Short Wave - ‘Black rain’ in Iran and the environmental cost of war

Episode Date: March 17, 2026

US-Israeli airstrikes on oil depots culminated in ‘black rain’ in Iran early last week – a phenomenon usually caused by large amounts of soot, carbon and other pollutants in the air. Usually, rain leaves the atmosphere cleaner than it was before. But in this case, the rain left Tehran’s residents with sore throats and burning eyes. Oily, sooty residue was all over the city. So, we talked to an environmental pollution expert to find out: What’s in this ‘black rain’, what are its potential short- and long-term environmental and health effects, and what could recovery look like?Interested in more science behind current events? Email us your question at [e-mail] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. The U.S. and Israel launched military strikes on Iran late last month. And those strikes have continued. Among the targets this month were oil refineries and depots in and around the capital city of Tehran. And that released thick plumes of black soot and smoke that drifted across the city. Some Iranians said it burned their eyes and throat and that it was painful to breathe. And then came the black rain, which Tehran. residents said left behind a dark oily residue. That's what they told the BBC. Black rain is a

phenomenon caused by large amounts of chemical pollutants in the air. That's according to Peter Ross, a toxicologist and senior scientist at Rain Coast Conservation Foundation in Sydney, British Columbia, in Canada. We're seeing a soup of chemicals, including the sulfur oxides, the nitrogen oxides that form acid rain. We're seeing metals. We're seeing other carcinogens and volatile chemicals that can cause dizziness, death, and or contribute to cancer. And after the rain fell, Iran's government urged residents to stay indoors. The World Health Organization backed them up. They warned Iranians of the potential health risks associated with breathing in these high levels of toxic pollutants.

The black rain and the acidic rain coming with it is indeed a danger for the population. Ali Jafarian, Iran's deputy health minister, told Al Jazeera that this rain is already contaminating the soil and water supply, which could indicate longer-term consequences for public health as well as the local environment. So today on the show, Iran's black rain. What we know about the chemicals contained in it, the potential effect of those pollutants, both short and long-term, and what it all says about the environmental cost of war. I'm Emily Kwong and you're listening to Shortwave, a science podcast from NPR. Okay, shortwavers, I'm here with Peter Ross, a toxicologist, to talk about Black Rain.

And Peter, I want to just back up a little. When a strike hits an oil storage facility, as has happened in Iran, what happens then, chemically in the air? Well, I think what we're talking about is explosion. These are, of course, fossil fuels. There are volatile gases. They're explosive in that mixture. There are liquid fuels that will also combust, so we'll get fire. And as a result of the explosion and the ensuing fire,

we're going to see a lot of different pollutants basically injected into the atmosphere and distributed through the neighborhoods. What else is in this chemical soup, we think? What other kinds of chemicals? And can you go into more specifics as to what damage they may cause, specifically to the body? Well, I'd be concerned about the health of people in the short term. So I'd be worried about airways.

I'd be worried about people that have asthma or COPA. PD or other lung ailments. So when we would have a forest fire or a major fire, we would see an increase in emergency room visits. We would see an increase in asthma attacks. And we would also see increases in mortality. So we can expect all of these things to be happening in Tehran right now. But in this smoke, in addition to the sulfur oxides, nitrogen oxides, carbon monoxide, the polycyclic aromatic hydrocarbons or pHs, we would also see benzene, toluene, and a number of other explosive gases that are very, very toxic. If we inhale them, these can cause dizziness, they can cause people to faint, they can cause outright

mortality. So we're going to see acute threats to public health. That'll be in the short term or the immediate term. And as the fires subside, we're going to start to see longer, longer term risks to public health, water quality, and habitat for wildlife. Yeah, I want to talk more about the long-term impacts on wildlife in a minute. I'm going to get a little atmospheric scientist for a second because most people, when they think of rain, they think of it as a cleansing, you know, phenomenon. That's not happening here. What's happening is as these explosions are happening, it's sending up chemicals, pollutants into the atmosphere, which are then mixing with water and oxygen and turning into other things,

and that mixes with natural precipitation and falls to the ground, or is it falling to the ground all on its own? We're seeing pollutants trapped in the atmosphere. We're seeing pollutants that are scavenged by water vapor, forming droplets and coming down in rain. Okay. So, yes, rainfall is a cleansing phenomenon that occurs in the atmosphere. But unfortunately, for what's on land, in terms of crops, in terms of water,

ways, this will actually disperse the pollutants across crop lands into streams, rivers, creeks, lakes, potentially down into groundwater. So in the long term, what we're talking about is really a distillation phenomena whereby we see the pollutants moving from the air to the land, into waterways, where they basically create a long-term risk for public health. Given that the potential for pollution to seep into groundwater, what could be the long-term impact there. Well, for drinking water supplies, we tend to rely on either surface water or groundwater. So groundwater, think of a spring, think of a well. It's basically a natural reservoir.

It is a little bit filtered out or cleaned out in terms of, you know, with the soils over top. But it's very vulnerable as well. So if we contaminate groundwater with chemicals of concern, and that would include some of the other compounds found in the black rain, then we're in it for the long haul. We're going to be relying on water that is degraded and potentially severely threatening as a drinking water source for humans. Beyond that, the potential harm for human health could also be worsened by Tehran's topography. I mean, I'm thinking about how the city lies at the base of the Albor's mountains, these beautiful mountains that can also block air circulatory. What do you think about the effect of topography on all of this? Well, I haven't seen any data from this, but we can very well expect that in such a semi-enclosed basin, as you describe it, with 10 million inhabitants, we've got smoke that is lingering at different altitudes, different levels.

We've got toxic gases that are basically permeating all the streets and alleyways. So not really a pleasant urban environment to live in. So with 10 million people living in these areas, we'd be worried about such measures as PM2.5. These are very small particles of soot basically invisible to the human eye, that when we breathe in, they can actually go right through the lungs into circulation. They can cause cardiac arrest. They can lead to cancer, lead to all sorts of ailments. So what we can expect right now is the alarm bells would be going off in terms of

those that are worried about air quality and human health. Yeah. I got to say, I think for people in the U.S., it's hard to picture this level of pollution. Maybe for some folks, the closest comparison might be wildfire smoke. How does this compare to something like wildfire smoke? Well, I think local citizens have reported apocalyptic sort of smoke and visuals in Tehran, not surprisingly. And certainly from the short-term perspective, people would be looking to manage their health and limit their exposure. these things by wearing masks, which will help to keep out some of the dust and soot and the fine

particles staying indoors. But, you know, in these sorts of environments or climates, it's very difficult to keep outdoor air out. A lot of the homes have circulation that opens up to the outside and can render people exposed indoors to basically the same thing that's happening outdoors. I mean, and is it realistic for people to even be able to stay indoors when perhaps some people are also trying to avoid strikes, right? So their homes may not be entirely safe in some places. Well, I think in any conflict area, you're always worried about your immediate physical safety, first and foremost. You know, air quality and water quality tend to come a little bit down the line. Right. You're just trying to stay alive.

You're trying to stay alive. Absolutely. But part of staying alive is being able to breathe and drink water. Without water, we are deceased within three to four days. So I'm very concerned about the acute short-term risk to people, pets, agricultural animals, wildlife. But I'm also concerned about water quality, drinking water that in the medium to long-term may be catastrophically threatened. Yeah. What would recovery look like for the environment and the health of millions of people in Tehran? I think as a scientist, I grew up thinking that Mother Nature was tolerant and could rebound readily. But in the case of petroleum accidents and incidents, we've really learned that it takes a long, long time to recover. In the case of the Exxon-Valdes oil spill, that was 1980. So we're talking 35 plus years ago. We can still find unweathered commercial oil from the tanker that ran aground under rocks and boulders.

Thousands of sea otters were killed outright. Herring and salmon stocks were impacted for years. It takes years, if not decades, to recover from the short term, the acute effects. But we're still seeing lingering risks associated. with that oil spill from 1989. And by comparison, Exxon Valdez was one oil tanker. This is multiple. Now we have several tankers on fire.

We've got oil depots on fire. We've got refineries on fire. We've got multiple sources of this complex mixture of pollutants that are going to be discharged into the air and impacted through this black rain phenomenon. This isn't happening just in Iran. There have been strikes on oil infrastructure in other parts of the Middle East due to this war. And making oil infrastructure a part of war not only is inherently dangerous, but what I'm hearing from you is it's very bad for the long-term health of the people and the environment.

And it really begs the question about the environmental impact of war in a way that I don't remember that being as much of a discussion we had as a society like during the wars in Iraq and Afghanistan. Is there a consciousness shift here? Are people asking new questions of war? Well, I think there's more immediate awareness because of media, social media, the internet. Those visuals are dramatic from Tehran as well as the neighboring states of Iran. We know that these pollutants know no borders. I think in this case, we've seen a rather unprecedented attack on oil facilities. As a toxicologist, I can only say that I have.

find that regrettable. It's really a crime against the environment, and many innocent bystanders are going to be impacted or threatened by poor water quality, poor air quality, and basically toxic crops to consume at the market. Toxicologist Peter Ross. Thank you so much for talking to us. Thanks, Emily. If you like this episode, please share it with a friend. It really helps our show out. This episode was produced by Rachel Carlson and edited by Vietnam. Arun Nair and Angela Zhang checked the facts.

Robert Rodriguez was the audio engineer. I'm Emily Kwong. Thank you for listening to Shortwave from NPR.