Researchers from IRD, the CNRS and UGA took part in a European study of sources of fine particulate matter that are harmful to health, coordinated by the Paul Scherrer Institute (PSI, Switzerland). Their results, published in the journal Nature on 18 November 2020, reveal the harmful nature of atmospheric particulate matter due to its oxidative potential. They suggest that this indicator should be taken into account in future air-quality regulation measures to protect the health of populations worldwide.
Air pollution is responsible for several million premature deaths each year worldwide, and is one of the five major health-risk factors, alongside high blood pressure, smoking, diabetes and obesity. To combat this phenomenon, measures to limit emissions are implemented above a certain mass concentration threshold of fine particulate matter suspended in the air. In addition to these quantitative control measures, scientists are seeking to understand what makes atmospheric particulate matter so dangerous.
Oxidative stress that intensifies inflammatory reactions
In this study, the researchers point out that the amount of fine particulate matter is not the only decisive factor regarding health risks. They examined the sources of air pollution in Europe, combining measurements of atmospheric chemical composition, toxicology and oxidative potential.
This indicator is used by scientists to estimate health-related exposure to air pollution,
Certain fine particulate matter generates oxidative stress in the lungs, which can cause damage to the cells and tissues of the human body."
Gaëlle Uzu, atmospheric biogeochemist at IRD and co-author of the study
To start with, researchers at PSI in Bern exposed cells from the human respiratory tract, known as bronchial epithelial cells, to samples of atmospheric particulate matter in order to test their biological response. At the same time, the Institute for Environmental Geosciences (IGE - CNRS/IRD/UGA/Grenoble INP) in Grenoble measured the oxidative potential for the same doses of particulate matter exposed to the cells. Both teams were able to show that fine particulate matter with increased oxidative potential intensifies the inflammatory response of cells, suggesting that oxidative potential is an indicator of the harmfulness of aerosols.
An increased health risk in European metropolises
In a second step, the researchers collected various samples of atmospheric particulate matter in Switzerland. They analyzed the composition of these samples using a mass spectrometry technique developed at the Paul Scherrer Institute. "The chemical profile of each sample of material obtained in this way indicates the source from which it came", explains Kaspar Dällenbach, an atmospheric chemist at PSI and lead author of the study.
At the same time, the IGE carried out measurements of their oxidative potential for all samples from five Swiss cities. By combining all these measurements with advanced mathematical processing, it was possible to determine the oxidative potential of each emission source and to use a computer model to identify the areas with the highest oxidative potential in Europe throughout the year. The similarity between the predicted values and the annual series of oxidative potential data previously measured on various French sites by the IGE enabled the validation of the model outside Switzerland.
Result: metropolitan areas, such as Paris and the valley of the River Po in Northern Italy, are critical regions for air pollution. Not only are people in urban areas exposed to higher quantities of fine particulate matter, but the particulates in these areas are also more harmful to health than the aerosols in rural areas.
Aerosols of human origin are more oxidative
This study shows that while most fine particles consist of minerals and inorganic (or "secondary") aerosols, such as the ammonium nitrate and ammonium sulphate used in agriculture, the oxidative potential of fine particulate matter is mainly due to organic (or "anthropogenic") aerosols from wood fires and metal emissions (originating from brake and tyre wear associated with road traffic, in particular).
To reduce air pollution, the authors therefore suggest that steps should taken not only to regulate the quantity of fine particulate matter, but also to take account of the different sources of particulates and their oxidative potential.
"One of the key issues for this research is to predict health-related exposure to air pollution on a continental level, particularly in the Global South where the acceleration of urban development will very soon require the monitoring of emissions in order to protect the health of populations", stresses Gaëlle Uzu.