P4000 fine particles probe

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The particle materials, "also known as" particulate matter "or PM, are a complex mixture of extremely small particles and liquid droplets. Particulate pollution is made up of a number of components, including acids (such as nitrates and sulfate), organic chemicals, metals, and soil particles or dust.

Particulate pollution is responsible for 42 000 premature deaths per year in France and many diseases (asthma, allergies, respiratory diseases and cardiovascular diseases, lung cancer).

The coarsest (larger than 2.5 micrometers) fall fast enough, their residence time in the air is of the order of 1 day, while the finest can stay up to 1 week in suspension and travel thousands of kilometers. Once deposited, the particles can then be resuspended by the wind or in urban areas under the action of traffic.


Principle of detection


Principle of detection particulates P4000

The P4000 uses laser diffraction technology (light scattering).
The principle is the following: when a laser beam passes through pure air, the beam is invisible. When the beam is visible, this is because the beam is diffracted onto particles along its path. If you look at the beam from the side and the more visible the beam is, the higher the particle density is.
Such a particle sensor uses a near-infrared source (laser diode). The sensor is an avalanche photodiode with amplifier. Infrared is used to avoid interference with the day light entering the chamber.


The dust density depends mainly on the air flow.
The laser and the sensor and the collimator lenses are placed in the upper position to prevent dust from depositing on the optical when the air flow source is turned off. (Note that a small heater warms the air in front of the sensor and the lighter hot air generates a constant flow).
The optimum angle between the source and sensor is the result of experiments.
Each particle which passes the laser beam diffracts a part of this beam to the sensor and the air flow being constant, the pulse width measured is used to classify the particles by size.
A running average of the quantities of particles by category is performed over a period of 30 seconds.
As large particles do not affect health, although present in the indoor environment (especially cloth fibers), particles larger than 10 micrometers are not counted.
The measurement is made according to the standard classification.
PM (particle matter) refers to the total weight of particles per volume of air. It is a vestige of the time when the available technology was not able to detect individual particles. For each particle size a typical mass is attributed to express the result on standardized unit in µg/m3.
Monitoring equipment such as the modern P4000 count the individual particles in three size classes that are correlated with PM10, PM2.5 and PM1. The hypothesis for the calculation of mass is that the particles are spherical which is not always the case.

Standard values


The size of particles is directly linked to their potential danger to health. Environmental organizations are concerned that the particles have a diameter less than or equal to 10 micrometers because they are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects.

Particles are classified into four categories:

  • PM 10, coarse inhalable particles such as those found near roadways and dusty industries, are less than 10 micrometers in diameter and include fine particles, very fine and ultrafine particles.
  • PM 2.5, fine particles such as those found in smoke and haze, are less than or equal to 2.5 micrometers in diameter. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air. Diesel engines are the main source. They include very fine and ultrafine particles.
  • PM 1, very fine particles (most hazardous for health) are less than or equal to 1 micron in diameter. They are virtually eliminated by precipitation and have time to accumulate in the air. They include ultrafine particles.
  • PM 0.1, ultrafine particles with a diameter less than 0.1 micrometer, also called "nanoparticles". Their residence time is very short, ranging from minutes to hours.

PM2.5 and PM1 can descend into the deepest part (alveolar) of the lung where gas exchange occurs between air and blood. These are the most dangerous particles because the alveolar portion of the lungs has no effective means to eliminate them and if the particles are water soluble, they can pass into the bloodstream within minutes. If they are not soluble in water, they remain in the alveolar lung for a long time. Soluble elements may be of PAHs (polycyclic aromatic hydrocarbons) or residues of benzene classified as carcinogenic.

Standards


  Europe (2010) W.H.O USA
  PM10 (<10 µm)
P50* daily limit 50 µg/m³ (less than 35 times/year)
50 µg/m³ 150 µg/m³
Annual limit 30 µg/m³
20 µg/m³ Cancelled in 2006
  PM2.5 (<2.5 µm)
P50* daily limit   25 µg/m³  
P98* daily limit     35 µg/m³
Annual limit 25 µg/m³ in 2010
20 µg/m³ in 2020
10 µg/m³ 15 µg/m³
*: The value must not exceed 50% (98%) of the time.


Performances





P4000 NanoSense particle matter probe

Maintenance


The more the sensor is exposed to dust the more it shall be serviced (cleaning lenses with a wet cotton swab). Do not use alcohol or solvents. Use only clean water.
This sensor does not have a reference beam to compare with the one exposed to dust using therefore cumulative sensor exposure to dust is used to determine preventive maintenance timing.
When cumulative exposure is exceeded, an LED indicates the need for cleaning.
After cleaning the lens, the counter will be reseted by pressing a button (more than 10 seconds). Acknowledgement is indicated by the switch-off of the LED.

Service time
PM2.5 Average Each
< 5 µg/m³ 1000 days
< 10 µg/m³ 500 days
< 25 µg/m³ 200 days
< 50 µg/m³ 100 days

Examples



Diesel soot particles Particulate in the air Particulate in the air Particulate in the air