Susan K. George

Bio: Susan K. George is an academic researcher from Vikram Sarabhai Space Centre. The author has contributed to research in topics: Aerosol & Chemical composition. The author has an hindex of 8, co-authored 8 publications receiving 461 citations. Previous affiliations of Susan K. George include Indian Ministry of Environment and Forests & Indian Space Research Organisation.

Wintertime aerosol characteristics over the Indo‐Gangetic Plain (IGP): Impacts of local boundary layer processes and long‐range transport

Abstract: [1] The Indo-Gangetic Plain (IGP) encompasses a vast area, (accounting for ∼21% of the land area of India), which is densely populated (accommodating ∼40% of the Indian population). Highly growing economy and population over this region results in a wide range of anthropogenic activities. A large number of thermal power plants (most of them coal fed) are clustered along this region. Despite its importance, detailed investigation of aerosols over this region is sparse. During an intense field campaign of winter 2004, extensive aerosol and atmospheric boundary layer measurements were made from three locations: Kharagpur (KGP), Allahabad (ALB), and Kanpur (KNP), within the IGP. These data are used (1) to understand the regional features of aerosols and BC over the IGP and their interdependencies, (2) to compare it with features at locations lying at far away from the IGP where the conditions are totally different, (3) to delineate the effects of mesoscale processes associated with changes in the local atmospheric boundary layer (ABL), (4) to investigate the effects of long-range transport or moving weather phenomena in modulating the aerosol properties as well as the ABL characteristics, and (5) to examine the changes as the season changes over to spring and summer. Our investigations have revealed very high concentrations of aerosols along the IGP, the average mass concentrations (MT) of total aerosols being in the range 260 to 300 μg m−3 and BC mass concentrations (MB) in the range 20 to 30 μg m−3 (both ∼5 to 8 times higher than the values observed at off-IGP stations) during December 2004. Despite, BC constituted about 10% to the total aerosol mass concentration, a value quite comparable to those observed elsewhere over India for this season. The dynamics of the local atmospheric boundary layer (ABL) as well as changes in local emissions strongly influence the diurnal variations of MT and MB, both being inversely correlated with the mixed layer height (Zi) and the ventilation coefficient (Vc). The share of BC to total aerosols is highest (∼12%) during early night and lowest (∼4%) in the early morning hours. While an increase in the Vc results in a reduction in the concentration almost simultaneously, an increase in Zimax has its most impact on the concentration after ∼1 day. Accumulation mode aerosols contributed ∼90% to the aerosol concentration at ALB, ∼77 % at KGP and 74% at KNP. The BC mass mixing ratio was ∼10% over all three locations and is comparable to the value reported for Trivandrum, a tropical coastal location in southern India. This indicates presence of submicron aerosols species other than BC (such as sulfate) over KGP and KNP. A cross-correlation analysis showed that the changes in MB at KGP is significantly correlated with those at KNP, located ∼850 km upwind, and ALB after a delay of ∼7 days, while no such delay was seen between ALB and KNP. Back trajectory analyses show an enhancement in MB associated with trajectories arriving from west, the farther from to the west they arrive, the more is the increase. This, along with the ABL characteristics, indicate two possibilities: (1) advection of aerosols from the west Asia and northwest India and (2) movement of a weather phenomena (such as cold air mass) conducive for build up of aerosols from the west to east. As the winter gives way to summer, the change in the wind direction and increased convective mixing lead to a rapid decrease in MB.

Seasonal trends in chemical composition of aerosols at a tropical coastal site of India

Abstract: [1] Chemical composition of near-surface aerosols at the tropical coastal location Trivandrum (8.55°N, 77°E) has been studied by analyzing the aerosol samples collected during a period of 16 months from October 2003 to January 2005. The annual mean aerosol mass loading at this site averages to around 54 ± 19 μg m−3. The chemical analysis of samples revealed Cl−, SO42−, and NO3− to be the major anionic species and Na, NH4+, Fe, and Ca to be the major cationic species. The total mass loading and the mass concentration of various chemical species showed pronounced seasonal dependence. The active aerosol sources at this location have been investigated in detail to delineate their relative dominance in different seasons. Ions like Na, Cl, Mg, and K, which are mainly of oceanic origin, showed peak during monsoon, indicating sea spray to be the most important source mechanism during the period. On the other hand, mass loading of SO42−, NH4+, PO43−, Fe, and Al and that of trace elements exhibited their maximum in winter/summer, indicating the dominance of continental/crustal sources during the period. The sea salt and non-sea salt components of individual ions like SO42−, K, Ca, and Mg also revealed distinctly different seasonal patterns. In spite of being a coastal site, the non-sea salt components dominated at this location. Dominance of non-sea salt SO42− throughout the year indicates significant anthropogenic influence at this location. On the basis of this study, a first-cut model for the chemical composition of aerosols at this tropical coastal site has been evolved.

Aerosol transport over the Gangetic basin during ISRO-GBP land campaign-II

Abstract: MODIS (Moderate Resolution Imaging Spectro- radiometer) Level-3 aerosol optical depth (AOD) data and NCEP (National Centre for Environmental Prediction) re- analysis winds were incorporated into an aerosol flux conti- nuity equation, for a quantitative assessment of the sources of aerosol generation over the Ganga basin in the winter month of December 2004 Preliminary analysis on the aerosol dis- tribution and wind fields showed wind convergence to be an important factor which, supported by the regional topogra- phy, confines aerosols in a long band over the Indo Gangetic plain (IGP) stretching from the west of the Thar desert into the Head-Bay-of-Bengal The prevailing winds of the sea- son carry the aerosols from Head-Bay-of-Bengal along the east coast as far as the southern tip of the peninsular India A detailed examination of MODIS data revealed significant day-to-day variations in aerosol loading in localised pock- ets over the central and eastern parts of the Indo Gangetic plain during the second half of December, with AOD values even exceeding unity Aerosols over the Ganga basin were dominated by fine particles (geometric mean radius 005- 01µm) while those over the central and western India were dominated by large particles (geometric mean radius 03- 07µm) Before introducing it into the flux equation, the MODIS derived AOD was validated through a comparison with the ground-based measurements collected at Kharagpur and Kanpur; two stations located over the Ganga basin The strength of the aerosol generation computed using the flux equation indicated the existence of aerosol sources whose lo- cations almost coincided with the concentration of thermal power plants The quantitative agreement between the source strength and the power plant concentration, with a correlation coefficient 085, pointed to thermal power plants as substan- tial contributors to the high aerosol loading over the Ganga Basin in winter The layout of aerosol sources also nearly matched the spatial distribution of the Respirable Suspended Particulate Matter (RSPM), derived from the Central Pollu- tion Control Board (CPCB) data, lending additional support to our inference

Surprising observation of large anthropogenic aerosol fraction over the “near‐pristine” southern Bay of Bengal: Climate implications

Abstract: The Bay of Bengal (BoB), a small oceanic region surrounded by landmasses with distinct natural and anthropogenic activities and under the influence of seasonally changing airmass types, is characterized by a rather complex and highly heterogeneous aerosol environment. Concurrent measurements of the physical, optical, and chemical (offline analysis) properties of BoB aerosols, made onboard extensive ship-cruises and aircraft sorties during Integrated Campaign for Aerosols, gases and Radiation Budget of March-April 2006, and satellite-retrieved aerosol optical depths and derived parameters, were synthesized following a synergistic approach to delineate the anthropogenic fraction to the composite aerosol parameters and its spatial variation. Quite interestingly and contrary to the general belief, our studies revealed that, despite of the very high aerosol loading (in the marine atmospheric boundary layer as well as in the vertical column) over the northern BoB and a steep decreasing gradient toward the southern latitudes, the anthropogenic fraction showed a steady increase from North to South (where no obvious anthropogenic source regions exist). Consequently, the direct radiative forcing at the top of the atmosphere due to anthropogenic aerosols remained nearly constant over the entire BoB with values in the range from -3.3 to -3.6 Wm(-2). This interesting finding, beyond doubts calls for a better understanding of the complex aerosol system over the BoB through more focused field campaigns.

Atmospheric pollutant outflow from southern Asia: a review

Abstract: . Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

A climatology of aerosol optical and microphysical properties over the Indian subcontinent from 9 years (2000–2008) of Multiangle Imaging Spectroradiometer (MISR) data

Abstract: Received 16 October 2009; revised 20 January 2010; accepted 25 January 2010; published 5 August 2010. [1] We present the first detailed analysis of a 9 year (2000–2008) seasonal climatology of size‐ and shape‐segregated aerosol optical depth (AOD) and Angstrom exponent (AE) over the Indian subcontinent derived from the Multiangle Imaging Spectroradiometer (MISR). Our analysis is evaluated against in situ observations to better understand the error characteristics of and to corroborate much of the space‐time variability found within the MISRaerosol properties. Thespace‐time variability isdiscussed interms ofaerosol sources, meteorology, and topography. We introduce indices based on aerosol size‐ and shape‐ segregated optical depth and their effect on AE that describe the relative seasonal change in anthropogenic and natural aerosols from the preceding season. Examples of major new findings include the following: (1) winter to premonsoon changes in aerosol properties are not just dominated by an increase in dust, as previously thought, but also by an increase in anthropogenic components, particularly in regions where biomass combustion is prevalent; (2) ∼15% of the AOD over the high wintertime pollution in the eastern Indo‐ Gangetic basin is due to large dust particles, resulting in the lowest AE (<0.8) over India in this season and likely caused by rural activities (e.g., agriculture, etc.) from the densely populated rural area; (3) while AOD decreases from the Indo‐Gangetic basin up to the Tibetan Plateau, a large peak in AE and the fraction of AOD due to particle radii <0.7 mm exists in the foothills of the Himalayas, particularly in the premonsoon season; and (4) the AOD due to nonspherical particles exhibits a strong ocean‐to‐land gradient over all seasons because of topographical and meteorological controls.