10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Aerosol Size Distributions over the Indo-Gangetic Plains Just Prior to the Onset of SW-Monsoon
MUKUNDA M GOGOI, Suresh Babu, S.K. Satheesh, Krishna K Moorthy, Vikram Sarabhai Space Centre
Abstract Number: 352 Working Group: Aerosols in Earth System
Abstract As part of the South West Asian Aerosol Monsoon Interaction (SWAAMI) experiment, we have investigated the three dimensional (spatio-temporal and vertical) properties of aerosol size distribution over three distinct geographic regions of northern India just prior (01 - 20, Jun 2016) to the onset of south west (SW) monsoon. This is based on observations on-board a beechcraft-200 aircraft over Jodhpur (JDR) in the northwestern India, Varanasi (VNS) in the central part of Indo-Gangetic Plains (IGP) and Bhubaneswar (BBR) in the eastern peninsula. Aerosol number size distributions, in general, followed bimodal structures having a prominent mode in sub-micron range (< 1µm), having highest magnitude over JDR, followed by VNS and BBR. Interestingly, aerosol mass size distributions showed higher values (beyond 10μm particle size range) at BBR, while the dominance of fine mode was significant over JDR. Vertically, aerosol total number concentrations (NT) decreased with altitude in the entire size spectra. The variation in aerosol size distributions from surface to the ceiling altitude of aircraft measurement was more conspicuous at VNS. Near the surface, coarse mode aerosol concentrations (NC) decreased from west (JDR) to east (BBR), while the accumulation mode concentrations (NA) remained highest at VNS. Regionally, the day to day variations (corresponding to each distinct flight direction) of the altitudinal distributions of aerosols were more conspicuous at BBR, indicating the contrasting influence of marine and anthropogenic components over near coastal location in the Indian peninsula. Vertical profiles of Black Carbon (BC) mass fractions are also examined for individual days during which the flight sorties were made along distinct directions. BC mass fraction remains lowest at JDR. At VNS, very high values are seen up to 1.5 km (probably the inversion height) above which the fraction steeply falls off. On the other hand, at BBR, though the surface BC fractions were low, it increased steadily with altitude up to 2 km and remained nearly steady thereafter. At BBR, the higher values are BC mass fractions were noticeable when the flight sorties were made over the region of thermal power plants located south west of the BBR base station. Over the same region, concentrations of NO2 and SO2 were also found high, indicating the emissions from coal burning in the region. Aerosol depolarization ratio and aerosol types derived from the cloud aerosol transportation system (CATS) onboard International Space Station (ISS) indicated the presence of dust loading at JDR, mixed with soot in the central IGP and a mixture soot, dust and sea-salt at BBR. Vertical cross section of the values of attenuated backscatter coefficients (from CATS) indicated that the vertical extension of aerosols reached as high as 5 km during the period of observation. Analysis of CloudSat data revealed the stronger influence of aerosols on cloud droplets properties over BBR, where the cloud effective radii were found to be lower in comparison to the values at VNS.