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Dust monitoring: Beijing PM10 exceeds 8000! How was this value measured?

by:Rika Sensors     2021-11-17
Dust monitoring: Beijing PM10 exceeds 8000! How was this value measured?
The sandstorm is coming.

According to the monitoring of the Fengyun-4 meteorological satellite, the strongest sand and dust attack in my country in the past 10 years: At 8 o'clock on March 15th, the area of u200bu200bvisible sand and dust in my country reached 466,000 square kilometers, Beijing 12 provinces, autonomous regions, and municipalities including Hebei, Hebei and Gansu were affected, and some areas experienced strong sandstorms with visibility of less than 500 meters.

Affected by the impact of sand and dust transmission and high wind blowing sand from upstream, the visibility of sand and dust transit areas has dropped significantly, and the concentration of PM10 pollutants has increased significantly. Taking Beijing as an example, the PM10 concentration of some monitoring sites exceeds 2000 micrograms/m3. In severe cases, the PM10 concentration exceeds 8000 micrograms/m3.

So how is the value of 8000 measured? Here are the detection principles of several dust sensors.

The dust mentioned here refers to the tiny particles composed of PM2.5, PM10, PM100 (TSP) in the air. These are important indicators for statistical air quality index (TSP will generally be filtered and precipitated by the nasopharynx, will not enter the deep part of the respiratory tract, and is not harmful to the human body, so it is generally not within the scope of statistics).

1. Infrared light scattering (turbidity method)

The so-called turbidity method is to emit light on one side and receive on the other. Air turbidity. The principle is as follows:

2. Laser scattering (particle counting method)

The sensor structure and circuit of the laser scattering principle are relatively complicated. The light source is a laser diode. The sampled air is pushed by a fan or a pump and passed through a complicatedly designed air duct for detection. When fine particles in the air enter the area where the laser beam is located, the laser will be scattered; scattered light is radiated at 360° in space. Place a photodetector at an appropriate position to receive the scattered light, and then pass through the photoelectric effect of the photodetector. After the current signal is amplified and processed by the operational amplifier circuit, the concentration of fine particles can be obtained. Compared with infrared light scattering, it can be measured quantitatively. The principle is as follows:

3. Beta ray method

The Beta ray method uses the principle of Beta ray attenuation. The ambient air is sucked into the sampling pipe by the sampling pump and discharged through the filter membrane. The particulate matter is deposited in the filter. On the membrane, when the beta rays pass through the filter film deposited with particulate matter, the energy of the Beta rays attenuates, and the concentration of particulate matter can be calculated by measuring the attenuation.

Four. Gravimetric method

At present, the determination of atmospheric particulate matter in my country mainly adopts the gravimetric method. The principle is to extract a quantitative volume of air at a constant speed through a sampler with certain cutting characteristics, so that PM2.5 and PM10 in the ambient air are trapped on the filter membrane of known quality. According to the quality difference of the filter membrane before and after sampling and Sampling volume, calculate the concentration of PM2.5 and PM10. It must be noted that the volume of the denominator in the unit ug/m3 for measuring particulate matter should be the volume under standard conditions (0℃, 101.3kPa), and the volume under the measured temperature and pressure should be converted to the volume under standard conditions.

This method requires extremely high weighing environment, which can only be achieved in a professional laboratory.

In recent years, more and more people are concerned about air quality issues, but everyone’s focus is often on PM2.5 particulate matter, which is the smog in everyone’s mouth. Many people think that PM2.5 is the main pollution. It ignores the existence of PM10. But in air quality monitoring, PM10 particulate matter concentration is also a key monitoring data.



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