Effect of the COVID-19 Pandemic on Air Quality

The results of studies in this regard indicate a significant reduction in air pollutants and improved air quality in the short lockdowns and national quarantines of the COVID-19 pandemic. ^{Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Saadat, Rawtani and Hussain13,Reference Lal, Kumar and Kumar16–Reference Shakil, Munim, Tasnia and Sarowar18,Reference Chakraborty, Roy and Bera43} Air pollutants, such as emissions of NO₂ and carbon dioxide (CO₂), were significantly reduced due to industrial shutdowns and reduced worldwide transportation. ^{Reference Lokhandwala and Gautam28} Also, the amount of greenhouse gases has decreased significantly in the short term. ^{Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11} In the study of Muhammad et al., air pollution was reduced by 30% and the level of mobility was reduced by about 90%. ^{Reference Muhammad, Long and Salman22} Collivignarelli reported a significant decrease in NO₂ concentration due to reduced traffic in different cities: in London from 71.1-80.8%, in Milan from 8.6-42.4%, and in Paris from 65.7-79.8%, respectively. ^{Reference Collivignarelli, De Rose and Abbà23} In their study of Southeast Asia, Kanniah reported that levels of PM10: 26-31%, PM2.5: 22-32%, NO₂: 63-64%, SO₂: 9-20%, and CO: 25-31% have decreased. ^{Reference Kanniah, Kamarul Zaman, Kaskaoutis and Latif24} By analyzing air quality before and after 21 days of lockdown in India, Srivastava showed that these restrictions had major effects on reducing the levels of NO₂, SO₂, CO, and PM2.5. ^{Reference Srivastava, Kumar and Bauddh35} During the COVID-19 pandemic, global demand for coal fuel in March and April 2020 decreased by 8% compared to the same time in 2019. In terms of emissions, the lockdown has reduced nitrogen oxide emissions by 20 to 30% in China, Italy, France, and Spain and by 77.3% in Sao Paulo, Brazil. Emissions of nitrogen oxides in India decreased between 20 and 77% and in different cities this reduction varied between 16 and 67%. Some studies have reported a reduction in particulate matter from 5–15% in Western Europe to 200% in New Delhi, which in turn has increased air quality in an unprecedented way in recent times. In some areas, such as New York, CO₂ emissions have been reduced by 5–10%. ^{Reference Menut, Bessagnet and Siour46} The air quality index in Baghdad improved by 13% compared to before the quarantine period and NO₂ emissions decreased by 35–40% compared to before. ^{Reference Hashim, Al-Naseri, Al-Maliki and Al-Ansari31}

Despite what has been said, studies have shown that the reduction in pollutants is short-lived and the level of PM2.5 has not changed. ^{Reference Bekbulat, Apte and Millet25} The findings do not support a reduction in greenhouse gases in the long run, because, after the cancelation of the national holiday, the start of economic activities, increased energy consumption, and subsequent increase in traffic, greenhouse gas emissions have increased again. ^{Reference Wang and Su10} A study by Bekbulat in the United States found that PM 2.5 was reported to be 1–30% higher than expected during home quarantine and that shortfalls in O₃, NO₂, and CO levels were short-lived after lockdown and PM2.5 did not change. ^{Reference Bekbulat, Apte and Millet25} According to the results of studies by Lal, Wang, Barchelo, and Zambrano, air pollution improves in the short term after closures and its long-term effects need further investigation. ^{Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Barcelo15,Reference Lal, Kumar and Kumar16}

Effect of the COVID-19 Pandemic on Water Quality

Findings from some studies have shown that the lockdown and COVID-19-induced quarantine have improved the water quality of some rivers, canals, and seas, and the pandemic has had beneficial effects on surface water quality in some areas. In total, 34% of the articles mentioned an increase in water quality indicators, its transparency, and an increase in the amount of dissolved oxygen in water. ^{Reference Saadat, Rawtani and Hussain13,Reference Kafeel, Ansari, Khan and Owens17,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Rupani, Nilashi and Abumalloh27,Reference Selvam, Jesuraja and Venkatramanan34,Reference Karunanidhi, Aravinthasamy and Deepali41,Reference Chakraborty, Roy and Bera43}

In Selvam’s study, a mirrored reduction in industrial waste was reported in industrial waste following the COVID-19 pandemic, and coliforms were reduced following the lockdown, COVID-19-induced quarantine, and closure of industrial activities, including fisheries. In addition, analytical factors showed better water quality. A significant decrease was observed in AS: 51.3%, Se: 42%, Fe: 60%, Pb: 50%, and NO₃: 56%. Total coliform and fecal coliform were estimated to be 52% and 48%, respectively. ^{Reference Selvam, Jesuraja and Venkatramanan34} In another study by Chakraborty in India, the heavy physical and chemical elements were beyond the standard in the pre-lockdown period. Cations and anions, including Mg, Ca, K, Na, NO₃, SO₄, Cl, and F, were observed in the lockdown period. Examination of water quality in the pre-lockdown period and COVID-19-induced quarantine showed that 100% of the water was highly polluted, and during the outbreak of COVID-19 disease and restrictions, about 90.90% of the samples were upgraded to good quality and 9.10% of the samples were moderately infected. ^{Reference Chakraborty, Roy and Bera43} In some studies, a decrease in water turbidity and suspended particles was also reported during the pandemic. ^{Reference Yunus, Masago and Hijioka49,Reference Patel, Mondal and Ghosh51} In Karunanidhi’s study in India, fluoride concentration decreased by 17%, and water pollution by nitrates decreased by 32.4%. ^{Reference Karunanidhi, Aravinthasamy and Deepali41} Another study reported an improvement in surface water quality at Vembanad Lake, India, showing that suspended particulate matter (SPM) concentrations decreased by an average of 15.9% compared to last year. ^{Reference Yunus, Masago and Hijioka49}

In contrast, in some studies, the content of Cr, Ca, Zn, and Cd was similar to before and fluoride did not show any change. E. coli and fecal streptococci did not change significantly in the waters of industrial coastal cities. ^{Reference Selvam, Jesuraja and Venkatramanan34} In a post-peak study in China, the re-reduction of water quality parameters and intensity of fluorescent components were recorded. ^{Reference Shen, Liu and Lv53} In the study conducted by Patel, the amount of changes in water quality was reported to be variable, and the need for more attention to increase domestic wastewater production during the disease and its impact on receiving water sources such as rivers was highlighted. ^{Reference Patel, Mondal and Ghosh51} In Bar’s study, it was reported that during the lockdown and COVID-19-induced quarantine, the use of a variety of means of transport on the river, such as motor boats and steamboats, was restricted. Some people in East Asia are economically dependent on river fishing. During this period, economic activities in rivers, including fisheries, stopped significantly. ^{Reference Mukherjee, Babu and Ghosh33} Overall, water quality worldwide has improved, ^{Reference Saadat, Rawtani and Hussain13,Reference Cheval, Adamescu and Georgiadis14} water pollution has been reduced, and surface and groundwater quality has been improved following the COVID-19 pandemic. ^{Reference Saadat, Rawtani and Hussain13,Reference Cheval, Adamescu and Georgiadis14,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Rupani, Nilashi and Abumalloh27,Reference Mukherjee, Babu and Ghosh33,Reference Karunanidhi, Aravinthasamy and Deepali41}

The Effect of the COVID-19 Pandemic on the Environment

The effects of this disease on the environment cannot yet be fully described. However, it seems that with the outbreak of the COVID-19 pandemic and the closures that have occurred in different parts of the world, especially in industrialized countries, the amount of air, water, and coastal pollution has decreased. ^{Reference Wang and Su10–Reference Cheval, Adamescu and Georgiadis14} The results of some studies indicate that noise pollution has decreased with the onset of the lockdown and COVID-19-induced quarantine. ^{Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Bar42} In Bar’s study, noise pollution was reported to be significantly below 60 db. ^{Reference Bar42} The quality of coastlines has improved, but household and medical waste has increased, and this increase in non-recyclable waste and medical waste leads to environmental and water pollution. For example, masks are used for a short time and usually daily. ^{Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Saadat, Rawtani and Hussain13} Their contamination is palpable after the outbreak of COVID-19. These contaminants have entered the living environment of animals on land and at sea, which will have consequences such as death and disease for them. ^{Reference Saadat, Rawtani and Hussain13} On the other hand, the resumption of activities and efforts to compensate for the lockdown and COVID-19-induced quarantine have different effects, which highlight the need for more research to identify these effects in the long run. ^{Reference Cheval, Adamescu and Georgiadis14}

This study aimed to investigate the effect of the COVID-19 pandemic on air quality, water resources quality, and the environment. The findings of most studies in this regard have compared previous measures with the post-lockdown and COVID-19-induced quarantine period. In this regard, quarantines and restricting communications have been effective in reducing toxic gases such as nitrogen dioxide, aerosols, atmospheric ozone, and particulate matter and improving air quality.

In a systematic review by Silva et al. ^{Reference Silva and Branco68} (2022), it was reported that air quality improved during quarantine compared to before the quarantine. According to the findings of this research, reductions between 9% and 60%, 21.4% and 61.6%, were reported for PM2.5, PM10, respectively. Studies have reported a reduction in pollutant concentrations during quarantine compared to the same period in previous years and even more robustly with historical data of more than 5 years. ^{Reference Silva and Branco68} Based on the results of a systematic review by Bakola et al. (2022), several air pollutants, including NO₂, NO, PM2.5, PM10, CO, carbon dioxide (CO₂), benzene, black carbon, and air quality index (AQI)) related to the quarantine of COVID-19, showed a significant and strong decrease. ^{Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69}

According to the results of a systematic review study by Faridi et al., ^{Reference Faridi, Yousefian and Janjani70} in 2021, quarantine measures related to the COVID-19 epidemic significantly reduced the concentration of PM2.5, NO₂, PM10, SO₂, and CO globally. Apart from measuring pollutants at ground stations, studies using satellite data have confirmed the results obtained with ground-level measurements and found that AQI improved during the quarantine period. A higher decrease was observed mainly for industrial areas. ^{Reference Gebeyehu, East, Wark and Islam71}

Several mechanisms have been reported to significantly reduce pollutant levels: reducing people’s driving and public transportation, ^{Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69,Reference Gebeyehu, East, Wark and Islam71} reducing or stopping the activity of industries and factories, ^{Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69} and reducing energy consumption ^{Reference Silva and Branco68} ; A remarkable point is that, in the case of some pollutants such as ozone, different results have been reported. Based on the results of the systematic review by Faridi et al. ^{Reference Faridi, Yousefian and Janjani70} (2021), Silva et al. ^{Reference Silva and Branco68} (2022), and Bakula et al. ^{Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69} (2022), O₃ concentration has increased compared to the conditions before COVID-19. Various reasons for the increase in O₃ have been reported: decrease in NO and increase in solar radiation, ^{Reference Silva and Branco68} decrease in the titration of O₃ by NO_X due to a significant decrease in local emission sources of NO_X, possible increase in solar activity level due to decrease in PM2.5, and increase in the number of Hydroperoxyl radicals (HO₂) as a mediator to increase ozone production. ^{Reference Gebeyehu, East, Wark and Islam71}

However, the findings do not indicate a long-term reduction in these gases because industrial activity has increased significantly after the restrictions were reduced. The results of some studies also indicate that the reduction of air pollutants during the pandemic is temporary, and after the end of the imposed restrictions and the removal of quarantine regulations, we will see an increase in air pollutants again. In the systematic review study by Silva et al. (2022), the increase in pollutants in the post-quarantine period was also reported. ^{Reference Silva and Branco68}

On the other hand, a significant increase in household and medical waste has led to further environmental pollution. China Center for Energy and Clean Air Research reports that SARS-CoV-2 emission control methods, such as quarantines and travel bans, have reduced carbon emissions by 25%. ^{Reference Zhang, Zhang, Lin, Feng, Fu and Wang72} The LIU’s study, published in May 2020, also found that global carbon emissions fell by 17% since quarantine in early April, which could reduce annual carbon emissions by up to 7%, the largest drop since World War II. Second, researchers attribute these reductions mainly to reduced use of transportation and industrial activities. ^{Reference Liu, Ciais, Deng, Lei, Davis and Feng73}

Following the application of traffic restrictions, the air pollution index decreased significantly and vehicle emissions such as sulfur dioxide and nitrogen dioxide were reduced, so the EU Air Pollution Monitoring Service reported the production of particulate matter by 20 to 30% and the reduction of sulfur dioxide and nitrogen dioxide emissions. ^{Reference Kafeel, Ansari, Khan and Owens17}

According to the results of the systematic review by Silva et al. ^{Reference Silva and Branco68} (2022), the amount of nitrogen dioxide has decreased 30-66% during the COVID-19 pandemic, and in the systematic review by Faridi et al. ^{Reference Faridi, Yousefian and Janjani70} (2021), this reduction was 18-96%.

Overall, the outbreak of the COVID-19 pandemic appears to have reduced air, water, and coastal pollution in the short term. This finding, in line with some other studies that have made it possible to compare atmospheric composition with and without the lockdown and COVID-19-induced quarantine, showed that the effect of lockdown was particularly important for several atmospheric components through the widespread reduction of traffic and industrial activity, which has been accompanied by a large decrease in NO₂ concentration, a decrease in particulate matter (PM) and air pollutants. ^{Reference Wang and Su10,Reference Lal, Kumar and Kumar16,Reference Abdullah, Mansor and Napi20,Reference Dantas, Siciliano and França21,Reference Rupani, Nilashi and Abumalloh27,Reference Rodríguez-Urrego and Rodríguez-Urrego36}

According to satellite imagery, one of the positive effects of COVID-19 has been clearer waters after 1 month of the national COVID-19 pandemic-induced lockdowns and quarantines. ^{Reference Khan, Shah and Shah19,Reference Chakraborty, Roy and Bera43,Reference Yunus, Masago and Hijioka49,Reference Patel, Mondal and Ghosh51}

Based on the results of the systematic review by Jiang et al. ^{Reference Jiang, Xu, Ye, Pahlow, Hu and Qu74} (2022), the improvement of the quality of coastal waters and the reduction of underwater pollution have been reported. It is noteworthy that COVID-19 has caused an increase in some environmental pollutants for several reasons. Due to the frequent washing of hands and the use of chemical detergents and the release of the resulting effluents, an increase in environmental pollution is expected. According to the results of a systematic review by Chirani et al. ^{Reference Chirani, Kowsari, Teymourian and Ramakrishna75} (2021), during the COVID-19 epidemic, frequent and increasing use of handwashing products leads to environmental pollution. Furthermore, the increase in the use of personal protective equipment (PPE) such as masks and gloves has also caused an increase in the production of waste and the release of these wastes into the environment and increased environmental pollution, especially with microplastic particles. ^{Reference Ammendolia, Saturno and Brooks76–Reference Rakib, De-la-Torre and Pizarro-Ortega86} According to the results of a systematic review by Jiang et al. ^{Reference Jiang, Xu, Ye, Pahlow, Hu and Qu74} (2022), the increase in medical waste related to COVID-19, such as PPE, leads to severe pollution that threatens the marine ecosystem and wildlife.

Travel bans and reduced boat traffic have led to sedimentation and reduced water turbidity, which have made the water clearer. The canals of Venice are illustrative; in the pre-pandemic period, the TSM concentration averaged 3 g/m, but during the COVID-19 pandemic it dropped to 1.4 g/m, that is, a 50% reduction in concentration was observed. ^{Reference Braga, Scarpa and Brando52} The unprecedented increase in the use of the mask and its release into the water and the environment has been one of the negative consequences of the COVID-19 pandemic. Other issues include the increasing use of detergents and their role in the state of wastewater.