What are the main components of smog?

Haze weather is a state of air pollution and a general manifestation of excessive suspended particulate matter content in the atmosphere. The smog we often talk about is actually a combination of fog and haze, but fog is fog, haze is haze, and fog and haze are very different. Simply put, tiny water droplets in the air are fog, which belongs to liquid, while smog is solid, which consists of tiny dust particles, sulfuric acid, nitric acid, inhalable particles and other particles in the air. It can make the air turbid and reduce visibility, and the combination of the two is smog. The combination of the two, figuratively speaking, is that children play with mud and mix sand with mud and water, which is mixed and dirty. Once the discharge of various pollutants exceeds the atmospheric circulation capacity and carrying capacity, the concentration of various particles will continue to accumulate. If the weather is still at this time, it is easy to have a wide range of smog.

Sulfur dioxide, nitrogen oxides and inhalable particles are the main components of smog. The first two are gaseous pollutants, and the last particulate matter is the chief culprit that aggravates smog weather pollution. They combine with fog and instantly turn the sky gray.

First, sulfur dioxide is the most common sulfur oxide, colorless gas, with a strong pungent smell, and it is also one of the main pollutants in the atmosphere. Both coal and oil contain sulfides, so sulfur dioxide will be produced when burning. Sulfur dioxide is easily soluble in water after being inhaled into the respiratory tract, so most of it is blocked in the upper respiratory tract. Corrosive sulfurous acid is generated on wet mucosa, and part of it is further oxidized into sulfuric acid, which enhances the stimulation. If the human body inhales sulfur dioxide with the concentration of 100 ppm every day, after 8 hours, there will be obvious irritation symptoms in the bronchi and lungs, which will damage the lung tissue.

If sulfur dioxide enters the deep layer of human lungs with airborne particles, its toxicity will increase by 3 ~ 4 times, leading to fibrous hyperplasia of alveolar wall. If the proliferation range spreads widely, it will form pulmonary fibrosis, which will break the pulmonary fibers and form emphysema. Sulfur dioxide can also be absorbed into the blood by the human body, which has a toxic effect on the whole body. It can destroy the activity of enzymes, affect human metabolism and do some damage to the liver.

Second, nitrogen oxides Nitrogen oxides refer to compounds composed of two elements: nitrogen and oxygen. Common ones are nitric oxide, nitrogen dioxide, nitric oxide and nitrogen pentoxide. As air pollutants, nitrogen oxides generally refer to nitric oxide and nitrogen dioxide. In addition to natural circulation, most nitrogen oxides in the atmosphere come from the combustion of fossil fuels, such as automobiles, airplanes and industrial boilers. Fertilizer plants and metal smelters also emit this gas.

Nitrogen oxides can stimulate the lungs, reduce people's resistance to respiratory diseases such as colds, and also cause damage to children's lung development. In addition, nitrogen oxides, mainly nitric oxide and nitrogen dioxide, will react with hydrocarbons under ultraviolet irradiation to form toxic smog, that is, photochemical smog. Photochemical smog has a special smell, which can irritate eyes, harm plants and reduce atmospheric visibility. 65438-0943, photochemical pollution occurred in Los Angeles, USA, killing more than 800 people. Many people have symptoms of eye pain, headache and difficulty breathing. In addition, 1970 photochemical smog incident in Tokyo, Japan also caused 20,000 people to suffer from pinkeye.

Photochemical smog is very harmful, but its formation must meet three conditions: first, there are a certain amount of pollutants in the atmosphere, mainly nitrogen oxides and hydrocarbons, which come from the exhaust of motor vehicles and power plants; Second, the weather is full of light, and only under such weather conditions can strong light promote the reaction; Third, volatile organic compounds (VOC) react actively with nitrogen oxides, and the concentration is seriously exceeding the standard, so don't worry too much.

3. Inhalable particles Generally speaking, particles with a particle size below 10 micron are called PM 10, also known as inhalable particles. It lasts for a long time in the ambient air and has a great influence on human health and atmospheric visibility. Some particulate matter comes from the direct discharge of pollution sources, such as chimneys, chemical section chiefs, industrial boilers, etc. Others are produced by the reaction of sulfur oxides, nitrogen oxides, volatile organic compounds and other compounds in the ambient air. The first way is the main source of inhalable particulate matter, and it is also an important object of inhalable particulate matter pollution control.

When it comes to inhalable particulate matter, everyone will definitely think of PM2.5, which is suspended in the atmosphere with PM 10, but with different particle sizes. PM2.5 is a part of PM 10, that is, particles with a diameter below 2.5 microns. Because the particle size of PM2.5 is very small, the nasal cavity and throat of the human body can't stop it. They can descend all the way, enter bronchioles and alveoli, then enter capillaries through alveolar walls, and then enter the whole blood circulation system. Damage to human respiratory system and cardiovascular system.

PM2.5 mainly comes from man-made emissions, including primary emissions and secondary transformation. Primary emission mainly comes from combustion process and dust. Secondary conversion refers to the formation of gaseous precursors such as sulfur dioxide, ammonia, nitrogen oxides and volatile organic compounds through chemical reactions in the atmosphere.