What are volatile organic compounds？

At present, there is no consistent definition of volatile organic compounds (VOCs) among various sectors. According to the American ASTM D3960-98 standard, any organic compound that can participate in atmospheric photochemical reactions can be referred to as VOCs. The definition of VOCs by the US Federal Environmental Protection Agency (EPA) is more specific. VOCs are any carbon compound that can participate in atmospheric photochemical reactions, but do not include CO, CO2, H2CO3, metal carbides, metal carbonates, and ammonium carbonate. The World Health Organization (WHO) refers to volatile organic compounds with melting points below room temperature and boiling points between 50-260 ℃ as total volatile organic compounds (TVOC). The international standard ISO 4618/1-1998 and the German standard DIN 55649-2000 define any organic liquid and/or solid that can spontaneously evaporate under normal temperature and pressure as VOCs. The "Unorganized Emission Control Standards for Volatile Organic Compounds" (GB37822-2019) issued and implemented by the Ministry of Ecology and Environment of China in 2019 defines VOCs as organic compounds determined in accordance with relevant regulations or organic compounds involved in atmospheric photochemical reactions.

The definition of the United States emphasizes whether it participates in photochemical reactions and does not limit the boiling point and initial boiling point of compounds. Compounds such as acetone and tetrachloroethylene that do not participate in atmospheric photochemical reactions are referred to as exempt solvents; The World Health Organization limits the boiling point or initial boiling point and does not emphasize whether it participates in photochemical reactions; The international standard ISO 4618/1-1998 and the German standard DIN55649-2000 do not emphasize whether it participates in photochemical reactions, nor do they limit its boiling point or initial boiling point. They only emphasize that it can evaporate on its own at room temperature and pressure.

There are various types and complex components of VOCs in the atmospheric environment, which are generally classified according to their chemical structure and elemental composition. According to their chemical structure, they can be divided into 12 categories: alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, aldehydes, ketones, ethers, esters, acids, halogenated hydrocarbons, and others; According to their elemental composition, they can be divided into six categories: non methane hydrocarbons (aromatic hydrocarbons, alkanes, alkenes, alkynes, etc.), oxygen-containing organic compounds (aldehydes, ketones, alcohols, ethers, etc.), halogenated organic compounds, nitrogen-containing organic compounds, sulfur-containing organic compounds, and others. VOCs in the environment often exist in gaseous form and are a significant gaseous pollutant that cannot be ignored. VOCs can directly and indirectly affect the environment. The main manifestation is that there are various types of VOCs in the environment, with different chemical properties and hazards, which can directly participate in atmospheric chemical reactions and affect the atmospheric environment. At the same time, they are toxic and directly threaten human health. At the same time, VOCs in the atmosphere usually have strong activity. They exist in the gaseous form of primary volatiles in the atmosphere, and can also be converted into solid, liquid, or coexisting secondary particulate matter under external environmental influences. They can also indirectly affect the atmospheric environment.