Long-term exposure to urban air pollution, especially NO2, may make COVID-19 more deadly, according to a study conducted in the United States.
The study, published in The Innovation journal, analysed key urban air pollutants, including fine particle matter (PM2.5), nitrogen dioxide (NO2), and ozone (O3), across 3,122 counties in the US from January to July.
"Both long-term and short-term exposure to air pollution has been associated with direct and indirect systemic impact on the human body by enhancing oxidative stress, acute inflammation, and respiratory infection risk," said Donghai Liang of Emory University in the US.
To examine the association between ambient air pollutants and the severity of COVID-19 outcomes, the researchers investigated two major death outcomes, the case-fatality rate -- number of deaths among the people who are diagnosed with COVID-19 -- and the mortality rate, which is the number of COVID-19 deaths in the population.
The two indicators can imply the biological susceptibility to deaths from COVID-19 and offer information of the severity of the COVID-19 deaths in the general population, respectively.
Of the pollutants analysed, NO2 had the strongest independent correlation with raising a person's susceptibility to death from COVID-19, according to the researchers.
A 4.6 parts per billion (ppb) increase of NO2 in the air was associated with 11.3 per cent and 16.2 per cent increases in COVID-19 case-fatality and mortality rate, respectively, they said.
The researchers discovered that just a 4.6 ppb reduction in long-term exposure to NO2 would have prevented 14,672 deaths among those who tested positive for the virus.
The team also observed a marginally significant association between PM2.5 exposure and COVID case-fatality rate, whereas no notable associations were found with O3.
"Long-term exposure to urban air pollution, especially nitrogen dioxide, might enhance populations' susceptibility to severe COVID-19 death outcomes," said Liang.
"It's essential to deliver this message to public health practitioners and policymakers in order for them to consider protecting vulnerable populations that lived in historically high NO2 pollution including the metropolitan areas in the state of New York, New Jersey, California, and Arizona," he said.
