Breathing Easy — Scientists Praise a Grassroots Movement as Air Quality Sensors Arrive At Our Doorstep
By: Perry Brissette
Tags: Health, Air Quality, Science, Science Communication, Internet of Things

Spurred by wildfires, climate change, and the Internet of Things, a citizen science movement takes root as thousands of low-cost air quality sensors are installed in homes and backyards around the world —and scientists are starting to take it seriously

A low-cost air sensor launches a citizen science movement — Inexpensive, easy to install, and able to share data via Internet Wi-Fi, the PurpleAir sensor has gained over 10,000 installations worldwide in just the past five years. Scientists and air quality experts are praising this movement as a success, citing how these sensors help build a more complete picture of air quality as they reach into under-served locations like schools, tribal land, recreation areas and parks. Image by PurpleAir

Adrian Dybwad vividly recalls the day in 2015 when his chance experiment gave birth to his start-up — PurpleAir, a company that would quickly go on to launch a community science movement for air quality monitoring around the world.

The computer scientist and hardware engineer had just purchased his first air quality sensors. Motivated by his own curiosity about the state of air quality near his home in Draper, Utah, Dybwad sat down at his workstation, placed the two identical sensors he’d just purchased next to each other, and locked them into an air-tight calibration chamber. That’s when he noticed something remarkable: they both agreed with the exact same reading.

This surprised Dybwad, because the devices he purchased were hardly professional-grade. In fact, they were two low-cost Plantower sensors, normally designed for use in home air purifiers, containing tiny laser instruments the size of matchboxes. The ones Dybwad bought were available off-the-shelf for about $25.00 each.

It was the readings themselves that took Dybwad most by surprise. From his simple, low-cost sensors, Dybwad was seeing measurements of airborne particulate matter comparable to professional-grade instruments — those used by government organizations like the E.P.A., and relied upon by scientists and air quality experts around the world; hardware vastly more accurate, stable and reliable that can cost more than $150,000.

Then, Dybwad did something even more remarkable: he wired his sensors into the Internet via Wi-Fi. This began a quest to freely share his air quality data for anyone in the world with an internet connection to view.

From these humble beginnings, and just five years later, PurpleAir, which Dybwad has led as CEO, has grown to include nearly 10,000 sensors installed in over a dozen countries around the world. During a two-day period at the height of the wildfires in Northern California, more than one million visitors navigated to the PurpleAir website to view up-to-the-minute air quality information.

Scientists Take Notice

It didn’t take long before PurpleAir caught the attention of scientists and experts in the field of air quality.

“I would put PurpleAir in a class of companies that are doing good — even great,” said Anthony Wexler, professor of mechanical and environmental engineering and director of the Air Quality Research Center at the University of California at Davis.

In the eyes of Wexler and many air quality experts, PurpleAir has offered serious advantages since its inception. The sensors Dybwad had chosen were low cost but accurate, enough so that users could get good, reliable data from them. And with a low price and ease-of-use, these sensors were designed to be affordable and more accessible for a mass audience. A PurpleAir sensor costs consumers about $200.

Easy Air Sensor Installation — A typical PurpleAir installation brings accurate air-quality sensors to more locations, with placement indoors or outdoors. With their low cost and ease of use, these sensors are finding their way into more locations, especially those under-represented by official air quality monitoring, including inner-city schools, refineries, mines, parks and tribal areas. Image from Coalition for Clean Air.

Driven by growing community adoption, the popularity of PurpleAir means that more sensors can be installed in vastly more locations, giving both scientists and the public a truer picture of air quality in more places. Experts refer to this as spatial distribution and stress its importance as a key factor to ensure accuracy in air quality monitoring.

What spatial distribution comes down to is this: because air pollution varies so widely from place to place, only by having more instruments in more places over a wider range of geographical terrain can scientists obtain a more accurate picture of air quality.

Having too few instruments spread out over too wide an area has long plagued experts in the field of air quality monitoring. By spreading more sensors to more places, PurpleAir helps overcome this fundamental problem posed by the spatial distribution of air pollution.

“Wherever you place that instrument, you’re only going to measure the air quality in that specific location at that specific time. One instrument cannot measure air quality in a whole city,” explains Wexler.

Motivating Citizens Through Community Science

The kind of movement that experts believe PurpleAir has spawned stems from the sensors’ low cost, ease of use, and flexible installation (sensors can work both for indoor or outdoor measurement).

Sensors are finding their way into schools and STEM classes, where students are able to see first-hand the state of air quality wherever they live. According to the American Lung Association’s annual “State of the Air” report, nearly half of all Americans live where air pollution reaches unhealthful levels — with 34.2 million children under the age of 18 being among those affected, many suffering from asthma.

Citizen Scientist — Mike Hekkers, a resident of Juneau, Alaska, is shown standing next to his PurpleAir sensor installed at his home in 2019. The City and Borough of Juneau, along with the Alaska Department of Environmental Conservation, have launched a project to recruit volunteers to help monitor air quality near Juneau’s busy cruise ship terminal. The project has installed a network of PurpleAir sensors around Juneau, a city with population around 32,300. And officials intend to gather much-needed data to determine the extent, sources and precise location of air pollution in Juneau. Image source: Juneau Empire.

Armed with more accurate data, these citizen scientists are helping to motivate interest across the country, inspiring not only learning but political action. Many are motivated to do something about the growing problem of air pollution where they live, work or play.

Measuring Particles Twenty Times Smaller Than a Human Hair

PurpleAir is in a class of air quality monitor that measures airborne particulate matter (PM). Larger particles (referred to as PM10) include dust, pollen and mold. Smaller particles (PM2.5) can result from wildfires, refining fossil fuels, and driving our cars.

Air quality scientists often stress two important facts about particulate matter and air pollution: 1), particulate matter is usually so small that we cannot see it or smell it; and, 2), we are inhaling particulate matter from the air all the time.

Air Pollution is Measured in Microns —PurpleAir sensors measure airborne particulate matter in billionths of a meter, particles so small they are 9-36 times smaller than a grain of beach sand, or 5-20 times smaller than the width of a human hair. Particulate matter can become especially harmful to human health when it interacts with chemicals and sunlight in the atmosphere. Image source: EPA

Particulate matter becomes unhealthful when it interacts and bonds with chemicals in the air, including sulfur dioxide and nitrogen oxides. Exposure to sunlight can cause particulate matter to form Ozone, a harmful and all too common air pollutant.

The smallest particulate matter (PM2.5) is considered more dangerous to humans because these lighter particles can remain suspended in the air for a long time — longer compared to larger and heavier particulate matter. And with more time in the air, PM2.5 has a greater likelihood of interacting with sunlight and other chemicals, exposing humans to more harmful air with each breath we take.

Normally, particulate matter remains low but can flare up due to a wide range of natural elements, such as wind, barometric pressure or high temperatures, or man-made events like refinery flares, diesel burning cars and trucks, mining operations, or in times of forest fires. Even fireworks can trigger elevated levels of particulate matter.

What scientists like most about PurpleAir is its ability to gain a more representative picture of air quality in areas where official sensors are lacking, especially in areas where air quality may be worse than normal, such as near refineries, heavily used roadways, shipping terminals and mines.

Sensors Prompt Praise from Scientific Scrutiny

In a recent study, scientists at the Lawrence Berkeley National Laboratory (LBL) used the wildfires that raged across western states to put air quality monitoring to the test.

They wanted to see how well low-cost sensors like PurpleAir perform compared to regulation-grade instruments during incidents of especially high amounts of airborne particulate matter. Their findings — encouraging for PurpleAir — reveal strongly consistent correlations in readings when changes in air quality occur over time.

Accuracy Put to the Test during Wildfires — In a recent study, scientists at the Lawrence Berkeley National Laboratory compared PurpleAir sensors with top-of-the-line air quality monitoring equipment during times of wildfires when levels of particulate matter are especially high. As particulate matter went up, the sensors correlated positively with their readings, leading air quality experts to conclude the low-cost sensors performed reliably well. Image source: Lawrence Berkeley National Lab.

“We compared the low-cost monitors to one that is used by regulatory agencies in air monitoring stations. It turns out their correlations are phenomenally good. When one goes up, the other goes up at the same time, and it is proportional. That gives us a lot of hope for being able to use them for real information,” said Woody Delp, a senior mechanical engineer who studies air quality instrumentation and one of the lead authors of the LBL study.

Feeding The Web With Citizen Science and the Internet of Things

PurpleAir has achieved for air quality what Waze, the GPS app, has done for navigating through traffic jams.

With an open design, PurpleAir’s biggest achievement may lie in its ability to share reliable, up-to-the-minute data on air quality and push that data over the internet for display on websites for all the world to see.

Through a simple Wi-Fi interface, measurements from any sensor can be streamed live over the internet for display on any number of websites, provided they are set up to receive the data in its standardized format.

More Sensors, More Data, More Websites — As recent wildfires raged across the West, a vastly more detailed picture of air quality emerged. PurpleAir sensors collect standardized data that can be shared via internet Wi-Fi and the data can be displaced on a variety of websites using the official Air Quality Index (AQI). This promotes greater access for government officials, scientists and the public.— Screenshot from September 11, 2020, from the PurpleAir website.

On its website, PurpleAir sensors display air quality measurements using the Air Quality Index (AQI), a standard measure used by official government agencies like the E.P.A. The data is then stored and archived as part of PurpleAir’s internet service offering.

Other websites, such as AirNow, an official source that is working in partnership with many air resources government agencies, including the E.P.A, NASA, NOAA, the National Park Service, and the U.S. Forest Service, has begun overlaying data from PurpleAir sensors alongside official data from government instruments. This further reflects PurpleAir’s growing acceptance within scientific circles.

Changing How We Think about Field Science Monitoring

For decades, air quality experts believed that having a single, expensive, high-quality, regulation-grade instrument located in one city or one area was enough to provide an accurate picture of air quality.

Today, the PurpleAir sensor is turning this traditional assumption upside down, by radically reshaping what’s possible. And with the success of PurpleAir for air quality, experts are re-thinking how low-cost instruments might soon find their way into other avenues of science where field monitoring is critically important.

In the future, environmental monitoring will look different, thanks to PurpleAir. Already, sensors are being developed to measure Ozone and other harmful pollution — using the same low-cost sensor design that has made PurpleAir a movement.

Other areas of sensors and monitoring may include noise levels and water quality where sharable data could help inform scientists about noise and water pollution. Low-cost sensors may soon find their way to lakes, rivers and streams near oil refineries or pipelines, locations typically not served by many official instruments.

Professor Wexler summed up the phenomenon: “Sensors like PurpleAir have opened up so many opportunities here: for education, for people to have greater appreciation for the quality of their air — which may not be clean even though it looks clean. And for scientists and engineers like me, those who really want to understand the spatial distribution of air pollution in a city or a region, wow, what a resource these things are.”