050 parts for each million (or 50 parts for every billion). Devices that produce over this can not be offered or shipped to California. CARB certification is usually a quick way to determine if an air ionizer provides lower levels of ozone. A different equivalent useful resource will be the https://allhealthmarket.com/product/home-care-2/oxygen-and-hydrogen-generator/hydrogen-inhalation-machine-300ml-450ml-inhalation-machine-molecular-oxygen-hydrogen-generator-h2-inhaler-water-ionizer-spe-pem/