Long-range transport of sulfur dioxide emissions from external sources to Tehran

Large-scale emissions of sulfur dioxide (SO2) from the combustion of heavy fuel oils are deteriorating the air quality in Tehran. Our analysis of the long-term SO2 emission data in Tehran showed that the magnitude of local SO2 emission sources is inadequate to reach current SO2 levels. Bivariate polar plots, k-mean cluster, pairwise polar correlation, and potential source contribution function analysis provided evidence of the impact of large-scale transport of SO2 emissions from external locations in the west/northwest, north/northeast, and south/southwestern areas of Tehran. Further observations of these hotspots were observed in analyses conducted on TROPOMI satellite data confirming significant SO2 emissions from the consumption of heavy fuel oils in thermal power plants and oil/gas refineries. These results also strongly agreed with the NASA global SO2 emission source catalog showing the location of major SO2 emissions in the region. All approaches confirmed that Tehran is predominantly affected by regional transport of SO2 from external sources further away located in Iraq, Saudi Arabia, and adjacent provinces neighboring Tehran. Approximately 80% of the total SO2 concentration in Tehran was observed to have impacts from the external hotspots outside of Tehran. While local emission sources only contribute around 20% of the total SO2 concentration. •SO2 is a critical air quality concern causing complex atmospheric pollution episodes in Tehran.•Comprehensive analysis of SO2 local and regional hotspot sources in Tehran was evaluated.•local emissions contribute a minor fraction (20%) to the total SO2 concentration in Tehran.•large-scale transport of SO2 emissions (80%) from external locations of Tehran was observed.•Tehran is affected by regional transport from external sources in provinces neighboring Tehran.