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Particulate matter sensing for air quality measurement

Update: 2019-10-22 15:08 Source: LUFTMY Reading: ↻ News
 

Particulate matter, abbreviated as "PM", refers to the mixture of solid particles and droplets in the inhalable air, which may cause serious health problems. PM contains particles with different characteristics (i.e. shape, optical properties, size and composition), but the most common is to classify them into subcategories based on particle size information. Different PM categories are usually reported under the general terms of PMX, where "X" defines the maximum particle size in an air borne particle mixture or "aerosol". For example, PM2.5 defines inhalable particles with a diameter of 2.5 microns or less, PM10 particles with a diameter of 10 microns or less, and so on.

PM10 and PM2.5 have historically been identified by governments as important monitoring levels to assess the quality of the air we breathe, because PM10 particles irritate exposed mucus such as the eyes and throat, and PM2.5 particles travel through the lungs all the way to the alveoli. New categories such as PM1.0 and PM4.0 are also entering air quality monitoring devices, as these new outputs provide additional information to traditional PM10 and PM2.5 levels, enable better analysis of particle pollution, and develop new device specific operations based on the type of aerosols detected, such as indoor dust and smoke.

The usual definition of PM includes particles no less than 100 nanometers. Particles smaller than 100 nanometers are reported as "ultrafine" or "UFPs" and are not discussed in this article. In the above definition of particulate matter, particles range in size from 0.1 micron to 10 microns, and the smaller they are, the more they penetrate our respiratory system and blood, posing a greater risk to our health. The world health organization (WHO) reported that particulate matter in the air is a class of carcinogens and the biggest environmental risk to health.

Although weight method has long been considered the most accurate method determination of mass concentration, but they spread in daily application of some practical limitations: these instruments bulky, expensive and time measurement only deals with a PM size (pm2.5), real time sampling is impossible, and they can't output particle number counting.

For these reasons, real-time optical particle counter (opc) is gradually entering the air quality monitoring market. These instruments are based on different optical principles, usually scattering or absorption, of which light scattering is the most common. In these opcs, particles pass through a light source (usually a laser beam) and cause scattering (or absorption) of incident light, which is then detected by a photodiode and converted into a real-time particle count and mass concentration.

Optical detection technology has become the most widely used technology due to its ease of use and incomparable cost performance. In recent years, opc has become small enough to be integrated into air conditioners, air quality monitors and air purifiers to regulate and control air quality in homes, cars and outdoor environments.

While the basic principles of opc may seem simple at first from an implementation perspective, not all opcs work the same way, and their measurement quality is largely determined by the engineering and design of such devices. Optical principles work well in particle counts, but since these devices are primarily used to estimate mass concentrations of PM, they are susceptible to estimation errors due to differences in the optical properties of the particles (such as shape and color) and mass density. Therefore, the mass of the mass estimate will vary greatly depending on the manufacturer's algorithm used to convert the measured optical signal into PM mass concentration. In addition, internal airflow engineering has a significant impact on the accuracy and drift of these sensors, because if poorly designed, particles can easily accumulate on their optical components (lasers, photodiodes, beam dumps) and reduce their output over time.

LD09 laser PM2.5 dust sensor
LD09 laser PM2.5 dust sensor

Guangzhou luftmy LD09 laser dust sensor is a high-precision particle concentration sensor based on laser Mie scattering theory. It can continuously collect and calculate the number of suspended particles with different particle sizes in the air per unit volume, i.e. particle concentration distribution, and then convert it into mass concentration, and output it in the form of general digital interface. The sensor can be embedded in various instruments or environmental improvement equipment related to the concentration of suspended particles in the air to provide timely and accurate concentration data.

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