Internal National Park Service modeling for the July Fourth show predicts dangerous pollution around the Mall and “very unhealthy” conditions across central D.C.

Fireworks for this year’s July Fourth celebration are expected to cause hazardous levels of pollution around the National Mall and “very unhealthy” conditions in central D.C., according to internal National Park Service documents reviewed by The Washington Post.

The show, billed by the Trump administration as the largest pyrotechnic display in history, will include some 850,000 fireworks in a roughly 40-minute show expected to start at 10:30 p.m. or 11 p.m., according to organizers. President Donald Trump will speak as part of the event, which marks the 250th anniversary of U.S. independence.

The combustion from large fireworks displays typically causes significant pollution because it generates fine particulate matter, also known as PM2.5. These small particles can penetrate deep into the heart and lungs, causing irritation and in some cases asthma attacks and other illnesses.

A draft air-quality analysis, based on the National Park Service’s modeling, states that people should “avoid prolonged exposure” to the pollution around the Mall.

The Interior Department and the National Park Service did not immediately respond to questions about the documents and pollution associated with the event.

In downtown D.C., Arlington and the Capitol Hill area, where pollution will be “very unhealthy,” the document says that people should “expect irritation symptoms” and limit their postshow exposure to the pollution. It projects that pollution will remain at elevated levels for three to six hours after the show.

The analysis highlights best, worst and most likely scenarios based on wind conditions, humidity and other factors.

In the “expected” or “most likely” scenario, the fireworks show will generate 600 to 1,200 micrograms of PM2.5 per cubic meter in the Mall area. A worst-case scenario would see more than 2,000 micrograms per cubic meter.

Levels of up to 1,200 micrograms per cubic meter match what have been recorded with other fireworks events but are nevertheless reason to take precautions, said George Thurston, a professor of medicine and population health at New York University. He added that the worst-case scenario would exceed anything he has seen previously recorded from pyrotechnic displays.

“People should use the precautionary principle, which is to minimize exposures,” Thurston said. “An N95 mask would be a good idea.”

He said that research on air pollution focuses on cars, power plants and other sources but is lacking on the health effects of fireworks-related pollution, as it often passes quickly.

Fireworks contain metals, such as copper, that help to create their vibrant colors but are hazardous to breathe when they enter the air, Thurston said.

People with respiratory conditions can stay inside during the fireworks display and wait for the wind to blow away the smoke, he said.

The Park Service, in a separate document, similarly said that people should “wear an n95 mask when outdoors” and “remain indoors as much as possible during and after the show.”

Another internal document designed to take demographics in the area into account advises Park Service staff to “not treat race, ethnicity, income, disability, age, or language as risks by themselves.”

The fireworks are planned to be set off at sites along the Potomac River and the National Mall, not far from areas such as Southeast Washington that are predominantly Black and lower-income.

Thurston said there is a greater prevalence of respiratory and cardiovascular problems, including asthma, in lower-income and minority populations.

“I definitely think that should not be ignored,” he said.