Air and Water Quality Improvement during COVID-19 Lockdown

Pedro Silva, Mariana Ávila and Márcia Gonçalves

Earth Observation Laboratory, Atlantic International Research (AIR) Centre, TERINOV- Terra Chã, Angra do Heroísmo,

Portugal

Keywords: Earth Observation, Remote Sensing, Copernicus, Sentinel-3A, Sentinel-3B, Sentinel-5P, NO

, PM2.5, PM10,

TSM.

Abstract: COVID-19 pandemic forced many countries to adopt lockdown measures, temporarily closing factories,

diminish maritime traffic and reducing the mobility of people in the cities. Analysis from the Tropospheric

Monitoring Instrument (TROPOMI) and Ocean and Land Colour Instrument (OLCI) on board Europe’s

Sentinel-5P, 3A/B respectively, for the first wave of the COVID-19, have shown a substantial improvement

in air and water quality. More specifically, since COVID-19 lockdown until the end April, Lisbon and Porto

were at their lowest PM10 levels of about 20% and a drop of 33% in 2 years, while Madrid had a significant

drop since lockdown with vales significantly below 2018 levels but still close to 2019 levels. In terms of NO

levels, Lisbon had an historical minimum of the last 2 years, dropping more than 40% during most of April

2020. Finally, Madrid had 2-year lowest level of more than 30% since lockdown. Concerning the water quality

in the Portuguese coastal waters, it was verified an increase in water transparency since confinement started

until May, accordingly to the Total Suspended Matter (TSM) indicator. From February to March, March to

April and April to May there was a reduction in TSM levels of 17%, 37% and 53% respectively.

1 INTRODUCTION

The novel coronavirus disease, COVID-19, became a

pandemic in 11

March 2020. This virus was firstly

identified in the city of Wuhan, China, in December

2019 and causes acute respiratory problems. In order

to protect the population from this pandemic, many

countries adopted lockdown measures, leading

companies to adapt the functions of their workers in

teleworking or lay-off mode. As a consequence, there

was a drastic reduction in the air traffic, motor traffic,

and industrial activity. All of these activities have an

impact in the air and water quality. According to the

World Health Organization, air pollution kills an

estimated seven million people worldwide every year

and that 9 out of 10 people breathe air containing high

levels of pollutants (World Health Organization,

2020). The urban centres of large cities are

characterized by a high population density, high

motor vehicle traffic, and intense industrial activity,

so they are naturally areas with high levels of air and

water pollution. Quantifying the status of pollution

during the lockdown period is an important task for

researchers to understand the effect of the COVID-19

spread on the environment in the short- and long-

term.

The most well-known pollutants from the troposphere

include ozone, carbon monoxide, nitrogen dioxide

and sulfur dioxide. Specifically, nitrogen dioxide

(NO

) is generated by vehicles, heavy industry and

power plants. The EU Ambient Air Quality

Directives limits the concentration of 200 μg/m

(not

to be exceeded more than 18 hours per year) and

annual average below 40 μg/m

. The main effects of

breathing NO2 relates to the increase of probability

of respiratory problems as in high doses it could

inflame the lining of the lungs and reduce immunity

to lung infections, causing problems like coughing,

colds and bronchitis.

Concerning aerosols, the levels of particulate

matter aerosols < 10μM (PM10) have a significant

impact in the air quality. These particulate matter

aerosols are microscopic particles of solid or liquid

matter suspended in the air and are measured in g/m

The main sources of these aerosols include i) human

origin such as industrial processes and product use,

agriculture, commercial, residential and households;

ii) natural our semi-natural sources such as desert

dust, biomass burning and sea salts. The EU Ambient

Air Quality Directives limits the daily average (with

no more than 35 days per year) below 50 μg/m

and

annual average below 40 μg/m

. PM10 affects

Silva, P., Ávila, M. and Gonçalves, M.

Air and Water Quality Improvement during COVID-19 Lockdown.

DOI: 10.5220/0010397201090115

In Proceedings of the 7th International Conference on Geographical Information Systems Theory, Applications and Management (GISTAM 2021), pages 109-115

ISBN: 978-989-758-503-6

109

cardiopulmonary and respiratory health, the immune

system and in last instance can cause lung cancer.

Recent studies found evidence of SARS-Cov-2 RNA

on PM10 air samples and other studies are pointing

towards a relation between PM10 and increased

mortality rate. The reduction in the air traffic, motor

traffic, vessel traffic and industrial activity naturally

has a positive impact on the level of the pollutants

previously referred in the troposphere. This was

confirmed on the 2

March 2020 by NASA and ESA,

that monitored the levels of NO

in China, from 1

January until 25

February and detected significant

decreases in these levels. According to the Ministry

of Ecology and Environment, China, the air quality

went up 11% in the category ‘good’ in as many as 337

cities (Henriques, 2020)

As already mentioned, maritime traffic also had a

sharp decrease during the lockdown, contributing to

an improvement in the water quality in the oceans.

Ocean health has a key role in the human life, as it

produces half of the world’s oxygen, absorbs 50 times

more carbon dioxide than the atmosphere, regulates

the climate, provides food and many other human

demands.

One of the indicators of water quality is the Total

Suspended Matter (TSM) levels, measured in mg/L,

which indicate the amount of suspended particles in

water bodies. Thus, it can be considered a parameter

to evaluate the turbidity of water and its health. Some

of these particles are present naturally in river and sea

waters, such as plankton, fine plant debris and

minerals, while others stem from human activity

(organic and inorganic matter). As TSM levels

increase, the appearance of the water becomes

cloudier as light penetration decreases which has a

negative impact on river and sea biology and can

affect photosynthesis with important effects on

biogeochemistry and life itself. High TSM levels can

also clog fish gills, either killing them or reducing

their growth rate. During the lockdown, it was

verified that the surface water quality of the

Vembanad Lake in India, had major improvements in

the Suspended Particulate Matter (SPM) (Yunus et

al., 2020).

With a visible trend towards improving

environmental qualities during the COVID-19

pandemic shown by several research groups, the

Earth Observation laboratory (EO lab) from Atlantic

International Research Centre (AIR Centre) was also

interested in monitoring the environmental impacts

during lockdown by monitoring air and water quality

in Portugal (Lisbon and Porto) and Spain (Madrid)

between the months of March and May 2020

corresponding to the first wave of the pandemic. The

results were produced through the use of Copernicus

data and services.

2 COPERNICUS IN SUPPORT OF

AIR AND WATER QUALITY

MONITORING

Copernicus is the European Union's Earth

Observation Programme, managed by the European

Comission. It is implemented in partnership with the

Member States, the European Space Agency (ESA),

the European Organisation for the Exploitation of

Meteorological Satellites (EUMETSAT), the

European Centre for Medium-Range Weather

Forecasts (ECMWF), EU Agencies and Mercator

Océan. With its Sentinels Constellation,

Copernicus offer information services in six

thematic lines: Atmosphere, Marine, Land, Climate

Change, Security and Emergency. For air quality,

Sentinel-5P and its instrument on board,

TROPOspheric Monitoring Instrument (TROPOMI)

offer quality data about key atmospheric species.

The Copernicus Atmosphere Monitoring Service

(CAMS) delivers Regional and Global Products

based on data from Sentinel-5P related to air

pollution and health, solar energy, greenhouse gases

and climate forcing.

Sentinel-3A and 3B have on board the Ocean

and Land Colour Instrument (OLCI), a visible

imaging push-broom radiometer with 21 spectral

bands from 400 to 1200 nm offer a large spectrum

of type of data, related to ocean, atmosphere,

and land. Some products range from water

surface directional reflectance, algal pigment

concentration, total suspended matter concentration,

among others.

3 RESULTS AND DISCUSSION

3.1 Air Quality

Figure 1 depicts the timeline of NO

emissions during

the COVID-19 outbreak in Portugal and Spain,

images from European satellite Copernicus Sentinel-

5P using TROPOMI (Tropospheric Monitoring

Instrument). The images show a drastic reduction in

contamination levels due to reduced industrial

activity, which helps mitigate the impact of the

COVID-19 outbreak.

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Figure 1: Tropospheric vertical column of nitrogen dioxide

(NO

) in the Iberian Peninsula in: a) 10

March 2020 and

b) 28

March 2020.

A timeline of NO

emissions in detail for Portugal

and Spain is presented in Figure 2, based on Regional

Products from CAMS service, and generated for 13h

UTC for several days, before and after the COVID

outbreak in Portugal. The difference from this data to

the data in Figure 1 is that the CAMS service digests

hourly values into a model, in this case the Ensemble

median, at the surface level, while data directly from

TROPOMI is representative of the total air column.

At the surface level and at a regional scale, NO

levels

are expressed in μg/m

. Results show a significant

reduction in NO

contamination levels due to reduced

industrial and other anthropogenic activity, both in

Portugal and Spain.

Figure 2: a) to b) – Total column Nitrogen Dioxide in air

for 10-03-2020 and 31-03-2020, respectively, in Atlantic

Regions.

Also, a less detailed analysis of NO

levels for 10

March and 31

March for the Atlantic Region was

carried out and is presented in Figure 3. This analysis

was generated through CAMS’s Global Products, so

the units are expressed in μg/m

. More specifically, it

is visible maritime traffic passing in the Strait of

Gibraltar, which is a sign that maritime commercial

activities continued to operate. Also, is possible to

observe a reduction in Europe, the same is true to the

USA but to a much less extent.

Figure 3: a) to b) – Mass concentration of Nitrogen Dioxide

in air for 10-03-2020, 11-03-2020 (before COVID outbreak

in Portugal); c) to i) 16, 18,20, 22,24,28-03-2020 and 1-4-

2020 respectively (after COVID-19 outbreak).

In Figure 4, are presented yearly NO

emissions

for Portugal and Spain, Lisbon, Porto and Madrid

generated using a 7-day average for daily values

determined at surface level and at 22h UTC, also

using CAMS service. The approach consisted in

verifying the regional NO

emission reduction for

Portugal and Spain and, also, in analysing the trends

for major cities within this territory. As expected, the

emissions for the whole region peak for lower

values, however the curves behaviour dampens local

anomalies that may be observed in specific urban

areas, such as Porto city, as detailed below. In

Portugal and Spain territory, in 2020, there is a

reduction of approximately 26% for April 30

comparing with 2018 and 2019 and scaling for values

above 40% in the first week of April.

At a local scale, on April 30 the NO

emissions

are at their historical minimum since 2018 in Lisbon

(reduction of approximately 4,8% for 2019 and 2018

and more than 40% in the first weeks of April) and

Madrid (30,2% for 2019 and 45,5% for 2018).

However, in Porto there is a significant drop in NO

emissions, but the current level is still above 2019 and

2018, which might be explained due to several factors

such as a different rainy season. Similarly, as for the

concentration of PM10, the concentrations of NO

the air are lower since the lockdown due to COVID-

19 in March for the three cities (20% for Lisbon,

30,7% for Porto and 50% for Madrid).

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111

Figure 4: a) to d) - Historical mass concentration of

Nitrogen Dioxide in air for Portugal, Spain, Lisbon, Porto

and Madrid for 2018 (blue), 2019 (orange) and 2020

(yellow).

The concentration of PM10 was also analysed in

the three cities for the period of January-April 2020

and compared with the same period in 2019 and 2018.

Figure 5: a) to d) - Yearly PM10 evolution in 2018 (blue),

2019 (orange) and 2020 (yellow) for Portugal and Spain,

Lisbon, Madrid and Porto, respectively.

Comparing the results, it can be stated that there

is a reduction of PM10 levels in April based on

Portugal and Spain regional assessment. Comparing

with the two previous years, the area registered

reduction up to 24% in the two first weeks of April,

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that decreases for 18% by 30 April. At a local

assessment, for Porto the PM10 levels are lower in

2020 than in the past two years for the end of March

and April. For the last day analysed (30 April 2020)

there is a reduction of approximately 22,9% for 2019

and 2018. For Lisbon, the PM10 levels are lower in

2020 than in the past two years in April, even though

there is a slight increase in some days of analysis,

matching the values of 2019, but then there was a

further drop in PM10 levels (reduction of 20% for

2019 and 2018, April 30). In the case of Madrid, the

reduction could only be verified from the second

week of April, and even so, in 30

there was a slight

increase of PM10 when comparing to 2019. The main

conclusion verified for the tree cities is that the

concentrations of PM10 in the air are lower since the

lockdown due to COVID-19 in March (33,3% for

Lisbon, 33,3% for Porto and 52,6% for Madrid).

All together, results from Figures 1-5 are

concordant with the results stated by Mesas-

Carrascosa et al., 2020 and Zhang et al., 2020.

3.1 Water Quality

The concentration of TSM has been analysed before

and after COVID-19 pandemic to understand if any

changes had occurred. The approach consisted of

mapping TSM concentration on four dates,

corresponding to a given day of the month before

COVID-19 confinement (February 2020) and a given

day of each month during confinement (March, April

and May), as well as mapping the TSM differences

between these dates. This study was carried out using

the Water Full Resolution (WFR) level 2 data from

Sentinel-3 OLCI sensor

The following pictures illustrate the TSM for a

given day per month from February to May 2020. The

dates have been chosen according to the best no-cloud

images available.

The Image Differencing Change Detection

method was applied using the software ARCGIS in

order to visualise the positive and negative

differences between the TSM along these months.

Change detection involves quantifying temporal

effects using multi temporal data sets. When the

interest is to understand the changes over large areas

and at frequent interval satellite data these methods

are commonly used.

Figure 6: a) to d) - Total Suspended Matter for 23-02-2020,

28-03-2020, 19-04-2020 and 06-05-2020, respectively.

Air and Water Quality Improvement during COVID-19 Lockdown

113

Figure 7: a) to c) Changes of TSM levels between 23-02-

2020 and 28-03-2020, 28-03-2020 and 19-04-2020, 19-04-

2020 and 06-05-2020, respectively.

The results suggest that there was a decrease on

the TSM concentration from February to March,

March to April and April to May of 17%, 37% and

53% respectively.

A similar approach was applied to compare the

TSM fluctuation between the months of 2020 with the

same fluctuation between the months of 2019 in order

to understand if there was any natural pattern on these

changes that can be affecting the results. In this case

the same method was applied to the images from 2019

and the results of this approach are summarised in the

chart below.

Figure 8: Percentage of TSM decrease between months in

2019 and 2020.

Although the TSM is not only a consequence of

human activities (Fernández-Nóvoa et al., 2017),

these results may indicate a pattern as a result of

COVID-19 restrictions.

4 CONCLUSIONS

This study has used, in a first stage, Sentinel-5P and

CAMS service to analyse the air quality in the

territory of Iberian Peninsula, as well as assess in

detail major cities within the region (Lisbon, Porto

and Madrid), for a period from January 2018 to April

2020. On a later stage, the data from Sentinel-3A and

3B allowed the analysis of water quality during the

months March, April and May 2020, in the

Portuguese coast. Regarding the air quality, NO

and

PM10 levels in the Iberian Peninsula were

consistently lower comparing with analogous periods

of late March and April of the two past years. In the

majority of the analysed cities, it was observed a

similar behaviour of the for the NO

and PM10

concentrations, except for a NO

in Porto that may

result from local anomalies. One aspect be taken into

account is that meteorological conditions such as

wind, rain and seasonal variations of boundary layer

have significant impact on the concentrations of these

air quality parameters. Concerning TSM levels, the

results suggest that there might be a pattern as a result

of COVID-19 restrictions, but seasonal variations

also play a role in this analysis, so it is required an

analysis with a more extended timeline to infer about

the role of COVID-19 pandemic in the transparency

of the coastal waters. In 2020 the reduction of TSM

concentration has been much more pronounced when

compared with the same period of 2019, which, most

likely, could be due to COVID-19 confinement.

As future work, it is necessary to consider a wider

sample of previous years in order to identify seasonal

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patterns and better conclude about the local

anomalies; also consider a cross-validation of these

findings with local water sampling reports and

results, as well with data from local atmosphere

pollution sensors.

ACKNOWLEDGEMENTS

We want to acknowledge the European Commission,

in partnership with the Member States, the European

Space Agency (ESA), the European Organisation for

the Exploitation of Meteorological Satellites

(EUMETSAT), the European Centre for Medium-

Range Weather Forecasts (ECMWF), EU Agencies

and Mercator Océan for providing data from Sentinel-

3A, 3B and 5P freely available to the public.

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7036

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Disclaimer: Neither AIR Centre, the European

Commission nor ECMWF is responsible for any use

that may be made of the information this report

contains.

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