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Why some of the US has the most polluted air in the world right now

Canada’s smoke blanketing the US is just the latest example of intensifying wildfires.

Smoke shrouds the sun as it rises behind the skyline of lower Manhattan in New York City on June 7, 2023.
Gary Hershorn/Getty Images
Rachel DuRose is a Future Perfect fellow, covering climate change, housing, mental health, and more. Rachel previously wrote about the workplace, hiring, and executive leadership for Business Insider.

New York City has had the worst air quality of any major city in the world for much of this week, according to air quality technology company IQAir. Now this smoke is spreading over other major cities, like Philadelphia, Washington, DC, and Detroit, and will soon blanket swaths of the southern and western US.

On Tuesday morning, the National Weather Service issued an air quality alert — a warning indicating high levels of air pollution and therefore related health risks — for residents in New York state, New Jersey, Pennsylvania, and Virginia. Unhealthy air pollution levels can lead to a range of adverse health reactions, from eye, nose, and throat irritation to decreased lung and heart function. It’s even worse for at-risk groups, such as children, seniors, and those with heart and lung problems.

Fortunately for New York City, where there’s smoke, there’s not always fire (at least in the immediate area). The flames causing this public health crisis are actually well over 300 miles away, in Quebec, Canada. Smoke is drifting across the northeastern US, and the dry winds accompanying it in New Jersey and Pennsylvania are increasing the risk of new fires cropping up.

“I don’t think people appreciate that smoke can travel for hundreds if not thousands of miles, and so it’s often that we don’t have control of the situation, even though we are dealing with the impacts of it,” said Edward Avol, professor emeritus of the environmental health division of the University of Southern California’s Keck School of Medicine.

Still, this extreme fire event and its long-ranging smoke trail indicate a much larger and concerning trend: wildfires are getting worse, lasting longer, and occurring more frequently, primarily due to climate change. Although wildfires are a natural part of an ecosystem’s life cycle, when extreme, they create catastrophic damage to both the natural and human world. The crucial thing, experts told Vox, is that we must learn to adapt, especially as extreme weather events become more regular.

“There’s no future where we don’t have fire,” said Matthew Hurteau, a biology professor at the University of New Mexico. “So we have to start thinking about: How do we live in a more smoky world?”

Climate change is making fire season more severe

Canada is on track to experience its most destructive wildfire season on record. More than 160 forest fires raging across Quebec contribute significantly to this unfortunate milestone. The province’s fire season normally begins in early May, and usually destroys only a square mile by early June. But this year, fires across the province consumed 600 square miles by June 3. (For more on why much of eastern Canada is having such an unusual season, read Benji Jones’s explainer.)

Last week, the Canadian province was only battling 10 blazes, but that number soared to 153 fires on Monday. As of Tuesday, Quebec only had enough wilderness firefighters on the ground to fight 30 of these fires, but Quebec Premier François Legault said in the coming week, 200 firefighters from France and the US will join the approximately 480 wilderness firefighters already on the ground.

Three ingredients — fuel in the form of vegetation, ignition via human causes or lightning, and hot, dry, windy weather — create the perfect conditions for extreme fire events like this, said Michael Flannigan, the research chair for predictive services, emergency management, and fire science at Thompson Rivers University in Canada.

“You get all three, you got fire,” he said. “The bottom line is the drier the fuel, the easier for fires to start, easier for fires to spread, and more fuel available to burn, which leads to higher-intensity fires which are difficult to impossible to extinguish through direct attack.” The fires in Quebec started due to lightning strikes, and low humidity and rain.

All three of these conditions are becoming more common due to climate change. Our atmosphere acts like a sponge, absorbing water from our ecosystems, said Hurteau, who studies climate change mitigation and adaptation in forest systems. The size of our atmospheric “sponge” depends on the temperature: the hotter the climate, the bigger the sponge.

Because of climate change, this sponge is gulping up a lot of our planet’s moisture, leading to drier, more fire-prone regions. “Those forests burn periodically. I think what’s unique about this year is that the forests are so dry that the fires are many times larger than they normally are,” said Hurteau.

In addition to worsening fires, climate change and the fossil fuels that cause it are increasing air pollution, both directly and indirectly. At a 2020 House Committee on Oversight and Reform hearing, Drew Shindell, a professor of earth science at Duke University, stated that limiting global warming to 2°C would prevent 4.5 million premature deaths (some due to air pollution) over the next 50 years.

A ferry is seen in relatively clear view passing in front of the Statue of Liberty in New York City, which is obscured in a red-brown haze of smoke.
The Statue of Liberty is shrouded in a reddish haze as a result of Canadian wildfires on June 6.
Lokman Vural Elibol/Anadolu Agency via Getty Images

Most of New York state, Connecticut, and parts of Pennsylvania and Massachusetts reported “unhealthy” Air Quality Index (AQI) levels Tuesday and Wednesday. AQI indicates the level of health concern from air pollution and provides guidance accordingly. The number, which is shared by the EPA, falls between zero and 500. As Vox’s Rebecca Leber explains: ”AQI numbers are color-coded from ‘good’ to ‘hazardous’: The higher the number, the worse the pollution and the darker the colors.”

An AQI of 101 to 150 — the orange zone — means the air is unhealthy for sensitive groups, like people with heart or lung disease, or children. New York City entered the red zone (150-200) for most of Tuesday, crossed into the purple zone that night (with an AQI up to 226), and reached the maroon tier Wednesday afternoon, with an AQI of 413 in parts of the city. At the red, purple, and maroon levels, the air is unhealthy for all groups and people should limit or completely avoid spending time outdoors.

To put it in perspective, the air quality in New York City hit the low 400s and some areas of upstate New York had reached levels as high as 460 on Wednesday afternoon. California’s AQI in the Bay Area during the peak of its notorious 2020 wildfire season lingered in the mid-200s. Early Thursday morning, Philadelphia had an AQI in the 360s.

Low- and high-pressure wind systems distribute the smoke and pollution from wildfires in different ways. “Sometimes it’s aloft, and so you get those gorgeous sunsets and sunrises but it doesn’t affect the air quality of the surface,” said Flannigan. “Sometimes their trajectory takes it to the surface, and you get what you got now in New York City.”

The New York Department of Environmental Conservation issued a citywide air-quality health advisory Tuesday, and NYC public schools will not have outdoor recess. Mayor Eric Adams said in a statement that conditions are “expected to deteriorate” Wednesday afternoon and evening.

Unfortunately, the incidence of extreme fire events like these will only become more likely from here, the United Nations Environment Programme predicts, with a 14 percent increase projected in the next seven years. “Some people like to call it a new normal,” said Flannigan of these fire events. “I don’t like that term because normal sounds like a steady-state plateau. We’re on a trajectory and it’s downhill.”

This isn’t to say all wildfires are universally bad. In moderation, fires serve an essential role in the natural world. Forest fires clear old, dead foliage, and release seeds that then sprout into new healthier, stronger growth.

But now, warmer and drier climates create these extreme fire events which prevent forests from regenerating post-fire. And, it’s important to note that not all types of forests can withstand the same frequency of fires, said Hurteau. For example, boreal systems, which are found across Canada, should burn very infrequently, he added.

“If it burns too frequently, you end up completely changing the vegetation,” said Hurteau. “Depending on the system, we can intervene in ways, and in some places that might be lighting fires, so that we’re restoring ecologically appropriate fire. And then in some places, it’s going to be trying to exclude fire.”

What to do when the air quality is unhealthy (or if smoke is coming your way)

Between 1960 and 2000, the air quality in the US was improving, but in recent years pollution from climate change-caused fires, droughts, and heat have begun to unravel this progress. Globally, air pollution results in an estimated 7 million premature deaths annually, which means recognizing the signs of this sometimes invisible killer is vital.

You can check AQI levels on your phone’s weather app, the EPA’s AirNow website, or with a physical air quality monitor. When AQI levels are in the red zone, like in New York currently, the guidance is to stay indoors and try to prevent smoky air from coming inside. Seal doors and windows as much as possible, and ensure that air conditioning systems have the right filtration systems. For those experiencing unhealthy air quality, even a window AC unit is “better than nothing,” said Avol, since at minimum it’ll filter larger particles. If you have a HEPA air filter lingering around from the early days of the pandemic, now it’s a good time to turn it on.

We also often underestimate exactly what we’re breathing in. It’s not just the smoke from a wildfire that can do damage, but also the way the particles from a fire chemically react in the air, which increases the level of other contaminants, like ozone, said Avol.

If a wildfire burns in a forest, then it’s primarily shrubbery and trees turning to ash, but when a fire destroys homes, power lines, cables, and other materials, it can release other dangerous, non-organic particles.

“The initial thing that people think of — because of the smoke — is it must be wood burning,” he said. “Which, 90 percent of the time that’s a big part of it, but it’s not the only thing and may not be the only thing of health concern.”

These chemical reactions that occur in the atmosphere also mean that the age of the smoke affects its toxicity. “Old smoke is more hazardous than new smoke,” Flannigan said.

If you can’t stay indoors, then following the same masking rules used to manage the Covid-19 pandemic provides the most significant level of protection. When possible, wear an N95 mask secured tightly across your face, covering your nose and mouth, said Avol. Avoid strenuous activity outdoors — such as a run — if you’re in a sensitive group. (Even if you are healthy, it’s still worth limiting your exposure outside as negative air pollution effects are cumulative.)

Last, because air quality can have such a detrimental effect on vulnerable populations — children, the elderly, pregnant people, those with lung and heart problems — check in on neighbors and loved ones. If you or someone you know is experiencing symptoms like dizziness, aggravated cough, or headaches, try to head to cleaner air indoors with the AC running. If the symptoms intensify to include chest tightness, pain when breathing, or difficulty breathing when not doing physical activity, seek medical attention.

These methods aren’t foolproof, but they will help us live through the smokier future ahead. “Even if we shut off fossil fuel emissions tomorrow, we still have a certain amount of warming in the system that’s already happened,” said Hurteau. “We’re going to have to figure out how to live with it. We’re going to have to figure out how to manage our relationship with fire, and we’re going to have to figure out how to manage the ecosystems as they’re impacted by fire in different ways.”

Update, June 8, 11:10 am ET: This story was originally published on June 7 and has been updated multiple times, most recently to reflect the current air quality information.

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