Sterilizing principles of plasma

Ultraviolet rays refer to the electromagnetic waves with the length from 100 to 400 nm. We cannot see ultraviolet rays with naked eyes.

The ultraviolet rays with the length from 100 to 400 nm are classified into UV-A, UV-B, UV-C and UV-V according to its influence on human body.

UV-A refers to the ultraviolet rays with the wavelength from 315 to 400 nm. It may cause black melanin to people's skin and make the skin black.

UV-B refers to the ultraviolet rays with the wavelength from 280 to 315. It may lead to cancer and cause wrinkles and aging to skin.

UV-C refers to the ultraviolet rays with the wavelength from 200 to 280 nm. The disinfection effect of ultraviolet rays with the wavelength from 240 to 270 is the strongest and they can directly damage cells. The DNA (desoxyribonucleic acid) and RNA (ribonucleic acid) can effectively decompose the ozone in water.

UV-V can produce ozone when its wavelength is within the range from 100 to 200 nm (utraviolet rays with the wavelength of 185 nm).The ozone in the air or dissolved in water can destroy the cell walls of microorganism through oxidation and thus make microorganism die immediately.

The sterilizing effect of ultraviolet rays is usually expressed as a killing ratio. For example, 99.9% means that 99.9% of original bacteria have been killed. Only 0.1% (1/1000) of them survives. Due to 3 in logarithm 1000103 (log), we usually use 3 log to represent the killing ratio. The sterilization rate of ultraviolet rays depends on two factors of (1) intensity of ultraviolet rays and (2) exposure time.