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Aerosol Optical Depth Over India.

Liji Mary David1, A R Ravishankara1, John K Kodros2

  • 1Department of Chemistry and Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA.

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|February 22, 2021
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Summary
This summary is machine-generated.

Tropospheric aerosol optical depth (AOD) over India was simulated using GEOS-Chem model. The SMOG inventory showed higher aerosol carbon content than the GEOS-Chem inventory, with significant transport from emission hotspots.

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Area of Science:

  • Atmospheric Science
  • Environmental Science
  • Climate Modeling

Background:

  • Tropospheric aerosol optical depth (AOD) is a critical parameter for understanding Earth's radiative balance and climate.
  • Accurate AOD simulations are essential for climate modeling and air quality assessments, particularly over regions with significant aerosol loading like India.

Purpose of the Study:

  • To simulate and evaluate tropospheric AOD over India using the GEOS-Chem chemical-transport model.
  • To compare the performance of two emission inventories, SMOG and GEOS-Chem (GC), in simulating AOD.
  • To identify major aerosol contributors and understand spatial and seasonal variations of AOD over India.

Main Methods:

  • Simulated AOD over India for 2012 using the Goddard Earth Observing System (GEOS)-Chem model.
  • Utilized two emission inventories: SMOG (Speciated Multi-pOllutant Generator from Indian Institute of Technology Bombay) and GC (current GEOS-Chem inventories).
  • Compared model simulations with satellite-derived AOD (MODIS, MISR) and ground-based AERONET data, including dust correction.

Main Results:

  • Simulated AODs were approximately 80% (SMOG) and 60% (GC) of satellite measurements.
  • SMOG inventory yielded higher particulate black and organic carbon AOD (factors of ~5 and ~3, respectively) compared to GC.
  • Model accurately captured fine-mode AOD but underpredicted coarse-mode AOD; dust was only simulated over Western India.
  • Highest AOD values were observed over the Indo-Gangetic Plain, Central, and Southern India, with significant aerosol transport into Eastern India.
  • Inorganic aerosol (41-64%), organic carbon (14-26%), and dust (7-32%) were the major contributors to total AOD over India.

Conclusions:

  • The GEOS-Chem model, particularly with the SMOG inventory, shows potential for simulating AOD over India, though underprediction of coarse-mode aerosols and dust transport needs improvement.
  • Aerosol optical depth over India is significantly higher (factor of 5+) than over the United States, highlighting regional disparities.
  • Inorganic aerosols and organic carbon are dominant contributors to AOD in India, with substantial long-range transport influencing regional aerosol loading.