One Take #11 - Turning Low-Cost Air Quality Sensors into Compliance Tools

Lidia Morawska's  paper provides a pragmatic framework for using low-cost PM2.5 sensors in regulatory indoor air quality monitoring, solving the longstanding problem of affordable compliance without sacrificing accuracy. This clever calibration system transforms inexpensive sensors into reliable monitoring networks by using yearly reference calibrations of key sensors and applying correction factors across similar devices.

• Low-cost sensors have revolutionized air quality monitoring but face accuracy challenges with PM2.5 measurement
• Traditional reference monitors are too expensive and complex for widespread indoor deployment
• Morawska's framework uses a network approach with designated reference sensors
• Annual calibration of key sensors against reference instruments provides correction factors for the entire network
• The system could include a central database of correction factors to prevent duplication of effort
• This approach enables dynamic ventilation control based on reliable PM2.5 measurements
• The framework moves us from "guessing and hoping" to "measuring and knowing"
• Implementation would provide accountability and evidence for meeting health-based building standards

Application of PM2.5 low-cost sensors for indoor
air quality compliance monitoring

Chapters

• 0:14 Welcome to Air Quality Matters
• 0:42 Essential Paper on PM2.5 Sensors
• 1:16 The Indoor Air Quality Challenge
• 2:10 Low-Cost Sensors: Benefits and Limitations
• 3:29 Smart Calibration Framework Explained
• 4:43 Practical Applications and Implications
• 6:23 Pragmatic Optimism for the Future
• 8:14 Episode Closing and Sponsors

Transcript

Speaker 1: 0:14

welcome back to air quality matters and one take one take my take on a paper or report on air quality, ventilation and the built environment. One take in that it's well in one take and tries to summarise for you a scientific perspective on something interesting in well usually 10 minutes or less, because who has the time to read all these amazing documents? Right? This week I'm digging into a paper that I think is, frankly, essential. It's titled Application of PM2.5 Low-Cost Sensors for Indoor Air Quality Compliance Monitoring and it's from a team including the one and only Lydia Murawska. Now, that name alone should tell you it's worth paying attention to.

Speaker 1: 1:00

This paper gets right to the heart of a problem we talk about consistently on this podcast. We know indoor air quality matters, we know we need to manage it, but the big elephant in the room has always been monitoring. How do we actually check on a massive scale whether the air in our schools, offices and public buildings is safe without spending a fortune on gear and an army of technicians? This paper doesn't just ask the question. It provides a real, pragmatic roadmap for an answer. So let's get into it. The starting point is one we all know Many people spend over 90% of their time indoors and for experts have been calling for proper regulation for indoor air quality on a par with what we have for outdoor air. The challenge, of course, is that it's just much more complex. Every building is its own little ecosystem. The traditional gold standard monitors, the ones we use for regulatory outdoor networks, are brilliant. The ones we use for regulatory outdoor networks are brilliant, but they are expensive, they're bulky and they're complex. It's just not feasible to put one in every single indoor space.

Speaker 1: 2:13

So what's the alternative? This is where low-cost sensors come into the picture. We've seen them explode in popularity and they've given us this incredible granular view of air pollution. That was unthinkable a decade ago. But and it's a big but we all know they're not perfect. Let's take PM, for example. They don't directly measure the mass of particles in the same way a reference monitor does. Instead, they estimate it by scattering light off them. And that process can be thrown off by all sorts of things the size, the shape and even the material of the particulate matter itself. A particle of soot from a candle looks very different to a sensor than a particle of dust. And then there's humidity. High humidity can make hydroscopic particles swell up with water, making the sensor think there's more pollution than there actually is. So the data from low cost sensors straight out of the box often comes with some pretty big asterisks next to it when you're talking about reference level kind of monitoring.

Speaker 1: 3:21

So what this paper by Murawska and her colleagues does which I think is clever is it doesn't just point out the problems. It proposes a realistic, workable framework to solve them, specifically by using PM2.5 sensors for compliance. It's a way of harnessing the power of these affordable sensors while building in the rigour we need for regulation, for example. The framework is broken down into a few key steps. First, you've got to set up the system right. This means thinking about your buildings as a network. The paper suggests you nominate one of the sensors as your reference sensor. This becomes your internal ground truth. Then you need an outdoor sensor and, crucially, this one should have a dryer or heater in its inlet to deal with the humidity problem we just talked about. This is so you have a reliable measure of what's coming in from outside, without the weather messing with the readings. And ideally all the sensors in your network should be the same model, from the same batch if possible, just to minimize variability from the get-go.

Speaker 1: 4:33

Now here's the really clever part the calibration. This is what stops the whole thing from being prohibitively expensive. You don't have to drag a 20,000 bit piece of reference kit with you to every sensor in your building. Instead, the framework says that once a year, you take your internal reference sensor and your external sensor and you locate them with a proper, high-grade reference instrument. You could do this by taking them to an official monitoring station or, if your building is very well sealed off from the outside, by bringing a reference instrument to the building. What this does is it gives you a robust, traceable calibration for the key nodes in your network, your indoor and outdoor reference points. You're not calibrating every sensor. You're calibrating the linchpins of the system and from that you get your magic numbers, your correction factors. These are the adjustments you need to apply to the raw sensor data to make it accurate. The paper goes one step further, in fact, and suggests that these correction factors should be held in a central, open database, maybe hosted by a regulatory body.

Speaker 1: 5:52

Imagine that for a second a shared resource where a building manager in one city can benefit from the calibration work done in another, especially if the building types and uses are similar. It stops everyone from having to reinvent the wheel, and it's building a community of practice around the data. So, when you pull all of this together, what you have is a pathway, effectively a roadmap. It moves us away from a world of guessing and hoping to a world of measuring and knowing. It's a system that's designed to be both scientifically robust and economically viable. The implications, I think, are pretty big.

Speaker 1: 6:35

This isn't just about getting a red or a green light on a screen. It's about feeding really reliable data back into your building management system. It allows for dynamic control of ventilation, bringing in more fresh air when the pm 2.5 levels rise in the building and maybe reducing it to save energy when the air is clean. It provides the evidence needed to show that a building is meeting a health-based standard and it creates accountability. It answers, in truth, I think, some of the question marks that still remain around the calibration of low-cost sensors in things like the World Building Standard. So, to wrap this up, what this paper really gives us is a dose of pragmatic optimism.

Speaker 1: 7:23

To wrap this up, what this paper really gives us is a dose of pragmatic optimism. It acknowledges the limitations of low cost sensors, but, instead of seeing them as a deal breaker. It treats them as an engineering challenge to be solved and it provides a solution, logical and scalable framework for taking these devices from being interesting gadgets to being a serious tool for compliance and public health protection. Of course, the authors note that there's still things to work out, like agreeing on standard protocols and understanding how different brands of sensors will behave within these networks. But the point is, the foundation is there. It essentially takes the argument away from the if we can do this and moves it firmly to the how we can do it, and for me that's a huge step forward. I hope you enjoyed this week's episode of One Take. Thanks a million, as always, to our sponsors, safe Traces and Imbiote. These podcasts wouldn't be possible without their support. See you next week.