Fine particlesFine grain, fine particles, PMtwo point five。Fine particles refer to those in ambient airaerodynamicsEquivalent diameter ≤ 2.5micronParticulate matter.It can be suspended in the air for a long time. The higher its concentration in the air, the more serious the air pollution.Although PMtwo point fiveIt is only a small component in the earth's atmosphere, but it has an important impact on air quality and visibility.Compared with the coarser atmospheric particles, PMtwo point fiveSmall particle size, large area, strong activity, easy to attach toxicHazardous substances(For example,heavy metal、microorganismAnd has a long residence time in the atmosphere and a long transport distance, so it has a greater impact on human health and atmospheric environment quality.
In February 2013, the National Science and Technology Terminology Examination and Approval Committee approved PMtwo point fiveIs namedFine particles。The chemical composition of fine particles mainly includesOrganic carbon（OC）、Elemental carbon（EC）、Nitrate、sulfate、ammonium salt、sodium salt(Na+), etc.
The composition of particulate matter is very complex, mainly depending on its source.There are mainly natural sources and man-made sources, but the latter is more harmful.In academic circles, it can be divided into primary aerosol and secondary aerosol.
Natural source
Natural sources include soil dust (containing oxide minerals and other components), sea salt (the second largest source of particulate matter, whose composition is similar to that of sea water), plant pollenSpore、BacteriaEtc.Disaster events in nature, such as volcanic eruptions, discharge a large amount of volcanic ash into the atmosphere, and forest fires or exposed coal fires and dust storms will transport a large number of fine particles into the atmosphere.
Human sources include fixed sources and mobile sources.Fixed sources include various fuel combustion sources, such as smoke and dust emitted from coal combustion and gas or fuel oil in various industrial processes such as power generation, metallurgy, petroleum, chemistry, textile printing and dyeing, heating, and cooking.The mobile source mainly refers to the exhaust gas discharged into the atmosphere when various vehicles use fuel during operation.
PM2.5 can be converted from sulfur and nitrogen oxides.These gas pollutants are often caused by the burning of fossil fuels (coal, oil, etc.) and garbage.In developing countries, coal combustion is the main way of household heating and energy supply.Diesel vehicles without advanced exhaust gas treatment devices are also sources of particulates.The impurities in the emissions of diesel burning trucks cause more particulates.
Indoor second-hand smoke is the main source of particulate matter.The source of particulates is incomplete combustion, so as long as tobacco products are burned, they will produce particles with serious harm. The use of high-quality cigarettes is just a self consolation for smokers, and may even cause greater harm because of the low odor;The same applies to burning gold paper, burning incense and burning mosquito repellent incense.However, when cooking for 5 minutes, PM2.5 increased by 20 times.[1]
Atmospheric chemical reaction
In addition to natural and man-made sources, gaseous precursor pollutants in the atmosphere will be generated by atmospheric chemical reactionSecondary particlesAnd realize the phase transformation from gas to particle.For example:
The gaseous sulfuric acid comes from the gaseous reaction of OH radical oxidation of sulfur dioxide SO ₂.[2]Salt hydrates: such as xCl · yH ₂ O, xNO ∨ · yH ₂ O, xSO ₄ · yH ₂ O. With the change of humidity, hydrates have a greater impact on PM2.5. Water not only forms hydrates with salt compounds, but also forms small solution droplets of salt due to the change of humidity.
Index standard
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The standard of fine particles was proposed by the United States in 1997, mainly to more effectively monitor the harmful fine particles that appeared with the growing industrialization and were ignored in the old standard.The fine particle index has become an important index to measure and control the degree of air pollution.
By the end of 2010, except that some countries in the United States and the European Union have included fine particles in their national standards and imposed mandatory restrictions, most countries in the world have not yet carried out the monitoring of fine particles, and most of them have generally monitored PM10.
New standard for air quality of PM2.5 detection network
According to the new air quality standard of PM2.5 detection network, the standard value distribution of 24-hour average value is as follows:
Air quality grade
Standard value of 24-hour average PM2.5
excellent
0~35μg/m³
good
35~75μg/m³
Slight pollution
75~115μg/m³
Moderate pollution
115~150μg/m³
Heavy pollution
150~250μg/m³
Serious pollution
More than 250μg/m³And above
[3]
World Health Organization (WHO) Air Quality Guidelines 2005
project
Average annual value
Daily average value
Criterion value
tenμg/m³
twenty-fiveμg/m³
Transition period objective 1
thirty-fiveμg/m³
seventy-fiveμg/m³
Transition period objective 2
twenty-fiveμg/m³
fiftyμg/m³
Transition period objective 3
fifteenμg/m³
thirty-seven point fiveμg/m³
China plans to implement the Air Quality Standards in 2016 (under comment)
project
Average annual value
Daily average value
Criterion value
thirty-fiveμg/m³
seventy-fiveμg/m³
Hazard impact
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Main hazards
About Pm2.5 Comics
Although fine particles are only a few components in the earth's atmosphere, they have an important impact on air quality and visibility.Compared with the coarser atmospheric particles, the fine particles are smaller in size, rich in a large number of toxic and harmful substances, and have a long residence time in the atmosphere and a long transport distance, so they have a greater impact on human health and the quality of the atmospheric environment.Research shows that the smaller the particles, the greater the harm to human health.Fine particles can float far away, so the influence range is large.
Fine particles are more harmful to human health, because the smaller the diameter, the deeper the part entering the respiratory tract.tenμM diameter particles are usually deposited in the upper respiratory tract, 2μThose below m can penetrate into bronchioles and alveoli.When fine particles enter the human body to the alveoli, they directly affect the ventilation function of the lungs, making the body vulnerable to hypoxia.
About 2.1 million people worldwide die each year from the rise of PM2.5 and other particulate matter concentrations
It is reported that the Global Environment Outlook 5 released by the United Nations Environment Programme in 2012 pointed out that 700000 people died of respiratory diseases caused by ozone every year, and nearly 2 million premature deaths were related to particulate pollution.The Journal of the National Academy of Sciences (PNAS) also published a research report, which said that the average life span of human beings may have been shortened by five and a half years due to air pollution.[4]
London Poison Fog Incident
The poison fog incident on December 5, 1952 was one of the most painful moments in London's history. The poison fog caused at least 4000 deaths, countless London citizens were breathless, traffic was paralyzed for many days, and millions of people were affected.
The World Health Organization first identified PM2.5 as carcinogenic
On October 17, 2013, the International Cancer Research Institute affiliated to the World Health Organization issued a report, identifying air pollution as a common and major environmental carcinogen for the first time.However, although air pollution has been proposed as a whole carcinogenic factor, its harm to human body may be the result of the simultaneous action of several major pollutants contained in it.
Injured organ
Long term exposure to particles can cause cardiovascular and respiratory diseases as well as lung cancer.[5]When the concentration of PM2.5 in the air is higher than 10 for a long timeμg/m³，Will lead to an increased risk of death.Every 10 increase in concentrationμg/m³，The total death risk increased by 4%, the death risk caused by cardiopulmonary disease increased by 6%, and the death risk caused by lung cancer increased by 8%.In addition, PM2.5 is very easy to absorb organic pollutants such as polycyclic aromatic hydrocarbons and heavy metals, which significantly increases the probability of carcinogenesis, teratogenicity and mutagenicity.
Influence climate
It is generally believed that PM2.5 is only air pollution.In fact, the impact of PM2.5 on the overall climate may be worse.PM2.5 can affect cloud formation and rainfall processes, and indirectly affect climate change.In addition to salt in seawater, PM2.5, a fine particle, is also an important source of condensation nodules of rainwater in the atmosphere.Under some conditions, there is too much PM2.5, which may "eat" water, making the cloud droplets in the sky small, and the blue sky and white clouds become less than before;Under some conditions, PM2.5 will increase the number of condensation nodules, which will increase the number of raindrops in the sky, and rainstorm may occur in extreme cases.[6]
Impact distribution map
Global Air Quality Map
NASA(NASA) released a global air quality map in September 2010, specifically showing the density of fine particles around the world.The map is created byDALHOUSIE University By two researchers.Based on the monitoring results of two NASA satellite monitors, they drew a map showing the average values of fine particles from 2001 to 2006.In this picture, red (that is, the highest density of fine particles) appears in North Africa, East Asia and China.The density index of fine particles in North China, East China and Central China is even close to 80 micrograms per cubic meter, even more than the Sahara Desert.
In this map of the average global air pollution situation between 2001 and 2006, the regions with the highest fine particles in the world are all in North Africa and North, East and Central China.The World Health Organization (WHO) believes that fine particles less than 10 is a safe value, while these areas in China are all above 50 and close to 80, much higher than the Sahara Desert.[7]
Distribution map of fine particle concentration and death toll in different regions of the world
Distribution map of fine particle concentration and death toll in different regions of the world[8]
NASA's Earth Observatory released a map showing the concentration changes of fine particles and the number of deaths of air pollutants in various regions of the world between 1850 and 2000.
In 2010, West published a research report based on a single computer model of the atmospheric environment to estimate the impact of global air pollution on people's health.West and his colleagues believe that using a series of different computer models of the atmospheric environment, a total of six, they can improve the accuracy of previous estimates.In 2013, they published their research paper in the Environmental Research Letters and concluded that 2.1 million people died every year due to outdoor toxic air pollutants and fine particles.
This map shows the change of global air pollution level from 1850 to 2000, and the distribution of the average number of deaths per square kilometer per year due to air pollution.The darker the color, the more air pollution deaths per square kilometer per year in the region.More people die prematurely in coffee colored areas than in light brown areas.The air quality in the blue area has improved since 1850, and the number of premature deaths has declined.
In eastern China, northern India and Europe, the urbanization brought about by the industrial revolution has led to a significant increase in fine particles in the air, and has had a great impact on people's health.In these densely populated and heavily polluted areas (dark brown), man-made air pollution causes more than 1000 premature deaths per square kilometer every year.
In a few areas (blue), such as the southeast of the United States, the concentration of fine particles has declined compared with the pre industrial level, and the number of premature deaths due to air pollution has declined.In the southeastern part of the United States, the decline of fine particle concentration may be related to the decline of local biomass combustion level in the past 160 years.[8-9]
Monitoring methods
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The Technical Indexes and Requirements for PM2.5 Automatic Monitoring Instruments (Trial) issued by China Environmental Monitoring Station in May 2012 identified three automatic monitoring methods for PM2.5, namelyβradialMethods The instrument is equipped with a dynamic heating system,βX-ray method instrument combined with dynamic heating systemLight scattering methodMicrooscillation balance method Instrument film dynamic measurement system (FDMS).[10]
Countermeasures
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Preventive methods
1. Filtration method
Including air conditioner, humidifier, air purifier, etc., the advantage is that the concentration of PM2.5 is significantly reduced, while the disadvantage is that the filter membrane needs to be cleaned or replaced.
2. Water adsorption method
Ultrasonic atomizer, indoor water curtain, pool, fish tank, etc. can absorb hydrophilic PM2.5 in the air, but the disadvantage is that the humidity is increased, and hydrophobic PM2.5 cannot be effectively removed.
3. Plant absorption method
Plant leaves have a large surface area and can absorb harmful gases and PM2.5. The advantage is that they can produce favorable gases, but the disadvantage is that the absorption efficiency is low. Some plants can produce harmful gases.[11]
Life coping
1. Open windows less in foggy weather, and it is better not to go out or do morning exercises
It is not recommended to open windows for ventilation in the morning and evening in haze weather. It is better to open windows for ventilation after the moon comes out.Haze weather is a "dangerous day" for patients with cardiovascular diseases, especially for the elderly with respiratory and cardiovascular diseases. It is better not to go out in foggy weather, let alone do morning exercises, or else it can induce illness, even heart attack, and cause life danger.Experts pointed out that the reason why foggy weather is a "dangerous day" for patients with cardiovascular diseases is that the air pressure is high when the fog starts, and the oxygen content in the air is increased. People are easy to feel chest tightness. The wet and cold fog in the morning can also cause cold stimulation, which is easy to lead to esophageal spasm, blood pressure fluctuations, and increased cardiac load.At the same time, some pathogens in the fog will cause headache, and even induce hypertension, cerebral hemorrhage and other diseases.Therefore, people suffering from cardiovascular diseases, especially the elderly and the infirm, should not go out in fog, let alone do morning exercises in fog to avoid danger.
2. Wear professional dust mask when going out
Generally, the conventional respirator will not work because the particles are too small, KN90, KN95,N95Only level of dust mask can effectively filter this kind of fine particles. At the same time, you should choose a mask that is suitable for you to avoid leakage caused by non sealing.In addition, wash the face and exposed skin immediately when returning from going out.The better masks against PM2.5 are mainly filters rather than masks. For example, masks with activated carbon filters and medical masks cannot prevent PM2.5.
3. Drink more "lung clearing and dust removing" tea drinks such as Tongplatycodon tea, Tongshen tea, Tongplatycodon granules, and Platycodon soup
Tongplatycodon grandiflorum tea has the function of clearing fire and filtering lung dust, can strengthen the ability of alveolar cells to discharge toxic fine particles, and can help the human body to discharge PM2.5 particles and other harmful substances accumulated in the body.
4. A small amount of vitamin D
In winter, there is more fog and less sunshine. Due to too little ultraviolet radiation, the production of vitamin D in the human body is insufficient. Some people will suffer from mental depression and depression. If necessary, some vitamin D can be added.
5. Eat a light diet and drink more honey water
The diet in foggy days should be light, easy to digest and rich in vitamins. Drink more water and eat more fresh vegetables and fruits. This can not only supplement various vitamins and inorganic salts, but also play a role in moistening the lungs, eliminating phlegm, relieving cough, strengthening the spleen and kidney.Eat less stimulating food and more pears, loquats, oranges, oranges and other foods.
6. Deep cleaning
The skin on the surface of the human body is in direct contact with the outside air, and is vulnerable to the damage of haze weather.Especially in the busy and noisy city with "haze" on all sides, in addition to the need to deal with the haze at any time, due to construction, automobile tail gas, industrial fuel combustion, fireworks and candles, and other reasons, there are many suspended particles, which will inevitably block pores and form blackheads, resulting in pore blockage, cutin accumulation, skin peeling and other skin problems,Therefore, the first measure for self-protection is to deeply clean the surface of the skin and clean the pores.
7. Try to reduce smoking or even no smoking
There is a large amount of PM2.5 in the smoke, which will have direct and indirect harm to the human body.If you can't stop people around you from smoking, you should try to stay away from smoke.[12-13]
National policies
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China
Terrible PM2.5
Since January 1, 2011, the Ministry of Environmental Protection has issued《Ambient air Determination of PM10 and PM2.5 Gravimetric method》Start implementation.The determination of PM2.5 was standardized for the first time, but it was carried out by the Ministry of Environmental Protection《Ambient air quality standard》In the revision, PM2.5 was not included in the mandatory monitoring indicators.
On October 11, 2012, Wu Xiaoqing, Vice Minister of the Ministry of Environmental Protection of China, said that after the promulgation of the new Ambient Air Quality Standard, the Ministry of Environmental Protection clearly proposed the "three-step" goal of implementing the new standard.According to the plan, by the end of 2012, Beijing Tianjin Hebei, Yangtze River Delta, Pearl River Delta and other key regions, as well as municipalities directly under the Central Government, cities specifically designated in the plan, and provincial capital cities should carry out monitoring and release data according to the new standards.So far, 195 stations nationwide have completed the installation, commissioning and trial operation of PM2.5 instruments, and 138 stations have started formal PM2.5 monitoring and releasing data.[15]
Germany
Short term solutions
First of all, ban certain types of vehicles, or prohibit all vehicles from driving in heavily polluted areas.The second is to restrict or shut down large boilers and industrial equipment.In addition, the closure of construction sites in cities also helps to alleviate pollution.Burning wood and garbage in the stove must be avoided.
Long term measures
one
Set emission standards for motor vehicles.
two
Strict emission standards for large boilers and industrial facilities.Europe has uniformly stipulated industrial emission standards and issued the Industrial Emission Order.
three
Set emission standards for small boiler equipment, such as heating equipment such as house heating.
four
Set emission standards for mechanical equipment, such as construction machinery.
five
An "environmental protection zone" has been set up. More than 40 cities in Germany and many European countries have set up "environmental protection zones", which only allow vehicles meeting emission standards to drive in.
six
Heavy trucks are prohibited.Heavy trucks usually have high pollutant emissions.
seven
Speed limit.
eight
Encourage public transportation and cycling through subsidies or publicity programs.
nine
The traffic can be better managed through reasonable changes of traffic indicator lights and the setting of special lanes for motor vehicles.[16]
France
Provide health advice to the public
In order to reduce pollutant emissions, improve air quality and prevent air pollution from harming human health, France issued an air quality decree in 2010, which stipulates the upper limits of PM2.5 and PM10 concentrations.In addition, the French government has also implemented a series of programs aimed at reducing air pollution, such as emission reduction program, particulate matter program, carbon emission trading system, local air quality program and atmospheric protection program.
In France, the Air Quality Monitoring Association is responsible for monitoring the concentration of pollutants in the air and providing air quality information to the public.According to the data provided by the Air Quality Monitoring Association, the French Environment and Energy Administration will publish the air quality index maps of the day and the next day on its website every day, and provide suggestions on how to improve air quality.When the pollutant index exceeds the standard, the local government will immediately take emergency measures to reduce pollutant emissions and provide health advice to the public.
In the report on air particle pollution released in April 2012, the French High Commission for Public Health listed a series of new recommendations for protecting public health, especially for sensitive populations such as patients with lung and heart diseases, young children and the elderly.It is suggested that when the concentration of PM10 in the air is 50 to 80 micrograms per cubic meter, patients with lung disease and heart disease who have shown symptoms should consider reducing outdoor activities and intense sports;When the PM10 concentration exceeds 80 micrograms per cubic meter, the sensitive population should reduce or even avoid outdoor activities and intense sports. Asthmatic patients may need to appropriately increase the use of inhaled drugs under the guidance of doctors. If the healthy population has symptoms such as cough, dyspnea or sore throat, they should also reduce outdoor activities and intense sports.[16]
U.S.A
Regularly review air quality monitoring standards
According to the website of the US Centers for Disease Control and Prevention, air pollution is a major problem facing modern society.The air pollution faced by the United States is mainly caused by six factors: gaseous pollutants, greenhouse gas effect, acid rain, ozone layer destruction, inhalable particles and climate impact.
The United States Environmental Protection Agency and other agencies established“Air quality index”And provide the public with timely and understandable information about local air quality and whether the air pollution level has reached a level that threatens public health.On the AIRNow website jointly run by the U.S. Environmental Protection Agency and other agencies, you can see the dynamic air quality index map, ozone index map, PM2.5 index map and the five worst air quality locations in the United States according to each index.
According to the Clean Air Act, the Environmental Protection Agency is required to regularly review air quality monitoring standards.In 2006, the US Environmental Protection Agency made the latest revision of the PM2.5 standard, which stipulated that the maximum concentration of PM2.5 in any area and any 24-hour cycle in the United States, whether in urban or rural areas, dropped from 65 micrograms per cubic meter to 35 micrograms per cubic meter, while the annual average concentration standard was less than or equal to 15 micrograms per cubic meter.The standard for inhalable particulate matter (PM10) with a diameter between 2.5 microns and 10 microns is 150 micrograms per cubic meter in a 24-hour cycle.According to the level of inhalable particulates, the Environmental Protection Agency classifies the air quality in different regions into three categories: substandard, substandard, or can be regarded as substandard despite insufficient data, and insufficient data.If an area is listed as substandard, the local state and local government need to develop an implementation plan within three years, listing how to reduce the emissions of pollutants that lead to the accumulation of inhalable particles in the area, so as to meet and maintain the air quality standards listed by the Environmental Protection Agency.[16]
britain
Delineation of "smoke and dust control zone" according to law
The poison fog incident on December 5, 1952, was one of the most tragic moments in London's history. At that time, the poison fog caused at least 4000 deaths, countless London citizens had difficulty breathing, traffic was paralyzed for many days, and millions of people were affected. After the disaster, the British government did remedial work.
In 1956, the British government issued the Clean Air Act, which defined the "smoke and dust control zone", and the towns in the zone were prohibited from directly burning coal.In addition, all coal-fired power plants in London have been shut down and moved to places outside the city.Through a series of measures, the air quality in London has been improving.
According to the data provided by the London Municipal Government, about 722000 people live outside London and come to London to work by various means of transportation every day.London's huge population and large scale of commuters mean that the road traffic network has been under great pressure.For example, in Waterloo Station, the busiest railway station in London, there are 51000 passengers in the three hours of peak traffic every day.The same is true for road traffic, with more than 3 million vehicles running on the road.Since the road congestion tax was levied in 2003, it is estimated that the daily traffic volume on the road has decreased by 70000 vehicles.
In the past 50 years, as the use of coal in London's households and industries has gradually disappeared, traffic emissions have become the largest source of air pollution.58% of nitrogen oxides and 68% of PM10 pollutant particles in the air of London come from vehicle exhaust emissions.
Professor Frank Kelly, a British environmental expert and from King's College, University of London, pointed out that due to the high population density, the large number of commuters and the endless flow of vehicles engaged in business and travel, this has brought pressure on air quality.In this regard, Kelly suggested that small displacement gasoline powered vehicles and clean public transport should be used as far as possible in urban areas, and diesel buses and taxis should be upgraded.[16]
monitoring data
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In 2021, in 339 cities at prefecture level and above monitored, fine particulate matter (PMtwo point five）The annual average concentration was 30 μ g/m3, down 9.1% over the previous year.[17]
The 2023 government work report points out that in the past five years,The average concentration of fine particulate matter (PM2.5) in cities at prefecture level and above decreased by 27.5%[18]。
