Where does the smell of the hotel lobby come from?

Generally, mid-range hotels use aromatherapy machines or sprayers to distribute fragrance. Express hotels and some KTV. Most perfumers and perfumers are used to increase the fragrance. In large four-and five-star hotels, they use central air-conditioning perfumers to float the fragrance to every corner of the hotel lobby with air supply. It is this kind of equipment, and I don't know which company it is. ?