A study by researchers at Istanbul Technical University (ITU) found that sulfur dioxide concentrations in Istanbul fell by about 24% between 2016 and 2025, reflecting the impact of energy transition and emission control policies.
The study analyzed data from air quality monitoring stations operated by the Ministry of Environment, Urbanization and Climate Change and the Istanbul Metropolitan Municipality. According to the findings, the city's average sulfur dioxide concentration declined from 5.4 micrograms per cubic meter in 2016 to 4.1 micrograms per cubic meter in 2025, a statistically significant decrease.
Researchers found that sulfur dioxide, once one of Istanbul's main air pollution indicators, now remains at much lower levels. However, the decline was not uniform across the city, with only the Kandilli monitoring station recording a statistically significant decrease after detailed analysis.
The study also showed that sulfur dioxide levels were higher during winter, averaging 4.9 micrograms per cubic meter, compared with 3.8 micrograms per cubic meter in summer. Researchers attributed the seasonal increase to residential heating and weather conditions that allow pollutants to accumulate in the atmosphere.
No significant difference was found between weekday and weekend pollution levels, suggesting that sulfur dioxide emissions stem mainly from residential heating rather than road traffic. Concentrations were lowest overnight and in the early morning before peaking during the afternoon.
The findings, published in the Journal of Research in Atmospheric Science, also showed that pollution levels dropped sharply in 2018 and remained below 4 micrograms per cubic meter for most of the period between 2022 and 2024.
Hüseyin Toros, head of the Climate Science and Meteorological Engineering Department at ITU's Faculty of Aeronautics and Astronautics, said sulfur dioxide levels in Istanbul exceeded 200 micrograms per cubic meter in 1992 but have since fallen to around 5 micrograms per cubic meter.
He attributed the improvement to the widespread use of natural gas, cleaner fuels, industrial modernization and technological advances, describing the decline as "an extremely significant achievement."
Toros added that sulfur dioxide levels recorded across Istanbul remain well below the 40 micrograms per cubic meter daily limit recommended by the World Health Organization and adopted in Türkiye and Europe. He also said the International Maritime Organization's low-sulfur fuel regulation, introduced in 2020, has helped reduce emissions from the 40,000 to 50,000 large vessels that pass through the Bosporus each year.
He noted that reducing coal use, expanding natural gas infrastructure and improving building insulation have also played a key role in improving the city's air quality.
