Particle Matter: The Parameter; Measurement Process - Libelium Smart Cities PRO Technical Manual

5.4.2. Particle matter: the parameter

Particle matter is composed of small solid or liquid particles floating in the air. The origin of these particles can be
the industrial activity, exhaust fumes from diesel motors, building heating, pollen, etc. This tiny particles enter our
bodies when we breath. High concentrations of particle matter can be harmful for humans or animals, leading to
respiratory and coronary diseases, and even lung cancer. That is why this is a key parameter for the Air Quality
Index.
Some examples:
Cat allergens: 0.1-5 μm
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Pollen: 10-100 μm
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Germs: 0.5-10 μm
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Oil smoke: 1-10 μm
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Cement dust: 5-100 μm
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Tobacco smoke: 0.01-1 μm
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The smaller the particles are, the more dangerous, because they can penetrate more in our lungs. Many times,
particles are classified:
PM1: Mass (in μg) of all particles smaller than 1 μm, in 1 m
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PM2.5: Mass (in μg) of all particles smaller than 2.5 μm, in 1 m
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PM10: Mass (in μg) of all particles smaller than 10 μm, in 1 m
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Many countries and health organizations have studied the effect of the particle matter in humans, and they have
set maximum thresholds. As a reference, the maximum allowed concentrations are about 20 μm/m
and about 50 μm/m for PM10.
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5.4.3. Measurement process

Like conventional optical particle counters, the OPC-N2 measures the light scattered by individual particles
carried in a sample air stream through a laser beam. These measurements are used to determine the particle size
(related to the intensity of light scattered via a calibration based on Mie scattering theory) and particle number
concentration. Particle mass loading- PM2.5 or PM10, are then calculated from the particle size spectra and
concentration data, assuming density and refractive index. To generate the air stream, the OPC-N2 uses only a
miniature low-power fan.
The OPC-N2 classifies each particle size, at rates up to ~10,000 particle per second, adding the particle diameter
to one of 16 "bins" covering the size range from ~0.38 to 17 μm. The resulting particle size histograms can be
evaluated over user-defined sampling times from 1 to 10 seconds duration, the histogram data being transmitted
along with other diagnostic and environmental data (air temperature and air pressure). When the histogram is
read, the variables in the library are updated automatically. See the API section to know how to manage and read
this sensor.
You can find a complete example code for reading the Particle Matter Sensor in the following link:
http://www.libelium.com/development/waspmote/examples/scp-v30-04-particle-matter-sensor
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