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A platform for research: civil engineering, architecture and urbanism
Regional sulfate drives long-term rise in AOD over megacity Kolkata, India
https://orcid.org/0000-0003-1549-4042
https://orcid.org/0000-0002-9463-9117
Abstract We present here the first long-term (2001–2017) record of aerosol optical depth (AOD; interchangeably, AOT) and contributions of aerosol chemical components to light extinction over Kolkata, the second-most polluted metropolis in India. For this purpose, we use daily gridded MODIS AOD measurements coupled with modeled AOT for 5 major aerosol constituents – sulfate, sea-salt, dust, organic carbon (OC) and black carbon (BC), from the MERRA-2 reanalysis system. We find that AOD over Kolkata has increased significantly (32% overall, 0.010 y−1; Mann-Kendall test with Thiel-Sen slope estimation; p < 0.01) over the past 17 y to a mean of 0.74 ± 0.10 in 2017, and an overwhelming majority of this increase is driven by a concurrent rise (70% overall, 0.007 y−1, p < 0.01) in sulfate AOT. This is followed by smaller but significant enhancements in OC (40% overall, 0.002 y−1, p < 0.01) and BC (20% overall, 0.0004 y−1, p < 0.01) AOT. Although a non-trivial fraction (24%) of AOT is associated with natural emissions (sea-salt and dust), these do not exhibit significant trends over time and therefore are not instrumental in driving the observed AOD rise. A concentration-weighted trajectory (CWT) analysis shows that sulfate aerosol over Kolkata is mostly regional (within ∼250 km) during winter and post-monsoon with significant footprints over thermal power plant clusters in neighboring states and areas with considerable residential biofuel use (eastern Indo-Gangetic Plain (IGP) and the Ganges-Brahmaputra Basin). In comparison, BC and OC AOT show a significant long-range component (∼1800 km) originating from northwestern and central IGP, especially during post-monsoon, when open agricultural residue burning is rampant. Overall, these results provide a preliminary indication that a considerable fraction of aerosol light extinction over Kolkata might be related to non-local, atmospherically transported aerosol. Once validated by ground-based measurements, these results would reinforce the need to bring regional and long-range emissions, in addition to within-the-city emissions, under the purview of air quality management policies.
Graphical abstract Display Omitted
Highlights •First long-term (2001-2017) record of AOD and chemical species AOTs over Kolkata. •AOD increased significantly (32%) in the past 17 y with a 2017 mean of 0.74 ± 0.10. AOD rise primarily driven by regionally transported (∼250 km) aerosol sulfate. Significant long-range transport of BC and OC from northwestern Indo-Gangetic Plain.
Regional sulfate drives long-term rise in AOD over megacity Kolkata, India
https://orcid.org/0000-0003-1549-4042
https://orcid.org/0000-0002-9463-9117
Abstract We present here the first long-term (2001–2017) record of aerosol optical depth (AOD; interchangeably, AOT) and contributions of aerosol chemical components to light extinction over Kolkata, the second-most polluted metropolis in India. For this purpose, we use daily gridded MODIS AOD measurements coupled with modeled AOT for 5 major aerosol constituents – sulfate, sea-salt, dust, organic carbon (OC) and black carbon (BC), from the MERRA-2 reanalysis system. We find that AOD over Kolkata has increased significantly (32% overall, 0.010 y−1; Mann-Kendall test with Thiel-Sen slope estimation; p < 0.01) over the past 17 y to a mean of 0.74 ± 0.10 in 2017, and an overwhelming majority of this increase is driven by a concurrent rise (70% overall, 0.007 y−1, p < 0.01) in sulfate AOT. This is followed by smaller but significant enhancements in OC (40% overall, 0.002 y−1, p < 0.01) and BC (20% overall, 0.0004 y−1, p < 0.01) AOT. Although a non-trivial fraction (24%) of AOT is associated with natural emissions (sea-salt and dust), these do not exhibit significant trends over time and therefore are not instrumental in driving the observed AOD rise. A concentration-weighted trajectory (CWT) analysis shows that sulfate aerosol over Kolkata is mostly regional (within ∼250 km) during winter and post-monsoon with significant footprints over thermal power plant clusters in neighboring states and areas with considerable residential biofuel use (eastern Indo-Gangetic Plain (IGP) and the Ganges-Brahmaputra Basin). In comparison, BC and OC AOT show a significant long-range component (∼1800 km) originating from northwestern and central IGP, especially during post-monsoon, when open agricultural residue burning is rampant. Overall, these results provide a preliminary indication that a considerable fraction of aerosol light extinction over Kolkata might be related to non-local, atmospherically transported aerosol. Once validated by ground-based measurements, these results would reinforce the need to bring regional and long-range emissions, in addition to within-the-city emissions, under the purview of air quality management policies.
Graphical abstract Display Omitted
Highlights •First long-term (2001-2017) record of AOD and chemical species AOTs over Kolkata. •AOD increased significantly (32%) in the past 17 y with a 2017 mean of 0.74 ± 0.10. AOD rise primarily driven by regionally transported (∼250 km) aerosol sulfate. Significant long-range transport of BC and OC from northwestern Indo-Gangetic Plain.
Regional sulfate drives long-term rise in AOD over megacity Kolkata, India
https://orcid.org/0000-0003-1549-4042
https://orcid.org/0000-0002-9463-9117
Abstract We present here the first long-term (2001–2017) record of aerosol optical depth (AOD; interchangeably, AOT) and contributions of aerosol chemical components to light extinction over Kolkata, the second-most polluted metropolis in India. For this purpose, we use daily gridded MODIS AOD measurements coupled with modeled AOT for 5 major aerosol constituents – sulfate, sea-salt, dust, organic carbon (OC) and black carbon (BC), from the MERRA-2 reanalysis system. We find that AOD over Kolkata has increased significantly (32% overall, 0.010 y−1; Mann-Kendall test with Thiel-Sen slope estimation; p < 0.01) over the past 17 y to a mean of 0.74 ± 0.10 in 2017, and an overwhelming majority of this increase is driven by a concurrent rise (70% overall, 0.007 y−1, p < 0.01) in sulfate AOT. This is followed by smaller but significant enhancements in OC (40% overall, 0.002 y−1, p < 0.01) and BC (20% overall, 0.0004 y−1, p < 0.01) AOT. Although a non-trivial fraction (24%) of AOT is associated with natural emissions (sea-salt and dust), these do not exhibit significant trends over time and therefore are not instrumental in driving the observed AOD rise. A concentration-weighted trajectory (CWT) analysis shows that sulfate aerosol over Kolkata is mostly regional (within ∼250 km) during winter and post-monsoon with significant footprints over thermal power plant clusters in neighboring states and areas with considerable residential biofuel use (eastern Indo-Gangetic Plain (IGP) and the Ganges-Brahmaputra Basin). In comparison, BC and OC AOT show a significant long-range component (∼1800 km) originating from northwestern and central IGP, especially during post-monsoon, when open agricultural residue burning is rampant. Overall, these results provide a preliminary indication that a considerable fraction of aerosol light extinction over Kolkata might be related to non-local, atmospherically transported aerosol. Once validated by ground-based measurements, these results would reinforce the need to bring regional and long-range emissions, in addition to within-the-city emissions, under the purview of air quality management policies.
Graphical abstract Display Omitted
Highlights •First long-term (2001-2017) record of AOD and chemical species AOTs over Kolkata. •AOD increased significantly (32%) in the past 17 y with a 2017 mean of 0.74 ± 0.10. AOD rise primarily driven by regionally transported (∼250 km) aerosol sulfate. Significant long-range transport of BC and OC from northwestern Indo-Gangetic Plain.
Regional sulfate drives long-term rise in AOD over megacity Kolkata, India
Rawat, Prashant (author) / Sarkar, Sayantan (author) / Jia, Shiguo (author) / Khillare, Pandit S. (author) / Sharma, Bijay (author)
Atmospheric Environment ; 209 ; 167-181
2019-04-13
15 pages
Article (Journal)
Electronic Resource
English
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