When it comes to PM10 and PM2.5, most people feel both familiar and unfamiliar. I say familiar because these two words appear frequently in various news reports, but if you ask what PM10 and PM2.5 mean exactly, and what is the difference? What are PM2.5 and PM10, what are the sources of PM2.5 and PM10, and what are the harms?
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1. What are PM2.5 and PM10?
First of all, PM is the abbreviation of Particulate Matter (particulate matter) in English, 2.5 and 10 after PM are used to indicate the numerical value of particle size, generally expressed in microns, 1 micron is equal to 10000000 m, the larger the value, the larger the particulate matter, but this value refers to the aerodynamic diameter of the particles, a "hypothetical" particle size that expresses particle motion.
In this way, it is easy to understand that PM2.5 refers to particulate matter in ambient air with an aerodynamic diameter of 2.5 microns or less, and it is also called fine particulate matter, particulate matter that can enter the lungs (can enter the lungs). Its diameter is less than 1/20th the thickness of a human hair, and it can be suspended in the air for a long time.
PM10 is a general term for particulate matter with a particle size equal to less than 10 microns, which refers to solid and liquid particulate matter floating in the air, and it is also called inhalable particulate matter.
It can be seen that PM2.5 is a type of PM10, and they are an inclusion relationship, and PM2.5 generally accounts for about 70% of PM10.
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2. PM2.5和PM10的来源
The main source of PM2.5 is the residue emitted through combustion in the process of daily power generation, industrial production, automobile exhaust emissions, etc., most of which contain toxic substances such as heavy metals. Generally speaking, PM2.5 mainly comes from the combustion of fossil fuels, such as motor vehicle exhaust, coal burning, etc., in addition to some volatile organic compounds.
Shijiazhuang under smog on January 14, 2019 (PM2.5 is the primary pollutant)
PM10 is emitted directly from sources such as chimneys and vehicles. Others are fine particulate matter formed by the interaction of sulfur oxides, nitrogen oxides, volatile organic compounds and other compounds in ambient air. In addition, motor vehicles driving on unpaved asphalt and cement roads, crushing and grinding of materials, and dust raised by the wind can also increase PM10 concentrations.
Sanmenxia under smog on December 3, 2018 (PM10 is the primary pollutant)
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3.PM2.5和PM10的危害
The health effects of particulate matter are closely related to the composition of particulate matter. To put it simply, particulate matter is like a variety of capsules sold in pharmacies, the capsules themselves do not cure the disease, but the drug ingredients in the capsule are cured, that is to say, the capsule plays a role in transporting the drug.
Compared with PM10, PM2.5 has a small particle size, a large specific surface area, strong activity, and is more likely to carry toxic and harmful substances (such as heavy metals, microorganisms, etc.), and has a long residence time in the atmosphere and a long transportation distance. At the same time, they are more likely to remain in the terminal bronchioles and alveoli, so PM2.5 from the same source has a greater health impact than PM10.
The dangers of PM2.5
The main components of PM2.5 include: carbon-containing particles (including elemental carbon and organic carbon, elemental carbon is mainly produced in high-temperature combustion processes, and organic carbon mainly comes from incomplete combustion products of relatively low-temperature processes), sulfates, nitrates, ammonium salts, heavy metals, etc. PM2.5 will further adsorb chemical components such as organic and metallic components and microbial components such as bacteria, viruses, and fungi in the air during air suspension.
PM2.5 enters the alveoli through the respiratory tract and is deposited in the lungs, and these particles have a strong adsorption capacity, which is the "carrier" and "catalyst" of a variety of pollutants, and sometimes can become a collection of multiple pollutants. They are deposited on the alveoli, which will interfere with the gas exchange of the lungs, damage the alveoli and mucous membranes, cause chronic fibrosis of lung tissue, lead to pulmonary heart disease, aggravate asthma, cause chronic nasopharyngitis, chronic bronchitis and a series of pathologies, especially for children and the elderly.
PM10 hazards
PM10, formerly known as dust, refers to substances that can float in the atmosphere for a long time. Because it can float in the atmosphere for a long time, it is easy to carry pollutants to great distances, resulting in the expansion of the scope of pollution, and it can also provide a reaction bed for chemical reactions in the atmosphere. PM10 is sedimentary due to its relatively large particle size, with concentrations highest near the ground and decreasing as the altitude increases.
PM10 can be directly inhaled into the respiratory tract, but some of it can be excreted through sputum, etc., and it can also be blocked by the villi inside the nasal cavity, which is relatively less harmful to human health than PM2.5.
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4. How to protect against smog days?
Severe haze can cause respiratory and other related diseases, and the public needs to do a good job of health protection whether they are at home or traveling, and can reduce the impact of smog on themselves by adjusting their dietary structure, opening windows less, and wearing masks when traveling.
Source: Xiji Ecological Environment