Air pollution, particularly PM2.5 and NO2, contributes significantly to COVID-19 spread and lethality, with less impact on PM10, but more research is needed to confirm this.

The role of air pollution (PM and NO2) in COVID-19 spread and lethality: A systematic review

A small increase in air pollution, particularly nitrogen oxides, leads to a large increase in COVID-19 infectivity and mortality rate in England.

Links between air pollution and COVID-19 in England

Outdoor air pollutants, particularly nitrogen dioxide and sulfur dioxide, are detrimental factors to COVID-19 outcomes, and reducing these levels could potentially reduce the pandemic burden.

Ambient air pollution and COVID-19 risk: Evidence from 35 observational studies

Air pollution studies on COVID-19 and SARS outbreaks have methodological shortcomings, highlighting the need for careful design and peer review in these studies.

Methodological Considerations for Epidemiological Studies of Air Pollution and the SARS and COVID-19 Coronavirus Outbreaks

Air pollution may increase COVID-19 severity and lethality through its impact on chronic diseases, decreased immune response, and complex interactions with particles and gases in the air.

The impact of outdoor air pollution on COVID-19: a review of evidence from in vitro, animal, and human studies

Both acute and chronic exposure to air pollution can affect COVID-19 epidemiology, with moderate evidence supporting chronic exposure.

Acute and chronic exposure to air pollution in relation with incidence, prevalence, severity and mortality of COVID-19: a rapid systematic review

Air pollution has a significant relationship with COVID-19 infection, potentially explaining the impact of national lockdowns and providing insights for control and prevention strategies.

Association between short-term exposure to air pollution and COVID-19 infection: Evidence from China

Air pollution contributes to about 15% of COVID-19 mortality worldwide, with fossil fuel use being responsible for 50-60% of the attributable, anthropogenic fraction.

Regional and global contributions of air pollution to risk of death from COVID-19

During the COVID-19 pandemic, air pollution levels in the U.S. showed significant declines in nitrogen dioxide and PM2.5, potentially impacting health effects and emissions control.

Changes in U.S. air pollution during the COVID-19 pandemic


               Abstract
               
                  Objectives
                  In areas of SARS-CoV-2 outbreak worldwide mean air pollutants concentrations vastly exceed the maximum limits. Chronic exposure to air pollutants have been associated with lung ACE-2 over-expression which is known to be the main receptor for SARS-coV2. The aim of this study was to analyse the relationship between air pollutants concentration (PM 2.5 and NO2) and COVID-19 outbreak, in terms of transmission, number of patients, severity of presentation and number of deaths.
               
               
                  Methods
                  COVID-19 cases, ICU admissions and mortality rate were correlated with severity of air pollution in the Italian regions.
               
               
                  Results
                  The highest number of COVID-19 cases were recorded in the most polluted regions with patients presenting with more severe forms of the disease requiring ICU admission. In these regions, mortality was two-fold higher than the other regions.
               
               
                  Conclusions
                  From the data available we propose a “double-hit hypothesis”: chronic exposure to PM 2.5 causes alveolar ACE-2 receptor overexpression. This may increase viral load in patients exposed to pollutants in turn depleting ACE-2 receptors and impairing host defences. High atmospheric NO2 may provide a second hit causing a severe form of SARS-CoV-19 in ACE-2 depleted lungs resulting in a worse outcome.
               
            

Severe air pollution links to higher mortality in COVID-19 patients: The “double-hit” hypothesis.

Air pollution levels in Paris, Lyon, and Marseille are linked to COVID-19-related deaths, with threshold values higher than European Parliament limits.

The relationship between air pollution and COVID-19-related deaths: An application to three French cities

Air pollution, particularly particulate matter, may play a role in the spread of COVID-19 and increase its morbidity and mortality rates.

Air Pollution and COVID-19: The Role of Particulate Matter in the Spread and Increase of COVID-19’s Morbidity and Mortality

COVID-19 lockdown activities in many countries led to a significant decrease in air pollution worldwide, benefiting the natural environment.

COVID-19: air pollution remains low as people stay at home

Heavy air pollution, particularly nitrogen dioxide and particulate matter, increases COVID-19 infection severity by overexpressing angiotensin-converting enzyme 2 in respiratory cells.

Air pollution by NO2 and PM2.5 explains COVID-19 infection severity by overexpression of angiotensin-converting enzyme 2 in respiratory cells: a review

Environmental factors, such as air pollution, climate, and the built environment, influence COVID-19 susceptibility and severity through increased risk of preexisting conditions, immune system impairment, viral survival, and increased viral exposure.

Environmental Factors Influencing COVID-19 Incidence and Severity

Long-term exposure to air pollutants, particularly NO2, PM2.5, and PM10, may increase population vulnerability to COVID-19 infection, but this relationship may be confounded by city population density.

Association between coronavirus disease 2019 (COVID-19) and long-term exposure to air pollution: Evidence from the first epidemic wave in China

Exposure to air pollution is associated with a higher risk of COVID-19 disease, with more pronounced associations for severe COVID-19.

Ambient Air Pollution in Relation to SARS-CoV-2 Infection, Antibody Response, and COVID-19 Disease: A Cohort Study in Catalonia, Spain (COVICAT Study)

Lockdowns during COVID-19 have led to significant reductions in ground-level nitrogen dioxide and particulate matter levels, with transportation sector emissions being largely responsible for these declines.

COVID-19 lockdowns cause global air pollution declines

Air pollutants nitrogen oxides and ozone are linked to increased COVID-19 cases and morbidity in England, providing a framework for health policy guidance during the pandemic.

These studies suggest that air pollution, particularly PM2.5 and NO2, is linked to increased COVID-19 spread, severity, and mortality.