Indo-Gangetic Plain Region Research Articles

Effect of COVID-19 shutdown on aerosol direct radiative forcing over the Indo-Gangetic Plain outflow region of the Bay of Bengal

The Indo Gangetic Plain (IGP), one of the most densely populated regions of the world, is a global hotspot of anthropogenic aerosol emissions. In the pre-monsoon season (March–May), the strong westerlies carry transported dust aerosols along with anthropogenic aerosols onto the Bay of Bengal (BoB). The outflow from IGP modulates the aerosol loading and the aerosol direct radiative forcing (ADRF) over the BoB. The quantification of the anthropogenic aerosol impact on the radiative forcing over the outflow region remains inadequate. The enforced shutdown amid the COVID-19 pandemic eased the anthropogenic activities across the country, which helped to examine the magnitude and variability of aerosol loading and subsequent changes in ADRF over IGP and the outflow region of the BoB. Wind trajectory analysis illustrates that the ADRF over the BoB is greater during the days when the winds originated from the IGP region (at the surface −54.2 ± 6.4 W m−2, at the top of the atmosphere, −26.9 ± 3.4 W m−2 and on the atmosphere, 27.0 ± 3.1 W m−2) compared to the seasonal average (−46.3 ± 7.1 W m−2, −24.9 ± 4.0 W m−2 and 20.6 ± 3.2 W m−2, respectively). This indicates that anthropogenic aerosols emission from IGP can contribute an additional 31% of the atmospheric ADRF over the IGP outflow region of the BoB. The reduced aerosol loading during the shutdown period resulted in a reduction of ADRF at the surface, at the top of the atmosphere, and on the atmosphere over the IGP outflow region of the BoB by 22.0 ± 3.1%, 20.9 ± 3.4% and 23.2 ± 3.3%, respectively. This resultant 20–25% reduction in ADRF over the IGP outflow region of BOB matches well with 10–25% reduction in aerosol optical depth (AOD) over the IGP during the shutdown period showing a robust coupling between IGP aerosol emissions and ADRF over the BoB.

Seismic attenuation model for data gap regions using recorded and simulated ground motions

In this study, seismic attenuation model is derived using recorded and simulated ground motions covering the data gap region of the Indo-Gangetic Plains (IGP), employing artificial neural networks (ANN) methodology. Four independent variables moment magnitude (Mw), focal depth, epicentral distance (Repi), and average shear wave velocity up to 30 m depth (Vs30) are selected to predict peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) (5% damping) between periods 0.01 to 4 s (twenty-five periods in total), utilizing 926 recordings (PESMOS, CIGN and synthetic database). A feed-forward ANN with Levenberg–Marquardt training algorithm is employed for training the network of input and output dataset. The optimal network architecture obtained in this study consists of 4–9–26 input, hidden and target nodes, respectively. In spite of the absence of presumed functional dependencies in ANN methodology, our model captured a number of sound physical features of earthquake ground motion: magnitude scaling, attenuation with distance and radiation damping. Further, the performance of the model is measured by the standard deviation of the error, σ(e), and compared with the four widely used conventional GMPEs applicable for IGP region of India. The standard deviations for our model varied between 0.208 and 0.263 which is less than the classical GMPEs at all twenty-six periods of PSA. Finally, the ANN model performance is compared with recorded ground motions at four stations and conventional GMPEs, and the results affirm that this model is competent to predict the response spectrum with good accuracy for IGP region.

Ecological weed management approaches for wheat under rice–wheat cropping system

Weeds are one of the most important yield limiting factor in wheat cultivation, causing a yield loss of 15–50% depending on relative proportion of weed flora, weed density and period of their infestation. To control the weeds effectively, the farmers of Indo-Gangetic Plains Region (IGPR) are mainly dependent on the chemical herbicides. However, the excessive herbicide use has led to development of resistance in many weed species and shift in weed flora besides negative residual effects on the succeeding crops and food quality as well. Therefore, there is an urgent need to look for alternate methods which are economically viable and ecologically stable. Several approaches like early sowing of wheat, soil solarization, adjustment in row spacing, sowing weed free seeds, adjusting seed rate, planting densities, crop rotations, competitive cultivars, stale seed bed technique, efficient nutrient management, proper irrigation scheduling, mechanical control, mulching, residue retention and tillage methods have been found effective in wheat in numerous field studies. Looking at the potential of such ecological approaches, there is need for in-depth research on various aspects of these methods. This paper reviews the available information on different ecological weed management approaches in wheat under rice–wheat cropping system of Indo-Gangetic plains.

Source Impact Analysis Using Char-EC/Soot-EC Ratios in the Central Indo-Gangetic Plain (IGP) of India

This study measured the carbonaceous aerosols in the atmospheric fine particulate matter (fPM; dia. < 2.5 µm, n = 102 samples) above an urban location (Prayagraj) on the central Indo-Gangetic Plain (IGP) for 1 year (December 2016–November 2017). During the study period, the fPM mass concentrations exhibited very high variability, ranging from 22 to 367 (avg. ± SD: 149 ± 87) µg m–3, and approximately 40% of the annual average consisted of carbonaceous aerosols (organic carbon [OC], water-soluble OC [WSOC], and elemental carbon [EC]). Furthermore, several diagnostic ratios (EC/fPM, OC/EC, char-EC/soot-EC, and WSOC/OC) indicated that the characteristics of the carbonaceous aerosols significantly differed between seasons, with emission sources, seasonal meteorology, and atmospheric chemistry driving the variation in abundance. Specifically, our trajectory analysis revealed an association between northwesterly air masses originating in northwestern India and higher concentrations of fPM and carbonaceous aerosols at the study site, which mainly occurred during the post-monsoon season and winter. However, anthropogenic emissions from local sources dominated the fPM and carbonaceous aerosols in summer and the monsoon season, during which we also observed the influence of air masses of mixed (continental/marine) origin. To identify the sources of the carbonaceous aerosols and evaluate their contributions, we analyzed the char-EC/soot-EC ratio in combination with the OC/EC ratio. Cross plots of these ratios identified biomass burning and fossil-fuel combustion as the largest sources during winter and the post-monsoon season, and summer and the monsoon season, respectively. Our results demonstrate the advantages of utilizing the char-EC/soot-EC ratio rather than the OC/EC ratio as a tracer of these two sources in the IGP region.

Food and Nutrition in the Indo-Gangetic Plain Region – A Disaggregate Level Analysis

India is an agriculture-based country which has experienced enormous change in food and nutrition utilization since financial changes in the mid-1990s. Agribusiness is considered as the backbone of Indian economy. Therefore, the Indo-Gangetic Plain (IGP) holds agricultural importance, contributing to a major share of our national income. High financial development rates of Indian economy have neglected to enhance food security in the country. The welfare of an expanding economy is not shared equally as the country is still home to one-third of the world’s poor. Hunger in India is considered as a genuine imprint on its development, and food security has now evolved as a principal issue. Presently, agriculture, nutrition, and dietary security are the prime worry for India to accomplish the target of encroachment. A large portion of the Indian population lacks healthy sustenance and nourishment. This article demonstrates nourishment utilization design across selected social and economic groups in the states falling under IGP region of India, which include West Bengal, Bihar, Uttar Pradesh, Punjab and Haryana. The analysis helps in distinguishing the disparities among calorie, protein and fat consumption in the IGP region. An effort is made to recognize socio-economic groups suffering from deficiencies in nutrition consumption.

Integrated crop management technology for enhanced productivity, resource-use efficiency and soil health in legumes – A review

Under impeding production–and resource–vulnerabilities in India, our approach to agriculture needs to be redefined with inclination towards climate resilient integrated crop and resource management (ICRM) having low risk vulnerability, high factor productivity and sustained farm profitability with safe food and environmental quality. In above context, integrated crop management (ICM) practices hold great potential which take into account economic, social and environment sustainability. In irrigated agro-ecosystem of Indo-Gangetic Plains Region (IGPR), continuous cultivation of rice-wheat cropping system (RWCS) with intensive input use has caused a serious threat to agricultural sustainability with numerous production constraints. In order to diversify the IGPR production systems, pulses and other legumes like soybean and pigeonpea etc. hold great promises. Thus, legume-based cropping systems coupled with ICM practices may bring overall sustainability in IGPR. As per FAO, ICM is a recent concept in agriculture. ICM practices are the integrated technology package of appropriate site-specific crop management, integrated nutrient management, crop residue recycling, tillage management, water management, crop diversification/legume intervention, varietal selection, crop protection, energy saving and post-harvest management. Overall, this review paper highlights sufficient research findings which establish the superiority of ICM practices; in addition, it invokes for further strengthening of this research area for improving agricultural productivity, resource use efficiency and soil health with special reference to legume crops.

Water-soluble organic and inorganic nitrogen in ambient aerosols over the Himalayan middle hills: Seasonality, sources, and transport pathways

Atmospheric nitrogen is ubiquitous in the environment and hence plays an essential role in the nutrient balance over the whole ecosystem. However, its abundance and characteristics, particularly in the Himalayas, are not well understood. Therefore, to understand the abundance, sources, and seasonality of soluble nitrogenous species in the middle hills of the central Himalayas, aerosol samples were collected at Dhulikhel in Nepal from January to December 2018. The results of this study revealed that water-soluble inorganic nitrogen (WSIN) contributed the most to water-soluble total nitrogen with an abundance of ammonium nitrogen (NH4+–N). Moreover, water-soluble organic nitrogen (WSON) contributed approximately 18% to aerosol total water-soluble nitrogen. The aerosol mass and WSIN species exhibited strong seasonality with considerably higher concentrations during dry periods and lower concentrations during the wet period. Furthermore, for dry periods, the HYSPLIT model revealed that nitrogen aerosols mainly originated from the Indo-Gangetic Plain region and were transported and deposited in the Himalayas through long-range atmospheric transport. The strong correlations of WSON with nssK+ (biomass burning) and nssCa2+ (crustal sources) and lack of a significant correlation with SO42− indicated that primary sources are responsible for generating WSON rather than secondary processes in the Himalayas. The estimated dry deposition fluxes for NO3−–N, NH4+–N, and WSON were 1.56, 8.35, and 4.06 kg ha−1 y−1, respectively. This study also shows that increasing air contaminants and emissions over South Asia can enter the Himalayas and affect the human health and ecology of this fragile area.

Status of Subclinical Mastitis in Crossbred Cattle of Peri-urban Unorganized Herd of Middle Indo-gangetic Plains

Background: Mastitis is the most common and economically important disease of dairy cattle. Subclinical mastitis is a more important form in India than clinical mastitis. Subclinical mastitis (SCM) detection done by periodic examination of the udder health by evaluation of milk at the herd level or the individual cow level by milk somatic cell count (SCC), followed by culture of random milk samples. The presented study was undertaken by survey and sampling of milk from lactating crossbred cattle of unorganized dairy farms and farmer’s dairy of the peri-urban region of middle Indo-Gangetic Plains. The objective of the study was to monitor the status of SCM in crossbred cattle and associated changes in milk constitutes and oxidative stress in milk. Methods: A total of 147 lactating crossbred cattle were screened for SCM using the modified California Mastitis Test (CMT) using detergent based CMT reagent and compared with conventional CMT reagent, followed by SCC, milk constituents, bacterial isolation and antibiotic sensitivity testing (ABST). General information was collected in pre-tested questionnaire. The data obtained were statistically treated to evaluate significance of the study.Conclusion: The overall prevalence of subclinical mastitis in peri-urban cross-bred cattle was 36.74% which varied with parity and stage of milking. Prevalence of subclinical mastitis was highest (55.77%) in cross-bred cattle in mid-lactation and Parity 3-5. The mean SCC was significantly higher (7.21±0.27) in subclinical mastitis compared to CMT negative (3.66±0.06) milk sample. Somatic cell count was positively and significantly correlated with CMT reactions using conventional CMT reagent (rs= 0.86) as well as modified CMT reagent (rs=0.815) attempted using Spearman rank-order correlation coefficient. The mean values of milk pH, fat and lactic acid acidity increased significantly (P£0.01) in SCM compared to the milk of healthy cattle, except lactose which decreased significantly in SCM milk. The common contagious bacteria responsible for SCM isolate were coagulase-positive Staphylococcus spp. (64.82%) isolates from these SCM milk followed by Streptococcus spp. ABST test conducted on random CMT positive milk sample indicated that gentamicin as most sensitive, followed by enrofloxacin. The present finding indicates the suitability of enrofloxacin as the most useful antibiotic for the treatment of subclinical mastitis in cross-bred cattle of the peri-urban area of middle Indo-Gangetic plains.

Appraisal of regional haze event and its relationship with PM2.5 concentration, crop residue burning and meteorology in Chandigarh, India

Air pollution affects not only the air quality in megacities but also in medium and small-sized cities due to rapid urbanization, industrialization, and other anthropogenic activities. From October 28, 2015 to November 3, 2015, the Indo-Gangetic Plains region, including Chandigarh encountered an episode of poor visibility during the daytime. The daily average PM2.5 concentration reached 191 μg/m3, and visibility reduced by ∼2.2 times in the Chandigarh region. PM2.5 concentration was found around 4 times higher than a non-haze day and more than 3 times higher than National Ambient Air Quality Standards for 24 h. A significant correlation between PM2.5 and CO (r: 0.87) during the haze period indicated similarity in their emission sources; which was attributed to the burning of solid organic matter. Further, satellite data and back-trajectory analysis of air masses showed large-scale rice stubble burning in the agricultural fields, adjoining to the city areas. The transboundary movement of air masses below 500 m and meteorological conditions played a major role in building the pollution load in the Chandigarh region. Moreover, the enhanced concentration of biomass burning tracers, i.e., organic carbon (∼3.8 times) and K+ ions (2∼ times) in PM2.5 and acetonitrile (∼2.3 times) in ambient air was observed during the haze event. The study demonstrates how regional emissions and meteorological conditions can affect the air quality in a city; which can be useful for proper planning and mitigation policies to minimize high air pollution episodes.

Concentration, sources and wet deposition of dissolved nitrogen and organic carbon in the Northern Indo-Gangetic Plain during monsoon

Precipitation represents an important phenomenon for carbon and nitrogen deposition. Here, the concentrations and fluxes of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) with their potential sources were analyzed in wet precipitation during summer monsoon from the Northern Indo-Gangetic Plain (IGP), important but neglected area. The volume-weighted mean (VWM) concentration of DOC and TDN were 687.04 and 1210.23 µg/L, respectively. Similarly, the VWM concentration of major ions were in a sequence of NH4+ > Ca2+ > SO42- > Na+ > K+ > NO3− > Cl− > Mg2+ > F− > NO2−, suggesting NH4+ and Ca2+ from agricultural activities and crustal dust played a vital role in precipitation chemistry. Moreover, the wet deposition flux of DOC and TDN were 9.95 and 17.06 kg/(ha⋅year), respectively. The wet deposition flux of inorganic nitrogen species such as NH4+-N and NO3−-N were 14.31 and 0.47 kg/(ha⋅year), respectively, demonstrating the strong influence of emission sources and precipitation volume. Source attribution from different analysis suggested the influence of biomass burning on DOC and anthropogenic activities (agriculture, animal husbandry) on nitrogenous species. The air-mass back trajectory analysis indicated the influence of air masses originating from the Bay of Bengal, which possibly carried marine and anthropogenic pollutants along with the biomass burning emissions to the sampling site. This study bridges the data gap in the less studied part of the northern IGP region and provides new information for policy makers to deal with pollution control.

Absorption and radiative characteristics of brown carbon aerosols during crop residue burning in the source region of Indo-Gangetic Plain

The north-western Indo-Gangetic Plain (IGP) experiences massive crop-residue burning (viz. paddy and wheat) on an annual and seasonal basis. The long-range transport of the particulates emitted from paddy- and wheat-residue burning (expressed as PRB and WRB, respectively) degrades the air quality, perturb the radiative budget, and alter the atmospheric chemistry of downwind IGP locations. Therefore, chemical, absorption and radiative characteristics of carbonaceous aerosols (total carbon; TC) were explored in this study. The fraction of TC in ambient PM2.5 (particulates with aerodynamic diameter ≤ 2.5 μm) was ~45% during PRB and ~24% during WRB. However, biomass burning emissions were the predominant source of TC during both PRB and WRB. The brown carbon (BrC) aerosols at Beas were ~2–3 times more abundant during PRB than in WRB. However, the absorption properties such as mass absorption efficiency and imaginary component of the refractive index for BrC at 405 nm (expressed as MAEBrC-405, kBrC-405, respectively) and radiative characteristics such as light absorption capacity were similar during both PRB and WRB. The similarity between these absorption and radiative characteristics indicate that BrC aerosols emitted during the burning of different biomass may depend only on their combustion condition. Further, the increased biomass burning emissions were linked with enhancement in the light absorption capacity of BrC during PRB. A similar light absorption capacity was observed (~30 W/g) for water-soluble BrC (WS-BrC) and total BrC during PRB. Moreover, the % contribution of BrC and EC to their total direct radiative forcing (DRFTC) during PRB and WRB (~40% and ~60% for BrC and EC, respectively) were also similar. The WS-BrC constitutes only ~15% of DRFTC during PRB. This difference signifies that non-WS-BrC aerosols were the predominant light-absorbing species during PRB (compared to WS-BrC), which needs to be factored into global climate models to mitigate uncertainties.

Potential of conservation agriculture modules for energy conservation and sustainability of rice-based production systems of Indo-Gangetic Plain region

Rice-based cropping systems are the most energy-intensive production systems in South Asia. Sustainability of the rice-based cropping systems is nowadays questioned with declining natural resource base, soil degradation, environmental pollution, and declining factor productivity. As a consequence, the search for energy and resource conservation agro-techniques is increasing for sustainable and cleaner production. Conservation agriculture (CA) practices have been recommended for resource conservation, soil health restoration and sustaining crop productivity. The present study aimed to assess the different CA modules in rice-based cropping systems for energy conservation, energy productivity, and to define energy-economic relations. A field experiment consisted of four different tillage-based crop establishment practices (puddled-transplanted rice followed by (fb) conventional-till maize/wheat (CTTPR-CT), non-puddled transplanted rice fb zero-till maize/wheat (NPTPR-ZT), zero-till transplanted rice fb zero-till maize/wheat (ZTTPR-ZT), zero-till direct-seeded rice fb zero-till maize/wheat (ZTDSR-ZT)), with two residue management treatments (residue removal, residue retention) in rice–wheat and rice–maize rotations were evaluated for energy budgeting and energy-economic relations. Conservation-tillage treatments (NPTPR-ZT, ZTTPR-ZT, and ZTDSR-ZT) reduced the energy requirements over conventional tillage treatments, with the greater reduction in ZTTPR-ZT and ZTDSR-ZT treatments. Savings of energy in conservation-tillage treatments were attributed to reduced energy use in land preparation (69–100%) and irrigation (23–27%), which consumed a large amount of fuel energy. Conservation-tillage treatments increased grain and straw/stover yields of crops, eventually increased the output energy (6–16%), net energy (14–26%), energy ratio (25–33%), and energy productivity (23–34%) as compared with CTTPR-CT. For these energy parameters, the treatment order was ZTDSR-ZT ≥ ZTTPR-ZT > NPTPR-ZT > CTTPR-CT (p < 0.05). Crop residue retention reduced net energy, energy ratio, and energy productivity when compared with residue removal. Our results of energy-economic relations favored the “conservative hypothesis,” which envisages that energy and monetary investments are not essentially the determinants of crop productivity. Thus, zero tillage-based crop establishments (ZTTPR-ZT, ZTDSR-ZT) in rice-based production systems could be the sustainable alternative to conventional tillage-based agriculture (CTTPR-CT) as they conserved non-renewable energy sources, reduced water requirement, and increased crop productivity.

Climatological trends in satellite-derived aerosol optical depth over North India and its relationship with crop residue burning: Rural-urban contrast

Columnar Aerosol Optical Depths (AOD) over an urban area (Chandigarh) and a rural area (Khera, Fatehgarh Sahib district) situated in the Indo-Gangetic Plains (IGP) of India were analysed to study their temporal heterogeneity in terms of interannual, seasonal and monthly variations. Over the last few decades, IGP has become one of the global hotspots of air pollution due to the increased anthropogenic activities such as traffic, industries, agricultural waste burning etc. Level-2 AODs (550 nm) were retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard NASA's Terra and Aqua satellites, for a period of 14 years (2005–2018). The climatological mean Terra-MODIS (Aqua-MODIS) AOD over the urban location was ~0.497 ± 0.238 (0.474 ± 0.228), whereas over the rural location it was 0.542 ± 0.269 (0.534 ± 0.282). Linear trend analysis estimated an increase in annual mean Terra-MODIS (Aqua-MODIS) AOD at a rate of ~0.009 (0.013) per year over the urban site; whereas over the rural location the rate of increase was ~0.003 (0.004) per year. Results show that the observed increase is ~1.49% (2.41%) of climatological mean AOD over the urban location for Terra-MODIS (Aqua-MODIS), whereas, over the rural location, it was ~0.50% (0.67%). Using the HYSPLIT trajectory model, it was concluded that, during post-monsoon, the observed high AODs can be related to massive crop residue burning in the IGP region. These AOD trends can also be used to track the regional anthropogenic air-pollution changes. An empirical relation between AOD and PM10 was established, which can be used to estimate PM10 over the urban and rural areas of IGP (using MODIS AODs), complementing the sparse ground-based monitoring. Further, satellite-based air pollution data can be used for baseline assessment and understanding the impact of control policies such as National Clean Air Programme and to support formulate evidence-based pollution control strategies.

El Nino/La Nina impact on crop production over different agro-climatic zones of Indo-Gangetic Plain of India

Estimates of fluctuation in climatic condition have a large impact on the production of selected crops such as rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), pulse, and sugarcane (Saccharum officinarum) which are the most prominent crops over Indo-Gangetic Plains (IGP). The influence of El Nino/La Nina on monsoon rainfall directly or indirectly affects the Indian crop over the Agro-Climatic Zones of Indo-Gangetic Plain (IGP). The detailed analysis has been carried out to show the impact of El Nino/La Nina and its association with crop production over sub-regions of IGP (lower, middle, upper, and trans IGP) during 1966–2009. During El Nino years, the production and yield of Rice and sugarcane have been affected in the middle and upper regions of IGP. The production of wheat decreased during La Nina events in the middle regions of IGP. The rice production has been severely affected by El Nino events over middle and upper IGP regions whereas wheat production increased. The decrease in maize production is observed in the upper and trans regions of IGP during El Nino. Pulse production decreased mainly in the middle, upper, and trans IGP during both events. The sugarcane production was highly affected during La Nina events overall sub-regions of IGP. The correlations among crop production, monsoon rainfall, and sea surface temperature (SST) anomaly of Nino 3.4 region during monsoon season are very insignificant during El Nino events. On other hand, La Nina event shows significant correlation over IGP. It has been noticed that on many occasions, deficit rainfall over IGP during summer monsoon season was responsible for decrease in crop production. Hence, alteration in Indian summer monsoon rainfall (ISMR) and sea surface temperature modulation of Nino 3.4 might have caused increase/decrease in the production of the crop.

Evaluation of convective storms using spaceborne radars over the Indo‐Gangetic Plains and western coast of India

AbstractMonsoonal convective systems are examined using four years (2014–2017) of radar reflectivity data from the Precipitation Features (PFs) database of the Global Precipitation Measurement (GPM) Microwave Imager (GMI) and Dual Precipitation Radar (DPR). The study classifies the cumulonimbus tower (PF‐CbT) at 12 km, and intense convective clouds at both 3 km (PF‐ICC3) and 8 km (PF‐ICC8) based on PFs' reflectivity threshold at a reference height over the Indo‐Gangetic Plains (IGP) and Indian Western coastal (WG) region, including the Arabian Sea and the Western Ghats. Results show that the regional variations are more enhanced for the PF‐ICC3 clouds with high occurrence over the IGP region. In the mixed‐phase regime, the median maximum reflectivity is greater for all cloud types over the IGP region. The occurrences of 20 and 40 dBZ echo the top height &gt; 5 km is higher in the IGP region, indicating the deep and intense convection. The aerosol–cloud interaction is examined for warm and mixed‐phase clouds. The vertical structure of aerosols shows the suppression of warm rainfall over the IGP region. However, rainfall intensity increases in mixed‐phase clouds because of the dominancy of ice processes. The significant positive (negative) correlation is observed between the echo top height and aerosol concentrations over the IGP (WG) region. The value of the novel findings clearly states the region‐specific demand for a closer examination of the radar reflectivity–aerosol interaction on regime‐dependent clouds over the IGP region as well as contrasts against other regions for similar and contrasting cloud–aerosol‐radiation interactions.

Spatial distribution patterns and human exposure risks of polycyclic aromatic hydrocarbons, organochlorine pesticides and polychlorinated biphenyls in Nepal using tree bark as a passive air sampler

Nepal is abutted between the populated Indo-Gangetic Plain (IGP) and Himalayan mountains. Currently, knowledge on the country-wide distribution and cancer risks of atmospheric organic toxicants in Nepal remains limited. In this study, the concentrations, sources, and distributions of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs), along with their cancer risks, were investigated in Nepal by using tree bark as a passive air sampler. After transferring by a bark/air partitioning model, the averaged concentrations of ∑PAHs, ∑DDTs, ∑HCHs, HCB, ∑Endo and ∑PCBs in the atmosphere of Nepal were 3.71 × 104 pg/m3, 1.10 × 103 pg/m3, 2.92 × 102 pg/m3, 4.38 × 102 pg/m3, 4.66 pg/m3 and 65.8 pg/m3, respectively. Source diagnosis suggested that biomass burning is the major source for PAHs, while local application and long-range transport jointly contribute to the high levels of DDT and HCH in the air. The ILCR (incremental lifetime cancer risk) value was used to assess the risks of various chemicals. Adults have a higher risk than other age groups; the major exposure pathway for risk is by inhalation; and PAHs and HCHs are the dominant chemical classes that lead to risk. It was also found that, in certain hotspots in south Nepal, the carcinogenic risks caused by DDT and HCH were particularly high (>1 × 10−4). Given that illegal and disordered use of legacy POPs in south Nepal and the IGP region is common, our results highlight an urgent need for voluntary regulation of the ongoing use of pesticides.

On the widespread enhancement in fine particulate matter across the Indo-Gangetic Plain towards winter

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) impacts the climate, reduces visibility and severely influences human health. The Indo-Gangetic Plain (IGP), home to about one-seventh of the world’s total population and a hotspot of aerosol loading, observes strong enhancements in the PM2.5 concentrations towards winter. We performed high-resolution (12 km × 12 km) atmospheric chemical transport modeling (WRF-Chem) for the post-monsoon to winter transition to unravel the underlying dynamics and influences of regional emissions over the region. Model, capturing the observed variations to an extent, reveals that the spatial distribution of PM2.5 having patches of enhanced concentrations (≥100 µgm−3) during post-monsoon, evolves dramatically into a widespread enhancement across the IGP region during winter. A sensitivity simulation, supported by satellite observations of fires, shows that biomass-burning emissions over the northwest IGP play a crucial role during post-monsoon. Whereas, in contrast, towards winter, a large-scale decline in the air temperature, significantly shallower atmospheric boundary layer, and weaker winds lead to stagnant conditions (ventilation coefficient lower by a factor of ~4) thereby confining the anthropogenic influences closer to the surface. Such changes in the controlling processes from post-monsoon to winter transition profoundly affect the composition of the fine aerosols over the IGP region. The study highlights the need to critically consider the distinct meteorological processes of west-to-east IGP and changes in dominant sources from post-monsoon to winter in the formulation of future pollution mitigation policies.

Inter-comparison of multi-satellites and Aeronet AOD over Indian Region

Aerosols affect global as well as regional climate by interacting with solar radiations and by altering the cloud properties. Due to the scarcity of ground observations over entire India, especially over Indo-Gangetic Plains (IGP), satellite-based measurements provide better spatial and temporal coverage for the evaluation of aerosol optical properties. This study presents the inter-comparison of multiple satellites (MISR, MODIS, and OMI) and ground-based aerosol optical depth (AOD) for the 2010–2017 (8 years) period over IGP (Gandhi College, Jaipur, and Kanpur) region. Satellite observations are spatially and temporally collocated by an average of 50 × 50 km square box and ±30 minutes, respectively. Results indicate a higher correlation with MODIS ( R 2 = 0.7 at Gandhi College) followed by MISR and OMI AOD. Irrespective of few observations (219) at Jaipur, MISR shows the highest percentage (58%) of data points within the error envelope because of multiple angle viewing and spectral capability gives the accurate information in high reflecting desert areas. MISR and OMI have a systematic negative bias trend for higher AOD at all test sites, while MODIS has a negative bias over the Jaipur region only. The temporal analysis reveals the higher concentration of fine mode aerosols captured by MISR and MODIS in December month over Gandhi College and Kanpur region, whereas Jaipur is over-loading with coarser aerosols during April to June month from the Thar Desert and Middle East dust storms. Seasonal distribution over the IGP region indicates higher AOD in summer owing to dust storms. Inter-comparison shows that MODIS has higher seasonal AOD as compared to MISR. The spatial correlation between MODIS and MISR is high during the summer and winter seasons. The OMI sensor performance over the IGP region has not been found to match with existing patterns. These findings are useful in the context of selecting the most reliable satellite AOD products for future studies. • MODIS, as compare to other sensors have high correlation with Aeronet. • OMI AOD underestimates over IGP region. • Seasonal AOD are positively bias by MODIS and negatively by MISR and OMI. • Spatial correlation between MODIS and MISR is high over IGP region.

Determination of dry deposition velocity of polycyclic aromatic hydrocarbons under the sub-tropical climate and its implication for regional cycling

Atmospheric dry deposition is a major pathway for removal of polycyclic aromatic hydrocarbons (PAHs) from the atmosphere. Despite its significance in the atmospheric environment, measurements of the dry deposition velocity (VDD) and deposition fluxes (FDD) of PAHs are relatively limited. In this study, a passive dry deposition (PAS-DD) collector was co-deployed with passive air sampler polyurethane foam (PAS-PUF) from November 2015 to November 2016 in two major cities (Kathmandu and Pokhara), Nepal, to investigate the VDD and FDD of PAHs. The VDD of PAHs ranged from 0.25 to 0.5 cm s−1 and the annual average was recorded as 0.37 ± 0.08 cm s−1. On the basis of measured VDD, the FDD of ∑15PAHs in Kathmandu and Pokhara were estimated as 66 and 5 kg yr−1 respectively. According to the measured VDD of Kathmandu and Pokhara in this study, and the previously published VDD data of Toronto, Canada, where the same PAS-DD collector was used, a significant multi-linear correlation (r2 = 0.79, p < 0.05) was found between VDD of higher molecular weight (HMW with MW ≥ 228.3 and ≥ 4 rings) PAHs and meteorological parameters (precipitation and wind speed) and vapor pressure of PAHs. To the best of our knowledge, this enabled the development of an empirical model that can exhibit the combined effects of meteorological conditions on the VDD of HMW PAHs. The model was used to estimate the VDD values for major cities in the Indo-Gangetic Plain (IGP) region and the maximum estimated proportion of HMW PAHs deposited by dry deposition reached up to 60% of total emissions. Although PAH emissions in the IGP region pose global risks, the results of this study highlight the considerable risk for local IGP residents, due to the large dry deposition proportion of HMW PAHs.

Seasonal Variation of OC, EC, and WSOC of PM10 and Their CWT Analysis Over the Eastern Himalaya

In the present study, seasonal transport trends and potential source regions of carbonaceous species [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), secondary organic carbon (SOC) and total carbonaceous aerosols (TCAs)] of PM10 was evaluated over Darjeeling, an eastern Himalayas of India during August 2018–June 2019. Backward trajectories, cluster analysis, and concentration-weighted trajectory (CWT) analysis were performed to evaluate the seasonal transport pathway of carbonaceous aerosols over the region. The annual average concentration of PM10 was recorded to be 55 ± 18 μg m−3, which is close to National Ambient Air Quality Standard (NAAQS; 60 μg m−3 for annual PM10) of India. The concentration of PM10 showed maxima in pre-monsoon season (63 ± 21 μg m−3) followed by post-monsoon (56 ± 16 μg m−3), monsoon (51 ± 13 μg m−3) and winter seasons (49 ± 17 μg m−3). The study revealed that the WSOC comprises about 72% of OC concentration with maxima in post-monsoon (81% of OC) followed by winter (74% of OC), pre-monsoon (67% of OC) and monsoon seasons (66% of OC). The concentration of SOC were estimated as 1.4 ± 0.9, 1.7 ± 1.0, 2.4 ± 0.9 and 1.9 ± 0.9 µg m−3 during pre-monsoon, monsoon, post-monsoon and winter, respectively (which are accounted for 27%, 49%, 41% and 35% to the OC mass concentration, respectively). The results indicated that biomass burning could be one of the major sources of carbonaceous aerosols in Darjeeling. Five days backward trajectory analysis (including cluster and CWT analysis) revealed that the air-mass flow of pollutants towards the sampling site of Darjeeling majorly coming from continental sites (Nepal and Indo-Gangetic plain (IGP) region of India) and the Bay of Bengal (BOB).