PM particulate matter, also known as dust. Solid or liquid particulate matter in the atmosphere. Particles can be divided into primary particles and secondary particles. Primary particulate matter refers to particles directly released into the atmosphere by natural and anthropogenic sources of pollution, such as soil particles, sea salt particles, combustion smoke, and so on. Secondary particulate matter is generated through photochemical oxidation, catalytic oxidation, or other chemical reactions between certain pollutant gas components in the atmosphere (such as sulfur dioxide, nitrogen oxides, hydrocarbons, etc.) or between these components and normal components in the atmosphere (such as oxygen), such as the conversion of sulfur dioxide into sulfates. The primary particulate matter generated from the combustion of coal and oil, as well as the secondary particulate matter generated from their transformation, have caused multiple pollution events worldwide. The natural source of primary particulate matter production is approximately 4.41 × 10 ^ 6 tons per day, while anthropogenic sources produce approximately 0.3 × 10 ^ 6 tons per day. The natural sources of secondary particulate matter produce approximately 6 × 10 ^ 6 tons per day, while anthropogenic sources produce approximately 0.37 × 10 ^ 6 tons per day. In terms of total amount, primary particles and secondary particles each account for about half. Most of the particulate matter is generated by natural sources, but in some areas, such as densely populated large cities and industrial and mining areas, the amount generated by human sources may be higher. Since the late 18th century, the amount of coal used has been continuously increasing. After the 1950s, industry and transportation developed rapidly, population became more concentrated, cities expanded, fuel consumption increased sharply, and particulate pollution caused by human factors became increasingly severe. There is currently no unified classification method for particulate matter. According to the settling characteristics of dust under gravity, it can be divided into drifting dust and falling dust. Traditionally, it is divided into: dust particles: coarser particles with a particle size greater than 75 microns. Dust: particles with a particle size of 1-75 microns, generally generated by industrial crushing and operation operations. Sub micron dust: dust with a particle size less than 1 micron. Jiong: Solid particles formed during combustion, sublimation, condensation, and other processes, with a particle size generally less than 1 micron. Fog dust: liquid droplets formed by supersaturated steam condensation and condensation, chemical reaction and liquid spray in industrial production. The particle size is generally less than 10 microns. The liquid mist formed by the condensation and coalescence of supersaturated steam is also known as haze. Smoke: A non-uniform system composed of solid particles and liquid droplets, including mist, dust, and soot, with particle sizes ranging from 0.01 to 1 micron. Chemical smog: divided into two types: sulfuric acid smog and photochemical smog. Sulfuric acid smoke is produced by the chemical reaction of sulfur dioxide or other sulfides, unburned coal dust, and high concentration fog dust, also known as London type smoke. Photochemical smog is formed by the photochemical reaction of hydrocarbons and nitrogen oxides in car exhaust, also known as Los Angeles type smog. Coal smoke: Coal particles or fly ash produced during combustion, with a particle size of 0.01 to 1 micron. Coal dust: Unburned coal particles carried out by flue gas. Due to different particle sizes, dust has different settling characteristics under the action of gravity. For example, particles with a particle size less than 10 microns can float in the air for a long time, which is called floating dust. Among them, particles with a particle size of 10 to 0.25 microns are also called cloud dust, and particles with a particle size less than 0.1 microns are called floating dust. Particles with a diameter greater than 10 microns can settle quickly, hence it is called dust reduction. Three modes In 1978, Whitby divided the particle size into three modes: nuclear mode (0.002-0.1 μ m), accumulation mode (0.1-1 μ m), and coarse mode (>1 μ m). Can nuclear models be further divided into pure nuclear models? Nucleation (0.002-0.02) and Aitken (0.02-0.1), the accumulation mode is divided into condensation mode (0.1-0.6) and droplet mode (0.6-1).? [1] 3. Particle concentration monitoring: The LD-5 laser dust analyzer from Judao Hesheng brand is a microcomputer laser dust analyzer with a new type of built-in filter membrane online sampler, which is at the advanced level of the new century. The instrument is developed by Beijing Judao Hesheng Technology Co., Ltd. in combination with * technology. While continuously monitoring dust concentration, it can collect particles for analysis of their composition and calculate the mass concentration conversion coefficient K value. It can directly read the dust mass concentration (mg/m) and has PM10, PM5, PM2.5, PM1.0, and TSP cutters to choose from The instrument adopts a powerful suction pump, making it more suitable for detecting the concentration of PM10 inhalable particulate matter at the air conditioning exhaust port that requires a longer sampling tube, and monitoring the concentration of inhalable dust PM2.5. The instrument complies with the hygiene standards for industrial enterprises (GBZ1-2002), the exposure limit for harmful factors in the workplace (GBZ2-2002), the WS/T206-2001 "Method for determination of inhalable particulate matter (PM10) in the air of public places - light scattering method" standard of the Ministry of Health, the LD98-1996 "Method for determination of dust concentration in the air by light scattering method" standard of the Ministry of Labor, the TB/T2323-92 "Method for determination of relative mass concentration and conversion of mass concentration of dust in the air of railway workplaces" and other industry standards, as well as the "Hygiene Specification for Centralized Air Conditioning Ventilation System in Public Places" issued by the Ministry of Health's Health Law Supervision [2003] No. 225 document. Main technical indicators: 1. Configure a 40mm filter membrane online sampler; 2. Has a replaceable particle cutter? PM10? 、 PM5, PM2.5, PM1.0, and? TSP for selection; 3. Direct reading of dust mass concentration (mg/m3),? 1. Results will be displayed in 1 minute. 4. Large screen LCD display with Chinese character menu prompts; 5. What? Detection sensitivity: LD5 (L) 0.01mg/m; LD5（H） 0.001mg/m。 6. Repeatability error: ± 2% 7. Measurement accuracy: ± 10% 8. Measurement range: LD5 (L) 0.01~100 mg/? m；LD5（H）0.001～10 mg/m。 9. Measurement time: The standard time is 1 minute, with 0.1 minutes and manual mode (sampling time can be set arbitrarily). 10. It has public place monitoring mode, atmospheric environment monitoring mode, and labor hygiene mode. Time weighted average (TWA) and short-term exposure allowable concentration (S) can be calculated. 11. Storage: It can cyclically store 999 sets of data. 12. Timed sampling: The measurement time can be set to (1~9999) seconds, the shutdown time can be set to (0~9999) seconds, the preheating time can be set to (0~10) seconds, and the sampling frequency can be set to (1~9999) times. 13. Alarm threshold setting for excessive dust concentration: maximum concentration threshold: 65mg/m3; Measurement time: (1~9999) seconds 14. Output interface: (1) PC communication interface: RS232; Optional RS485; Optional wireless data transmission radio station; Optional GPRS communication (2) mini printer output interface; (3) Analog output interface: 01V; optional 4-20mA (4) digital output interface: level signal. 15. Power supply: Ni MH rechargeable battery pack (1.2V x 4), capable of continuous use for 8 hours; Attached is a 220VAC/12VDC power adapter. 16. In addition, it is equipped with humidity correction function, with more data. 17. Weight: 2.4kg. 195mm * 85mm * 132mm. 18. Standard configuration: instrument, battery, power adapter, leather bag, small screwdriver, cutter, filter membrane, small plastic bag, manual, certificate of conformity, warranty form. 19. Optional: instrument communication software, micro printer, sampling rod (with domestic hose), standard external cutter. The composition of particles is very complex and varies greatly. It can be roughly divided into three categories: organic components, water-soluble components, and water-insoluble components, with the latter two mainly being inorganic components. The organic content can reach up to 50% by weight, with the majority being insoluble in benzene and structurally complex organic carbon compounds. Organic compounds soluble in benzene usually account for less than 10%, including fatty hydrocarbons, aromatic hydrocarbons, polycyclic aromatic hydrocarbons, alcohols, ketones, acids, lipids, etc. Some polycyclic aromatic hydrocarbons have carcinogenic effects on the human body, such as benzo (a) pyrene. The water-soluble components mainly include sulfates, nitrates, chlorides, etc., with sulfate content reaching up to about 10%. The water-insoluble components in particulate matter mainly come from the Earth's crust, which can reflect the characteristics of the parent material in soil. They are mainly composed of oxides of elements such as silicon, aluminum, iron, calcium, magnesium, sodium, and potassium. The content of silicon dioxide accounts for about 10-40%, in addition to various trace and trace metal elements, some of which are harmful to the human body, such as mercury, lead, cadmium, etc. The dust concentration is determined by measuring the weight (in grams or milligrams) of dust per unit volume of gas under standard conditions (i.e. pressure of 760 mmHg and temperature of 273K). The main measurement methods include the weight method, also known as the weight concentration method, which uses a filter or other separator to collect dust and weigh it, making it a reliable method for determining dust content. Filters can be made of filter paper, polystyrene microfiltration membranes, etc. There are various measuring instruments, such as electrostatic precipitator weight analyzer, which can measure concentrations as low as 10 micrograms of dust per standard cubic meter. If a dust collection device with a known effective surface area is placed in an appropriate location outdoors, a sufficient amount of dust particles can be collected and weighed to determine the amount of dust reduction. The concentration specification table comparison method is widely used in the Ringman coal smoke concentration table proposed by M.R. Ringman (see table). This table depicts black grid lines with widths of 1.0, 2.3, 3.7, 5.5, and 10.0 millimeters on white paper with a length of 14 centimeters and a width of 20 centimeters. The black areas inside the rectangular white cardboard are approximately 0, 20, 40, 60, 80, and 99%, respectively, to distinguish the smoke concentration into 6 levels, which are called 0, 1, 2, 3, 4, and 5 degrees. Under standard conditions, a smoke concentration of 1 degree is equivalent to 0.25 grams per cubic meter, 2 degrees is equivalent to 0.7 grams per cubic meter, 3 degrees is equivalent to 1.2 grams per cubic meter, 4 degrees is approximately 2.3 grams per cubic meter, and 5 degrees is approximately 4-5 grams per cubic meter. When in use, stand the concentration meter at approximately the same height as the observer's eyes, and then look at the cardboard at a distance of 16 meters and 40 meters from the chimney, comparing it with the smoke concentration at a distance of 30-45 centimeters from the chimney mouth. When observing, the observer should be at a right angle to the direction of the smoke flow and should not face the sunlight. There should be no obstacles such as buildings or mountains on the background of the chimney exit. In addition to the Ringman coal smoke concentration meter, there are other forms of concentration meters and measuring instruments for concentration comparison, such as telescope type coal smoke concentration meters and smoke transparency tubes. The advantage of the concentration specification table comparison method is that it is simple and easy to implement, but the disadvantage is that it is prone to errors. The photometry method uses a certain intensity of light to pass through the tested gas, or washes a certain amount of the tested gas with water to allow dust particles in the gas to enter the water. Then, a certain intensity of light is passed through the dusty water, and the gas or dust particles in the water reflect and scatter the light. The transmitted or scattered light intensity is measured using photoelectric devices and compared with the standard luminosity to convert it into dust concentration. The particle calculation method settles dust in a known volume of air onto a transparent surface, and then counts the number of dust particles under a microscope. The measurement result is expressed as the number of particles per cubic centimeter, which can be converted to dust concentration if necessary. The approximate value of the conversion is: there are 500 dust particles per cubic centimeter, which is equivalent to a dust concentration of about 2 milligrams per cubic meter under standard conditions, 2000 dust particles are about 10 milligrams per cubic meter, and 20000 dust particles are about 100 milligrams per cubic meter. ⑤ Indirect measurement method: The dusty airflow passes through the measuring tube in a turbulent state. Due to the friction between the dust particles and the inner wall of the tube, the dust particles become charged. By measuring the current, the dust concentration can be calculated based on the standard curve. In addition, using thermocouples to measure the radiation heat absorbed by dust particles from a specific light source can indirectly measure the dust concentration. Measure the attenuation of ion flow by dust particles in the air inside the ionization chamber. This method can also calculate the dust concentration. The lower limit of determination can reach 200 dust particles per cubic centimeter. These methods and photometry can be used for continuous measurement. Particles below 1 micron in hazardous particulate matter have a slow settling speed, remain in the atmosphere for a long time, and can be blown to distant places under atmospheric dynamics. So particulate matter pollution often affects a large area and even becomes a sexual problem. Particles with a particle size of 0.1 to 1 micron have a wavelength similar to visible light and have a strong scattering effect on visible light. This is the main reason for the decrease in atmospheric visibility. The main cause of acid rain is the generation of sulfuric acid and nitric acid particles through the chemical conversion of sulfur dioxide and nitrogen oxides. A large amount of particulate matter falls on plant leaves, affecting plant growth, and can contaminate and corrode buildings and clothing. Particles with a particle size below 3.5 microns can be inhaled into the bronchi and alveoli of humans and deposited, causing or exacerbating respiratory diseases. The large amount of particulate matter in the atmosphere interferes with the radiation of the sun and the ground, thereby affecting regional and even global climate. There are three natural ways to remove particulate matter from the atmosphere: ① Rain removal (which forms raindrops as condensation nuclei and falls) and precipitation erosion. This is the most effective way to clear. ② Captured on the surface of the ground, plants, or other objects due to impact under atmospheric dynamics. ③ Due to its own weight, it naturally settles. The control of particulate matter emissions is mainly achieved through the use of dust collectors. For secondary particulate matter, only its precursor material can be controlled. The formation and variation of secondary particulate matter is one of the major research topics in environmental science. There are many particulate matter in the atmosphere that can be harmful to human health, so in cities with high PM, it is advisable to wear a mask when going out. Reference: 1. Anna Pugatshova?