Influence of regional emissions on SO2 concentrations over Bhubaneswar, a capital city in eastern India downwind of the Indian SO2 hotspots

Abstract

In a scenario when haze and smog events are wreaking havoc in many parts of the world, accurate information on ambient sulfur dioxide (SO2) sources is a required input to models for prediction and mitigation of air pollution. Globally, India is one of the highest emitters of anthropogenic SO2. However, the Ozone Monitoring Instrument (OMI) data reveal that unlike many other anthropogenic air pollutants, the strongest anthropogenic SO2 sources are not located in the Indo-Gangetic plain (IGP) but over the coal belts of North Eastern peninsular India. In this study, we report SO2 measurements conducted at Bhubaneswar, a rapidly developing smart city in the Eastern Coast of India. The city is ideally located just downwind of the Indian SO2 hotspots during winter, when SO2 concentrations are the highest, reaching 14.3 ppbv for hourly averaged data. The measurements, reported here from the summer of 2010 to the summer of 2012, show that despite being a rapidly developing location, SO2 over Bhubaneswar is dominated by regional emissions rather than local sources like vehicular exhausts. The influence of regional emissions is strongest in winter as the city is directly downwind of 6 of the 10 largest thermal power plants and 7 out of the 13 largest integrated steel plants in India with a mean SO2 concentration of 3.2 ppbv. This is evinced by multiple pointers viz. Concentration-Weighted Trajectory (CWT) analysis for surface SO2 data, correlation analysis for OMI SO2 data, analysis of surface concentrations of SO2, organic carbon, black carbon and carbon monoxide; which reveal SO2 emissions from the industrial and mining regions of Chhattisgarh and north-west Odisha. This is the same region that shows up as hotspots of SO2 in OMI retrievals over India. However, despite being downwind of major SO2 sources during winter, SO2 concentrations in Bhubaneswar are lower than over some other cities (Kolkata, Kanpur) in the IGP, due to influence of strong local sources in the later cases. Unlike most other urban regions in India, the diurnal variation of SO2 over Bhubaneswar shows elevated daytime values due to predominant influence of regional emissions.