It stands for volatile organic compounds. In the field of environmental protection, volatile organic compounds can cause harm, mainly from fuel combustion and transportation. In our life, such as natural gas, smoking, heating, cooking, decorative materials and so on. Common examples of VOCs that may be present in our daily lives are benzene, ethylene glycol, formaldehyde, dichloromethane, tetrachloroethylene, toluene, xylene, and 1, 3-butadiene. These harmful volatile organic compounds can cause lung, blood, kidney and liver poisoning. In the public environment, sulfur dioxide, nitrogen oxide and other gases can easily form nitrate, sulfate and so on, causing the increase of PM2.5 in the air. It is called "smog".