Airborne particulate matter from the deserts of North Africa is reaching Europe in ever-increasing quantities. This has implications for health and for solar energy installations. A comprehensive study led by the Paul Scherrer Institute PSI published in Nature shows that this type of pollution is on the rise – a trend that could be further exacerbated by climate change.
While, thanks to strict regulations, particulate matter air pollution due to emissions from human activity in transportation, households, and industry are decreasing in Europe, another source is developing in the opposite direction: desert dust.
To determine more accurately the level of desert dust pollution in different regions of the continent, researchers at the Paul Scherrer Institute PSI, in cooperation with colleagues from across Europe, have collected data acquired over the past ten years from more than a hundred measuring stations and combined it with artificial intelligence. The result: in southern Europe, the average concentration of desert dust is 5.3 micrograms per cubic metre of air – more than twice as high as in central and northern Europe, where an average of 2.1 micrograms was measured. Overall, the amount of dust has increased by about half a microgram per cubic metre during this period. “That corresponds to an increase in this dust pollution of ten to twenty-five percent,” says project leader Kaspar Dällenbach from the PSI Center for Energy and Environmental Sciences. “This is not negligible, both in terms of the efficiency and cost-effectiveness of large solar installations and with regard to the health impacts of increased particulate matter pollution.”
To enable scientists to make longer-term comparisons, the relevant data collection at most measuring stations does not extend far enough into the past. Therefore the researchers also used ice core data from Colle Gnifetti on the Swiss-Italian border in the study: dust particles trapped in the ice of the Alpine glacier over recent centuries reveal that the concentration of desert dust there has more than doubled over the course of industrialisation – that is, over the last 150 years.
Desert dust is easy to distinguish from other particulate matter
As a reliable indicator for desert dust, the researchers used the concentration of aluminium in airborne particulate matter. This element is characteristic of dust particles transported from deserts. Particulate matter from urban construction sites, for example, is very high in calcium, and particules from traffic and household emissions contains mainly soot or carbon from the combustion of petroleum. “Through chemical analyses, we can determine the origin of particulate matter found at ground level very accurately,” says Petros Vasilakos, another researcher at the PSI Center for Energy and Environmental Sciences and lead author of the study.
There are concerns that desert dust concentrations will continue to rise, partially undermining efforts to curb human-caused emissions of particulate matter. This study identifies the increasing desiccation of the Sahara in North Africa as the cause. In addition, altered atmospheric circulation patterns are bringing increasingly strong winds from this region to Europe. “It is not yet definitively clear to what extent human-induced climate change has contributed to this development or whether it is further intensifying it,” says Kaspar Dällenbach. “However, our current understanding suggests that the increase in desert dust is at least facilitated by human greenhouse gas emissions and the associated global warming. This leads to drier conditions in certain regions and the expansion of deserts.”
Desert dust can put stress on human health
With regard to the health consequences of elevated desert dust concentrations in Europe, the researchers evaluated the current state of epidemiological studies. Long-term effects from transported desert dust, such as pneumoconiosis, asthma, and chronic bronchitis, could only be proven definitively through extensive long-term studies. The immediate increase in mortality on days with elevated levels of airborne desert dust, however, is well documented: measurably more people die as a result of heart attacks and respiratory problems on days with dust pollution than on other days. “The number of storms carrying desert dust to us from the Sahara and the Arabian Desert has not actually increased,” Petros Vasilakos says. “But they have become more intense over the ten years studied, and as a result they are now transporting more dust to Europe than they did before.”
Southern Europe is particularly affected – from Greece in the east through Italy to Spain and Portugal. The study also detected elevated dust levels in western France. “This is because,” explains co-author Imad El Haddad, who also conducts research at the PSI Center for Energy and Environmental Sciences, “air masses from the Sahara often flow out into the Atlantic and then turn north again towards western Europe.”
A unique combination of physical data and AI
What makes this study special is, first of all, that it represents probably the most comprehensive data collection to date on desert dust in Europe: “We included virtually all available measurement series on this topic, because we were able to recruit more than 50 colleagues across Europe to participate,” says El Haddad. The PSI researchers benefited from their membership in the pan-European research network ACTRIS, in which aerosol researchers join forces to coordinate their series of long-term measurements of aerosols, clouds, and trace gases internationally and to make them freely accessible.
Furthermore, the researchers used artificial intelligence to extend existing, purely physical models of particulate matter distribution: “While conventional models are good at predicting strong desert dust episodes, they rarely capture smaller dust events and have difficulty accurately determining the dust concentration at ground level,” says Kaspar Dällenbach. “With our measurement data and the AI, which estimates concentrations for other regions of Europe on the basis of measurements from more than a hundred locations, we were able to supplement the model with this information and thus create a reliable, health-relevant particulate matter map of dust particles for all of Europe.” The data collected in this way can now also serve as a basis for future studies investigating long-term health consequences.
Unlike particulate matter directly attributable to human activity, such as exhaust fumes, chimney smoke, and abrasion processes, desert dust emissions cannot be reduced by any direct intervention. However, comprehensive climate protection measures to limit global warming could, in the long term, help to curb the desiccation of desert areas and thus the expansion of these dust sources. For now, though, Europe has to live with the increase in desert dust.
It would be conceivable to establish warning systems for high concentrations, similar to those used for urban particulate matter, so that particularly sensitive individuals or those with lung conditions can take precautions on dusty days. The energy sector would also benefit: desert dust in the air shades solar panels and accumulates on them, reducing their electricity production. If energy providers could anticipate this, they could compensate by boosting production from other power plants, thus ensuring the stability of the grid.