key: cord-1041868-q1qwboa1
authors: Mahato, Susanta; Pal, Swades; Ghosh, Krishna Gopal
title: Effect of lockdown amid COVID-19 pandemic on air quality of the megacity Delhi, India
date: 2020-04-29
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2020.139086
sha: 432196306423dc81b1fda82255304ec59283b8f5
doc_id: 1041868
cord_uid: q1qwboa1

Abstract Amid the COVID-19 pandemic, a nationwide lockdown is imposed in India initially for three weeks from 24th March to 14th April 2020 and extended up to 3rd May 2020. Due to the forced restrictions, pollution level in cities across the country drastically slowed down just within few days which magnetize discussions regarding lockdown to be the effectual alternative measures to be implemented for controlling air pollution. The present article eventually worked on this direction to look upon the air quality scenario amidst the lockdown period scientifically with special reference to the megacity Delhi. With the aid of air quality data of seven pollutant parameters (PM10, PM2.5, SO2, NO2, CO, O3 and NH3) for 34 monitoring stations spread over the megacity we have employed National Air Quality Index (NAQI) to show the spatial pattern of air quality in pre and during-lockdown phases. The results demonstrated that during lockdown air quality is significantly improved. Among the selected pollutants, concentrations of PM10 and PM2.5 have witnessed maximum reduction (>50%) in compare to the pre-lockdown phase. In compare to the last year (i.e. 2019) during the said time period the reduction of PM10 and PM2.5 is as high as about 60% and 39% respectively. Among other pollutants, NO2 (−52.68%) and CO (−30.35%) level have also reduced during-lockdown phase. About 40% to 50% improvement in air quality is identified just after four days of commencing lockdown. About 54%, 49%, 43%, 37% and 31% reduction in NAQI have been observed in Central, Eastern, Southern, Western and Northern parts of the megacity. Overall, the study is thought to be a useful supplement to the regulatory bodies since it showed the pollution source control can attenuate the air quality. Temporary such source control in a suitable time interval may heal the environment.

J o u r n a l P r e -p r o o f 4 Mass scale health problems due to air pollution also imposes considerable burden to the national economy, particularly for the developing countries where government is the foremost contributor of the health care facilities (WHO 2006) . As per the estimation of the World Bank (World Bank 2016; Lim et al. 2012) welfare expenditure is equivalent to about 8% of national GDP in the developing countries. In order to minimize the health burden due to air pollution the Central government and the government of NCT Delhi, have imposed several regulation measures since long as per international guidelines. For instance, CPCB ENVIS (2012) identified 17 categories of highly polluting industries with restricted operation within the jurisdiction of the NCT Delhi; implementation of strict emission standard for vehicles, renovating complete municipal transportation to CNG fuel, converting coal-based power plants to natural gas (CPCB 2011), ban on entrance of weighty vehicles during peak hours, odd-even car trial system (Kumar et al. 2017) and many more. In spite of these efforts, air pollution level is not reduced considerably in Delhi.

However, efficacy of these policy interventions has generated lots of questions for achieving success. Therefore, unless effective counter measures are taken and implemented, ambient air quality will not be restored.

COVID-19 is a highly contagious disease firstly identified in Wuhan, Central China in December 2019. Up to March 23 globally, over 14,000 people have died, and more than 334,000 have been infected by COVID-19 (WHO 2020) . The death toll is reached to 200000 as on 26.04.2020 over the world. Due to the contagion of COVID-19, a nationwide lockdown is imposed in India from March 24th for three weeks up to 14th of April and later extended up to 3rd May. By this nationwide lockdown almost all industrial activities and mass transportation have been prohibited. As a result, the pollution level in 88 cities across the country drastically reduced down only after four days of commencing lockdown event according to the J o u r n a l P r e -p r o o f 5 official data from the CPCB. Therefore lockdown presumes to be the effective alternative measure to be implemented for controlling air pollution and the present work intended to explore the degree of air quality change during lockdown at spatial scale in the megacity Delhi.

In order to express the magnitude of air pollution of a region, Air Quality Index (AQI) often in addition is termed as Air Pollution Index (API) (Shenfeld 1970 ; Thom and Ott 1976; Ott and Thom 1976; Murena 2004) or in few cases Pollutant Standards Index (PSI) (Ott and Hunt 1976; USEPA 1994) are commonly in use. Green Index (GI) (Green 1966) , Fenstock Air Quality Index (FAQI) (Fenstock 1969) , Ontario Air Pollution Index (OAPI) (Shenfeld 1970) , Most Undesirable Respirable Contaminants Index (MURC) (taken from Ott 1978) and Oak Ridge Air Quality Index (ORAQI) (Babcock and Nagda 1972) are some of the earlier methods to appraise the air quality in built-up areas. In 1976, the USEPA has launched Pollutant Standards Index (PSI) in order evaluate air quality incorporating five major pollutants (PM 10 , O 3 , SO 2 , NO 2 and CO).

However, PSI has excluded several other pollutants, a few of which possibly harmful for persons having respiratory trouble (Radojevic and Hassan 1999; Qian et al. 2004) . In this course, Integral Air Pollution Index (IAPI) has been developed particularly for the metropolis of Russia (Bezuglaya et al. 1993) . Later on in 1999 PSI was renamed as Air Quality Index (AQI) by the US EPA (1999) incorporating few other pollutants parameters. Subsequently, several other indices have come into force like Aggregate Air Quality Index, (AQI) (Kyrkilis et al. 2007 (Kumar and Goyal 2013) are some of the recent development. However, among the commonly J o u r n a l P r e -p r o o f 6 used air quality indices there is no unanimously accepted methodology does exist fit for all circumstances (Stieb et al. 2005; Maynard and Coster 1999) . Of late technological advancement along with information technology collection and compilation real-time of site-specific air pollution data is in practice throughout the world. In India the attempt to quantify integrated air quality started much later only after 1984 in name of National Air Quality Monitoring Programme. Up to date only few handful studies (Agharkar 1982; Swami and Tyagi 1999; Gurjar et al. 2008; Beig et al. 2010a and 2010b etc.) have successfully attempted to quantify and report air quality for megacities of the country. However, eclipsing and ambiguity are frequent to many of the indices used in those studies and there is found considerable discrepancy among air quality professed by the indices and real air quality. In this direction, in place of additive and multiplicative indices developed earlier the CPCB (2014) have come up with a new revised National Air Quality Index (NAQI) derived from Maximum operator approach in an attempt to remove uncertainty and eclipsing. In this regard, the CPCB has also notified a fresh set of Indian National Air Quality Standards (INAQS) (http://www.cpcb.nic.in). In the present work NAQI is used for interim estimation of air quality of the megacity Delhi amidst the lockdown period.

Overall the significance and impacts of lockdown are still not well understood and likely to have significant role on restoration of air quality. Nationwide lockdown amid the COVID-19 pandemic provides a unique opportunity to work in this direction. Consequently, quantitative appraisal of air pollution desires to be carried out so as to understand the upshot of lockdown measures on air quality particularly when there is a need to implement such alternative control actions. The present study is an effort in this direction to assess the usefulness of the lockdown as an alternative strategy for diminution of air pollution level in NCT Delhi. The objectives of the present study is (i) to compare the atmospheric pollutant concentrations in Delhi during the pre J o u r n a l P r e -p r o o f 7 and during lockdown periods, (ii) to quantify the integrated air quality due to the implementation of lockdown regulation during Lockdown period and (iii) to unveil the level of major pollutant concentration in the past few years during the same window period. Focusing on the NCT of Delhi, the study is thought to be a conceivable addition to the scientific community and policy makers not only to assess the impacts of lockdown on air quality, but also its efficiency as an easy alternative action plans for upgrading in air quality of NCT Delhi with public involvement in upcoming years.

The present study has focused on Delhi as the administrative and second financial capital of India. The National Capital Territory (NCT) Delhi is the second leading megacity in the world (The World's Cities in 2018 , Data Booklet, United Nations, 2018 and the largest urban agglomeration in India with 1.68 crore residents exhibiting a decadal growth rate of 21% and density of 11297person/km 2 (Census 2011; http://census2011.co.in). NCT Delhi occupies an area about 1485 km 2 which lies between geo-coordinate 28°24'17''N to 28053'00"N and 76°50'24"E to 77°20'37"E ( Figure 1 ). Geographically the megacity is located within the Indo-Gangetic alluvial plain region with an altitude range of 198 m to 220m above msl and surrounded by lesser Himalaya in the north, peninsular region in the south, hilly region in the east and Great Indian Desert in the west (Sahay 2018; Yadav et al. 2017) . NCT Delhi has dual status as a city and a state incorporating Kanjhawla Block, MehrauliBlock,Najafgarh Block and Shahadra Block. The Monsoon (Jun-Sept), short Post-monsoon (Oct-Nov), Winter (Dec-Feb) and Pre-monsoon (March-May) . Temperature ranges between 4°C to 10°C in winter and 42° C to 48°C in summer (Kumar et al. 2017 ). More than 80% of the total annual precipitation occurs during the monsoon months (Perrino et al. 2011) . A momentous proportion (about 90%) of the population working in NCT Delhi residing in urban areas, which is much higher than the nationwide average of 31.16% (SAD 2014). About 6.93 million registered vehicles was on roads during 2011 in Delhi which is the highest in the country and it is further expected to increase as much as 25.6 million by 2030 (Kumar et al. 2017) . NCT Delhi's existing road length is 33198 km with about 864 km signalized road and 418 blinkers traffic intersections (NCR 2013; GoD 2016). 

The AQI is usually based on pollutants criteria where the deliberation of an individual pollutant is transformed into a sole index using appropriate aggregation method (Ott 1978) .

Conventionally, calculation of the AQI was supposed as a maximum sub-index approach using five criteria pollutants (i.e. PM 10 and PM 2.5 , SO 2 , NO 2 and CO) (Sharma 2001 (Table 3) 

The selection of the 7 parameters is primarily based on the objectives outlined earlier, period, monitoring regularity and data accessibility. Furthermore, in the present scheme, six National Air Quality Index (NAQI) categories (CPCB 2015) (Table 3 ) is used to assess the expected health exposure (also called-Health Breakpoints) in different quality classes as approved by the NAQS. The sub-indices for entity pollutants at a monitoring station has been calculated based on 24-hrs mean (8hrs for CO and O 3 ) data and health breakpoint range (CPCB 2015) . However, all the seven pollutants may possibly not monitor at all the stations simultaneously. Largely NAQI is measured if data does exist for at least three pollutants and must include PM 2.5 or PM 10 within the three. Otherwise, data are regarded as inadequate for NAQI calculation. Likewise, at least 16 hours' data is required for sub-index calculation and air quality of a pollutant is the sub-index value of that pollutant. Currently CPCB also provide real time NAQI rooted in a web-based system. The web-based system is programmed for the continuously monitoring stations whereas for manual monitoring stations an NAQI calculator has developed to obtain the NAQI value.

Calculation procedure of NAQI is briefly outlined following CPCB (2015).

Principally two steps are implicated to formulate an NAQI- Second: Combination of sub-indices to obtain the NAQI.

Formulation of sub-indices (I 1 , I 2 , I 3 ...., In) for n pollutants (X 1 , X 2 , X 3 ...., X n ) are measured using sub-index functions. Every sub-index corresponds to an association between pollutant concentration and health impact. Combination of sub-indices is simply mathematical summation or multiplication or a maximum operator.

Sub-index function symbolizes the relationship among pollutant concentration X i and subsequent [eq. 8]

After declaration of three weeks of lockdown starting from 24 th of March, 2020, pollution of the megacity Delhi has witnessed substantial diminution of the pollutants (Figure 2 and Table 4 ).

Especially, during the study period PM 10 , PM 2.5 , NO 2 and CO concentration have shown significant declining trends (Figure 2a 

April (lockdown started on 24 th March) in NCT Delhi, India 

In order to minimize the movement and social contact of the people as it could be expected strict measures have been implemented to execute the lockdown. This has substantially reduced the movement of vehicles and the closing of industries, restaurants, shops, administrative centers and many others. This has caused drastic improvement of air quality particularly the primary dominated ones like PM 10 , PM 2.5 , NO 2 and CO (Figure 4 to Figure 7) .

The most momentous dissimilarity is evident for PM 10 ( Figure 4) NCT Delhi is a low SO 2 city (Appendix 2) because of its interior location beyond the sea, since the majority of this pollutant starts off from shipping emissions (large cargo ships, cruises and ferries). For this reason concentration of SO 2 in NCT Delhi usually remains much below the acceptable limit ( Figure 2c ) and during this lockdown period SO 2 concentration has experienced slight decrease in comparison to the pre-lockdown phase. On the other hand it is a widely accepted fact that NH 3 originated from the non-agricultural sources is negligible (Sutton et al. J o u r n a l P r e -p r o o f 26 1995). Therefore, concentration of NH 3 is also much below the acceptable limit ( Figure 2g ).

However, significant decrease in NH 3 concentration during the lockdown phase (Appendix 3) is due to the fact that petrol engine vehicles comprise a foremost cause of urban NH 3 (Kean et al. 2000; Kirchner et al. 2002) and during lockdown transportation activity strictly restricted.

In order to supplement the PM 10 and PM 2.5 observations as highlighted in the earlier sub-sections, we have explored the 24hrs pattern of concentration of the two pollutants over the last four years (from 2017 to 2020) for the same two months window (i.e. March and April) (Figure 9 ). and -38.68% respectively. The maximum concentration of PM 10 was during 2017 and that of PM 2.5 was during 2017 counting as high as 398.80μg/m 3 and 185.90μg/m 3 respectively. This has reduced to 110μg/m 3 (-72.42% maximum reduction) and 94μg/m 3 (-49.44% maximum reduction) respectively during 2020. The results again are a sign that implementation of lockdown may lead to substantial improvement of the air quality and could be put into practice as an alternative measure for pollution reduction. This results in gathering of local and transported pollutants and augmentation of pollution level during the season. Therefore, in order to consider lockdown as an alternative policy measure once or twice a year in a long-distance race, examination of seasonal variation of pollutant concentration with respect to regional meteorological conditions is also necessary. Appendix 4,

Appendix 5 and Appendix 6 may supplement this type of future research to the scientific community.

The correlations between different air pollutants concentration in NCT Delhi during the study period (i.e. 3 rd March to 14 th of April) are shown in Figure 10 . The daily (24hrs) average concentration of PM 2.5 is highly correlated with the daily average concentration of SO 2 (r = 0.59), NO 2 (r = 0.35) as well as 8hrs average concentration of CO (r = 0.45). Likewise, the daily average concentration of PM 10 is also strongly correlated with the daily average concentration of SO 2 (r = 0.47), NO 2 (r = 0.46), NH 3 (r = 0.30) as well as 8hrs average concentration of CO (r = 0.39). This visibly implies that the augmented control of regional transport activity compared to local contributions in the mega city is the key responsible factor for the reduction of pollutants concentration ) as during the lockdown period the regional transportation has Mega cities of India are often listed within the world's topmost polluted cities that exceed the ambient air quality standard and therefore a comprehensive account of air quality improvement in the megacity Delhi has international relevance of its own. Lockdown measures in different parts of the world fortunately have brought opportunity to rationalize human impact on the environment. Therefore results of the present article may help to rethink how far we are responsible for our misery. It may also help to consider whether lockdown would be an unconventional measure for restoring the environment and providing a quality ecosystem to the urban people. Because in urban areas in aim of fulfilling the target economic growth often the sources of ecosystem services are ignored due to which people undergo health threat. The dreadful virus in one hand threatening our life and on the other hand the mechanism of the environmental restoration process is also going on. Hence, global concern for air pollution has lead to draw significant attention for analyzing air pollution in the course of the pandemic. In

China about 30% NO 2 and 25% carbon emission have reduced in the lockdown state (Lauri 2020; Jeff 2020). Study conducted by Watts and Kommenda (2020) also reported a temporary cut of air pollutants amid industrial shutdown in this period. Cadotte (2020) also identified diminishing air pollutants over the major cities of the world where the outbreak of COVID 19 is very strong. Ogen (2020) found a strong linkage between the concentration of NO 2 and fatal outcome caused by COVID-19.Study of Coccia (2020) reveals that the acceleration and vast dispersion of COVID-19in north Italy province capitals has a high connection with air pollution particularly PM 10 and Ozone. There are quite a few other study concerning changes in air quality during the lockdown amid SARS-CoV-2 epidemic with special reference to many areas throughout the globe listed in table 5.Therefore, the result outlined in the present swat is not an isolated one as improvement of air quality due to lockdown is also evident throughout the world. Regions with poor air quality are associated with higher mortality rate. Lockdown in some cities led to upgrading in air quality and lessened premature deaths. There is a considerable relationship between air pollution and COVID-19infection -Isaifan (2020) -Wang and Su (2020) Accelerated transmissions of COVID-19are principally by means of "air pollution-to-human transmission" rather than "human-to-human transmission".

Coccia (2020) In the present article the effect of lockdown (since the third week of March 2020) imposed in order to restrict the rapid spread of COVID-19 pandemic in India on the air quality of the National Capital City Delhi has been assessed based on National Air Quality Index and concentration of seven major pollutants. Delhi is internationally recognized for its extreme pollution level. Among the selected pollutants PM 10 and PM 2.5 have witnessed maximum reduction followed by NO 2 , CO and NH 3 . In compare to the past three year average concentration of PM 10 and PM 2.5 has decreased by about -57% and -33% respectively. On a contrary there is a slight increase in O 3 concentration which is expected to be primarily due to the decrease in the concentration of NOx and particulate matter. Moreover, as anticipated, a considerable reduction in NAQI is observed during the window period of lockdown throughout guideline of lockdown has been obeying, the air quality improvement is found high there.

Therefore study is thought to be a useful supplement to the regulatory authorities that may lead to rethinking of the existing regulatory plans and may provide assurance towards implementing strict alternative measures like short term (2 to 4 day) lockdown in aim to control air quality.

The study reported here is only highlighted the changes in air quality during the lockdown period. However, in order to implement short term (2-4 day) lockdown as an alternative policy measure for pollution reduction and its vis-à-vis effect on economy need to be study rigorously.

Because cost effectiveness will be one of the key issue to the policy-makers while deciding such control measures. Moreover, with inter-seasonal disparity in the meteorological condition, concentrations of pollutants significantly differ in a region. Therefore, to facilitate fruitful implementation of this type of measures once or twice a year in a long-distance race in-depth analysis of the seasonal change in air quality in relation to regional meteorological condition is also required to be studied.

Quantitative evaluation of source interventions for urban air quality improvement-A case study of Delhi city

Evaluation of emissions and air quality in megacities

Particles, air quality, policy and health

Enhanced secondary pollution offset reduction of primary emissions during COVID-19 lockdown in China

Indian Council of Medical Research, Public Health Foundation of India, Institute for Health Metrics and Evaluation. India: Health of the Nation's States-The India State-Level Disease Burden Initiative

What caused severe air pollution episode of

On-road measurement of ammonia and other motor vehicle exhaust emissions

Ammonia emissions from vehicles and the effects on ambient air concentrations

Forecasting of air quality index in Delhi using neural network based on principal component analysis

The influence of odd-even car trial on fine and coarse particles in Delhi

Development of an aggregate Air Quality Index for an urban Mediterranean agglomeration: Relation to potential health effects

Air pollution and symptoms of depression in elderly adults

Development of fuzzy air quality index using soft computing approach

Informing the public about air pollution

Statistics Related to Climate Change-India

Ministry of Environment, Forest and Climate Change (MoEFCC), Government of India

Government of India

An analysis of the annual and seasonal trends of air quality index of Delhi

Notification Issued for Introduction of BS IV Compliant Four Wheel Motor Vehicle. Ministry of Road Transport and Highways, Govt

COVID-19 pandemic and environmental pollution: A blessing in disguise

Measuring air quality over large urban areas: development and application of an air pollution index at the urban area of Naples

Who changed Delhi's air

National Capital Region Regional Plan. Draft Revised Regional Plan 2021, National Capital Region

A quantitative evaluation of the pollutant standards index

Air pollution index systems in the United States and Canada

Environmental Indices: Theory and Practice

Chemical characterization of atmospheric PM in Delhi, India, during different periods of the year including Diwali festival

Biofuel Roadmap for India

Air quality in Brunei Darussalam during the 1998 haze episode

Air pollution in Delhi: its magnitude and effects on health

Environmental perspective of COVID-19. Science of The Total Environment

Directorate of economics & statistics. New Delhi: Government of NCT of Delhi

Urban adaptation to climate sensitive health effect: Evaluation of coping strategies for dengue in Delhi

Effect of restricted emissions during COVID-19 on air quality in India

Effect of restricted emissions during COVID-19 on air quality in India

Ontario's Air Pollution Index and Alert System

Cost-effective electric vehicle charging infrastructure siting for Delhi

Lockdown caused by COVID-19 pandemic reduces air pollution in cities worldwide

Vehicle Sales and Projections. Society of Indian Automobile Manufacturing, Government of India

Air quality trends and potential health effects-development of an aggregate risk index

Estimating the public health burden attributable to air pollution: an illustration using the development of an alternative air quality index

Assessment of the magnitude of ammonia emissions in the United Kingdom

Formation of an air pollution index

A PROPOSED UNIFORM AIR POLLUTION INDEX

Air pollution indices: a compendium and assessment of indices used in the United States and Canada. The Council

Delhi: New writings on the megacity

Changes in air quality during the lockdown in Barcelona (Spain) one month into the SARS-CoV-2 epidemic

Environmental Protection Agency 451: K-94-001 Environmental Protection Agency

United Nations, 2016. The world's cities in 2016

revision of world urbanization prospects

Comparing urban air quality in Europe in real time: A review of existing air quality indices and the proposal of a common alternative

Severe air pollution events not avoided by reduced anthropogenic activities during COVID-19 outbreak. Resources, Conservation and Recycling

Ambient air pollution: a global assessment of exposure and burden of disease

Preventing disease through healthy environments-towards an estimate of the environmental burden of disease. / Prüss-Üstün A, & Corvalán C

WHO Global Urban Ambient Air Pollution Database

WHO Global Urban Ambient Air Pollution Database (Update

Ambient Air Pollution: a Global Assessment of Exposure and Burden of Disease. World Health Organization (WHO)

State of Global Air: A Special Report on Global Exposure to Air Pollution and its

Burden of Disease from Ambient Air Pollution for 2012

The Cost of Air Pollution: Strengthening the Economic Case for Action. The World Bank Group

Study of intra-city urban heat island intensity and its influence on atmospheric chemistry and energy consumption in Delhi