Aerosol Optical Depth Over India

Abstract

Abstract Tropospheric aerosol optical depth (AOD) over India was simulated by Goddard Earth Observing System (GEOS)‐Chem, a global 3‐D chemical‐transport model, using SMOG (Speciated Multi‐pOllutant Generator from Indian Institute of Technology Bombay) and GEOS‐Chem (GC) (current inventories used in the GEOS‐Chem model) inventories for 2012. The simulated AODs were ~80% (SMOG) and 60% (GC) of those measured by the satellites (Moderate Resolution Imaging Spectroradiometer and Multi‐angle Imaging SpectroRadiometer). There is no strong seasonal variation in AOD over India. The peak AOD values are observed/simulated during summer. The simulated AOD using SMOG inventory has particulate black and organic carbon AOD higher by a factor ~5 and 3, respectively, compared to GC inventory. The model underpredicted coarse‐mode AOD but agreed for fine‐mode AOD with Aerosol Robotic Network data. It captured dust only over Western India, which is a desert, and not elsewhere, probably due to inaccurate dust transport and/or noninclusion of other dust sources. The calculated AOD, after dust correction, showed the general features in its observed spatial variation. Highest AOD values were observed over the Indo‐Gangetic Plain followed by Central and Southern India with lowest values in Northern India. Transport of aerosols from Indo‐Gangetic Plain and Central India into Eastern India, where emissions are low, is significant. The major contributors to total AOD over India are inorganic aerosol (41–64%), organic carbon (14–26%), and dust (7–32%). AOD over most regions of India is a factor of 5 or higher than over the United States.