25 ozone. Fine particulate matter measuring 2.5 microns or less in width (PM2.5) ranks as one of the most concerning toxic air pollutants. In 2020, the US Environmental Protection Agency (EPA) and the US Forest Service (USFS) collaborated to release the AirNow Fire and Smoke Map, a first-of-its-kind map powered by GIS technology that combines official data on fine particulate matter with more granular readings from a vast network of low-cost sensors run by volunteers. Compared with older government air maps, the new map increased the total number of PM2.5 monitoring locations almost fivefold, to more than 900 cities. President Biden has called the enhanced map “an important tool,” and in early June 2023, a day after White House press secretary Karine Jean-Pierre mentioned AirNow. gov during a White House briefing, a record 12.4 million people visited. “It’s really important for EPA to be able to deliver this information,” John Millett, communications director for the EPA’s Air and Radiation Office, which runs AirNow.gov, told The Washingtonian at the time. The AirNow app, he added, “was actually able to edge out TikTok for highest number of downloads for a little while.” Enter your location at fire.airnow.gov, and you’ll likely see a map sprinkled with icons. Flames indicate reported fires, circles represent official AirNow monitors, triangles show temporary monitors set up by state or federal agencies, and squares indicate air sensors run by members of the public. Colors, from green to dark purple, indicate the quality of the air at that location, from good to hazardous. Click on any sensor and a pop-up box reveals more details. When the air quality index (AQI) value is above 100 for more than 24 hours, the air is considered unhealthy, according to the EPA, at first for certain sensitive groups of people, then for everyone as AQI values get higher. A reading of 300 or higher means the air quality is hazardous. In that case, cautions the map, “Avoid all physical activity outdoors.” The Rise of PurpleAir and Crowdsourced Air Quality Data Though it looks simple, the new map was a complex undertaking and built on a national air monitoring system, which was decades in the making. Under the Clean Air Act, a partnership led by the EPA and state and federal agencies, along with Canada and Mexico, built and maintains a network of air sensors now numbering in the thousands. Data from these monitors appears on the standard map at the EPA’s airnow.gov site and mobile app and informs 24-hour air quality forecasts developed by NOAA. But since 2020, air monitoring has undergone a technological revolution, led in part by a small company called PurpleAir. The company was born after a self-proclaimed tech geek named Adrian Dybwad grew worried about the choking dust blowing into his town of Draper, Utah, from a nearby gravel pit. Like many places, Draper has historically lacked extensive sensor networks to monitor airborne particulate matter; even big cities such as New York and San Francisco only have about a dozen government-managed sensors in the AirNow network. Checking the AirNow map didn’t help much. Buying his sensors was also out of the question: the systems on the market cost thousands of dollars and weren’t designed to quickly detect the effects of dust and smoke particulate matter. So Dybwad built his device, using low-cost circuit boards, PVC pipe, and lasers. He found enough volunteers around the Salt Lake Valley willing to host the homemade sensors and started building a small network before officially launching PurpleAir in 2015. The company, which now sells three models from $199 and up, has shipped more than 30,000 devices over the past five years. Users have the option of sharing their data with PurpleAir to enrich its real-time map. Like AirNow, PurpleAir by default uses the EPA’s AQI, which measures levels of pollution on a scale from 0 to 500. The index governs the five pollutants regulated by the Clean Air Act—particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. PurpleAir’s sensors only measure PM2.5. Climate Action
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