Spain practices outside before the World Cup final as smoke fills the air in northern New Jersey

With the sun obstructed by haze, Spain's players practiced Thursday ahead of the World Cup final outside in northern New Jersey while air conditions are hazardous because of smoke from Canadian wildfires .

It was not clear how fast-paced a practice Spain held. Media members are only able to observe the first 15 minutes of what was scheduled to be a hourlong session in East Hanover beginning at 11 a.m. EDT.

Argentina remained in the Atlanta area to work out less than 24 hours after rallying to beat England and reach the final for a second consecutive tournament. Marietta, Georgia, is far enough south to avoid the effects of the fire, which are being windblown to the southeast from northern Ontario, triggering warnings from the U.S. Midwest through the Northeast.

Officials urged people to stay inside or wear masks outside as air quality reached unhealthy to hazardous levels, meaning it’s unhealthy for anyone, regardless of health conditions. Experts expressed concern over holding practice outdoors.

“These are high-level athletes who are moving a lot of air through their lungs during every practice in every game, and really they shouldn’t be practicing outside if the air quality levels are at hazardous sort of ranges for wildfire-related air pollution,” said Dr. Courtney Howard, an emergency room physician and Global Climate and Health Alliance official. “That’s the time to schedule a practice inside. You could put an N95 mask on them, but trying to make sure that everybody’s mask is well-fitted, I suspect that’s not the best choice. I would go find an air-conditioned indoor facility that’s a clean-air shelter.”

Messages sent to FIFA and the Spanish Football Association asking whether that was considered or possible were not immediately returned. The smoke is expected to clear the area well before the championship game Sunday in East Rutherford, New Jersey, with kickoff scheduled for 3 p.m.

The air quality in East Hanover on Thursday started early in the morning as “unhealthy” but got cleaner, so by mid-afternoon it was merely “unhealthy for sensitive groups,” according to the U.S. Environmental Protection Agency’s Air Now monitoring system. Particle pollution in New Jersey on Thursday was more than seven times higher than the World Health Organization standard. The forecast calls for an improvement to “moderate” for Sunday .

Smoke from wildfires — which are burning more of North America as Earth warms — attacks nearly every system in the body, killing tens of thousands of people a year, numerous medical studies show.

It attacks the body immediately, spiking asthma cases with increased ambulance runs within hours. Smoke can trigger inflammation in different parts of the body, often attacking a person’s weakest points, which can then cascade into different effects of an immune system trying to fight a nasty irritant, doctors and scientists said.

“It’s not healthy for anyone to be in the smoke, especially if you’re exercising,” Harvard School of Public Health environmental health research scientist Mary Johnson said. “You're exchanging more air, so you’re being exposed to even more pollutants, and even healthy individuals at some point will have some type of health effect from the exposure to the smoke. So, even though these are healthy, young individuals, it’s not a good idea to be exercising in this type of environment.”

Scientists have counted at least 1,000 toxins in wildfire smoke, according to Colorado State University environmental toxicologist Luke Montrose.

“If I gave you a list you would recognize some of these as being very bad often times associated with the burning of diesel fuel or cigarette smoke things like formaldehyde or volatile organic compounds,” Montrose said. “Just the smoke itself can be bad.”

Climate video producer Teresa de Miguel in Washington and SNTV videographers Lissette Romero in East Hanover, New Jersey, and Max Feliu in Marietta, Georgia, contributed to this report.

See more of AP’s World Cup coverage here