Sensing the Air Quality

A low-cost IoT air quality monitor based on a Raspberry Pi 4.

Sensing the Air Quality

A low-cost IoT air quality monitor based on the new Raspberry Pi 4.

I have the privilege of living in one of the most beautiful countries in the world, but unfortunately, it’s not all roses. Chile during winter season suffers a lot with air contamination, mainly due to particulate materials as dust and smog.

Because of cold weather, in the south, air contamination is mainly due to wood-based calefactors and in Santiago (the main capital in the center of the country) mixed from industries, cars, and its unique geographic situation between 2 huge mountains chains.

Nowadays, air pollution is a big problem all over the world and in this article we will explore how to develop a low expensive homemade Air Quality monitor, based on a Raspberry Pi.

If you are interested to understand more about air quality, please visit the “World Air Quality Index” Project.

Particulate Matter (PM): What Is it? How Does It Get Into the Air?

So, to understand pollution or air contamination, we must study the particles that are related to that, that are also known as particulate matter. Looking at the graphs on the previous section we can observe that they mentioned PM2.5 and PM10. Let’s give a quick overview of that.

PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.

Particles come in a wide range of sizes. Particles less than or equal to 10 micrometers in diameter are so small that they can get into the lungs, potentially causing serious health problems. Ten micrometers is less than the width of a single human hair.

Particle pollution includes:

  • Coarse dust particles (PM10): inhalable particles, with diameters that are generally 10 micrometers and smaller. Sources include crushing or grinding operations and dust stirred up by vehicles on roads.
  • Fine particles (PM2.5) : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller. Fine particles are produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes

You can find more about particulate matter on EPA site: United States Environmental Protection Agency

Why Is It Important to Care About Those Particulate Matters?

As described by GERARDO ALVARADO Z. in his work at Chile University, studies of episodes of high air pollution in the Meuse Valley (Belgium) in 1930, Donora (Pennsylvania) in 1948 and London in 1952 have been the first documented sources that related mortality with particle contamination (Préndez, 1993). Advances in the investigation of the effects of air pollution on people’s health have determined that health risks are caused by inhalable particles, depending on their penetration and deposition in different sections of the respiratory system, and the Biological response to deposited materials.

The thickest particles, about 5 μm, are filtered by the joint action of the cilia of the nasal passage and the mucosa that covers the nasal cavity and the trachea. Particles with a diameter between 0.5 and 5 μm can be deposited in the bronchi and even in the pulmonary alveoli, however, they are eliminated by the cilia of bronchi and bronchioles after a few hours. Particles smaller than 0.5 μm can penetrate deeply until they are deposited in the pulmonary alveoli, remaining from weeks to years, since there is no mucociliary transport mechanism that facilitates elimination.

The following figure shows the penetration of the particles in the respiratory system depending on their size.

So, to spot both types of particles (PM2.5 and PM10) are very important and the good news is that both are readable by a simple and not expensive sensor, the SDS011.

The Particle Sensor — SDS011

Air Quality monitoring is well known and established science which started back in the 80’s. At that time, the technology was quite limited, and the solution used to quantify the air pollution complex, cumbersome and really expensive.

Fortunately, nowadays, with the most recent and modern technologies, the solutions used for Air Quality monitoring are becoming not only more precise but also faster at measuring. Devices are becoming smaller, and cost much more affordable than ever before.

In this article we will focus on a particle sensor, that can detect the amount of dust in the air. While the first generation was just able to detect the amount of opacity, most recent sensors as the SDS011 from INOVAFIT, a spin-off from the University of Jinan (in Shandong), can now detect PM2.5 and PM10.

With its size, the SDS011 is probably one of the best sensors in terms of accuracy and price (less than USD40.00).

Specifications

  • Measured values: PM2.5, PM10
  • Range: 0–999.9 μg /m³
  • Supply voltage: 5V (4.7–5.3V)
  • Power consumption (work): 70mA±10mA
  • Power consumption (sleep mode laser & fan): < 4mA
  • Storage temperature: -20 to +60C
  • Work temperature: -10 to +50C
  • Humidity (storage): Max. 90%
  • Humidity (work): Max. 70% (condensation of water vapor falsify readings)
  • Accuracy: 70% for 0.3μm and 98% for 0.5μm
  • Size: 71x70x23 mm
  • Certification: CE, FCC, RoHS

The SD011 use the PCB as one side of the casing, allowing to reduce its cost. The receptor diode is mounted on the PCB side (this is mandatory as any noise between the diode and the LNA should be avoided). The emitter laser is mounted on the plastic box and connected to the PCB via a flexible wire.

Source: Sensing the Air Quality

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