There are several grades, such as 1 100 million and 200 million. Our old man bought it once, 250 million. I moved to a new home in January and opened it every day when I got home. I feel the air is getting better and better. I haven't coughed recently, and I haven't suffered from insomnia recently. I don't know if I should owe it to it. Anyway, my dad thinks so.