This week, I’m going to share with you how our team created PEEKair, our PM2.5 air quality monitor. I will go though in detail why PM2.5 monitors need to be specifically calibrated for its city of use, in order to be accurate. It all began in early 2015...
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I always want to make sure that our children are as safe as possible from the effects of air pollution. Not a month goes by without someone telling me that their child has asthma. I had always wondered whether the air purifiers that we have spent tens of thousands of dollars on, really did anything. My husband was adamant that the filters didn’t need changing as often as we were told. Friends asked the same question. Nowhere in Hong Kong could I find a monitoring device that would give me the solution.
With the local air pollution problem and lack of a proper monitoring device never far from my mind, the idea behind PEEKair started to take shape. I wanted to bring a consumer device that would display understandable readings, in real-time, to families in Hong Kong.
My list of demands began...I wanted something that would be immediately useable, straight from the box - no need to setup and programme before getting results (The 'Simple-enough-that-even-Grandma-can-use-it' test). Consumers should be able to use it to check that they have enough air purifiers to cover every corner of their home (or workplace). And that the purifiers they already have are still effective.
I wanted the device to be accessible to as many families as possible so the device had to be affordable. It had to be effective for households on limited budgets so they could still benefit from only having one device rather than needing a device for every room. This meant that the monitor had to be portable, battery powered and responsive so that it could be moved from room to room, giving an immediate reading. Just a simple to use, real-time, stand-alone device that would fit in the palm.
The device had to be durable as it would be used daily, helping families decide when to turn up their air purifiers if their indoor air pollution is bad. And, when to turn down their purifiers if the air is good - saving electricity and extending filter life. Knowing the indoor air quality and making decisions based on actual readings, was the aim. Hopefully this could then reduce the number and severity of particularly sensitive children and adults suffering from breathing difficulties.I thought that the ‘journey’ would be as simple as taking an off-the-shelf product and reselling it. How very wrong I was!!
PM2.5 is defined as the total weight of the fine particles in a given volume of air and is measured as a concentration in µg/m3. You should read my blog about air pollution in Hong Kong first if you have not done so already.
I started searching the market worldwide for PM2.5 monitors. I quickly found that most of the manufacturers were based in China. This made sense – China has a huge air pollution problem and what electronic device isn’t made in China these days?
I found that devices with built-in microbalances which can weigh the particles in real-time were far too expensive and designed for the lab. Light scattering (or nephelometers) was by far the only technology which met my criteria by being affordable, real-time and small enough to be moved from room to room. The technology works by measuring particle concentrations based on the light scattering produced by those particles. It assigns an average weight to those particles to provide a PM2.5 concentration measurement. The device doesn’t actually need to weigh the particles, reducing the cost and size of the monitor dramatically.
I started ordering samples of these devices. A lot were eliminated because they were designed for an industrial setting so were too ugly and expensive. Others would continuously send a variety of collected measurements over the Internet, connected to apps which track your location and god knows what else!!! - which was a step too far for my privacy-concerned self. Some didn’t give readings that could be easily interpreted so I excluded particle counters. In the end, I had a handful of devices to choose from.
As each sample arrived, I went from excitement to a sulky “grump-lump”; like my children coming off a sugar high. None of the monitors were accurate compared to the Hong Kong Government’s air quality monitoring stations. The worst were the monitors that used infrared as a source of light, commonly found built into household air purifiers. They sometimes gave very clean readings when the pollution was confirmed to be terrible but detected cigarette and cooking smoke quite well. Monitors using laser light sources gave me readings that seemed to move with the pollution levels but the numbers were just wrong when compared to official government measurements. The manufacturers kept on telling me that their products were accurate in Beijing and against expensive reference instruments calibrated to industry standards based on the same light scattering technology.
I refused to sell a product that simply did not read accurately. So what to do...my eyes turn to my unsuspecting husband!! Armed with his Engineering Masters Degree from Cambridge University, he was soon “encouraged” to set about solving my problem. In typical fashion, he dove straight into the deep-end and reviewed a few dozen scientific papers on the subject. 24 hours later he told me something that now seems blindingly obvious. "Your monitors don’t weigh the particles. They assume that PM2.5 particles have the same mass regardless of which city you live in - this assumption is WRONG. Pollution composition is different between cities. This means that the average particle mass will be different between cities.” It made perfect sense to him that a monitor which reads accurately in Beijing will never read accurately in Hong Kong. 26% of the PM2.5 pollution observed in Beijing is from coal burning versus only 3% in Guangdong just over the border. He gave me these charts to show the varying pollution composition and in case I thought it was just a Chinese phenomenon, he included one for the US as well.
But what about those instruments calibrated to industry standards costing tens and thousands of dollars that I kept hearing about? They are calibrated using Arizona road dust! Yes, ground up dirt from the USA! They even give this dirt a special name - ISO 12103-1, A2. It resembles nothing like pollution in most parts of the world. A study from Harvard shows how a deployment of a group of factory calibrated TSI DustTraks (which many Chinese monitor manufacturers use for calibration) read up to two times higher than reality in Baltimore, MD and Boston, MA. Similar US studies showed the same result with a different magnitude of error depending on the city. My husband has a hypothesis that by pure coincidence, Beijing pollution might just resemble Arizona Road dust. Yuck! Imagine filling your lungs with road dust every day. Is that why they have such hacking coughs there?
What do we do for Hong Kong? “We need to correlate real pollution levels with devices calibrated for Arizona road dust”, he said. I could see the light at the end of the tunnel. We would take the best off-the-shelf monitor and have our team of engineers customise the calibration specifically for Hong Kong.
We used the Hong Kong Government’s air quality monitoring stations as the real levels of pollution. Their automated machines use a microbalance to weigh a sample of particles in the air every hour. These machines are regularly checked against a manual method where a filter of a known weight captures PM2.5 particles, which is then reweighed after a known amount of air passes through it, making sure that they are accurate to within 10%.
Fig 3: Data collection for PEEKair
Readings of air pollution were collected from areas adjacent to various Government monitoring stations with our numerous devices, collecting data to correlate later. With these data points, our team could formulate a calibration curve for the range of pollutants we experience in Hong Kong. PEEKair was born.
We focused the sensitivity of the calibration on the range (0-125µg/m3) that we predominately experience in Hong Kong.
Having cracked the calibration, our final step was to customise the device for our audience. We worked with programmers, designers, third party manufacturers and printers to produce a product that would operate intuitively, look elegant, conform to Hong Kong safety standards, with a clear and concise operating manual.
So how well does PEEKair work? It’s very accurate and it is the only consumer monitor calibrated specifically for Hong Kong at the time of writing.
After the best part of a year of work, I pleased to bring a unique household PM2.5 air quality monitor for Hong Kong. Affordable for most families; aesthetically complimentary to your home and most importantly, putting you in control of the air your family breathes. Click here to purchase PEEKair.
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PEEKair was created for indoor use, in your home or office. The outdoor readings discussed in this blog post were taken under specific conditions for data collection, calibration and testing purposes.