Air Quality Sensors

Measuring CO2 And Toxic Gases

Air Quality Sensors measures various parameters within the air, including particulate matter (PM), volatile organic compounds (VOCs), carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), and other pollutants.

Often, such sensors also measure temperature and humidity.

They provide real-time data on air pollution levels, helping to assess the overall air quality and potential health risks.

Not all sensors measure all parameters, and it depends on sensor type and architecture how accurately the parameters are detected.

Determining Air Quality

In normal environments, the most important sensor parameters for determining average air quality typically include:

  1. Particulate Matter (PM): PM2.5 and PM10 are important indicators of airborne particles, including dust, pollen, smoke, and other pollutants. High levels of PM can lead to respiratory issues and reduced visibility.

  2. Carbon Dioxide (CO2): CO2 levels are indicative of indoor air quality and ventilation. Elevated CO2 levels can indicate poor ventilation or the presence of occupants, which may lead to discomfort and reduced cognitive function.

  3. Volatile Organic Compounds (VOCs): VOCs are emitted from various sources such as paints, solvents, cleaning products, and building materials. Monitoring VOC levels is crucial for assessing indoor air quality and potential health risks.

  4. Carbon Monoxide (CO): CO is a colorless, odorless gas produced by incomplete combustion of fuels such as gas, oil, and wood. High levels of CO can be deadly and are a major concern in indoor environments.

  5. Ozone (O3): Ozone is a reactive gas formed by the interaction of sunlight with pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). While ozone at ground level can be harmful to health, it is typically less of a concern in normal indoor environments.

  6. Temperature and Humidity: Monitoring temperature and humidity levels is important for comfort and can also affect the dispersion and concentration of airborne pollutants.

These parameters collectively provide insights into the overall air quality, indoor comfort, and potential health risks in normal environments.

Measuring CO2

There are many different approaches to measure CO2 levels, varying in complexity (and thus sensor cost) and accuracy.

Cheap MOS Sensors

The cheapest way of measuring carbon dioxide (CO2) levels is using solid-state sensors, such as metal-oxide semiconductor (MOS) sensors. They operate by detecting changes in electrical conductivity when exposed to gases like CO2.

MOS sensors measure changes in conductivity rather than directly detecting CO2 molecules: their results are affected by other gases or environmental factors present in the air. You need to calibrate such sensors in fresh air. You then get an estimate for the overall air quality compared to the fresh air that you used for calibration.

This may be sufficient to get a rough low-cost air quality overview.

Expensive NDIS Sensors

Non-Dispersive Infrared (NDIR) sensors measure the concentration of CO2 by detecting its absorption of infrared radiation at specific wavelengths. In contrast to MOS sensors, NDIS sensors specifically measure CO2 and are known for their reliability and accuracy.

NDIS sensors are widely used in high quality indoor air quality monitors.

Since NDIS sensors are much more complex, they are also much more expensive than MOS sensors and start at around 20 Euro.

When you purchase air quality monitoring devices off the shelf, the used sensor type is often not disclosed. Since NDIS sensors alone cost at least 20 EUR, it is safe to assume that cheap air quality monitors use simple MOS sensors and allow just rough guesses about the air quality.

Other Sensors

There are many other sensor types for scientific and industrial use. Their increased accuracy is irrelevant for normal use cases, and their prices are prohibitive.

Such sensors involve Chemical Absorption using chemical reagents, gas chromatography, photoacoustic spectroscopy (PAS), and Tunable Diode Laser Absorption Spectroscopy (TDLAS).

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(content created Jun 04, 2024)