Air pollution is an issue that is becoming increasingly more urgent to solve, it directly impacts the health of people living, for example, in areas near big industry fabs. This problem affects not only this type of environment but it concerns also the big cities all across the world, due to smog emissions of vehicles crowding the streets, especially of the cities that don’t have a good alternative internal net of communications (eg. subway, intra-city train, etc.)
The control of air quality of an environment may be a high priority to preserve the health of the habitants from the risks of the presence of polluted air; furthermore the level of pollution is related to the CO2 level of the air (see Figure 1):
The CO2 level nowadays is at the highest level in history (Source espertocasaclima.com)
How is it possible to effectively measure the level of CO2 in an environment by utilizing a cost effective solution?
The answer to this question could be found in the electronics technology that is progressively influencing our daily life at a constantly increasing rate: the NDIR is an electronic sensor which is able to measure the level of CO2 gas in a controlled environment (see Figure 2).
The CO2 measurement in a controlled environment (Source: espertocasaclima.com)
How does the NDIR sensor work? An infrared lamp directs light through a tube immersed in the air to be monitored using an infrared (IR) light detector, a thermopile, which measures the amount of IR light that strikes it. When light passes through the tube, the gas molecules that are the same size of the wavelength of the infrared light, only absorb the frequencies of the infrared light, and the gas molecules pass the other frequencies corresponding to other wavelengths of the light that passes through the air of the environment to be monitored (see Figure 3). The remaining light hits an optical filter that absorbs any specific wavelength of light except the part of the wavelength absorbed by the CO2 .
Finally, an IR detector reads the amount of light that was not absorbed by the CO2 molecules or the optical filter. The difference between the amount of light radiated by the IR lamp and the amount of light received by the IR detector is measured. This difference is proportional to the number of CO2 molecules in the air inside the tube, following the equation:
The above equation correlates the output voltage of the thermophile, V, and the level of the CO2 concentration, c, in a controlled environment, which can hence be indirectly monitored by a measurement of the voltage level of the thermophile itself.
The NDIR sensor (Source: International Light Technologies)
In the second part of this blog series I will further describe the strengths and the potentialities of the NDIR technology applied to air quality control, which is a really promising example of the application of electronic technology to environmental control.