Browsing by Author "Shani Tiwari"

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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 climatology over the Bay of Bengal and Arabian Sea inferred from space-borne radiometers and lidar observations
(AAGR Aerosol and Air Quality Research, 2016) Shani Tiwari; Amit K. Mishra; Abhay K. Singh
Atmospheric aerosols over the oceanic region are very important air pollutant and play a vital role in Earth’s radiation budget and climate change. This study presents the aerosol climatology over the Bay of Bengal (BoB) and Arabian sea (AS) using long term (2006–2012) data from space-borne radiometers [Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI)] and space-based active lidar onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). AS experiences higher AOD as compared to that over BoB during the study period. A good periodicity along with strong intra-seasonal/annual variability in aerosol loading is also observed over both the study regions. Approximately one month lag is found for maximum aerosol loading period over AS and BoB for almost every year i.e., June–July for AS and May–June for BoB. This lag could be explained by pathway and timing of summer monsoon over the Indian subcontinent. Elevated layers of absorbing dust up to 2–4 km altitudes are observed during the pre-monsoon and monsoon seasons over both the regions. The CALIPSO measurements show strong seasonal heterogeneity in aerosol properties over both the regions, which is well corroborated with MODIS and OMI observations. This significant seasonal heterogeneity in aerosol loading has been explained by the role of transportation of aerosols from various emission sources using NOAA HYSPLIT back trajectory model at three different altitude levels viz. 500, 1500 and 2500 m height. The possible role of Indian summer monsoon in modulating the aerosol behaviour over AS and BoB is another important aspect of this study that need further analyses using higher spatio-temporal resolution data. © Taiwan Association for Aerosol Research.
Aerosol columnar characteristics and their heterogeneous nature over Varanasi, in the central Ganges valley
(Springer Verlag, 2018) Shani Tiwari; Dimitris Kaskaoutis; Vijay Kumar Soni; Shiv Dev Attri; Abhay Kumar Singh
The Indo–Gangetic Basin (IGB) experiences one of the highest aerosol loading over the globe with pronounced inter-/intra-seasonal variability. Four-year (January 2011–December 2014) continuous MICROTOPS-II sun-photometer measurements at Varanasi, central Ganges valley, provide an opportunity to investigate the aerosol physical and optical properties and their variability. A large variation in aerosol optical depth (AOD: from 0.23 to 1.89, mean of 0.82 ± 0.31) and Ångström exponent (AE: from 0.19 to 1.44, mean of 0.96 ± 0.27) is observed, indicating a highly turbid atmospheric environment with significant heterogeneity in aerosol sources, types and optical properties. The highest seasonal means of both AOD and AE are observed in the post-monsoon (October–November) season (0.95 ± 0.31 for AOD and 1.16 ± 0.14 for AE) followed by winter (December, January, February; 0.97 ± 0.34 for AOD and 1.09 ± 0.20 for AE) and are mainly attributed to the accumulation of aerosols from urban and biomass/crop residue burning emissions within a shallow boundary layer. In contrast, during the pre-monsoon and monsoon seasons, the aerosols are mostly coming from natural origin (desert and mineral dust) mixed with pollution in several cases. The spectral dependence of AE, the aerosol “curvature” effect and other graphical techniques are used for the identification of the aerosol types and their mixing processes in the atmosphere. Furthermore, the aerosol source–apportionment assessment using the weighted potential source contribution function (WPSCF) analysis reveals the different aerosol types, emission sources and transport pathways. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Assessment of equivalent black carbon variations and its source apportionment over Varanasi, Indo-Gangetic Basin
(Elsevier B.V., 2024) Prashant Kumar Chauhan; Shani Tiwari; Dileep Kumar Gupta; Akhilesh Kumar; Vineet Pratap; Abhay Kumar Singh
In this study, the temporal variation of Equivalent Black Carbon (eBC) and its source apportionment is studied using a yearlong (Dec. 2020–Nov. 2021) multiwavelength Aethalometer (AE-33 model) measurements over Varanasi, located in the central Indo-Gangetic Basin (IGB). Results suggest that mean mass concentrations of eBC vary in the range between 0.46 ± 0.13 to 11.22 ± 5.09 μg m−3 with an annual mean value of ∼3.57 ± 2.39 μg m−3 during the study period. A strong temporal variation in eBC and its components i.e., eBCff (eBC from fossil fuel), and eBCbb (eBC from biomass burning) are found which shows a large variation on different temporal scales with an average value during winter (6.21 ± 3.56 μg m−3), summer (5.09 ± 3.61 μg m−3), monsoon season (1.52 ± 1.03 μg m−3), and post-monsoon (3.75 ± 2.68 μg m−3). The diurnal variation of eBC shows two different maxima between 07:00–08:00 a.m. and 08:00–10:00 p.m. An inverse relationship between eBC concentration and all meteorological parameters (temperature, wind speed, and boundary layer height) is found except relative humidity. The concentration of eBC increases with respect to RH (up to 70 %) suggesting hygroscopic growth while for higher RH (>70 %) value, eBC concentration decreases and indicates the possible wet scavenging processes in the atmosphere. Source apportionment of eBC using the “Aethalometer Model” reveals that eBCff is dominant over eBCbb in total eBC loading during the study period. Cluster analysis of HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model computed five days airmass back-trajectory suggests that airmass reached at Varanasi passes through a highly dense fire count region over the northwestern IGB and surrounding which could be the most responsible for the black carbon loading over the study region. © 2024 Turkish National Committee for Air Pollution Research and Control
Assessment of two intense dust storm characteristics over Indo – Gangetic basin and their radiative impacts: A case study
(Elsevier Ltd, 2019) Shani Tiwari; Akhilesh Kumar; Vineet Pratap; A.K. Singh
The present study is focused to examine the impacts of two intense dust storms on aerosol characteristics and their radiative impacts occurred in pre-monsoon season of 2018 (i.e. 17 May and 14 June 2018) over Kanpur (26.51° N, 80.23° E, 123 above msl). Moderate Resolution Imaging Spectroradiometer (MODIS) true colour images, trajectory pathways of dust storm along with satellite observation and AErosol RObotic NETwork (AERONET) measurements confirms that both the dust storms are either originated from or transported over the Thar Desert, causing a higher aerosol loading which spread over entire Indian-Gangetic Basin (IGB) and modifying the aerosol optical (i.e. aerosol optical depth, angstrom exponent, refractive index etc.), physical (i.e. size distribution) and radiative properties (i.e. single scattering albedo, asymmetric parameter). The space-borne Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) - retrieved aerosol measurements reveal the presence of elevated dust/polluted dust aerosol (up to 3–5 km) over IGB which is well corroborated with aerosol characteristics observed by MODIS, Ozone Monitoring Instrument (OMI) and Atmospheric Infrared Sounder (AIRS). The Dust Regional Atmospheric Model (DREAM8b) shows a good agreement with satellite retrievals with higher value of surface dust concentration in the range of 320–640 μg/m3 over Kanpur during the dust storm days. An enhancement in monthly mean outgoing longwave radiation (up to 60 Wm−2) is observed over IGB and downwind flow region during the dust storm days. The atmospheric aerosol radiative forcing is found 124 Wm−2 and 84 Wm−2 during both the dust storm days (17 May and 14 June 2018) associated with heating rate 2.69 K day−1 and 1.84 K day−1 respectively which may be significant to affect the regional atmospheric dynamics and hence the climate system also. © 2019
ATMOSPHERIC REMOTE SENSING: Principles and Applications
(Elsevier, 2022) Abhay Kumar Singh; Shani Tiwari
Atmospheric Remote Sensing: Principles and Applications discusses the fundamental principles of atmospheric remote sensing and their applications in different research domains. Furthermore, the book covers the basic concepts of satellite remote sensing of the atmosphere, followed by Ionospheric remote sensing tools like Global Positioning System (GPS) and Very Low Frequency (VLF) wave. Sections emphasize the applications of atmospheric remote study in Ionospheric perturbation, fire detection, aerosol characteristics over land, ocean and Himalayan regions. In addition, the application of atmospheric remote sensing in disaster management like dust storms, cyclones, smoke plume, aerosol-cloud interaction, and their impact on climate change are discussed. This book is a valuable reference for students, researchers and professionals working in atmospheric science, remote sensing, and related disciplines. © 2023 Elsevier Ltd. All rights reserved.
Characterization and radiative impact of dust aerosols over northwestern part of India: a case study during a severe dust storm
(Springer-Verlag Wien, 2016) Atinderpal Singh; Shani Tiwari; Deepti Sharma; Darshan Singh; Suresh Tiwari; Atul Kumar Srivastava; Neeraj Rastogi; A.K. Singh
The present study focused on examining the impact of a severe dust storm (DS) on aerosol properties over Patiala (30.33°N, 76.4°E), a site located in the northwestern part of India during 20th–23rd March, 2012. On 20th March, average PM10 mass concentration increased abruptly from 182 to 817 µg m−3 along with significant increase in the number density of coarser particles (diameter >0.45 µm). During DS, spectral aerosol optical depth (AOD) increases significantly with more increase at longer wavelengths resulting in weak wavelength dependence (AOD at 380 nm increases by ~210 % and at 870 nm by ~270 % on 20th March). Significant decrease in Ångström exponent (AE; α380–870) from 0.56 to 0.11 and fine-mode fraction (FMF; PM2.5/PM10) from 0.49 to 0.25 indicates dominance of coarser particles over the station. Net short wave (SW) radiation flux has been decreased by ~20 % and single scattering albedo (SSA675) has been increased from 0.86 (19th March) to 0.90 (20th March). This observation is attributed to additional loading of scattering type aerosols on arrival of DS. Wavelength dependence of SSA reverses during DS and it increases with wavelength due to dominance of coarse-mode particles. Atmospheric aerosol radiative forcing (ATM ARF) during DS ranged from +45 to +77 W m−2, consequently heating the lower atmosphere up to 2.2 K day−1. Significant atmospheric heating rate due to severe dust storm may affect the regional atmospheric dynamics and hence the climate system. © 2016, Springer-Verlag Wien.
Chemical characteristics of particulate matters and their emission sources over Varanasi during winter season
(Springer Science+Business Media B.V., 2020) Vineet Pratap; Akhilesh Kumar; Shani Tiwari; Pradeep Kumar; Avneesh Kumar Tripathi; Abhay Kumar Singh
The chemical composition of particulate matter impacts both human health and climate. In this study, the chemical characteristics of particulate matter was measured for four months (November 2016–February 2017) at Varanasi, which is located in the middle of the Indo-Gangetic Basin (IGB). The daily observed mean values of PM10 and PM2.5 are 134 ± 48 and 213 ± 80 μg/m3, respectively, which exceeds both national and international standards. The average value of PM2.5/PM10 ratio is 0.64 ± 0.16 which indicates a relatively higher fraction of fine particles that are attributed to anthropogenic emission sources (biomass/post-harvest burning) as corroborated by MODIS fire counts and back trajectory analysis. Ion chromatographic measurements showed that SO42−, Cl−, K+, NO3−, Na+, Ca2+, Mg2+ are the major ionic species present in the aerosol. Scanning Electron Microscopy with Energy Dispersive X-Ray (SEM–EDX) analysis shows the prevalence of carbon-rich particles at Varanasi which is likely due to biomass burning and other anthropogenic sources. © 2020, Springer Nature B.V.
COVID-19 lockdown induced air pollution reduction over India: A lesson for future air pollution mitigation strategies
(Springer, 2021) Vineet Pratap; Shani Tiwari; Akhilesh Kumar; Abhay Kumar Singh
Air pollution is one of the biggest problems worldwide and needs to be addressed potentially with the implementation of updated stringent policies and legislative laws. The nationwide lockdown imposed to prevent the COVID-19 outbreak, has given us a unique opportunity to understand the contribution of anthropogenic emissions to the total atmospheric pollutant burden on a global as well as regional scale. Thus, in the present study, we try to investigate the impact of COVID-19 induced lockdown on common ambient air pollutants (i.e., PM2.5, NO2, and SO2) concentration over 22 cities in India using in-situ measurement under a network of Centre Pollution and Control Board (CPCB). A significant reduction in the mean mass concentration of all the studied air pollutants (i.e., PM2.5, NO2, and SO2) (nearly 10–70%) is found during different phases of lockdown which reached within the National Ambient Air Quality Standard (i.e., NAAQS). The reduction in studied air pollutants is more prominent during the first phase of lockdown (mainly NO2) which could be due to the complete shutdown of industrial activities. The outcome of the present study will be helpful for policymakers to design cost-effective and accurate air pollution mitigation strategies for the development of a sustainable environment. The study also suggests that well-planned short-term and periodical lockdown could be an alternative effective tool of air pollution mitigation. © 2021, Indian Academy of Sciences.
High aerosol loading over mega city Delhi in the western Indo-Gangetic plain: Optical characteristics
(India Meteorological Department, 2016) S.D. Attri; V.K. Soni; S. Tiwari; A.K. Srivastava; Shani Tiwari; Kanika Taneja
Measurements of aerosol optical properties were carried out at an urban mega city Delhi, which is situated in the western Indo-Gangetic Plain (IGP) region in north India using an automatic sun/sky radiometer during 2006-2008. The present study revealed high aerosol loading over the station, which could be due to its topography surrounded by different natural and anthropogenic emission sources, and may have major implications towards health, air quality and climate system. Results show a large variability in AOD during the study period, with nearly equal values during winter (0.67 ± 0.06) and summer (0.71 ± 0.11). The Ångström exponent (AE) values were found to be relatively higher during winter (1.19 ± 0.07, suggests dominance of fine-mode aerosols) and lower during summer (0.74±0.06, suggests dominance of coarse-mode aerosols). A slight decrease in single scattering albedo (SSA) was observed during the study period, with a mean value of ~0.9. SSA was found to be about 0.93 during post-monsoon and 0.96 during the winter period whereas during summer and monsoon, SSA was about 0.95. The estimated monthly absorption Ångström exponent (AAE) values over the station varied from 0.11 to 1.87, which were found to be less than 1.0 by ~55% time (mostly during winter and monsoon), and greater than 1.0 by ~45% time (mostly during summer and post-monsoon). © 2016, India Meteorological Department. All rights reserved.
Impacts of black carbon on environment and health
(Elsevier, 2021) Shani Tiwari; Bing Chen; Sachchidanand Singh; A.K. Singh; Atul K. Srivastava
During the last few decades, black carbon (BC) has attracted significant attention among scientific communities due to its observable hostile effects on air quality, agriculture, forests, human health, the economy, and environment. BC is a light-absorbing particle in the atmosphere that is emitted mainly from fossil fuels, biomass burning, and vehicular emissions. Although ample studies on BC aerosol characteristics have been carried out worldwide, significant uncertainties remain due to the different emission sources and their interactions with complex atmospheric processes. Thus, an in-depth understanding of BC and its potential impacts is greatly needed. This chapter presents a brief overview of the characteristics, sources, and transport mechanisms of BC and its impacts on the environment as well as human health. In addition, the chapter also highlights instructions to the public, policymakers, and local environmental bodies to control BC emissions. © 2021 Elsevier Inc. All rights reserved.
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.
Intra-urban variability of particulate matter (PM2.5 and PM10) and its relationship with optical properties of aerosols over Delhi, India
(Elsevier Ltd, 2015) Suresh Tiwari; Philip K. Hopke; Atar S. Pipal; Atul K. Srivastava; Deewan S. Bisht; Shani Tiwari; Abhay K. Singh; Vijay K. Soni; Shiv D. Attri
Highly time-resolved measurements of particulate matter (PM: PM2.5 and PM10) were made at three different sites across Delhi (CCRI: a highly traffic site, IMD: a less traffic site and IITM: an urban background site) from 1st December, 2011 to 30th June, 2013. Also, coarse mode (PM10-2.5) mass was estimated as the difference between PM10 and PM2.5. In addition, columnar aerosol optical properties such as aerosol optical depth (AOD) and Angstrom exponent (AE) were studied concurrently over IMD. The mean mass concentrations of PM2.5, PM10-2.5 and PM10 were 118.3±81.7, 113.6±70.4 and 232.1±131.1μgm-3, respectively. Among the three sites, relatively higher mass concentrations of PM2.5 (~35% and 3%) were observed at CRRI compared to IMD and IITM.PM10 and PM10-2.5 were higher at these sites by ~31% and 19%; and 27% and 40%, respectively, compared to CRRI. Coefficients of divergence (COD) and correlation coefficients (r) were calculated between site pairs to assess the spatial and temporal heterogeneity of PM and moderate spatial divergence was found over the three sites. Traffic emission particles (PM2.5) exhibited high spatial heterogeneity as well. The mass concentrations of PM2.5 and PM10 were found to be higher during the night compared to the day. The mean PM2.5/PM10 ratio was ~51%, indicating generally equal amounts of coarse and fine mode PM in the Delhi urban atmosphere. AOD and PM2.5 were positively correlated and a negative correlation was observed between AE and PM10-2.5. PM2.5 particles were significantly correlated with AOD during post-monsoon and winter. Because of the lower vehicular emissions on weekends compared to weekdays, PM at CRRI, IMD, and IITM were separated by day of week and large heterogeneities were found. During weekdays, the mass concentrations of PM10 were ~4, 2, and 12% higher than on weekends. However, for PM2.5, weekend values were 5, 7, and 9% higher for CRRI, IMD and IITM, respectively. © 2015 Elsevier B.V.
Study of the carbonaceous aerosol and morphological analysis of fine particles along with their mixing state in Delhi, India: A case study
(Springer Verlag, 2015) S. Tiwari; A.S. Pipal; Philip K. Hopke; D.S. Bisht; A.K. Srivastava; Shani Tiwari; P.N. Saxena; A.H. Khan; S. Pervez
Because of high emissions of anthropogenic as well as natural particles over the Indo-Gangetic Plains (IGP), it is important to study the characteristics of fine (PM2.5) and inhalable particles (PM10), including their morphology, physical and chemical characteristics, etc., in Delhi during winter 2013. The mean mass concentrations of fine (PM2.5) and inhalable (PM10) (continuous) was 117.6±79.1 and 191.0± 127.6 μg m−3, respectively, whereas the coarse mode (PM10–2.5) particle PM mass was 73.38±28.5 μg m−3. During the same period, offline gravimetric monitoring of PM2.5 was conducted for morphological analysis, and its concentration was ~37% higher compared to the continuous measurement. Carbonaceous PM such as organic carbon (OC) and elemental carbon (EC) were analyzed on the collected filters, and their mean concentration was respectively 33.8 and 4.0 μg m−3 during the daytime, while at night it was 41.2 and 10.1 μg m−3, respectively. The average OC/EC ratio was 8.97 and 3.96 during the day and night, respectively, indicating the formation of secondary organic aerosols during daytime. Effective carbon ratio was studied to see the effect of aerosols on climate, and its mean value was 0.52 and 1.79 during night and day, indicating the dominance of absorbing and scattering types of aerosols respectively into the atmosphere over the study region. Elemental analysis of individual particles indicates that Si is the most abundant element (~37–90%), followed by O (oxide) and Al. Circularity and aspect ratio was studied, which indicates that particles are not perfectly spherical and not elongated in any direction. Trajectory analysis indicated that in the months of February and March, air masses appear to be transported from the Middle Eastern part along with neighboring countries and over Thar Desert region, while in January it was from the northeast direction which resulted in high concentrations of fine particles. © Springer-Verlag Berlin Heidelberg 2015.