050 parts for every million (or 50 parts for each billion). Gadgets that make more than this can not be bought or shipped to California. CARB certification can be a quick way to determine if an air ionizer creates minimal levels of ozone. Another related source is the listing of https://allhealthmarket.com/product/home-care-2/hydrogen-generator/hydrogen-inhalation-machine-300ml-450ml-hydrogen-water-generator-h2-inhaler-therapy-hydrogen-gas-generator-water-purifier-ionizer-2/