An ion (/ˈaɪɒn, -ən/) is an atom or molecule that has a net electrical charge. Ions in their gas-like state are highly reactive and will rapidly interact with ions of opposite charge to give neutral molecules. As reactive charged particles, they are also used in air purification by disrupting microbes, and in household items such as smoke detectors. Ions are ubiquitous in nature and are responsible for diverse phenomena from the luminescence of the Sun to the existence of the Earth's ionosphere. Negative ions occur naturally around large bodies of moving water such as waterfalls and rivers. They are also prevalent after a rainy day.

Properties of Ions and Negative Ions

Ions are electrically charged molecules or atoms in the atmosphere. An air ion is formed when a gaseous molecule or atom receives sufficiently high energy to eject an electron. Negative Ions are those that gain an electron, while positive air ions lose an electron. The natural and artificial energy sources for Ions include:
(1) radiant or cosmic rays in the atmosphere  (2) sunlight including ultraviolet  (3) natural and artificial corona discharge including thunder and lightning  (4) the shearing forces of water (Lenard effect)  (5) plant-based sources of energy.

  Anions and cations

Since the electric charge on a proton is equal in magnitude to the charge on an electron, the net electric charge on an ion is equal to the number of protons in the ion minus the number of electrons.

An anion (−) (/ˈænˌaɪ.ən/), from the Greek word ἄνω (ánō), meaning “up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged). A cation (+) (/ˈkætˌaɪ.ən/), from the Greek word κάτω (káto), meaning "down", is an ion with fewer electrons than protons, giving it a positive charge.

There are additional names used for ions with multiple charges. For example, an ion with a −2 charge is known as a dianion and an ion with a +2 charge is known as a dication. A zwitterion is a neutral molecule with positive and negative charges at different locations within that molecule. Cations and anions are measured by their ionic radius and they differ in relative size: "Cations are small, most of them less than 10−10 m (10−8 cm) in radius. But most anions are large, as is the most common Earth anion, oxygen. From this fact it is apparent that most of the space of a crystal is occupied by the anion and that the cations fit into the spaces between them.”

  Ion Usages around us

Ions can be non-chemically prepared using various ion sources, usually involving high voltage or temperature. These are used in a multitude of devices such as mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters, and ion engines.

As reactive charged particles, they are also used in air purification by disrupting microbes, and in household items such as smoke detectors.

As signalling and metabolism in organisms are controlled by a precise ionic gradient across membranes, the disruption of this gradient contributes to cell death. This is a common mechanism exploited by natural and artificial biocides, including the ion channels gramicidin and amphotericin (a fungicide).

Inorganic dissolved ions are a component of total dissolved solids, a widely known indicator of water quality.

Air ionisers are often used in places where work is done involving static-electricity-sensitive electronic components (like in microelectronics cleanrooms), to eliminate the build-up of static charges on non-conductors. As those elements are very sensitive to electricity, they cannot be grounded because the discharge will destroy them as well. Usually, the work is done over a special dissipative table mat, which allows a very slow discharge, and under the air gush of an ioniser.

 Ions versus ozone

Ionisers are distinct from ozone generators, although both devices operate in a similar way. Ionisers use electrostatically charged plates to produce positively or negatively charged gas ions (for instance N2− or O2−) that particulate matter sticks to in an effect similar to static electricity.
Some Ion Purufiers will also produce a small amount of ozone—triatomic oxygen, O3—the higher quantity of which is not good for human consumption. Ozone generators are optimised to attract an extra oxygen ion to an O2 molecule, using either a corona discharge tube or UV light.

 How do we make artificial Ion production?

Artificial corona discharge is an efficient way to generate negative Ions. When a high negative voltage is applied to a conductor/electrode and generated electric field is high enough, corona discharge occurred.
If a charged conductor/electrode has a needle-type with a sharp point, the electric field around the tip will be significantly higher than other parts and air near the electrode can become ionized and ionss are generated. Intensity of corona discharge depends on the shape and size of the conductors as well as applied voltage. Irregular conductor, especially with a sharp point, gives rise to more corona than a smooth conductor and large-diameter conductors produce lower corona than small-diameter conductors; the higher the voltage applied, more ions are generated.
The closer the distance to corona point, the higher Ion concentration is detected as continuous generation of Ions by corona discharge is related to Townesned electron avalanche. .