Atmospheric aerosols in the Indo-Gangetic Plain (IGP) depicts high spatial and temporal heterogeneity in their radiative properties. Despite the fact that significant advancement in terms of characterizing aerosols radiative and physiochemical properties in the IGP have been made, information regarding the organic content towards total absorbing aerosol budget is lacking. In the present study we have analyzed two years of aerosol spectral light absorption measurements from the central-IGP, Gorakhpur (26.75°N, 83.38°E, 85m amsl), in order to study their seasonal behavior and to quantify their magnitude in terms of absorbing aerosols loading and source speciation. Remote sensing data in the form of 'Cloud corrected Fire Count' from MODIS Terra and 'Absorption Aerosol Index' from OMI satellites platform have been used to identify absorbing aerosol source regions. Spectral absorption analysis reveals a four-fold enhancement in absorption in the winter (W) and the post-monsoon (PoM) seasons at UV wavelengths as compared to 880 nm on account of increased biomass aerosol contribution to total absorbing aerosol load. Despite having higher fire events and absorption aerosol index, both indicating high biomass burning activities, in the pre-monsoon (PM) season, aerosols from the biomass sources contribute ~ 27% during the W and the PoM seasons as against ~17% in the PM season to the total absorbing aerosol content. This is due to near stagnant wind conditions and shallow height of air masses travelling to the central IGP in the W and the PoM seasons.
In view of the increasing anthropogenic presence and influence of aerosols in the northern polar regions, long-term continuous measurements of aerosol optical parameters have been investigated over the Svalbard region of Norwegian Arctic (Ny-Ålesund, 79°N, 12°E, 8 m ASL). This study has shown a consistent enhancement in the aerosol scattering and absorption coefficients during spring. The relative dominance of absorbing aerosols is more near the surface (lower single scattering albedo), compared to that at the higher altitude. This is indicative of the presence of local anthropogenic activities. In addition, long-range transported biomass burning aerosols (inferred from the spectral variation of absorption coefficient) also contribute significantly to the higher aerosol absorption in the Arctic spring. Aerosol optical depth (AOD) estimates from ground based Microtop sun-photometer measurements reveals that the columnar abundance of aerosols reaches the peak during spring season. Comparison of AODs between ground based and satellite remote sensing indicates that deep blue algorithm of Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals over Arctic snow surfaces overestimate the columnar AOD.
Characteristics of atmospheric aerosols and their radiative impacts show large variations in space and time, leading to
large uncertainties in the climate impact assessment. Despite the concerted efforts in the last decade through several
field campaigns, the uncertainty still persists. This essentially arises due to lack of a comprehensive data on several
aerosol parameters with adequate spatial resolution and for long duration. This is particularly true for the Indian region,
with large geographical diversities, large density of population, diverse living habits and rapid industrialization. With a
view to addressing to this problem and to evolve a regional scale database for assessing the radiative impacts of
aerosols, an integrated, multi-platform field campaign, ICARB, was carried out during March-May 2006, under the
ISRO's Geosphere Biosphere Programme. The campaign involved participation by more than 100 scientists from about
35 different institutions across the country and collocated observation over the mainland, over oceans and same time
measurements of altitude profiles using aircrafts. A campaign of this magnitude is carried out for the first time in this
region, and perhaps for the first time globally. The mainland observations included a network of aerosol observatories
over Indian landmass and from islands in the Arabian Sea and Bay of Bengal, while a dedicated scientific cruise of 64-
days duration covered the vast oceanic regions around India. Altitude profiles were obtained using research aircraft of
the National Remote Sensing Agency, from 5 different bases. The details of the campaign and the preliminary findings
will be presented.
Continuous and near-real-time measurements of BC were made for a period of two years from the I-LARC (ISRO Laboratory for Aerosol Radiation and Chemistry) station in Port Blair as a part of the ISRO Geosphere Biosphere Programme (I-GBP). These are used to characterize BC, for the first time over the Bay of Bengal (BoB), which is surrounded by distinct landmasses having highly varying anthropogenic activities. Significantly high concentrations (~2.4 μg m-3) occur during the period September to April. During this period, BC contributes ~ 6.5 % to the composite aerosol mass concentration. The concentration and its share to the composite aerosols decrease rapidly (by a factor of >3) and remain so during the period June to August when the station is under the influence of monsoon winds coming from the Indian Ocean. Back-trajectory analyses reveal five potential advection pathways, which are seasonal in nature and have a strong influence on the BC concentrations over the island. The results and their implications will be discussed.
Enhanced aerosol loading over the Indo-Gangetic Plain (IGP) is a regular feature during winter months. In addition to the environmental degradation and reduced visibility, these aerosols can cause significant radiative impact also. In view of this, a campaign mode observation under ISRO-GBP was conducted in December 2004 to characterize the aerosol properties over the IGP. As part of this, extensive measurements of aerosol BC were made from Kharagpur, an inland rural location lying at the eastern end of the Indo Gangetic Plain. It also lies close to several industrialized regions and area having lot of mining activities
Results showed, extremely high BC concentration, often exceeding ~20 mg m-2, prevailed during December. During this period, BC concentration also showed large diurnal variation. Simultaneous measurements of the local atmospheric boundary layer height and wind fields revealed a very close association between the BC concentration and the ventilation coefficient (defined as the product of the boundary layer height and the transport wind). Back trajectory analyses using HYSPLIT revealed that in addition to the local boundary layer dynamics, the changes in the advection pathways also influence the concentration of BC.
In this paper, we report the results of extensive, and all-season, collocated, measurements of several aerosol parameters
[such as spectral aerosol optical depth (AOD) at 10 bands spanning from UV to IR; mass size distribution and mass
concentration of composite aerosols; as well as mass concentration and mass mixing ratio of aerosol black carbon (BC)]
for over a 4-year period (January 2000 to December 2003), from an unindustrialized coastal location, Trivandrum
(8.55°N, 76.9°E), close to the southern tip of Indian peninsula and use these properties to estimate the aerosol short wave
radiative forcing. The results show that the top of the atmosphere (TOA) forcing is significantly positive during winter
while it changes to negative during monsoon and post monsoon seasons. The surface forcing decreases from winter to
summer. Consequently, the net atmospheric absorption decreases from a high value in winter to low values during
monsoon.
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