050 parts per million (or 50 parts per billion). Devices that deliver over this can not be offered or shipped to California. CARB certification is usually a quick way to determine if an air ionizer creates very low levels of ozone. Yet another equivalent useful resource is definitely the list https://allhealthmarket.com/product/home-care-2/hydrogen-generator/hydrogen-water-generator-150ml-hydrogen-inhalation-machine-h2-hydrogen-gas-generator-inhaler-therapy-purifier-ionizer-spe-pem/