Browsing by Author "V.K. Soni"

Now showing 1 - 9 of 9

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 and their relationship with meteorological parameters during wintertime in Delhi, India
(Elsevier Ltd, 2015) S. Tiwari; G. Pandithurai; S.D. Attri; A.K. Srivastava; V.K. Soni; D.S. Bisht; V. Anil Kumar; Manoj K. Srivastava
In situ and columnar measurements of aerosol optical properties (AOPs) [Aerosol optical depth (AOD), Angstrom Exponent (AE), Aerosol scattering (σscat) and absorption (σabs) coefficients and single scattering albedo (SSA)] along with soot particles (Black carbon: BC) and fine particles (PM2.5: d ≤2.5) were continuously measured at an urban site in Delhi, India during winter period (December 2011 to March 2012). Average values of AOD, σscat, σabs, and SSA at 500nm; and AE for the observation period were found to be 0.95±0.32, 1027.36±797.1Mm-1, 85.95±73.2Mm-1 and 0.93±0.03; and 0.94±0.19, respectively. Higher values of σscat and σabs were occurred in the month of December (1857 and 148Mm-1) while relatively lower values of σscat (585Mm-1) and σabs (44Mm-1) were occurred in March and February respectively. SSA, however, was higher during January (0.94) and lower in March (0.89). The mass concentration of PM2.5 and BC were 195.34±157.99 and 10.11±8.83μgm-3 respectively during study period. Bimodal distributions were observed in σscat and σabs coefficients during 0800 and 0900h LT (traffic rush hours) and at 2200 and 2300h LT (low boundary layer conditions) with lower values during daytime between 1500 and 1700h LT, respectively. The σscat peak in morning may be attributed to large emissions of aerosol in the traffic rush hours and production of secondary aerosols with increasing solar radiation and temperature. During study period, the σscat (mean) coefficient was 13% lower during daytime as compared to nighttime. An interesting feature was seen in monthly analysis of σscat in between day and nighttime which was 18% and 22% higher in December and January in nighttime however ~4% lower during February and March; it is due to effect of local meteorology. The impact of meteorological parameters such as wind speed (WS), wind direction (WD), visibility (VIS) and mixed layer depths (MLDs) on AOPs along with fine and soot particles were studied. A clear negative significant correlation between atmospheric visibility with σscat (-0.64); σabs (-0.57) and PM2.5 (-0.56) were observed. During foggy days (VIS ≤1000m), the AOPs, fine and soot particles were substantially (~1.8 times) higher as compared to clean days, however, it was ~2.3 times higher during dense foggy days (VIS ≤500m). Similarly higher (~2 times) AOPs and aerosol concentrations were also seen below 200m MLDs. In addition to this, ~4 times higher AOPs and aerosol mass concentrations were observed when WS was below 1m/s. In view of the above results and regression analysis, we can say that the meteorological parameters play a crucial role in enhancement of aerosols at ground level during winter period over Delhi. © 2014 Elsevier B.V.
Convective weather event monitoring with multispectral image analysis of INSAT-3D/3DRover Indian domain
(India Meteorological Department, 2023) C.S. Tomar; Rajiv Bhatla; V.K. Soni; R.K. Giri
Pre-monsoon season (March to May) is very challenging as convective activities prevails almost throughout the country. Most of the Rabi crops harvesting affected and sometimes suffer great losses due to sudden rain or high winds. INSAT-3D/3DR satellite images and derived products provides continuous support to the forecasters and end users in monitoring such events and thereafter significant value addition improves the prediction. This information was found to be very useful where actual ground based or upper air observations are limited or especially over data sparse or difficult terrain regions. In this work, we have examined three weather events at different Geographical locations (i) Rainfall over Bihar-24-26 June, 2020 (ii) Delhi & NCR region on 17 June, 2022 (iii) NE region activity in 16-18 June, 2022. The Real Time Analysis of Products and Information Dissemination (RAPID) web based tool was utilized in monitoring and diagnosing the convective weather events based on the brightness temperature & derived products like Outgoing longwave radiation, upper tropospheric humidity, insolation etc & RGB imagery composite in terms of day & night time microphysics daily operational products. The time series of the wind derived products for Delhi NCR rainfall and NE rainfall products also generated through RAPID. The synoptic model analysis provides valuable inputs for these mesoscale convective weather events. The southerly wind flow (at 925 hPa) and velocity convergence (at 500 hPa) analysis of European Centre for Medium Range Weather Forecasting (ECMWF) supports the severity of NE event occurred on 16-18 June, 2022. Therefore, utilization of near real time INSAT-3D/3DR products along with appropriate synoptic model analysis can help the forecasters to understand better about such mesoscale convective events & accurate forecast with sufficient lead time can save the life and property. © 2023, India Meteorological Department. All rights reserved.
Effect of unusual dust event on meteorological parameters & aerosol optical and radiative properties
(India Meteorological Department, 2018) V.K. Soni; Sanjay Bist; R. Bhatla; S.C. Bhan; Gajendra Kumar; M. Sateesh; Siddhartha Singh; D.R. Pattanaik
A very unusual dust plume generated from dust-storm activities over the Arabian Peninsula and Southwest Asia affected the north-west region of India between March 20 and 23, 2012, causing significant reductions in air quality and consequently changes in meteorological parameters. Ground based measurements of aerosol optical depth at 500 nm reached 1.015 ± 0.24 and 0.837 ± 0.042 at Jodhpur while Angstrom exponent dropped to-0.030 and-0.065 on March 20 and 21, 2012 respectively. The AOD reached 0.959 in Delhi while Angstrom exponent dropped to 0.006 on March 21, 2012. PM10 concentration peaked at an unusually high value of more than 1800 μgm-3 during dust storm hours of March 20, 2012 at Delhi. Moderate Resolution Imaging Spectrometer (MODIS) retrieved aerosol optical depth also exhibited high values as well along the path of dust storm and dust plume. The intensity of the dust plume was such that it caused significant cooling at the surface. The large reduction in the radiative flux at the surface level had caused a drop in surface temperature by approximately 2-10 °C. Shortwave and longwave Direct Aerosol Radiative Forcing was calculated using SBDART during the dust period. © 2018, India Meteorological Department. All rights reserved.
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.
Inter-comparison of GNSS-IPWV with ERA-5 IPWV and monitoring of convective events over the Indian region
(India Meteorological Department, 2024) C.S. Tomar; Rajiv Bhatla; Nand Lal Singh; V.K. Soni; R.K. Giri
The present study deals with (i) An Inter-comparison study of ground based Global Navigation Satellite System (GNSS) derived Integrated Precipitable Water Vapour (IPWV) with 5th generation global climate reanalysis data of European Centre for Medium Range Weather Forecast (ERA-5) (ii) IPWV thresholds of GNSS data (iii) case studies of IPWV analysis. It is found that both the datasets (GNSS and ERA-5) are strongly correlated & the correlation coefficient ranging between 0.97 and 0.99. Monthly Thresholds of IPWV (MTI) are generated with 2017-2020 data sets from Indian GNSS station having continuous data and found very useful input as value addition to know the possibility of building up /decaying of convection in day to day daily forecast issued to the public. Case studies shows an increase of IPWV, 3 to 4 hour prior to the occurrence of convective event around the GNSS station and found very useful for nowcasting. Therefore, utilization of IPWV (model as wells GNSS based) have found useful for better understanding about the convective activity and its forecasting. This supplement information along with other analysis products (model, surface, upper air, satellite or radar etc.) can support further in appropriate decision making to the forecasters, decision makers and the end users of the society. © 2024, India Meteorological Department. All rights reserved.
Long-term (2005–2012) measurements of near-surface air pollutants at an urban location in the Indo-Gangetic Basin
(Springer, 2019) N. Kishore; A.K. Srivastava; Hemwati Nandan; Chhavi P Pandey; S. Agrawal; N. Singh; V.K. Soni; D.S. Bisht; S. Tiwari; Manoj K Srivastava
Simultaneous long-term measurements of near-surface air pollutants at an urban station, New Delhi, were studied during 2005–2012 to understand their distribution on different temporal scales. The annual mean mass concentrations of nitrogen dioxide (NO 2) , sulphur dioxide (SO 2) , particulate matter less than 10μm (PM 10) and suspended particulate matter (SPM) were found to be 62.0±27.6, 12.5±8.2, 253.7±134 and 529.2±213.1μg/m3, respectively. The 24-hr mean mass concentrations of NO 2, PM 10 and SPM were exceeded on ∼ 27%, 87% and 99% days that of total available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for SO 2, which could be attributed to reduction of sulphur in diesel, use of cleaner fuels such as compressed natural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of NO 2, PM 10 and SPM showed an increasing trend while SO 2 appears to be decreasing since 2008. Air mass cluster analysis showed that north–northwest trajectories accounted for the highest mass concentrations of air pollutants (more prominent in the winter/post-monsoon season); however, the lowest were associated with the southeast trajectory cluster. © 2019, Indian Academy of Sciences.
Variability in optical properties of atmospheric aerosols and their frequency distribution over a mega city “New Delhi,” India
(Springer Verlag, 2016) S. Tiwari; Suresh Tiwari; P.K. Hopke; S.D. Attri; V.K. Soni; Abhay Kumar Singh
The role of atmospheric aerosols in climate and climate change is one of the largest uncertainties in understanding the present climate and in capability to predict future climate change. Due to this, the study of optical properties of atmospheric aerosols over a mega city “New Delhi” which is highly polluted and populated were conducted for two years long to see the aerosol loading and its seasonal variability using sun/sky radiometer data. Relatively higher mean aerosol optical depth (AOD) (0.90 ± 0.38) at 500 nm and associated Angstrom exponent (AE) (0.82 ± 0.35) for a pair of wavelength 400–870 nm is observed during the study period indicating highly turbid atmosphere throughout the year. Maximum AOD value is observed in the months of June and November while minimum is in transition months March and September. Apart from this, highest value of AOD (AE) value is observed in the post-monsoon [1.00 ± 0.42 (1.02 ± 0.16)] season followed by the winter [0.95 ± 0.36 (1.02 ± 0.20)] attributed to significance contribution of urban as well as biomass/crop residue burning aerosol which is further confirmed by aerosol type discrimination based on AOD vs AE. During the pre-monsoon season, mostly dust and mixed types aerosols are dominated. AODs value at shorter wavelength observed maximum in June and November while at longer wavelength maximum AOD is observed in June only. For the better understanding of seasonal aerosol modification process, the aerosol curvature effect is studied which show a strong seasonal dependency under a high turbid atmosphere, which are mainly associated with various emission sources. Five days air mass back trajectories were computed. They suggest different patterns of particle transport during the different seasons. Results suggest that mixtures of aerosols are present in the urban environment, which affect the regional air quality as well as climate. The present study will be very much useful to the modeler for validation of satellite data with observed data during estimation of radiative effect. © 2016, Springer-Verlag Berlin Heidelberg.
What caused severe air pollution episode of November 2016 in New Delhi?
(Elsevier Ltd, 2020) V.P. Kanawade; A.K. Srivastava; K. Ram; E. Asmi; V. Vakkari; V.K. Soni; V. Varaprasad; C. Sarangi
In recent years, South Asia is experiencing severely degraded air quality, with particulate matter less than 2.5 μm (PM2.5) reaching unprecedented high levels. Here, we investigate a severe air pollution episode (SAPE) witnessed in New Delhi during 1–7 November 2016. This was a very unusual air pollution episode wherein air quality index exceeded >500 and was persistent for about a week encapsulating the entire Indo-Gangetic Plain (IGP). We demonstrate that a stagnant weather condition was the dominant cause of the SAPE. Mean concentration of PM2.5 in New Delhi before, during, and after the SAPE were 142 μg/m3, 563 μg/m3, and 240 μg/m3, respectively. Satellite-based aerosol optical depth (AOD), ultraviolet-aerosol index (UV-AI) and surface carbon monoxide (CO) concentrations also showed significant enhancements over large locale spatially by about 50–70% during the SAPE. A large and simultaneous increase in UV-AI and CO downwind of a large number of fire hotspots (Punjab and Haryana) is a clear indication of biomass burning aerosols. Analysis of absorption Ångström exponent further substantiates this finding, showing a large fraction of light absorbing carbonaceous-type aerosols. Radiosonde observations clearly showed that stagnant atmospheric conditions led to SAPE in New Delhi by allowing pollution to accumulate and persist in the near-surface environment. As a result new particle formation was suppressed due to very high pre-existing aerosol concentrations during the SAPE. The heating rate induced by light absorbing aerosols into an atmospheric layer during SAPE was also very high (3.1 ± 0.7 K/day). These findings will help in understanding air quality and climate effects, as well as in formulating policies to mitigate these complex pollution episodes in an anthropogenic future. © 2019 Elsevier Ltd