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<p>Air pollution is a major environmental concern in India, especially in the Indo-Gangetic Plain (IGP), with particulate matter (PM) concentrations being very high. During the post-monsoon and winter seasons, several episodic events with severe levels of PM in IGP have been reported in the recent past. Other than regular anthropogenic emissions, smoke from agricultural residue burning is considered as one of the major contributing factors to aerosols in IGP. Ground based point measurements are not sufficient to monitor the synoptic distribution and long-range transportation of smoke aerosols to study their implication on air-quality (AQ). On the other hand, satellite-retrieved aerosol optical depth (AOD) is directly linked to PM concentration, making it a viable tool for AQ monitoring on a synoptic scale. In this work, using the operational EOS-06/Oceansat-3 Ocean Colour Monitor (OCM) Aerosol Optical Depth (AOD) product, a comprehensive and regional variation of AOD over India has been carried out for the period September 2023 to January 2024, offering insights into the prevailing AQ conditions. To discern the sources contributing to AQ in the IGP during the study period, MODIS active fire product and HYSPLIT trajectory modelling are also used. Unlike the recent trends, during the study period, only Punjab has shown fires associated with agricultural residue burning. Analysis shows that most of the fire events happened between October 25 to November 15 with peak fire count on 2 November 02, 2023. OCM-3 AOD and AERONET ground measurements are in agreement with high correlation (<i>R</i> = 0.87) and both have shown a sudden 2–3 fold increase in AOD in Punjab and adjoining states just after the onset of fire activities in Punjab. The presence of smoke aerosol is confirmed by a sudden increase in fine mode particles as observed in AERONET retrievals. However, the impact of smoke aerosols seemed spatially limited from Punjab to Uttar Pradesh only. Towards the end of stubble burning activities in December, improvement in AQ is observed. However, another surge in AOD was observed in January 2024 across the entire IGP with no evidence of fire events. Analysis of MERRA-2 model meteorological parameters confirms that this surge is caused by atmospheric stability and local anthropogenic emissions, leading to the accumulation of aerosols for a prolonged period in lower atmosphere. Despite overall high pollution levels across Delhi, OCM-3 AOD successfully delineates spatial variability of AOD induced by local factors— not typically visible in available coarse resolution products. Overall, this work successfully identifies the aerosol sources and their implication on AQ and establishes that the OCM-3 AOD product, due to its high spatial resolution and accuracy, is suitable for AQ monitoring in the Indian context, including the monitoring of temporal and spatial variations within urban centers in India.</p>

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An Assessment of Aerosol Optical Depth (AOD) for Air Quality Monitoring in India and Adjoining Regions During Post-Monsoon Season Using EOS-6 OCM

  • 期刊论文

  • 发表日期：

    2025年7月11日

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  • Manoj K. Mishra,
  • S. F. Shameela,
  • Raj Kumar

摘要

Air pollution is a major environmental concern in India, especially in the Indo-Gangetic Plain (IGP), with particulate matter (PM) concentrations being very high. During the post-monsoon and winter seasons, several episodic events with severe levels of PM in IGP have been reported in the recent past. Other than regular anthropogenic emissions, smoke from agricultural residue burning is considered as one of the major contributing factors to aerosols in IGP. Ground based point measurements are not sufficient to monitor the synoptic distribution and long-range transportation of smoke aerosols to study their implication on air-quality (AQ). On the other hand, satellite-retrieved aerosol optical depth (AOD) is directly linked to PM concentration, making it a viable tool for AQ monitoring on a synoptic scale. In this work, using the operational EOS-06/Oceansat-3 Ocean Colour Monitor (OCM) Aerosol Optical Depth (AOD) product, a comprehensive and regional variation of AOD over India has been carried out for the period September 2023 to January 2024, offering insights into the prevailing AQ conditions. To discern the sources contributing to AQ in the IGP during the study period, MODIS active fire product and HYSPLIT trajectory modelling are also used. Unlike the recent trends, during the study period, only Punjab has shown fires associated with agricultural residue burning. Analysis shows that most of the fire events happened between October 25 to November 15 with peak fire count on 2 November 02, 2023. OCM-3 AOD and AERONET ground measurements are in agreement with high correlation (R = 0.87) and both have shown a sudden 2–3 fold increase in AOD in Punjab and adjoining states just after the onset of fire activities in Punjab. The presence of smoke aerosol is confirmed by a sudden increase in fine mode particles as observed in AERONET retrievals. However, the impact of smoke aerosols seemed spatially limited from Punjab to Uttar Pradesh only. Towards the end of stubble burning activities in December, improvement in AQ is observed. However, another surge in AOD was observed in January 2024 across the entire IGP with no evidence of fire events. Analysis of MERRA-2 model meteorological parameters confirms that this surge is caused by atmospheric stability and local anthropogenic emissions, leading to the accumulation of aerosols for a prolonged period in lower atmosphere. Despite overall high pollution levels across Delhi, OCM-3 AOD successfully delineates spatial variability of AOD induced by local factors— not typically visible in available coarse resolution products. Overall, this work successfully identifies the aerosol sources and their implication on AQ and establishes that the OCM-3 AOD product, due to its high spatial resolution and accuracy, is suitable for AQ monitoring in the Indian context, including the monitoring of temporal and spatial variations within urban centers in India.