If it is first time contact, "PM2.5" this string of characters may make you look in the clouds and fogs, mystified.It has an easy to understand Chinese name - fine particulate matter, is the diameter of less than or equal to 2.5 micron in the air the floorboard of the solid particles or liquid droplets.These particles so tiny, is invisible to the naked eye, they can float in the air for several days.Human fine hair is about 70 microns in diameter, it is nearly three times larger than the largest PM2.5.

PM is English particulate matter (particulate matter) acronym.Accurate definition of PM2.5 to add a modifier before the "diameter" "air dynamics", this can not be withdrawn.Spherical particles in the air is not rules, that how to define how to measure its diameter?In practice, if the particles through detecting instrument of aerodynamic characteristics with diameter less than or equal to 2.5 microns and is 1 g/cm3 density spherical particles are consistent, that is referred to as PM2.5.Such a definition would be decided in the determination of PM2.5, the need to use aerodynamics to separate PM2.5 and larger particles, not with pore size of 2.5 micron filtration membrane to separate.

Know the definition of PM2.5, it is easy to draw the definition of PM10 - will be defined in 2.5 to 10, PM10, also known as particulate matter.In PM10, 2.5 to 10 microns in diameter of particles known as coarse particulate matter, as opposed to a fine particulate matter.

What ingredients 1. PM2.5 come from where, have?

Although the natural process also produces PM2.5, but its main source or man-made emissions.Human both direct discharge of PM2.5, also some gas pollutant discharge, in the air to PM2.5.Direct emissions come mainly from the combustion process, such as fossil fuels (coal, gasoline, diesel) burning, burning biomass (straw, wood), waste incineration.Converted into the air PM2.5 main gas pollution of sulfur dioxide, nitrogen, ammonia, volatile organic compounds.Other anthropogenic sources include: road dust, construction dust, industrial dust, smoke in the kitchen.Natural sources include: winnowing dust, ash, forest fires, floating in the sea salt, pollen, spores, bacteria.

The source of PM2.5 complex, nature is also very complex.Main ingredients are elements carbon, organic carbon compounds, sulfate, nitrate, ammonium salt.Other common ingredients include all kinds of metal elements, both sodium, magnesium, calcium, aluminum, iron, such as abundant element in the earth's crust, there are also such as lead, zinc, arsenic, cadmium, copper mainly comes from human pollution of heavy metal elements.

In 2000, the researchers determined the PM2.5 source: Beijing dust (20%);The transformed gaseous pollutants of sulfate, nitrate, ammonium salt each accounted for 17%, 10%, 6%;Burning coal to produce 7%;Use diesel, petrol and emissions contribute 7%;Biomass crops contribution to 6%;Plant debris contribution of 1%.It is interesting to note that smoking also contributed 1%, but it's only a rough estimate, the science is not necessarily accurate.In this study is to determine the composition of PM2.5 in Beijing: carbon particles, sulfate, nitrate, ammonium root weight added together accounted for 69%.Similarly, the determination of Shanghai in 1999 41.6% of PM2.5 is ammonium sulfate, ammonium nitrate, 41.4% of the carbon material.

2. PM2.5 what harm to health?

PM2.5 mainly deal damage to respiratory and cardiovascular system, including from irritation of respiratory tract, coughing, dyspnea, reduced lung function, increase asthma, chronic bronchitis, arrhythmia, non-fatal heart attack, heart and lung disease of premature death.Children, the elderly, and cardiopulmonary disease is sensitive crowd of PM2.5 pollution.

If the concentration of PM2.5 in the air for a long time higher than that of 10 micrograms per cubic meter, the death risk began to rise.Increased concentration per 10 micrograms per cubic meter, the overall mortality risk rose 4%, have a 6% increased risk of death of cardiopulmonary disease, lung cancer mortality risk rose 8%.

The harm of PM2.5 is can not be ignored, but are not to be compared with smoking.For smokers, don't have a "can't anyway, air pollution, smoke the same" psychology.Smoking may make men 22 times increased risk of lung cancer death (up 2200%), 12 times increased risk of women (1200%).Middle-aged make a two-fold increased risk of heart disease death (200%).（Editor's note: in this paper, the discussion has modified.Thank the netizens' correct and discussed.About the risk of smoking and air pollution）

From the perspective of the whole society, reduce the risk of these seemingly small PM2.5, income is very big.The epa in 2003 made a estimate: "if PM2.5 standard, the United States can avoid tens of thousands of people each year die earlier, tens of thousands of people in the hospital, millions of time delays, millions of children have to respiratory system disease".Compared to the current China, the United States at the time of air quality is quite good, only a few areas there is a bit overweight.If China's PM2.5 standard, social benefits will be enormous.

The risk of death of PM2.5 data derived from 2002, published in the journal of the American medical association in a paper.This paper analyzes the participants in a long-term study of the relationship between the mortality rate and air pollution, found that higher mortality associated with PM2.5 and sulfur dioxide pollution, and associated with coarse particulate matter pollution is not reliable.The prospective study in the United States began in 1982, was recruited 1.2 million participants.Paper's conclusion is based on 16 years of follow-up data, is currently on PM2.5 pollution increased mortality risk of the most reliable evidence.

3. If there is no pollution, the concentration of the PM how high, how high is the actual now?

Even without human pollution, also have a certain concentration of PM2.5 in the air, the concentration is called background concentration.In the United States and Western Europe, background concentration is about 3-5 micrograms per cubic meter, the Australian background concentration is around 5 micrograms per cubic meter.Background concentrations of China have many tall?There is no open data, but should not vary too big and the other countries.

China has not conducted a wide range of PM2.5 monitoring, public PM2.5 data is very limited.In the environmental protection of guangzhou south China environmental science research institute, starting from June 13, 2011 daily publish PM2.5 monitoring value, as of November 20, concentration range between 0.6 and 99 micrograms per cubic meter (note: 0.6 the figures should be caused by equipment failure, normal, but not so low), average of 38 micrograms per cubic meter, this value is more than the annual average standard plans to release (35 micrograms per cubic meter).Have been in this 121 days, 6 days more than the average daily standard plans to release (75 micrograms per cubic meter).From the scientific papers published in recent years, can find some of China's big cities at some stage in the area of PM2.5 measurements.In 2000, for example, the five monitoring stations in Beijing measured PM2.5 average of 101 micrograms per cubic meter;The 17 days of 2008 Beijing Olympic Games, in the north of the lowest 28.2, the highest 147.4 micrograms per cubic meter, an average of 64.7 micrograms per cubic meter.In 1999, two monitoring stations in Shanghai determination of PM2.5 average of 57.9 and 57.9 micrograms per cubic meter.The annual average are far higher than the proposed standard (35 micrograms per cubic meter).

In addition to scattered data refer to the above, we can also according to the data to estimate for the PM10 concentration of PM2.5.According to China's current air quality standard, PM10 is routine surveillance indicators, a national monitoring has been carried out more than a decade.From 2001 to 2001, the national average of PM10 in major cities from 125 to 90 microgram/cubic meter.The ratio between the PM2.5 and PM10 is usually between 0.5 0.8, we take an extreme estimates available: 0.8 do 2009 major cities of the country's average PM2.5 is 72 micrograms per cubic meter, is 2.1 times of the new standard (35 micrograms per cubic meter).Compared with America's air quality, the difference how many?In 2009, the United States worst 9.9 micrograms per cubic meter, more than 90% in the 724 monitoring stations monitoring point average less than 12.6 micrograms per cubic meter.

The national average is used to reflect the overall situation of particle pollution in our country, for the evaluation of our city's air quality meaning is not big.We need more attention from our life, work, the recent monitoring data.This data where there is?

But it is worth mentioning that although the us embassy's monitoring instruments (see q&a 8) is a professional, but instrument calibration and operation will greatly affect the final measurement results.Embassy, after all, not environmental monitoring departments, there is no evidence to suggest that their staff have corresponding professional knowledge, and they often measure PM2.5 value than the environmental protection department and the third party measuring PM10 is higher, it is not normal.So, the us embassy's data can be used as a reference, but don't have to use it as the only source.

However, we more and more people don't live in Beijing, not even when you are in Beijing near the U.S. embassy, where we should see the data?Real-time PM10 data of major cities in China can check it on the environmental monitoring station's web site, several monitoring points of every city, and we can choose the nearest the point for reference.Since studies have shown that, PM2.5, PM10 generally from 0.5 to 0.8, if you are optimistic, then you can estimate PM2.5 = PM10 x 0.5, if you are very pessimistic, then estimate the PM2.5 = PM10 x 0.8.

4. Other countries implement PM2.5 standard, what is the standard?

Since in 1997 the United States take the lead in the air quality standards for PM2.5, many countries are following suit to include PM2.5 monitoring indicators.If only starting from the purpose of protecting human health, national standard should be the same, because is the same for standards of the scientific research results.Standards, however, still need to consider the pollution present situation and the level of economic development of all countries, in a serious air pollution in developing countries are extremely strict air quality standards can only become a magnificent decoration, no practical significance.According to the American cancer society and the results of the study at Harvard University, the world health organization (WHO) made the criterion value of PM2.5 in 2005.Higher than this value, the risk of death will rise significantly.WHO also set up three transition target, for it is not a one-off area provides milestones, including target - 1 standard is the most liberal, and target - 3 most strictly.

The following table lists the WHO standard and several typical countries.China plans to implement the standard with the same goal - 1 WHO transition.American and Japanese standards, and the target - 3 are basically identical.Eu standard easing slightly, consistent with the goals - 2, Australia the most strict standard, and the average standard value is lower than the WHO standards.Standard basic reflects the resulting degree of national air quality, air quality, the better the country will have the ability to formulate and implement more stringent standards.

【The world health organization (WHO) and some countries of PM2.5 standard (unit: microgram per cubic meter)】

5. Than PM2.5 standards and other countries, China is very backward?

China standard of PM2.5 are putting into effect in 2016, although behind the United States for one hundred and twenty years, but compared with those of the eu's 2015 is not too late.If only from the perspective of the value of standard, China's upcoming new standards have been consistent with the goals - 1 WHO transition, although lagging behind the developed countries, but also be started the first step of three steps.However, even if the same standard and standard to judge whether the way is different, binding is great different.For example, China's current air quality standards in 1996, the standard for the average daily PM10 in the 150 microgram/cubic meter, on the surface, as well as the current standards strictly.In accordance with the standards of the United States, however, there can be at most 1 day per year on average, even if not up to standard, standard parts need to submit improvement plan and implement.While in China the standard file, there is no similar provisions.Regions in implementing standard, just calculate annual standards "days" and "success rate".PM10 standard has been carried out for 15 years, a 86.2% success rate also can be used as positive news reports.

In the upcoming release of the new standard of PM2.5, not much high success rate is still acceptable.WHO and how is the other countries?WHO asked three days per year to exceed bid success rate (99%), Australia up to five days, and the United States and Japan asks the success rate of 98%.Behind not only in the standard of Chinese PM2.5 standard, what is more important on the binding.

6. New standards to be released, why until 2016 to implement??

For this question, standard setters are replied: "considering the environmental air quality standards implementation is a complicated system project, and at present, the state of the national environmental monitoring capacity, combining with the experience in the process of the implementation of current standards, to ensure data accuracy and comparability, keeping the unified national implementation of this standard to January 1, 2016, in order to set aside enough time to prepare for the region, strengthen the standard implementation of the relevant supporting work."

That make sense?We might as well consult other countries do.In the United States and Australia, the environmental protection department website for PM2.5 standards process has a very detailed memo, we in the two countries, for example.

The United States as early as 1994, announced that it would increase the index of PM2.5.From 1994 to 1996, opened a conference for many times, at the end of 1996 issued a draft.Comments took 14000 through the telephone, received 4000 emails, 50000 written or oral, and many times through the hearings, meetings, TV program for advice.After this sincerity for real comment, finally on September 16, 1997 issued the standard of PM2.5.But at the time, has not yet been a nationwide monitoring of PM2.5, until 1999, the state started in succession, routinization PM2.5 monitoring in 2000.

Australia in 2001 began to consider, and in 2003 made the optional standard of PM2.5.For the purpose of this standard is to collect data, in order to review this standard is reasonable, and ready to start considering compulsive standard in 2005.In the process of advice, opponents think that should be mandatory standards directly, or the lack of binding, meaning also is less.Australian environmental protection commission (NEPC) thought the lack of enough PM2.5 monitoring data, can't very well what the effects evaluation is not up to standard, adhere to the original approach.Until this year (2011), Australia's PM2.5 is still not mandatory indicators, but this period has been doing a lot of monitoring and the basic research work.

China of PM2.5 standard is for advice, and is implemented in 2016, the meaning of "implementing" should be refer to conduct regular testing and publish the results.The United States from 1997 in 2000 the national standard to the monitoring of routinization spent two or three years.Australia's 2003 optional standard, then the national monitoring.Considering the China's national conditions, delayed a few years "implementation" has its rationality, but four or five years is too long?

7. How to measure pm2.5?

With various sizes of particles floating in the air, PM2.5 is one of a small part of the definition (see question 1).It is not hard to think of, measuring the concentration of PM2.5 need two-step: (1) the PM2.5 and larger particles separation;(2) the weight of the separate determination of PM2.5.Widely used at present, the national environmental protection department of PM2.5 there are three kinds of method: weight method, beta ray absorption method and trace oscillating balance method.The first step of these three methods is the same, the difference is that the second step.

Intercept the PM2.5 directly to the membrane, and then use weighing scales, that is the weight method.It is worth mentioning that membrane filter doesn't collect all of PM2.5, some tiny particles can still wear membranes.As long as the membrane filter for 0.3 microns particles of more than 99% of the entrapment efficiency, it is qualified.Loss of part of the tiny particles on the result of influence is not big, because the weight of that part of PM2.5 particles contribution is very small.

Weight method is the most direct, the most reliable method, is to verify whether other methods accurate benchmarking.However weight method to artificial weighing, program trival time consuming.If in order to realize automatic monitoring, you need to use the other two methods.

Beta ray absorption method: PM2.5 collected on the filter paper, and then illuminate a bunch of beta ray, ray through the filter paper and particulate matter caused by scattering and attenuation, the degree of attenuation is directly proportional to the weight of PM2.5.According to the X-ray attenuation can be calculated the weight of PM2.5.The us embassy's high-profile machine is based on this principle.

Trace oscillation balance method: a thick a fine head of the hollow glass tube, thick head fixed, fine head is equipped with filter.From the rough head into the air, head out, PM2.5 is trapped on the filter element.Under the action of electric field, the fine head at a certain frequency oscillations, the frequency and fine head weight varies inversely as the square root.Then, according to the change of the oscillation frequency, it can be collected to calculate the weight of PM2.5.

To isolate PM2.5 cutter is how to work?Under the action of pump, the air at a certain velocity through the cutter, the larger particles because of inertia, a head of bump on parts of oil paint and trapped, inertia small PM2.5 can, for the most part, with the air to go through.You may have noticed that this happened and the situation is very similar in our respiratory tract: big particles interception by the nose, throat, trachea, and fine particle is easier to reach the depths of the lungs, resulting in a greater health risk.

For the cutter of PM2.5, 2.5 micron is a step on the touchline in size.To 2.5 microns in diameter particles have a 50% chance of can pass the cutter.Not all greater than 2.5 micron particles trapped, and less than 2.5 microns particles are not all can pass.For example, according to the ambient air on the determination of PM10 and PM2.5 weight method "requirement, 3.0 microns particles pass rate should be less than 16%, and 2.1 micron particles is much bigger than the passing rate of 84%.

Special structure and specific air velocity determines the separation effect of the cutter for particles together, and a slight change of the two, will produce a great impact on the determination, and lose the results comparable.Therefore, the U.S. environmental protection agency in 1997 to develop the world's first PM2.5 standard, along with all the provisions of the specific structure of the cutter.So, although there are many brands of PM2.5 measuring instruments, but they look very similar.

8. Some phones on the market size of instrument which can measure PM2.5, by spectrum?

And the environmental protection department USES the standard method, compared with non-professional instruments measured PM2.5 obviously is not reliable, but it's hard to say how much, only compare standard method with the know.Measured data may explain a little problem, can distinguish anyone smoking in the room, for example, just swept the ground, but these your nose can do it.

The non-professional instruments available in the market by using the principle of light scattering particle concentration measurement, this method is not adopted by national environmental protection department as the standard method, but there are made according to the principle of professional equipment, also has used in scientific research.The higher the concentration of particulate matter in the air, the stronger the scattering of light.Light scattering is relatively easy to measure, measure it, in theory can calculate the concentration of particulate matter.But in practice, things are not so simple.Light scattering and the relationship between the concentration of particulate matter is very uncertain, influenced by many factors, such as chemical composition, shape, weight of particles, size distribution, but it all depends on the composition of pollution sources.This means that the light scattering particle concentration and the conversion formula between may change at any time and place, users need to instrument constantly correction using standard methods, without scientific training of amateur is unlikely to make it.Some researchers have made theoretical calculation: light scattering instrument has been applied to the determination of PM2.5 and the uncertainty of at least 30-40%.This uncertainty is inherent in this kind of instrument, quality and reliable professional instruments and if so, what's more, the quality of the instruments on the market are not ideal.

Because our country did not incorporate PM2.5, ozone pollutants such as detection system, often appear the status of the air quality index is contrary to public perception.By non-specialists non-professional operation or quality, however, professional instrument to monitor air quality is not high, can not fundamentally solve the problem.More effective means of supervision, may be called for the environmental protection department in more site monitoring PM2.5 as soon as possible, and let all the data on people is more open, transparent.Now new "ambient air quality standard" is to solicit comments from the public, and is implemented in 2016, the voice of the public may be able to make this place much earlier.

9. The ash haze days is caused PM2.5?

Although invisible to the naked eye the particles in the air, but it can reduce the visibility of air particulates, eradicate the blue sky, the sky becomes grey, this kind of weather is gray haze days.In 2010, according to the grey haze pilot monitoring report, in the ash haze days, the concentration of PM2.5 is significantly higher than normal, the higher the concentration of PM2.5, the less visibility.

Although different sizes of particles in the air can reduce visibility, but compared with the coarse particulate matter, more small PM2.5 stronger ability to reduce visibility.Visibility to reduce its essence is the transmission of visible light.When the diameter of the particles and the wavelength of visible light is close to the maximum particle scattering of light extinction.The wavelength of visible light between 0.4 to 0.7 microns, and particle size near the size of particles is the main part of PM2.5.Theoretical calculation data also made it clear that this point: the extinction coefficient of the coarse particle is about 0.6 m2 / g, and extinction coefficient of PM2.5 are much larger, between 1.25 to 10 square metres per gram, among them the main composition of PM2.5 ammonium sulfate, ammonium nitrate and organic particles extinction coefficient at about 3, 5 times that of coarse particles.So, PM2.5 is the main cause of gray haze days visibility.

It is worth mentioning that is particulate matter pollution caused by the ash haze days, while the fog is a natural weather phenomenon, and is there no necessary relation between the man-made pollution.The main difference is that the air humidity, usually called the fog when humidity is more than 90%, and the humidity is less than 80% when called haze, humidity between 80-90% is a mix of fog.