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. 2022 Dec 23;234(1):13. doi: 10.1007/s11270-022-06024-7

Monitoring Air Pollution in Greek Urban Areas During the Lockdowns, as a Response Measure of SARS-CoV-2 (COVID-19)

Maria M Avdoulou 1,✉, Aristidis G Golfinopoulos 1, Ioannis K Kalavrouziotis 1
PMCID: PMC9782276  PMID: 36575694

Abstract

On March 11, 2020, the World Health Organization declared COVID-19 (SARS-CoV-2) a pandemic. Countries all over the world imposed restriction measures, in an attempt to limit the expansion of the pandemic. Provided that human activities in large urban areas affect air quality, we studied the concentrations of gaseous pollutants ΝΟ, ΝΟ2, O3, C6H6, and particulate matter PM10 in the air, through gas pollution measuring stations in the center of Athens (Greek capital), the center of Piraeus (Greece’s largest port), Athens International Airport (most international and domestic flights within Greece). We monitored and compared the concentrations of ΝΟ, ΝΟ2, O3, C6H6, and ΡΜ10, of 2020 to those of the previous years and found that the primary air pollutants, ΝΟ, ΝΟ2, and C6H6, recorded decreased compared to those of the past years. The O3, which is produced secondarily at the ground of the earth being inversely dependent on NO/NO2, had in most cases increased. The particulate matter PM10, although reduced by the cessation of human activities, was inextricably linked to natural conditions, such as wind velocity and direction transporting African desert dust masses through storms, during which at certain periods was showing increased in concentrations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11270-022-06024-7.

Keywords: Air pollution, Lockdown, COVID-19, Greece, Urban areas, Port, Airport

Introduction

The coronavirus pandemic (COVID-19) (SARS-CoV-2) (WHO, 2020a) was first identified and the first case reported, in Wuhan, China, in December 2019 (WHO, 2020b, c). The first case of COVID-19 in Greece was recorded on February 26, 2020.

Greece, like most Member States of the European Union, implemented measures against the reduction of COVID-19, which had as their main feature the avoidance of movement and social distancing, with restricting citizens to their permanent residences by imposing a curfew.

At this moment, studies from all over the world have shown the effects of lockdowns on air pollution (Baldasano, 2020; Kaskaoutis et al., 2021; Piccoli et al., 2020; Tobías et al., 2020; Vandrevu et al., 2020; Vuong et al., 2020) and how gaseous pollutants and air quality in urban centers were affected (Broomandi et al., 2020; Han et al., 2020; Lonati & Riva, 2021; Marlier et al., 2020; Seo et al., 2020).

The measures began to be implemented gradually with the increase in cases. On March 10, 2020, prohibited the operation of kindergartens, nurseries, schools, higher education institutions, foreign language centers, tuition centers, and all kinds of educational structures, public and private, of all types and degrees of the country. That was the first of numerous measures that the Greek government took with repeated decisions until it needed to impose a total lockdown. At the beginning of the reduction of cases, they took decisions to lift the restrictive measures and the lockdown ended on 15 July 2020. The restart put the country in full operation, initially having a stable situation, but at the end of October, there was a rapid increase in cases of COVID-19 (NOPHG, 2020) reaching 2056 cases. That made the Prime Minister of Greece announce a new lockdown from 7/11/2020 until the end of spring 2021, opening and closing on a case-by-case basis for each region or territory, depending on the epidemiological data.

Air Pollution

This pollution all over the world has serious economic consequences and consequences for human well-being as it contributes to premature mortality (OECD, 2020).

Particulate Matters (PMs)

The main pollutants with adverse health effects are as follows: fine particulate matters having a diameter of 10 μm (PM10) or less than 2.5 μm (PM2.5) which are primary emission particles resulting from the combustion of fuels for the production of energy, by domestic shipping; heating burners, vehicle engines or even from burning wood for heating (Diapouli et al., 2017; Matthaios et al., 2016; Theodosi et al., 2018). In the case of Greece, the main source of emissions in large urban centers, which are known, is mainly traffic and secondarily the burning of biomass and the heterogeneous connection between the gaseous emissions from the traffic with the suspended sea salt, which are converted into a marine aerosol (Eleftheriadis et al., 2014; Saraga et al., 2019).

Nitrogen Dioxide NO2

The NO2 of which 30% is measured in the general area of Attica and is formed mainly from the exhaust gases of vehicles driven by oil combustion (generally from public transport) and power plants and as it is a primary pollutant that contributes to the formation of particulate matters (PMs) (Fameli & Assimakopoulos, 2015; Mavroidis & Ilia, 2012).

Ozone O3

The O3 is formed in the troposphere secondarily by the chemical reaction triggered by solar radiation between volatile organic compounds and pollutants emitted by vehicle exhaust, such as NO2 (Dimitriou & Kassomenos, 2014; Zoran et al., 2020). There are no direct primary ozone emissions (Verykios, 2003).

Benzene C6H6

The C6H6 is produced by incomplete combustion during the cracking of organic material and in large urban centers and is mainly anthropogenic emission, such as from vehicles, ports and airports, oil refining, incineration, asphalt production, and agricultural biomass combustion (Manoli et al., 2015).

The European Union has set out in European Directive 2008/50/EC the limit values for pollutants for the protection of human health and the target values for particulate matter (Table 1).

Table 1.

Pollutant limit values based on European Directive 2008/50/EC (European Parliament, 2008)

Pollutant Average Period Limit values for the protection of human health according to “DIRECTIVE 2008/50/EU” μg/m3 Margin of tolerance
ΝO2 1 h 200 μg/m3 should not be exceeded more than 18 times in a calendar year 50% on 19 July 1999, decreasing from 1 January 2001 onwards for 12 months at equal annual rates to reach 0% on 1st January 2010
Per year 40 μg/m3 50% on 19 July 1999, decreasing from 1 January 2001 onwards for 12 months at equal annual rates to reach 0% on 1st January 2010
C6H6 Per year 5 μg/m3 5 μg/m3 (100%) on 13 December 2000, decreasing from 1 January 2006 onwards for a period of 12 months by 1 μg / m3 to reach 0% on 1st January 2010
CO Maximum daily average of 8 h (1) 10 mg/m3 60%
PM10 1 day 50 μg/m3 should not exceed 35 times per calendar year 50%
Per year 40 μg/m3 20%
Ο3 Maximum daily average of 8 h (1) 120 μg/m3 should not exceed more than 25 times per calendar year on average in 3 years (3)
PM2,5 Per year Target level from 1st January 2020 20 μg/m3
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(1) The maximum daily 8-h average concentration value is selected by examining the 8-h moving averages calculated from hourly data and updated per hour. Each proportionally calculated 8-h average corresponds to the day on which it expires, i.e., the first period of calculation for one day is the period from 17:00 of the previous day until 1:00 of that day the last period of calculation of any day is the period of 16:00 to 24:00 of this day

(2) The limit value is observed from January 1st, 2010, in the immediate vicinity of the specific industrial sources located in locations polluted by decades of industrial activity

(3) If the average for the 3 years cannot be calculated on the basis of a complete and continuous annual data set, then valid data for 1 year are obtained

In the present study, we draw our conclusions from the monitoring of gaseous pollutant measuring stations in urban environments, in Athens and Thessaloniki in the largest port of Greece and the Mediterranean Sea, Piraeus (PPA, 2022), and finally in the area of the Athens International Airport, the largest airport in Greece. We selected to observe the gaseous pollutants ΝΟ, ΝΟ2, C6H6, O3, and P.M10 for the periods of March to July and October to December of the years 2018, 2019, and 2020 respectively. We used stations both of the Hellenic Ministry of Environment and Energy (MEE) and Athens International Airport Eleftherios Venizelos (AIA). The aim of this study was to research the possible changes in the concentrations of gaseous pollutants during the periods of lockdown according to the plans of the Hellenic Government.

Methodology

The stations were selected with the criterion of covering a large spatial area in an almost triangular arrangement with each other. More specifically, we selected in the area of Athens the stations Aristotelous (Urban-traffic) No2 (ARI) (Fig. 1), Athens (Urban-traffic) No1 (ATH) (Fig. 1), and Liossia (Suburban–Background) No4 (LIO) (Fig. 1), while for the area of Thessaloniki, we select station of Agia Sofia (Urban-traffic) No86 (AGS) (Fig. 2). For the area of the Port of Piraeus, the selected station is Piraeus I (Urban-Traffic) No9 (PIR) (Fig. 1). Each air pollution measuring station records specific atmospheric pollutants, the measurements are from the website of the MEECC, where they are posted every year as air pollution data (MEE, 2021). For the AIA, we were given measurement from the environment service of AIA (AIA, 2021), for the stations Spata (SPA) No148 (Fig. 1), Koropi (KOR) No146 (Fig. 1), and Markopoulos (MAR) No149 (Fig. 1) (Ministry of climate crisis and civil protection, 2022).

Fig. 1.

Fig. 1

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Athens, port of Piraeus and AIA atmospheric pollution measurement stations (Ministry of climate crisis and civil protection, 2022)

Fig. 2.

Fig. 2

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Thessaloniki atmospheric pollution measurement stations (Ministry of climate crisis and civil protection, 2022)

All calculations and processing of measurements, as well as tables, charts, box plots, air quality calculations, and calculations of average daily, monthly, and annual case-by-case concentrations, were calculated in Excel files. The measurements of the gaseous pollution recording stations of the National Air Pollution Monitoring Network (EDPAR) are taken every hour for 24 h per day, i.e., we have twenty-four values per day; from there, we calculate the average daily value, and there for the average monthly value of the pollutants. In cases where for technical reasons no measurement has been recorded, the average daily value is not calculated (MEE, 2021).

The recording by the atmospheric pollution stations of the Environment Service of AIA gives measurements every half hour for 24 h per day, so 48 values per day are being recorded, which can be used to calculate the average daily value and there for the average monthly value (AIA, 2021). By application of statistical methods, the changes in the concentrations of gaseous pollutants in the atmosphere can be recorded during periods of travel restrictions, social distancing, and stoppage of commercial and productive activities and recognize their possible interaction effects on the concentrations of gaseous pollutants in the atmosphere.

Results and Discussion

NO

Τable S1 shows statistics for the monthly average values of the two lockdown periods in 2020, in comparison with the values of the same periods in 2018 and 2019. The boxplot in Fig. 3 is the distribution of values of NO at the lockdown periods in comparison with the values of the same periods in 2018 and 2019. It is clearly shown that during the periods of the lockdown, the values decreased in every station.

Fig. 3.

Fig. 3

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Boxplots for the distributions of the lockdown periods for NO concentrations in 2018, 2019, and 2020, Athens, Thessaloniki, Port of Piraeus, and AIA (whiskers: minimum–maximum range; box: q3-q1 range)

The higher reduction, recorded for the lockdown periods, are as follows: the period, March to July 2020, in the area of Athens for the ATH station recorded for April, decrease up to − 78%; for the ARI station, − 44%; and for the LIO station, − 51%, in April. At the Thessaloniki station, AGS decrease by − 11%. At the AIA, the KOR station measured in July a decrease of − 35%; at the MAR station in April, − 43%; and at the SPA station in April, − 45%. In Port of Piraeus, there was a decrease of − 45% in May. In April of 2019, there were no recorded measurements in Piraeus, so we did not take into account those values. In the second period from October to December 2020, a decrease was still recorded in all stations; in the ATH station, a decrease of − 56% in December; in the ARI station, − 50% in December; in the LIO station, − 40% in December; in the AGS station in November, − 26%. In the AIA, KOR station in October and November 2020 did not record measurements, for December recorded a decrease of − 51%; in the MAR station, in November − 36% and in December − 49%; in the SPA station, in November − 57%, but also in December − 52%.

As it seems NO, the imposition of stringent restrictions on travel, social interaction, and access to public spaces, in urban areas of Athens-Thessaloniki, the port of Piraeus, and AIA, to limit the spread of COVID-19, played a key role in the reduction of NO levels in the atmosphere, during both periods.

NO2

Table S2 shows statistics for the monthly average values of the two lockdown periods in 2020 in comparison with the values of the same periods in 2018 and 2019.

The boxplots in Fig. 4 are the distribution of values of NO2 during the lockdown periods in comparison with the values of the same periods in 2018 and 2019. The tables (Table S2) and the boxplots (Fig. 4) show again clearly that during the periods of the lockdown, the values decreased in every station. The higher reduction recorded, in the period March to July 2020, in the area of Athens at the ATH station in April and June, a decrease of up to − 73%; in the ARI station, − 34%; in the LIO station, − 54%, in April; and at the Thessaloniki station AGS, a decrease of − 28%, in May.

Fig. 4.

Fig. 4

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Boxplots for the distributions of the lockdown periods for NO2 concentrations in 2018, 2019, and 2020, Athens, Thessaloniki, Port of Piraeus, and AIA (whiskers: minimum–maximum range; box: q3-q1 range)

At the AIA, the KOR station recorded in July a decrease of − 10%; for March, April, and May, we observe an increase of 30%, 8%, and 17% respectively, in NO2 concentrations, in contrast to the concentrations at the other stations; at the MAR station in April, − 80%; and at the SPA station in March, − 47%. By observing the boxplots (Fig. 4), we can observe that only in the KOR station that there was an increase in the NO2 concentrations in 2020, compared to 2019. In the other two stations, the concentrations of NO2 in 2020 were lower, influenced probably by a local factor. In Port of Piraeus, there was a decrease of − 20% in May. Because of technical reasons, no value was recorded in April of 2019, so we did not take into account the values of Aprils for Piraeus.

It is remarkable that in 2019, we assume that the recordings of measurements of the KOR station are individual and that Piraeus in July 2020 recorded the higher average daily value, which is the highest of all periods for Piraeus and coincides with the first sails for summer tourist season at the beginning of July. For the second period, from October to December 2020, a decrease was recorded in all stations. In the ATH station, a decrease of − 29% in December; in the ARI station, − 25% in October, and November and December recorded an increase in concentrations of NO2 about 1% and 9% respectively, an isolated incident that may be due to local factors; in the LIO station, − 42% in November; in the AGS station in October, − 23%. In the AIA, for the KOR station, we do not have a sufficient sample to draw conclusions. In the MAR station in November, − 24%, and in December, − 36%; in the SPA station, in November, − 42%.

As it seems for NO2, like NO, the restricted measures, in urban areas of Athens and Thessaloniki, port of Piraeus, and AIA, were crucial in the reduction of NO2 levels in the atmosphere, during both periods. From the tables and boxplots, the measurements in majority, except from the station of KOR, which was an isolated incident that probably due to local factors, shows that the concentrations of NO2 are decreased.

O3

For O3, we observe, that in opposition to the concentrations of NO and NO2 mainly was increased in several cases. From Table S3 and boxplots in Fig. 5 for the period March to July, in Athens, the ATH station recorded reductions in the average concentrations per month, while the LIO station recorded increases, the same as the AGS station in Thessaloniki. The ATH station in March, May, June, and July recorded a decrease of the O3 concentrations, with higher reduction concentrations in June, − 46% and April recorded + 7% increase. The LIO station recorded an increase in concentrations of O3 during March, April, and May with a maximum value of 31% and during the months of June and July, a decrease of − 14% and − 1% respectively. At the Thessaloniki station, AGS recorded an increase during March, April, and May with a maximum price of 8%, and during the months of June and July a 9% and 8% decrease respectively. In the area of AIA, we observe that, in opposition to the concentrations in the urban centers of Athens and Thessaloniki, the stations of KOR and MAR did not record large differences in concentrations, compared to the respective periods I and II of 2018, while the SPA station, although in general recorded decreases, only in April recorded an increase. The KOR station in March, May, June, and July recorded a decrease in O3 concentrations, with a higher decrease in March − 11% and in April an increase of + 6%. The MAR station in March, May, June, and July recorded a decrease of the O3 concentration with a higher decrease in May, − 16%, and in April, an increase of + 6%. The SPA station recorded an increase during March (+ 6%), April (+ 26%), May (+ 6), and July (+ 3) and a decrease during June. In the Port of Piraeus, we observe the same phenomenon with the recordings in the urban environment of Athens and Thessaloniki, since during most months, the average monthly O3 concentrations were increased. The PIR station recorded an increase in March + 10%, April + 3%, and May + 15%; during June and July, we observe a decrease of − 14% and − 5% respectively. The concentrations of O3 in the atmosphere for the period from October to December were as follows: At the ATH station in October, we recorded a decrease of − 23% while November and December recorded an increase of 2% and 38% respectively. At the LIO station in October, we recorded a decrease of − 10% while November and December, we recorded an increase of 12% and 60% respectively. At the Thessaloniki AGS station during October, November, and December, we recorded an increase of 26%, 34%, and 22% respectively. At AIA in the KOR station during October, we recorded a decrease of − 8%, and during November and December, we recorded an increase of + 6%. In the MAR station in October, we recorded a decrease of − 9% and during November and December, an increase of + 2% and + 13%. The SPA station has recorded only for December, where it shows an increase of + 26%. In the PIR station, we recorded an increase of + 21% and + 33% in December, while during October, we observe a decrease of − 3%.

Fig. 5.

Fig. 5

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Boxplots for the distributions of lockdown periods for O3 concentrations in 2018, 2019, and 2020, Athens, Thessaloniki, Port of Piraeus, and AIA (whiskers: minimum–maximum range; box: q3-q1 range)

O3 is an important oxidant in the troposphere and is formed through chemical reactions between NOx, volatile organic compounds (VOCs), and carbon monoxide (CO) under the influence of sunlight. VOCs can be natural from biogenic emissions such as isoprene and terpene emissions originating from trees and vegetations but also can be increased in the urban atmosphere because of anthropogenic emissions such as road traffic and the use of products that contain organic solvents. After the photochemical chain reaction that takes place and produces ozone, products like peroxyacetyl nitrate, aldehydes, and nitric acid are formed. High concentrations of NO locally scavenge O3, a fact that leads to the formation of NO2. High concentrations of NO2 blocked the oxidation step of VOCs by producing nitric acid which prevents the net formation of O3. This has resulted in an increase in O3 by the decrease of NOx, at low VOCs/NOx ratios, in the cities. Also, all processes can be affected by local winds that may carry precursors from maritime emissions and biogenic emissions, high temperatures, and humidity (EEA, 2016).

Various studies seem so far (Kang et al., 2021) that traffic restrictions have, as a result, the decrease of NO and NO2, in the atmosphere of urban centers and at the same time an increase of O3 (Brancher, 2021; Campell et al., 2021; Lian et al., 2020). The same effect is observed in the present study; a decrease of NO and NO2, during the restricted measures, is inextricably related to the increase of O3.

C6H6

For C6H6, we have concentration values only from the PIR station. The panel in Table S4, and the boxplots (Fig. 6) show again clearly that during the periods of the lockdown, the values decreased. During March to July, the largest decrease was recorded in April, with a decrease of − 71%, followed by May with a decrease of − 45%, June with a decrease of − 38%, July with a decrease of − 21%, and the month March with a decrease of − 14%. During October to December, the higher decrease was recorded in December, − 42%, followed by the November with a decrease of − 36%, and in October, − 9%. It is certain that in the case of C6H6, the measures of restriction of COVID-19 played a decisive role in reducing C6H6 in the port of Piraeus during both periods.

Fig. 6.

Fig. 6

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Boxplots for the distributions of the lockdown periods for C6H6 concentrations in 2018, 2019, and 2020, Port of Piraeus (whiskers: minimum–maximum range; box: q3-q1 range)

PM10

For PM10, we have recorded concentration values only from the ARI station, for Athens. Τable S5 and the boxplots (Fig. 7) show that during the lockdown periods, there was generally a decrease in concentrations of PM10, but for some months, there was an increase. For March to July, there was a decrease in concentrations. The higher decrease of PM10 concentrations in Athens was recorded in April − 35%, − 26% in June, − 14% in March, an increase of + 1% in July, and finally, in May with an increase of + 9%. At the AGS station in Thessaloniki, the higher decrease of PM10 concentrations was 29% during March, while in June, there was a decrease of − 19%, April − 4%, May an increase of + 12%, and July 0. At the KOR station in AIA, the higher decrease was − 26% and was recorded during June, while in April, there was a decrease of − 23%, in March − 7%, and during May and July, an increase of + 37% and + 16% respectively. At the MAR station, the higher decrease was − 32% and was recorded in June, while in April, there was a decrease of − 24% and during March, May, and July, we recorded an increase of + 7%, + 26%, and + 8% respectively. At the SPA station, the higher decrease was − 35% and was recorded in June, while in April, there was a decrease of − 28%, in March − 6%, and in May and July, an increase of + 14% and + 11% respectively. At the Port of Piraeus PIR station, we recorded a decrease of − 36% in June, April − 31%, March − 13%, July − 5%, and May − 5%. For the period from October to December, the higher decrease was − 47%, at the AGS station in Thessaloniki in October. In Athens, at the ARI station, we recorded a decrease of − 31% in December, a decrease of − 2% in October, and in November, no measurements have been recorded. For Thessaloniki, at the AGS station except for the higher decrease − 47% in October, we recorded an increase of + 19% and + 11% in November and December respectively. For AIA at the KOR station, the higher decrease was − 27% and recorded in November, while in October, we recoded a decrease of − 21% and in December − 16%. At the MAR station, the maximum decrease was − 28% and recorded during October, and December and November recorded an increase of + 23%. At the SPA station, the maximum decrease was − 27% in November, while in October, we recorded a decrease of − 21% and during December − 20%. From the recorded values, during the months of May and July 2020 in the Attica basin (Athens and AIA), we observed a slight increase as well as the month of November 2020.

Fig. 7.

Fig. 7

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Boxplots for the distributions of the lockdown periods for PM10 concentrations in 2018, 2019, and 2020, Athens, Thessaloniki, Port of Piraeus, and AIA (whiskers: minimum–maximum range; box: q3-q1 range)

After observing the meteosat, 9 s-generation satellite recordings with the option of presenting dust every 15 min, for May, July, and November 2020, we quote images (Fig. 8) referring to May 10, 2020, and May 19, 2020, indicative of the situation that prevailed in the atmosphere during the month of May 2020. In Fig. 9, we can see the situation that prevailed in the atmosphere on November 18, 2020. We know that in addition to the anthropogenic factors that affect the concentration levels of suspended particles in the atmosphere (and while there were restrictions due to lockdown), it is also may happen from the transportation of African dust masses through gaseous currents (Querol et al., 2019), a phenomenon which we see in Figs. 8 and 9. From the monitoring of Meteosat 9 and 10 satellites, for July of 2020, records from Meteosat 9 and 10 appears that no African dust was transferred, but it was the month of the intensive lifting of the measures. It is certain that in the case of PM10, the measures to limit COVID-19 played a key role in reducing PM10 during both periods of general traffic restrictions; this is also very clear in boxplots (Fig. 7), but also, their concentrations depended on other phenomena. According to the European Directive 2008/50/EC, the limit value for the protection of human health for a calendar year is 40 μg/m3, with a tolerance of 20%. After calculating the average annual PM10 concentrations for all stations, according to Table 2, we observe that even with these increases that we had in some months in Athens, AIA, and Thessaloniki, in the whole year, there was a decrease in the average price of PM10 concentrations in relation to 2019.

Fig. 8.

Fig. 8

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Transport of African dust in the region of Greece, during the month of May 2020, images from the second generation satellites Meteosat 9 and 10 (Meteologix (a), 2020)

Fig. 9.

Fig. 9

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Transport of African dust in the region of Greece, during the month of November 2020, images from the second generation satellites Meteosat 9 and 10. (Meteologix (b), 2020)

Table 2.

Average annual concentration of PM10 from all Stations. Yearly average values are calculated from the measurements of the air pollution stations (MEE, 2021; AIA, 2021)

PM10 (μg/m3) ARI-Athens AGS-Thessalonikh KOR-international airport of Athens MAR-international airport of Athens SPA-international airport of Athens PIR – port of Piraeus
2018 36.47 42.69 - 32.29 33.68 39.36
2019 36.37 42.05 23.6 24 23.85 35.85
2020 31.78 36.88 21.89 21.39 20.93 29.76
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The reduction of the average annual concentration of PM10 in 2020 compared to 2019 in large urban centers is greater than at Athens International Airport SA. It is also important that in almost all cases, except AGS, from the year 2018 to the year 2020, PM10 concentrations did not exceed the permissible limit set by the European Directive per year.

Conclusions

In the present study, the conclusions we have drawn are particularly interesting. The fact that we simultaneously monitored pollution concentrations in the largest urban centers of Greece, Athens—Thessaloniki, the largest airport (A.I.A.) and the largest Port (OLPA) of Greece, during the period of travel restriction as a measure to limit COVID-19, places it unique in its category. According to the study, in all cases, i.e., in urban environment but also in the areas of the airport and the port, the pollutants NO, NO2, and C6H6 showed a significant reduction of their concentrations in the atmosphere during the two periods of lockdown, which were used as a response to COVID-19.

More detail about NO, for the first period of lockdown, the higher decreases in urban areas were − 78% in the ΑΤΗ station of Athens and − 11% in the AGS station of Thessaloniki; in the International Airport of Athens, − 35%, − 43%, and − 45% from the stations KOR, MAR, and SPA, and at the port of Piraeus − 45%. During the second period of lockdown, the higher decreases in urban areas were − 56% in the ATH station of Athens and − 26% in the AGS station of Thessaloniki. In the International Airport of Athens, − 49% and − 57% from the stations MAR and SPA and at the port of Piraeus − 42%.

About NO2, the first period of lockdown, the higher decreases in urban areas were − 73% in ΑΤΗ station of Athens and − 28% in the AGS station of Thessaloniki; in the International Airport of Athens, − 10%, − 44%, and − 47% from the stations KOR, MAR, and SPA and at the port of Piraeus − 47%. In the second period of lockdown, the higher decreases in urban areas were − 42% in the LIO station of Athens and − 23% in the AGS station of Thessaloniki; in the International Airport of Athens, − 3%, − 26, and − 42% from the stations KOR, MAR, and SPA and at the port of Piraeus − 21%.

About O3, the first period of lockdown, the higher decreases in urban areas were 46% in the ΑΤΗ station of Athens and − 9% in the AGS station of Thessaloniki; in the International Airport of Athens, − 11%, − 16%, and − 3% from the stations KOR, MAR, and SPA and at the port of Piraeus − 14%. During the second period of lockdown, the higher decreases in urban areas were − 23% in the LIO station of Athens. In the AGS station of Thessaloniki, we recorded an increase of + 34%; in the International Airport of Athens, − 8% and − 9 from the stations KOR and MAR and at the port of Piraeus − 3%. The remarkable with O3 is that the increase values are much more than the decreases. For the concentrations of O3 in the atmosphere, in all cases, it is inextricably linked and inversely related to the concentrations of NO and NO2. As the concentrations of NO and NO2 decrease in the atmosphere, the production of O3 increases, and its concentrations in the atmosphere increase.

About the PM10, the first period of lockdown, the higher decreases in urban areas were − 35% in the ΑΤΗ station of Athens and − 29% in the AGS station of Thessaloniki; in the International Airport of Athens, − 26%, − 32%, and − 35% from the stations KOR, MAR, and SPA and at the port of Piraeus − 36%. During the second period of lockdown, the higher decreases in urban areas were − 31% in the ATH station of Athens and − 47% in the AGS station of Thessaloniki; in the International Airport of Athens, − 27%, − 28, and − 27% from the stations KOR, MAR, and SPA and at the port of Piraeus − 29%. Regarding the atmospheric concentrations of particulate matter PM10, it appears that they decreased mainly during restrictions as a measure against COVID-19. However, it is clear that these concentrations also depend on weather and natural phenomena, which under suitable conditions, like the transport of African dust masses with the help of very strong winds, drastically increase the concentrations of PM10 particles in the atmosphere. As it turns out, the avoidance of movement and social distancing, with restricting citizens to their permanent residences by imposing a curfew, which was implemented as a measure to deal with COVID-19 locally and globally, reduced the concentrations of pollutants in the atmosphere and 2020 ensured better air quality and daily values within the limits for protection of citizens’ health, from the concentrations of pollutants.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary file1 (PDF 74 KB) (73.8KB, pdf)

Acknowledgements

We would like to thank Evdokia Anamaterou Specialist, Air Quality, Climate Change and Community Engagement of Athens International Airport for giving us the measurements from the air pollution measuring stations of Koropi, Spata, and Markopoulo, which without them we could not study the area of the Athens International airport.

Author Contribution

Maria M. Avdoulou collect the required measurements, data interpretation, data analysis, and the drafting of the article. Aristidis G. Golfinopoulos and Ioannis K. Kalavrouziotis devised the study and performed critical revisions of the article including the final approval of the version to be published.

Data Availability

Data are available upon request from the authors (mail to abdoulu_maria@hotmail.com).

Code Availability

Not applicable.

Declarations

Ethics Approval

Not applicable.

Consent to Participate

Not applicable.

The research does not involve human participants or animals.

Conflict of Interest

The authors declare no competing interests.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Maria M. Avdoulou, Email: abdoulu_maria@hotmail.com

Aristidis G. Golfinopoulos, Email: gkolfinopoulos.aristeidis@ac.eap.gr

Ioannis K. Kalavrouziotis, Email: ikalabro@eap.gr

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary file1 (PDF 74 KB) (73.8KB, pdf)

Data Availability Statement

Data are available upon request from the authors (mail to abdoulu_maria@hotmail.com).

Not applicable.

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