Update: 2019-11-11 17:37 Source: LUFTMY
Ambient air particle monitoring is more concerned than ever before. The reason is that the public has a new understanding of the health effects of small particles suspended in the air, and more and more vehicles are also discharging these particles.
"PM" stands for particulate matter. A value (usually 10 or 2.5) indicates the size of the particle being monitored. PM10 refers to particle diameter of 10 μ m or less, and PM2.5 particle diameter is less than or equal to 2.5 μ m.
Technically speaking, the appearance and working principle of sampling PM2.5 monitor and sampling PM10 monitor are identical. The surrounding air passes through a special inlet (more below), then through a fine particulate filter. Knowing the air flow, the weight of a clean filter, and the weight of the filter after exposure to a known amount of air flow, you can calculate the weight of particles per volume.
The inlet head is the difference between the sampling PM2.5 monitor and the sampling PM10 monitor. In both cases, it includes a carefully designed and manufactured system of tubes and impact plates. When the air flows through the pipe and changes direction, the centrifugal force makes the heavier particles impact and stick to the surface of the impact plate. Therefore, only lighter, thus (effectively) smaller particles can pass through the head. By applying different sizes to the tube and plate, the "cut-off" diameter of the particles can be set. Only the fraction of particles below the cut-off diameter will continue to accumulate with the flow and on subsequent filters.
"Cut-off" is misleading. Without sharp edges, all particles exceeding the limit are rejected, and all particles below the limit are accepted. PM number indicates particle diameter, of which 50% of particles are rejected. However, the "classification curve" of standardized head is still similar to the "classification curve" of human respiratory organs, which can well estimate what people actually contact.
There is also a set of PM monitors that use totally different technologies.The laser beam is focused on a very small volume in the air flow.When a particle passes through that volume, some or all of the light is reflected or refracted.This is a brief pulse of light detected by the sensor.The intensity of the detected light represents the size of the particle.The concentration of PM10 and / or PM2.5 can be determined by measuring the air flow and the cumulative amount and size of particles over time.Some of these instruments use the same "cut-off" input as the sampling monitor, while others use "open" input to separate PM10 and / or PM2.5 scores only by processing signals from the detector.
So why there are two standards: PM10 and PM2.5? Traditionally, PM10 is the standardized parameter of monitoring.However, the smaller the particles, the deeper they enter the lungs, and the greater the damage.Combined with the air pollution control technology of modern cars, the fraction of small particles is higher than that of large particles, which makes people's attention turn to PM2.5 or even smaller particle fraction.Now, there are instruments to measure pm1.0 or even pm0.1 concentration.However, PM10 and PM2.5 are still the most widely used instruments.