050 parts for every million (or 50 parts per billion). Equipment that generate over this can't be marketed or shipped to California. CARB certification is a quick way to determine if an air ionizer produces low amounts of ozone. An additional equivalent source is the listing of certified home air https://allhealthmarket.com/product/home-care-2/oxygen-and-hydrogen-generator/hydrogen-water-generator-450ml-hydrogen-and-oxygen-inhalation-machine-molecular-h2-inhaler-water-ionizer-home-care/