Recently, this rare scientific phenomenon attracted global attention after reports from Tehran in March 2026 indicated that residents saw ‘dark rain’ following air strikes on oil storage facilities. This led to a massive fire which spread thick smoke into the atmosphere. When rain clouds formed over the city, raindrops fell into the clouds, causing black rain. This was seen when black drops fell on the city.At the same time, residents reported headaches and difficulty breathing. Emergency officials in Iran indicated that rain following the fires could be hazardous or even acidic. Know the science behind black rain, its causes, environmental impacts and more.
Understanding ‘black rain’: the rare phenomenon and the science behind the recent Tehran incident
Black rain is an unusual atmospheric phenomenon in which rain appears dark in color due to large amounts of suspended matter such as soot, ash, dust or oil droplets. From a scientific perspective, black rain is rain that becomes contaminated while passing through the atmosphere, especially in highly polluted atmospheric layers. Rain falling from the atmosphere consists of dark, often black, brown or oily droplets.Beginning in March 2026, various oil installations in Tehran were targeted during military operations. This caused a massive fire creating huge clouds of smoke. However, as rain clouds formed over the area, water droplets were able to collect particles in the atmosphere as they fell. It was observed that the rain was dark in color and left behind traces of oil. Environmental experts said contaminated rain is usually caused by extremely high levels of smoke in the atmosphere.
What causes black rain or atmospheric cleansing?
Precipitation is formed when water vapor condenses around small particles called condensation nuclei. These particles can be dust, salt crystals, pollen and pollutants. Under normal circumstances, the amount of material that raindrops carry with them is negligible. However, in cases when the amount of ash in the air is unusually high, raindrops carry enormous amounts of the material as they fall through the air.This phenomenon is called atmospheric cleaning. In cases when the amount of the material in the air is exceptionally high, rainwater will appear colored.
Environmental conditions that cause black rain
Black rain can occur due to environmental events:Factories, refineries and coal-burning plants can release soot and carbon particles into the atmosphere. During rainfall, these pollutants can mix with water droplets and turn the rainwater black.Large wildfires produce heavy smoke filled with ash and burnt organic matter. Rain falling through these smoke layers may appear brown or black due to the captured particles.Explosive eruptions produce ash clouds that are composed of fine volcanic particles. Rain passing through these ash clouds may be cloudy or black.When petroleum burns, thick black smoke is released, which contains hydrocarbons and carbon particles. When it rains in these conditions, the rain can soak up oil residues and soot, resulting in black or oily rain, as was the recent case in Tehran.
Black rain: impact on environment and health
Black rain can cause many environmental and health problems.environmental problems
- soil contamination
- agricultural land contamination
- Pollution of lakes, rivers and groundwater
- damage to vegetation
- damage to crops
human health problems
- Skin irritation from contact with contaminated water
- Respiratory problems due to breathing in contaminated substances
- Possible contact with chemicals released in a fire or accident
Historical examples of black rain
Black rain is a rare phenomenon; It has been recorded as a number of major events in history. The most famous event was the nuclear attack on Hiroshima. In this attack, a nuclear bomb was dropped which spread ash, debris and radioactive material in the air. When clouds were formed, the substances got mixed with the rain falling from the clouds.Such conditions were also seen in incidents of large-scale pollution, forest fires and burning oil fields.