What is black rain? How oil fires, smoke and air pollution are darkening and potentially damaging rainfall |

This rare scientific phenomenon has recently received global attention, with reports from Tehran in March 2026 indicating that residents observed “dark rain” following an airstrike on an oil storage facility. This resulted in massive fires and released thick smoke into the atmosphere. When rain clouds form over cities, raindrops fall into the clouds, forming dark rain. People witnessed this as black water droplets fell over the city.Meanwhile, residents reported headaches and difficulty breathing. Iranian emergency officials said the rain that fell after the fires could be dangerous and even acidic. Learn the science behind black rain, its causes, environmental impacts, and more.

Understanding ‘Black Rain’: The Science Behind the Rare Phenomenon and Recent Tehran Incident

Black rain is an uncommon atmospheric phenomenon in which rain appears dark due to the presence of large amounts of suspended matter such as soot, ash, dust or oil droplets. From a scientific perspective, black rain is rainwater that becomes contaminated as it passes through the atmosphere, especially in highly polluted atmospheres. Rain that falls from the atmosphere contains dark, often black, gray, or oily water droplets.In early March 2026, multiple oil facilities in Tehran were targeted during military operations. This sparked massive fires, leading to the formation of huge smoke clouds. However, as rain clouds form in the region, water droplets are able to collect atmospheric particles as they fall. It was observed that the rain had a black appearance and left traces of oil. Environmental experts point out that contaminated rainwater is often caused by extremely high concentrations of smog in the atmosphere.

What causes black rain or atmospheric clearing

Rain forms when water vapor condenses around small particles called condensation nuclei. These particles can be dust, salt crystals, pollen and pollutants. Under normal circumstances, raindrops carry negligible amounts of material. However, when there are unusually high levels of ash in the air, raindrops can pick up large amounts of the material as they fall through the air.This phenomenon is called atmospheric scavenging. If there are particularly high levels of substances in the air, the rain will appear colored.

Environmental conditions that cause black rain

Environmental events can cause black rain:Factories, refineries and coal-burning plants can release soot and carbon particles into the atmosphere. During rainfall, these pollutants may mix with water droplets, darkening the color of the rain.Large wildfires produce huge plumes of smoke filled with ash and burning organic matter. Rainwater passing through these smoke layers may appear gray or black due to trapped particles.Explosive eruptions release clouds of ash composed of fine volcanic particles. Rain that passes through these gray clouds may become cloudy or dark.When oil burns, it produces thick black smoke that contains hydrocarbons and carbon particles. When it rains under these conditions, it can absorb oil residue and soot, causing black rain or oil rain, as happened recently in Tehran.

Black Rain: Environmental and Health Effects

Black rain can cause a number of environmental and health problems.environmental issues

human health issues

Historical examples of black rain

Black rain is rare; several significant events have been recorded throughout history. The most famous event was the nuclear attack on Hiroshima. During the attack, a nuclear bomb was dropped, sending ash, debris and radioactive material into the air. When clouds form, these materials mix with rainwater that falls from the clouds.This situation is also reflected in large-scale pollution, wildfires, oil field burning and other incidents.