How to Measure Volatile Organic Compounds In the Air
Measuring our indoor air for concentrations of volatile organic compounds and other harmful chemicals can be very beneficial for our environmental health. By identifying the main sources of nitrogen oxides and VOCs in our homes and places of work, actions can be taken to reduce their impact. To keep track of your exposure to dangerous emissions, such as VOC concentrations or carbon monoxide, for example, a smart indoor air quality monitor is advisable.
What types of sensors are used to detect VOCs concentration?
VOC measurements can be made with a variety of sensors for different purposes and chemicals.
Photoionization detector (PID)
A photoionization detector can analyze a wide range of chemicals, including aromatic hydrocarbons, but excluding low molecular weight hydrocarbons. PID works by using ultraviolet light to break down airborne VOCs into either positive or negative ions. Once broken down, the detector can then measure or detect the charge of the ionized gas. It should be mentioned that PID only temporarily changes the VOC sample it detects and does not permanently change them. Methylene chloride is an example of a dangerous VOC PID is useful in detecting.
Flame ionization detector (FID)
Flame ionization detection is used largely in the automotive industry and is used as the standard in measuring hydrocarbons emission. It works by introducing a sample gas to a hydrogen flame which makes any hydrocarbons within the sample start to produce ions. These ions can then be detected with a metal detector.
Metal oxide semiconductor sensors (MOS)
Metal oxide semiconductor sensors can detect a large number of gases, including benzene, ethanol, and toluene. They use a sensitive film that reacts with gases and can trigger a signal when they reach toxic levels. Because MOS sensors can work in low humidity, they are considered quite effective.
Other useful sensors
NDIR CO2 sensor
Although CO2 is not classified as a VOC and it is also not considered poisonous, it can be useful to monitor it in certain work environments. NDIR (non-dispersive infrared) sensors are the most commonly used when measuring CO2.
They work by using an infrared lamp that shines a light through a tube where air has been introduced. At the other end of the tube, there is a detector that senses how much of the infrared light hits it. The gaps of infrared light that don’t hit the detector at the end indicate how much light was absorbed by CO2. The device then compares the amount of light that was emitted from the infrared lamp and what reached the end, which provides a percentage of how much CO2 there is.
Additional things to consider
When measuring the air for harmful chemical emissions, it is also important to understand the following:
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Air pollution can come in many forms and it is useful to know the difference between ozone and particle pollution, for example, and how we can limit them for our environmental protection.
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While many hazardous emissions are man-made, plenty of volatile organic compounds have natural sources. On top of that, some compounds that are produced by humans, such as carbon dioxide are not as dangerous to people’s health as most people believe them to be.
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Products such as wood, paint, carpets, and other building materials outgas VOC emissions. These can be reduced with the appropriate measures, such as airing out newly refurbished properties.
Measuring the difference airborne chemicals can be done in a variety of ways. Before installing a device in a home or workplace it is worth considering what is the most harmful substance people may be exposed to and what is the best type of sensor to detect it.
Sources
1. https://www.sciencedirect.com/topics/neuroscience/flame-ionization-detector
2. http://www.tsi.com/uploadedFiles/_Site_Root/Products/Literature/Application_Notes/TSI-147_Photo_Ionization_Detection_Technology-A4.pdf
3. https://www.cambustion.com/products/hfr500/fast-fid-principles
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5539520/
5. https://www.thomasnet.com/articles/instruments-controls/How-Gas-Detectors-Work
6. https://www.epa.gov/indoor-air-quality-iaq/technical-overview-volatile-organic-compounds
7. https://www.thoughtco.com/carbon-dioxide-poisonous-607545
8. https://www.pureairemonitoring.com/why-co2-monitor-needed/
9. https://www.co2meter.com/blogs/news/6010192-how-does-an-ndir-co2-sensor-work
10. https://principia-scientific.org/at-what-concentration-does-co2-becomes-toxic-to-humans/
