When oil refineries burn during military strikes, the toxic smoke doesn't just disappear—it settles over entire cities, creating what residents describe as "apocalyptic" conditions. In March, Israeli attacks on four major oil facilities in and around Tehran exposed millions of Iranians to a complex mixture of hazardous pollutants, including black carbon particles, sulfur dioxide, and trace metals like nickel and vanadium. The resulting "black rain"—sulfuric acid formed when sulfur dioxide from burning crude oil mixes with moisture in the air—raised serious concerns about both immediate respiratory harm and long-term environmental contamination for Tehran's population of over 9 million people.

What Exactly Is in the Smoke from Oil Fires?

The smoke billowing from burning oil facilities isn't a simple cloud—it's a toxic cocktail of gases and particles created when hydrocarbons and industrial materials burn incompletely. Understanding what residents breathed helps explain why health officials were so alarmed. The primary pollutants include:

• Carbon Monoxide: A colorless, odorless gas that reduces oxygen delivery to the brain and heart, particularly dangerous during acute exposure events.
• Sulfur Dioxide: A pungent gas that irritates the respiratory tract and, when combined with moisture, forms the acidic "black rain" that fell over Tehran.
• Nitrogen Oxides: Gases that trigger inflammation in the lungs and can worsen asthma and other respiratory conditions.
• Volatile Organic Compounds (VOCs): Carbon-based chemicals that evaporate into the air and can cause respiratory irritation and neurological effects.
• Black Carbon and Soot Particles: Tiny particles from incomplete combustion that penetrate deep into lung tissue and can carry toxic substances like polycyclic aromatic hydrocarbons (PAHs) on their surfaces.
• Trace Metals: Naturally occurring elements in crude oil, including nickel and vanadium, which cause respiratory irritation and inflammatory responses in the body.

Of particular concern is black carbon, a near-pure carbonaceous component of soot. Acute exposure to black carbon can trigger respiratory disorders, especially in high-risk groups like people with asthma and older adults. Because these particles are extremely small, they bypass the body's natural defenses and lodge deep in the lungs, where they can remain for extended periods.

Why Is Tehran's Geography Making the Pollution Worse?

The location of Tehran amplifies the health crisis in ways that many cities wouldn't experience. The city sits in a semi-enclosed basin surrounded by the Alborz Mountains, with peaks rising 6,500 to 13,000 feet—far above the typical daytime boundary layer (the lowest part of the atmosphere where pollution gets trapped) of only 3,300 to 4,900 feet. This geography creates a natural "lid" that traps pollutants over the city rather than allowing them to disperse.

The situation worsens dramatically after sunset. The boundary layer collapses to just a few hundred feet, concentrating pollutants near ground level where people breathe. This means the worst air quality occurs overnight and in early morning hours—exactly when people are sleeping with windows closed or when they step outside before dawn. Additionally, Tehran's dense urban layout creates "urban canyons" where tall buildings restrict airflow, forming swirling vortices that trap pollutants at street level even when winds above rooftops are moving.

How Does "Acid Rain" Affect Your Health?

Reports from Tehran described "toxic acid rain"—a phenomenon caused when sulfur dioxide from burning sour crude oil (crude oil with high sulfur content) transforms into sulfuric acid in raindrops. Depending on concentration, sulfuric acid exposure can irritate the eyes and respiratory tract. However, the health effects are complicated because residents aren't exposed to sulfuric acid alone; they're exposed to a mixture of soot, acidic gases, and other combustion byproducts like dioxins and furans, which act together rather than in isolation.

The problem is compounded by the fact that rain—which normally helps "clean" air by removing hazardous particles and gases—has been limited so far. Without significant rainfall, the toxic smoke continues accumulating within the boundary layer, prolonging exposure for the entire population.

Ways to Reduce Exposure During Severe Air Pollution Events

While the situation in Tehran is extreme, these protective measures apply to anyone facing acute air pollution from industrial fires or other sources:

• Seal Your Indoor Space: Close windows and doors to prevent outdoor pollutants from entering. Studies in Tehran showed that outdoor particulate pollution readily infiltrates residential buildings that rely on natural ventilation, meaning indoor particle concentrations frequently track outdoor levels during severe pollution episodes. Use weatherstripping or tape around door frames if possible.
• Use Air Filtration: If available, run HEPA (high-efficiency particulate air) filters or air purifiers indoors. Fine particles deposited on furnishings can resuspend into the air, prolonging exposure for hours or days, especially if cleaning isn't possible.
• Limit Outdoor Time: Stay inside during peak pollution hours, which in Tehran's case are overnight and early morning when the boundary layer collapses. Check local air quality forecasts and plan outdoor activities for times when pollution levels are lower.
• Wear Appropriate Masks: If outdoor exposure is unavoidable, use N95 or P100 respirators (not cloth masks) that can filter fine particles. Surgical masks offer minimal protection against the small particles in oil fire smoke.
• Monitor Vulnerable Populations: Pay special attention to people with asthma, chronic obstructive pulmonary disease (COPD), heart disease, older adults, and young children, who face higher risks from acute pollution exposure.

What Are the Long-Term Health Risks?

While the acute health impacts of breathing toxic smoke are immediate—respiratory irritation, coughing, eye irritation, and difficulty breathing—the long-term consequences are equally concerning. Pollutants deposited onto Tehran's urban landscape—roads, roofs, soils, and croplands—can accumulate and become sources of secondary exposure. When winds resuspend these particles back into the air, residents face repeated exposure even after the fires are extinguished.

The health literature on long-term exposure to air pollution is well-established, showing links to cardiovascular disease, respiratory decline, and increased mortality rates. However, the specific long-term effects of acute exposure to this particular mixture of pollutants—combined with the stress of ongoing conflict and potential exposure to other environmental hazards like pulverized building materials from blasts—remains an area requiring further study.

For Tehran's 9 million residents, the immediate crisis is clear: toxic smoke from burning oil facilities creates a complex health emergency that geography, weather patterns, and urban design all make worse. Without significant rainfall to clear the air and with fires still burning days after the initial strikes, the population faces prolonged exposure to pollutants that penetrate deep into the lungs and accumulate in the body over time.