Scientists monitoring air quality in Tehran say recent air strikes were followed by episodes of black rain and a sharp deterioration in pollution levels.
Researchers described the pollution as unusual for the city’s typical seasonal patterns, citing soot-like particles and elevated concentrations of airborne contaminants.
Public health officials advised residents to limit outdoor exposure during periods of poor air quality, while environmental teams continued sampling.
Authorities said assessments were ongoing to determine the scale, duration, and sources of the pollutants detected after the strikes.
Scientists tracking Tehran’s atmosphere reported episodes of black rain and what they described as unprecedented pollution levels in the days following air strikes, according to preliminary monitoring and field observations. Researchers said the rainfall appeared to carry dark particulate matter consistent with soot and combustion byproducts, coinciding with a marked decline in air quality across parts of the capital.
Environmental scientists and air-quality specialists in Tehran said they observed a rapid shift in atmospheric conditions after air strikes, including rainfall that left dark residue on surfaces and a sustained haze in some districts. The researchers said the pattern differed from typical pollution episodes in the city, which are often linked to traffic emissions, temperature inversions, and seasonal dust.
Teams conducting measurements reported elevated levels of particulate pollution during and after the rainfall events. While full laboratory results were still being compiled, scientists said the combination of blackened precipitation and degraded visibility suggested a significant presence of fine particles produced by combustion.
Officials responsible for public health messaging urged residents to reduce outdoor activity during periods when air quality readings indicated unhealthy conditions. Guidance focused on limiting exposure for children, older adults, and people with respiratory or cardiovascular conditions, as well as avoiding strenuous outdoor exercise when pollution levels were high.
Scientists said the immediate priority was to characterize the particles and gases present in the air and in collected rainwater samples. They said this would help determine whether the pollution was dominated by soot, ash, or other materials associated with fires and damaged infrastructure, and how long the contaminants might persist.
## Black rain observations and sampling
Researchers said reports of “black rain” emerged after precipitation fell over parts of Tehran following the strikes. Field teams documented dark streaking on vehicles, windows, and outdoor surfaces, and collected samples for analysis.
Scientists said black rain can occur when airborne particles are scavenged by raindrops and deposited on the ground. In urban settings, the phenomenon is often associated with high concentrations of soot or smoke, though the exact composition can vary depending on the source of emissions.
In Tehran, researchers said the timing of the rainfall relative to the air strikes raised concerns that smoke and particulate matter from combustion had been lofted into the atmosphere and then washed out by precipitation. They cautioned that determining causality requires chemical fingerprinting of the particles, including analysis of carbon content and trace elements.
Environmental specialists also noted that rainfall can temporarily reduce airborne particle concentrations by removing pollutants from the air, while simultaneously increasing surface contamination as particles are deposited. They said this can complicate short-term assessments, making it necessary to combine air-monitoring data with ground and water sampling.
## Air quality impacts and health guidance
Scientists described the pollution levels as unusual compared with Tehran’s typical fluctuations, using the term “unprecedented” to indicate the magnitude or character of the observed contamination. They said the episode appeared to involve a sharp increase in particulate pollution, which can penetrate deep into the lungs and is associated with respiratory irritation.
Public health officials advised residents to follow air-quality updates and to take precautions during periods of poor air quality. Recommendations included staying indoors when possible, keeping windows closed during heavy smoke or haze, and seeking medical advice if symptoms such as persistent coughing, shortness of breath, or chest discomfort developed.
Experts said that in addition to particulate matter, combustion-related pollution can include gases and volatile compounds that may contribute to eye and throat irritation. They said monitoring should include both particle measurements and screening for common combustion byproducts to better understand potential health risks.
Scientists also emphasized that impacts can vary by neighborhood depending on wind patterns, proximity to smoke sources, and local topography. Tehran’s basin-like geography can trap pollutants under certain weather conditions, potentially prolonging exposure in some areas.
## What scientists are looking for next
Researchers said they were continuing to collect air and rainwater samples to determine the composition of the pollutants and to assess whether contamination levels were declining or persisting. They said laboratory analysis would help distinguish between typical urban emissions and materials more consistent with large-scale combustion.
Key questions include the size distribution of particles, which influences how long they remain suspended and how deeply they can be inhaled, and the presence of specific chemical markers that can indicate burning of fuels, plastics, or other materials.
Scientists said they were also evaluating meteorological data, including wind direction and precipitation intensity, to understand how pollutants moved across the city and where deposition was greatest. They said this information could support targeted cleanup guidance if surface residues were found to contain harmful substances.
Authorities said assessments were ongoing and that further updates would depend on the results of continued monitoring and laboratory testing. Scientists said the episode underscored the need for sustained air-quality surveillance during and after major combustion events, particularly in densely populated urban areas.
