After attacks on Iran's oil facilities, toxic black rain endangers the
public
[March 16, 2026]
By TAMMY WEBBER
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:
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 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.
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 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.
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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)
 “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.
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.”
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