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

Large-scale emissions of sulfur dioxide (SO) from the combustion of heavy fuel oils are deteriorating the air quality in Tehran. Our analysis of the long-term SO emission data in Tehran showed that the magnitude of local SO emission sources is inadequate to reach current SO 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 SO 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 SO 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 SO emission source catalog showing the location of major SO emissions in the region. All approaches confirmed that Tehran is predominantly affected by regional transport of SO from external sources further away located in Iraq, Saudi Arabia, and adjacent provinces neighboring Tehran. Approximately 80% of the total SO 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 SO concentration.