What are the levels of smokeless ovens?

Smokeless barbecue should include two levels: First, the chemical emissions that are not burned during barbecue: all barbecues that use fuel as a heat source, such as charcoal fire, even fully burned red charcoal, white charcoal barbecue, and then liquefied gas, medium Gas barbecue, even if it is burning and full of barbecue equipment, whether we can not see black smoke, chemical emissions still exist, and the emitted substances still pollute food and the environment. Among all the heat sources used for barbecue, electricity is the cleanest heat source, and electricity as a heat source has no chemical emissions. Second, there is no oily fume when grilling: the oily fume is firstly caused by the oil droplets falling on the high-temperature heat source body during the grilling, such as oil droplets falling on the charcoal fire, dripping on the electric heating tube, and immediately turning into oil smoke; secondly, Oil fume also comes from the frying process of food. The oil quality when frying food will deteriorate, and oil fume will also be produced, which will pollute food and pollute the environment.