16
COVID-19 NATIONWIDE LOCKDOWN OF 2020- OBSERVATIONS ON
PROMINENT POLLUTANT IN THE COASTAL CITIES OF CHENNAI AND
MUMBAI
Priyanka Puri
Associate Professor, Dept. of Geography, Miranda House, Delhi University, Delhi, India
Email: priyanka.puri@mirandahouse.ac.in

How to cite this paper:
Puri, Priyanka (2022) Covid19 Nationwide Lockdown of
2020-Observationson
Prominent
Pollutantthe
Coastal Cities of Chennai andMumbai, Journal of Global
Resources, Vol. 08 (02)DOI:
10.46587/JGR.2022.v08i02.016

Received: 20 March 2022
Reviewed: 25 April 2022
Revised: 29 April 2022
Final Accepted: 24 June 2022

Abstract: The pan-India Lockdown of 2020 due to COVID19 pandemic as a turning point in impacting theenvironment and generating new trends lends it to specificanalysis. In this context, the urban scenarios are mostwidely discussed and the Indian metropolitan cities standpertinent examination. While many studies exist on
analyzing air quality and air quality parameters in
distribution and varying trends, works on highlighting thenature of dominant pollutant in time and space is notobserved. The current study is distinctive in method as it
tends to observe the evolving nature and distribution ofprimary pollutant in the air of two coastal cities of Chennai
and Mumbai for every day of the COVID-19 nationwide
Lockdown period of 2020. A comparative analysis isfurther attempted by taking air quality data for the period ofnational Lockdown in the matrix of 92*7 plus 92*4 time
periods for Mumbai and Chennai respectively. Results
reveal that despite being coastal in location, both cities
have a distinct nature and distribution of Prominent
Pollutant during this period. An examination of such a kindis pertinent in outlining the nature of pollution and its
geographical dimensions across an urban area. This canhelp in the observation and management of pollution
problem in a practical dimension.
Key words: Air Pollution, COVID-19, Chennai, Mumbai,
Pollutant, Prominent

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Introduction
The metropolitan cities of Chennai and Mumbai both face the concern of air pollution indifferent forms (India P. T., 2022; Omjasvin, 2022). The problem fluctuates from moderate air
quality to poor air quality levels (India P. T., 2021; India P. T., 2022). Chennai has been
observed as being in the five top- most polluted cities of India with pollution levels of more than
five times the World Health Organisation standards (Omjasvin, 2022). What is most significant
in this regard is the fact that as per records, the city’s levels of pollution are either at the lower
side or are moderate because of the breeze from the sea; otherwise it would have faced severe
pollution levels (Kurian, 2019; Environment, 2022). Transport and industry are highlighted tobe the main causes of this problem with particulate matter 2.5 being at levels amongst thehighest in the country (Express, 2021). Along with this, heavy metal traces have also beenfound in the city’s air which is very disturbing (Prabhakar, 2021). However, at times it also
reports the cleanest air among Indian metropolitan cities but that is mainly due to natural
factors, particulalry winds from the sea (Ray & Lahiri, 2010). But in general, a fall in air quality
is a cause of unprecdented perturbation for the city (Thirumurthy, 2021).
Mumbai is the capital of the state of Maharsahtra and is the commercial capital of thecountry (Chakravarthi, 2021; Maharashtra, 2022). It is also facing the problem of population
growth and vehicular traffic and other urban concerns (Grover & Singh, 2019). High levels of
air pollution make the city second in detahs due to air pollution (Borwankar, 2021). Currently,
the city is setting trends with highest levels of winter air pollution (Chatterjee, 2020), high levelsof coal usage in industrial centers causing severe deterioration in air quality making it
equivalent to the polluted Delhi’s air (Staff, 2021),doubling of vehicle generated pollution(Bhalerao, 2021) and is amongst the top 10 polluted cities of the world (Sethi, 2022).
In above such contexts, it becomes intetresting to record which pollutant/s are theactual cause of concern for both the cities and which areas of the cities are facing maximum
concern also becomes significant. Besides, the Lockdown period has in general highlighted an
improvement in the air quality of Indian cities (Bedi, Dhaka, Vijay, Aulakh, & Gill, 2020; Singh& Tyagi, 2021).
Literature Review
Pollution is defined as an accretion of contaminants in an environment (Brusseau, Pepper andGerba, 2019) which have a capacity to harm (Spellman, 2017). Also called environmental
pollution (Nathanson n.d.; Mackenzie and Turrentine, 2021), it is the addition of any solid, liquid
or gas that has the potential to harm. Pollution is an outcome of pollutants (Boechler, Elbaz,
Hanania, Stenhouse, & Donev, 2021), and is commonly present every where (Brusseau,
Pepper and Gerba, 2019). Pollutants are identified as the particles involved in generating
pollution which can harm life and environment (Berg, 2017) due to their ill effects (Boechler,
Elbaz, Hanania, Stenhouse, & Donev, 2021). Pollution can be identified in forms as related toair, water, soil, light and noise (Bradford, 2018) and also radioactive contamination and othercategories (Spellman, 2017) such as plastic pollution (Nathanson, n.d.). Currently, pollution isobserved to be caused by discharges in the Earth’s physical realm largely due to humanactivities (Shafi, 2005). To ‘truly’ understand pollution, the nature and characteristics ofcontaminats requires examination (Brusseau, Pepper and Gerba, 2019).
There are many ways to classify what constiutes a pollutant (Shafi, 2005; Spellman,
2017; Brusseau, Pepper, & Gerba, 2019). Generally observed air pollutants are called ‘Criteria
Pollutants’ (Saxena and Sonwani, 2019; Agency E.P., 2021). These are lead, ground-levelozone, particulate matter, nitrogen dioxide, sulphur dioxide and carbon monoxide gases(Agency, 2021; Organisation, 2021). The study of air pollution can take many forms but theones dealing with the most observed pollutant in time and space for a geographical set up is
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not observed. In the current study, this examination is done for the two coastal cities of IndiaChennai and Mumbai.
Although air pollution study is not simplistic in nature (Lyons & Scott, 1990) as a
combination of location, meteorology and sources of pollution (Shen, et al., 2021) play a rolein determing the nature and amount of pollution (Arya, 1999; Jury, 2020). But still it can beconveniently said that if the nature of the pollutants is known over a space time matrix, thenthe problem can be tackled more practically. Mumbai ranks fifth in the country with regards topollution deaths (Borwankar, 2021) and according to a global study is amongst the top ten
most polluted cities of the world (Sethi, 2022). Despite having a geographical advantage ofbeing located along the sea and subsequent windy conditions, air pollution is a major problem(Borwankar, 2021). Similarly, Chennai city being coastal in nature also shares a geographic
advantage with regards to dispersal of pollutants in air (Chaitanya, 2021) but still air pollution
is a seriously emerging concern (Chaitanya, 2021).
The purpose of this examination is to observe the most Prominent Pollutant/s in the airof these two cities during the historic COVID-19 complete Lockdown periods from 25th March31st May’20. In addition, for a better explanatory analysis, the full month of March is considered.
COVID-19 Lockdown in the country was applied in phases for a time period of three months
and four phases from 25th March to 31st May’20 (Singh S. G., 2020) and the period has been
historic with regards to exceptional improvements in air quality in India as well (Singh &Chauhan, 2020; Sharma, et al., 2020 and Naqvi, et al., 2021).
In this regard numerous studies can be observed as monitoring and measuring air
quality across India and Indian cities particularly with respect to criteria pollutants (Singh &Chauhan, 2020; Sharma, et al., 2020 and Naqvi, et al., 2021). The ease of comparison arises
from the fact that both cities are located along the coast of India and the differences andsimilarities in the nature of prominent pollution will be insightful for examining the air pollution
issue. Mumbai city is located along on the western coastal region of the country and Chennai
on the eastern coastal region, as can be seen in Figure 01.
Study Area
The cities of Chennai and Mumbai are capitals of Tamil Nadu and Maharashtra states of India
respectively. Along with an area of 426 Sq. kms., a total population of 10,971,018 persons in2020 (Review, 2021) and a density of 26,903 persons per square km. (Tamil Nadu, 2021); thedistrict of Chennai a prominent commercial, cultural, educational and economic centre of South
India. In a similar manner, the city also has industrial clusters organised as zones in the North,West, South West and South (Girdonia, 2021). Chennai district is central to the Chennai urban
agglomeration; it is the country’s fourth largest one as per 2011 and is less than half the sizeof Great Mumbai (Srivasthan, 2011). The coastline of the city in the east faces the Bay of
Bengal with a length of coast at 19 kms. (India G. O., 2011).
Mumbai district is surrounded by the waters of the Arabian Sea in its west and south
and Thane Creek in the east (Maharashtra, 2021). Mumbai district has a coastline of about
150 km. in length (Musafir, 2016). With an area of 157 sq.km., population of 20,411,274(Review, 2021), it has a population density of 32,000 persons per sq.km. in 2020 (Review,2021). As a major economic center of the country; the city requires no introduction and is an
economy in operation in itself (Raghavan, 2021). It is the country’s major economic region andthe financial, commercial, industrial and celluloid capital of India.

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Figure 01: Location of Study Area

Source: Author, 2021

It was observed to be the ‘most car congested city’ of the country in 2019 although it’s
total car count is one third of the car count of Delhi (Sun, 2021 b.), the city in the country withthe greatest number of vehicles (Sun, 2021a.).
Methodology
The study is conducted on air quality monitoring data from Central Pollution Control Board(CPCB), Government of India website- https://app.cpcbccr.com/AQI_India. This real time
database provides information on air quality across these stations in the states of the country.
The data available on the website is in the form of Air Quality Index (AQI), amount of various
criteria pollutant and hazardous pollutants during various time of the day (Board, 2021).
Besides this information, the Prominent Pollutant during specific time of the day on an hourly
basis is also provided for air quality monitoring stations in the respective states. To carry thisexamination for the selected time period of COVID-19 Lockdown of 2020 for data for the cities
of Chennai and Mumbai is taken from the mentioned website. Further, to extend this analysis
to a more insightful study, 15 days prior to this Lockdown are also taken. Since post COVID19 unlock was in phases, it did not seem appropriate to include this immediate period forstudy.
For this purpose, data was recorded for each day for these stations from the website.
The time period for data was taken as that of 4.00 pm of the day assuming some kind of activity
might have generated its impact on air. The nature of data is that of statistical ‘population’,
which makes the study quite comprehensive. The only limitation in this case arises from thefact that data during the Lockdown period was not available for some days from the website.
The data base and methodology interaction are systematically depicted as follows:a. Data Collection- This is done on a matrix of 92*7 and 92*4. The total number of days from
1st March- 31st May add up to 92 and for each day data has been recorded for the available
air quality monitoring stations- 7 for Mumbai and 4 for Chennai. The data pertains to theProminent Pollutant as recorded for each day of the selected time period for each station.
This data is then subjected to ‘population’ analysis.

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Details of Lockdown period of 2020- From 25 March’ 20- 31 May’20. The dates for thiswere as under (Desk Net, 2020):• Phase 1: 25 March’ 20 – 14 April’ 20 (21 days) •• Phase 3: 4 May’ 20 – 17 May’ 20 (14 days)•

Phase 2: 15 April’ 20 – 3 May’ 20 (19 days)
Phase 4: 18 May’ 20 – 31 May’ 20 (14 days)

As mentioned above, to make the observations comparative, data from 1st March onwards
is taken for examination.
b. Examination of Population- ‘Population’ here is 92*7 + 92*4= 644+ 368 time points. The
total ‘population’ becomes 1012 points of time. N or the number of elements is 644+368
since both cities are studies as a part of this population. This N is subjected to P analysis
which is an indicator of the proportion of population elements that have a particularattribute. This data is analysed and plotted on the basis of various dimensions as reflectedin the analysis.
c. Spatial Examination- The Prominent Pollutant is observed for its spatial pattern for the time
periods selected for the study and mapped. This information is derived from Sentinel 5P
TROPOMI and MODIS satellite data through the Google Earth Engine Code Editor fromthe Copernicus Sentinel-5 Precursor (Sentinel-5P) mission. This is the first Copernicus
mission for observing Earth’s atmosphere through a collaboration between the European
Space Agency, the European Commission, the Netherlands Space Office, industry, data
users and scientists. The mission has a satellite which holds the Tropospheric Monitoring
Instrument (TROPOMI). The main aim of the Copernicus Sentinel- 5P mission is to carryout measurements in the atmosphere with high space- time resolution for the purpose ofmonitoring & forecasting air quality and climate. Derived from satellite data, the maps areplotted on WGS 84 coordinate reference system with EPGS 4326, with all analysis donein QGIS 3.16 software.
d. Organisation of data- Data pertaining to the study was available from the CPCB website
for the following stations of Chennai and Mumbai respectivelya. Chennai
Alandur Bus Depot, Chennai - CPCB
Manali Village, Chennai - CPCB
Manali, Chennai - CPCB
Velachery Res. Area, Chennai - CPCB

b. Mumbai
Bandra, Mumbai - MPCB
Chhatrapati Shivaji Intl. Airport (T2), Mumbai Airport- MPCB
Colaba, Mumbai - MPCB
Kurla, Mumbai - MPCB
Powai, Mumbai- MPCB
Sion, Mumbai - MPCB
Worli, Mumbai-MPCB

The observations are recorded, described plotted and analysed.
Results and Discussions
The observations for the Prominent Pollutant and its spatio-temporal trend for the cities ofChennai and Mumbai are as follows:
Chennai: Aggregate Prominent Pollutant Analysis
It was observed that there was a shift in the nature of Prominent Pollutant in the city pre andpost Lockdown periods. Prior to the Lockdown and immediately after the Lockdown period forthe month of March, PM (Particulate Matter) 2.5 was the main pollutant with an exceptional
day pre Lockdown recording Ammonia (NH3) as the main pollutant. Post lock down in April
Journal of Global Resources, July 2022, Volume 08 (02) Priyanka Puri P a g e | 1 2 4and May, this trend was altered with Ozone and Carbon Monoxide dominating the Prominent
Pollutant category. The details can be seen in Figure 02.
Figure 02: Chennai- Prominent Pollutant

Source: Author, 2021; data from CPCB (Board, 2021)

PM 2.5 was the Prominent Pollutant pre and immediate post Lockdown with a share of around
50% which came down constantly. Ozone was the Prominent Pollutant for the city during thisperiod with a maximum recorded observation of 131 days out of a total of 644 days.
Figure 03: Chennai- Station wise Prominent Pollutant

Station i- Alandur Bus Depot, Chennai – CPCB Station ii- Manali Village, Chennai – TNPC

Station iii- Manali, Chennai CPCB
Station iv- Velachery Residential Area, Chennai CPCB
Source: Author, 2021; data from CPCB (Board, 2021)

As can be observed from Figure 03., PM 2.5 is gradually replaced as a Prominent
Pollutant by Ozone in April but in May again PM2.5 takes over as the Prominent Pollutant
probably indicating the role of meteorological factors and/or the limited activities that were
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operational during the Lockdown period such as power generation. Manali Village station
exhibited a significant decline in all pollutants after the Lockdown and Ozone turned to be themost dominant pollutant in this period. There is a fluctuation in the dominant pollutant in the
Bus Depot station while the station in the Village has the least fluctuation. Ozone is theProminent Pollutant in the Village station along with Carbon Monoxide in the post Lockdown
period. The residential area of Velachery observed Carbon monoxide as the main pollutant fora major number of days post Lockdown. So, it can be clearly said that post Lockdown period
did induce changes in the nature of air pollution. Out of 368 days of data, 131 days observed
Ozone as the Prominent Pollutant followed by PM2.5 for 118 days.
Mumbai: Aggregate Prominent Pollutant Analysis
For Mumbai’s data, one notable point is that data is not available for some days on the website.
Particulate Matter (PM) 10 as the Prominent Pollutant. Regardless of the Lockdown, this wasobserved as the dominant pollutant throughout the time period. This is a significant
observation.
Figure 04: Mumbai- Prominent Pollutant

Source: Author, 2021; data from CPCB (Board, 2021)

The observations on Prominent Pollutant are indicative that besides human activities,
there is/are other factors which contribute to PM 10 to Mumbai’s air. Otherwise, across all time
periods, there is a variation in the nature or Prominent Pollutant, except in March immediately
after the Lockdown. Ozone takes over as the next dominant pollutant particularly post
Lockdown. Sulphur Dioxide (SO2) exhibits an increase in the month of May. It is also to be
forwarded here that for Mumbai, data was not available for a period of 21 days out of 644 days
which is shown as NA in the diagram.
The observations above indicate that maximum variation in the nature of Prominent
Pollutant is observed in the month of May for all stations, except Worli. On the whole, PM 10
was observed as the most observed pollutant for Mumbai. Ozone is a major contributor as apollutant at Colaba. The Mumbai airport and Worli stations have a uniformity in the nature ofProminent Pollutant.
Spatial Examination
In this analysis, satellite data from Sentinel-5P TROPOMI is derived to highlight thegeographical behaviour of the Prominent Pollutant across both the cities respectively for theselected time periods. The radiation has a tendency to interact with aerosols which are defined
as fine solid and/or liquid particles suspended in the air—before being intercepted by satellite
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sensors. This causes distortion which is a strong indicator of an affirmative correlation with
PM2.5 and PM10.
Figure 05: Mumbai- Station wise Prominent Pollutant

Station i- Bandra

Station ii- Mumbai Airport

Station iii - Colaba

Station iv – Kurla

Station v - Powai

Station vi- Sion

Station vii- Worli
Source: Author, 2021; data from CPCB (Board, 2021)

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OBSERVATION
Chennai
The maps are derived from SENTINEL 5P TROPOMI AND MODIS MCD19A2.006: Terra &Aqua MAIAC Land Aerosol Optical Depth Daily 1km respectively for Ozone and A erosol
Optical Depth(AOD). The geographical distribution of the Prominent Pollutant for the taken
period shows that- PM2.5 was observed for the first two time periods and Ozone for theremaining two. Further, there is no direct satellite measurements of PM 2.5 and PM 10
pollutants and along with ground monitoring AOD is taken as the indicator (Kloog, et al., 2015).
More AOD depth is an indicator of more concentration of Particulate Matter in an area (Kloog,
et al., 2015; Maheshwarkar & Sunder, 2021).This is well supplemented well by ground level
observations. The results depict averages of the data. The value of AOD 047 from SENTINELTROPOMI ranges on a band of -100 to 5000 units with an increasing value indicating an
increasing concentration of aerosols (Agency E. S., 2021).
For Ozone, direct information is available from TROPOMI as Offline Ozone and Near
Real Time. Here, Offline Ozone is taken since this is a mean analysis for the time periods. As
can be observed from satellite data, AOD concentration is declining from high concentration
to a decreased one as the Lockdown period proceeds. It is observed that PM concentration is
declining. Further, in both periods where PM 2.5 is the dominant pollutant, the concentration
is more on the western side of the city. Ozone concentration indicates an increasing trend but
no specific pattern is spatially observed in this regard. Ozone is measured by the satellite as
mol/m^2 (Engine, 2021).
From Figure 06, it can be clearly forwarded that even though PM 2.5 pollutes Chennai’s
air maximum, its concentration over the city constantly declines when human activity is limited
as is observed before the Lockdown and immediately after the Lockdown. In both the time
periods, the western part of the city shows the maximum pollutant concentration indicating
towards some specific activity contributing to the same. AOD can range from a minimum of 100 to a maximum of 5000 units for this optical depth. Next, when Ozone takes over as thedominant pollutant, its concentration shows an increasing trend temporally. However, nospatial trend is observed, probably indicating the presence of certain meteorological and/or
any activity such as power generation or any specific production taking place at that point oftime.
Figure 06: Chennai– Spatial Distribution of Prominent Pollutant

Unit- AOD- absolute units, Ozone - mol/m^2 (Scaling factor not applied)
Source: Author, 2021; derived from Google Earth Engine Code Editor

The pattern of Ozone concentration pre Lockdown was in the western part of the city
showing a similarity with PM2.5 concentration; while in the immediate post Lockdown period,
it shifted to the south of the city, but with an increased value (Engine, 2021). The operation of
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distance factor away from the sea can be observed to be directly operating in affecting theconcentration of pollutants in the city.
MumbaiA similar analysis for the city reveals that PM 10 was the most Prominent Pollutant and its
distribution as discussed above was observed through AOD. PM 10 through AOD analysis
shows that temporally its value has shown only a slight variation for the city temporally. Even
when a short time span of March immediately after the Lockdown is observed, there is a highconcentration of PM 10. Studied at 1000 metres resolution, through the ‘Blue Band’ withwavelength of 0.47um, AOD is measured through Optical Depth 047 by the satellite (Engine,2021).
The maps indicate averages for the respective period of lockdowns. AOD can range
from a minimum of -100 to a maximum of 5000 units for this optical depth and the exact rangeof these values is shown in Figure 07.The spatial pattern highights that the north-eastern partof the city is having the maximum concentration of PM 10. Further, there is a fluctuation in thevalue of AOD across the Lockdown period. This can be proably attributed to natural factors as
pollution causing human activities are not dominant. The main factor is location next to the sea
as has been discussed earlier as well.
Figure 07: Mumbai– Spatial Distribution of Prominent Pollutant

Unit- AOD- absolute units (Scaling factor not applied)
Source: Author, 2021; derived from Google Earth Engine Code Editor

The lowest value of AOD and consequently the Particulate Matter can be said to havedeclined the maximum in the month of May. Geographically, the northern, central and easternparts of the city indicate concentration of pollution. This is also in sync with the fact of location
away from the sea. The Lockdown did record a significant decline in the value of all pollutants
across the city (Borwankar, 2020; Desai, 2022).
Conclusions and recommendations
It can be clearly said that despite being coastal in nature, there is a marked difference in thenature and behaviour of the Prominent Pollutant for both the cities. While Mumbai recorded
PM 10 as the Prominent Pollutant, Chennai had a varying trend with PM 2.5 and then Ozone
arising out of the Lockdown period as the Prominent Pollutant. Besides human activities,
natural phenomena also appear to be influencing the same to an extent. Both the urban centres
have observed an increasing trend of Ozone as the Prominent Pollutant. But it can be definitely
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forwarded that periods of limited human activity such as the Lockdown, do have an influencein changing the spatial and temporal distribution of pollutants. Thus, the nature of pollution canbe said to have a mix of location, processes and activities which tend to generate a pattern. In
the current analysis, the attribute of activities is deleted due to almost an absence of humanactivities due to the complete Lockdown. Hence, a window of studying air pollution is opened
which is very pertinent in many forms. The presence of satellite data makes it all the more
relevant and unprecedented.
In the context of observations, it can be forwarded that pollution is an issue in both thecities. It is recommended to have a spatial outlook at the concern which is largely missing inplanning. This relates to the factors and locations where the geographical extent of thepollutant is the maximum. Since, the study is examining only the prominent pollutant in boththe cities, it is also recommended to study the other criteria pollutant in spatio-temporal extent
so that a broader conclusion can be drawn. This requires a further detailed and a similar
examination.
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Journal of Global Resources, July 2022, Volume 08 (02) Priyanka Puri P a g e | 1 3 1