The Study Also Revealed That the Decline Was Not Uniform Across All Parts

The average SO₂ level dropped from about 5.4 micrograms per cubic meter in 2016 to roughly 4.1 micrograms per cubic meter in 2025, a statistically significant decline. The research, led by Prof. Hüseyin Toros, Dr. Özkan Çapraz, and Dr. Nisa Özge Önal Tuğrul, analyzed data from air quality monitoring stations operated by the Ministry of Environment, Urbanization and Climate Change and the Istanbul Metropolitan Municipality. Station-level analysis found a significant decrease only at the Kandilli station, while changes at other stations were not statistically pronounced.

The study also revealed that the decline was not uniform across all parts of the city. Seasonal patterns showed winter SO₂ levels averaging 4.9 micrograms per cubic meter, compared to 3.8 in summer, with the difference statistically significant. Researchers attributed higher winter concentrations to increased residential heating and meteorological conditions like low wind speeds and temperature inversions.

No significant difference was observed between weekdays and weekends, suggesting the pollutant is largely influenced by non-traffic sources such as residential heating rather than vehicles. Diurnal analysis showed SO₂ concentrations were lowest at night and early morning, rising to peak levels in the afternoon. The citywide average, which exceeded 5 micrograms per cubic meter in 2016 and 2017, dropped markedly to 4 micrograms per cubic meter in 2018. Despite limited increases in 2019 and 2021, the overall downward trend held, with averages below 4 micrograms per cubic meter in 2022, 2023, and 2024. A slight rise in 2025 still left levels significantly lower than at the start of the study period.

The findings were published in the Journal of Research in Atmospheric Science under the title "Temporal Variation of SO₂ Concentrations in Istanbul (2016-2025). Prof. Toros, head of the Climate Science and Meteorology Engineering Department at İTÜ, said sulfur dioxide is a major atmospheric pollutant measured regularly worldwide, primarily emitted from burning fossil fuels such as diesel, fuel-oil, industrial facilities, ships, and diesel vehicles. He noted that inhaled SO₂ can combine with atmospheric particles to form fine particulate matter, harming the respiratory system, lungs, and cardiovascular system.

Toros also highlighted environmental impacts, explaining that SO₂ reacts with water vapor to form sulfuric acid, which can damage forests and historical structures. He said the study aimed to raise awareness about air pollution by examining how sulfur dioxide levels in the city have changed over the past decade."