Abstract
ABSTRACT A study was conducted on the impact of biomass burning plumes transported from the Eastern Ghats region on the chemical characteristics of size-segregated aerosols over Kolkata, a tropical megacity situated in the eastern part of the Indo-Gangetic Plain. A Micro Orifice Uniform Deposit Impactor (MOUDI) was used to collect size-segregated aerosols affected and unaffected by the influence of transported biomass burning plumes during the pre-monsoon season (March–May) in 2016. Satellite observations revealed the presence of a thick polluted aerosol layer over Kolkata during the fire episodes, whereas a clean marine aerosol layer was observed during the normal episodes. Transported plumes enhanced the fine-mode aerosols, whereas the coarse-mode aerosols remained unaffected. PM1.0-0.1 and PM0.1 were greatly affected by the transported plumes, with a threefold increase during the fire episodes. K+, NH4+ and SO42– showed significant increases in the accumulation-mode (PM1.0-0.1) under the influence of biomass burning plumes, whereas NO3– showed an increase in the coarse-mode aerosols. The transported plumes did not change the mass-size distribution patterns of K+, NH4+ and SO42– (in which the unimodal fine-mode was dominant), but NO3– showed a change from a bimodal to a unimodal coarse-mode distribution under the influence of the plumes. It was observed that the biomass burning plumes interacted strongly with the accumulation- and superfine-mode (PM0.1) sea-salt particles, leading to the depletion of chloride. The maximum chloride depletion (~80%) was observed in the size range of 0.56–0.32 µm. It was observed that non-sea-SO42– was the key constituent responsible for the chloride loss from sea-salt particles. The biomass burning plume was found to have the potential to shift the dominance from coarse- to fine-mode particles in the mass-size distribution pattern of the total aerosols.
Highlights
The classification of the episodes was made mainly based on the number of fire pixels (MODIS) from the biomass burning over Eastern Ghats region, backward trajectory analysis and the identification of polluted aerosol layer over Kolkata using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)
The present study was conducted in order to investigate the impact of biomass burning plumes transported from the Eastern Ghats region on the size-segregated aerosol chemistry over Kolkata, a tropical metropolis on the Indo-Gangetic Plain during the pre-monsoon season (March–May) of 2016
The major findings of the study are as follows: ● Trajectory analysis and satellite based observations have shown the transport of biomass burning plumes from the Eastern Ghats region and the formation of a thick polluted dust layer over Kolkata
Summary
The classification of the episodes was made mainly based on the number of fire pixels (MODIS) from the biomass burning over Eastern Ghats region, backward trajectory analysis and the identification of polluted aerosol layer over Kolkata using CALIPSO. No such polluted smoke or dust aerosol layer was observed during the normal episodes rather the clean marine aerosol layer was identified over Kolkata suggesting the advection of sea-salt particles from the Bay of Bengal driven by the marine air masses.
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