. Most environmental pollutants are produced by human production and living activities. Some substances are originally useful substances in production, and even essential nutrients for humans and living things. They are discharged in large quantities due to underutilization, which not only causes waste of resources, but also may become environmental pollutants.
With the rapid development of human economic activities and production, while consuming large amounts of energy, it also discharges a large amount of exhaust gas and soot into the atmosphere, seriously affecting the quality of the atmospheric environment, especially in densely populated cities and Industrial area. The so-called dry clean air refers to the air in the natural state (composed of mixed gas, water gas and impurities) to remove water vapor and impurities, the main component is nitrogen , accounting for 78.09%; oxygen , accounting for 20.94%; Rare gases account for 0.93%; other kinds of trace gases (such as helium, neon, carbon dioxide, helium, etc.) with less than 0.1%
The following substances are the different primary types of pollutants:
1. Sulfur dioxide (SO2): emitted by certain industrial processes (especially in the paper industry or refining) and especially by the use of fossil sulfur fuels. It is one of the main contributors of acidic deposition due to its transformation in the atmosphere into sulfuric acid (H2 SO4);
2. Nitrogen oxides (NOx), in particular nitrogen dioxide (NO2), the emission of which mainly results from the combustion of fossil fuels, in particular by vehicles, which have the effect of contributing to the formation of ozone in the atmosphere;
3. Polycyclic Aromatic Hydrocarbons (PAHs), emitted by the incomplete combustion of fuel oils or coals and which are generally in the air, bound to particles. Some of them are recognized as very carcinogenic;
4. Volatile organic compounds (VOCs), which include hydrocarbons (including benzene, toluene and xylenes). They are issued by many sources, including various industrial processes and vehicles. Methane, a greenhouse gas that is rapidly increasing in concentration in the atmosphere, is a volatile organic compound.
Secondary pollutants . Secondary pollutants refer to new atmospheric pollutants formed by chemical interaction or photochemical reaction of primary pollutants in the atmosphere, which are completely different from the physical and chemical properties of primary pollutants. Their toxicity is stronger than primary pollutants. The most common secondary pollutants such as sulfuric acid and sulfate aerosols, nitric acid and nitrate aerosols, ozone , photochemical oxidants OX, and many active intermediates (also known as free radicals) of different lifetimes, such as HO2, HO, etc
Fine particles. From a health point of view, these particles deserve special attention. Indeed, they may serve as vectors for other substances, such as carcinogenic polycyclic aromatic hydrocarbons (PAHs), which is particularly worrying given the capacity of the finest particles (less than 1um) to develop in the pulmonary alveoli, or even to enter the blood.
Effective solutions to combat this particulate pollution are now well known: the synthesis of the main standards and recommendations identified to date in the tertiary sector is clearly pointing towards filtration levels well above the requirements of the work code.