Over the past year, air pollution in Iranian cities has visibly worsened. But the smoke that hangs over Tehran, Zanjan, and Bushehr is more than seasonal haze — it is the result of a deliberate shift in energy policy.
Confidential data from Iran’s Ministry of Oil, obtained and reviewed by Iran Open Data, reveal that mazut consumption in power plants rose by an average of 46 % during the past Iranian year — from March 2024 to March 2025. In some provinces, the increase was far more dramatic: Bushehr saw a 543 % surge, Zanjan 172 %, and Kohgiluyeh and Boyer-Ahmad 157 %. Even Tehran recorded an 82 % rise.
These figures stand in sharp contrast to recent public statements by Tehran’s governor, who both apologized for the worsening air quality and insisted that “no power plant in the capital burns mazut.”
See the details of mazut burning in provinces: LINK
A Dangerous Blend
Despite official claims that Tehran’s fuel complies with Euro 4 standards, internal government data tell another story. To compensate for a growing gasoline shortfall, Iran’s fuel supply chain has increasingly turned to chemical blending — adding petrochemical derivatives such as methyl tert-butyl ether (MTBE) and other aromatics to regular gasoline.
MTBE is banned in many countries due to its high risk of contaminating groundwater. Yet according to the oil ministry’s internal figures, Iran’s MTBE usage has quadrupled between 1401 and 1403. The country’s largest producer of Euro-grade gasoline, the Shazand refinery, reportedly adds 350 000 litres of MTBE daily. Isfahan refinery adds another 325 000 litres.
While about one-third of Iranian gasoline is marketed as Euro 4 or Euro 5, the data show these blends frequently fall short of international safety standards once such additives are included.
Fuel No One Wants
Mazut is one of the dirtiest fossil fuels — more polluting than coal. Its sulfur content in Iran stands at around 3.5 %, nearly seven times the maximum allowed in international maritime fuel. Due to these impurities, Iran struggles to find foreign buyers, leaving most of its mazut stock to be burned domestically in thermal power stations and urban industries.
The result is a steady and toxic rise in sulfur dioxide and particulate emissions. Even diesel fuel, supposedly cleaner, is heavily contaminated. In Tehran’s Damavand power plant, diesel was found to contain 530 mg/kg of sulfur — ten times the legal threshold. At Parand power plant, the sulfur level was 6657 mg/kg, or 120 times the limit. By comparison, the mazut used in the Rajai power plant reached a staggering 30 000 mg/kg.
Public Health Costs
The surge in heavy-fuel use coincides with a public health warning. The head of Iran’s Emergency Services reported a “rare increase” in emergency calls for heart and respiratory issues, particularly during recent air pollution peaks.
As winter sets in and energy demand rises, so does reliance on cheap, dirty fuels — with public health bearing the cost. Meanwhile, official narratives continue to insist that Iran’s fuels are clean, Euro-standard, and safe.
The pattern is becoming clear: when energy gets scarce, Iran chooses pollution over transparency. The government’s own data contradict its public reassurances. With mazut burning up and chemical additives rising, Iran’s energy crisis is no longer hidden underground — it’s in the air, in the lungs, and in the water.
For now, the only thing improving is the opacity.
The article was published on Iran Open Data Centerhttps://iranopendata.org/en/article/295-iran-dirty-revival-mazut-burning-surge/