Odor grade refers to several grades of odor intensity determined by human sense of smell according to olfactory threshold. Generally, the odor intensity is divided into six grades: 0 tasteless, 1- detection threshold, 2 cognitive threshold, 3 obvious detection, 4 strong odor and 5 sudden odor. If the ammonia concentration is lppm, it is rated as 2.5, 2ppm is 3, and 5ppm is 3.5. The odor level of various odors exceeds 2.5-3.5, indicating that the atmosphere is polluted by odor and needs to take preventive measures.