Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions.[1]
UVGI is used in a variety of applications, such as food, air, and water purification.
UV-C light is weak at the Earth’s surface as the ozone layer of the atmosphere blocks it.[2]
High-efficiency particulate arrestance (HEPA),[1][2] originally called high-efficiency particulate absorber but also sometimes called high-efficiency particulate arresting or high-efficiency particulate air, is a type of air filter. Filters meeting the HEPA standard have many applications, including use in medical facilities, automobiles, aircraft and homes.
The filter must satisfy certain standards of efficiency such as those set by the United States Department of Energy (DOE).
To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size of 0.3 µm.[3]
HEPA was commercialized in the 1950s, and the original term became a registered trademark and later a generic term for highly efficient filters.[4]

1. HEPA Company glossary of terms
2. Originally ‘High Efficiency Particulate Arrestment – see thefreedictionary.com
3. American Society of Mechanical Engineers, ASME AG-1a–2004, “Addenda to ASME AG-1–2003 Code on Nuclear Air and Gas Treatment”, 2004
4. .: a b Gantz, Carroll (2012-09-21). The Vacuum Cleaner: A History. McFarland. p. 128. ISBN 9780786493210.