After attacks on Iran's oil facilities, toxic black rain endangers the public

Clouds of toxic smoke unleashed into the atmosphere by U.S.-Israeli airstrikes on Iranian oil facilities made a dangerous return to Earth in the form of “black rain,” prompting international health officials to warn of serious risks to the public.

Residents in Tehran complained last week of burning eyes and difficulty breathing when the dark and oily precipitation fell near the Iranian capital after several fuel oil depots and a refinery were struck.

Plumes of dark smoke have also been seen across other parts of the region over two weeks of war, as Iran retaliates against U.S.-Israeli airstrikes by firing drones and missiles at the oil and natural gas facilities of its Persian Gulf neighbors.

Rain washes hazardous chemicals out of the atmosphere in a relatively short period of time, experts said, but people exposed to black rain should take precautions to avoid short- and long-term health risks.

Here's what to know:

It occurs when soot, ash and toxic chemicals combine with water droplets in the atmosphere, then fall back to Earth when it rains. It's common after oil refineries or oil fields catch fire, and also can be caused by wildfires, volcanic eruptions and industrial pollution.

In Iran, microscopic soot formed when hydrocarbons in the fuel oil burned incompletely, experts said. Burning oil also forms compounds called polycyclic aromatic hydrocarbons, or PAHs, as well as toxic gases such as sulfur dioxide and nitrogen oxides, which cause acid rain, said Peter Adams, a civil and environmental engineering professor at Carnegie Mellon University.

Microscopic soot, whose particles are about 40 times smaller than the width of a human hair, can lodge deep in the lungs and enter the bloodstream, causing breathing and heart problems that can lead to premature death, experts said. Exposure to PAHs can increase cancer risk.

In Iran, the World Health Organization and the country's health and environmental officials advised people to stay indoors and wear masks. They warned that the rainfall was highly acidic and could burn the skin and cause lung damage.

“We can definitely expect acute health effects from an event like this,” said V. Faye McNeill, a chemical engineering professor at Columbia University who specializes in atmospheric chemistry.

Even regular air pollution events can trigger health problems and lead to more hospitalizations, especially among the elderly, children and people who already had health problems, she said. “But this is a higher level, so there likely are health problems going on right now because of it.”

Some Iranians fear the polluted rain, which also contains heavy metals, could contaminate drinking-water reservoirs and waterways.

It usually takes only hours for fuel tanks to burn out. But — as happened in Kuwait during the Gulf War 25 years ago — oil fields can burn for months, said Adams.

For fires that burn out more quickly, most of the soot and chemicals will disperse on the wind and wash out of the atmosphere in about three to seven days, Adams said.

“So if we don’t create more problems, at least what’s in the atmosphere is going to go away,” even if long-term health risks haven't, Adams said.

“But we don’t know what’s going to happen with future strikes and whether other tanks will be struck or whether oil fields will be struck,” he added. “I'm less concerned about longer-term or regional stuff, but it's a real mess for the people in the immediate vicinity.”

The Associated Press’ climate and environmental coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org.

A man rides a bike as fires and plumes of smoke rise after debris from an intercepted Iranian drone struck an oil facility, according to authorities, in Fujairah, United Arab Emirates, Saturday, March 14, 2026. (AP Photo/Altaf Qadri)

Residents look on and take pictures as flames and smoke rise from an oil storage facility struck as attacks hit the city during the U.S.–Israeli military campaign in Tehran, Iran, Saturday, March 7, 2026. (Alireza Sotakbar/ISNA via AP)

FILE - A thick plume of smoke rises from an oil storage facility hit by a U.S.-Israeli strike in Tehran, Iran, March 8, 2026. (AP Photo/Vahid Salemi, file)

Clothes clips covered in soot from burned fuel are seen as smoke from a U.S.-Israeli strike on an oil facility late Saturday lingers in the cloudy sky over Tehran, Iran, Sunday, March 8, 2026. (AP Photo/Vahid Salemi)

Two women from the Iranian Red Crescent Society stand as a thick plume of smoke from a U.S.-Israeli strike on an oil storage facility late Saturday rises in the sky in Tehran, Iran, Sunday, March 8, 2026. (AP Photo/Vahid Salemi)

YEREVAN, Armenia (AP) — European leaders on Monday said that U.S. President Donald Trump’s snap decision to pull thousands of U.S. troops out of Germany came as a surprise but is a fresh sign that Europe must take care of its own security.

The Pentagon announced last week that it would pull some 5,000 troops out of Germany, but Trump told reporters on Saturday that “we’re going to cut way down. And we’re cutting a lot further than 5,000.”

He offered no reason for the move, which blindsided NATO, but his decision came amid an escalating dispute with German Chancellor Friedrich Merz over the U.S-Israeli war on Iran, and Trump’s anger that European allies have been reluctant to get involved in the conflict in the Middle East.

Asked about the decision to pull out 5,000 troops from Germany, Norwegian Prime Minister Jonas Gahr Støre said: “I wouldn’t exaggerate that because I think we are expecting that Europe is taking more charge of its own security.

“I do not see those figures as dramatic, but I think they should be handled in a harmonious way inside the framework of NATO,” he told reporters in Yerevan, Armenia, where European leaders are holding a summit.

The European Union’s foreign policy chief, Kaja Kallas, said “there has been a talk about withdrawal of U.S. troops for a long time from Europe. But of course, the timing of this announcement comes as a surprise.”

“I think it shows that we have to really strengthen the European pillar in NATO,” she said.

Asked whether she believes that Trump is trying to punish Merz, who said that the U.S. has been humiliated by Iran in talks to end the war, Kallas said: “I don’t see into the head of President Trump, so he has to explain it himself.”

Over the weekend, NATO spokesperson Allison Hart said that officials at the 32-nation military alliance “are working with the U.S. to understand the details of their decision on force posture in Germany.”

European allies and Canada have known since just after he came to office again last year that Trump would pull troops out of Europe — indeed some left Romania in October — but U.S. officials had pledged to coordinate any moves with their NATO allies to avoid creating a security vacuum.

NATO Secretary-General Mark Rutte played down the move, saying that “there has been at this point disappointment on the U.S. side” about European support for the war on Iran.

Notably France, Spain and the U.K. have declined to give U.S. forces free rein to use bases on their territory to attack Iran. Spain has denied them the use of its airspace and bases there for the war.

But Rutte, who has championed Trump’s leadership at NATO despite the U.S. president's criticism of the majority of the allies, said: “I would say the Europeans have heard a message. They are now making sure that all the bilateral basing agreements are being implemented.”

Rutte added that European nations “have decided to pre-position assets, key assets, close to the theater for the next phase.”

He provided no details, but the Europeans have insisted they would not help police the Strait of Hormuz, a key energy trade route, until the war is over.

French President Emmanuel Macron said “if the United States is ready to reopen Hormuz, that’s great. That’s what we’ve been asking for since the beginning.” But he underlined that the Europeans are not ready to get involved in any operation “that does not seem clear to us.”

In another sign of friction with Merz, Trump has accused the EU of not complying with its U.S. trade deal and announced plans to increase tariffs next week on cars and trucks produced in the bloc to 25%, a move that would be particularly damaging to Germany, a major automobile manufacturer.

Without mentioning Trump or the United States, European Commission President Ursula von der Leyen listed recent trade deals that the bloc has sealed with Australia and India, and is now working on with Mexico.

“With like-minded friends, you have stable, reliable supply chains and Europe has the biggest network of free trade agreements,” von der Leyen, who is from Germany, told reporters.

Cook reported from Brussels.

French President Emmanuel Macron speaks with the media as he arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)

European Commission President Ursula von der Leyen speaks with the media as she arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)

European Union foreign policy chief Kaja Kallas speaks with the media as she arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)

NATO Secretary General Mark Rutte speaks with the media as he arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)

Norway's Prime Minister Jonas Gahr Store speaks with the media as he arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)

Britain's Prime Minister Keir Starmer arrives for a meeting of the European Political Community in Yerevan, Armenia, Monday, May 4, 2026. (AP Photo/Anthony Pizzoferrato)