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Optical monitoring of particulate matter

Update: 2019-10-22 15:15 Source: LUFTMY Reading: ↻ News
 

Particle optical monitoring (PM) is a method of measuring the diameter of flying particles. Optical monitors are a low-cost way to get real-time data about particles in the air. They are an electronic version of automation, like the effect of dust in a dark room when the sun shines on it.

Working principle of optical particle sensor

A sensor and a beam of light are at an Angle to each other. When a particle passes in front of the light, some of the light is reflected off the sensor. As soon as the particles reflect light on the sensor, the sensor records a pulse. If the air is moving at a constant speed, the length of the pulse can be used to estimate the diameter of the particle.

By estimating the particle diameter and average particle density, the particle concentration in the air can be inferred. These estimates are not perfect because they are not very direct considering the particle density and the amount of water in the droplet model particles. Both of these problems complicate the process of optical PM measurement associated with regulatory monitoring.

Optical particle data problem

Humidity and optical PM measurements

Optical monitors can detect water droplets and dust, and water droplets are usually "wet" and absorb moisture from humidity.

Humidity measurements are usually used to correct for the expected effect of humidity on droplets. These modifications are based on assumptions about the percentage of dust and the percentage of dust that is in droplet mode and tends to wet.

Variable particle density

Most low-cost optical monitors assume standard particle density based on "test dust," such as the standard "Arizona road dust," which is now ISO 12103-1:1997.

Some of the more expensive optical monitors combine optical monitors with filter-based PM monitors. The filter is weighed (" gravimetric ") before and after sampling to create a calibration factor for particle density.

The modified equation was used to simulate the influence factors of PM2.5 and PM10

PM management standards are technology-based, which means that PM10 measurements must be related to the results of a particular PM10 monitor. While optical monitors can set "sharp" cutoff times for particles, the filter-based federal approach relies on a mechanical classification of "impactors," which has a shorter cutoff time.

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