
(2) Atmospheric diffusion caused by UV rays
(3) Thunder/Lenard's effects
(4) Electron diffusion caused by alpha rays emitted from the inside of the earth
(5) Electron diffusion caused by beta rays emitted when the earth's crust moves
(6) Electron diffusion caused by gamma rays when atmospheric pressure falls

Water droplets are generated when water splashes down onto the water surface and rocks. A water droplet forms a two-layer structure whose inner/outer surface is charged negatively/positively when it is smashed.

Thus, the outer surface of newly created droplets are charged positively and the air, which touches them, is charged negatively. This is how negative ions are created by splashing water.

This theory referred to as the Leonard effect was reported by German physicist Dr. Phillip Leonard. For more information, you can refer to "The Leonard effect" (Japanese only).

Cigarette smoke contains highly concentrated positive ions ranging about 2,000-30,000 (pcs/cc). These positive ions neutralize negative ions in the air and the negative ion count decreases, which can cause symptoms such as headache. Negative ions vanish due to human presence. It is reported that the amount of negative ions neutralized by one smoking person is equal to that of 100 non-smoking people.

Negative ion generation depends on humidity and the negative ion count decreases when it is raining. Negative ions combine with clusters of tiny water droplets to exist in the air.

Thus, the number of negative ions increases as the number of clusters increases. The number of tiny water droplets decreases when humidity is high such as a rainy day because they combine with each other.

A water droplet forms an electric double layer ^* as shown on the left image.The inner/outer surface is charged negatively/positively, respectively. When it splits into some droplets, the newly created surface obtains positive electricity from air molecules in order to become positively charged, thus the air molecules are negatively charged. This is how the air is negatively ionized.

* What is an an electric double layer?
When two different phases such as a solid and a liquid come into contact each other, positive and negative charges appear on the boundary surface with a distance of the molecular level.

Positive ions found in living space are generated by:

1. Car exhaust
2. Factory exhaust
3. Home appliances

When humidity is high, electricity is released through water contained in the air. On the contrary, when humidity is low and there is little moisture in the air, electricity is more likely to stay where it was created to become static electricity. This is why static electricity increases in dry air.

Theoretically, negative ions can cancel out static electricity if they posses the same amount of electronic charge as negative ions and static electricity are charged negatively and positively, respectively in living space. Technically, it is not easy to completely neutralize and eliminate static electricity charged on the human body. This principle is utilized in the semiconductor industry for ESD (Electro-Static Discharge) protection where sensitive devices can be destroyed by static electricity.

Plants generate very few negative ions at most. If there are massive plants, it is possible that you can enjoy negative ions in the area.

The potted plant Sansevieria trifasciata commonly called "Snake plant" has been featured on a TV program as it generates some negative ions but it will not be able to fill a room with the negative ions.