Exposure to each small (1 gram per cubic metre) increase in long-term fine inhalable particle (PM2.5) was associated with an 8 per cent increase in mortality during the pandemic, said researchers in the commentary, published online in the journal Annals of the American Thoracic Society.
The team, led by Stephen Andrew Mein, from the Department of Medicine at Beth Israel Deaconess Medical Centre in Boston, US, examined published research that discussed whether air pollution may be linked to worse Covid-19 outcomes, as well the relationship between pollution, respiratory viruses and health disparities.
They found that air pollution contributed to 15 percent of Covid-19 mortality worldwide.
Exposure to ambient air pollution -- harmful pollutants, such as small particles and toxic gases, emitted by industries, households, cars and trucks -- was found to worsen viral respiratory infections.
"The Covid-19 pandemic has highlighted the widespread health consequences of ambient air pollution, including acute effects on respiratory immune defences and chronic effects that lead to higher risk of chronic cardiopulmonary disease and acute respiratory distress syndrome (ARDS)," Mein said.
These chronic health effects likely explain the higher Covid-19 mortality among those exposed to more air pollution.
Earlier, a study led by German researchers found that elevated levels of nitrogen dioxide in the air may be associated with a high number of deaths from novel coronavirus (Covid-19).
Similar findings by researchers at the Harvard University also noted that even a small increase in long-term exposure to PM2.5, or particulate matter with a diametre of 2.5 micrometres or less, can lead to a large increase in the death rate from Covid-19.
While the exact mechanisms are not fully known, scientists suggest that long-term exposure to air pollution may impair the immune system, leading to both increased susceptibility to viruses and more severe viral infections.
It is also associated with higher rates of heart disease and metabolic disorders such as diabetes, a known risk factors for severe disease and death from Covid-19.
The findings highlight the urgent need to address the global problem of air pollution through sustainable local and national policies to improve respiratory health and equity worldwide.