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Community and Q&A

Evaluating Indoor Air Quality Sensors

andyfrog | Posted in General Questions on

Does anyone here have experience with indoor air quality sensors in the $200-1,000 range for UFP, PM1.0, PM2.5, PM10, Radon, TVOC, CO, CO2, ozone, NOx? Are there any other metrics I might be forgetting?

I found this site, but it only covers some particulates, ozone, and NO/NO2. However, it is quite good. It appears that there are not really any accurate NOx sensors in the aforementioned price range.

I’m wondering what the options are.

Does anyone know of any good literature reviews or lectures covering the basics of IAQ sensing? For example, something that might explain if ozone is a good proxy measure of NOx, etc, or explains what exactly TVOC is (is it a standard, or just something made up by manufacturers, etc?)


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  1. prometheanfire | | #1

    I'd be interested in how the airthings line stands up to those tests.

  2. charlie_sullivan | | #2

    I'd been holding off on buying one because every time I dug into it, I found reasons why each of the candidates wasn't quite the right thing. Then I listened to this podcast interviewing one of the founders of AirThings:

    I was impressed by the company's approach, and also learned that the new "view plus" has all of the sensors that any home monitors have--I don't think that model was out last time I had shopped for them. So I bought one and am very pleased with the results. My only caveat is that an all-in-one unit precludes leaving the individual sensors in the areas where that variable is the largest concern: I would want to leave the radon sensor in the lowest level and the CO2 sensor in the bedroom. But the all-in-one unit was a lot cheaper than buying separate units so it's not unreasonable to get it and then plan to add individual sensors for variables you want to monitor in individual locations.

    1. prometheanfire | | #3

      I use the view plus mounted next to my thermostat (tapped into the 24 VAC thermostat line, converted to 5 VDC). It's on the main level (ranch). I also have the wave plus mounted in the basement, it phones home via the view plus (which can relay since it has power). I could add more sensors but I think this is good for now.

      I've attached a pic showing both sensors in the dashboard, lets see if you can tell when I finished sealing the basement for radon (all those cracks and corners).

  3. andyfrog | | #4 I found this good overview if anyone was curious. It doesn't go into specific monitor models but it's a good intro.

  4. bigred | | #5

    Let me see if I can help out with some of your questions. I've been doing ambient air monitoring for the last 40 years and have even helped develop some AQ sensors First most of the hand-held sensors for gases pollutants in the less than $1000 level are going to have lessor levels of accuracy and precision. Most electrochemical cells do a pretty good job at relative precision (they increase and decrease according to pollutant concentration) but may have relatively low accuracy (+/- 30% or more). In addition, both their accuracy and precision will be impacted by the pollutant's concentration. Normally a sensor is most accurate in 20 - 80% of full scale. Below 10% of scale, accuracy and be downright poor depending on the sensor and the sensor technology.

    In particular, you mentioned NOx. NOx is generally considered to be NO and NO2. From combustion sources, we create NO, then sunlight and ozone react to create NO2. No is fairly harmless, but NO2 is respiratory irritant. Without sunlight, NO2 and O3 react to "titrate" NO2 to form NO and O2. So, I would not conclude that O3 is a proxy for NO2 or NOx. Also, other than a chemiluminescent detection system NO or NO2 (electrochemical cells will be specific to the NOx type) analyzers tend to present low levels of both precision and accuracy, particularly at lower levels.

    Particulate sensors tend to under report PM levels compared to reference methods, but do a pretty good job at determining relative levels. These laser or nephelometry based methods are getting better but are still not approved as a reference method. They will definitely tell you if PM levels are increasing or decreasing or if they are higher today than yesterday and tend to have good repeatability but will almost always read lower than the "true" value.

    In summary, the hand-held portable are useful instruments but recognize that they have limitations. These may be instruments I would use for industrial hygiene purposes, but would not use for regulatory compliance.

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