Covid-19 deaths exacerbated by urban air pollution

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 2020.

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 people diagnosed with the virus) and the mortality rate (number of Covid-19 deaths in the population).

Of the pollutants studied, NO2 had the strongest independent correlation with raising a person’s susceptibility to death from Covid-19. 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.

The researchers believe 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, although no notable associations were found with O3.

“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 researcher Donghai Liang.

“Long-term exposure to urban air pollution, especially nitrogen dioxide, might enhance populations’ susceptibility to severe Covid-19 death outcomes,” he added.

“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 [places with] historically high NO2 pollution, including the metropolitan areas in the state of New York, New Jersey, California and Arizona.”

Liang also said that air pollution is a health equity issue: the burden of NO2 pollution is not evenly shared. People with lower income and people of colour often face higher exposure to ambient air pollution and may experience a more significant impact from the pollutants. Not having many choices in residency, many live by highways or industrial sites, which makes them especially vulnerable to air pollution.

“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 United States,” Liang said.

The global lockdowns resulting from the pandemic have been shown to lower air pollution in many areas, with one study estimating that 11,000 lives were saved in Europe as a result of lower emissions due to fewer cars on the road and reduced industry activity.

However, a recent analysis in Scotland found that the level of toxic fine particles in the air had not declined at all, despite a 65 per cent reduction in the number of vehicles on the country’s roads.

Furthermore, while China saw a temporary respite in its air pollution levels during the height of lockdown, as soon as restrictions were eased, levels rose again to a peak higher than pre-lockdown conditions.