"Very unhealthy" and "hazardous" air quality put the health of people across the Washington, D.C., area at risk Thursday as smoke from wildfires in Canada brings some of the most polluted air ever recorded in the region.
The air quality worsened from a code red ("unhealthy") on Wednesday to purple ("very unhealthy"), and then maroon ("hazardous") in parts of D.C. on Thursday, the federal government's AirNow website said.
The air quality since has returned to code red, Storm Team4 Chief Meteorologist Doug Kammerer said, but for a time Thursday, the D.C. area had the worst air quality in the world.
The Metropolitan Washington Council of Governments (MWCOG) issued a code purple health advisory, noting it's the region's first code purple day for fine particle pollution.
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“We’re asking people to take heed. I think the basics of it are: If you don’t have to be outside, don’t be outside. If you do need to be outside, wear a mask,” D.C. Mayor Muriel Bowser said Thursday morning.
Heavy smog surrounded D.C.’s monuments and Northern Virginia’s airports. Many people on the streets wore face masks.
The Washington Nationals postponed their Thursday game against the Arizona Diamondbacks. Tickets for the delayed game will be honored for the rescheduled date, June 22, the team said. The Washington Commanders moved their practice into their indoor practice bubble.
The National Zoo closed because of the poor air quality, schools moved recess indoors and people who work outside reported feeling weighed down. Anyone who needs to spend time outside is advised to wear an N95 or KN95 mask.
People with heart or lung conditions are urged to be extra cautious and reduce activity levels.
It’s the unseen pollution that poses the greatest health risk, health and environmental officials say.
D.C.’s Air Quality Index (AQI) for PM2.5 — teeny tiny and potentially dangerous particulate matter in the air — hit 314 on Thursday morning. Anything above 301 is considered hazardous.
PM2.5 particulate matter is so small that it can get deep into the lungs, and possibly your bloodstream. Even short-term exposure can be dangerous, according to the American Lung Association (ALA).
“Premature deaths from breathing these particles can occur on the very day that particle levels are high, or up to a month or two afterward. Most premature deaths are from respiratory and cardiovascular causes,” the ALA said.
Coughing, wheezing, reduced lung function, asthma attacks, heart attacks and strokes are also linked to particle pollution.
That’s why health officials are encouraging people to stay inside and avoid activities that would lead them to breathe in more polluted air.
Air purifiers can help reduce pollution in your home; even running an air conditioner can help — as long as it doesn't pull in air from outside, AirNow said. You can also use a box fan, cheap filter and some twine to create a DIY filter, NBC News' Jacob Ward explained on TikTok.
DC mayor urges everyone to 'stay indoors as much as possible' or mask
All groups should stay inside as much as possible, and anyone who must work outside should reduce outdoor time and wear an N95 or KN95 mask, Bowser said in a release Thursday.
"This problem is likely to continue or worsen through Friday," Bowser said on Twitter.
President Joe Biden postponed a Pride Month celebration with thousands of guests on the White House lawn. The event scheduled for Thursday night will be held on Saturday instead. It’s intended to be a high-profile show of support for LGBTQ+ people at a time when the community feels under attack and the White House has little recourse to beat back state-level legislation against them.
Metro warned that the smog may be visible in Metrorail stations, as it’s an open-air system. Metro trains and buses have filtration systems designed to purify the air, the agency said.
Prince George’s County suspended health, construction and property enforcement inspections for Thursday.
In Montgomery County, Ride On buses will be free to ride for the duration of the code red alert in an effort to get people indoors. Ride On Flex and Ride On Extra bus service was suspended as of 3:30 p.m. Thursday and for all of Friday.
Brace for impacts on air travel
The Federal Aviation Administration said reduced visibility from the smoke affected air travel on Thursday.
"We will likely need to take steps to manage the flow of traffic safely into New York City, D.C., Philadelphia and Charlotte," the FAA said.
There were more than three dozen cancellations at the airports in the D.C. area on Wednesday.
Delays and cancellations began early Thursday at Ronald Reagan Washington National Airport.
Schools cancel outdoor activities, field trips
Prince George’s County canceled all outdoor programming because of the smoky conditions. Officials urged people to avoid visiting playgrounds, trails, parks and golf courses. The facilities that provide indoor space will remain open.
Prince George's County, Montgomery County, Fairfax County and D.C. Public Schools all canceled outdoor activities including recess on Thursday. Fairfax County canceled field trips.
On Wednesday, the poor air quality caused problems up and down the East Coast, including travel delays and school cancellations. In New York City, the air quality was ranked as the worst in the world, and a Yankees game was postponed because of the hazardous conditions.
Poor air quality can harm your health
Dr. Bobby Mahajan with the American Lung Association recommended that people with underlying heart and lung conditions stay inside.
“People with emphysema, people with asthma — those individuals are at higher risk of getting exacerbations of their disease. So, they've got to be really careful about their symptoms," he said.
Mahajan said everyone should keep an eye out for any symptoms. Even young, healthy people may feel the effects of the smog if they walk around outside or go running.
Don’t let a lack of immediate symptoms in children fool you. Kids’ health can deteriorate as a day progresses, Dr. Shilpa Patel of Children’s National Hospital said. Look out for any irritation to the airways, particularly for a child with asthma.
More than 400 active wildfires are still burning in Canadian provinces and territories.
When will the air quality improve in the DC area?
The bad news is that the air Friday is still expected to be very unhealthy to breathe, Storm Team4 said. Expect to be under code red and code orange (unhealthy for sensitive groups) throughout the day.
The good news is that improvements are possible Saturday. Sunday is finally looking better, after the wind changes directions.
The Associated Press contributed to this report.
Stay with NBC Washington and Storm Team4 for updates.
