Historic wildfires on the West Coast of the United States have filled the skies with burnt-orange haze and thick ash, forcing residents to consider whether it’s even safe to step outside and take in a lungful of air. A warming climate means that wildfire seasons will likely continue to grow in duration and destructiveness. As smoke blankets the Western states, people have increasingly turned to air quality measurements to understand the air they’re breathing.

This data has become easily accessible online only in the last few years. While government agencies have been monitoring air quality for decades as part of the requirements of the Clean Air Act, low-cost air quality sensors obtainable by the general public only recently took off, filling in the gaps with more localized and frequent readings.

Before air quality maps were available on apps such as AirNow, IQAir, and PurpleAir, “you would get the L.A. Times and look at the weather page and see what the prediction was,” says Joe Lyou, president and CEO of the Coalition for Clean Air, a nonprofit in California. That’s not especially helpful when thousands of acres are burning in your community.

Monitoring wildfire country

Tim Dye, a meteorologist who runs the air quality data firm TD Environmental Services, plans his personal activities using air quality information. During the wildfires in September, he called off a hike because it was smoky out, waiting a few days until there were blue skies and the air was clear.

“You wouldn’t go out playing golf in a rainstorm,” Dye says. “Why would you go out and run in the middle of a smog storm or a smoke storm?”

When the smoke is dense enough, you can smell it, and you might not need a phone app to let you know that the air is unhealthy to breathe. But when it’s just slightly hazy out, it’s difficult to know whether the concentration of fine particles is moderate or hazardous.

Smoke is full of carbon dioxide, carbon monoxide, and particulate matter. It can also contain other chemicals depending on what’s burning. During a wildfire, about 90 percent of the particles in the smoke are smaller than roughly a thirtieth the diameter of a strand of hair.

These particles, identified as PM2.5 (particulate matter measuring 2.5 microns or smaller), are so fine, they’re capable of entering your lungs and even your bloodstream. These are the particles in smoke that cause the worst health impacts, stressing people’s hearts and lungs. When looking at an air quality map to determine whether it’s healthy to go outside during wildfire season, you’re largely looking at the concentration of these microscopic particles in the air, as well as larger particles that are not as dangerous but can still be inhaled.

The numbers on these maps are from a scale known as the Air Quality Index (AQI), a uniform system developed by the Environmental Protection Agency. The AQI converts ambient concentrations of air pollutants into numbers ranging from 0 to 500, increasing from good to hazardous. Up to 50 is good, which means the air quality is satisfactory, and between 50 and 100 is acceptable air quality. Above 100, the air is classified as “unhealthy for sensitive groups”, and above 150 threatens some members of the general public. Above 200 presents a risk of health effects for everyone. Air quality during the West Coast wildfires was recorded above 500 in some areas, which is simply deemed as “beyond index.”

Three different types of monitors are used to take these measurements, says Charles Pearson of the California Air Resources Board’s Monitoring & Laboratory Division. Air monitoring stations in compliance with EPA regulations have trained staff continuously maintaining them to produce high-quality data.

Portable air monitors, about six feet tall, can also be deployed. These have filter tape on a reel “kind of like a cassette,” Pearson says. Air is pulled over the filter tape, which is then compared to a clean filter. These monitors can be set up in about 45 minutes, and while they aren’t as high quality as the stationary monitors, the data is close. Pearson says a trained technician visits the monitors every two weeks to clean, reset, and recalibrate them.

And then there are low-cost sensors, which are much smaller and less expensive than the other two. They are about the size of a coffee cup and provide near real-time measurements, using lasers to count particles in the air. The data is not as high quality and can be skewed by external factors, such as humidity or even a spider crawling into the sensor.

Citizen scientists can buy these for about $200, connect them to WiFi, and the monitor will show up on the associated air quality map. PurpleAir, a startup tech company, designs one of the more popular sensors, which are now used by the federal government and clean air agencies. Those who purchase their own PurpleAir sensor are able to register it on the company’s crowdsourced map, which allows them to go in and check the individual device’s readings in near-real time.

The lower-cost sensors available today have spread across the West Coast, and millions of people are now monitoring the air on websites and apps. IQAir, which provides real-time air quality data on its website and app, added more than two million new users between August 17 and September 10, when the wildfires picked up in intensity.

The future of measuring the air

The AQI scores on PurpleAir don’t always match the air quality measurements from professional monitors, as the lower-cost sensors tend to overreport particulate matter levels.

The EPA and other agencies are working to make corrections to the algorithms of low-cost sensors to churn out data more in line with higher-quality monitors. AirNow, the air quality map run by the EPA, launched a Fire and Smoke map this year that includes data from PurpleAir sensors. The commercial monitors allow coverage of communities that don’t have a high-quality air monitor nearby, providing hyper-localized data.

Dye says that the lower-cost sensors have gotten a lot more accurate over the last four or five years, but they are still susceptible to interference, such as an idling vehicle, a barbecue, or fog droplets.

The clean air agency is also working on solar-powered, satellite-linked data transmission, Pearson says, so that you could put a monitor anywhere, rather than just in areas with a network connection. Such sensors wouldn’t risk losing data if they lose power, and California has seen scores of power outages lately, some caused by fires, others planned to reduce the danger of sparks from downed power lines. When that happens, “you’re flying in the dark,” Pearson says.

New air monitoring technology affords the public the ability to easily measure something that they couldn’t access before. As wildfires become more frequent, and microscopic pollutants continue to spew into the air, checking the air quality might become as commonplace as checking the weather. “There’s an opportunity to get a better understanding of our environment and how it changes and how we fit into it,” Dye says.

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