050 parts for each million (or fifty parts for every billion). Equipment that produce over this can not be bought or shipped to California. CARB certification is usually a quick way to find out if an air ionizer produces lower levels of ozone. An additional comparable resource will be the 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/