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

Abstract

Studies have pointed out that air pollution may be a contributing factor to the coronavirus disease 2019 (COVID-19) pandemic. However, the specific links between air pollution and severe acute respiratory syndrome-coronavirus-2 infection remain unclear. Here we provide evidence from in vitro, animal and human studies from the existing literature. Epidemiological investigations have related various air pollutants to COVID-19 morbidity and mortality at the population level, however, those studies suffer from several limitations. Air pollution may be linked to an increase in COVID-19 severity and lethality through its impact on chronic diseases, such as cardiopulmonary diseases and diabetes. Experimental studies have shown that exposure to air pollution leads to a decreased immune response, thus facilitating viral penetration and replication. Viruses may persist in air through complex interactions with particles and gases depending on: 1) chemical composition; 2) electric charges of particles; and 3) meteorological conditions such as relative humidity, ultraviolet (UV) radiation and temperature. In addition, by reducing UV radiation, air pollutants may promote viral persistence in air and reduce vitamin D synthesis. Further epidemiological studies are needed to better estimate the impact of air pollution on COVID-19. In vitro and in vivo studies are also strongly needed, in particular to more precisely explore the particle–virus interaction in air.

Long-term air pollution and other risk factors associated with COVID-19 at the census tract level in Colorado

“…However, estimated effects for the same increase in PM2.5 reported elsewhere have ranged from a 4% decrease ( Travaglio et al, 2021 ) to a 17% increase ( Tian et al, 2020 ). Multiple systematic reviews have found that long-term air pollution may enhance COVD-19 severity, but have emphasized the need for studies that include additional covariates and account for spatial autocorrelation ( Ali et al, 2021 ; Bourdrel et al, 2021 ). Further, there is no universally-accepted standard for measuring community-scale exposure to PM2.5 air pollution, and studies to date have not compared effect estimates reported from different PM2.5 exposure surfaces.…”

The COVID-19 Pandemic and the Need for an Integrated and Equitable Approach: An International Expert Consensus Paper

“…The burden of the COVID-19 crisis varies considerably not only across countries, but also across regions and municipalities within urban agglomerations. Areas with higher population density, environmental degradation, air pollution, poverty and social inequalities have been hit harder by the pandemic 96 ,. 97 , 98 ,99 Optimal temperature and humidity may also favor virus dissemination.…”

COVID-19 Air Transmission and Precautions

“…[5][6] A number of quick studies on COVID-19 strengthened our understanding about its spread. [6][7][8][9][10] According to studies, possibility of airborne transmission of COVID-19 are high in the dry air (below 40% RH). 5,8 Based on an indoor experiment from Chinese cities during Jan-March 2020, it was found that less than 40% RH activates the evaporation of water in the cough droplets, leading to droplet shrinkage and prolonged suspension in air whereas high RH at 95% will increase the droplet size due to hygroscopic growth with higher deposition fractions both on humans and on ground.…”

“…Similarly, more comprehensive In vitro and in vivo studies are needed to understand air particle-virus interactions. 10 Since, at present it is established that the COVID-19 spread is possible through inhalation, there is a need to avoid crowdedness at various places such as market, offices, hospitals and other common places. Isolation of infected person will further help in controlling the spread of viruses.…”