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   Recently, the news about PM2.5 has been overwhelming, and it has stimulated our central nervous system for a while - panic, anxiety... but more is incomprehensible and awkward. How harmful is PM2.5? There are even reports that Shanghai PM2.5 has exceeded the standard in the past five years, and everyone can’t help but exclaim: The original haze has long been on our heads, and we have already practiced the ability to “do not invadeâ€.
Of course, gossip, of course, we need to understand this "uninvited guest" who has already arrived. So what exactly is PM2.5? Where are they from? Is there a good way to monitor? China Biomaterials Network has carefully compiled relevant information in order to share with friends and friends.
Figure 1. Over the city with PM2.5 exceeding the standard
1. What is PM2.5
PM, the English full name is "particulate matter". PM2.5 refers to particulate matter with a diameter less than or equal to 2.5 microns in the atmosphere, also known as accessible particulate matter. What is the concept of 2.5 microns? 1/20 of the diameter of the hair. A friend who has studied chemical micro-nanoparticles may know that the smaller the particle, the larger the specific surface area; and the general particles are charged, causing these particles to carry a large number of environmental pollution source molecules.
2. Source
The sources are mainly residues that are burned during the process of daily power generation, industrial production, and automobile exhaust emissions, and most of them contain toxic substances such as heavy metals. It is not difficult to understand here that society is increasingly dependent on the demand for energy. Especially in large cities such as Beishangguang, industrial waste gas and automobile exhaust pollution are the first to bear the brunt. The city is full of high-rise buildings, and the pollutants are difficult to disperse. In the long run, the exhaust molecules will adhere to some dust and particles, making these particles disguised as “killersâ€. In fact, according to the author, PM2.5 pollutants are divided into four categories: (1) carbon, nitrogen and other specific element components, (2) free ions, (3) heavy metals, (4) polycyclic aromatic hydrocarbons and other organic matter. Below we discuss the above-mentioned several types of substances.
3. Monitoring
(1) Specific elemental components such as carbon and nitrogen
Here is an example of elemental carbon. Chen Kui and others studied the fine particulate matter and chemical composition of the Nanjing area. ( Download , extraction code ) PM2.5 samples were taken and the contents of organic carbon (OC) and elemental carbon (EC) were determined. The author here monitors the mass concentration of PM2.5 with a PM2.5 auto-monitor and samples the PM with an ACCU autosampler. The EC and OC concentrations in the samples were measured using a thermo-optical carbon analyzer. The results show that the concentrations of PM2.5, OC and EC in the atmosphere of Nanjing are ranging from 12.1 to 287.1, 2.6 to 47.0 and 1.0 to 33.6 μg/m3, respectively. Among them, the OC, EC, total carbon content (TC) concentration and OC to EC ratio of the next day were 2.0, 1.8, 1.9 and 1.7 times of the next day, respectively.
(2) free ion
Li Shuxian and others collected atmospheric PM 2.5 samples for one month in Wanchangsha, Guangzhou, and analyzed SO 4 2- , NO 3 - , NH 4 + , Cl - , Na + , K + , Ca 2+ , C 2 O 4 2- , F - , NO 2 - and HCOO - 11 water-soluble ion contents. ( Download , extract code ) The results show that the total aqueous ion mass concentration of normal weather and ash weather PM2. 5 is 38. 99 and 52. 74 μg / m 3 respectively . Here, the authors used a large flow sampler (Anderson Model GUV -16HBL) for sampling, then immersed the sample in the membrane, and ultrasonically filtered the 11 water-soluble ions in PM2.5 using a Metrohm COMPACT 761 ion chromatograph. concentration.
(3) Heavy metals
Take mercury (Hg) as an example. Du Jinhua et al. studied the pollution characteristics of mercury in PM2.5 in Shenzhen ( download , extract code ). They applied cold atomic fluorescence spectrometry to analyze the total mercury content in the particulate state. The results show that the total mercury content in Shenzhen is 1.93 ~ 249.27pg / m 3 , the average is 72.11pg / m 3 , compared with the results of similar research at home and abroad, it is at a medium pollution level.
Figure 4. The mining industry produces large amounts of gases containing heavy metals.
(4) Organic substances such as polycyclic aromatic hydrocarbons
Zhang Zhigang et al. conducted seasonal sampling in Fushun City and quantitatively studied 16 polycyclic aromatic hydrocarbons (PAHs) in respirable particulate matter (PM10 and PM2.5) in urban air. ( Download , extract code )
The PM10 and PM2.5 are used to collect the dual-channel TH-15S PM10 and PM2.5 samplers produced by Wuhan Tianhong Intelligent Instrument Factory. The analysis was carried out with a German SARARIUS balance of one hundred thousandth; the LPDA (ion exchange low performance liquid chromatography) was used for the PDA-100 Photodiode Array Detector produced by American Dion. The model is an RF 2000 Fluorescence Detector. The analytical method was performed by ultrasonic extraction in the fourth edition of the Air and Exhaust Gas Monitoring and Analysis Method compiled by the State Environmental Protection Administration. The pretreatment was performed by ultrasonic extraction, and the extracted concentrate was measured by high performance liquid chromatography.
The results show that the PAHs in the PM10 and PM2.5 are more polluted, and the winter is higher than other seasons. The PAHs are mainly enriched in fine particles of PM2.5 and below.
The above is the finishing of our recent data on PM2.5. The analysis and detection methods of common pollutants in PM2.5 are mainly discussed. Netizens are welcome to participate in the discussion and wish our environment is better.