Following U.S.-Israeli airstrikes on Iranian oil facilities over the weekend, residents of Tehran reported an unusual phenomenon: black rain falling across several neighborhoods. Some local media outlets described it as “acid rain,” while eyewitnesses said the dark, oily precipitation left visible residue on buildings and vehicles—and triggered headaches and respiratory distress among those exposed.
More Than Just Acid Rain
An atmospheric scientist and air pollution engineer, speaking to The Conversation, called the reports deeply concerning. “I believe these observations point to something far more serious than conventional acid rain,” he said. The rain likely contains not only acids—but also a dangerous cocktail of toxic pollutants harmful to human health and the environment, both immediately and over time. In fact, it may be even more hazardous than the term “acid rain” suggests.
What’s in the Rain?
Heavy clouds of black, toxic smoke have blanketed densely populated areas of Iran—a serious threat to anyone breathing that air, the expert added. He explained how rain naturally washes airborne pollutants from the atmosphere: when pollutant levels are extremely high, raindrops collect and deposit them onto the ground. That process helps explain why residents saw black rain after the strikes—evidence of severely degraded air quality.
This rain likely carries toxic hydrocarbons, ultrafine particulate matter (PM2.5), and carcinogenic polycyclic aromatic hydrocarbons (PAHs). It may also contain unknown chemical compounds—including heavy metals and inorganic substances released from damaged infrastructure, construction materials, and other debris incinerated in the blasts and subsequent fires.
Smoke from the bombed oil installations also emits sulfur dioxide and nitrogen dioxide—precursor gases that react in the atmosphere to form sulfuric and nitric acids. These dissolve into rain droplets, producing what is commonly known as acid rain. Historically, acid rain was linked mainly to sulfur dioxide emissions from burning fossil fuels—but this event involves a far more complex and dangerous mix of contaminants.
Health Risks
In the short term, exposure can cause irritation of the eyes, nose, and throat; coughing; wheezing; and worsening of pre-existing respiratory conditions like asthma. Long-term risks include increased likelihood of cardiovascular disease, lung damage, and elevated cancer risk—particularly from PAHs and heavy metals.