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Devising effective national-level climate action plans requires a more detailed understanding of the regional distribution of sources and sinks of greenhouse gases. Due to insufficient observations and modelling capabilities, India's current carbon source–sink estimates are uncertain. This study uses a high-resolution Lagrangian transport model to examine the potential of available CO 2 observations over India for inverse estimation of regional carbon fluxes. We use four different sites in India that vary in the measurement technique, frequency and spatial representation. These observations exhibit substantial seasonal (7.5 to 9.2 ppm) and intra-seasonal (2 to 12 ppm) variability. Our modelling framework, a high-resolution Weather Research and Forecasting Model combined with the Stochastic Time-Inverted Lagrangian Transport model (WRF–STILT), performs better in simulating seasonal (R2=0.50 to 0.96) and diurnal (R2=0.96) variability (for the Mohali station) of observed CO 2 than the current-generation global models (CarboScope, CarbonTracker and ECMWF EGG4). The seasonal CO 2 concentration variability in Mohali, associated with crop residue burning, is largely underestimated by the models. WRF–STILT captures the seasonal biospheric variability over Nainital better than the global models but underestimates the strength of the CO 2 uptake by crops. The choice of emission inventory in the modelling framework alone leads to significant biases in simulations (5 to 10 ppm), endorsing the need for accounting for emission fluxes, especially for non-background sites. Our study highlights the possibility of using the CO 2 observations from these Indian stations for deducing carbon flux information at regional (Nainital) and suburban to urban (Mohali, Shadnagar and Nagpur) scales with the help of a high-resolution model. On accounting for observed variability in CO 2 , the global carbon data assimilation system can benefit from the measurements from the Indian subcontinent. [ABSTRACT FROM AUTHOR]

An integrated campaign "Suryagrahan‐2019" with multi‐institutional support was conducted by launching a series of radiosondes/ozonesondes over 6‐different locations in India along with the operation of ST/MST radars and launching of RH‐200 rockets during the annular solar eclipse of 26 December 2019. We present the eclipse‐induced changes in the thermal structure, dynamics and trace gases in the lower and middle atmosphere. One of the novel findings is the formation of three step‐like isothermal structures in the lower stratosphere with a layer height of 1.4, 2.5, and 4 km, which is attributed to the adiabatic compression and expansion of the air parcel. These structures have both warming and cooling effect of the order of ±6 K. A significant increase of ozone by 20% in post‐eclipse scenario between 29 and 32 km is observed over Cochin. Strong downdrafts of ∼−0.25 m s−1 are observed between 12 and 16 km during the eclipse event, which is attributed to the atmospheric compression due to the sudden cooling during the eclipse event. Due to the changes in thermal structure, the atmospheric circulation changes are observed in the meridional wind. During the maximum obscuration, there is a sudden decrease in near‐surface and boundary layer ozone by 12–15 ppbv. The present study reiterates that the eclipse‐induced perturbations depend on the local time of the eclipse event and place of observations. It is envisaged that the results discussed in the study will improve our understanding of the eclipse induced perturbations in the Earth's atmosphere. Plain Language Summary: Solar eclipse provides a well‐characterized reduction in solar radiation for a few hours, which provides a natural laboratory to understand and quantify the atmosphere's response to the abrupt cut‐off in the solar radiation. In this context, an integrated campaign "Suryagrahan‐2019" was conducted in India by launching a series of radiosonde/ozonesonde along with the operation of ST/MST radars during the annular solar eclipse event occurred on 26 December 2019. Several isothermal structures, followed by warming and cooling effect in the different stratospheric heights were observed. Alter in the ozone profile, especially in the lower stratosphere was one of the causative mechanism behind the modulations of thermal structure. Adiabatic compression and expansion of the air parcel in the lower stratosphere are explained in term of solar eclipse induced effects. Change in meridional circulation due to sudden solar cut‐off is reported. Key Points: Solar eclipse induced isothermal structure and adiabatic compression and expansion in the lower stratosphere were observedIncrease in ozone in the lower stratosphere during post‐eclipse scenario, whereas spontaneous decrease of surface ozone were reportedChange in meridional circulation due to sudden cut‐off of solar radiation [ABSTRACT FROM AUTHOR]

Devising effective national-level climate action plans needs a more detailed understanding of the regional distribution of sources and sinks of greenhouse gases. Due to insufficient observations and modelling capabilities, India's current carbon source-sink estimates are uncertain. This study uses a high-resolution transport model to examine the potential of CO2 observations over India for inverse estimation of regional carbon fluxes. We make use of four different sites in India that vary in measurement technique, frequency and spatial representation. These observations exhibit substantial seasonal (7.5 to 9.2 ppm) and intra-seasonal (2 to 12 ppm) variability. Our modelling approach, a high-resolution Weather Research and Forecasting Model combined with Stochastic Time Inverted Lagrangian Transport (WRF-STILT) model, performs better in simulating seasonal (R2 = 0.50 to 0.96) and diurnal (R2 = 0.96) variability of observed CO2 than the current generation global models analysed in the study. Representation of local flux variability like biomass burning in the model needs further refinement, depending on the site location. During the agricultural season, crop biospheric uptake in the Indo-Gangetic Plain region significantly modulates the CO2 variability in the northern Indian stations. Depending on the region and time of the year, the anthropogenic and biospheric emission components contribute differently to CO2 variability. The choice of emission inventory in the modelling framework alone leads to significant biases in simulations (5 to 10 ppm), endorsing the need for accounting emission fluxes, especially for non-background sites. By implementing a high-resolution model, our results emphasise that observations from Indian sites can be useful in deducing carbon flux information at regional (Nainital) and sub-urban to urban (Mohali, Shadnagar, Nagpur) scales. On accounting for observed variability, the global carbon data assimilation system can thus benefit from the measurements from the Indian subcontinent. [ABSTRACT FROM AUTHOR]

Escalating emissions of several air pollutants over South Asia could play a detrimental role in the regional and global atmosphere. Therefore, it is necessary to investigate these emissions within the boundary layer and at higher heights utilizing satellite data that are more inclusionary, where limited in situ observations are available. Here, we utilize the Infrared Atmospheric Sounding Interferometer (IASI), Ozone Monitoring Instruments (OMI), TROPOspheric Monitoring Instrument (TROPOMI), and Global Ozone Monitoring Experiment (GOME-2) hyperspectral satellite data to assess the changes in emission sources during Indian lockdown with a primary focus on the tropospheric profiles of ozone and carbon monoxide (CO). A significant reduction (> 20%) in the tropospheric ozone was seen over northern and northeast regions compared to 2018, while a dramatic increase (> 20%) compared to 2019 was seen. The subtropical dynamics mainly contributed to the increased ozone over the northern region. An analysis of the ozone production regime showed mostly NO2 limited regime over the major part of India and VOC limited regime over thermal power plants regions. Unlike in the boundary layer, where CO showed reduction (15–20%), CO profiles showed a consistent increase (as high as 31%) in the free troposphere over the majority of cities and thermal power plants. The CO total column also showed an increase (~ 20%) over central and western India and a slight decrease (5%) over northern India. Similar to CO, an increase (~ 15%) of NO2 column over the western region was observed particularly compared to 2019. However, unlike ozone and CO, reduction of tropospheric NO2 columns was seen over the major part of India, with the highest reduction over northern regions (20–52%). Furthermore, homogeneous yearly differences (> 30%) between OMI and TROPOMI NO2 observations were also seen distinctly over the remote areas. Contrary to surface-based studies, the present study shows an increase in CO, ozone (decrease), and NO2 at several locations and in the free troposphere during the lockdown. [ABSTRACT FROM AUTHOR]

The Himalayan region is adversely affected by the increasing anthropogenic emissions from the adjacent Indo-Gangetic plain. However, source apportionment studies for the Himalayan region that are crucial for estimating CO concentration, are grossly insufficient, to say the least. It is in this context that our study reported here assumes significance. This study utilizes five years (2014–2018) of ground-based observations of eBC and multiple linear regression framework (MLR) to estimate CO and segregate its fossil fuel and biomass emission fractions at a high-altitude (1958 m) site in the Central Himalayas. The results show that MERRA2 always underestimates the observed CO; MOPITT has a high monthly difference ranging from −32% to +57% while WRF-Chem simulations underestimate CO from February to June and overestimate in other months. In contrast, CO estimated from MLR replicates diurnal and monthly variations and estimates CO with an r2 > 0.8 for 2014–2017. The CO predicted during 2018 closely follows the observed variations, and its mixing ratios lie within ±17% of the observed CO. The results reveal a unimodal diurnal variation of CO, CO ff (ff: fossil fuel) and CO bb (bb: biomass burning) governed by the boundary layer evolution and upslope winds. CO ff has a higher diurnal amplitude (39.1–67.8 ppb) than CO bb (5.7–33.5 ppb). Overall, CO ff is the major contributor (27%) in CO after its background fraction (58%). CO bb fraction reaches a maximum (28%) during spring, a period of increased agricultural and forest fires in Northern India. In comparison, WRF-Chem tracer runs underestimate CO bb (−38% to −98%) while they overestimate the anthropogenic CO during monsoon. This study thus attempts to address the lack of continuous CO monitoring and the need to segregate its fossil fuel and biomass sources, specifically over the Central Himalayas, by employing a methodology that utilizes the existing network of eBC observations. [Display omitted] • MLR CO estimates perform better than WRF-Chem, MOPITT and MERRA2. • CO observations infer higher fossil fuel (27%) contribution than biomass (15%). • Regional fire lead to highest biomass CO in spring (28%). • Significant contribution of background CO (58%), followed by fossil fuel (27%). [ABSTRACT FROM AUTHOR]

The combustion of fossil fuels (coal and petroleum products) constitutes a source of continuous release of anthropogenic SO2into the atmosphere. Furthermore, natural sources such as volcanoes can inject large amounts of SO2directly into the troposphere and sometimes even into the stratosphere. These event-based volcanic eruptions provide solitary opportunities to study the transport and transformation of atmospheric constituents. In this study, we present an episode of high SO2concentration over northern India as a result of long-range transport from Africa using multiple satellite observations. Monthly averaged column SO2values over the Indo-Gangetic Plain (IGP) were observed in the range of 0.6–0.9 Dobson units (DU) during November 2008 using observations from the Ozone Monitoring Instrument (OMI). These concentrations were conspicuously higher than the background concentrations (<0.3 DU) observed during 2005–2010 over this region. The columnar SO2loadings were highest on 6 November over most of the IGP region and even exceeded 6 DU, a factor of 10–20 higher than background levels in some places. These enhanced SO2levels were not reciprocated in satellite-derived NO2or CO columns, indicating transport from a non-anthropogenic SO2source. As most of the local aerosols over the IGP region occur below 3 km, a well-separated layer at 4–5 km was observed from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. Wind fields and back-trajectory analysis revealed a strong flow originating from the Dalaffilla volcanic eruption in Ethiopia during 4–6 November 2008. Although volcanic SO2plumes have been extensively studied over many parts of Asia, Europe, and the USA, analysis of such events for the IGP region is being reported for the first time in this study. [ABSTRACT FROM PUBLISHER]

Collocated measurements of the boundary layer evolution and surface ozone, made for the first time at a tropical rural site (Gadanki 13.5°N, 79.2°E, 375 m amsl) in India, are presented here. The boundary layer related observations were made utilizing a lower atmospheric wind profiler and surface ozone observations were made using a UV analyzer simultaneously in April month. Daytime average boundary layer height varied from 1.5 km (on a rainy day) to a maximum of 2.5 km (on a sunny day). Correlated day-to-day variability in the daytime boundary layer height and ozone mixing ratios is observed. Days of higher ozone mixing ratios are associated with the higher boundary layer height and vice versa. It is shown that higher height of the boundary layer can lead to the mixing of near surface air with the ozone rich air aloft, resulting in the observed enhancements in surface ozone. A chemical box model simulation indicates about 17% reduction in the daytime ozone levels during the conditions of suppressed PBL in comparison with those of higher PBL conditions. On a few occasions, substantially elevated ozone levels (as high as 90 ppbv) were observed during late evening hours, when photochemistry is not intense. These events are shown to be due to southwesterly wind with uplifting and northeasterly winds with downward motions bringing ozone rich air from nearby urban centers. This was further corroborated by backward trajectory simulations. [ABSTRACT FROM AUTHOR]

The impact of long-range transported dust aerosols, originating from the Thar Desert region, to a high-altitude station in the central Himalayas was studied with the help of micro-pulse lidar (MPL) observations. A drastic change in lidar back-scatter profile was observed on a dust day as compared with that on a pre-dust day. The back-scatter coefficient on a dust day revealed that the dust layer peaked at an altitude ∼1300 m above ground level (AGL) and extended up to ∼3000 m AGL, with maximum value ∼3 × 10–5 m–1 sr–1. Aerosol Index (AI) and air mass back-trajectory analysis substantiate the transport of dust aerosols from the far-off Thar Desert region to the experimental site. A significant effect of dust aerosols was also observed over the station on the spectral aerosol optical depths (AODs), measured using a Microtops-II Sunphotometer. It showed significantly different spectral behaviour of AOD on a dust day as compared with that on a pre-dust day. The Ångström exponent (α) showed a marked decrease from 0.42 to 0.04 from the pre-dust day to the dust day. The aerosol radiative forcing estimated using the Santa Barbara DISORT (discrete ordinate radiative transfer) atmospheric radiative transfer (SBDART) model, in conjunction with the optical properties of aerosol and cloud (OPAC) model, showed values of about –30, –45 and +15 W m–2, respectively, at top-of-atmosphere (TOA), surface and in the atmosphere on the dust day. The positive atmosphere forcing caused an estimated heating of the lower atmosphere by ∼0.4 K day–1. [ABSTRACT FROM AUTHOR]

Measurements of surface ozone, CO, CH4 and oxides of nitrogen have been made at a high altitude site Mt Abu (24.6°N, 72.7°E, 1680 m asl), India for the period 1993–2000. Diurnal patterns in ozone do not show daytime in situ photochemical buildup at this site throughout the year. On the contrary, lower ozone mixing ratios are observed during the day. Interestingly, diurnal pattern changes significantly after the northeast monsoon period (winter) and shows a unique double hump in spring at this site. Seasonal variation in ozone shows a pronounced maximum (monthly average about 46 ppbv) in the late autumn and winter, unlike many other global sites. Local pollutants are major contributors to the ozone levels during this period, while regional transport plays a role in spring. Lowest ozone mixing ratio (monthly average about 25 ppbv) is observed during southwest monsoon period (summer), when clean marine air from the Arabian Sea and Indian Ocean reaches to this site. The unique meteorology over this region seems to play an important role in seasonal as well as in diurnal variations in ozone. Background and continental ozone levels are estimated to be 33.4±13.3 and 48.1±9 ppbv, respectively, over this region of India. A correlation study between ozone and CO indicates possibility of incomplete photochemical processes over Asia. Annual average mixing ratios of CO, CH4 and oxides of nitrogen are observed to be about 131.4±35.8 ppbv, 1.63±0.04 ppmv and 1.5±1.4 ppbv, respectively. [Copyright &y& Elsevier]

Introduction: To evaluate the role of tamsulosin in clearance of fragments after SWL to renal calculi. Methods: In this open-label prospective randomized study conducted at our institute during 2006-2007, 139 patients with normal renal-function, bearing single radioopaque renal calculus 5-20 mm undergoing SWL were enrolled. All patients underwent SWL 3-weekly till success or maximum 3 months. They were randomly assigned into two groups (A & B) with-respect-to whether or not receiving tamsulosin 0.4mg/d, respectively. Primary end-point was success-rate and secondary were clearance-time, sessions required for clearance, pain-intensity, incidence of steinstrasse & need for auxiliary procedures. Results: Fifty-one in group-A and 65 in Indian group-B completed requisite followup. Demographic profile of both the groups was comparable. Success-rate after one SWL-session was higher in group-A (52.9% vs. 32.8%, respectively; P<0.05). However, overall success rate including re-treatments was similar at 3months (96.1% vs. 96.9%, respectively; P=1.00). Total days (35.53±19.47 vs. 47.22±23.64; P=0.006) & SWL-sessions (1.66 vs. 2.16; P=0.005) required for clearance, and pain (VAS-28.67±20.35 vs. 47.30±24.98, respectively; P=0.0001) were significantly less in group-A. Two patients in group-A and 9 in group-B developed steinstrasse (P=0.10); conservative management was successful in one in each group (P=0.345). Three patients in group-A and 10 in B required auxiliary procedures (P=0.14). Conclusions: Tamsulosin facilitates clearance of fragments after SWL to renal calculi and helps reduce the severity of pain. It tends to facilitate spontaneous clearance of steinstrasse; however, this requires further evaluation. [ABSTRACT FROM AUTHOR]

Introduction: To evaluate the role of tamsulosin in clearance of fragments after shock wave lithotripsy (SWL) to ureteric calculi. Methods: A prospective, randomized, open-label study was conducted during 2006-2007 enrolling 40 patients with single ureteric stone undergoing SWL. They were randomly divided based on whether or not receiving 0.4mg tamsulosin (group-A & B, respectively) during treatment and underwent evaluation & SWL 3-weekly till success or maximum of 3months. Clearance-rate, clearance-time, sessions required for clearance, pain-intensity, incidence of steinstrasse and need for auxiliary procedures were assessed. Results: Demographic profile of both the groups was comparable. Success-rate was higher in group-A after one SWL-session (55% vs. 25%, respectively; P=0.05). However, overall success rate was similar at 3 months (95% each group; P=1.00). Total number of days (30.68±19.65 vs. 37.89±19.89; P=0.269), number of SWL sessions (1.65 vs. 2.00; P=0.10) and pain experienced (score on visual analog scale- 25.27±17.86 vs. 38.33±28.02, respectively; P=0.10) tended to be less (though statistically insignificant) in group-A. Three patients in group-A and 5 in group B developed steinstrasse (15% vs. 25%; P=0.69); conservative management was successful in 2 of group-A & 3 of B (67% vs. 60%; P=1.00). Overall one in group-A required auxiliary procedures as compared to 4 in control group (5.0% vs. 20.0%, respectively; P=0.37). Conclusions: Tamsulosin facilitates clearance of stone fragments after SWL to ureteric calculi. It tends to reduce pain experienced during clearance and auxiliary procedures required for complication/clearance; however it requires further evaluation. [ABSTRACT FROM AUTHOR]

The RAWEX-GVAX field campaign has been carried out from June 2011 to March 2012 over a high altitude site Manora Peak, Nainital (29.4°N; 79.2°E; 1958 m amsl) in the central Himalayas to assess the impacts of absorbing aerosols on atmospheric thermodynamics and clouds. This paper presents the preliminary results of the observations and data analysis of the Doppler Lidar, installed at Nainital. Strong updrafts with vertical winds in the range of ~2-4 ms-1 occurred during the daytime and throughout the season indicating thermally driven convection. On the other hand during nighttime, weak downdrafts persisted during stable conditions. Plan Position Indicator scan of Doppler Lidar showed north-northwesterly winds in the boundary layer. The mixing layer height, derived from the vertical velocity variance, showed diurnal variations, in the range ~0.7-1 km above ground level during daytime and very shallow during nighttime. [ABSTRACT FROM AUTHOR]

In this study, we assess the response of ambient aerosol black carbon (BC) mass concentrations and spectral absorption properties across Indian mainland during the nation-wide lockdown (LD) in connection with the Coronavirus Disease 19 (COVID-19) pandemic. The LD had brought near to total cut-off of emissions from industrial, traffic (road, railways, marine and air) and energy sectors, though the domestic emissions remained fairly unaltered. This provided a unique opportunity to delineate the impact of fossil fuel combustion sources on atmospheric BC characteristics. In this context, the primary data of BC measured at the national network of aerosol observatories (ARFINET) under ISRO-GBP are examined to assess the response to the seizure of emissions over distinct geographic parts of the country. Results indicate that average BC concentrations over the Indian mainland are curbed down significantly (10–40%) from prelockdown observations during the first and most intense phase of lockdown. This decline is significant with respect to the long-term (2015–2019) averaged (climatological mean) values. The drop in BC is most pronounced over the Indo-Gangetic Plain (>60%) and north-eastern India (>30%) during the second phase of lockdown, while significant reduction is seen during LD1 (16–60%) over central and peninsular Indian as well as Himalayan and sub-Himalayan regions. Despite such a large reduction, the absolute magnitude of BC remained higher over the IGP and north-eastern sites compared to other parts of India. Notably, the spectral absorption index of aerosols changed very little over most of the locations, indicating the still persisting contribution of fossil-fuel emissions over most of the locations. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric carbonaceous aerosols of South Asian origin have received immense concerns in the Anthropocene owing to their plausible role in the observed regional to inter-continental scale climate anomalies. Tracking plausible sources and alterations during their transport (secondary processes) are keys to understanding their net influence on regional climate. Here, we report elemental concentrations of C and N (TC and TN), their isotopes (δ13C, δ15N) and TC/TN ratios of bulk carbonaceous aerosol particles over northern Indian Ocean [Bay of Bengal (BOB) and Arabian Sea (AS)] collected as a part of Integrated Campaign for Aerosol, Gases and Radiation Budget (ICARB) during March–May, 2006. In order to understand typical sources, we also measured same parameters of (i) aerosols emitted from typical biomasses conventionally burnt in north and northeastern India and (ii) aerosols particles present in ambient air over selected Indian cities during pre-monsoon season. Bulk aerosols over AS are characterized by significantly higher TC/TN ratios (∼50 ± 10) compared to aerosol over Indian cities (5.6 ± 2.6) as well as over BOB (6.8 ± 12.5), most likely due to having significant inorganic carbon contributed by mineral dust. δ13C of aerosols over AS and BOB do not show significant variation (−25.6‰ ± 0.6, −26.5‰ ± 0.8; n = 24 and 21 respectively), however δ15N values showed a conspicuous difference between the two braches of northern Indian Ocean (10.6‰ ± 2.7 over BOB and 1.4‰ ± 3.3 over the AS). Depleted δ15N of aerosols over AS can be interpreted in terms of significant mixing of isotopically depleted nitrogenous compounds (NH3 and NOxs) emitted from the underlying (denitrifying) waters. [Copyright &y& Elsevier]

Abstract: This study pertains to the variations observed in the mixing ratios of surface ozone, its prominent precursor NOx∗ and the meteorological parameters (solar radiation, temperature, relative humidity and wind speed) during the annular solar eclipse that occurred on 15 January 2010 at Kannur (11.9°N, 75.4°E, 5 m amsl), a tropical coastal site in the southern region of India. The solar eclipse started at 11:05 IST (IST is 5.5 h ahead of UTC), reached to the maximum obscuration at 13:20 IST and ended at 15:05 IST. The observations made at Kannur show influences of the solar eclipse phenomenon on the surface ozone and NOx∗ mixing ratios. A sharp decline in the surface ozone was observed during the eclipse, due to the decreased efficiency of the photochemical ozone formation. The NO2 ∗ levels were found to increase during the eclipse period while the NO levels remained unchanged. The eclipse induced reduction in surface ozone and enhancement in NOx∗are estimated to be 57.5% and 62.5% respectively. Reductions in the air temperature, relative humidity and wind speed were also observed during the event of solar eclipse. Simulation from a chemical box model indicates about 94% reduction in the NO2 photolysis rates during the eclipse period, which is leading to about 59% reduction in the surface ozone. Observations as well as model simulations indicate that the reduced photochemical ozone production from NO2 photolysis is possibly the main driver of ozone reduction during the eclipse at this site. [Copyright &y& Elsevier]

Measurements of methane (CH4) and sulfur hexafluoride (SF6) have been made using gas chromatographic technique at a coastal site, Thumba (8.6°N, 77°E), India from the flask air samples collected during 1996–2000. The growth rates of CH4 and SF6 are observed to be 30 and 0.25 pptv yr−1 respectively. The growth rate of CH4 at Thumba is found to be much higher than its average growth rate of about 7 ppbv yr−1 at other tropical monitoring sites. The observed growth rate of SF6 at Thumba is similar to that found at other tropical stations. Seasonal amplitudes in CH4 and SF6 are higher at Thumba when compared to the other sites. The large growth rate of CH4 at Thumba could be attributed to the increase in regional sources, and the greater seasonal amplitude is shown to be caused by the change in dynamical structure from Northern Hemisphere summer to winter. [Copyright &y& Elsevier]