Air Pollution Raises Coronavirus Death Rate
Is there a higher Covid-19 death rate in districts with high air pollution? A new study by Harvard University scientists suggests this is the case in the US — and should lead to both short-term and general consequences regarding air quality and particulate matter measurement.
The general link between polluted air and health problems has repeatedly been covered here on the air-Q air quality blog. Breathing bad air burdens the airways — and can trigger allergic asthma, hay fever, or atopic dermatitis (more on this in this blog post). The European Environment Agency attributed more than 410,000 premature deaths in 41 European countries in 2016 to air pollution from particulate matter (PM2.5), another 71,000 to nitrogen oxides, and 15,100 deaths to ground-level ozone exposure (article from October 17, 2019).
Scientists at the Harvard T.H. Chan School of Public Health have now examined, in a current statistical analysis, what influence air pollution in American counties has on the death rate from the coronavirus (SARS-CoV-2):
If particulate matter concentration rises by just 1 μg/m³, the Covid-19 death rate rises by 15 percent.
Patients who breathe bad air for more than 15 years are more likely to develop pre-existing conditions, since particulate matter particles can penetrate via the alveoli into the bloodstream and human cells, reaching the lungs and brain. This often causes prolonged inflammation in lung tissue, which in extreme cases can lead to cancer. These pre-existing conditions are subsequently a decisive factor in whether a Covid infection runs mild, severe, or even fatal.
Effect of air pollution in Manhattan
The Harvard study's findings are clear: had Manhattan reduced its air pollution over recent decades accordingly by 1 μg/m³, there would very likely have been around 250 fewer deaths by April 4.
Besides lung damage, diabetes and cardiovascular problems are among the most common pre-existing conditions found in Covid-19 ICU patients in the US. Four out of five of these patients have such a pre-existing condition.
According to study lead and biostatistics professor Dr. Francesca Dominici, this link between PM2.5 air pollution and the Covid-19 death rate is 20 times stronger than previously determined links between air pollution and a general death rate. The so-called Medicare study (2017) had shown a 0.7 percent rise in death rate for each unit increase in air pollution.
Other risk factors were factored out of the statistics as far as possible: this includes, for example, the density of available ICU beds relative to population size, or patients' obesity.
The Harvard scientists' findings mean that, in the short term, American counties with traditionally high air pollution should prepare for more severe cases of the coronavirus epidemic. This also affects the supply of ventilators and respiratory masks within a state. According to the study, especially many severe cases could occur in the agriculture-dominated "Central Valley" county (California) or in "Cuyahoga" county (Ohio), which has particularly many industrial businesses.
Differentiated measurements of particulate matter of every size needed
For the time after the Corona crisis, though, broader measurements especially of the smallest particulate matter particles (ultrafine particulate matter) should be considered medium-term — also in Europe. "New studies show that smaller particulate matter particles and ultrafine particulate matter remain airborne for a very long time, in some cases indefinitely, since these particles only fall to the ground once they've attached to larger particles," says particulate matter expert Frank Hoferecht, managing director of ETE EmTechEngineering GmbH — the first spin-off from the DBFZ German Biomass Research Centre non-profit GmbH.
To date, however, there are no comprehensive surveys of the number of such ultrafine particulate matter particles in ambient air, for example in cities. "With modern combustion engines, this fact is even deliberately exploited," says Hoferecht — here, smaller, more dangerous particulate matter is produced in favor of reducing coarse particulate matter. Hoferecht: "So the most modern high-pressure direct-injection engines produce significantly more ultrafine particulate matter compared to conventional engines, since the fuel is already broken down into extremely fine particles before combustion."
To recognize the dangers to one's own health, corresponding particulate matter measurement data should be collected and published in a more differentiated way, demands Mario Körösi, managing director of Corant GmbH. "The mass figure is misleading for ordinary citizens. It suggests that the same mass per volume means the same level of harm. Scientific findings suggest, however, that particle count matters more. For example, at the same mass, up to a million more particles can hide in ultrafine particulate matter PM0.1 compared to PM10."
Instead of focusing solely on the misleading mass figure, particulate matter should be distinguished by particle size down to ultrafine particulate matter (PM0.1), by mass per volume (µg/m³), and additionally by particle count, says Körösi. "If this data isn't measured in a differentiated way and made accessible to people, misinterpretations occur that prevent progress and, ultimately, can harm the health of many."
Harvard scientists plan to evaluate further data
The Harvard scientists have submitted their study "Air Pollution and Mortality in the Medicare Population" to the New England Journal of Medicine for publication in a peer-reviewed journal. The researchers have published the underlying datasets here. Further research will include, among other things, data that narrows down coronavirus cases more regionally. Beyond the death rate, socio-demographic factors are also to be examined.