Particulate matter (PM) has been linked to numerous adverse health effects in humans, with exposure being a significant factor in cardiovascular diseases and increased rates of mortality and morbidity. This study analyzed the concentrations of PM1, PM2.5, and PM10 during a dust storm in Western India in January and February, primarily affecting Ahmedabad, Pune, and Mumbai. Under typical atmospheric conditions, the monthly average inhaled concentrations of PM1, PM2.5, and PM10 in Ahmedabad were 30, 65, and 117 µg/m3, respectively. In comparison, Mumbai recorded 41, 80, and 143 µg/m3, while Pune reported 62 and 100 µg/m3 for PM2.5 and PM10. During the dust storm, however, these levels rose sharply: Ahmedabad reached 72, 154, and 269 µg/m3, Mumbai escalated to 136, 310, and 544 µg/m3, and Pune increased to 150 and 251 µg/m3. The findings highlight the substantial elevation in PM exposure associated with dust storm events, underscoring their potential implications for air quality and public health in urban regions of Western IndiaThe study employed the Multiple-Path Particle Dosimetry (MPPD) model to deepen the analysis to evaluate age-specific particle deposition in the three cities. Coarse particles (PM10) predominantly settled in the head and tracheobronchial regions, whereas finer particles (PM2.5 and PM1) were mainly deposited in the pulmonary areas. PM2.5 deposition was observed to be highest in children, followed by the elderly and adults. A detailed lobar analysis indicated that the left lower lobes experienced the highest deposition, followed by the right and middle lobes. PM2.5 emerged as the dominant particle size fraction deposited across all lobes for individuals of all age groups, including infants, children, and adults. The findings underscore the critical role of PMs in lung deposition and their relevance in assessing health risks, such as oxidative stress and toxicity from particle accumulation.

In this study, an eco-friendly chitosan/carboxymethyl cellulose/bentonite/CuO nanocomposite (CS/CMC/BN/CuO NC) was synthesized utilizing algal-mediated copper oxide nanoparticles (CuO NPs). The resulting hybrid nanocomposite was thoroughly characterized using advanced techniques, including XRD, FTIR, UV-vis, FE-SEM, HR-TEM, and BET analysis. The photocatalytic activity of the hybrid nanocomposite was assessed by the degradation of brilliant cresyl blue (BCB) dye under visible light irradiation, while the antibacterial activity of the hybrid nanocomposite was evaluated against both Gram-positive and Gram-negative bacterial strains. XRD analysis confirmed the successful synthesis of the hybrid nanocomposite (CS/CMC/BN/CuO NC) with a crystallite size of 9.66 nm. The UV-vis analysis and Tauc plot revealed that the hybrid nanocomposite exhibited an absorbance peak at 249 nm and a band gap of 2.81 eV, respectively. FE-SEM and HR-TEM analysis highlighted its unique broken-tile structure. Furthermore, the hybrid nanocomposite exhibited outstanding photocatalytic performance, achieving 98.38% degradation of BCB dye within 60 min under optimal conditions. The scavenging experiments showed that electrons (e-) and superoxide anion radicals (O2(center dot)-) are the major reactive species involved in the degradation of BCB dye. Additionally, it demonstrated remarkable antibacterial efficacy, showing a 40 mm zone of inhibition (ZOI) against the Gram-negative Pseudomonas aeruginosa strain. The findings indicate that the synthesized CS/CMC/BN/CuO NC holds significant promise for the photodegradation of organic dyes. Furthermore, it exhibits strong antibacterial properties, making it a potential disinfectant for treating wastewater contaminated with pathogenic bacteria.

Background: In the current scenario, the synthesis of nanoparticles (NPs) using environmentally benign methods has gained significant attention due to their facile processes, cost-effectiveness, and eco-friendly nature. Methods: In the present study, copper oxide nanoparticles (CuO NPs) were synthesized using aqueous extract of Coelastrella terrestris algae as a reducing, stabilizing, and capping agent. The synthesized CuO NPs were characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Results: XRD investigation revealed that the biosynthesized CuO NPs were nanocrystalline with high-phase purity and size in the range of 4.26 nm to 28.51 nm. FTIR spectra confirmed the existence of secondary metabolites on the surface of the synthesized CuO NPs, with characteristic Cu-O vibrations being identified around 600 cm -1 , 496 cm -1 , and 440 cm -1 . The FE-SEM images predicted that the enhancement of the algal extract amount converted the flattened rice-like structures of CuO NPs into flower petal-like structures. Furthermore, the degradation ability of biosynthesized CuO NPs was investigated against Amido black 10B (AB10B) dye. The results displayed that the optimal degradation efficacy of AB10B dye was 94.19%, obtained at 6 pH, 50 ppm concentration of dye, and 0.05 g dosage of CuO NPs in 90 min with a pseudo-first-order rate constant of 0.0296 min -1 . The CuO-1 NPs synthesized through algae exhibited notable antibacterial efficacy against S. aureus with a zone of inhibition (ZOI) of 22 mm and against P. aeruginosa with a ZOI of 17 mm. Conclusion: Based on the findings of this study, it can be concluded that utilizing Coelastrella terrestris algae for the synthesis of CuO NPs presents a promising solution for addressing environmental contamination.

Nanotechnology has been progressively developed recently and used extensively in all disciplines. These nanoscale particles overpower the use of conventional technological metal particles. Applications of Cu nanoparticles in agriculture enhance production and soil fertility, albeit their usage in excess amounts causes toxicity for soil fauna. So, we studied and collated the toxicity research trends of copper nanoparticles in the worm’s species (earthworms and enchytraeids) and their activities to assess the consequences of copper nanoparticles in varied sizes and oxidation states. Various Cu NPs have a high capacity for adsorbing biomolecules and interacting with biological receptors. Cu NPs can interact with the host organism’s inherent immunity and impair the host’s immune system when confronted with different dose concentrations. These artificially induced nanoparticles interpret the biological cell system and manipulate cell receptors in situ. Nations all across the world are currently attempting to establish a global policy on the regulation of nanomaterials as per their ecological safety. In some cases, they have been reported to be more hazardous than the comparable ions and micromaterials in some cases. As a result, nanoparticle safety research has far-reaching ramifications for national economies. These studies will be extremely significant in regulating the environmental outcome of nanoparticles.

This study addresses the spatio-temporal variability and plausible sources of criteria air pollutants in the Western Indian city-Ahmedabad. The air pollutants PM 10 , PM 2.5 , O 3 , NO 2 , SO 2, and CO have been analyzed at ten locations in Ahmedabad from 2017 to 2019. The seasonal variability indicates that the air pollutant concentration is highest during winter, followed by pre-monsoon, post-monsoon, and monsoon seasons. The concentration of PM 2.5 (59.52 ± 16.68–89.72 ± 20.68) and PM 10 (107.25 ± 30.43–176.04 ± 38.34) crosses the National Ambient Air Quality Standards (NAAQS) in all seasons. However, the seasonal difference from winter to pre-monsoon is not highly significant (p > 0.05), indicating that the pollution remains fairly similar during these two seasons. The spatial variability of air pollutants over Ahmedabad indicates that the concentration is highest in the south and central region of Ahmedabad and lowest at the east location. The Ventilation Coefficient (VC) has been used to understand the dispersion of air pollutants. The K-means clustering was performed to assess the locations within Ahmedabad with similar air pollutants sources followed by source identification using Principal Component Analysis-Multiple Linear Regression method (PCA-MLR) of 5 clusters. The different locations identified were industrial, residential, and traffic which mainly contribute to the air pollutants in Ahmedabad city. The health risk assessment indicates PMs are the leading pollutant and causing excess risk (ER > 1) at all the locations. With the help of the different statistical techniques, it helps in ascertaining the hotspots of air pollution in a region which will be beneficial in studying health exposure and for policymakers to adopt mitigation strategies.

The prediction of surface ozone is essential attributing to its impact on human and environmental health. Volatile organic compounds (VOCs) are crucial in driving ozone concentration; particularly in urban areas where VOC limited regimes are prominent. The limited measurements of VOCs, however, hinder assessing the VOC-ozone relationship. This work applies machine learning (ML) algorithms for temporal forecasting of surface ozone over a metropolitan city in India. The availability of continuous VOCs measurement data along with meteorology and other pollutants during 2014-2016 makes it possible to deduce the influence of various input parameters on surface ozone prediction. After evaluating the best ML model for ozone prediction, simulations were carried out using varied input combinations. The combination with isoprene, meteorology, NOx, and CO (Isop + MNC) was the best with RMSE 4.41 ppbv and MAPE 6.77%. A season-wise comparison of simulations having all data, only meteorological data and Isop + MNC as input showed that Isop + MNC simulation gives the best results during the summer season (RMSE: 5.86 ppbv, MAPE: 7.05%). This shows the increased ability of the model to capture ozone peaks (high ozone during summer) relatively better when isoprene data is used. The overall results highlight that using all available data doesn't necessarily give best prediction results; also critical thinking is essential when evaluating the model results.

Water samples collected from water resources in Chittorgarh district of Rajasthan were processed radiochemically to evaluate uranium concentration along with associated geochemical parameters. LED fluorimetry was used to measure uranium concentration, while multi-parameter kits were used to evaluate the geochemical parameters. The mean uranium concentration was 14.0 ± 11.4 μgL−1 in the premonsoon period and 16.3 ± 13.2 μgL−1 in the postmonsoon period, which was found to be within the limit of 30 μgL−1, as recommended by the Bureau of Indian Standards (BIS, 2021). Geochemical parameters such as pH, conductivity, total dissolved solid (TDS), oxidation reduction potential, dissolved oxygen, chloride, fluoride, nitrate, hardness, and alkalinity ranged from 7.1–9.4, 226–4540 μScm−1, 125–2630 ppm, 149–287 mV, 9.1–11.4 ppm, 14–690 ppm, 0.1–2.2 ppm, 12–181 ppm, 135–990 ppm, and 129–1266 ppm, respectively. TDS, hardness, alkalinity, and nitrate were observed to be higher than the BIS limit at some locations. Maximum geochemical parameters were within the guidance limit for drinking water (BIS, 2012) excluding nitrate. The distribution of geochemical parameters and uranium content were vastly heterogeneous, signifying the influence of regional lithology and geochemistry.

The present article explores the synthesis of copper oxide nanoparticles (CuO NPs) utilizing Asterarcys quadricellulare algal extract and examines the effect of various reaction parameters on the size and morphology of the nanoparticles. The samples were thoroughly characterized using XRD, FTIR, UV-vis, FE-SEM, and EDS techniques. The XRD analysis disclosed that the size of the synthesized nanoparticles could be controlled by adjusting the reaction parameters, ranging from 4.76 nm to 13.70 nm along the highest intensity plane (111). FTIR spectroscopy provided evidence that the phytochemicals are present in the algal extract. We have compared the photocatalytic activity of biologically and chemically synthesized CuO NPs and observed that biologically synthesized CuO NPs showed better photocatalytic activity than chemically synthesized CuO NPs. The biosynthesized CuO NPs (S8) demonstrated outstanding photodegradation activity towards four different organic dyes, namely BBY, BG, EBT, and MG, with degradation percentages of 95.78%, 98.02%, 94.15%, and 96.04%, respectively. The maximum degradation efficacy of 98.02% was observed for the BG dye at optimized reaction conditions and 60 min of visible light exposure. The kinetics of the photodegradation reaction followed the pseudo-first-order kinetic model, and the rate constant (k) was calculated using the Langmuir-Hinshelwood model for each dye. This study provides an efficient and sustainable approach for synthesizing CuO NPs with superior photocatalytic degradation efficiency towards organic dyes.

An investigation of soil and water resources is essential to determine the future scenario of water management and water resources to attain food and water security. The improper management of watersheds results in a huge amount of sediment loss and surface runoff. Therefore, the present study was carried out to estimate the surface runoff and soil erosion using the Soil Conservation Service Curve Number (SCS-CN) method and RUSLE approach, respectively. These have been estimated using geospatial technologies for the ungauged Mandri river watershed from the Kanker district of Chhattisgarh State in India. The runoff potential zones, which are defined by the area's impermeable surfaces for a given quantity of precipitation were identified based on curve numbers at the sub-watershed levels. The land use data were collected from LISS IV images of 2009. The results showed that the average volume of runoff generated throughout the 16 years (2000-2015) was 14.37 million cubic meters (mM3). While average annual soil loss was found to be 17.23 tons/ha/year. Most of the eroded area was found to be around the major stream in a drainage system of Mandri River and on higher slopes of the terrain in the watershed. This study revealed that surface runoff and soil erosion are primary issues, which adversely affected the soil and water resources in this watershed. Therefore, suitable water harvesting sites and structures can be constructed based on the potential runoff zone and severity of soil erosion to conserve the soil and water in the watershed.

Given the detrimental impact of excessive and improper usage of dangerous chemical compounds on environmental pollution, it is imperative to explore facile and eco-friendly methods for the synthesis of nanoparticles (NPs). In this regard, a novel green synthetic protocol was adopted for the synthesis of copper hydroxide nanoparticles (Cu(OH)(2) NPs), using Coelastrella terrestris algal extract. The biosynthesized and chemically synthesized Cu(OH)(2) NPs were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-visible (UV-Vis), and field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive spectroscopy (EDS). The XRD confirmed the formation of an orthorhombic phase of Cu(OH)(2) NPs and revealed that the crystallite size of biosynthesized Cu(OH)(2) NPs (Bio-Cu(OH)(2) NPs) and chemically synthesized Cu(OH)(2) NPs (Chem-Cu(OH)(2) NPs) were 29.32 nm and 24.69 nm, respectively, corresponding to the major crystallographic plane (021). The synthesized Cu(OH)(2) NPs were utilized efficiently for important applications, such as photocatalytic and antimicrobial activities. Bio-Cu(OH)(2) NPs demonstrated exceptional photocatalytic activity, achieving degradation efficiencies of 85.67% for Amido black 10B (AB10B) and 98.87% for Fast green (FG) dyes, respectively. They also exhibited potent antibacterial activity against a multidrug-resistant Pseudomonas aeruginosa bacterial strain with a 50 mu g/mL MIC value and superior antifungal activity against Candida albicans fungal strain with a 250 mu g/mL MIC value. These findings highlight the potential of algal-mediated Cu(OH)(2) NPs as versatile agents for wastewater treatment and antimicrobial applications. Our work underscores the importance of green synthesis methods and the promising future of these nanoparticles in addressing environmental and health challenges.

Uranium, naturally occurring radionuclide is chemotoxic and nephrotoxic beyond acceptable limit. The presence of uranium beyond acceptable limit in surface and ground water, adversely affecting people's health. In the present investigation, the uranium concentration in surface and ground water of Chittorgarh, Rajasthan was studied along with the physico-chemical parameters of water (n = 87). The ground water was further sub-categorised into well water, handpump water, and borewell water. The mean uranium concentration was observed at 2.5 ± 1.9 µgL−1 and 16.5 ± 1.4 µgL−1 in the surface and ground water samples, respectively. In sub-categories of ground water, the highest uranium concentration was found in borewell water (23.3 ± 17.0 µgL−1), followed by handpump water (13.5 ± 9.1 µgL−1) and well water (6.0 ± 5.5 µgL−1). The uranium concentration was correlated significantly with the depth of the ground water table. It also correlated significantly with electrical conductivity, total dissolved solids and nitrate concentration. 100

The outbreak of COVID-19 is a global public health challenge and has affected many countries, including India. The nationwide lockdown was imposed in India from March 25 to May 31, 2020 to prevent the transmission of COVID-19. The study intends to assess the impact of the absence of major anthropogenic activities during the various phases of the COVID-19 lockdown (LDN) period on the daily mean concentrations of PM 2.5 and PM 10 in six populated cities of Jaipur, Jodhpur, Kota, Udaipur, Ajmer, and Alwar in the state of Rajasthan. Investigation has been done for the different periods, including the pre-lockdown—PRELD (January 1–March 4, 2020), partial lockdown—PLDN (March 5–24, 2020), COVID-19 lockdown—LDN (March 25–May 31, 2020), and unlocking—ULC (June 1–August 31, 2020) phases. We have also compared the mean concentrations of PM 2.5 and PM 10 with the same period of the year 2019. A significant improvement in air quality during the COVID-19 LDN period was noticed in all cities compared to 2019 and for the same period of the year 2020. However, the levels of PM 2.5 and PM 10 were seen to rise during the second, third, and fourth LDN phases compared to the first LDN, indicating that the subsequent lockdowns started with some relaxations and dusty conditions. On the other hand, wind-blown dust is another vital source of PM 10 , resulting in high concentrations in the summer months (April–May). Significant reductions in PM 2.5 (~25–50%) and PM 10 (20–37%) in all six cities during the LDN period compared with PRELD were estimated. However, with significant variations from city to city, the lowest reductions in PM 2.5 (~25%) and PM 10 (~20%) were measured in Jodhpur and Ajmer, respectively. It was noticed that the episodes of rainfall and transport of oceanic air masses resulted in a reduction of particles during the ULC period compared to the LDN period. The air quality index was, more or less, in the “good to satisfactory” category during the first 3 LDN periods, whereas it was moderate for Jodhpur, Jaipur, and Ajmer during the last LDN period. The study will be helpful to determine mitigation policies to minimize air pollution, especially in developing regions.

The investigation was executed to assess outflows of CO2 and CH4 gases from the two landfill sites of Udaipur using commonly applied multiple methodologies for the field to ascertain the accuracy and reliability of data imparted by each of these. To examine the potentiality of each gas discharge quantum for prospective energy that could be used further in waste-to-energy (WtE) projects, a field study was conducted for a period from January 2018 to December 2019 with the division of these landfill sites into segments. The gas samples were recorded onsite at demarked points in each segment by inverting the open portion of the Static Flux Chambers (SFCs) on the landfill surface to stop the ingress of air. This SFC was separately connected with the CO2 and CH4 gas analysers to record their onsite concentrations. The recorded data was further analysed to observe the annual quantitative spatial and temporal variations in the fluxes of these two gases. The mean CO2 and CH4 fluxes of Balicha Landfill Site (BLS) ranged between 932-1876 mu g/m2/hr and 359-1173 mu g/m2/hr, respectively. On the other hand the mean CH4 and CO2 fluxes of Titardi Landfill Site (TLS) ranged between 672 -1483 mu g/m2/hr and 157 -958 mu g/m2/hr, respectively. These fluxes emitted from BLS and TLS generated the carbon footprint (CF) of 180000 and 78000 ton of CO2 equivalent (tCO2 eq.) sequentially. In order to ensure the significance of the method used and to get best energy output for the WtE project the obtained gas flux data of both the sites was analysed and compared. This studied data would provide a guideline for the concerned authorities to plan & execute gas extraction operations at these two sites.

Diwali is a festival of joy and happiness celebrated by displaying extensive fireworks across India for a week. In the present scenario of the COVID-19 pandemic, to curtail the concentration of air pollutants in the atmosphere for better health, a ban on fireworks during the Diwali festival was imposed by many State Governments of India. This study aimed to investigate the prohibition of fireworks on concentrations of air pollutants during the Diwali festival in metropolitan cities of India. For this study, eight major metropolitan cities- Delhi, Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Jaipur and Lucknow and air pollutants (PM2.5, PM10, NOx, SO2 and O3) were taken and compared with the data of Diwali festival 2019. The analysis suggested that PM2.5, PM10, NOx, SO2, which were released from the bursting of firecrackers, were reduced on Diwali days in all the eight cities in 2020 in comparison to Diwali day of 2019. On the other hand, O3 was increased because of a reduction in NO concentration, which decreased the intake of O3. Overall, the ban improved the air quality of the different cities across India.

Diwali is a five-day festival celebrated every year with lamp illumination and bursting of firecrackers in India. Considering the present situation of the COVID-19 pandemic, the Rajasthan government imposed a ban on firecrackers during the five-day festivities in the year 2020 to tackle air pollution caused by the emission of harmful pollutant gases from their burning. This paper has assessed the concentration of PM10, PM2.5, CO and SO2 pollutants, which are released from fireworks in large amounts in the environment during the Diwali festival. Seven air quality monitoring stations viz. Ajmer, Alwar, Jaipur, Jodhpur, Kota, Pali and Udaipur in Rajasthan state were selected to examine the effect of a ban on the use of firecrackers during the Diwali festival. The analysis was done by comparing the mean concentrations of baseline data and Diwali day data of 2019 and 2020. The results depict that the firecracker ban helped in declining the concentrations of all the air pollutants (PM2.5, PM10, CO and SO2) taken into consideration, which significantly improved the ambient air quality of Rajasthan during the Diwali festival, and it is suggested that such regulations should be implemented from time to time to improve the quality of air and human health effectively.

Understanding and quantifying the influence of volatile organic compounds (VOCs) on ozone and secondary organic aerosol formation is essential for better prediction/estimation of these products. A total of 9 VOCs along with surface ozone were measured during the year 2019 at Pune (India) location. The ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) estimations are compared for 2 methods-using measured VOC concentrations and using their photochemical initial concentrations (PIC). The OFP and SOAFP estimated based on the measured VOC concentrations provide an incomplete understanding of these 2 formation processes. This is mainly because measured VOCs don't account for the photochemical losses that compounds undergo from the source to the receptor. The PIC values of VOCs have been estimated in this study to highlight the importance of considering the photochemical losses. For example, the PIC value of highly reactive compound, isoprene, was found to be 152% higher (1.48 ppbv) than its measured value (0.59 ppbv). The resultant total OFP estimate based on PIC values of all the VOCs was found to be 53.30 & PLUSMN; 35.02 ppbv as compared to 45.99 +/- 29.35 ppbv obtained from measured VOCs. Based on k-means clustering analysis, it was found that the highest ozone formation was favored under transition regime chemistry when PIC values were considered. The average total SOAFP based on PIC values was found to be 1.32 +/- 1.40 ppbv, while it was 1.17 +/- 1.18 ppbv for measured VOCs. The aromatics contributed to over 90% of total SOAFP estimated for the region.

Climate change adversely affects human health due to fluctuations in temperature, rainfall pattern and natural hazards etc. The impact of climate change is also on agriculture where food security is greatly affected by climate change. The present paper deals with change in cropping and irrigation intensity in western part of Rajasthan due to climate change. The study includes comparison of cropping intensity and irrigation intensity of 12 districts of Rajasthan and found that Jhunjhunu have the highest cropping intensity from 2006 to 2016 which means a higher portion of the net area is being cropped more than once during one agricultural year. While, Barmer recorded the lowest cropping intensity for both years 2006 and 2016. Sikar did not show change in cropping intensity in this duration while churu had a decline in cropping intensity from 2006 to 2016. Further, Sri Ganganagar district have an increase in cropping intensity in 2015-2016 as compared to 2006-2007. Jaisalmer and Hanumangarh recorded the highest irrigation intensity which increased from 2006 to 2016 and the lowest irrigation intensity was recorded in Pali and Jhunjhunu. Pali and Jalore district had not shown change in irrigation intensity form 2006 to 2016. While Barmer, Jhunjhunu and Sikar districts showed a decrease in irrigation intensity from 2006 to 2016. Henceforth, the study shows the scenario of cropping and irrigation intensity as well as variation due to climate change in western part of Rajasthan.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Investigating the Impact of VOC Sources during Different Seasons on the Air Quality of a Metropolitan Region in IndiaAuthorsRiteshKalbandeiDSujitMajiRaviYadavDevendra SinghRathoreGufranBeigSee all authors Ritesh KalbandeiD• Submitting AuthorIndian Institute of Tropical MeteorologyiDhttps://orcid.org/0000-0001-7998-8020view email addressThe email was not providedcopy email addressSujit MajiIndian Institute of Tropical Meteorologyview email addressThe email was not providedcopy email addressRavi YadavIndian Institute of Tropical Meteorologyview email addressThe email was not providedcopy email addressDevendra Singh RathoreMohanlal Sukhadia Universityview email addressThe email was not providedcopy email addressGufran BeigCorresponding AuthorIndian Institute of Tropical Meteorologyview email addressThe email was not providedcopy email address

The emulsion is a disperse system which is thermodynamically unstable. To improve the stability of the disperse system microemulsion or nanoemulsion was prepared to improve thermodynamic stability. Zeta potential is a physical property which is exhibited by any particle in suspension/emulsion, i.e., in colloidal dispersion. It can be used to optimize the formulations of suspensions and emulsions. Zeta potential is the measure of overall charges acquired by particles in a particular medium and is considered as one of the benchmarks of stability of the colloidal system. As a rule of thumb, suspensions/dispersed system with zeta potential above 30 mV (absolute value) are physically stable. Suspensions with a potential above 60 mV show excellent stability. Suspensions below 20 mV are of limited stability; below 5 mV they undergo pronounced aggregation if the system is stabilized by the electrostatic mechanism. If the values are low for visually stable emulsions, it could be attributed to steric repulsion between approaching molecules, i.e., system is sterically stabilized. Such sterically stabilized colloidal systems though they have low zeta potential values are found to be stable during storage. Tween is well accepted steric stabilizer for colloidal systems. Stability of such a visually stable emulsion or microemulsions should be carried out under accelerated or long-term stability conditions to confirm the globule size and zeta potential on aging.

The COVID-19 lockdown has not only helped in combating the community transmission of SARS-CoV-2 but also improved air quality in a very emphatic manner in most of the countries. In India, the first phase of COVID-19 lockdown came into force on March 25, 2020, which was later continued in the next phases. The purpose of this study was to investigate the result of lockdown on air quality of major metropolitan cities—Delhi, Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Jaipur, and Lucknow—from March 25 to May 3, 2020. For this study, the concentration of six criteria air pollutants (PM2.5, PM10, CO, NO2, SO2, and O3) and air quality index during the COVID-19 lockdown period was compared with the same period of the previous year 2019. The results indicate a substantial improvement in air quality with a drastic decrease in the concentration of PM2.5, PM10, CO, and NO2, while there is a moderate reduction in SO2 and O3 concentration. During the lockdown period, the maximum reduction in the concentration of PM2.5, PM10, CO, NO2, SO2, and O3 was observed to be − 49% (Lucknow), − 57% (Delhi), − 75% (Mumbai), − 68% (Kolkata), − 48% (Mumbai), and − 29% (Hyderabad), respectively. The value of the air quality index (AQI) also dwindled significantly during the COVID-19 lockdown period. The maximum decline in AQI was observed – 52% in Bengaluru and Lucknow. The order of AQI was satisfactory > moderate > good > poor and the frequency order of prominent pollutants was O3 > PM10 > PM2.5 > CO > NO2 > SO2 during the lockdown period in all the aforementioned metropolitan cities.