Radiative characterization of aerosols in the central Indo-Gangetic plain

Gorakhpur (26.75°N, 83.38°E and 85 m amsl), is strategically located in the central Indo-Gangetic Plain (IGP), near the foot hills of Himalayas and hence is an ideal place for studying long-range transport as well as local sources of aerosols and its radiative implications. Here we present results from two years, October 2013 until September 2015, of measurements of spectral aerosol optical depth (AOD) utilizing ground based, Multi- Wavelength Radiometer (MWR), and satellite, MODIS Terra remote sensing platforms. Mean AOD at 500 nm (AOD500) is 0.63±0.35, associated with a moderate Angstrom exponent (α) of 1.03±0.22 is found for the study period using MWR measurements. Highest AOD500 is found during the pre-monsoon months of May and June while lowest AOD500 in the post-monsoon months of October and November. The MWR observations have been compared with MODIS Terra derived AOD and a good correlation of 0.74 is found. We used HYSPLIT Lagrangian trajectory model to investigate long-range transport of aerosols to the study region. Aerosol sources in winter season are from the North-West part of the study region while that during pre-monsoon season lies in the south-westerly arid regions. This finding is also reflected in the α values which are high during winter months suggesting significant urban and biomass-burning contribution. α values are low and the turbidity coefficient (β) is high during pre-monsoon months indicating long-range transport of coarse dust particles carried by south westerly winds from the westerly desert regions.

[1]  K. V. S. Badarinath,et al.  Variations in the aerosol optical properties and types over the tropical urban site of Hyderabad, India , 2009 .

[2]  Sachchidanand Singh,et al.  Wavelength Dependence of the Aerosol Angstrom Exponent and Its Implications Over Delhi, India , 2011 .

[3]  Krishan Kumar,et al.  Aerosol climatology at Delhi in the western Indo‐Gangetic Plain: Microphysics, long‐term trends, and source strengths , 2013 .

[4]  Larry Di Girolamo,et al.  A climatology of aerosol optical and microphysical properties over the Indian subcontinent from 9 years (2000–2008) of Multiangle Imaging Spectroradiometer (MISR) data , 2010 .

[5]  Prabha R. Nair,et al.  Multiwavelength solar radiometer network and features of aerosol spectral optical depth at Trivandrum , 1989 .

[6]  Rachel T. Pinker,et al.  Aerosol radiative forcing during dust events over New Delhi, India , 2008 .

[7]  Sachchidanand Singh,et al.  Variation between near-surface and columnar aerosol characteristics during the winter and summer at Delhi in the Indo-Gangetic Basin , 2012 .

[8]  K. V. S. Badarinath,et al.  Black carbon aerosol variations over Patiala city, Punjab, India—A study during agriculture crop residue burning period using ground measurements and satellite data , 2012 .

[9]  S. Rao,et al.  Aerosol climatology over an urban site, Tirupati (India) derived from columnar and surface measurements: First time results obtained from a 30-day campaign , 2011 .

[10]  S. Babu,et al.  Climatology of columnar aerosol properties and the influence of synoptic conditions: First-time results from the northeastern region of India , 2009 .

[11]  Bo G Leckner,et al.  The spectral distribution of solar radiation at the earth's surface—elements of a model , 1978 .

[12]  Brent N. Holben,et al.  Variability of aerosol parameters over Kanpur, northern India , 2004 .

[13]  Glenn E. Shaw,et al.  Investigations of Atmospheric Extinction Using Direct Solar Radiation Measurements Made with a Multiple Wavelength Radiometer. , 1973 .

[14]  R. Draxler.  HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY Website , 2010 .

[15]  K. Moorthy,et al.  Investigations of marine aerosols over the tropical Indian Ocean , 1997 .

[16]  S. Ramachandran.  Aerosol optical depth and fine mode fraction variations deduced from Moderate Resolution Imaging Spectroradiometer (MODIS) over four urban areas in India , 2007 .

[17]  J. Lelieveld,et al.  Atmospheric pollutant outflow from southern Asia: a review , 2010 .

[18]  K. Lau,et al.  Accumulation of aerosols over the Indo-Gangetic plains and southern slopes of the Himalayas: distribution, properties and radiative effects during the 2009 pre-monsoon season , 2011 .

[19]  K. Badarinath,et al.  Impact of agriculture crop residue burning on atmospheric aerosol loading – a study over Punjab State, India , 2010 .

[20]  S. Suresh Babu,et al.  Buildup of aerosols over the Indian Region , 2013 .

[21]  Oleg Dubovik,et al.  Angstrom exponent and bimodal aerosol size distributions , 2006 .

[22]  W. Hall,et al.  A Theoretical Study of the Wet Removal of Atmospheric Pollutants. Part I: The Redistribution of Aerosol Particles Captured through Nucleation and Impaction Scavenging by Growing Cloud Drops , 1985 .