The thick blanket of smoke over the Northeast and Midwest -- funneling south from Canadian wildfires -- is chock full of toxic pollutants that are harmful to everyone's health.
But unlike man-made pollution, wildfire smoke can't be regulated by the Environmental Protection Agency, which is charged with protecting human health and the environment.
The EPA and the landmark Clean Air Act treat wildfires as exceptional natural events -- that is, events that aren't caused by humans and don't happen regularly.
"You can't say it's illegal for lightning to hit a tree and catch it on fire," said James Boylan, a top air quality official for Georgia's Environmental Division, and a member of the EPA's Clean Air Scientific Advisory Committee. "It's hard to regulate something that's naturally occurring like wildfires."
But the human-caused climate crisis is stacking the deck in favor of larger and more frequent wildfires as temperatures rise, and has renewed the debate over regulation.
The Clean Air Scientific Advisory Committee -- a group of physicians, state environmental officials and academics who are tasked with advising the EPA on air quality -- has written letters to EPA administrator Michael Regan asking the agency to take a harder look at whether wildfire smoke should be classified as a natural or exceptional event.
"A lot of the (committee) members felt that is something EPA ought to reconsider and not exclude, especially with climate change and the more frequent fires," committee member Dr. Mark Frampton, a pulmonary disease specialist at the University of Rochester Medical Center, told CNN. "It's certainly having adverse health effects on people."
Committee chair Lianne Sheppard, a public health professor at the University of Washington, said that while her committee's recommendation doesn't weigh in on whether wildfire smoke could or should be regulated, it emphasizes that raging fires are increasingly common.
"Treating these as exceptional events, that implies they're unusual. But they're getting to be so common that from a protecting public health view that doesn't make sense," Sheppard told CNN.
Other environmental experts called on the agency to stop classifying wildfires as natural events.
"These things are clearly, according to some in the scientific community, linked to climate change. That's linked to humans," said Jonathan Skinner-Thompson, a former EPA attorney and a law professor at the University of Colorado Boulder.
Experts say the task is extraordinarily tricky, made all the more difficult by the fact that the current smoke choking Northeast cities is coming from wildfires in another country.
"There are some things we just can't control," Boylan said. "Unfortunately, there's not a whole lot [to do] regulatory-wise besides greenhouse gas reductions. People just have to look after their own health and make smart decisions on days like this."
It's up to individuals to heed air quality warnings and stay inside, not exercise outdoors and use masks to avoid inhaling toxic smoke, Boylan and Frampton said.
What can be done?
If the EPA can't regulate wildfire smoke altogether, experts said it can tweak regulations to make it easier for states and Native American tribes to perform prescribed burns -- essentially, fighting fire with fire.
Even though the EPA considers wildfires natural events, prescribed burns are categorized as human-caused, which means there are more regulatory hoops to jump through before initiating a prescribed burn, Skinner-Thompson said.
"I get that tension there, but EPA and others have put out studies saying prescribed fire emissions health benefits outweigh the cost," he added.
Experts noted the EPA is issuing rules to address the underlying causes of human caused climate change -- pollution from burning oil, gas, and coal.
"By regulating greenhouse gases, in theory, that could reduce the number of wildfires, and EPA does have a number of initiatives for reducing greenhouse gases," Boylan said.
But ultimately, both are longterm solutions.
Room for Congress to act
For the EPA to make any significant changes to how it treats wildfire smoke, Congress would likely have to weigh in on the Clean Air Act. That could come with plenty of pitfalls of its own, according to Skinner-Thompson.
"In light of the political climate today, I bet both sides would like to amend the Clean Air Act and update it," he said, adding, "They're going to have very little appetite for consensus changes to the Clean Air Act to address wildfires."
Western lawmakers -- who represent the states with the largest wildfire threat -- said watching smoke fill Washington, DC, this week was concerning -- but also gave them hope that more could be done to prevent and fight fires.
Sen. Michael Bennet of Colorado, a Democrat, said the smoke enveloping DC could bring more urgency and understanding on wildfires from his East Coast colleagues.
"I wouldn't wish it on anybody, but a couple years ago when we had the smoke from the California fires, it made everybody pay attention here in a way that they didn't," Bennet told CNN. "I hope we'll act as a result of this."
"We have to recognize that given climate change, we're going to have more of these fires," Republican Sen. Mitt Romney of Utah told CNN. "The way we've addressed them in the past is going to be insufficient for the future."