For years, Cynthia Robertson had a particular morning routine: Every day, she would display a flag on her front porch in Sulphur, Louisiana, the color of which corresponded to the current air quality. On one far end of the spectrum, a purple flag meant there was hazardous air filled with particulate matter, and everyone’s health effects were increased; on the other end, a green flag meant the air quality was “satisfactory,” with air pollution posing little or no risk. In between were red, orange, and yellow flags.
Residents already know there’s pollution in their neighborhood, thanks primarily to the 16-plus industrial plants that surround their city. “We can smell it,” Robertson says. But the flags helped to quantify just how bad the air was on any particular day.
Robertson is the executive director of Micah 6:8 Mission, an environmental nonprofit in Southwest Louisiana. The front porch where she would display flags was actually the nonprofit’s property, where there’s also a community garden, an orchard, a pond, goats, chickens, and educational programs open to the community. Micah 6:8 Mission would also post a picture of the day’s flag, and the color chart explaining its meaning, to its Facebook page—details that helped residents gauge whether they should be spending time outdoors, or wait it out inside.
“Particulate matter is a killer,” Robertson says, referring to particles that are 2.5 micrometers or less in size, and which can come from all sorts of pollution, from vehicle exhaust to burning fuels. “That tells you, ‘Don’t go out and garden this morning. Wait until the air calms down after the overnight releases from the plants.’”
“We didn’t want to be the poster child for ‘here’s what happens if you defy the CAMRA law’”
But last year, Robertson stopped displaying the flags and making those Facebook posts. In 2024, Louisiana passed a law (the Community Air Monitoring Reliability Act, or CAMRA) that seems to prohibit community groups from using their own air sensors and sharing air quality data—particularly if the data points to bad air quality—or risk hefty fines.
Any sharing of such data has to include clear explanations, context, and all “relevant uncertainties” around the data, but community groups say the state hasn’t made clear what that all means, exactly, or what they could do to make their air quality comments acceptable.
CAMRA also prohibits groups from sharing information for the purposes of enforcement actions or to allege violations of clean air laws. Environmental lawyers say this means that sharing air monitoring data is allowed if it shows that the air quality is good, but that data can’t be shared if it shows the air quality is bad.
“Because there wasn’t any clarity on what they considered [relevant uncertainties and so on], we said okay, we can’t afford to run afoul of this,” Robertson says. (Fines begin at $32,500 per day.) “We didn’t want to be the poster child for ‘here’s what happens if you defy the CAMRA law.’”
That uncertainty, experts say, essentially means the law not only discourages air quality monitoring but also discourages community groups from talking about their own air quality data—constraints that potentially run afoul of the First Amendment.
Though the Louisiana law may be particularly strict, it’s not the only law that has recently been passed or considered by state legislatures around the public’s ability to monitor and use air quality data. That’s a trend environmentalists find concerning as the Trump administration rolls back environmental protections, gives coal plants free rein to pollute, and restricts access to environmental data.
The importance of low-cost community air monitoring
Sulphur, Louisiana, sits downwind of petrochemical sites, and the region has experienced a disproportionate level of health impacts from pollution, including rates of cancer higher than the national average. Micah 6:8 Mission’s air quality alerts—first, thanks to a low-cost sensor from air quality monitor startup PurpleAir, and then from a sensor the nonprofit received as part of an Environmental Protection Agency grant—helped residents control their pollution exposure. People paid attention to the alerts: If the day’s flag was orange, Robertson says she’d hear people say, “Well, I guess I’m not going to garden this morning.”
The EPA does have its own air quality monitors, but they don’t give a full picture of air pollution. The EPA’s monitors are expensive and there are only a few of them in any given city. That leaves bigs gaps in the data. “What we know about air pollution, and particularly about air pollutants that vary in space and time, is that what people are actually exposed to doesn’t necessarily correspond with what’s measured at the EPA sensor,” says Noelle Selin, an atmospheric chemist at the Massachusetts Institute of Technology.
Air pollution can be an extremely local issue, differing from one city block to the next. The EPA’s sensors may miss all the pollution from car exhaust happening on one particular traffic-heavy street, or all the downwind pollution from factories if the agency’s monitor is placed upwind.
Low-cost sensors like those from PurpleAir—whose sensors start at under $200, and which purports to have the world’s largest air quality dataset—have helped fill some of those data gaps. “The government network is monitoring background levels [of air pollution],” says PurpleAir CEO Adrian Dybwad. “It’s not meant to tell you your kids’ school has wildfire smoke around it right now, or to bring your kids inside because the air quality is looking poor.”
PurpleAir can provide a more hyperlocal picture. Dybwad hears from users often about how they use PurpleAir’s data: It helps parents manage their kids’ asthma by choosing when to let them play outside, and athletes use it to plan their exercise schedules. In one instance, in Arkansas, a mass of buried tree stumps caught fire, sending smoke up from the ground and out into the streets. No one was paying attention to that, Dybwad recalls hearing, until PurpleAir sensors near the site spurred local news coverage that led to an EPA response.
Even scientists have come to rely on low-cost community air monitors. And though a low-cost sensor may come with a little less accuracy and a few more uncertainties than a $10,000 model, it still provides useful, real-time, and vital information—particularly, Selin says, around pollution exposure for certain populations that aren’t well covered by EPA sensors.
“No one is using PurpleAir’s data to enforce regulations on polluters”
Micah 6:8 Mission is now part of a federal lawsuit, alongside six other community groups, alleging that Louisiana’s CAMRA law violates their constitutional rights—primarily, the right to free speech. That lawsuit was filed in May, and the lawyers involved expect a response to their complaint from the state this week.
Community air monitoring has been growing across the country because people are simply more aware of bad air quality events, like intense wildfires or pollution that they can see or smell for themselves.
It’s also grown thanks to the 2022 Inflation Reduction Act, which included $117 million in grants for community air pollution monitoring and supported the purchase of air quality sensors. The CAMRA law came about as a way to standardize such community programs—and was backed by industrial groups like the Louisiana Chemical Association.
Kentucky also passed a law this year preventing low-cost air sensors from being used as the basis for regulatory enforcement of environmental laws. Ohio considered legislation that would restrict community air monitoring data from being used for the enforcement of environmental laws, though that language was ultimately removed. And in West Virginia, proposed statutes would have restricted community air monitoring data from being used for fines or any regulatory- or rule-creation actions, though those statutes have so far failed.
Dybwad warns that there have always been limitations on how people can use data from low-cost sensors like those from PurpleAir. For something like a court case, to enforce environmental regulations, or to take a polluter to task, you need certified data, he says, noting, “That’s always been the case. No one is using PurpleAir’s data to enforce regulations on polluters.”
The fight to keep monitoring the air
So these bills may not materially change how individuals or community groups use low-cost sensors. But according to David Bookbinder, the director of law and policy at the Environmental Integrity Project—which, along with Public Citizen Litigation Group, filed that lawsuit on behalf of the community groups—they’re still part of a disconcerting trend. (The Environmental Integrity Project also publishes Oil & Gas Watch News, which has reported on this wave of bills.)
“That’s why we thought it was important to go challenge the Louisiana statute and say, ‘You can’t tell people what they’re allowed to say,’” Bookbinder says. To him, the law is “designed to discourage monitoring, and to absolutely gag people from talking about it.”
The fact that Trump is now president adds even more concern, Bookbinder says. Trump has already repeatedly rolled back environmental protections, including giving the worst-polluting coal power plants exemptions from toxic pollution limits. That individuals and community groups can access low-cost sensors to monitor whether the air they’re breathing is healthy is “incredibly important,” Bookbinder says, especially when “the EPA is clearly going out of the business of protecting public health.”
Community air sensors have helped put pollution data into anyone’s hands, and any threat to that would hurt Americans. Selin, the MIT professor, doesn’t have specific knowledge of the Louisiana lawsuit, but she emphasizes how crucial such sensors are, saying, “It’s really important to encourage people to understand their environment and to democratize access to measurements and science.”
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