The formal business format of shops can be divided into catering shops and non-catering shops. At the beginning of the construction, restaurants reserved smoke exhaust pipes and fresh air pipes. The fresh air system is to balance the air pressure when smoking in the kitchen, which is also called kitchen air supply. The kitchen oil fume is purified by the air purifier in the kitchen and directly discharged to the outside through the reserved smoke exhaust pipeline. Some large shopping malls will have secondary air purification equipment.