15 COVID-19 Pandemic: An Unprecedented Blessing for Nature
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been rising by about 1% per year [44]. Sulphur dioxide (SO 2 ) is one of the primary
forms of sulphur in the atmosphere other than dimethyl sulphide ((CH 3 ) 2 S) and
hydrogen sulphide (H 2 S). SO 2 is a toxic gas produced during burning of fossil fuels
and industrial activities. About 66.6% of SO 2 comes from human sources. Each year
anthropogenic activities such as combustion of fossils fuels add approximately 100
million metric tons of sulphur to the global atmosphere primarily as SO 2 [26].
A reduction in the emissions of CO, CO 2 and SO 2 was also observed globally.
Querre et al. [44] estimated that by early April 2020, the daily global CO 2 emissions
have declined by 17%, when compared with the mean 2019 levels. A similar decline
of about 1 million tons of carbon emissions (i.e. 25%) has been reported for China
by Wang and Su [6]. The mentioned per cent decline in China is equivalent to 6% of
global emissions over the same period. An overall reduction in the carbon foot print
was observed between −5.6 and −10.6 Mt CO 2 (20%) during the lockdown in Italy
[45] compared to the same period in 2019. A decrease in the concentration of CO
and SO 2 was also observed in the lockdown. According to Wang and Su [6], China
had an overall reduction of 6 and 21% for CO and SO 2 , respectively. A reduction in
CO and SO 2 levels was recorded to be 22 and 15% for Shanghai [31], 23 and 4%
for Wuhan [21], 5 and 7% for northern China [8] and 20% and 16% for 366 urban
areas in China’s mainland [25]. Other countries which have a reported decline in
these gases are Malaysia (CO 25–31%; SO 2 9–20%) [37], Sau Paulo, Brazil (CO
65%) [41], Rio de Janeiro, Brazil (CO 30–49%) [46], Milan, Italy (CO 58%; SO 2
25%) [39], Kazakhstan (CO 49%) [10] and Morocco (SO 2 49%) [42]. Most of the
studies in India showed a declining trend in the concentration of CO and SO 2 during
the lockdown [20, 22, 23, 34, 35]. The levels of CO and SO 2 in some of the urban
cities of India such as Bangalore, Chennai, Delhi, Gujarat, Mumbai, Nagpur were
reduced by 24% and 81%, 24% and 69%, 30% and 18%, 25% and 40%, 46% and
47%, and 63% and 91%, respectively [20, 22, 35]. Navinya et al. [35] estimated the
overall reduction for CO across the cities of India as 14%.
Another important pollutant that was monitored and documented in research articles is O 3 . O 3 is a compound which forms a protective shield known as the ‘ozone
layer’ in the stratosphere. The layer screens out the harmful rays and ultraviolet
radiations. However, O 3 formation in the troposphere acts as a nuisance pollutant
which threats human-health (respiratory diseases), vegetation (destroys cell lining in
plants) and materials [1]. Human sources such as industrial processes and vehicular
emissions are the primary reasons for the formation of ground-level O 3 . Unlike the
other major pollutants, O 3 showed an incrementing trend at places such as Brazil
[41], China [31, 32], France [47], India [20, 22], Italy [39, 45] and Kazakhstan [10]
(Table 15.1).
15.2.1.3 Particulate Matter and Aerosol
Apart from the gases, the Earth’s atmosphere also consists of various airborne
microorganisms (bacteria and fungi) and particles such as dust, salt, soot pollens and
ice. An aerosol is a suspension of solid particles or liquid droplets (or a combination
357
been rising by about 1% per year [44]. Sulphur dioxide (SO 2 ) is one of the primary
forms of sulphur in the atmosphere other than dimethyl sulphide ((CH 3 ) 2 S) and
hydrogen sulphide (H 2 S). SO 2 is a toxic gas produced during burning of fossil fuels
and industrial activities. About 66.6% of SO 2 comes from human sources. Each year
anthropogenic activities such as combustion of fossils fuels add approximately 100
million metric tons of sulphur to the global atmosphere primarily as SO 2 [26].
A reduction in the emissions of CO, CO 2 and SO 2 was also observed globally.
Querre et al. [44] estimated that by early April 2020, the daily global CO 2 emissions
have declined by 17%, when compared with the mean 2019 levels. A similar decline
of about 1 million tons of carbon emissions (i.e. 25%) has been reported for China
by Wang and Su [6]. The mentioned per cent decline in China is equivalent to 6% of
global emissions over the same period. An overall reduction in the carbon foot print
was observed between −5.6 and −10.6 Mt CO 2 (20%) during the lockdown in Italy
[45] compared to the same period in 2019. A decrease in the concentration of CO
and SO 2 was also observed in the lockdown. According to Wang and Su [6], China
had an overall reduction of 6 and 21% for CO and SO 2 , respectively. A reduction in
CO and SO 2 levels was recorded to be 22 and 15% for Shanghai [31], 23 and 4%
for Wuhan [21], 5 and 7% for northern China [8] and 20% and 16% for 366 urban
areas in China’s mainland [25]. Other countries which have a reported decline in
these gases are Malaysia (CO 25–31%; SO 2 9–20%) [37], Sau Paulo, Brazil (CO
65%) [41], Rio de Janeiro, Brazil (CO 30–49%) [46], Milan, Italy (CO 58%; SO 2
25%) [39], Kazakhstan (CO 49%) [10] and Morocco (SO 2 49%) [42]. Most of the
studies in India showed a declining trend in the concentration of CO and SO 2 during
the lockdown [20, 22, 23, 34, 35]. The levels of CO and SO 2 in some of the urban
cities of India such as Bangalore, Chennai, Delhi, Gujarat, Mumbai, Nagpur were
reduced by 24% and 81%, 24% and 69%, 30% and 18%, 25% and 40%, 46% and
47%, and 63% and 91%, respectively [20, 22, 35]. Navinya et al. [35] estimated the
overall reduction for CO across the cities of India as 14%.
Another important pollutant that was monitored and documented in research articles is O 3 . O 3 is a compound which forms a protective shield known as the ‘ozone
layer’ in the stratosphere. The layer screens out the harmful rays and ultraviolet
radiations. However, O 3 formation in the troposphere acts as a nuisance pollutant
which threats human-health (respiratory diseases), vegetation (destroys cell lining in
plants) and materials [1]. Human sources such as industrial processes and vehicular
emissions are the primary reasons for the formation of ground-level O 3 . Unlike the
other major pollutants, O 3 showed an incrementing trend at places such as Brazil
[41], China [31, 32], France [47], India [20, 22], Italy [39, 45] and Kazakhstan [10]
(Table 15.1).
15.2.1.3 Particulate Matter and Aerosol
Apart from the gases, the Earth’s atmosphere also consists of various airborne
microorganisms (bacteria and fungi) and particles such as dust, salt, soot pollens and
ice. An aerosol is a suspension of solid particles or liquid droplets (or a combination