companies to oxidize and permanently remove smoke, mold, and odor damage are considered a valuable and effective tool when used correctly for commercial and industrial purposes. However, there is a growing body of evidence that these machines can produce undesirable by-products. In September 2007, the California Air Resources Board announced a ban of indoor air cleaning devices which produce ozone above a legal limit. This law, which took effect in 2010, requires testing and certification of all types of indoor air cleaning devices to verify that they do not emit excessive ozone. Industry and markets As of 2015, the United States residential air purifier total addressable market was estimated at around $2 billion per year. See also Air sanitizer PCO (Photocatalytic oxidation) PECO (Photoelectrochemical oxidation) Nose filter NASA Clean Air Study Smog tower Scrubber Corsi–Rosenthal Box References External links CADR.org Information on Clean Air Delivery Rate by AHAM DOE HEPA Filter Standards HEPA filter specifications for DOE contractors Potera, C. (2011), Wood-Burning Stoves Get Help from HEPA Filters US National Institutes of Health Indoor Air Quality (IAQ) by United States Environmental Protection Agency Do-it-yourself (DIY) air cleaners: Evidence on effectiveness and considerations for safe operation by National Collaborating Centre for Environmental Health Building biology Medical equipment Filters Industrial gases Gas technologies