Temperature reversal in fog or Saharan dust promotes fine particles in the air. Their high concentration can worsen the consequences of COVID-19.
From October to March, a large part of the Swiss Plateau and the Po plain can be covered with fog or mist. These thermal inversions act like a hat and trap fine particles that reach excessive values under the inversion layer and worsen the consequences of COVID-19. © NASA-OB-DAAC, AQUA - MODIS-Satellite
The correlation between high fine particle concentration and the severity of influenza waves is well known to epidemiologists. An interdisciplinary team from the University of Geneva (UNIGE) and Meteodat, a spin-off from the Swiss Federal Institute of Technology Zurich, has been investigating the possible interactions between very high levels of fine particulate matter and the virulence of COVID-19. Their findings, published in the journal Earth Systems and Environment, suggest that high concentrations of fine particles under 2.5 micrometers can modulate, or even amplify, waves of SARS-CoV-2 contamination and partly explain the unique profile of the COVID-19 pandemic. The increase in fine particles is generally favored by air temperature inversions, characterized by fog situations, or by intrusion of Saharan dust. The study provides preventive air pollution leads to limit future coronavirus disease and mortality outbreaks.
Epidemiologists widely agree that acute and locally elevated fine-particle concentrations are correlated with severity of influenza waves. “We looked into whether such a link also existed with the virulence of COVID-19 disease,” says Mario Rohrer, a researcher at the Institute of Environmental Sciences in the UNIGE Faculty of Science and Director of Meteodat.
A surprising time lag
COVID-19 studies in Italy and France suggest that SARS-CoV-2 was already present in Europe at the end of 2019, while the sharp increase in morbidity and mortality was only recorded in spring 2020 in Paris and London. 'This time lag is surprising. It suggests that, in addition to the contact between people, another factor could promote the transmission and especially the severity of the infection,” said Rohrer. His research team was able to show that these increases in cases follow phases in which the levels of fine particles in the air are higher.
The team made similar observations in the canton of Ticino, where fine particle pollution increased sharply during a period of shallow haze on the Magadino plain and the Sotto Ceneri, observed in late February 2020. “Soon after, there was an explosive increase in hospital admissions due to COVID-19 in Ticino. The fact that a large carnival event with some 150,000 visitors took place at the same time probably had an additional impact on the spread of the virus,” said Mario Rohrer.
This information is important for Switzerland, as the increase in fine particulate matter concentrations is particularly frequent in the case of thermal inversions, i.e. when fog is formed on the Swiss Plateau, thereby limiting the exchange of air masses so that emissions accumulate in the air layer below the fog. Dust from the sand storms in the Sahara, which was also highlighted in this study, is also a frequent feature of Switzerland.
Aggravating factor
The Swiss research team shows that acute concentrations of fine particles, particularly those smaller than 2.5 micrometers, cause inflammation of the respiratory, pulmonary and cardiovascular pathways and thicken the blood. 'In combination with a viral infection, these inflammations can lead to severe disease progression. Inflammation also helps the virus to attach to our cells,' the researcher says. Moreover, it is possible that the coronavirus could also be transported in fine particles. ‘This has already been demonstrated for influenza and an Italian study found coronavirus RNA on fine particles. Of course, this remains to be demonstrated, but it is a possibility,' he adds.
A multifactorial pandemic
Although fine-particle pollution influences the virulence of the coronavirus and the progression to severe COVID-19, researchers make clear that physiological, social, or economic factors also influence the pandemic. Mr. Rohrer concludes: "The results of this study provide an opportunity to take preventive measures in the event of future increases in the concentrations of fine particles. This would allow us to take action to try to limit a new outbreak of morbidity and mortality due to COVID-19.”
Full publication (Fr) : UNIVERSITÉ DE GENÈVE Published in November 2020