Sunday, 15 March 2026
Sunday, 15 March 2026
Clouds of toxic smoke unleashed into the atmosphere by US-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 US-Israeli airstrikes by firing drones and missiles at the oil and natural gas facilities of its Persian Gulf neighbours.
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
What is black rain
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 it can also be caused by wildfires, volcanic eruptions and industrial pollution.
The World Health Organization warned on Tuesday that the "black rain" and toxic compounds in the air in Iran after strikes on oil facilities could cause respiratory problems, and it backed Iran’s advisory urging people to remain indoors. The U.N. health agency, which has an office in Iran and works with authorities on health emergencies, said it has received multiple reports of oil-laden rain this week. Tehran was choked in black smoke on Monday after an oil refinery was hit, in an escalation in strikes on Iran's domestic energy supplies as part of the U.S.-Israeli campaign.
"The black rain and the acidic rain coming with it is indeed a danger for the population, respiratory mainly," WHO spokesperson Christian Lindmeier told a press briefing in Geneva, adding that Iran had advised people to stay indoors.
What are the health risks of exposure
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 Organisation 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 specialises in atmospheric chemistry.
Even regular air pollution events can trigger health problems and lead to more hospitalisations, especially among the elderly, children and people who already have 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.
How long do the chemicals last in the atmosphere
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."
