Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 1 | 22 REVIEW ARTICLE The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study Butros M. Dahu1, Ahmad Aburayya2 , Beenish Shameem 2 , Fanar Shwedeh2 , Maryam Alawadhi3 , Shaima Aljasmi 3, Said A. Salloum4 , Hamza Aburayya5 , Ihssan Aburayya6 1 Institute of Data Science and Informatics, University of Missouri, Columbia, USA; 2 Assistant Professor, Business Administration College, City University College of Ajman, Ajman, UAE; 3 Senior Specialist Registrar, Primary Health Care Sector, Dubai Health Authority, Dubai, UAE; 4 School of Science, Engineering, and Environment, University of Salford, UK; 5Faculty of Medicine, Jordan University of Science & Technology, Irbid, Jordan; 6Faculty of Medicine, University of Constantine 3, Constantine, Algeria; Corresponding author: Dr. Ahmad Aburayya. Assistant Professor, Business Administration College, City University College of Ajman, Ajman, UAE. Address: City University College of Ajman, Ajman, UAE. Email: a.aburrayya@cuca.ae mailto:a.aburrayya@cuca.ae Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 2 | 22 Abstract Background: The purpose of this article was to review the published literature and evaluate the association between air quality/air pollution and the lockdown/stay-at-home orders during COVID-19 pandemic. Our goal is to identify the various environmental factors, such as urban and rural air quality, which were affected by the lockdown during the coronavirus disease (COVID-19) pandemic. Methods: We searched PubMed (2000–2021) for eligible articles using the following: (1) Aerosol[Title/Abstract], AND (2) air quality[Title/Abstract] OR air pollution[Title/Abstract] AND (3) COVID-19[Title/Abstract]. A total of 39 articles were identified through the search conducted in PubMed. We first screened the title and the abstract of those 39 articles for eligibility. A total of 24 articles did not meet the eligibility criteria and were excluded based on the title and the abstract review. The 15 remaining articles were assessed in full text for eligibility and data extraction. After a full-text review, 3 articles were excluded. Finally, a total of 12 selected articles were confirmed for data extraction. Results: Among the 12 studies, 5 articles focused on the effect of the air pollution, fine particulate matter, and air pollutants of COVID-19 pandemic’s lockdown, while 1 article targeted the relationship between the weather/air quality and COVID-19 death rate during lockdown. In addition, 5 papers focused on the association between the environmental factors, air pollution and air quality and COVID-19 mortality rate. Finally, 1 research study paper aimed to study the COVID-19 positivity rate and the effect of air quality during the stay-at-home order or the lockdown which was occurred in March 2020. It is important to note that it has been found that an increase in the average PM2.5 concentration was correlated with a relative increase in the COVID-19 test positivity rate. This explains the increase in the number of COVID cases during the period of the wildfire smoke from August to October 2020 (1). Conclusion: The findings indicate that the COVID-19 lockdown has significant impact on the air quality across the world. The lockdown significantly reduces the air pollutants such as NO2, CO, O3 and Particulate Matter PM2.5 and PM10. This reduction led to a much healthier and safer outdoor air and hence improved the air quality during the lockdown/stay-at-home orders. More research is needed to validate that the air pollutants (NO2, CO, O3, PM2.5 and PM10) have a significant impact on the COVID-19 mortality and fatality rates. Keywords: COVID-19; Lockdowns; Air Quality; Air Pollution; Environmental Factors Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 3 | 22 Introduction The coronavirus disease (COVID-19) is an infectious disease caused by the SARS-CoV- 2 virus. The COVID-19 pandemic has infected more than 262 million people and killed more than 5.2 million lives worldwide. The coronavirus pandemic has also caused an enormous economic, public health, and social damages. It is important to note that the risk factors of COVID-19 are still under investigations, but some environmental factors, such as urban and rural air pollution and air quality play a vital role in increasing the population sensitivity to COVID-19 pathogenesis (2). The United States National Oceanic and Atmospheric Administration stated almost 30% decrease in nitrogen oxides (NO2) emissions in the urban northeast during April 2020. In addition, there was a huge reduction in the volatile organic compound concentrations (3). Research studies have proven that exposure to the fine particulate matter PM2.5 may cause a major harmful health effect. Those effects include cardiovascular, respiratory, diabetes, kidney disease mortality and morbidity (4). Additionally, ecological studies indicate that living in areas with higher levels of ambient fine particulate matter air pollution (PM2.5) increase the chance of having a higher risk of adverse COVID-19 outcomes (5). The COVID-19 restrictions have reduced the emission of the primary air pollutants worldwide in general and in the United States particularly due to the decrease in industrial activities and transportation (6). The coronavirus disease (COVID-19) pandemic has created so many challenges to the United States government to balance economy and public safety. President Donald Trump declared a national emergency on March 13, 2020, where all municipalities and states issued different degrees of stay-at- home and/or lockdowns policies matching the local specific conditions.(7). These local policies have impacted the air quality through decreasing the non-necessary energy consumption and transportation. According to the U.S. Environmental Protection Agency (EPA), the air pollutants and the national emissions contains 59% of carbon monoxide (CO), and 74% of nitrogen oxides (NOx, sum of nitrogen dioxide [NO2] and nitric oxide [NO]) as well as emissions from electric generation and the on-and-off road traffic (7). In addition, the ambient levels of the two pollutants PM2.5 and PM10 (particulate matter with aerodynamic diameters below 2.5 and 10 μm, respectively) might be the most affected by the lockdown (L. W. A. Chen et al., 2020). It is important to mention that the Ozone (O3) is developed in the atmosphere through the photochemical reaction of the volatile organic compounds (VOCs) and NOx. Also, reducing the VOCs and NOx emissions could either lower or lift the ozone (O3) concentrations depending on the local photochemical regime (7). Our aim is to estimate the association between air quality/air pollution and the lockdown/ stay-at-home orders during COVID-19 pandemic. We sought to identify changes that were made to the air gases, air pollutants and particular matters during the COVID-19 pandemic lockdown. In addition, our goal is to identify the various environmental factors, such as urban and rural air quality, which were affected by the lockdown during the coronavirus disease (COVID-19) pandemic. Finally, we will evaluate whether there was a uniform improvement in air quality during the COVID-19 lockdown. We will also estimate the association between the COVID-19 fatality rate and air quality by dragging our Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 4 | 22 attention on the direct relationship between the air quality and the COVID-19 mortality across the world. Furthermore, the changes in mobility were correlated with the relevant air quality parameters, such as NO2, which in turn was highly correlated to O3. The study provides data and analysis to support future planning and response efforts in Sharjah (United Arab Emirates) (8,9). Also, previous studies show the large impact of human activities on the quality of air and present an opportunity for policymakers and decision-makers to design stimulus packages to overcome the economic slow-down, with strategies to accelerate the transition to resilient, low-emission economies and societies more connected to the nature that protect human health and the environment (9,10). Methods Data Sources We searched PubMed (2000–2021) for eligible articles using combinations of the following search terms: (1) (Aerosol[Title/Abstract])), (2) and (air quality[Title/Abstract])) or (3) (air pollution[Title/Abstract])) and (4) (COVID- 19[Title/Abstract])). We also systematically searched the reference lists of the included studies and relevant reviews. We found 39 eligible articles on PubMed. Inclusion and Exclusion Criteria The researchers reviewed the titles and abstracts of the identified citations and identified eligible articles based on the following criteria. The inclusion criteria included any randomized controlled trial, quasi-experimental study, or pre–post study evaluating the effect of the lockdown on the air quality. The included studies measured health outcomes, processes of care and the effect of the lockdown on the pollution rates in the United States major cities. In addition, we excluded studies published in a language other than English was excluded. Furthermore, data that is not related to COVID-19 were excluded (no other disease). Study Selection and Data Extraction The process of selection was performed in two steps. In the first step, we read the titles and abstracts of the citations by the search query to screen the articles based on the inclusion/exclusion criteria mentioned above. In the second step, we read the full text of the citations selected by the first step and based on that we decide if the paper is eligible for inclusion. The search criteria did not limit by publication date; due to recency of the field, the earliest eligible article was published in 2020. In addition, the researchers collected the following information from each article that was eligible: author and year, study objective, methods/tools, geographic location, particulate, and gases measured, source of data, samples collected for analysis and major findings and results. Figure 1. shows, a total of 39 articles were identified through the search conducted in PubMed. We first screened the title and the abstract of those 39 articles for eligibility. A total of 24 articles did not meet the eligibility criteria and were excluded based on the title and the abstract review. The 15 remaining articles were assessed in full text for eligibility and data extraction. After a full- text review, 3 articles were excluded. Finally, a total of 12 selected articles were confirmed for data extraction. Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 5 | 22 Figure 1. PRISMA Flow Diagram We summarize the basic information of the selected papers. For each paper, we evaluated the main aspects which include but are not limited to the following: 1) descriptions of the study design, 2) sample size, 3) air particles, 4) duration of study, 5) COVID-19 mortality rate, 6) control groups, 7) process and outcome measures, 8) statistical significance, 9) effect of the ambient ozone, 10) ambient air pollutants, 11) urban air pollution, 12) ambient PM2.5 and PM10, 13) disparities in nitrogen dioxide pollution and 14) COVID-19 fatality rate. Results Among the 12 studies, 5 articles focused on the effect of the air pollution, fine particulate matter, and air pollutants on COVID-19 pandemic’s lockdown, while 1 article targeted the relationship between the weather/air quality and COVID-19 death rate during lockdown. In addition, 5 papers focused on the association between the environmental factors, air pollution and air quality and COVID-19 mortality rate. Finally, 1 research study paper aimed to study the COVID-19 positivity rate and the Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 6 | 22 effect of air quality during the stay-at-home order or the lockdown which was occurred in March 2020. One of the study results shows that the COVID-19 lockdown reduced the disparity in air quality between the census tracts with low and high segments of non- white population in some of the rural areas of the United States (for example New York city). On the other hand, the racial gap in air quality remained the same with no notable change in urban areas (3). Additionally, some research findings which have massive environmental policy relevance, indicating that mobility reductions by itself may be insufficient to reduce and decrease the particulate matter PM2.5 uniformly and substantially (4). It is important to note that it has been found that an increase in the average PM2.5 concentration was correlated with a relative increase in the COVID-19 test positivity rate. This explains the increase in the number of COVID cases during the period of the wildfire smoke from August to October 2020 (1). Our results show that counties with higher air pollutants (NO2, O3, CO, PM2.5 and PM10) rates were found to be significantly associated with higher rates of COVID-19 mortality rates. Additionally, counties with higher average daily Particulate Matter (PM2.5) tend to have a significantly higher COVID-19 mortality rate (11). On the other hand, counties with higher average temperatures are significantly associated with much lower mortality rates for COVID- 19 (12). During the COVID-19 lockdown the Ozone (O3) concentration decreases which caused a decrease in the air pollution and improve the air quality. This makes the outdoor air much healthier and safer for the human lungs. It has been noticed that the ozone levels are negatively correlated with the COVID-19 death rates (13). The lockdown reduced the concentration of the particulate matter PM2.5 which improves the air quality. Our findings showed that an increase in PM2.5 would cause an increase in the risk of hospitalization caused by COVID- 19 (12). It is important to mention that the association of PM2.5 and risk of hospitalization among COVID-19 patients was present in each wave of the pandemic. Also, our study analysis suggested that there was higher risk of hospitalization associated with PM2.5 in Black people compared to White people and in those who living in socioeconomically disadvantaged neighborhoods (5). The COVID-19 lockdown reduced the two air toxicants (i.e., nitrogen dioxide or NO2, and benzidine), which caused an improvement in the air quality. Our results proved that there is a relationship between the COVID-19 lockdown and the air quality. It also confirmed the previously reported environmental factors associated with COVID-19 mortality rate (14). Our systematic review results show that the NO2 (one of the air pollutants) concentrations were positively associated with COVID-19 mortality and fatality rates (15). Additionally, after adjusting for co-pollutants, per interquartile-range (IQR) increase in NO2, the COVID-19 case mortality rate and fatality rate were associated with an increase as well. We should note that we did not notice or observe any significant association between the long term exposure to O3 or PM2.5 and COVID-19 mortality and fatality rates per IQR increase (2,11,16). The reductions of CO and NO2 are statistically significant with the COVID-19 pandemic lockdown. It is also significant at two thirds of the sites and tend to increase with local population density. Additionally, the lockdown has a significant reduction on particulate matter (PM2.5 and PM10), which also has a significant impact on the air quality (L. W. A. Chen et al., 2020). The air pollution levels did not significantly change, compared with historical trends (5). In summary, our Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 7 | 22 results showed that the COVID-19 locked down which occurred in March 2020 has affective the air quality positively. It has improved the air quality by decreasing the pollution rate. It also helps in decreasing the polluted gases such as NO2, CO, O3, PM2.5 and PM10. Additionally, the air quality affected the COVID-19 testing and positivity rates. This systematic review study has shown that the COVID-19 testing, and positivity rates are higher in the areas with high pollution rates. The lockdown has improved the air quality, decreased the pollution rates, and decreased the COVID-19 mortality and fatality rates. Table 1. Summary of the Results Analysis Study Objective Methods/Tools Geographic Location Particulate & Gases Measured Samples Collected for Analysis air pollution and the risk of hospitalization Adjusted Poisson regression United States PM2.5 with risk of hospitalization national cohort of 169,102 COVID- 19 to evaluate the air quality To estimate the confidence interval & Bootstrapping Northeast and California/Nevada metropolises, United States (NO2), (CO), (O3) & (PM2.5, PM10) Six weeks or 42 days between March 15 and April 25, 2020 impacts of COVID-19 lockdowns on PM2.5 regression model & synthetic control method” (SCM) 455 PM2.5 monitoring sites across the United States the level of PM2.5 in air 455 monitors Association of COVID- 19 mortality multivariable regression model county-level United States NO2 and benzidine 337 variables To estimate the association between weather and COVID- 19 fatality rates Models included state-level social distancing measures county-level longitudinal design across the United States min & max daily temperature, precipitation, O3, PM2.5 concentrations & U.V. light index time-constant factors at the county level, and linear and nonlinear time- varying factors examine whether wildfire smoke associated with an increased rate of COVID time-series analysis western United States, in Reno, Nevada ambient PM2.5 hourly Beta Attenuation Monitors with a very sharp cut cyclone estimate the association between NO2, PM2.5 and O3 & COVID-19 mortality conducted a cross-sectional nationwide study County level – United States NO2, PM2.5 and O3 3141 US counties estimate the association between NO2, PM2.5, and O3 and county-level COVID-19 case- fatality and mortality rates a cross-sectional nationwide study United States counties average NO2 concentrations, and long-term exposure to PM2.5 or O3 monitors were hourly Beta Attenuation Monitors with a very sharp cut cyclone (VSCC) and temperature and humidity data. evaluate the association between opioid-related mortality & COVID-19 mortality A multivariable negative-binomial regression model counties across the U.S. PM exposure estimate within each county Data from 3142 counties across the U.S. identify changes in pediatric asthma- related health care utilization viral transmissions were enacted in Philadelphia Philadelphia, United States pollution data for 4 criteria air pollutants Changes in encounter characteristics, viral testing patterns, and air pollution before and after Mar 17, 2020 investigated whether long-term average exposure to (PM 2.5) is associated with an increased risk of COVID-19 death in the United States included a random intercept by state to account for potential correlation 3,000 counties in the United States Particulate matter PM 2.5 negative binomial mixed models using county-level COVID-19 deaths to investigate causality between the economic lockdown and changes in air quality triple difference-in- differences model high and low shares of non-white population in rural New York the change in PM2.5 pollution three samples: AOD, PM2.5-at- monitor, and AOD-at-monitor Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 8 | 22 Discussion Our findings suggested that the urban combustion sources such as traffic, may increase susceptibility to severe COVID-19 outcomes due to the long-term exposure to NO2. This is independent from the long term exposure of O3 and PM2.5. Our results also support directed public health actions to protect the highly polluted regions with prominent levels of NO2. The lockdown lowers the traffic emissions and ambient air pollution which will improve the air quality and reduce the risk of COVID-19 case mortality and fatality (11). It is worth noting that exposure to higher levels of the particulate matter PM2.5 plays a very vital and direct role in increasing the risk of hospitalization among COVID-19 infected patients. Our results show that Black race and people who are living in disadvantaged neighborhoods have a higher risk of hospitalization in the setting of COVID-19 due to the untoward effect of PM2.5 (11). We have also found that wildfires cause an increase in air pollution due to the elevated PM2.5 (13). This will increase the COVID- 19 test positivity rate. Our research findings have indicated that PM2.5 from other sources, such as industry and vehicle traffic increase the susceptibility of COVID-19 (1). Lockdown reduces the emissions of PM2.5 coming from industries and vehicle traffic and hence reduce the air pollution and improve the air quality (1). There is also a direct relationship between weather changes and the US COVID-19 fatality rates. It only appeared with the ozone levels and the minimum temperature. Our study analysis showed an increase in the minimum daily temperature during the lockdown period which also associated with higher COVID-19 fatality rates. In addition, fewer COVID-19 deaths were associated with higher ozone levels (13). The methodology used in previous studies can be applied to evaluate the impacts of COVID-19 or similar events on people’s mobility, air quality and utility consumption at other geographical locations (17)(10). Particulate matter concentrations show a quite different pattern from the rest of pollutants examined and with substantial week-to-week variations (10)(17)(8). The current study concludes that due to declining automobile and industrial emissions in The Northern Emirates of the United Arab Emirates (NEUAE), the lockdown initiatives lowered NO2, AOD, and Surface Urban Heat Island Intensity (SUHII). In addition, the aerosols did not alter significantly since they are often linked to the natural occurrence of dust (10). Our study has various limitations that are worth noting. In some of the eligible articles used in this literature review, the health care, demographic, utilization, and viral testing data were taken from a single institution and collected as part of routine care (18-25). Additionally, the electronic health record (EHR) data is subject to bias and error. These errors are hard to be controlled and do not allow us to observe significant changes. Lastly, future studies are necessary to refine our findings and improve our understanding of the effects of the COVID-19 pandemic lockdown on the air quality (6). Conclusion The findings indicate that the COVID-19 lockdown has significant impact on the air quality across the world. The lockdown significantly reduces the air pollutants such as NO2, CO, O3, and Particulate Matter PM2.5 and PM10. This reduction led to a much healthier and safer outdoor air and Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 9 | 22 hence improved the air quality during the lockdown/stay-at-home orders. More research is needed to validate that the air pollutants (NO2, CO, O3, PM2.5 and PM10) have a significant impact on the COVID-19 mortality and fatality rates. The lockdown during the COVID-19 pandemic improved the air quality as well as decreasing the exposure and the emissions of the particulate matter PM2.5. This will help decrease the risk of hospitalization among COVID-19 infected individuals. Lastly, this study indicates the need for public health efforts during the hard hit of COVID-19. It also improves the advantage of the lockdown on the air pollution and air quality. References 1. Kiser D, Elhanan G, Metcalf WJ, Schnieder B, Grzymski JJ. 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AlSuwaidi SR, Alshurideh M, Al Kurdi B, Aburayya A. The main catalysts for collaborative R&D projects in Dubai industrial sector. In: Proceedings of the International Conference on Artificial Intelligence and Computer Vision (AICV2021). Cham: Springer International Publishing; 2021: 795–806. _________________________________________________________________________________ Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 12 | 22 Appendix 1 Table 2. Data Analysis of the Impact of the COVID-19 Lockdown on Air Quality Author & Year Study Objective Methods/ Tools Geographic Location Particulate & Gases Measured Source of Data Samples Collected for Analysis Major Findings & Results Bowe et al., 2021 air pollution and the risk of hospitaliz ation among COVID-19 positive individual s Adjusted Poisson regression United States PM2.5 with risk of hospitalizati on the US Department of Veterans Affairs national healthcare databases and VA Corporate Data Warehouse (CDW) Outpatient and Inpatient Encounters national cohort of 169,102 COVID-19 positive United States Veterans There were 25,422 (15.0%) hospitalizatio ns; 5,448 (11.9%), 5,056 (13.0%), 7,159 (16.1%), and 7,759 (19.4%) were in the lowest to highest PM2.5 quartile, respectively. In models adjusted for State, demographic and behavioral factors, contextual characteristic s, and characteristic s of the pandemic a one interquartile range increase in PM2.5 (1.9 µg/m3) was associated with a 10% (95% CI: 8%- 12%) increase in risk of hospitalizatio n. The association of PM2.5 and Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 13 | 22 risk of hospitalizatio n among COVID-19 individuals was present in each wave of the pandemic. Models of non-linear exposure- response suggested increased risk at PM2.5 concentratio ns below the national standard 12 µg/m3. Formal effect modification analyses suggested higher risk of hospitalizatio n associated with PM2.5 in Black people compared to White people (p = 0.045), and in those living in socioeconom ically disadvantage d neighborhoo ds (p < 0.001). Chen et al., 2020 to evaluate the air quality response to reduced economic activities. To estimate the confidence interval of ΔI%, a bootstrappi ng procedure Northeast and California/Ne vada metropolises , United States nitrogen dioxide (NO2) and carbon monoxide (CO), ozone (O3), particulate matter (PM2.5 and PM10) EPA National Core (NCore) network, and Airnowtech & EPA AirData website Six weeks or 42 days between March 15 and April 25, 2020, was designated as the first- phase lockdown period (P1). A reference period deemed business as The reductions, up to 49% for NO2 and 37% for CO, are statistically significant at two thirds of the sites and tend to increase with local population density. Significant Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 14 | 22 usual between January 25 and March 7, 2020 (P0) was selected reductions of particulate matter (PM2.5 and PM10) only occurred in the Northeast and California/Ne vada metropolises where NO2 declined the most, while the changes in ozone (O3) were mixed and minor. Chen et al., 2021 impacts of COVID-19 lockdown s on PM2.5 regression model & synthetic control method” (SCM) 455 PM2.5 monitoring sites across the United States the level of PM2.5 in air EPA Air Quality System (AQS), EPA Air Now system, & Google Earth Engine 455 monitors remain to be used in our analyses the findings have immense environment al policy relevance, suggesting that mobility reductions alone may be insufficient to reduce PM2.5 substantially and uniformly. Hu et al., 2021 Associatio n of COVID-19 mortality multivariab le regression model county-level United States nitrogen dioxide or NO2, and benzidine nationwide county-level COVID-19 mortality data in the contiguous US 337 variables characterizi ng the external exposome from 8 data sources were integrated, harmonized , and spatiotemp orally linked to each county All the 4 variables that were significant in both sets in Phase 1 remained statistically significant in Phase 2, including two air toxicants (i.e., nitrogen dioxide or NO2, and benzidine), one vacant land measure, and one food environment Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 15 | 22 measure. This is the first external exposome study of COVID-19 mortality. It confirmed some of the previously reported environment al factors associated with COVID- 19 mortality, but also generated unexpected predictors that may warrant more focused evaluation. Karimi et al., 2021 To estimate the associatio n between weather and COVID-19 fatality rates Models included state-level social distancing measures county-level longitudinal design across the United States primary measures included minimum and maximum daily temperature , precipitation , ozone concentratio n, PM2.5 concentratio ns, and U.V. light index. analyzed COVID-19 deaths from public health departments’ daily reports Models included state-level social distancing measures, Census Bureau demographic s, daily weather information, and daily air pollution. time- constant factors using fixed effects at the county level, and linear and nonlinear time- varying factors, and serial correlation, social distancing measures 3141 US counties A 1 °F increase in the minimum temperature was associated with 1.9% (95% CI, 0.2% to 3.6%) increase in deaths 20 days later. An ozone concentratio n increases of 1 ppb (part per billion) decreased daily deaths by 2.0% (95% CI, 0.1% to 3.6%); ozone levels below 38 ppb negatively correlated with deaths. Kiser et al., 2021 examine whether wildfire smoke from the time-series analysis using generalize western United States, in ambient PM2.5 Environment al Protection Agency’s (EPA’s) internet monitors were hourly Beta Attenuation Monitors they found that a 10 µg/m3 increase in the 7-day Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 16 | 22 2020 wildfires associate d with an increased rate of SARS- CoV-2 infections d additive models Reno, Nevada database, from four air quality monitors located in Reno and Sparks. Temperature and humidity data were obtained from the KRNO weather station (via mesowest.ut ah.edu) (Met One BAM 1020s) with a very sharp cut cyclone (VSCC) and temperatur e and humidity data. average PM2.5 concentratio n was associated with a 6.3% relative increase in the SARS- CoV-2 test positivity rate, with a 95% confidence interval (CI) of 2.5 to 10.3%. This corresponde d to an estimated 17.7% (CI: 14.4-20.1%) increase in the number of cases during the period most affected by wildfire smoke, from 16 Aug to 10 Oct. Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 17 | 22 Liang et al., 20 to estimate the associatio n between long-term (2010- 2016) county- level exposures to NO2, PM2.5 and O3 and county- level COVID-19 case- fatality and mortality rates in the US conducted a cross- sectional nationwide study using zero- inflated negative binomial models County level – United States NO2, PM2.5 and O3 from three databases: the New York Times, USAFACTS, and 1Point3Acres .com between long-term (2010- 2016) county-level exposures to NO2, PM2.5 and O3 and county-level COVID-19 case-fatality and mortality rates 1,027,799 COVID cases and 58,489 deaths were reported in 3,122 US counties from January 22, 2020, to April 29, 2020, with an overall observed case-fatality rate of 5.8%. Spatial variations were observed for both COVID death outcomes and long- term ambient air pollutant levels. County-level average NO2 concentratio ns were positively associated with both COVID-19 case-fatality rate and mortality rate in single-, bi- & tri-pollutant models (p- values<0.05) . Per inter- quartile range (IQR) increase in NO2 (4.6 ppb), COVID-19 case fatality rate and mortality rate were associated with an increase of 7.1% (95% CI 1.2% to 13.4%) and Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 18 | 22 11.2% (95% CI 3.4% to 19.5%), respectively. No observe significant associations between long-term exposures to PM2.5 or O3 and COVID- 19 death outcomes (p- values>0.05) , although per IQR inc in PM2.5 (3.4 ug/m3) was marginally associated with 10.8% (95% CI: - 1.1% to 24.1%) increase in COVID-19 mortality rate Liang et al., 2020 to estimate the associatio n between long-term (2010- 2016) county- level exposures to NO2, PM2.5, and O3 and county- level COVID-19 case- fatality and mortality rates in a cross- sectional nationwide study using zero- inflated negative binomial models used both single- and multi- pollutant models and controlled for spatial trends and a comprehe nsive set of potential United States counties average NO2 concentratio ns, and long-term exposure to PM2.5 or O3 obtained the number of daily county- level COVID- 19 confirmed cases and deaths that occurred from January 22, 2020, the day of the first confirmed case in the United States, through July 17, 2020, in the United States from three databases: the New York Times,2 USAFacts,3 3,076 US counties From January 22, 2020, to July 17, 2020, 3,659,828 COVID-19 cases and 138,552 deaths were reported in 3,076 US counties, with an overall observed case-fatality rate of 3.8%. County-level average NO2 concentratio ns were positively associated with both COVID-19 Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 19 | 22 the United States confounde rs and 1Point3Acres .com case-fatality rate and mortality rate in single-, bi-, and tri- pollutant models. When adjusted for co-pollutants, per interquartile- range (IQR) increase in NO2 (4.6 ppb), COVID-19 case-fatality rate and mortality rate were associated with an increase of 11.3% (95% CI 4.9%- 18.2%) and 16.2% (95% CI 8.7%- 24.0%), respectively. We did not observe significant associations between COVID-19 case-fatality rate and long-term exposure to PM2.5 or O3, although per IQR increase in PM2.5 (2.6 μg/m3) was marginally associated, with a 14.9% (95% CI 0.0%-31.9%) increase in COVID-19 mortality rate when adjusted for co-pollutants. Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 20 | 22 Qeada n et al., 2021 to evaluate the associatio n between opioid- related mortality and COVID-19 mortality A multivariab le negative- binomial regression model counties across the U.S. PM exposure estimate within each county Johns Hopkins University Center for Systems Science and Engineering Coronavirus site CDC WONDER Data from 3142 counties across the U.S. were used After controlling for covariates, counties with higher rates of opioid- related mortality per 100,000 persons were found to be significantly associated with higher rates of COVID-19 mortality (aMRR: 1.0134; 95% CI [1.0054, 1.0214]; P = 0.001). Counties with higher average daily Particulate Matter (PM2.5) exposure also saw significantly higher rates of COVID-19 mortality. Analyses revealed rural counties, counties with higher percentages of non- Hispanic whites, and counties with increased average maximum temperatures are significantly associated with lower mortality rates from COVID-19. Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 21 | 22 Taquec hel et al., 2020 sought to identify changes in pediatric asthma- related health care utilization, respirator y viral testing, and air pollution during the COVID-19 pandemic viral transmissi ons were enacted in Philadelphi a, were assessed, and compared with data from 2015 to 2019 as a historical reference Philadelphia, United States pollution data for 4 criteria air pollutants data were extracted from Children's Hospital of Philadelphia electronic health records, and pollution data for 4 criteria air pollutants were extracted from AirNow Changes in encounter characterist ics, viral testing patterns, and air pollution before and after Mar 17, 2020 After March 17, 2020, in- person asthma encounters decreased by 87% (outpatient) and 84% (emergency + inpatient). Video telemedicine, which was not previously available, became the most universally used asthma encounter modality (61% of all visits), and telephone encounters increased by 19%. Concurrently, asthma- related systemic steroid prescriptions and frequency of rhinovirus test positivity decreased, although air pollution levels did not change, compared with historical trends. Wu et al., 2020 investigat ed whether long-term average exposure to fine particulate matter (PM 2.5) is included a random intercept by state to account for potential correlation in counties within the same state & 3,000 counties in the United States Particulate matter PM 2.5 collected for more than 3,000 counties in the United States (representing 98% of the population) up to April 22, 2020, it negative binomial mixed models using county-level COVID-19 deaths as the outcome and county- They found that an increase of only 1 μg/m 3 in PM 2.5 is associated with an 8% increase in the COVID- 19 death rate (95% Dahu BM, Aburayya A, Shameem B, Shwedeh F, Maryam A, Aljasmi Sh, Salloum SA, Aburayya H, Aburayya I. The Impact of COVID-19 Lockdowns on Air Quality: A Systematic Review Study (Review Article). SEEJPH 2022, posted: 09 October 2022. DOI: 10.11576/seejph-5929 P a g e 22 | 22 associate d with an increased risk of COVID-19 death in the United States conducted more than 68 additional sensitivity analyses from Johns Hopkins University level long- term average of PM 2.5 as the exposure confidence interval [CI]: 2%, 15%). The results were statistically significant and robust to secondary and sensitivity analyses. Zhang et al, 2021 to investigat e causality between the economic lockdown and changes in air quality triple difference- in- differences model high and low shares of non-white population in rural New York the change in PM2.5 pollution NASA’s satellite imagery data, aerosol optical depth (AOD), Environment al Protection Agency’s (EPA) & Moderate Resolution Imaging Spectroradio meter three samples: AOD, PM2.5-at- monitor, and AOD- at-monitor the lockdown narrowed the disparity in air quality between census tracts with high and low shares of non-white population in rural New York, whereas the racial gap in air quality remained unchanged in urban New York.