Spatial Variability and Radiative Impact of Aerosol along the Brahmaputra River Valley in India: Results from a Campaign

Abstract

The first ever land campaign to study the spatial variability of the aerosol characteristics along the Brahmaputra river valley (BRV) in Assam, North-Eastern India, was conducted during 2011. Measurements were made over 13 locations for Aerosol Optical Depth (AOD), scattering coefficient, particulate matter, black carbon (BC) concentration and meteorological parameters. The BRV is divided into three sectors longitudinally viz western sector (WS), central sector (CS), and eastern sector (ES). Significant Spatial heterogeneity in AOD and BC concentration was observed (p < 0.05) with the highest values over WS and a continual decrease from WS to ES with aerosol dominance in PM2.5 category along the entire valley. The Angstrom coefficient measured using different wavelength pairs showed spatial variability indicating dominance of fine particles over WS and coarse particles in ES with a probable bimodal distribution. The scattering and absorption coefficient shows dominance of both types of aerosol over WS than other areas. The shortwave radiative forcing was higher over the WS than CS and ES of the valley. The campaign revealed that under favorable wind conditions, the BRV is loaded with significant amount of natural and anthropogenic aerosol during local winter and is influenced by the long-range transport of aerosols from the Indo-Gangetic plain.

Observation and model simulation of aerosol optical properties and size distribution over the hilly terrain of Northeast India

“…The study region is chosen because it is of genuine research importance due to the simultaneous existence of a range of both natural and anthropogenic aerosols (e.g., sand dust, marine, forest re, industrial emission, etc.,) as reported in earlier works (Pathak et al 2015; Kundu et al 2018; Barman et al 2018; 2019) that makes the region hotspot for aerosol research. The station witnessed high precipitation throughout the monsoon every year and a larger water body nearby, causing a greater rate of evaporation/condensation over the study area.…”

Impact of Biomass Burning on Black Carbon and NO2 Over North Eastern Region of India Using Multi-satellite Observations

“…Production of high absorbing aerosol (BC) over different parts of Assam during the winter season has been reported by Kundu et al ( 2018 ), due to rice crop residue burning, small-scale forest fires, shrubs etc. Transportation of aerosol from IGP by strong westerly wind also contributes to high BC concentrations during the January and February months.…”

“…BC also rises simultaneously. Cluster analysis of seasonal wind back trajectories showed that the majority of them are passed through the IGP and Bangladesh region, which is relatively polluted from industrial emissions, brick kiln releases, burning of fossil fuels, firewood, and cow dung burning and stubble (Barman et al, 2018 ; Kundu et al, 2018 ; Pathak et al, 2015 ). As evident by seasonal mean trajectories, gaseous pollutants, including BC, are being imported by the winds.…”

“…During the burning phase, a considerable reduction in direct solar radiation and lower visibility was reported in the same study. Kundu et al ( 2018 ) demonstrated that the Brahmaputra river valley in NER is burdened with a lot of natural and anthropogenic aerosol during local winter and is modified by the prolonged dispersion of pollutants from the Indo-Gangetic plain (IGP). Dahutia et al ( 2018 ) reported the aerosol features and their climatic consequences over the region by employing numerous satellites and reanalysis datasets.…”

A New Method to Estimate Aerosol Radiative Forcing on Photosynthetically Active Radiation

“…Model-model comparisons have shown that different radiative transfer codes may agree well if they are run with identical optical properties as input (Halthore et al, 2005). The SBDART model is selected here by its high accuracy (Li et al, 2010), besides it has been consistently developed over the past few decades (Kundu et al, 2018) and has been extensively applied to ARF in studies of atmosphere energy budget and also in satellite remote sensing (Luo et al, 2019).…”