050 parts per million (or fifty parts per billion). Gadgets that deliver over this cannot be marketed or shipped to California. CARB certification is a quick way to determine if an air ionizer provides minimal amounts of ozone. Yet another equivalent source would be the list of Accredited area air https://allhealthmarket.com/product/home-care-2/oxygen-and-hydrogen-generator/hydrogen-water-generator-300ml-450ml-hydrogen-inhalation-machine-99-99-oxygen-and-hydrogen-generator-ionizer-home-care/