COVID-19 lockdown and air quality of SAFAR-India metro cities

doi:10.1016/j.uclim.2020.100729

Urban Climate

Volume 34, December 2020, 100729

https://doi.org/10.1016/j.uclim.2020.100729 Get rights and content

Highlights

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The COVID-19 lockdown SAFAR data of the major pollutants compared with past several years (2013 to 2019) of quality assured data in 4 Mega cities of India.
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A sharp decline observed immediately after lockdown, by 60–65% in NO₂ levels and by 30–50% in PM_2.5 and PM₁₀ levels.
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Reductions in PM_2.5 and PM₁₀ (~50%) is higher in Delhi and Ahmedabad as compared to Mumbai and Pune.
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PM_2.5 and PM₁₀ levels in Pune were below national standards while 3.7% data of PM_2.5 in Delhi exceeded the permissible limit during lockdown.
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Results are likely to have implications to policy framework and control strategies.

Abstract

A drastic decline in the sources of emissions of pollutants under COVID-19 induced lockdown resulted in an unprecedented trends in most hazardous pollutants PM_2.5, PM₁₀ and NO₂ in India. To realize the impact of lockdown in the concentrations of PM_2.5, PM₁₀ and NO₂, we compared the trend of lockdown period (20nd March to 15th April) with several (3–7) years of past data in four Indian mega cities (Delhi, Pune, Mumbai, and Ahmedabad) of different micro-climate and geography. The significant reduction in the concentrations of NO₂ in the ranges of ~60–65% is noticed in four megacities within the lockdown period when compared with the averaged data of past years. However, relatively low reduction in PM_2.5 (~25–50%) and PM_{10 (}~36–50%) is observed and city to city variation is found to be significant. The prevailing secondary aerosol formation and enhancement of any natural source of emissions could be some factors preventing PM_2.5 levels to go down significantly. Under near negligible fossil fuel emission, contrary to the expectation, an increase in the ratio as compared to normal scenario is observed in Delhi on some days whereas on some selected days, PM_2.5/PM₁₀ ratio is found to decline significantly.

Graphical abstract

Bar diagram indicates the percentage reduction during COVID-19 Lockdown period in the year of 2020 in four megacities including Delhi, Ahmedabad, Mumbai and Pune of India with respect to the mean of previous years for the same period.

Introduction

Air pollution level in urban cities has increased over the years due to rapid urbanization and industrialization where anthropogenic emissions such as vehicle exhaust and industrial process contribute substantially to air pollution (Harley et al., 2005; Sahu et al., 2011a; Yadav et al., 2019a). These sources can emit a wide range of particulate matter (e.g. PM_2.5 and PM₁₀) (Beig et al., 2020a; Fuzzi et al., 2015; Yadav et al., 2017) and trace gases (Maji et al., 2020; Streets et al., 2003). A new type of transmittable virus, afterwards named corona (COVID-19) was identified first time in Wuhan city in the central Hubei Province of China in the end of December 2019 (Jing, 2020; Zhu et al., 2020). Within 2–3 months, the transmittable disease had spread in many countries such as Africa, Asia, America, Europe and Oceania of the world and became global pandemic (WHO, 2020). Therefore, the worldwide countries have decided to restrict free movement, encouraging social distancing, and even locking the cities based on their specific condition to control the spread of COVID-19. The first positive COVID-19 case in India was identified on January 30th, 2020 and the cases jump in the first week of March (https://www.mohfw.gov.in/). To prevent the growth of its transmission, India fully locked down all states with 1.3 billion people and strictly restricted human mobility, shutting down business, social activities, transport (flights, trains and vehicles), shops, cinema complex, academic activities and economic activities from 25 March 2020 (Chandrashekhar, 2020; Sharma et al., 2020; Beig et al., 2020b). The condition has been worsening day by day due to epidemic disease which is affecting human life and economy at global level despite lockdown. The worldwide COVID-19 pandemic has affected more than ~3 million people as of 30 April 2020 (https://coronavirus.jhu.edu/map.html). At the same time as on 30 April 2020, the COVID-19 has affected ~33,062 people and caused ~1079 deaths in India (https://coronavirus.jhu.edu/map.html). Therefore, the fast spread of COVID-19 became a global health challenge while COVID-19 lockdown has improved environmental conditions like improvement in air quality for the moment. The reduction in air pollution has been observed by satellite in other countries like China, Italy, Spain, and France (ESA, 2020; NASA, 2020). On the other hand, the air quality of many cities such as Delhi, and Mumbai of India has also improved to good category (Singh and Chakraborty, 2020). Satellite images recorded using Copernicus Sentinel-5P satellite in March and April 2020 indicated a clear reduction in traffic and combustion related pollutants in India (https://earthsky.org/earth/satellite-images-air-pollution-india-covid19). Furthermore, recent studies have reported the significant improvement in air quality in Indian cities. For Example: Mahato et al. (2020) considered the period (3rd March to 14th April 2020) to study the change in the trends of PM₁₀, PM_2.5, NO₂ and CO in Delhi and reported 40–50% improvement in the national air quality index during the COVID-19 lockdown as compared to pre-lockdown in 2020 using Central Pollution control Board (CPCB) real-time air quality data. Sharma et al. (2020) reported around 43, 31, 10, and 18% reduction in PM_2.5, PM₁₀, CO, and NO₂, respectively during lockdown period in 2020 by comparing the previous year (2017–2019) using CPCB real-time air quality data in different regions of India. Singh et al. (2020) reported the significant reduction in PM_2.5, PM₁₀ and NO₂ during the COVID-19 lockdown period (25th March to 03th May) in 2020 by comparing the most recent previous year (2017–2019) using CPCB real-time air quality data from 134 stations over India. Navinya et al. (2020) considered the COVID-19 lockdown period (6 weeks) and reported a large reduction in PM_2.5, PM₁₀ and NO₂ in northern regions of India in comparison to the 2019 year. Jain and Sharma (2020) considered a shorter period (25th March to 6th April 2020) and reported significant reduction PM_2.5, PM₁₀, NO₂ and CO during the lockdown with comparison to the before lockdown in 2020 in Delhi and other megacities using CPCB real-time air quality data. Srivastava et al. (2020) reported the improvement in air quality over Lucknow and New Delhi while Kumari and Toshniwal (2020) have shown a lesser reduction in smaller cities other than metropolitan cities. Additionally, the data in the studies for comparison was limited to recent past years. On the other hand, some studies have reported the excessive health risk and mortalities linked up with air pollution could have reduced during the lockdown period (Dutheil et al., 2020; Chen et al., 2020a, Chen et al., 2020b). Combustion related pollutants such as particles and nitrogen dioxide (NO₂) are the major pollutants affecting human health. PM_2.5 is a common reason for adverse health effects such as chronic obstructive pulmonary disease (COPD) and lower respiratory infection (LRI) causing death of over ~3 million people at global level (GBD, 2018). NO₂ is the most important cause of childhood asthma in urban atmospheres of the world (Achakulwisut et al., 2019). Moreover, the air pollution is the largest environmental health risk. Several studies have been done on short term control measures for betterment of air quality all over the world. For example: 1. Levy et al. (2006) reported a measurable role on air quality during the Democratic National Convention in Boston in 2004 due to road closures. The study highlights that such events help us to understand the air pollution and their sources. 2. Li et al., 2019a, Li et al., 2019b have studied the role of control measures on various ambient pollutants during the G-20 summit in Hangzhou in the year of 2016 and observed short-term betterment in air quality. 3. Yi and Sung (2018) observed reduction in PM_2.5 levels in Yeongdong, South Korea, during a temporary shutdown of power plants. In India, odd-even strategy has been regulated in the year of 2016 in New Delhi to improve the air quality with minor changes (Chowdhury et al., 2017). The role of control measures on distributions of air pollution is still not clear in India. Therefore, understanding the role of COVID-19 lockdown for betterment of air quality in the troposphere provides a unique opportunity to study processes and implications of policy changes to reduce air pollution in future. Pan-India COVID-19 lockdown was announced officially from 25th March 2020. However, there are two major reasons for considering data as 20th March rather than 25th March: (a) These 4 cities were worst affected by COVID-19 and provincial governments in these states started restrictions well before the national lockdown announced. In Mumbai and Delhi where panic gripped even a few days earlier than that of 20th March and all emission activities cane to a halt whereas in Ahmedabad and Pune, it's around 20th March when cities made a deserted look. (b) The Government of India (Prime minister) announced “Janata Curfew” for a day on 22nd March which was more of voluntarily but it was complete shutdown and thereafter nation was virtually shut. Although provincial lockdown, Janata curfew, national lockdown had different dates but we applied our judgment and also observed the declining trend in pollutants and decided to keep data of collective lockdown as 20th March as our best judgment to keep uniformity for all cities. The present study reveals the role of COVID-19 lockdown on PM_2.5, PM₁₀ and NO₂ in four Indian megacities including Delhi, Ahmedabad, Mumbai and Pune by comparing the data of identical period for previous (3–7) years. Therefore, the comparison of air pollutants in the previous years would help understand and quantify the possible consequence of restricted emissions during the lockdown period.

Section snippets

Topography, climatology and emissions

Our study is focused on four megacities viz., Delhi, Ahmedabad, Mumbai and Pune of northern and western part of India are shown in Fig. 1. In all these cities, anthropogenic emissions are dominated by fossil fuel emissions, besides others. Delhi (28.7° N, 77.1° E and 216 m ASL) is the capital city of India and highly urbanized landlocked megacity which is located in the northern part of India with ~17 million inhabitants with annual mean growth rate of 1.92% (http://census2011.co.in). Delhi has

Variability in PM_2.5, PM₁₀ and NO₂ during Covid-19

The time series plots of daily means of PM_2.5, PM₁₀ and NO₂ during COVID-19 lockdown period (20 March −15 April 2020) with comparison to the same period of previous years in Delhi, Pune, Mumbai and Ahmedabad are shown in Fig. 3. Overall, the daily mean concentrations of PM_2.5, PM₁₀ and NO₂ show clear trends with the lowest in the year of 2020 during COVID-19 lockdown period and highest in the previous year for the same period in all cities. The daily mean concentrations of PM_2.5 were in the

Conclusions

The Indian mega cities have become one of the most polluted cities across the world that often crossed the permissible limit of air quality standard. Amid catastrophe, the temporary control measure in India has provided a unique opportunity to realize the impact of decrease in human mobility on the environment. The time series variations in ambient concentrations of PM_2.5, PM₁₀ and NO₂ were examined in four megacities including Delhi, Ahmedabad, Mumbai and Pune of India during COVID-19 lockdown

CRediT author statement

GB conceived and designed the study and provided overall supervision. RY drafted the paper with final analysis. AR, VA, NK and SB did the detailed analysis, and rest of all other authors critically edited and made value addition to the paper.

Declaration of Competing Interest

The authors affirm that they have no known competing financial interests or personal relationships that could have appeared to influence the work informed in the manuscript.

Acknowledgement

The primary funding for this work is from core research project of Indian Institute of Tropical Meteorology, Pune (IITM) including PROMOTE (APHH) project. Authors are grateful to the Director, IITM and Secretary, Ministry of Earth Sciences (Govt. of India) for the encouragement and support.

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Citation Excerpt :
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COVID-19 lockdown and air quality of SAFAR-India metro cities

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Topography, climatology and emissions

Variability in PM2.5, PM10 and NO2 during Covid-19

Conclusions

CRediT author statement

Declaration of Competing Interest

Acknowledgement

The Lancet Planetary Health

Environ. Pollut.

India. Atmos. Environ.

Sci. Total Environ

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Bull. Environ. Contam. Toxicol.

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Atmos. Environ.

Atmos. Res.

Environ. Pollut.

Environ. Pollut.

Urban Clim.

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System of air quality forecasting and research (SAFAR-India). GAW report no. 217

SAFAR-High Resolution Emission Inventory of Mega City Delhi −2018

Variability in PM_2.5, PM₁₀ and NO₂ during Covid-19