Additional reporting by Katie Honan and Jose Martinez

This article, which was first published on June 7, has been updated.

On June 7, the air quality index in New York City reached 484 AQI, a measure of various air pollutants on a single scale — the highest ever recorded here. Flights were grounded. Public beaches closed. And alternate side parking was suspended.

That may not be the last time this summer that smoke from wildfires will muddle the skyline and smell up city streets.

In recent summers, wildfire smoke has reached New York City from the West Coast, but the haze blowing in from Canada this year was the most severe in decades. And we’re likely in for more of the same as a result of climate change.

“Climate change leads to things like warmer temperatures, worsening drought, drier soil, etcetera, which all act to make wildfires larger and more intense,” said Dan Westervelt, an associate research professor at Columbia University’s Lamont-Doherty Earth Observatory. “It also causes the fire season to last longer.”

More fires elsewhere means smoke could blanket New York City more frequently, depending on weather patterns. The higher the AQI scores, the worse the air quality. Scores above 300 are considered hazardous.

The poor conditions — brought on by smoke in the atmosphere that contains chemicals and particulate matter that can damage the lungs, heart and other organs — caught many New Yorkers off guard in early June, particularly since city officials were slow to communicate as the haze poured in.

THE CITY spoke with experts about how New Yorkers should stay safe during the dip in air quality. Here’s our guide, which we will continue to update with new information:

How worried should you be?

If you are in what officials call a vulnerable or sensitive group — the elderly, pregnant people, children and people with respiratory, heart or other health issues — you should take this seriously. Stay inside and monitor any symptoms as they arise, health officials say. Particulate matter exposure can worsen heart and lung diseases, trigger asthma attacks and heart attacks.

All New Yorkers should limit their outdoor activity. “Avoid going outside unless you absolutely have to,” said city health commissioner Ashwin Vasan in early June.

How do I make sure my indoor air is clean? Can I run an air conditioner?

Staying inside isn’t enough without taking steps to ensure the air is as clean as possible. THE CITY wrote a guide to doing just that, focusing on monitoring the air quality, reducing sources of indoor pollution and filtering the dirty air.

If you do run your air conditioner, make sure the filter is high-quality, clean and functioning properly. Otherwise, the air conditioner may just be blowing in dirty air from outside without cleaning it — which won’t help you at all.

The good news, said Ilias Kavouras, professor of environmental sciences at the CUNY Graduate School of Public Health, is “the vast majority of air conditioners don’t bring outside air inside.”

“They cool it down by circulating indoor air,” he told THE CITY.

The Environmental Protection Agency has more tips here on using an air conditioner during smoky conditions.

Run a high-quality air purifier, if you have one — and if you don’t, you can make a DIY version using air filters and a box fan. Some experts recommended purchasing air filters rated MERV-13 in bulk in advance of smoke events, so they’re ready to go when you need them.

Dr. Mary Prunicki, director of air pollution and health research at Stanford University’s Sean N. Parker Center for Allergy and Asthma Research, suggested holding off on cooking with gas stoves when ventilation isn’t possible, as combusting a fossil fuel indoors negatively impacts air quality.

Should I open my window?

Generally, you should not open your window if the air quality is bad. Instead, keep your windows as sealed and closed as possible. You can stuff rags, towels or sheets against leaky windows and doors to keep the smoke out.

However, heat can compound the negative health effects of exposure to smoke. Those without air conditioning must find a way to cool their homes, as heat can be “a deadlier and more immediate threat than smoke,” according to Sarah Coefield, air quality specialist at the Missoula County Health Department.

“That may mean opening the windows to let in cooler air (and smoke). Once your home has cooled down, close doors and windows and turn on your air cleaning solution to get rid of the smoke,” she said via email.

What should I do if I have to work outside? Should I wear a mask?

Yes, according to Vasan. While the city has an air quality alert in effect, wear a tight-fitting, high-quality mask like a KN95 or N95 while outside — whether you’re working or just taking a walk.

Kavouras of CUNY echoed that advice.

“We should be very cautious and concerned,” he said. “People should wear their masks. I hope by now everyone at least has a couple of them leftover from what we went through the last three years.”

Should I exercise outside?

No. Vigorous activity outside, even for healthy people, can cause symptoms like inflammation, fatigue, difficulty breaking or irritation of the eyes, nose or throat. Heavy breathing can result in increased inhalation of particulate matter.

“This is not the day to train for a marathon,” said Mayor Eric Adams in early June when the city had record high pollution.

When should I see a doctor or go to the hospital?

Each individual has their own level of sensitivity to smoke, so it’s important to seek medical attention if you feel as though there’s something wrong.

“If you feel like you’re experiencing any type of respiratory distress or obviously any type of anything related to your heart — especially if you’re an older person, especially in more vulnerable populations or those who have pre-existing conditions — you should just go in and get checked out,” said Prunicki.

She also advised refilling inhalers or other prescriptions for asthma in advance of smoky days. 

How do I take care of my pets?

Smoke can affect the health of animals and, just like humans, pets with cardiovascular or respiratory problems are at a higher risk. Keeping pets indoors as much as possible and maintaining a high air quality in your home are important for animals as much as for humans. 

“Animals process poor air differently. They have different respiratory systems, and they can’t wear masks, so we are recommending that you don’t take your pets outside either, or at least limit and reduce the amount of time you have your pets outside,” Vashan said on June 7.

If animals are experiencing coughing or gagging, difficulty breathing, eye irritation, weakness or other symptoms, you should call your veterinarian, according to guidance from the American Veterinary Medical Association.

How do smoky days compare to “typical” bad air quality days?

An AQI between 0 and 50 is good, with little to no risk, according to the National Weather Service. New York City’s average air quality in recent years has remained in that range, per IQAir, a Switzerland-based air quality tech company.

The threshold for an air quality alert from the city’s Office of Emergency Management is 100 AQI, according to Zachary Iscol, the agency’s commissioner.

Dr. George Thurston, a professor of medicine and population health at New York University School of Medicine, said the particulate matter from wood burning is less toxic — on a per-mass basis — than the particulate matter that comes from burning fossil fuels.

New Yorkers should worry more, he said, about the toxic fumes they breathe every day from traffic exhaust than about isolated, relatively rare wildfire smoke events.

“Over the long haul, those have a much greater cumulative effect on their health than a brief high episode like this,” Thurston said in an email.

And while New York City’s air quality has improved considerably over the past few decades as a result of city, state and federal regulations, the same meteorological effects that blow smoke from wildfires elsewhere also blow pollution into New York City.

“In so-called normal times, we get a fair amount of our pollution from power plants in the midwest, like Ohio,” said Dr. Steven Markowitz, director of the Barry Commoner Center for Health and the Environment at Queens College, who for over a decade has run air quality monitors around the city.

People who live or work in neighborhoods that typically tend to have worse air quality because of power plants or industrial facilities located nearby or highways running through — like in the South Bronx — may be even more at risk than others. You can learn about different neighborhood’s usual air quality using this tool from the city health department.

The wildfire smoke would cause “a double whammy,” Thurston said. In those neighborhoods, which tend to be poorer, the rates of emergency room visits for asthma are three times higher than in more affluent areas.

He added that the most effective way to reduce air pollution is to decrease fossil fuel combustion locally, as well as slash emissions from vehicles, buildings and power plants.

How safe is the air in the subway system?

There is no publicly available data on air quality within the train system, but during the early June smoke event, Dr. Terry Gordon, a professor in the department of medicine at NYU School of Medicine, sent two of his students to the Broadway/Lafayette stop to collect some.

They “measured nearly the same absurdly high particle concentrations above ground and in the subway,” Gordon said at the time. “So, yes, right now people should be concerned about the air quality in the subway stations and above ground. It appears that the wildfire smoke is penetrating the subways.”

During the June 7 smoke event, MTA spokesperson Kayla Shults said, “The MTA is closely monitoring reports of atmospheric conditions which are being pushed into the New York metropolitan area, including smoke, and recommends heeding guidance that the City and State are providing to the public.”

The agency appears to have different advice for its workers. In an internal bulletin sent out during the air quality emergency obtained by THE CITY, a New York City Transit safety official wrote that N95 or KN95 masks “must be provided to employees upon request.” 

Within train cars, the MTA has piloted air filtration systems designed to replace the air inside a car a dozen times an hour. But those systems are installed only in a fraction of subway cars.

Where can I monitor the air quality in my neighborhood?

There are a number of places to see what the Air Quality Index, or AQI, is in your area.

Sites like IQAir and AirNow provide real-time information about the concentration of pollutants in the air. The National Weather Service also publishes air quality notifications, as does the state Department of Environmental Protection.

Colleen Reid, a geography professor who researches smoke impacts at the University of Colorado Boulder, recommends installing the EPA’s Smoke Sense app — available on the App Store or Google Play Store — on your phone.

“You put in your zip code and it gives your current air quality index and tomorrow’s air quality index. It also has places where people can record their observations of the air quality and/or their symptoms, which the EPA uses for data analysis.”

Experts say it’s important to check on localized air quality, as certain neighborhoods experience worse effects, and the pollution in any given location changes over a day. 

Anything else I can do?

If you have capacity, make sure the people around you are okay and have what they need.

“When it’s really, really terrible and smoky, it’s a hard time for everyone. It’s stressful,” said Coefield. “That’s an opportunity for us to check in with our neighbors and our family and see how people are doing. Offer help if you can give it.”

Quinn Redwoods, director of Mask Oakland, which distributes masks during wildfire smoke events, encouraged giving out masks and educating others.

“If you’re reading articles about this, you’re probably more educated than the average person, so share that information and let people know,” they said.

Have a question for THE CITY newsroom about the air quality situation? Email with the subject line “Air.”