050 parts per million (or 50 parts for every billion). Products that develop in excess of this cannot be offered or shipped to California. CARB certification is usually a quick way to determine if an air ionizer provides minimal levels of ozone. One more identical resource is definitely the list https://allhealthmarket.com/product/home-care-2/oxygen-and-hydrogen-generator/hydrogen-inhalation-machine-150ml-h2-hydrogen-gas-generator-hydrogen-purification-device-spe-pem-water-ionizer-for-home-gift/