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Present study aims to examine the impact of lockdown on spatio-temporal concentration of PM2.5 and PM10 - categorized and recorded based on its levels during pre-lockdown, lockdown and unlock phases while noting the relationship of these levels with meteorological parameters (temperature, wind speed, relative humidity, rainfall, pressure, sun hour and cloud cover) in Delhi. To aid the study, a comparison was made with the last two years (2018 to 2019), covering the same periods of pre-lockdown, lockdown and unlock phases of 2020. Correlation analysis, linear regression (LR) was used to examine the impact of meteorological parameters on particulate matter (PM) concentrations in Delhi, India. The findings showed that (i) substantial decline of PM concentration in Delhi during lockdown period, (ii) there were substantial seasonal variation of particulate matter concentration in city and (iii) meteorological parameters have close associations with PM concentrations. The findings will help planners and policy makers to understand the impact of air pollutants and meteorological parameters on infectious disease and to adopt effective strategies for future., Graphical abstract Unlabelled Image

In South Asia, combustion of solid fuel for residential heating and cooking is a major emission source of particulate-phase polycyclic aromatic hydrocarbons (p-PAHs), a potent carcinogen for human health. The emission factors (EFs) and source diagnostic ratios of PAHs currently used in regional inventory models have been estimated from controlled laboratory tests, which do not accurately reflect real-world combustion scenarios observed in rural Indian households. Consequently, the health effects associated with p-PAH levels in indoor and ambient air could be severely underestimated and undervalued. We performed a nationwide study across ten different states in the Indian subcontinent to evaluate the EFs and source diagnostic ratios of sixteen U.S. Environmental Protection Agency (EPA) identified high priority p-PAHs emitted from residential solid biomass combustion. Our estimated average annual EFs were 2.4–18.3 fold higher than those reported from previous laboratory-based investigations. Carcinogenic toxicity analysis shows that combustion of dung cake and coal ball, both widely used residential solid fuels, posed the most risk (80% and 59% respectively) in comparison to other PAHs owing to predominant emission of benzo[a]pyrene. Our findings underscore the importance of improved laboratory testing and field validations as crucial steps toward more accurate emission inventories and better assessment of public health impacts.

A short-term study was conducted with a view to assess the ambient air quality in the surroundings area of compost plant at Okhla, Delhi. Three selected locations viz., CRRI Campus, Hazi Colony, and Gaffar Manzil were selected during the month of November 2008. The study revealed that 24 hourly average concentration of respirable suspended particulate matter (RSPM) at all selected locations were alarmingly high as compared to National Ambient Air Quality Standards (NAAQS) specified by Central Pollution Control Board (CPCB) 2009, during the study period. The 24 hourly average concentrations of sulphur dioxide (SO2) and ammonia (NH3) were within the permissible limits prescribed by the NAAQS. Nitrogen dioxide (NO2) concentration was found to exceed the permissible limits at all the three locations with percent exceedence ranging between 67%-75%. High concentrations of NO2 could be due to auto-exhaust emissions on Delhi- Mathura road, burning of LPG gas for domestic use, incinerator stack gases and diesel run electric generator. The concentrations of H2S were low, which could be due to aerobic nature of waste processing composting plant. The 8 hourly average concentration of CO was quite high at all the three monitoring stations. Percent exceedence of CO levels ranged between 83% - 86%. The localized domestic and automobile emissions in surrounding areas could be the major contributor of CO. The overall assessment of the air quality during the study period at selected locations indicated that the maximum contribution of pollutant responsible for critical Air Quality Index (AQI) values was the respirable particulate matter (RSPM) which fell under the category of severe on majority of the days. Keywords: Compost Plant, Air Pollutants, Air Quality Index (AQI)

Air pollution in India during COVID-19 lockdown, which imposed on 25th March to 31st May 2020, has brought a significant improvement in air quality. The present paper mainly focuses on the scenario of air pollution level (PM2.5, PM10, SO2, NO2 and O3) across 57 urban agglomerations (UAs) of India during lockdown. For analysis, India has been divided into six regions - Northern, Western, Central, Southern, Eastern and North-Eastern. Various spatial statistical modelling with composite air quality index (CAQI) have been utilised to examine the spatial pattern of air pollution level. The result shows that concentration of all air pollutants decreased significantly (except O3) during lockdown. The maximum decrease is the concentration of NO2 (40%) followed by PM2.5 (32%), PM10 (24%) and SO2 (18%). Among 57 UA’s, only five - Panipat (1.00), Ghaziabad (0.76), Delhi (0.74), Gurugram (0.72) and Varanasi (0.71) had least improvement in air pollution level considering entire lockdown period. The outcome of this study has an immense scope to understand the regional scenario of air pollution level and to implement effective strategies for environmental sustainability.

Measurement of biological particles (bioaerosols) in ambient air is of great importance as it is directly linked with the health issues. However, data on the bioaerosols characterization are scarce. Here we report on the concentration and characterization of bioaerosols (including bacterial and fungal aerosols) as well as determination of organic and elemental carbon (OC and EC) in total suspended particulate matter (TSPM) at a busy roadside restaurants-cluster site in New Delhi. In addition, 14 carbonyl volatile organic compounds (carbonyl VOCs) were also measured and their relationship with bioaerosols and OC/EC is assessed. The culturable airborne bacterial and fungal concentrations (CAB and CAF) at restaurant area varied significantly in different seasons ranging from 1.7 x 10(4)-9.8 x 10(4) (averaged 6.3 x 10(4) +/- 2.6 x 10(4) cfu m(-3)) and 3.5 x 10(2)-9.5 x 10(3) (3.9 x 10(3) +/- 3.1 x 10(3) cfu m(-3)) cfu m(-3), respectively. Major concentration peaks of TSPM, OC, EC as well as bacterial and fungal aerosols were found in winter and spring seasons. These peaks can be attributed to the low atmospheric boundary layer (ABL) height and favourable meteorological conditions for microbial growth in winter and spring seasons in New Delhi. Good correlations (R-2 > 0.5) were observed between CAB, CAF, TSPM and OC. On the other hand, CAB and CAF were not found to be correlated with carbonyl compounds (R2 < 0.2) indicative of their diverse sources. The bacterial identification was done by 16s rDNA sequencing and the identified strains were Bacillus sp., Bacillus firmus, Bacillus licheniformis, Bacillus cereus, Bacillus pumilus, Acinetobacter sp. and Acinetobactor radioresistens gene. Predominant fungal genera identified were Aspergillus, Cladosporium, Alternaria and Fusarium, which are known for adverse health effects causing numerous allergic and pathogenic inflammations.

Size-segregated aerosol samplings were carried out during 2013-14 at Okhla landfills, Delhi, which is a municipal solid waste dumping station. Aerosol samples were collected on quartz filters using an Andersen impactor sampler having 9-stages with cut-off diameter >9.0, 9.0-5.8, 5.8-4.7, 4.7-3.3, 3.3-2.1, 2.1-1.1, 1.1-0.65, 0.65-0.43, 9.0 μm. Fungal spores mostly peaked in coarse sizes (2.1-5.8 μm) and showed unimodal size distribution. Predominant identified bacterial strains were mostly belonged to Bacillus, Staphylococcus, Streptococcus, Klebseilla and Escherichia genera. Most of the identified fungal spores are known for adverse health effects causing numerous allergic and pathogenic inflammations. These results suggest that the open-solid waste dumping sites are a major source of bioaerosols, and residents living in the nearby areas of landfills are at high health risks.

A fugitive emission of natural gas during the extraction of oil and gas and its transportation through the pipeline has potential threat to the environment. Natural gas (NG) is the mixture of hydrocarbon gases consisting primarily of methane and other varying hydrocarbons, a small fraction of carbon dioxide, hydrogen, nitrogen, hydrogen sulphide and rare trace gases like helium, neon, xenon etc. The colorless and odorless NG has a wide range of applications as a cleaner fuel. The rapid urbanization, industrialization and economic growth all over the world demand the increasing transportation capacity of NG. Though the transportation pipeline are laid with well-equipped sophisticated technology and leak detection sensors, however still there are risk factor associated for leakage of the gases and explosion. The impacts of man-made disaster are in terms of deaths, injury, losses in economics, property and also having the adverse effect on ecology. The integrity of the NG pipeline system can be achieved by adopting continuous sophisticated up gradation technology. It also requires operation and maintenance of the pipeline at regular interval.

The GW contamination has become a grave problem due to rapid growth of population, expansion of irrigation activities, industrialization and high rate of urbanization in India. Over the last few decades, the land and water use patterns have changed drastically in India. GW is an important resource for drinking purpose which contains over 90% of the fresh water resources (Sabahi et al. 2009). The untreated industrial effluents discharged into the surface water sources cause severe GW pollution in the industrial belt (Mondal et al. 2005). People are becoming more aware of the complexity of the nature and the delicate balance that exist with the global ecosystem (Ahmet et al. 2006). The National Capital Territory (NCT) of Delhi, India is a water scare state with a deficit in the drinking water supply to its resident (Shekhar et al. 2009). The Yamuna flood plain is only potential fresh GW resources in Delhi. The exploration, exploitation and unscientific management of GW resources in the NCT of Delhi, India have posed a serious threat of reduction in quantity and deterioration of quality (Adhikary et al. 2009). In Delhi, GW level has gone down approximately 8 m per year in the last 10 years which is at the rate of about 0.8 m per year (CGWB 2006). Annual replenishable GW sources of NCT Delhi are about 297 million cubic meter while the GW draft is about 480 million cubic meter (Chatterjee et al. 2009). Thus out of nine districts, seven districts of NCT Delhi have been categorized as overexploited with regards to the dynamic GW resources (CGWB 2006).The city is forced to meet 50 % of its water requirement from GW (Kumar et al. 2006). Solid and liquid waste emanating from the industry are inevitability the by products of manufacturing process which contains toxic chemicals and trace metals. The open unlined drains and availability of dumping of toxic industrial waste in nearby recharge of GW areas, act as the source of GW pollution (Dutta et al. 1997).

A study was conducted in the residential areas of Delhi, India, to assess the variation in ambient air quality and ambient noise levels during pre-Diwali month (DM), Diwali day (DD) and post-Diwali month during the period 2006 to 2008. The use of fireworks during DD showed 1.3 to 4.0 times increase in concentration of respirable particulate matter (PM(10)) and 1.6 to 2.5 times increase in concentration of total suspended particulate matter (TSP) than the concentration during DM. There was a significant increase in sulfur dioxide (SO(2)) concentration but the concentration of nitrogen dioxide (NO(2)) did not show any considerable variation. Ambient noise level were 1.2 to 1.3 times higher than normal day. The study also showed a strong correlation between PM(10) and TSP (R (2) ≥ 0.9) and SO(2) and NO(2) (R (2) ≥ 0.9) on DD. The correlation between noise level and gaseous pollutant were moderate (R (2) ≥ 0.5). The average concentration of the pollutants during DD was found higher in 2007 which could be due to adverse meteorological conditions. The statistical interpretation of data indicated that the celebration of Diwali festival affects the ambient air and noise quality. The study would provide public awareness about the health risks associated with the celebrations of Diwali festival so as to take proper precautions.

Yamuna river pollution has been extensively studied with regard to some selected parameters in five locations at Palla, Nizamuddin Midstream, Nizamuddin Quarter Stream, Agra Canal Midstream, and Agra Canal Quarter Stream in Delhi, India. Seasonal and location-wise variation of pollutants namely dissolve oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), ammonia (AMM), total coliform and fecal coliform were studied for 6 years during the period of 2000–2005. The study results revealed the lowest level of pollution during monsoon. The statistical analysis revealed a positive correlation between DO, BOD, COD, TKN, and AMM.