Browsing by Author "U.C. Dumka"

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Aerosol chemical characterization and role of carbonaceous aerosol on radiative effect over Varanasi in central Indo-Gangetic Plain
(Elsevier Ltd, 2016) S. Tiwari; U.C. Dumka; D.G. Kaskaoutis; Kirpa Ram; A.S. Panicker; M.K. Srivastava; Shani Tiwari; S.D. Attri; V.K. Soni; A.K. Pandey
This study investigates the chemical composition of PM10 aerosols at Varanasi, in the central Indo-Gangetic Plain (IGP) during April to July 2011, with emphasis on examining the contribution of elemental carbon (EC) to the estimates of direct aerosol radiative effect (DARE). PM10 samples are analysed for carbonaceous aerosols (Organic Carbon, OC and EC) and water-soluble ionic species (WSIS: Cl-, SO42-, NO3-, PO42- NH4+, Na+, K+, Mg2+ and Ca2+) and several diagnostic ratios (OC/EC, K+/EC, etc) have been also used for studying the aerosol sources at Varanasi. PM10 mass concentration varies between 53 and 310 μgm-3 (mean of 168 ± 73 μgm-3), which is much higher than the National and International air quality standards. The OC mass concentration varies from 6 μg m-3 to 24 μg m-3 (mean of 12 ± 5 μg m-3; 7% of PM10 mass), whereas EC ranges between 1.0 and 14.3 μg m-3 (4.4 ± 3.9 μg m-3; ~3% of PM10 mass). The relative low OC/EC of 3.9 ± 2.0 and strong correlation (R2 = 0.82) between them suggest the dominance of primary carbonaceous aerosols. The contribution of WSIS to PM10 is found to be ~12%, out of which ~57% and 43% are anions and cations, respectively. The composite DARE estimates via SBDART model reveal significant radiative effect and atmospheric heating rates (0.9-2.3 Kday-1). Although the EC contributes only ~3% to the PM10 mass, its contribution to the surface and atmospheric forcing is significantly high (37-63% and 54-77%, respectively), thus playing a major role in climate implications over Varanasi. © 2015 Elsevier Ltd.
Aerosol optical properties over delhi and manora peak during a rare dust event in early april 2005
(Taylor and Francis Ltd., 2011) S.K. Srivastava; M.K. Srivastava; A. Saha; S. Tiwari; S. Singh; U.C. Dumka; B.P. Singh; N.P. Singh
Dust storm events are annual phenomena observed over the Indo-Gangetic plain (IGP) during the pre-monsoon period (May-June). These dust storms affect the air quality, weather conditions and radiation budget of the region. In this paper we characterize the aerosol optical parameters associated with a rare dust storm event that hit the IGP during early April 2005. This event was considered rare as it occurred much earlier than the general occurrence of dust storms in India (May-June), and in the year 2005, the warmest year in the span of the previous hundred years. In this study we considered the optical aerosol parameters for two places in the IGP: Delhi (28.5° N, 77.2° E, 325 m asl) and the high altitude station, Manora Peak (29.4° N, 79.5° E, 1958 m asl). Of the two selected stations, Delhi represents a highly populated and polluted location whereas Manora Peak represents a cleaner location in the central Himalayan region. During this dust storm event, the aerosol optical depth (AOD) was observed to increase considerably. The increment was 2.6-4.6 times over Delhi and 1.6-3.2 times over Manora Peak at wavelengths 380 and 1020 nm, respectively, with respect to the background values, whereas the Ångström exponent (α) for both the stations remained close to zero during the event. The effect shows a considerable increase in direct dust radiative forcing in terms of a reduction in the broadband global irradiance for Delhi as well as for Manora Peak stations. The direct aerosol radiative forcing thus obtained was about 34% in the 400-1100 nm wavelength band at Manora Peak. © 2011 Taylor & Francis.
Intra-seasonal variability of black carbon aerosols over a coal field area at Dhanbad, India
(Elsevier Ltd, 2015) S. Singh; S. Tiwari; D.P. Gond; U.C. Dumka; D.S. Bisht; Shani Tiwari; G. Pandithurai; A. Sinha
Black carbon (BC) aerosols, which are optically absorbing parts of carbonaceous aerosols and have significantly different optical and radiative properties were continuously measured at a coal field area in Dhanbad (23° 47' N, 86° 30' E: 222m amsl), India for the first time from 1st January to 31st December, 2012. Daily BC mass concentrations varied within the range of 0.84-17.0μgm-3 with an annual average of 6.3±2.7μgm-3. About 45% of samples of the measured days exceeded the mean level of BC indicating the high loading of soot particles over the study region. Intra-seasonal variation in BC concentrations exhibited a strong seasonal cycle with the highest concentrations during winter (8.2±2.8μgm-3), followed by post-monsoon (6.4±2.6μgm-3), pre-monsoon (5.5±1.9μgm-3) and monsoon (4.6±1.7μgm-3). In diurnal analysis, BC showed a significant peak from 06:00 to 10:00 local time (LT) during all the seasons whereas the lowest concentrations were found during 14:00 to 17:00 LT in the late afternoon. The difference between maximum and minimum concentrations of BC was found to be higher during winter (8.3μgm-3) followed by post-monsoon (4.7μgm-3), pre-monsoon (4.3μgm-3) and monsoon (1.7μgm-3). An interesting feature was seen in the difference between morning and evening peaks, it was maximum during winter (4.8μgm-3) followed by pre-monsoon (1.5μgm-3) and post-monsoon (1.3μgm-3), however, during monsoon, it was opposite i.e. ~23% lower during morning time. During day-time and night-time variability analyses, it fluctuated largely, varying from 1% (December) to 35% (June) higher during night-time as compared to day-time as whole mean was ~19%. Data of BC were separated as stable (<1ms-1) and unstable weather conditions (>1ms-1), the corresponding values of BC were 6.06 and 3.75μgm-3 respectively which is ~38% higher during stable weather condition indicating that the major portion of BC was mainly emitted from local sources instead of transported from remote sources. Apart from this, it was observed that the concentration of BC mass during winter was ~78% higher (8.2μgm-3) as compared to monsoon (4.6μgm-3) when the winds were from the SE (158°) direction. © 2015 Elsevier B.V.
Scattering and absorption properties of near-surface aerosol over Gangetic-Himalayan region: The role of boundary-layer dynamics and long-range transport
(Copernicus GmbH, 2015) U.C. Dumka; D.G. Kaskaoutis; M.K. Srivastava; P.C.S. Devara
Light scattering and absorption properties of atmospheric aerosols are of vital importance for evaluating their types, sources and radiative forcing. This is of particular interest over the Gangetic-Himalayan (GH) region due to uplift of aerosol from the plains to the Himalayan range, causing serious effects on atmospheric heating, glaciology and monsoon circulation. In this respect, the Ganges Valley Aerosol Experiment (GVAX) was initiated in Nainital from June 2011 to March 2012 with the aim of examining the aerosol properties, source regions, uplift mechanisms and aerosol-radiation-cloud interactions. The present study examines the temporal (diurnal, monthly, seasonal) evolution of scattering (σsp) and absorption (σap) coefficients, their wavelength dependence, and the role of the Indo-Gangetic plains (IGP), boundary-layer dynamics (BLD) and long-range transport (LRT) in aerosol evolution via the Atmospheric Radiation Measurement Mobile Facility. The analysis is separated for particles 10μm and <1 μm in diameter in order to examine the influence of particle size on optical properties. The σsp and σap exhibit a pronounced seasonal variation between the monsoon low and post-monsoon (November) high, while the scattering wavelength exponent exhibits higher values during the monsoon, in contrast to the absorption Ångström exponent which maximizes in December-March. The elevated-background measuring site provides the advantage of examining the LRT of natural and anthropogenic aerosols from the IGP and southwest Asia and the role of BLD in the aerosol lifting processes. The results reveal higher aerosol concentrations at noontime along with an increase in mixing height, suggesting influence from IGP. The locally emitted aerosols present higher wavelength dependence of the absorption in October-March compared to the rather well-mixed and aged transported aerosols. Monsoon rainfall and seasonally changing air masses contribute to the alteration of the extensive and intensive aerosol properties.
Seasonal inhomogeneity of soot particles over the central indo-gangetic plains, India: Influence of meteorology
(Chinese Meteorological Society, 2015) B.P. Singh; S. Tiwari; Philip K. Hopke; R.S. Singh; D.S. Bisht; A.K. Srivastava; R.K. Singh; U.C. Dumka; A.K. Singh; B.N. Rai; Manoj K. Srivastava
Black carbon (BC) particles play a unique and important role in earth’s climate system. BC was measured (in-situ) in the central part of the Indo-Gangetic Plains (IGP) at Varanasi, which is a highly populated and polluted region due to its topography and extensive emission sources. The annual mean BC mass concentration was 8.92 ± 7.0 μg m−3, with 34% of samples exceeding the average value. Seasonally, BC was highest during the post-monsoon and winter periods (approximately 18 μg m−3) and lower in the premonsoon/ monsoon seasons (approximately 6 μg m−3). The highest frequency (approximately 46%) observed for BC mass was in the interval from 5 to 10 μg m−3. However, during the post-monsoon season, the most common values (approximately 23%) were between 20 and 25 μg m−3. The nighttime concentrations of BC were approximately twice as much as the daytime values because of lower boundary layer heights at nighttime. The Ångström exponent was significantly positively correlated (0.55) with ground-level BC concentrations, indicating the impact of BC on the columnar aerosol properties. The estimated mean absorption Ångström exponent was 1.02 ± 0.08 μg m−3, indicating that the major source of BC was from fossil fuel combustion. Significant negative correlations between BC mass and meteorological parameters indicate a pronounced effect of atmospheric dynamics on the BC mass in this region. The highest mean BC mass concentration (18.1 ± 6.9 μg m−3) as a function of wind speed was under calm wind conditions (38% of the time). © The Chinese Meteorological Society and Springer-Verlag Berlin Heidelberg 2015.