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The increasing air pollution in the urban atmosphere is adversely impacts the environment, climate and human health. The alarming degradation of air quality, atmospheric conditions, economy and human life due to air pollution needs significant in-depth studies to ascertain causes, contributions and impacts for developing and implementing an effective policy to combat these issues. This work lies in its multifaceted approach towards comprehensive understanding and mitigating severe pollution episodes in Delhi and its surrounding areas. We investigated the aerosol dynamics in the post-monsoon season (PMS) from 2019 to 2022 under the influence of both crop residue burning and meteorological conditions. The study involves a broad spectrum of factors, including PM2.5 concentrations, active fire events, and meteorological parameters, shedding light on previously unexplored studies. The average AOD550 (0.79) and PM2.5 concentration (140.12 μg/m³) were the highest in 2019. PM2.5 was higher from mid-October to mid-November each year, exceeding the WHO guideline of 15 μg/m³ (24 h) by 27-34 times, signifying a public health emergency. A moderate to strong correlation between PM2.5 and AOD was found (r = 0.65) in 2021. The hotspot region accounts for almost 50% (2019), 47.51% (2020), 57.91% (2021) and 36.61% (2022) of the total fire events. A statistically significant negative non-linear correlation (r) was observed between wind speed (WS) and both AOD and PM2.5 concentration, influencing air quality over the region. HYSPLIT model and Windrose result show the movement of air masses predominated from the North and North-West direction during PMS. This study suggest to promotes strategies such as alternative waste management, encouraging modern agricultural practices in hot-spot regions, and enforcing strict emission norms for industries and vehicles to reducing air pollution and its detrimental effects on public health in the region and also highlights the need for future possibilities of research to attract the global attention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Secondary aerosols constitute a significant fraction of atmospheric aerosols, yet our understanding of their formation mechanism and fate is very limited. In this work, the secondary organic aerosol (SOA) formation and aging of ambient air of Delhi are studied using a potential aerosol mass (PAM) reactor, an oxidation flow reactor (OFR), coupled with aerosol chemical speciation monitor (ACSM), proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS), and scanning mobility particle sizer with counter (SMPS + C). The setup mimics atmospheric aging of up to several days with the generation of OH radicals. Variations in primary volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs) as a function of photochemical age were investigated. Primary VOCs such as benzene, toluene, xylene, trimethyl benzene, etc. decrease and OVOCs like formic acid, formaldehyde, acetone, ethanol, etc. increase substantially upon oxidation in OFR. The highest organic aerosol (OA) enhancement was observed for the 4.2 equivalent photochemical days of aging i.e., 1.84 times the ambient concentration, and net OA loss was observed at very high OH exposure, typically after 8.4 days of photochemical aging due to heterogeneous oxidation followed by fragmentation/evaporation. In ambient air, OA enhancement is highest during nighttime due to the high concentrations of precursor VOCs in the atmosphere. SMPS + C results demonstrated substantial new particle formation upon aging and decrement in preexisting aerosol mass. This is the first experimental study conducting an in-situ evaluation of potential SOA mass generated from the ambient aerosols in India., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The article presents a case study which retrieves vertical information on aerosols with the use of satellite data which have the advantage of more frequent global coverage in Kanpur, India. Data from scanning imaging absorption spectrometer for atmospheric cartography (SCIAMACHY) on board environmental satellite (ENVISAT) provides spectral data in O2 A- and B-band. It combines the use of the bands in the estimation algorithm to retrieve vertical profile of aerosol.

Mountain glaciers are of immense importance for the balanced natural ecosystem. Billions of human life depend on this natural reserve. However, there is an alarming situation worldwide to save this resource. The melting rate of glaciers is a matter of serious concern and one of the driving forces is air pollution. Many research studies have suggested that the deposition of aerosol particles is closely associated with the intensification of glacier retreat. We are witnessing the imperative necessity to understand the regional role of aerosol pollutants in glaciers melting. The third largest glacier occupier, the Himalayan mountain glacier has also unexceptionally countersigned many calamities such as glacial lake outburst floods, flash floods, landslides and biodiversity loss. Since the geography, climate, population, human activities, culture and pollution patterns are divergent at different mountain glaciers, thus regional studies should be encouraged to understand the role of pollutants on glaciers. On-site monitoring requires studying the regional aerosols behavior in mountain glaciers specially the most sensitive regions such as Sikkim Himalaya region. Sikkim Himalaya region has experienced a rise in temperature and an increase in glacial lakes number as well as area. This review paper suggests that the in-situ study of aerosols in ecologically sensitive mountain glaciers region is our utmost need in the current research time. As many glaciers are on the verge of disappearing and different types of aerosols deposition blamed for it at different places. The regional aerosol information may help in saving this precious natural reserve. [ABSTRACT FROM AUTHOR]

A better understanding of aerosol–cloud interaction processes is important to quantify the role of clouds and aerosols on the climate system. There have been significant efforts to explain the ways aerosols modulate cloud properties. However, from the observational point of view, it is indeed challenging to observe and/or verify some of these processes because no single instrument or platform has been proven to be sufficient. Discrimination between aerosol and cloud is vital for the quantification of aerosol–cloud interaction. With this motivation, a set of observational field campaigns named balloon-borne aerosol–cloud interaction studies (BACIS) is proposed and conducted using balloon-borne in situ measurements in addition to the ground-based (lidar; mesosphere, stratosphere and troposphere (MST) radar; lower atmospheric wind profiler; microwave radiometer; ceilometer) and space-borne (CALIPSO) remote sensing instruments from Gadanki (13.45 ∘ N, 79.2 ∘ E), India. So far, 15 campaigns have been conducted as a part of BACIS campaigns from 2017 to 2020. This paper presents the concept of the observational approach, lists the major objectives of the campaigns, describes the instruments deployed, and discusses results from selected campaigns. Balloon-borne measurements of aerosol and cloud backscatter ratio and cloud particle count are qualitatively assessed using the range-corrected data from simultaneous observations of ground-based and space-borne lidars. Aerosol and cloud vertical profiles obtained in multi-instrumental observations are found to reasonably agree. Apart from this, balloon-borne profiling is found to provide information on clouds missed by ground-based and/or space-borne lidar. A combination of the Compact Optical Backscatter AerosoL Detector (COBALD) and Cloud Particle Sensor (CPS) sonde is employed for the first time in this study to discriminate cloud and aerosol in an in situ profile. A threshold value of the COBALD colour index (CI) for ice clouds is found to be between 18 and 20, and CI values for coarse-mode aerosol particles range between 11 and 15. Using the data from balloon measurements, the relationship between cloud and aerosol is quantified for the liquid clouds. A statistically significant slope (aerosol–cloud interaction index) of 0.77 found between aerosol backscatter and cloud particle count reveals the role of aerosol in the cloud activation process. In a nutshell, the results presented here demonstrate the observational approach to quantifying aerosol–cloud interactions. [ABSTRACT FROM AUTHOR]

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To reduce the pollution from the atmosphere or polluted cities like the capital city Delhi of India, use of artificial rain is a solution. In this paper, we have proposed and analyzed a nonlinear mathematical model to reduce the pollution level by rain making. In the proposed model five variables are considered, namely; (i) number density of water vapor, (ii) number density of cloud drops, (iii) number density of raindrops, (iv) cumulative concentration of aerosols, and (v) concentration of pollutant particles suspended in the region of consideration. The effect of environmental fluctuations has been studied with the help of Lyapunov functionals. The model is analyzed in the presence of white noise and proved that if rain persists, the pollutants can be totally washed out. It has been observed that the environmental disturbances are not much favorable in such experiments as the presence of environmental disturbance may destabilize the system. It is found that to remove pollutants completely, it is necessary to prevent the formation of pollutants. The simulation is performed to support the analytical findings. [ABSTRACT FROM AUTHOR]

This study estimates the health risk due to PM 2.5 and ADE primarily in 4 regions across Northern Hemisphere during 2013-2017. Mortality in China due to PM 2.5 dipped from 1.15 million (95%CI (Confidence Interval) 0.64-1.6 million) to 1.02 million (95%CI 0.59-1.49 million) during 2013-2017 as a result of reduction in PM 2.5 population weighted concentration (PWC) from 29.26 μg/m 3 to 22.05 μg/m 3 while India overtook China in terms of death due to PM 2.5 which increased to 1.16 million (95%CI 0.72-1.67 million) from 1.07 million (95%CI 0.62-1.53 million) as a result of increase in PWC from 38.18 to 44.47 μg/m 3 . The years of life lost per person (YLL/person) due to PM 2.5 was still observed to be high in China with 5.58 YLL/person followed by India (4.13), Europe (2.19) and US (0.46) in 2017. Aerosols such as PM 2.5 have the capability to scatter or absorb solar radiation resulting in perturbation of ground meteorology which further affects dispersion of pollutants and it's resultant health impacts. ADE resulted in 7.27% of total or 77,866 deaths in India during 2013 which increased to 8.05% or 93,575 deaths in 2017 which was highest among all regions while in China ADE deaths reduced from 59,529 (5.15% of total) to 40,470 (3.94% of total) deaths during the same period, other regions too reported reduction in ADE deaths with US reporting 906 (-1.27%) lower deaths while Europe also reported 785 (-0.46%) lower deaths in 2017 as compared to 2013. ADE resulted in increased YLL/person in India from 0.29 to 0.33 during 2013-2017 while it was observed to reduce in all other regions, in China it reduced from 0.37 to 0.22 likewise YLL/person also reduced in US from 0.04 to 0.01 and in Europe from 0.01 to 0.002., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Major/crustal elements (Al, Ca, Mg, K, and Fe) and trace metals (Mn, Cr, Cu, Pb, Zn, and Ni) in atmospheric particulate matter at three sites in Goa (a coastal city in the Eastern Arabian Sea) were assessed during winter (December) and summer (March-May) months of 2015. A significant spatial and temporal variability was observed in PM10 mass concentration, crustal element, and trace metal composition at the sampling area (pristine, urban, and industrial locations). Using a diagnostic crustal element ratio (Fe/Al, Ca/Al, and Mg/Al), mineral dust components were characterized and found to show large spatial and temporal variability. The concentration levels of trace metals were further assessed for enrichment factor (EF) analysis, wherein reported elements were classified into two major groups. The first group consists of Cr, Cu, and Pb with 10< EF < 100 compared to continental crustal values (w.r.t. Al), suggesting a dominant contribution from anthropogenic sources with minor contribution from natural sources; the second group consists of Zn and Ni showing very high EF (>100)-these are solely derived from anthropogenic sources. Source identification for trace metals was further assessed based on principle component analysis (PCA). PCA highlights that the major contribution of trace metals is from anthropogenic emissions at all three locations. However, contributions from mineral dust were observed at pristine and urban locations during winter months. The reported data of trace metal concentrations in aerosols give baseline information on the atmospheric supply of micronutrients to the Arabian Sea, which has implications for the various surface ocean biogeochemical processes. Implications : This paper reports on crustal and trace metal composition and concentration level in atmospheric aerosols over a coastal city located on the Eastern Arabian Sea. This study highlights the role of various factors (meteorology and emission sources) controlling the abundance of metals over a coastal site. The contribution from various sources (anthropogenic vis-à-vis natural) has also been identified using enrichment factor analysis as well as principle component analysis. This study has implications for the supply of micronutrients to the coastal Arabian Sea, which can significantly impact various surface ocean biogeochemical processes.

Deteriorating air quality with high levels of fine particulate matter (PM 2.5 ) over National Capital Region (NCR) of India is one of the serious environmental and scientific issues. In this paper, PM 2.5 samples were collected for 24 h twice or thrice a week during December 2016-December 2017 at three sites [Delhi (IG), Modinagar (MN) and Mahendragarh (HR)] over NCR to analyse the carbonaceous aerosols. Source apportionment of PM 2.5 was attempted using Principal Component analysis (PCA) and Positive Matrix Factorization (PMF) based on the analysed carbonaceous fractions [Organic carbon, Elemental carbon, Secondary organic carbon (SOC)]. Organic compounds: alkanes, hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), phthalates, levoglucosan and n-alkanoic acids were analysed to distinguish the emission sources. Total Carbonaceous Aerosols (TCA) contributed significantly (∼26%) to PM 2.5 which revealed their importance in source apportionment. Estimated SOC contributed 43.2%, 42.2% and 58.2% to OC and 5.4%, 5.3% and 7.8% to PM 2.5 at IG, MN and HR sites respectively. PCA and PMF apportion five emission sources i.e., vehicular emissions (34.6%), biomass burning (26.8%), cooking emissions (15.7%), plastic and waste burning (13.5%) and secondary organic carbon (9.5%) for PM 2.5 . Source attributed health risk has also been calculated in terms of Lung cancer risk (LCR) associated with PAHs exposure and concluded that vehicular emissions (40.3%), biomass burning (38.1%), secondary organic carbon (12.8%) contributed higher to LCR (503.2 × 10 -5 ; ∼503 cases in 1,00,000). Health risk assessment combined with source apportionment inferences signifies the immediate implementation of emissions reduction strategies with special target on transport sector and biomass burning over the NCR of India., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

This paper presents the lightning activity, aerosol optical depth (AOD) and climatic parameters (Bowen ratio, relative humidity, rainfall, maximum surface temperature and maximum updraft speed) over wet (Northeast India—NEI) and dry (Northwest India—NWI) land surfaces in a comparative analysis. The analyses are performed on flash counts and weather data of 17 years (1998–2014) retrieved from the Tropical Rainfall Measuring Mission (TRMM) lightning imaging sensors (LIS) and the Moderate Resolution Imaging Spectroradiometer (MODIS), respectively. The first higher peak for flash counts during pre-monsoon (April–May) and second lower peak during September over wet NEI and dry NWI regions indicate the development of strong electrified storms during pre-monsoon and weakly electrified clouds during the withdrawal phase of the southwest summer monsoon. The monthly means of flash counts, Bowen ratio, maximum surface temperature, AOD and maximum updraft speed are higher by 27, 81, 16, 50 and 16%, respectively, for NWI than those of NEI. The relative humidity and rainfall are higher by 12% and 73% for NEI than those of NWI, respectively. The Pearson's correlation coefficients of lightning activity with climatic parameters and AOD demonstrate the distinctive orographic lifting, moisture content and vertical wind shear in the upper troposphere in the regional climatic zone of dry NWI in comparison to that of wet NEI. [ABSTRACT FROM AUTHOR]

Clear-sky, direct shortwave aerosol radiative forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products, as an important part of the South West Asian Aerosol Monsoon Interactions (SWAAMI) which is a joint Indo-UK research field campaign focused at understanding the variabilities in atmospheric aerosols and their interactions with the Indian summer monsoon. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatories and multi-satellite products, as described in Part 1 of this two-part paper. The ARF, thus estimated, is assessed for its superiority or otherwise over other ARF estimates based on satellite-retrieved aerosol products, over the Indian region, by comparing the radiative fluxes (upward) at the top of the atmosphere (TOA) estimated using assimilated and satellite products with spatiotemporally matched radiative flux values provided by CERES (Clouds and Earth's Radiant Energy System) single-scan footprint (SSF) product. This clearly demonstrated improved accuracy of the forcing estimates using the assimilated vis-à-vis satellite-based aerosol datasets at regional, subregional and seasonal scales. The regional distribution of diurnally averaged ARF estimates has revealed (a) significant differences from similar estimates made using currently available satellite data, not only in terms of magnitude but also the sign of TOA forcing; (b) the largest magnitudes of surface cooling and atmospheric warming over the Indo-Gangetic Plain (IGP) and arid regions from north-western India; and (c) negative TOA forcing over most parts of the Indian region, except for three subregions – the IGP, north-western India and eastern parts of peninsular India where the TOA forcing changes to positive during pre-monsoon season. Aerosol-induced atmospheric warming rates, estimated using the assimilated data, demonstrate substantial spatial heterogeneities (∼0.2 to 2.0 K d -1) over the study domain with the IGP demonstrating relatively stronger atmospheric heating rates (∼0.6 to 2.0 K d -1). There exists a strong seasonality as well, with atmospheric warming being highest during pre-monsoon and lowest during winter seasons. It is to be noted that the present ARF estimates demonstrate substantially smaller uncertainties than their satellite counterparts, which is a natural consequence of reduced uncertainties in assimilated vis-à-vis satellite aerosol properties. The results demonstrate the potential application of the assimilated datasets and ARF estimates for improving accuracies of climate impact assessments at regional and subregional scales. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are ubiquitous in our environment. Its presence in air, water, and soil makes it a serious threat to living organisms and has become a critical challenge across ecosystems. Present study aimed to assess the abundance of MPs in aerosols and street dust in Varanasi, a typical urban city in Northern India. Airborne particulates and street dust samples were collected from various sampling sites around Varanasi City. The physical identification of MPs was conducted by binocular microscopy, fluorescence microscopy, and scanning electron microscopy (SEM), while elemental analysis was made by energy-dispersive X-ray (EDX). Finally, Fourier-transform infrared spectroscopy (FTIR) was used for chemical characterization of MPs. Presence of MPs in both aerosols and street dust from all selected sampling sites was confirmed, however with varying magnitude. MPs of different colors having the shape of fragments, films, spherules, and fibers were recorded in the study while fragments (42%) in street dust and fibers (44%) dominated in aerosols. Majority of the MPs were < 1 mm in size and were primarily polypropylene, polystyrene, polyethylene, polyethylene terephthalate, polyester, and polyvinyl chloride types. The EDX spectra showed the presence of toxic inorganic contaminants like metallic elements on MPs, especially elements like aluminum, cadmium, magnesium, sodium, and silicon found to adsorb on the MPs. Presence of MPs in the airborne particulates and street dust in Varanasi is reported for the first time, thus initiating further research and call for a source-specific management plan to reduce its impact on human health and environment. [ABSTRACT FROM AUTHOR]

Objective: There is an urgent need to test and incorporate new molecules with promising efficacy and novel mode of action to control insecticide-resistant mosquito vectors for disease control. We tested a new compound, clothianidin (SumiShield 50 WG), for its efficacy as an indoor residual spray (IRS) for the control of pyrethroid-resistant Anopheles culicifacies (Diptera: Culicidae) in comparison with pirimiphos methyl (Actellic CS) as a positive control., Methods: Ten villages were selected, five each for IRS with clothianidin (300 mg AI/m 2 ) and pirimiphos methyl (1000 mg AI/m 2 ) in Almatti Dam catchment area in Karnataka state, India. Entomological parameters were monitored in these sprayed villages using standard methods. Assessment of quality of spray was performed by analysing the insecticide content in the filter paper samples collected from sprayed houses. Perceptions of spray men and inhabitants were recorded post-spray on safety of these molecules., Results: The mean applied to target ratio of content was 1.7 (n = 29) for clothianidin and 1.8 (n = 50) for pirimiphos methyl on filter paper samples analysed. Residual activity (≥80% mortality in exposed mosquitoes) after 24 h post-exposure of SumiShield WG was 5 months and increased to 6 months when the holding period was extended to 120 h and that of Actellic CS was 3 months at 24-h holding period and extended to 4 months at 120-h extended holding period. The mean densities of An. culicifacies in both arms fell drastically post-spray. In light trap collections, density of mosquitoes collected indoors was lower than outdoors in both arms indicating effectiveness of IRS. SumiShield WG was more efficacious in reducing the per-structure density than Actellic CS. The proportion of nulliparous mosquitoes was higher than that of parous mosquitoes during post-spray collections in both arms. The majority of adverse events reported were transitory and subsided without medication., Conclusion: Indoor residual spraying with SumiShield WG was found effective, operationally feasible and safe, and it is effective for up to 6 months., (© 2018 John Wiley & Sons Ltd.)

India has aggressive plans for scaling up photovoltaic installations in the coming decades. Currently fixed tilt, flat plate crystalline silicon (c‐Si) technology sets the standard for cost and performance and is both robust and relatively easy to deploy. Concentrator photovoltaics (CPV) systems have a different cost structure; using solar cells with the highest efficiencies, system efficiencies greater than 30% are possible, but the system is also more sensitive to meteorological conditions. India has a complex and varied atmosphere that prevents a straightforward comparison of technologies, and hence, in this paper, we use a computer model to simulate the power output from CPV systems located in locations in India where the Aerosol Robotic Network (AERONET) stations are based and additionally, in Bangalore where we have a CPV test station. We quantify the increased intermittency suffered by CPV systems that arises from the larger dynamic range in direct beam irradiance over global irradiance. Nevertheless, by calculating the target system costs required to attain a competitive levelized cost of electricity (LCOE), we find that CPV systems in some, but not all locations have the opportunity to compete against dual‐axis tracked and inclined c‐Si based PV in India The potential for solar power in India is huge and is likely to be tapped using conventional photovoltaic panels. However, concentrator photovoltaic (CPV) systems can offer some advantages, but the complex atmospheric conditions in India make the comparison of CPV systems with conventional technology difficult. Here, we use a computer model to simulate the energy yield from CPV systems located at four locations in India using detailed meteorological parameters. From this analysis, we establish a target CPV system cost that is required for the technology to become competitive against flat plate technology. [ABSTRACT FROM AUTHOR]

The paper reports the observations of the aerosol studies carried-out for three years (2004-2007) during the summers and winters at Kaikhali (22.0220 N & 88.6140E) lying in the east coast of India inside a special mangrove ecosystem: 'The Sundarbans'. Aerosol optical depths were measured using a five filter channel sunphotometer with wavelengths at 340, 500,870, 936 and 1020 nm respectively. The sampling site enjoys a tropical climate and is under the strong influence of the southwest or summer monsoon and weak northeast or winter monsoon. The mean aerosol optical depth (AOD) during the winters (2004-2007) for the filter channels 340, 500, 870, 936 and 1020 nm have been found to be 1.478, 1.014, 0.579, 0.541 and 0.523 respectively whereas for the summer periods, they have been found to be 1.173, 0.859, 0.603, 0.564 and 0.597 respectively. The mean values of the angstrom exponent calculated for the winter and summer months over the years 2004-2007 have been found to be 1.283, 0.999, 1.285 and 1.094, 1.167 and 1.91 respectively. Generally the higher angstrom exponent values during the winter periods over the years from 2004-2007 except for the year 2005-2006 indicate high ratio of smaller fractions to larger fractions. The values of Angstrom exponents observed at the site suggest that the aerosol comprise mostly of the small size particles. An attempt has been made in the paper to compare the aerosol optical depth and angstrom exponent values with another study conducted in a different coastal zone in India. [ABSTRACT FROM AUTHOR]

This paper explores the observation made by the Earth Probe Total Ozone Mapping Spectrometer EPTOMS to analyse the predictability of daily total ozone concentration over Kolkata, India. Latitude, longitude, aerosol index, reflectivity, sulphur dioxide index and total ozone concentration of a given day have been used as independent variables to predict total ozone concentration of the next day. Artificial neural network in the forms of a multilayer perceptron, generalized feed forward neural network, a radial basis function network and a modular neural network have been trained to generate predictive models. Performances of the models in the test cases have been judged with the help of four statistical parameters. Finally the models have been compared with multiple linear regression and the potential of generalized feed forward neural network has been established over the other proposed models. Copyright © 2008 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The rising emissions of reactive nitrogen (Nr) from transport, industrial, and agricultural sectors in India have resulted in its consequent interactions with the removal mechanism of the atmospheric dust. This study, therefore, reports the fluxes of reactive nitrogen along with other inorganic species through dustfall over six sites of Delhi-National Capital Region (NCR) characterized by the changing dynamics of its different land-use pattern. The highest Nr fluxes were observed at site SMA Industrial estate (SMA; NO3− = 16.45 ± 10.17 mg m−2 day−1, NH4+ = 16.33 ± 16.00 mg m−2 day−1) and lowest at site Chuchchakwas village (CV; NO3− = 1.24 ± 0.16 mg m−2 day−1, NH4+ = 0 mg m−2 day−1). Sites Mukherjee Nagar (MN), Peeragarhi Chowk (PC), Jawaharlal Nehru University (JNU), and Noida Phase II (N-II), on the other hand, showed 3.59 ± 1.00, 3.39 ± 0.61, 2.98 ± 0.84, and 3.36 ± 0.78 mg m−2 day−1 of NO3− fluxes and 0.30 ± 0.06, 0.22 ± 0.04, 0.21 ± 0.04, and 0.22 ± 0.05 mg m−2 day−1 of NH4+ fluxes, respectively. The fraction of the total ions in the water soluble extract of the dustfall was also noticed to be the highest at the SMA site (22.2%) and lowest at the CV site (1.5%) with MN, PC, JNU, and N-II showing 3.5%, 3.7%, 2.9%, and 3.9% of their respective contributions. Relative abundances of Ca2+ and SO42− in the dustfall substantiated the stoichiometric reactions involved in Nr scavenging. The role of Ca2+ in the spatiotemporal variability of Nr fluxes was established with the help of neutralization ratios and regression plots. Morphological and particle size analysis further confirmed the anthropogenic-induced crustal interferences in the summertime dustfall fluxes of Nr species. [ABSTRACT FROM AUTHOR]

This paper reports the PAHs levels in the atmosphere of an urbanised industrial site of India. A high-resolution capillary gas chromatograph with a mass spectrometric detector (HRCGC-MS) and a high performance liquid chromatograph (HPLC) equipped with a fluorescence detector were used for the identification and quantitation of PAHs. The atmospheric levels of PAHs were higher (4.66 ng/m3 yearly average) than most of the concentrations previously reported in the literature. Indian sites were found more contaminated with potently carcinogenic: four and above ringed PAHs. Based on a good correlation between the levels of lead, vanadium, BaP and BghiP, the vehicular emission appears to be a major source of the PAHs. Further, the higher levels of observed PAHs could be attributed to the vertical distribution of the aerosols, the preference of the PAHs for the particulate phase and the greater availability of the substrate in the atmosphere for their sorption. This paper also discusses the need for development of a PAHs monitoring protocol and related health effect studies in developing countries such as India. [ABSTRACT FROM AUTHOR]

The spring 2020 COVID-19 lockdowns led to a rapid reduction in aerosol and aerosol precursor emissions. These emission reductions provide a unique opportunity for model evaluation and to assess the potential efficacy of future emission control measures. We investigate changes in observed regional aerosol optical depth (AOD) during the COVID-19 lockdowns and use these observed anomalies to evaluate Earth system model simulations forced with COVID-19-like reductions in aerosols and greenhouse gases. Most anthropogenic source regions do not exhibit statistically significant changes in satellite retrievals of total or dust-subtracted AOD, despite the dramatic economic and lifestyle changes associated with the pandemic. Of the regions considered, only India exhibits an AOD anomaly that exceeds internal variability. Earth system models reproduce the observed responses reasonably well over India but initially appear to overestimate the magnitude of response in East China and when averaging over the Northern Hemisphere (0–70 ∘ N) as a whole. We conduct a series of sensitivity tests to systematically assess the contributions of internal variability, model input uncertainty, and observational sampling to the aerosol signal, and we demonstrate that the discrepancies between observed and simulated AOD can be partially resolved through the use of an updated emission inventory. The discrepancies can also be explained in part by characteristics of the observational datasets. Overall our results suggest that current Earth system models have potential to accurately capture the effects of future emission reductions. [ABSTRACT FROM AUTHOR]

Jaipur is a key site to study Aerosol Optical Depth (AOD) due to unpredictable variation of atmospheric Aerosols particles in the recent years. Aerosols Optical Depth (AOD) and Angstrom Exponent (AE) were investigated over the semi-arid region, Jaipur (26.9124° N, 75.7873° E) Northwestern India during the April-2009 to December-2017 utilizing AERONET CIMEL sun-photometer level-2 data for aerosols spatial and temporal characteristics. The Aerosols Optical Depth AOD500 nm, AOD440 nm, and AOD340 nm were observed maximum in July-2011 and minimum observed in March-2013. The monthly mean Angstrom Exponent (AE) was maximum (1.53 ± 0.43) for 500-870 nm, (1.49 ± 0.4) for 440-870 nm, and (1.19 ± 0.32) for 340-440 nm in September 2011, while the lowest value recorded (0.26 ± 0.12) for 340-440 nm, (0.16 ± 0.08) for 440-870 nm and (0.15 ± 0.07) for 500-870 nm during June 2014. The backward trajectories analysis was performed using the Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) model to determine the sources of large aerosol loadings over the Jaipur region, and air mass simulations from the back trajectory, suggest that the Thar desert northwestern part of India is the source of highest aerosols dust particle over the study area during the pre-monsoon season. [ABSTRACT FROM AUTHOR]

A study of the assessment and management of air quality was carried out at 11 coal mines in India. Long-term observations (about 13 years, March 2000-December 2012) and modeling of aerosol loading over coal mines in India are analyzed in the present study. In this respect, the Box-Jenkins popular autoregressive integrated moving average (ARIMA) model was applied to simulate the monthly mean Terra Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) over 11 sites in the coal mines region. The ARIMA model was found as the most suitable model with least normalized Bayesian information criterion (BIC) and root mean square error and high value of R. Estimation was done with the Ljung-Box test. Finally, a forecast for a 3-year period from January 2013 to December 2015 was calculated which showed that the model forecasted values are following the observed trend quite well over all mining areas in India. The average values of AOD for the next 3 years (2013-2015) at all sites are found to be 0.575 ± 0.13 (Raniganj), 0.452 ± 0.12 (Jharia), 0.339 ± 0.13 (Bokaro), 0.280 ± 0.09 (Bishrampur), 0.353 ± 0.13 (Korba), 0.308 ± 0.08 (Talcher), 0.370 ± 0.11 (Wardha), 0.35 ± 0.10 (Adilabad), 0.325 ± 0.09 (Warangal), 0.467 ± 0.09 (Godavari Valley), and 0.236 ± 0.07 (Cuddapah), respectively. In addition, long-term lowest monthly mean AOD values are observed over Bishrampur followed by Cuddapah, Talcher, Warangal, Adilabad, Korba, Wardha, Godavari Valley, Jharia, and Raniganj. Raniganj and Jharia exhibit the highest AOD values due to opencast mines and extensive mining activities as well as a large number of coal fires. Similarly, the highest AOD values are observed during the monsoon season among all four seasons over all the mining sites. Raniganj exhibits the highest AOD value at all seasons and at all sites. In contrast, the lowest seasonal AOD values are observed during the post-monsoon season over Raniganj, Talcher, Wardha, Adilabad, Warangal, and Godavari Valley. Similarly, over Jharia, Bokaro, Bishrampur, Korba, and Cuddapah, the lowest AOD values are found in the winter season. Increasing trends in AOD have been observed over Raniganj, Bokaro, Bishrampur, Korba, Talcher, and Wardha as well as over Adilabad and Godavari Valley, which is in agreement with previous works. Negative or decreasing AOD trend is found only over Jharia, Warangal, and Cuddapah without being statistically significant. Seasonal trends in AODs have also been studied in the present paper. [ABSTRACT FROM AUTHOR]

In this study, potential regional and local sources influencing PM2.5(particulate matter with an aerodynamic diameter >2.5 μm) concentrations in Delhi, India, are identified and their possible impact evaluated through diverse approaches based on study of variability of synoptic and local airflow patterns that transport aerosol concentrations from these emission sources to an urban receptor site in Delhi, India. Trajectory clustering of 72-hr and 48-hr back trajectories simulated at arrival heights of 500 m and 100 m, respectively, every hour for representative years 2008–2010 are used to assess the relative influence of long-distance, regional, and subregional sources on this site. Nonparametric statistical procedures are employed on trajectory clusters to better delineate various distinct regional pollutant source regions. Trajectory clustering and concentration-weighted trajectory (CWT) analyses indicate that regional and subregional PM2.5emission sources in neighboring country of Pakistan and adjacent states of Punjab, Haryana, and Uttar Pradesh contribute significantly to the total surplus of aerosol concentrations in the Delhi region. Conditional probability function and Bayesian approach used to identify local source regions have established substantial influence from highly urbanized satellite towns located southwest (above 25%) and southeast (above 45%) of receptor location. There is significant seasonal variability in synoptic and local air circulation patterns, which is discerned in variability in seasonal concentrations. Mean of daily averaged PM2.5concentrations at the Income Tax Office (ITO) receptor site over Delhi at 95% confidence level is highest in winter, ranging between 209 and 185 μg m−3for the entire study period. The annual variability in air transport pathways is more in winter than in other seasons. Year-to-year variability is present in aerosol concentrations, especially during winter, with standard deviations varying from a minimum of 60 µg m−3in winter 2009 to a maximum of 109 µg m−3in winter 2010. Implications: The rapid urban development of Delhi, capital of India, has resulted in increased concentrations of aerosols, which far exceed National Ambient Air Quality Standards making Delhi one of the worst polluted areas. Hence, the region demands development of appropriate emission control strategies that minimize the air quality impacts. This paper addresses the impacts of transboundary air pollutants and local emissions on Delhi’s air quality and reveals the influence of air circulation patterns on aerosol concentrations. These factors must be considered in designing of effective emission reduction strategies in Delhi region. [ABSTRACT FROM PUBLISHER]

Aerosol samples of PM(10) and PM(2.5) were collected from 38 sampling locations in and around the industrial area. The 24 h average mass concentration of PM(10) and PM(2.5) was 137.5 and 61.5 μg/m(3) respectively during summer, 122 and 97.5 μg/m(3) respectively in winter and 70 and 54 μg/m(3) respectively during post monsoon season. The relative contribution of coarse, fine and ultrafine particle to ambient air was analyzed for its temporal and seasonal variability in an industrialized area. This paper aims to establish baseline between PM(10) and PM(2.5) mass concentration levels.

Background: There is an urgent need for an improved understanding of the sources, distributions and properties of atmospheric aerosol in order to control the atmospheric pollution over northeastern Himalayas where rising anthropogenic interferences from rapid urbanization and development is becoming an increasing concern., Methodology/principal Findings: An extensive aerosol sampling program was conducted in Darjeeling (altitude approximately 2200 meter above sea level (masl), latitude 27 degrees 01'N and longitude 88 degrees 15'E), a high altitude station in northeastern Himalayas, during January-December 2005. Samples were collected using a respirable dust sampler and a fine dust sampler simultaneously. Ion chromatograph was used to analyze the water soluble ionic species of aerosol. The average concentrations of fine and coarse mode aerosol were found to be 29.5+/-20.8 microg m(-3) and 19.6+/-11.1 microg m(-3) respectively. Fine mode aerosol dominated during dry seasons and coarse mode aerosol dominated during monsoon. Nitrate existed as NH(4)NO(3) in fine mode aerosol during winter and as NaNO(3) in coarse mode aerosol during monsoon. Gas phase photochemical oxidation of SO(2) during premonsoon and aqueous phase oxidation during winter and postmonsoon were the major pathways for the formation of SO(4)(2-) in the atmosphere. Long range transport of dust aerosol from arid regions of western India was observed during premonsoon. The acidity of fine mode aerosol was higher in dry seasons compared to monsoon whereas the coarse mode acidity was higher in monsoon compared to dry seasons. Biomass burning, vehicular emissions and dust particles were the major types of aerosol from local and continental regions whereas sea salt particles were the major types of aerosol from marine source regions., Conclusions/significance: The year-long data presented in this paper provide substantial improvements to the heretofore poor knowledge regarding aerosol chemistry over northeastern Himalayas, and should be useful to policy makers in making control strategies.

The spectral and temporal variations of aerosol optical depths (AOD) observed over Anantapur (a semi-arid region) located in the Southern part of India are investigated by analyzing the data obtained from a Multiwavelength Solar Radiometer (MWR) during January 2005-December 2006 (a total of 404 clear-sky observations) using the Langley technique. In this paper, we highlighted the studies on monthly, seasonal and spectral variations of aerosol optical depth and their implications. The results showed seasonal variation with higher values during pre-monsoon (March-May) and lower in the monsoon (June-November) season at all wavelengths. The pre-monsoon increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The post-monsoon (December-February) AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the post-monsoon, direction of winds in association with high or low pressure weather systems and the air brings more aerosol content to the region which is surrounded by a number of cement plants, lime kilns, slab polishing and brick making units. The quantity of AOD values in pre-monsoon is higher (low during post-monsoon) for wavelength, such as shortwave infrared (SWIR) or near infrared (NIR), which shows that coarse particles contribute more compare with the sub-micron particles. The composite aerosols near the surface follow suit with the share of the accumulation mode to the total mass concentration decreasing from approximately 70% to 30% from post-monsoon to pre-monsoon. Coarse mode particle loading observed to be high during pre-monsoon and accumulation mode particles observed to be high during post-monsoon. The backward trajectories at three representative altitudes with source point at the observing site indicate a possible transport from the outflow regions into Bay of Bengal, southern peninsular India and Arabian Sea. The temporal variations of AOD, Angstrom wavelength exponent and precipitable water content over Anantapur have also been compared with those reported from selected locations in India.

Atmospheric aerosols are an important contributing factor to turbidity in urban areas besides having impact on health. Aerosol characteristics show a high degree of variability in space and time as nthropogenic share of total aerosol loading is quite substantial and is essential to monitor the aerosol features over long time scales. In the present study extensive observations of columnar aerosol optical depth (AOD), total columnar ozone (TCO) and precipitable water content (PWC) have been carried over a tropical urban city of Hyderabad, India. Significant variations of AOD have been observed during course of the day with low values of AOD during morning and evening hours and high values during afternoon hours. Spectral variation of AOD exhibits high AOD at smaller wavelengths and vice versa except a slight enhancement in AOD at 500 nm. Anomalies in AOD, particulate matter and black carbon concentrations have been observed during May, 2003. Back trajectory analysis of air mass during these episodes suggested variation in air mass trajectories. Analysis of the results suggests that air trajectories from land region north of study area cause high loading of atmospheric aerosols. The results are discussed in the paper.

The detection of possible changes in extreme climate events, in terms of the frequency, intensity as well as duration assumes profound importance on the local, regional, and national scales, due to the associated critical socioeconomic consequences. Therefore, an attempt ismade in this paper to evaluate various aspects of future projections of precipitation extremes over India, as projected by a state-of-art regional climatemodeling system, known as PRECIS (Providing REgional Climates for Impacts Studies) towards the end of the 21st century (that is, 2071-2100) using standardized indices. Study reveals that PRECIS simulations under scenarios of increasing greenhouse gas concentration and sulphate aerosols indicate marked increase in precipitation towards the end of the 21st century and is expected to increase throughout the year. However the changes in daily precipitation and the precipitation extremes during summer monsoon (June through September) season are prominent than during the rest of year. PRECIS simulations under both A2 and B2 scenarios indicate increase in frequency of heavy precipitation events and also enhancement in their intensity towards the end of the 21st century. Both A2 and B2 scenarios show similar patterns of projected changes in the precipitation extremes towards the end of the 21st century. However, the magnitudes of changes in B2 scenario are on the lower side. [ABSTRACT FROM AUTHOR]

The Finnish Meteorological Institute (FMI), together with The Energy and Resources Institute of India (TERI), contributed to the European Integrated project on Aerosol Cloud Climate and Air Quality Interactions, EUCAARI, by conducting aerosol measurements in Gual Pahari, India, from December 2007 to January 2010. This paper describes the station setup in detail for the first time and provides results from the aerosol in-situ measurements, which include PM and BCe masses, aerosol size distribution from 4 nm to 10 μm, and the scattering and absorption coefficients. The seasonal variation of the aerosol characteristics was very distinct in Gual Pahari. The highest concentrations were observed during the winter and the lowest during the rainy season. The average PM10 concentration (at STP conditions) was 216 μgm-3 and the average PM2.5 concentration was 126 μgm-3. A high percentage (4-9%) of the PM10 mass consisted of BCe which indicates anthropogenic influence. The percentage of BCe was higher during the winter; and according to the diurnal pattern of the BCe fraction, the peak occurred during active traffic hours. Another important source of aerosol particles in the area was new particle formation. The nucleated particles grew rapidly reaching the Aitken and accumulation mode size, thus contributing considerably to the aerosol load. The rainy season decreased the average fraction of particle mass in the PM2.5 size range, i.e. of secondary origin. The other mechanism decreasing the surface concentrations was based on convective mixing and boundary layer evolution. This diluted the aerosol when sun radiation and the temperature was high, i.e. especially during the pre-monsoon day time. The lighter and smaller particles were more effectively diluted. [ABSTRACT FROM AUTHOR]

In this concept study, we develop a strategy for the monitoring of nighttime aerosol particle optical properties over land using artificial lights on the earth's surface. We demonstrate the possibility of detecting significant aerosol events and deriving variations in aerosol optical depth using the operational linescan system (OLS) on defence meteorological satellite program (DMSP) platforms. Since the OLS instruments have no on-board calibration, only a qualitative study of the potential to estimate aerosol and cloud properties using city lights at night is shown in this paper. The technique is demonstrated using China and India as test regions. With the launch of the visible/infrared imager/radiometer suite (VIIRS) instrument on the national polar-orbiting operational environmental satellite system (NPOESS) in the coming decade, fully quantitative retrieval of nighttime aerosol particle optical properties from space observations using such methods will become possible. Such work will benefit aerosol forecasting, safety of navigation, aerosol data assimilation and climate studies. [ABSTRACT FROM AUTHOR]

Abstract: PM10 and its chemical species mass concentrations were measured once in a week at residential (Kasba) and industrial (Cossipore) sites of an urban region of Kolkata for a period of 24 h during November 2003 to November 2004. At each monitoring site, 53 sets of daily average PM10 samples were collected during the study period. Approximately 55% of the monitoring days are weekdays, while 45% are weekends. The PM10 mass concentrations ranged from 68.2 to 280.6 μg m−3 at the residential site, and 62.4 to 401.2 μg m−3 at the industrial site. Polycyclic aromatic hydrocarbon compounds (PAH), fluoranthene (Fl), pyrene (Py), benzo(a)anthracene (BaA), benzo(b)fluoranthene (BbF) and benzo(a)pyrene (BaP) have been analyzed using Gas Chromatoghaphy. Metals in PM10 deposited on quartz microfibre filter papers were measured using an Inductively Coupled Plasma-Atomic Emission Spectrometer. Chromium (Cr), zinc (Zn), lead (Pb), cadmium (Cd), nickel (Ni), manganese (Mn) and iron (Fe) are the seven toxic trace metals quantified from the measured PM10 concentrations. Total carbon (TC), inorganic carbon (IC) and organic carbon (OC) were analyzed using a Carbon analyzer. Exposed quartz microfibre filter papers were also analyzed for water-soluble anions of fluoride (F−), chloride (Cl−), nitrate (NO3 −), phosphate (PO4 3−) and sulfate (SO4 2−) using ion chromatography. In this study, principal component analysis (PCA)/absolute principal component scores (APCS) model was applied to the mass concentrations of PM10 and its chemical species. Principal component analysis with varimax rotation identified five possible sources; solid waste dumping, vehicular emission, coal combustion, cooking and soil dust at residential site. The extracted possible sources at the industrial site were vehicular emissions, coal combustion, electroplating industry, tyre wear and secondary aerosol. A quantitative estimation by principal component analysis–multiple linear regression (PCA–MLR) model indicated that solid waste dumping contributed 36%, vehicular emissions 26%, coal combustion 13%, cooking 8% and soil dust 4% at the residential site. The PCA–MLR apportioned 37% to vehicular emissions, 29% to coal combustion, 18% to electroplating industry, 8% to tyre wear and 1% to secondary aerosol at the industrial site. Due to the limitation in source marker species analyzed, 13% at Kasba and 7% at Cossipore could not be apportioned to any possible sources by this technique. [Copyright &y& Elsevier]

Monitoring of ambient PM10 (particulate matter which passes through a size selective impactor inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter) has been done at residential (Kasba) and industrial (Cossipore) sites of an urban region of Kolkata during November 2003 to November 2004. These sites were selected depending on the dominant anthropogenic activities. Metal constituents of atmospheric PM10 deposited on glass fibre filter paper were estimated using Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Chromium (Cr), zinc (Zn), lead (Pb), cadmium (Cd), nickel (Ni), manganese (Mn) and iron (Fe) are the seven toxic trace metals quantified from the measured PM10 concentrations. The 24 h average concentrations of Cr, Zn, Pb, Cd, Ni, Mn and Fe from ninety PM10 particulate samples of Kolkata were found to be 6.9, 506.1, 79.1, 3.3, 7.4, 2.4 and 103.6 ng/m3, respectively. The 24 h average PM10 concentration exceeded national ambient air quality standard (NAAQS) as specified by central pollution control board, India at both residential (Kasba) and industrial (Cossipore) areas with mean concentration of 140.1 and 196.6 μg/m3, respectively. A simultaneous meteorology study was performed to assess the influence of air masses by wind speed, wind direction, rainfall, relative humidity and temperature. The measured toxic trace metals generally showed inverse relationship with wind speed, relative humidity and temperature. Factor analysis, a receptor modeling technique has been used for identification of the possible sources contributing to the PM10. Varimax rotated factor analysis identified four possible sources of measured trace metals comprising solid waste dumping, vehicular traffic with the influence of road dust, road dust and soil dust at residential site (Kasba), while vehicular traffic with the influence of soil dust, road dust, galvanizing and electroplating industry, and tanning industry at industrial site (Cossipore). [ABSTRACT FROM AUTHOR]

Aerosol‐cloud interactions, also known as aerosol indirect effect (AIE), substantially impact rainfall frequency and intensity. Here, we analyze NEX‐GDDP, a multimodel ensemble of high‐resolution (0.25°) historical simulations and future projections statistically downscaled from 21 CMIP5 models, to quantify the importance of AIE on extreme climate indices, specifically consecutive dry days (CDD), consecutive wet days (CWD), and simple daily intensity index (SDII). The 21 NEX‐GDDP CMIP5 models are classified into models with reliable (REM) and unreliable (UREM) monsoon climate simulated over India based on their simulations of the climate indices. The REM group is further decomposed based on whether the models represent only the direct (REMADE) or the direct and indirect (REMALL) aerosol effects. Compared to REMADE, including all aerosol effects significantly improves the model skills in simulating the observed historical trends of all three climate indices over India. Specifically, AIE enhances dry days and reduces wet days in India in the historical period, consistent with the observed changes. However, by the middle and end of the 21st century, there is a relative decrease in dry days and an increase in wet days and precipitation intensity. Moreover, the REMALL simulated future CWD and CDD changes are mostly opposite to those in REMADE, indicating the substantial role of AIE in the future projection of dry and wet climates. These findings underscore the crucial role of AIE in future projections of the Indian hydroclimate and motivate efforts to accurately represent AIE in climate models. Plain Language Summary: We investigate the impacts of aerosol on India's wet and dry climate. High‐resolution downscaled CMIP5 models were used to calculate extreme indices like CDD (consecutive dry days), CWD (consecutive wet days), SDII (precipitation intensity). From the group of 22 models, 12 reliable models were chosen based on their fidelity to the observations. Amongst the reliable models, certain models incorporate only aerosol‐radiation interaction (REMADE), while others have both aerosol‐radiation and aerosol‐cloud interaction (REMALL). We found that the simulated trends in the REMAll were similar to the observed trends. In the current period (1975–2005), the aerosol‐cloud interactions led to the reduction in rainfall (both frequency and intensity wise) and enhanced the dry days, however in the future projections, the reduction in aerosol emissions leads to a wetter climate (increase in wet days and rainfall intensity) over India. Key Points: Using statistical metrics downscaled CMIP5 models are classified into reliable models for better simulating the wet and dry indices over IndiaDownscaled reliable models that included all aerosol effects (AIE + ADE) improved the simulated trends in the historical period than the models with only ADEThere is a general drying‐up (frequency‐wise and intensity‐wise) in the historical period. In the future projections, the reduction in aerosols lead to a wetter climate (frequency‐wise and intensity‐wise) [ABSTRACT FROM AUTHOR]

Estimation of aerosol radiative forcing continues to suffer from large uncertainties, partially from a lack of observations of aerosol optical properties. Limited measurements of the atmospheric aerosol imaginary refractive index (iRI) have been made, especially in some of the world's most polluted regions. In this study, we measured aerosol optical and micro‐physical properties at a regional site, Rohtak, India, representative of polluted cities in the Indo‐Gangetic plains in northern India. The average PM2.5 measured during the campaign was 163 μg/m3 with a single‐scatter albedo of 0.7, indicating the presence of strongly absorbing aerosol components. Measurements of aerosol absorption, scattering, and particle number size distributions were used to estimate the effective refractive index using an established Mie inversion technique. The calculated iRI was spectrally invariant in the visible region with values ranging between 0.076 and 0.145. Brown carbon absorption, estimated using an existing Mie optimization method, ranged 34–88 Mm−1, with strongly absorbing mass absorption cross‐sections (∼1.9 m2/g). Higher iRI were observed during periods with higher brown carbon absorption, which are likely directly emitted from combustion sources. Low volatility organic carbon fractions dominated during these periods, with likely persistence of atmospheric absorption. The iRI values are at the upper end of previously reported ranges of urban aerosol iRI. In a sensitivity analysis to measured parameters, the absorption had the dominant effect on estimated iRI. Measured single scatter albedos, were lower than those from climate model simulations over the region, demonstrating the need for intrinsic property measurements to evaluate and constrain climate models. Plain Language Summary: Particles in the atmosphere, called aerosol, can absorb or reflect/scatter sunlight to heat or cool the atmosphere, depending upon their physical and chemical properties. Climate models try to simulate these properties to understand their effect on the climate. The strength of the absorption is determined by the size of the particle (generally the diameter) and its refractive index (a complex number) which is a material property. In this study, we measure the refractive index of atmospheric aerosol at Rohtak, which lies in the highly polluted Indo‐Gangetic plains in India. We find that the aerosol are very absorbing in nature, that is, they are warming the atmosphere, and that the absorbing/imaginary part of the refractive index is in the higher range of previously reported values. The aerosol at the site are dominated by emissions from fossil fuel and biomass burning sources. On comparing these absorbing properties with those simulated by climate models, we find that the climate models are not able to simulate the absorbing nature of these aerosol well. Hence, there is a need for more such measurements of the aerosol refractive index to improve climate models and ultimately improve our understanding of the effect of aerosol on our climate. Key Points: Estimate the aerosol effective refractive index (RI); imaginary RI ranges 0.076–0.145, higher than previously reported valuesA single scatter albedo of 0.7 reveals strongly absorbing components, with brown carbon absorption of 34–88 Mm−1Imaginary RI correlates well with near‐UV absorption by brown carbon, which has low volatility and is likely emitted from combustion sources [ABSTRACT FROM AUTHOR]

Profiles of aerosols and cloud layers have been investigated over a high-altitude urban atmosphere in the eastern Himalayas in India, for the first time, using a Raman LIDAR. The study was conducted post-monsoon season over Darjeeling (latitude 27°01 ′ N longitude 88°36 ′ E, 2200 masl), a tourist destination in north-eastern India. In addition to the aerosols and cloud characterization and atmospheric boundary layer detection, the profile of the water vapor mixing ratio has also been analyzed. Effects of atmospheric dynamics have been studied using the vertical profiles of the normalized standard deviation of RCS along with the water vapor mixing ratio. The aerosol optical characteristics below and above the Atmospheric Boundary Layer (ABL) region were studied separately, along with the interrelation of their optical and microphysical properties with synoptic meteorological parameters. The backscatter coefficient and the extinction coefficient were found in the range from 7.15 × 10 − 10 m − 1 sr − 1 to 3.01 × 10 − 5 m − 1 sr − 1 and from 1.02 × 10 − 5 m − 1 to 2.28 × 10 − 3 m − 1 , respectively. The LIDAR ratio varies between 3.9 to 78.39 sr over all altitudes. The variation of the linear depolarization ratio from 0.19 to 0.32 indicates the dominance, of non-spherical particles. The periodicity observed in different parameters may be indicative of atmospheric wave phenomena. Cloud parameters, such as scattering coefficients, top and bottom height, and optical depth for different cloud phases, have been evaluated. A co-located Micro Rain Radar has been used with LIDAR for cloud life cycle study. [ABSTRACT FROM AUTHOR]

Two relatively long‐term satellite aerosol products during 1983–2020 and 2000–2020 are employed to investigate interannual relationships between anomalous aerosol loadings over the Bay of Bengal (BoB) and Arabian Sea (AS) in the early summer and Asian monsoon rainfall anomalies. It is shown that increased aerosol loading (IAL) over the BoB is primarily attributed to an intensified upstream aerosol transport by anomalous subtropical westerly winds and coincides with local sea surface temperature (SST) cooling due to intensified prevailing wind and the aerosol dimming effect, and vice versa. A deficient rainfall in India tends to concur with a BoB IAL while excessive rainfall with an AS IAL in May and June. In June, a BoB IAL coincides with significantly deficient rainfall in the southwestern China‐Huaihe River Basin primarily linked to an anomalous cyclone off the coast of Southeast China. Meanwhile a related overturning of Walker Circulation is identified to be driven by the contrast of anomalous convective activity between the southeastern Indian‐BoB and the South China Sea‐Philippine Sea. An AS IAL is associated with air warming in North India due to an elevated aerosol semi‐direct effect and remote forcing that reinforces the meridional air temperature gradient. The IAL over the respective BoB and AS in June are both preceded by cold SST anomalies in the western Indian Ocean that can be traced back to the preceding winter, but the corresponding atmospheric circulations driving aerosol‐monsoon interactions differ distinctly. The above aerosol‐monsoon relationships are sustained primarily during 2000–2020 and vague during 1983–2020. Plain Language Summary: The year‐by‐year aerosol variations over the Bay of Bengal (BoB) and Arabian Sea (AS) in early spring and their relationship to the Asian summer monsoon rainfall anomalies are studied using satellite‐observed aerosol products. Increased aerosol loading (IAL) over the BoB is revealed to be accompanied by deficient rainfall in India and excessive rainfall in the northern South China Sea‐Philippine Sea (NSCSPS), driven by the changes in Walker Circulation primarily caused by the contrast of anomalous convective activity between the southeastern Indian‐BoB and the NSCSPS. An IAL over the AS tends to concur with excessive monsoon rainfall in India in May and June and is associated with air warming in northern South Asia partially due to the aerosol semi‐direct effect that reinforces the meridional air temperature gradient. The aerosol dimming effect associated with an IAL over the BoB and AS, along with the intensified prevailing westerly, might be responsible for the cooling of the local sea surface temperature (SST) in early spring and vice versa. The SST anomaly in the western Indian Ocean, which can be traced back to the preceding winter, plays an important role in driving the aforementioned associated changes in the atmospheric circulations and monsoon rainfall anomalies. Key Points: Anomalous aerosol loadings over the Bay of Bengal concur with an out‐of‐phase rainfall change in South and East Asia in early summerAerosol‐monsoon interaction over the Arabian Sea tends to modulate Indian rainfall by changing the meridional air temperature gradientSea surface temperature anomalies in Indian Ocean play an important role in stimulation of the aforementioned aerosol‐monsoon interaction [ABSTRACT FROM AUTHOR]

The study differentiates and quantifies the impacts of aerosols emitted locally within the north-east (NE) India region and those transported from outside this region to ascertain whether local or transported aerosols are more impactful in influencing this region's rainfall during the pre-monsoon season (March–April–May). Due to the existence of a declining pre-monsoon rainfall trend in NE India, the study also quantified the role of different aerosol effects in radiative forcing (RF) and rainfall. The study has been carried out using the WRF-Chem model by comparing simulation scenarios where emissions were turned on and off within and outside the NE region. The impact of all emissions as a whole and black carbon (BC) specifically was studied. Results show that aerosols transported primarily from the Indo-Gangetic Plain (IGP) were responsible for 93.98 % of the PM 10 mass over NE India's atmosphere and 64.18 % of near-surface PM 10 concentration. Transported aerosols contributed >50 % of BC, organic carbon, sulfate, nitrate, ammonium and dust aerosol concentration and are hence a major contributor to air pollution. Hence, the aerosol effects were much greater with transported aerosols. An indirect aerosol effect was found to be the major effect and more impactful, with transported aerosols that dominated both rainfall and RF and suppressed rainfall more significantly than the direct and semi-direct effect. However, the increase in direct radiative effects with an increase in transported BC counteracted the rainfall suppression caused by relevant processes of other aerosol effects. Thus, this study shows atmospheric transport to be an important process for this region, as transported emissions, specifically from the IGP, were also found to have greater control over the region's rainfall. Thus, emission control policies implemented in the IGP will reduce air pollution as well as the climatic impacts of aerosols over the NE India region. [ABSTRACT FROM AUTHOR]

The rapid industrial and economic development in India leads to high level of pollution in environment. Due to increased level of aerosols oceans are warming. This paper highlights on aerosols effect on sea surface wind and sea surface temperature by using remote sensing data. The windplays important role in Aerosol Optical Depth (AOD) and radiative forcing and is analyzed using National Centers for Environmental Prediction (NCEP) monthly wind data. The radiative forcing observed is much higher and up to 60% of total AOD during summer monsoon. SeaSurface Temperature (SST) is another important parameter in ocean atmosphere system and a key variable in coupling the atmosphere and ocean. The SST has changed during the change of atmospheric pattern and it plays an important role in aerosols mechanism. The study observed that during summer monsoon SST over the South Eastern Tropical Indian Ocean (SETIO) much higher than Western Tropical Indian Ocean (WTIO) and it plays important role in aerosols mechanism. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density using an aerosol spectrometer, covering a period of 28 months from September 2011 to December 2013. The diurnal pattern of aerosol number density is characterized by day time low and a two-fold increase during nighttime and these changes are closely associated with the strong mesoscale features namely the sea breeze and land breeze prevailing at the site. Aerosol Number Size Distribution (NSD) depicts a multi-modal nature with two prominent modes, one ≤0.1 μm and other ∼1 μm. Two other less pronounced modes are also observed in the NSD, one ∼0.3–0.5 μm and other ∼5–8 μm. The NSDs also exhibited strong seasonal changes linked with the synoptic meteorological feature of this region namely the South Asian monsoon. The seasonal NSDs were parameterized and analyzed. In addition to this, the effects of meteorological parameters temperature, relative humidity, and wind speed and airflow patterns on aerosol number density as revealed by partial correlation analysis were found to be aerosol size dependent. [ABSTRACT FROM AUTHOR]

One side effect of the Spring 2020 COVID-19 lockdowns was a rapid reduction in aerosol and aerosol precursor emissions. These emission reductions provide a unique opportunity for model evaluation, and to assess the potential efficacy of future policy decisions. We investigate changes in observed regional aerosol burdens during the COVID-19 lockdowns, and compare these observed anomalies to predictions from Earth System Models forced with COVID-19-like reductions in aerosol and greenhouse gas emissions. Despite the dramatic economic and lifestyle changes associated with the pandemic, most anthropogenic source regions do not exhibit detectable changes in satellite retrievals of total or dust-subtracted aerosol optical depth. Only India exhibits an aerosol optical depth anomaly that exceeds internal variability. These conclusions are broadly reproduced by Earth System Models when confounding factors have been accounted for. We present a systematic assessment of the contributions of internal variability, model input uncertainty, and observational sampling to the aerosol signal, and highlight the impacts of observational uncertainty on model evaluation analyses. These results are encouraging, suggesting that current Earth System Models may be able to realistically capture the effects of future emission reductions. [ABSTRACT FROM AUTHOR]

We studied the potential of using machine learning to downscale global-scale climate model output towards ground station data. The aim was to simultaneously analyze both city-level air quality and regional- and global-scale radiative forcing values for anthropogenic aerosols. As the city-level air pollution values are typically underestimated in global-scale models, we used a machine learning approach to downscale fine particulate (PM 2.5) concentrations towards measured values. We first simulated the global climate with the aerosol–climate model ECHAM-HAMMOZ and corrected the PM 2.5 values for the Indian megacity New Delhi. The downscaling procedure clearly improved the seasonal variation in the model data. The seasonal trends were much better captured in the corrected PM 2.5 than in original ECHAM-HAMMOZ PM 2.5 when compared to the reference PM 2.5 from the ground stations. However, short-term variations showed less extreme values with the downscaling approach. We applied the downscaling model also to simulations where the aerosol emissions were following two different future scenarios: one following the current legislation and one assuming currently maximum feasible emission reductions. The corrected PM 2.5 concentrations for the year 2030 showed that mitigating anthropogenic aerosols improves local air quality in New Delhi, with organic carbon reductions contributing most to these improvements. In addition, aerosol emission mitigation also resulted in negative radiative forcing values over most of India. This was mainly due to reductions in absorbing black carbon emissions. For the two future emission scenarios modeled, the radiative forcing due to aerosol–radiation interactions over India was -0.09±0.26 and -0.53±0.31 W m -2 , respectively, while the effective radiative forcing values were -2.1±4.6 and 0.06±3.39 W m -2 , respectively. Although accompanied by relatively large uncertainties, the obtained results indicate that aerosol mitigation could bring a double benefit in India: better air quality and decreased warming of the local climate. Our results demonstrate that downscaling and bias correction allow more versatile utilization of global-scale climate models. With the help of downscaling, global climate models can be used in applications where one aims to analyze both global and regional effects of policies related to mitigating anthropogenic emissions. [ABSTRACT FROM AUTHOR]

In the Indo-Gangetic Plains, extensive crop residue burning (CRB) of wheat stubble is done during the month of May. Soot emitted following CRB, a serious environmental pollutant, affects cloud properties. Though important, it is poorly understood as an ice nucleating particle. During the summer season, on 13 May 2020, an unusually heavy rainfall event occurred over Rajasthan, India, which was studied using ground- and satellite-data. The sun photometer observations of the AERONET station on 12 May 2020 yielded an absorption Ångstorm exponent value of 1.01. This value corresponds to black carbon (BC) and indicates its dominance as a fine aerosol associated with CRB. The HYSPLIT model indicated a downwind trajectory towards Rajasthan from Haryana and Punjab (source of CRB). Atmospheric ageing and oxygenation of BC probably increased the number of hydrophilic surface sites. Thus, soot comprising BC particles got activated into cloud droplets through the heterogeneous nucleation of water vapour. As a result, the prevailing sub-saturation condition with 80% RH led to the wetting of BC particles through the nucleation of water vapour and increased ice concentration in the cloud anvils in the late night of 12 May 2020 and precipitated on 13 May 2020 (up to 58.2 mm). AERONET data highlights that the region had an abundance of BC produced from CRB. Apart from its water affinity, other particle characteristics such as porosity and polarity also augmented ice nucleation. [ABSTRACT FROM AUTHOR]

Agriculture crop residue burning in the tropics is a major source of the global atmospheric aerosols and monitoring their long-range transport is an important element in climate change studies. In this paper, we study the effects of agriculture crop residue burning on aerosol properties and long-range transport over northern India during a smoke event that occurred between 09 and 17 November 2013, with the help of satellite measurements and model simulation data. Satellite data observations on aerosol properties suggested transport of particles from agriculture crop residue burning in Indo-Gangetic Plains (IGP) over large regions. Additionally, ECMWF winds at 850 hPa have been used to trace the source, path and spatial extent of smoke events. Most of the smoke aerosols, during the study period, travel from a west-to-east pathway from the source-to-sink region. Furthermore, aerosol vertical profiles from CALIPSO show a layer of thick smoke extending from surface to an altitude of about 3 km. Smoke aerosols emitted from biomass burning activity from Punjab have been found to be a major contributor to the deterioration of local air quality over the NE Indian region due to their long range transport. [ABSTRACT FROM AUTHOR]

The national and global restrictions in response to the COVID-19 pandemic led to a sudden, albeit temporary, emission reduction of many greenhouse gases (GHGs) and anthropogenic aerosols, whose near-term climate impact were previously found to be negligible when focusing on global- and/or annual-mean scales. Our study aims to investigate the monthly scale coupled climate-and-circulation response to regional, COVID-19-related aerosol emission reductions, using the output from 10 Earth system models participating in the Covid model intercomparison project (CovidMIP). We focus on January–February and March–May 2020, which represent the seasons of largest emission changes in sulfate (SO2) and black carbon (BC). During January–February (JF), a marked decrease in aerosol emissions over eastern China, the main emission region, resulted in a lower aerosol burden, leading to an increase in surface downwelling radiation and ensuing surface warming. Regional sea-level pressure and circulation adjustments drive a precipitation increase over the Maritime Continent, embedded in a negative Pacific Decadal Oscillation (PDO)- and/or El Niño–Southern Oscillation (ENSO)-like response over the Pacific, in turn associated with a northwestward displacement and zonal shrinking of the Indo-Pacific Walker cell. Remote climate anomalies across the Northern Hemisphere, including a weakening of the Siberian High and Aleutian Low, as well as anomalous temperature patterns in the northern mid-latitudes, arise primarily as a result of stationary Rossby wave trains generated over East Asia. The anomalous climate pattern and driving dynamical mechanism reverse polarity between JF and MAM (March–May) 2020, which is shown to be consistent with an underlying shift of the dominant region of SO2 emission reduction from eastern China in JF to India in MAM. Our findings highlight the prominent role of large-scale dynamical adjustments in generating a hemispheric-wide aerosol climate imprint even on short timescales, which are largely consistent with longer-term (decadal) trends. Furthermore, our analysis shows the sensitivity of the climate response to the geographical location of the aerosol emission region, even after relatively small, but abrupt, emission changes. Scientific advances in understanding the climate impact of regional aerosol perturbations, especially the rapidly evolving emissions over China and India, are critically needed to reduce current uncertainties in near-future climate projections and to develop scientifically informed hazard mitigation and adaptation policies. [ABSTRACT FROM AUTHOR]

Asia is one of the continents where aerosol levels are comparatively higher across the world. India and Sri Lanka are some of the regions in the South Asian continent where pollution is increasing rapidly due to the rise in industrialization. The present study investigated the interactions between atmospheric aerosol and cloud microphysical properties and their spatial, temporal, and seasonal variation at local and regional scales during 2000–2020 using remotely sensed data sets in south India and Sri Lanka. High values (>0.5) of annual mean aerosol optical depth (AOD) were detected over southern India. On the other hand, lower values (0.2) were detected over Sri Lanka. In terms of seasonality, a high level of AOD was registered in both southern India and Sri Lanka during the premonsoon and monsoon periods. The angstrom exponent (AE412‐470) revealed the dominance of fine‐mode particles during winter and the postmonsoon, generally from biomass burning and industrial activities. The long‐term analysis exhibited an increasing trend of atmospheric aerosol concentration over southern India and Sri Lanka. Interestingly, there was a decrease in AOD during the year 2020; the reduction in anthropogenic activities in the region was attributed to the COVID‐19 lockdown, hence less accumulation of pollutants in the atmosphere. AOD showed a positive correlation with cloud effective radius over the western areas along with the Indian Ocean, north, southeast, and southern end of India, while negatively correlated with high AOD areas such as northeast of the study domain. The AOD and cloud optical depth were positively correlated over continental areas, while negative correlations were notable over the Indian Ocean around Sri Lanka, implying heterogeneities of aerosol's effect on cloud microphysical properties over the study area. Finally, the results from wind circulation and backward air mass trajectories reveal higher concentrations of fine‐mode particles associated with the continent, whereas coarse‐mode particles originate from the oceans. [ABSTRACT FROM AUTHOR]

The inter-annual variability of aerosol over Indian region and its possible implications on the Indian summer monsoon is investigated using Aerosol Optical Depth (AOD) data from Moderate Resolution Imaging Spectrometer (MODIS) during the period 2001 to 2016. An attempt has been made to link the seasonal aerosol distribution over South Asia during spring and summer season to Indian Summer Monsoon Rainfall (ISMR) distribution. AOD derived from MODIS Terra observations shows large spatial inhomogeneity and characteristic variability with distinct temporal distributions. The pre-monsoon (spring) seasons (March-April-May; MAM) is characterized by high aerosol concentration over north-west part of India along with IGP region. During the south-west monsoon (summer) seasons (June-July-August-September; JJAS), wide area of high aerosol loading along Indo Gangetic plains extending from North Arabian sea through north-west India and up to Himalayan foothills. The regional rainfall distribution and its relationship with spatial and temporal aerosol distribution are then evaluated. Further, distinct variability in the aerosol distribution with respect to excess, deficit and normal monsoon years are analysed to understand the role of aerosols on the inter-annual variability of ISMR. Monthly aerosol distribution over Central India [CI;15° -25° N;75° -88° E] and Indo Gangetic plain [IGP;25°- 35°N;70°- 90° E] shows increased aerosol loading during deficit rainfall years and corresponding delay in the monthly rainfall peak. This study emphasises the active role of regional aerosol loading on regulating the inter-annual variability of regional Indian summer monsoon rainfall. [ABSTRACT FROM AUTHOR]

In order to understand the regional climate implications of aerosols over Indo-Gangetic Plains (IGP), a major Indo-US field experiment, Ganges Valley Aerosol Experiment (GVAX) was conducted during 2011-12. Atmospheric Radiation Measurement (ARM) mobile facility (AMF) was deployed at the northern Indo-Gangetic Plain over the high-altitude site, Manora Peak, Nainital (29°21'33.84"N, 79°27'29.27"E, 1980 m amsl) in Central Himalayas, for an year-round meas- urement of aerosols, clouds and other climate-relevant atmospheric parameters. One of the objectives of GVAX was examining the ability of models to simulate aerosols over Indian region and validate the simulations. In part-1 of this two-part paper, we examine use of the chemical transport model 'CHIMERE' to simulate aerosol fields over Indian region (4-37.5°N; 67-88.5°E) for multiple years (2006, 2007 and 2008) by simulating the spatial and temporal distribution of PM10, BC mass concentrations and OC/BC ratios. It is seen that the model successfully captures the broad features of the regional distribution of aerosols, including the most conspicuous IGP hotspot and its seasonality. [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]

BACKGROUND: Sewage treatment plant workers (STPs) are exposed to gaseous pollutants (H2S) and bioaerosols and their health is at risk. OBJECTIVE: The aim of the study was to evaluate exposures to dust, 1,3 Beta D Glucans, endotoxins and gaseous pollutants in different process plants and to provide suitable recommendations. METHODS: Gaseous pollutants and bioaerosols (inhalable dust, 1,3 beta D-glucans and endotoxins) were evaluated in two sewage treatment plants (STPs) of Ahmedabad city, India. The concentration of H2S, CO, CH4 and Cl2 were monitored in two process areas of STPs using real-time gas detectors. The dust, 1,3 beta D-glucans and endotoxins were evaluated as per standard methods. RESULTS: The mean concentration of H2S exceeded the permissible exposure limit of 10 ppm, whereas the concentration of other gaseous pollutants (CO, Cl2 and CH4) were below the permissible exposure limits of Indian Factories Act, 1948. The inhalable dust concentration was also within the permissible exposure limit of 10 mg/m3 as per Indian Factories Act, 1948. CONCLUSIONS: Significant exposures to gaseous and bioaerosols were found in the work environment of STPs. The paired t-test result showed a significant difference between two STPs for H2S, 1,3 beta D-Glucans and endotoxins. STPs were advised to reduce the exposure to H2S and bioaerosols as per CPCB guidelines applicable to India to prevent health effects. [ABSTRACT FROM AUTHOR]

The vertical structure of atmospheric aerosols over the Indian mainland and the surrounding oceans and its spatial distinctiveness and resultant atmospheric heating are characterised using long-term (2007–2020) satellite observations, assimilated aerosol single scattering albedo, and radiative transfer calculations. The results show strong, seasonally varying zonal gradients in the concentration and vertical extent of aerosols over the study region. Compared to the surrounding oceans, where the vertical extent of aerosols is confined within 3 km, the aerosol extinction coefficients extend to considerably higher altitudes over the mainland, reaching as high as 6 km during pre-monsoon and monsoon seasons. Longitudinally, the vertical extent is highest around 75 ∘ E and decreasing gradually towards either side of the study region, particularly over peninsular India. Particulate depolarisation ratio profiles affirm the ubiquity of dust aerosols in western India from the surface to nearly 6 km. While the presence of low-altitude dust aerosols decreases further east, the high-altitude (above 4 km) dust layers remain aloft throughout the year with seasonal variations in the zonal distribution over north-western India. High-altitude (around 4 km) dust aerosols are observed over southern peninsular India and the surrounding oceans during the monsoon season. Radiative transfer calculations show that these changes in the vertical distribution of aerosols result in enhanced atmospheric heating at the lower altitudes during the pre-monsoon, especially in the 2–3 km altitude range throughout the Indian region. These results have strong implications for aerosol–radiation interactions in regional climate simulations. [ABSTRACT FROM AUTHOR]