Open and Accurate Air Quality Monitors
We design professional, accurate and long-lasting air quality monitors that are open-source and open-hardware so that you have full control on how you want to use the monitor.
Learn Moreby Achim Haug on January 18, 2025
I’ve been thinking a lot about something that’s been bugging me in the air quality monitoring world for some time. It feels like there’s this race happening, a rush to see who can cram the most pollutant measurements into a single device. “The new 14-in-1 air quality monitor!” the headlines shout. At first glance, you might think, “Wow, that’s comprehensive!” But here at AirGradient, we’ve always believed in something different: honesty, accuracy, and giving you real value. That’s what really matters.
This push for quantity comes at the expense of quality. The marketing might sound impressive, but the truth is that many of these “all-in-one” low-cost sensors struggle – and often outright fail – to measure these wide ranges of pollutants accurately. Now, if these manufacturers were transparent about it, it would be okay. But most are not, creating this false sense of security for the consumer. Or worse, misleading data that could actually impact the decisions they make for their health.
Let’s be honest: lower-cost monitors often rely on sensors with limited capabilities because very accurate ones, like reference devices, are just too expensive - often costing tens of thousands of dollars. So these manufacturers - by going into quantity - often need to make compromises on the quality. It might be cheaper sensor modules or saving costs in the calibration and testing of the monitors they sell.
Why we remove PM1 and PM10 from our marketing
At AirGradient, we’ve always tried to be straight with you, even when it means making tough calls. We’ve been carefully watching how our own monitors perform, and we’ve also been looking at what others are doing. And what we’ve consistently seen is this: low-cost sensors generally do a reasonable job with PM2.5 but offer limited additional value for PM1 or might completely fail for PM10.
PM1 readings are often so closely tied to PM2.5 that they don’t really tell you anything extra that’s useful. This strong correlation is also stated by many other sources. For example, “For most locations, PM1 is often nearly equal to PM2.5. This indicates that most fine PM is in the range of PM1.” [3] Also important to note is that with the PM sensors we use - Plantower PMS5003 and PMS5003Ts, PM1 is actually included in the PM2.5 measurement.
Therefore, providing both PM1 and PM2.5 often leads to redundant information, adding complexity without substantial benefit.
The real problem, however, is PM10. These sensors often completely miss larger PM10 particles, like the ones you get during a sandstorm. This view is also supported by the US EPA, “Optical particle sensors are known to have varying accuracy, particularly at high concentrations and with larger particle sizes.” [1] Many research papers also suggest that most low-cost optical PM sensors perform well for smaller particles, but their accuracy drops for large particles.
So, imagine relying on one of these “14-in-1” devices and thinking your air is okay during a sandstorm! This isn’t some secret kept behind closed doors in the industry. Many of us know that these broad “all-in-one” claims are more about marketing than reliable measurement. But this crucial information? It rarely reaches the consumer. The result? A lack of transparency and information that can be downright misleading.
PM2.5: The Global Standard for Health and Air Quality
It also makes sense to focus on PM2.5 because leading health organizations and regulatory bodies worldwide have recognized PM2.5 as the most critical indicator of air quality’s impact on human health. The World Health Organization (WHO), for instance, has established stringent guidelines specifically for PM2.5. “Fine particulate matter (PM2.5) is the air pollutant that poses the greatest risk to health globally,” the WHO states. “There is clear evidence of the health effects associated with exposure to this pollutant.” [2]
While there is emerging evidence that PM1 is also very harmful - and perhaps more harmful than PM2.5 - we believe in the importance of measuring both of these metrics. Again, it’s important to note that the PM2.5 readings from our sensors also include PM1, giving you one aggregated reading of the two most harmful particle types.
By concentrating on PM2.5, we’re aligning with these established standards, making it straightforward for you to understand the health implications of the air around you.
The Problem with Low-Cost Gas Sensing
And it’s not just about particles. We’re seeing the same thing with gas measurements. Some manufacturers brag about their monitors measuring all sorts of volatile organic compounds (VOCs) – ethanol, carbon monoxide, hydrogen, ammonia, the whole shebang. Sounds impressive, right? But the truth is, many of these low-cost monitors use sensor modules that simply can’t tell the difference between these different pollutants. These sensors react to a bunch of different gases and then estimate the levels of each one using some algorithms and assumptions. That’s not real measurement; that’s guesswork, and often not very good guesswork at that.
If you want to learn more about the caveats with low-cost gas sensors, please feel free to refer to this article we recently wrote.
Sometimes, Less Really Is More
So, we have recently changed the information on our website, primarily highlighting PM2.5. We implemented the same on our dashboard. The monitors still measure and transmit PM1 and PM10 data, and you can make them visible on the dashboard under advanced settings for people who need to understand the limitations of that data.
We know our monitors, like most affordable options, are primarily calibrated for PM2.5, and to make absolutely sure we’re giving you the most accurate PM2.5 readings possible, we use a proper, reference-grade instrument – the Palas Fidas 200 in our test chamber. This allows us to fine-tune the PM2.5 calibration and give you data you can trust. Instead of trying to be mediocre at measuring everything, we’re focusing our energy on being really good at measuring what matters most.
“Sensor calibration is essential for ensuring accurate and reliable measurements,” highlights a report by the South Coast Air Quality Management District. “Regular calibration and maintenance are crucial for maintaining sensor performance over time.” [4]
Right now, we’re also looking closely at the NOx signal from the Sensirion SGP41 sensor in our devices. We’re still evaluating its accuracy and can’t give a definitive judgment yet. But I want to be clear: all the other parameters that AirGradient monitors provide have been thoroughly tested and are accurate and useful. We have a strong scientific team here at AirGradient led by Dr. Anika Krause, who continuously tests and characterizes our monitors.
Furthermore, we want to emphasize that this is not a cost-cutting measure as we are not removing any functionality or sensors from the device. All PM measurements come from the same sensor, and the ability to enable PM1 and PM10 readings on the dashboard will still be present.
We Believe in Honest Data
We don’t believe that stepping back from emphasising PM1 and PM10 is a step backwards. Instead, we see it as a step forward in our commitment, which is to provide honest, transparent, and open air quality monitoring. We want to give you the tools you need to understand your environment, without the marketing fluff and misleading claims.
I understand the desire for all the data. As technology gets better and we can get our hands on affordable and accurate sensors for more pollutants, we’ll definitely explore adding them. But until then, we’re not going to compromise on accuracy just to have a bigger number on a spec sheet.
What do you think about this trend of “more is better” in air quality monitoring? Have you seen misleading claims out there? I’d really like to hear your thoughts in the comments below!
[1] United States Environmental Protection Agency. (2021). Performance Testing Protocols, Metrics, and Target Values for Fine Particulate Matter Air Sensors: Use in Ambient, Outdoor, Fixed Site, Non-Regulatory Supplemental and Informational Monitoring Applications, Version 3
[2] World Health Organization. (2021). WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide.
[3] Crilley, L. R., Shaw, M., & Pound, R. (2018). Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring. Atmospheric Measurement Techniques, 11(12), 709-720.
[4] South Coast Air Quality Management District. (2017). Air Quality Sensor Performance Evaluation Center (AQ-SPEC) Field Evaluation Report: Alphasense OPC-N2.
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Join our NewsletterWe design professional, accurate and long-lasting air quality monitors that are open-source and open-hardware so that you have full control on how you want to use the monitor.
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