What to know about ‘black rain’ that fell in Iran after strikes on oil reserves

The “black rain” that fell for days in Tehran as a result of air strikes on major Iranian oil storage facilities could have lasting impacts on human health and the environment, according to scientists.

Fires caused by Israeli strikes on oil reservoirs on Saturday burned for multiple days, prompting Iranian officials to warn residents against acid and toxic rain that resulted from the significant amount of pollutants in the air.

Four major oil facilities were targeted: the oil depots in Karaj, Shehran, Aghdasiyeh and the refinery in Tehran, according to the Conflict and Environment Observatory, a U.K.-based nonprofit that monitors the environmental consequences of armed conflict and military activities. The Tehran facility alone has the capacity to process about 225,000 barrels of oil per day.

An Iranian civil defence member walks next to a destroyed fuel tanker vehicle near an ongoing fire following an overnight airstrike on the Shahran oil refinery in northwestern Tehran, March 8, 2026.
AFP via Getty Images
When fossil fuels such as oil, coal and gas burn, the combustion sends toxic compounds such as hydrocarbons, nitrogen oxides, sulfur dioxide, heavy metals and particulate matter into the atmosphere. The massive fires caused the pollutants to hover over Tehran, a city of nearly 10 million residents.

A storm system over the weekend then brought areas of rain to parts of the country, causing the pollutants to precipitate as acid and toxic rain — including an oily “black rain,” according to Iranian officials.

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For black rain to be produced, the concentrations of pollutants must be “extremely high,” Charles Driscoll, a professor of environmental engineering at Syracuse University, told ABC News.

What resulted was a “major environmental incident,” CEOBS, a U.K.-based nonprofit that monitors the environmental consequences of armed conflict and military activities.

Images from Tehran show thick plumes of black smoke covering Iran’s capital. Some residents described a thick, oily film covering cars and rooftops, The New York Times reported.

A smoke plume rises from an ongoing fire following an overnight airstrike on the Shahran oil refinery in northwestern Tehran, March 8, 2026.
AFP via Getty Images
The Red Crescent Society warned residents to stay indoors to avoid the acid rain, as well as toxic gases, which could cause chemical burns to the skin and serious damage to the lungs. The World Health Organization warned on Tuesday that the “massive release” of toxic hydrocarbons, sulphur oxides and nitrogen compounds and the black and acid rain that fell are a danger to Iranians and could cause long-term health effects.

“It has to be a horrendous situation,” Driscoll said. “I just cannot even imagine how bad.”

The risks are especially acute for vulnerable populations, such as those with existing respiratory illness, the elderly and children, who have a much narrower airway, Rachel Cleetus, policy director for the Climate and Energy Program at the Union of Concerned Scientists, told ABC News.

“It isn’t easy to just stay safe when the whole air around is filled with these kinds of toxins,” Cleetus said.

Residents described the environment as the toxic rain fell as “apocalyptic,” according to the CEOBS. Depending on the winds, the pollutants can also get carried over long distances, Cleetus said.

“It’s a huge human health catastrophe,” Cleetus said. “It’s obviously an ecological catastrophe as well.”

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Long-term environmental impacts

The toxins and chemicals will likely pose long-term environmental impacts on Tehran and the surrounding areas, Bryan Berger, a professor of chemical engineering at the University of Virginia, told ABC News.

In addition to the hydrocarbons and other toxic compounds, forever chemicals, likely present in materials like flame retardants built into the facilities, can contaminate groundwater and could “easily” become airborne and end up back in the rain.

Iran, especially Tehran, already lacks the regulations needed for healthy air quality, Driscoll said.

The acid rain can also be corrosive, depending on the concentration, and accelerate the corrosion that buildings in Tehran face regularly due to the poor air quality, Driscoll said.

Building materials that are burning are also producing a variety of organic compounds that could be highly toxic, Driscoll said. The human-made materials could have trace metals that could be toxic and also contaminate the soil and water systems.

Smoke rises after a reported strike on Shahran fuel tanks, amid the U.S.-Israeli conflict with Iran, in Tehran, Iran, March 8, 2026.
Majid Asgaripour/West Asia News Agencyvia Reuters
In this region, there is no precedent for the impact the burning of fossil fuels could have on a populated area, Driscoll said. When former Iraqi president Saddam Hussein bombed hundreds of Kuwaiti oil wells in 1991, the surrounding land was unoccupied.

“Given the prominence of oil resources [in the Middle East], this has got to be close to a worst-case scenario,” Driscoll said.

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Strikes could be viewed as ‘chemical warfare’

The attack on the oil depots could be construed as chemical warfare, which violates international law, because the aggressors likely knew the hazards the civilians who live in Tehran would face, Cleetus said.

Iranian Foreign Ministry Spokesperson Esmaeil Baghaei wrote on X that the U.S. and Israel have taken the war into “a dangerous new phase.”

“These attacks on fuel storage facilities amount to nothing less than intentional chemical warfare against the Iranian citizens,” Baghaei wrote on Sunday.

In the event of contact with toxic acid rain, the Red Crescent Society advised people not to rub the area and to only wash with a continuous stream of cold water, as well as immediately change clothes and place them in a sealed bag.

The Israeli Defense Forces said in a statement Monday that its Air Force struck several fuel storage depots in Tehran “with precise guidance” from military intelligence.

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The strike was “significant,” the IDF said, adding that it will continue to “act forcefully” to remove the threats to the State of Israel.

“The military forces of the Iranian terror regime use these fuel tanks directly and frequently to operate military infrastructure, and with their help, the Iranian terror regime transfers fuel to various consumers, including military entities in Iran,” the IDF said.

Measures had been taken to minimize the product storage before the strike, the National Iranian Oil Refining and Distribution Company said in a statement. Fuel supply to Tehran and Alborz is being carried out sustainably from other sources, the company said.