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To monitor the spread of the novel coronavirus (COVID-19), India, during the last week of March 2020, imposed national restrictions on the movement of its citizens (lockdown). Although India's economy was shut down due to restrictions, the nation observed a sharp decline in particulate matter (PM) concentrations. In recent years, Delhi has experienced rapid economic growth, leading to pollution, especially in urban and industrial areas. In this paper, we explored the linkages between air quality and the nationwide lockdown of the city of Delhi using a geographic information system (GIS)-based approach. Data from 37 stations were monitored from 12 March, 2020 to 2 April, 2020 and it was found that the Air Quality Index for the city was almost reduced by 37% and 46% concerning PM2.5 and PM10, respectively. The study highlights that, in regular conditions, the atmosphere's natural healing rate against anthropogenic activities is lower, as indicated by a higher AQI. However, during the lockdown, this sudden cessation of anthropogenic activities leads to a period in which the natural healing rate is greater than the induced disturbances, resulting in a lower AQI, and thus proving that this pandemic has given a small window for the environment to breathe and helped the districts of Delhi to recover from serious issues related to bad air quality. If such healing windows are incorporated into policy and decision-making, these can prove to be effective measures for controlling air pollution in heavily polluted regions of the World. [ABSTRACT FROM AUTHOR]

We use a state-of-the-art regional chemistry transport model (WRF-Chem v4.2.1) to simulate particulate air pollution over northern India during September–November 2016. This period includes a severe air pollution episode marked by exceedingly high levels of hourly PM 2.5 (particulate matter having an aerodynamic diameter ≤ 2.5 µ m) during 30 October to 7 November, particularly over the wider Indo-Gangetic Plain (IGP). We provide a comprehensive evaluation of simulated seasonal meteorology (nudged by ERA5 reanalysis products) and aerosol chemistry (PM 2.5 and its black carbon (BC) component) using a range of ground-based, satellite and reanalysis products, with a focus on the November 2016 haze episode. We find the daily and diurnal features in simulated surface temperature show the best agreement followed by relative humidity, with the largest discrepancies being an overestimate of night-time wind speeds (up to 1.5 m s -1) confirmed by both ground and radiosonde observations. Upper-air meteorology comparisons with radiosonde observations show excellent model skill in reproducing the vertical temperature gradient (r>0.9). We evaluate modelled PM 2.5 at 20 observation sites across the IGP including eight in Delhi and compare simulated aerosol optical depth (AOD) with data from four AERONET sites. We also compare our model aerosol results with MERRA-2 reanalysis aerosol fields and MODIS satellite AOD. We find that the model captures many features of the observed aerosol distributions but tends to overestimate PM 2.5 during September (by a factor of 2) due to too much dust, and underestimate peak PM 2.5 during the severe episode. Delhi experiences some of the highest daily mean PM 2.5 concentrations within the study region, with dominant components nitrate (∼25 %), dust (∼25 %), secondary organic aerosols (∼20 %) and ammonium (∼10 %). Modelled PM 2.5 and BC spatially correlate well with MERRA-2 products across the whole domain. High AOD at 550nm across the IGP is also well predicted by the model relative to MODIS satellite (r≥0.8) and ground-based AERONET observations (r≥0.7), except during September. Overall, the model realistically captures the seasonal and spatial variations of meteorology and ambient pollution over northern India. However, the observed underestimations in pollutant concentrations likely come from a combination of underestimated emissions, too much night-time dispersion, and some missing or poorly represented aerosol chemistry processes. Nevertheless, we find the model is sufficiently accurate to be a useful tool for exploring the sources and processes that control PM 2.5 levels during severe pollution episodes. [ABSTRACT FROM AUTHOR]

Air pollution has become a growing problem in megacities and large urban areas through out the globe, and transportation is recognized as the major source of air pollution in many cities, especially in developing countries. Contribution of automobiles is reported in the range of 40 to 80% of the total air pollution. The challenge facing megacities is how to reduce the adverse environmental impacts and other negative effects of transportation without giving up the benefits of mobility. The dilemma becomes most pressing under conditions of rapid urban growth, which is likely to increase travel demand significantly. The paper is aimed at understanding the problem of vehicular pollution vis-a-vis ambient air quality for a highly traffic affected megacity, Delhi, wherein, the contribution of transport sector was estimated to be as high as 72%. An effort has been made to review and evaluate the benefits (in terms of improved air quality) of the technological interventions/policies adopted for vehicular pollution control in Delhi. It also highlights the outcome of the efforts and suggests further improvements thereon. The importance of public participation and awareness are also discussed. The paper focuses on deriving the benefits of the implementation of management strategies, supported by scientific and technical data/interpretation, so that the people can realize and participate in the government's endeavor for clean city drive in a more effective manner. [ABSTRACT FROM AUTHOR]

Air pollution is one of the major environmental problems in India, affecting health of thousands of ‘urban’ residents residing in mega cities. The need of the day is to evolve an ‘effective’ and ‘efficient’ air quality management plan (AQMP) encompassing the essential ‘key players’ and ‘stakeholders.’ This paper describes the formulation of an AQMP for mega cities like Delhi in India taking into account the aforementioned key ‘inputs.’ The AQMP formulation methodology is based on past studies of Longhurst et al., ( Atmospheric Environment, 30, 3975–3985, 1996); Longhurst & Elsom, ((1997). Air Pollution-II, Vol. 2 (pp. 525–532)) and Beatti et al., ( Atmospheric Environment, 35, 1479–1490, 2001). Further, the vulnerability analysis (VA) has been carried out to evaluate the stresses due to air pollution in the study area. The VA has given the vulnerability index (VI) of ‘medium to high’ and ‘low’ at urban roadways/intersections and residential areas, respectively. [ABSTRACT FROM AUTHOR]

A number of policy measures have been activated in India in order to control the levels of air pollutants such as particulate matter, sulphur dioxide (SO2) and nitrogen dioxide (NO2). Delhi, which is one of the most polluted cities in the world, is also going through the implementation phase of the control policies. Ambient air quality data monitored during 2000 to 2003, at 10 sites in Delhi, were analyzed to assess the impact of implementation of these measures, specifically fuel change in vehicles. This paper presents the impact of policy measures on ambient air quality levels and also the source apportionment. CO and NO2 concentration levels in ambient air are found to be associated with the mobile sources. The temporal variation of air quality data shows the significant effect of shift to CNG (Compressed Natural Gas) in vehicles. [ABSTRACT FROM AUTHOR]

The enormity of air pollution has always been a matter of concern due to rapid development and urbanization over a long period. The increasing level of pollutants in ambient air in 2016-2017 has deteriorated the air quality of Delhi at an alarming rate. This brought us to focus our study on air quality in Delhi region. The prediction of future air quality has been carried out by analyzing the pollutants using data analysis techniques. In our previous study, we had analyzed the data from 2011-2015. Detailed analysis from 2009-2017 of air pollutants has been proposed in this extended paper along with the critical observation of 2016-2017 air pollutants trend in Delhi. Descriptive analysis and predictive analysis have been used to study the trends of various air pollutants like sulphur dioxide (SO 2 ), nitrogen dioxide (NO 2 ), suspended particulate matter (PM), ozone (O 3 ) carbon monoxide (CO), benzene, and forecast the future trend. We have observed through data analytics techniques that SO 2 is likely to increase by 1.24ug/m 3 , NO 2 is likely to increase by 16.77ug/m 3 , O3 is likely to increase by 6.11 mg/m 3 , benzene is likely to reduce by 1.33 mg/m 3 and NO 2 is predicted to reduce by 0.169 mg/m 3 in the coming years. [ABSTRACT FROM AUTHOR]

The present study investigates the reduction in nitrogen dioxide (NO2) levels using satellite-based (Sentinel-5P TROPOMI) and ground-based (Central Pollution Control Board) observations of 2020. The lockdown duration, monthly, seasonal and annual changes in NO2 were assessed comparing the similar time period in 2019. The study also examines the role of atmospheric parameters like wind speed, air temperature, relative humidity, solar radiation and atmospheric pressure in altering the monthly and annual values of the pollutant. It was ascertained that there was a mean reduction of ~ 61% (~ 66.5%), ~ 58% (~ 51%) in daily mean NO2 pollution during lockdown phase 1 when compared with similar period of 2019 and pre-lockdown phase in 2020 from ground-based (satellite-based) measurements. April month with ~ 57% (~ 57%), summer season with ~ 48% (~ 32%) decline and an annual reduction of ~ 20% (~ 18%) in tropospheric NO2 values were observed (p < 0.001) compared to similar time periods of 2019. It was assessed that the meteorological parameters remained almost similar during various parts of the year in 2019 and 2020, indicating a negligent role in reducing the values of atmospheric pollution, particularly NO2 in the study area. It was concluded that the halt in anthropogenic activities and associated factors was mainly responsible for the reduced values in the Delhi conglomerate. Similar work can be proposed for other pollutants to holistically describe the pollution scenario as an aftermath of COVID-19-induced lockdown. [ABSTRACT FROM AUTHOR]

Air pollution in Delhi is a serious environmental problem. In this paper, the effects of meteorological conditions on local air quality are quantitatively assessed by determining the relationships between concentrations of Suspended Particulate Matter (SPM), Respirable Suspended Particulate Matter (RSPM), sulphur dioxide (SO2) and nitrogen dioxide (NO2) with meteorological parameters on monthly basis, from 2000 to 2006. The multi-linear regression approach, used in the study, has facilitated analysis of the air quality-meteorology relationship and predicted the concentrations of SPM and RSPM within a scatter of ±18% and of SO2 and NO2 within a scatter of ±14%. [ABSTRACT FROM AUTHOR]

Atmospheric concentrations of polycyclic aromatic hydrocarbons (PAHs) in Delhi were evaluated to study particulate PAHs profiles during the different seasons of 2003. Samples of urban suspended particulate matter were collected during January 2003 to December 2003 at three locations (Okhla, Dhaulakuan and Daryaganj), using a high volume sampler provided with glass fiber filters. Samples were analyzed using the gas chromatography technique. The annual average concentrations of total PAHs were found as 1,049.3 ng/m3 at Okhla, 1,344.37 ng/m3 at Daryaganj, and 1,117.14 ng/m3 at Dhaulakuan. The seasonal average concentrations were found to be maximum in winter and minimum during the monsoon season. Principal Component Analysis (PCA) of the data was also carried out and the results indicate that diesel and gasoline driven vehicles are the principal sources of PAHs at all the three sites under investigation. Other sources might come from stationary combustion sources such as cooking fuel combustion and industrial emission. [ABSTRACT FROM AUTHOR]

This paper uses spectral methods to analyze changes in air quality at a single monitoring site in Delhi since 2000. Power spectral density calculations of daily concentration data for particulate matter (PM10), carbon monoxide (CO), oxides of nitrogen (NO x ) and oxides of sulfur (SO x ) reveal the presence of trends and periodic oscillations for all the pollutants. Singular Spectrum Analysis (SSA) is used to decompose daily data into statistically significant non-linear trends, seasonal cycles and other oscillations. Periods of sharp reductions were observed for both SO x and CO concentrations in 2001 and 2002, respectively. NO x concentration trends show a sustained rise from 2000 to 2004, followed by small decline thereafter. PM10 concentration trends remain essentially unchanged over the time period. All pollutants also show strong annual and biannual cycles. The observed trends in CO and NO x likely relate changes in Delhi''s vehicular traffic emissions. The sharp drop in both the trend and amplitude of the seasonal cycle of CO coincides with the switch to Compressed Natural Gas (CNG) as a fuel for Delhi''s public transport fleet. Observed changes in SO x and PM10 concentrations were most likely caused by sources unrelated to vehicular traffic. [Copyright &y& Elsevier]

High consumption of fossil fuels, increased greenhouse gas emissions and deterioration of local air quality have resulted from rapid industrialization and urbanization in India in the last decade. India has taken many initiatives to address these problems such as new automobile fuel policies, energy efficiency measures, promotion of renewable energy use, relocation of highly polluting industries, enforcing use of low emission fuels like CNG for public transport in large cities, and introducing metro rail networks in megacities. This paper highlights results of adopted policies in Delhi showing relationships between air quality and climate change and having sustainable development as the driving force with focus on environmental and social dimensions. [ABSTRACT FROM AUTHOR]

Although lockdown of the industrial and transport sector and stay at home advisories to counter the COVID-19 pandemic have shown that the air quality has improved during this time, very little is known about the role of ambient air pollutants and meteorology in facilitating its transmission. This paper presents the findings from a study that was conducted to evaluate whether air quality index (AQI), three primary pollutants (PM 2.5 , PM 10 and CO), Ground level ozone (O 3) and three meteorological variables (temperature, relative humidity, wind speed) have promoted the COVID-19 transmission in five megacities of India. The results show significant correlation of PM 2.5 , PM 10 , CO, O 3 concentrations, AQI and meteorological parameters with the confirmed cases and deaths during the lockdown period. Among the meteorological variables considered, temperature strongly correlated with the COVID-19 cases and deaths during the lockdown (r = 0.54 ; 0.25) and unlock period (r = 0.66 ; 0.25). Among the pollutants, ozone, and among the meteorological variables, temperature, explained the highest variability, up to 34% and 30% respectively, for COVID-19 confirmed cases and deaths. AQI was not a significant parameter for explaining the variations in confirmed and death cases. WS and RH could explain 10–11% and 4–6% variations of COVID-19 cases. A GLM model could explain 74% and 35% variability for confirmed cases and deaths during the lockdown and 66% and 19% variability during the unlock period. The results suggest that meteorological parameters may have promoted the COVID-19 incidences, especially the confirmed cases. Our findings may encourage future studies to explore more about the role of ambient air pollutants and meteorology on transmission of COVID-19 and similar infectious diseases. [Display omitted] • During lockdown for COVID-19, air quality improved in five megacities of India. • PM 2.5 , PM 10 , CO concentration across the megacities reduced during the lockdown. • Delhi and Kolkata experienced rise in O 3 concentration during lockdown. • PM 2.5 , PM 10 , CO, O 3 , AQI and T correlated with COVID-19 confirmed cases and deaths. • Temperature explained up to 30% variability for COVID-19 cases during the lockdown. [ABSTRACT FROM AUTHOR]

Presents the results of a study conducted on the levels of death in Delhi, India which relate to air pollution, between 1991 and 1994, while examining the health benefits of air pollution control. Effects of air pollution on human health; Reasons for controlling air pollution; Details on the health damages associated with air pollution.

The present study proposed to investigate the atmospheric distribution, sources, and inhalation health risks of polycyclic aromatic hydrocarbons (PAHs) in a tropical megacity (Delhi, India). To this end, 16 US EPA priority PAHs were measured in the inhalable fraction of atmospheric particles (PM; aerodynamic diameter, ≤10 μm) collected weekly at three residential areas in Delhi from December 2008 to November 2009. Mean annual 24 h PM levels at the sites (166.5-192.3 μg m) were eight to ten times the WHO limit. Weekday/weekend effects on PM and associated PAHs were investigated. ΣPAH concentrations (sum of 16 PAHs analyzed; overall annual mean, 105.3 ng m; overall range, 10.5-511.9 ng m) observed were at least an order of magnitude greater than values reported from European and US cities. Spatial variations in PAHs were influenced by nearness to traffic and thermal power plants while seasonal variation trends showed highest concentrations in winter. Associations between ΣPAHs and various meteorological parameters were investigated. The overall PAH profile was dominated by combustion-derived large-ring species (85-87 %) that were essentially local in origin. Carcinogenic PAHs contributed 58-62 % to ΣPAH loads at the sites. Molecular diagnostic ratios were used for preliminary assessment of PAH sources. Principal component analysis coupled with multiple linear regression-identified vehicular emissions as the predominant source (62-83 %), followed by coal combustion (18-19 %), residential fuel use (19 %), and industrial emissions (16 %). Spatio-temporal variations and time-evolution of source contributions were studied. Inhalation cancer risk assessment showed that a maximum of 39,780 excess cancer cases might occur due to lifetime inhalation exposure to the analyzed PAH concentrations. [ABSTRACT FROM AUTHOR]

Urban areas are facing increasing fog frequencies that may result due to increased air pollution emanating from variety of sources. The increased pollution levels may lead to the atmospheric reactions resulting into the formation of secondary pollutants that may also lead to increased aerosol number concentrations (ANC) in the atmosphere. This could cause enhanced water aerosols in the presence of favourable meteorological conditions and high relative humidity. This study deals with the atmospheric pollution and visibility during winter season of megacity Delhi in order to assess the relationship between the two specifically during fog episodes. Thus, this study analyses the levels of air pollutants, aerosol spectrum and meteorological conditions during one week each in the winter season of the years 2004 and 2006 in order to have an improved understanding of their role in fog formation in mega-city Delhi. More than 300 h of measurements which included episodes of dense, thick and moderate fogs of about 25 h, were studied. The measurements cover most of the accumulation mode and greater size spectrum of aerosols. Thus, the analysis is performed for the entire period, specifically, before the fog sets up, during and afterwards. In general, the relatively small variations in number concentration show larger variations in visibility prior and post dense fog formation than during dense fog episodes. Preliminary analysis of monthly averaged RSPM (Respirable Suspended particulate Matter or PM10) concentration values for four winter months for a period of 6 years (1996–2001) and visibility did not show a good correlation with total occurrences of fog. However, daily averaged RSPM concentration showed a good correlation with the occurrences of thick fog. Diurnal variation of Sulfur-dioxide and Nitrogen dioxide were found to have inverse relationship with visibility during fog which may be due to formation of secondary pollutants such as sulfate and to a lesser extent nitrates. Amongst, the daily averaged concentrations of all the criteria pollutants, RSPM was found to be best correlated with the fog in comparison to other pollutants. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) was used to understand the differences in morphology, elemental composition and particle density of aerosols in different five size ranges to further investigate the potential sources as well as transport of pollutants from/at a much polluted and a very clean area of Delhi. Aerosol samples were obtained in five different size ranges viz. ≥10.9, 10.9–5.4, 5.4–1.6, 1.6–0.7 and ≤0.7 μm from a considerably very clean and a much polluted area of Delhi. It was observed that at polluted area most of the particles irrespective of size are of anthropogenic origin. At clean area, in coarse size fractions particles are of natural origin while in fine size range the presence of anthropogenic particles suggests the transport of particles from one area to the other. [ABSTRACT FROM AUTHOR]

The use of alternative fuel is considered to be an effective measure to improve the urban air quality. Concerned over deteriorating air quality in Delhi, the Delhi government initiated different measures including stringent emission norms, improved fuel quality and above all introduction of cleaner fuel-CNG in public transport system. The entire city bus fleet was converted to CNG mode by 2002. The present study reports the comparative assessment of the status of air quality with respect to PM10 and PAH before and after the introduction of CNG in public transport system in Delhi. The study has been carried out for two different time periods: first in the year 1998 and second in the year 2004. Following the total conversion of public transport system to CNG in 2002, Post-CNG data indicate a sharp reduction of 51–74% in the PM10 concentration and 58–68% in the TPAH concentration as compared to the Pre-CNG data. [ABSTRACT FROM AUTHOR]

The study focuses on assessing the status of respiratory morbidity in Delhi over a four years period from 2000–2003. An attempt was made to investigate the role of important pollutants (SO2, NO2, SPM and RSPM) and various meteorological factors (temperature minimum & maximum, relative humidity at 0830 and 1730 hrs. and wind speed) in being responsible for respiratory admissions on account of COPD, asthma and emphysema. The study showed that winter months had greater exposure risk as pollutants often get trapped in the lower layers of atmosphere resulting in high concentrations. Statistical analysis revealed that two pollutants have significant positive correlation with the number of COPD cases viz., SPM ( r = 0.474; p < 0.01) and RSPM ( r = 0.353; p < 0.05), while a meteorological factor temperature (minimum) has a significant negative correlation ( r = −0.318; p < 0.05) with COPD. Stepwise multiple regression analysis was performed for COPD as dependent variable and R2 value of 0.33 was obtained indicating that SPM and RH(1730) were able to explain 33 percent variability in COPD. The partial correlation of SPM and RH(1730) on COPD was higher than any other combination and therefore they can be regarded as important contributing variables on COPD. [ABSTRACT FROM AUTHOR]

Studies the impact of atmospheric pollution on vitamin D status of infants and toddlers in Delhi, India. Mean total serum concentration of children in the Mori Gate and Gurgaon areas; Vitamin D deficiency; Source of vitamin D.