Ship-Borne Measurements of Columnar and Surface Aerosol Loading over the Bay of Bengal during W-ICARB Campaign: Role of Airmass Transport, Latitudinal and Longitudinal Gradients

Abstract

The present study analyzes simultaneous and collocated measurements of spectral columnar aerosol optical depth (AOD) and the variations in total mass concentration of near surface aerosols in the marine atmosphere over the Bay of Bengal (BoB) during the winter phase of the Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) expedition of December and January 2008/2009 on board the Oceanographic Research Vessel (ORV) of Sagar Kanya. High AOD 500 values (> 0.8) are found close to coastal regions in the western and northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plain (IGP). In these regions, the Ångström exponent α 380-1020 values are also found to be high (~1.2-1.3), indicating relative abundance of accumulation-mode continental aerosols. Low AOD 500 (0.1-0.2) values are observed in central and southern BoB, far away from the mainland. The AOD 500 and total aerosol mass loading increased along with the latitude. The total mass concentration is found to vary between 15 μg/m 3 and 45 μg/m 3 , with higher loadings near the east coast and northern parts of the BoB. NCEP reanalysis of the data with winds at 925 hPa, along with airmass trajectories calculated using the HYSPLIT model, suggest transport of continental aerosols from central and northern India over the BoB at lower heights, and mineral dust aerosol transport from arid regions in the west of India at higher altitudes; while the increase in aerosol loading over eastern BoB was strongly affected by airmasses originating from Southeast Asia. The spatial correlation map between the MODIS and MISR AOD data is analyzed, revealing a strong correlation between the two datasets. The influence of wind speed and continental airmass on AOD is also examined, which provides information on the effects of the adjoining landmass on the marine aerosol field.

Carbonaceous aerosols over Pune and Hyderabad (India) and influence of meteorological factors

“…The backward trajectories terminating over Pune on 21 and 28 November 2010 originate over the Bay of Bengal (BoB) and traverse through Indian landmass located to the southeast of Pune. Studies based on measurements over the BoB indicate that atmospheric aerosol loading over the BoB is influenced by anthropogenic emission over eastern and southern India along with biomass burning in Burma (Kumar et al 2013;Kumar et al 2015). In addition to it, the MODIS fire counts during post-monsoon season as depicted in Fig.…”

The Impact of Lockdown on Air Quality in Pakistan during the COVID-19 Pandemic Inferred from the Multi-sensor Remote Sensed Data

“…Results clearly show that a sharp decline in both AOT and PM2.5 values is observed during the first week of lockdown; however after some time, (during the last week of DLP-2020) a sudden increment in both the parameters is noticed attributed to the end of lockdown phase and the regain in anthropogenic activities associated with the restoration of social and commercial pursuits and increase in temperature (Sachin et al, 2020;Yueling et al, 2020). Since, relative humidity (RH) plays an effective role in the hygroscopic growth of atmospheric pollutants (Carrico et al, 2003;Kumar et al, 2013;Ahlawat et al, 2020).…”

Sensitivity of aerosol radiative forcing to various aerosol parameters over the Bay of Bengal

“…Detailed studies have been carried out regarding the heterogeneity of aerosols and aerosol loading over the BoB for different seasons (Moorthy et al 2003(Moorthy et al , 2008(Moorthy et al , 2010Kumar et al 2011Kumar et al , 2013. During the W-ICARB (Winter Integrated Campaign for Aerosols, Gases and Radiation Budget) field experiment during December 2008 and January 2009, it was found that there was an abundance of fine mode aerosols (highly absorbing), mostly of anthropogenic origins from the nearby continents (Moorthy et al 2010;Kaskaoutis et al 2011;Kumar et al 2013). These aerosols are mainly confined to the boundary layer (BL) due to the sources being near.…”