New York, Oct 8 : In a major study, researchers have found that long-term exposure to urban air pollution may have made Covid-19 more deadly. "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 study author Donghai Liang from Emory University in the US. For the study, published in the journal The Innovation, the researchers 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. To examine the association between ambient air pollutants and the severity of Covid-19 outcomes, they 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 (number of Covid-19 deaths in the population). The two indicators can imply the biological susceptibility to deaths from Covid-19 and offer information about the severity of the Covid-19 deaths in the general population, respectively. Of the pollutants analyzed, NO2 had the strongest independent correlation with raising a person's susceptibility to death from Covid-19, the researchers said. According to the study, 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. Moreover, the team 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," Liang added. "The continuations and expansions of current efforts to lower traffic emissions and ambient air pollution might be an important component of reducing the population-level risk of Covid-19 case-fatality and mortality in the US," the authors wrote. Recently, a study, published in the journal 'Sciences Advances', provided the most comprehensive evidence on the causal link between long-term exposure to fine particulate (PM2.5) air pollution and premature death. /IANS