Road traffic, but also modern exhaust gas cleaning systems, release a particularly large amount of ultra-fine dust – particles less than 0.1 microns in size. A long-term study in three German cities now shows that it is precisely these smallest particles that have the greatest impact on human health. They increase the risk of dying from a lung and respiratory disease more than the coarser particulate matter. So far, however, the exposure to this ultra-fine dust has not been measured and reported separately.
Particulate matter is a global problem. The tiny particles with diameters of less than 100 nanometers up to a few micrometers in size can arise through natural processes, but a large part now comes from anthropogenic sources such as agriculture, industry, the burning of fossil fuels in power plants or heating systems or transport. Depending on the source, the composition and size of the particulate matter vary.
Consequences of ultrafine dust at a glance
Studies show that modern coal-fired power plants and other plants with new exhaust gas cleaning technology are good at filtering out coarser fine dust, but they produce a particularly large amount of ultra-fine dust with sizes of less than 0.1 microns. Due to their small size and mass, these ultrafine particles (UFP) only make a negligible contribution to the total particulate matter mass. In terms of the number of particles, however, they represent the largest proportion of fine dust. If these particles are inhaled, they can penetrate particularly far into the lungs and tissue. In addition, these smallest particles have a large surface area and high reactivity, which means that they could also have a greater biochemical effect.
Maximilian Schwarz from Helmholtz Zentrum München and his colleagues have now examined the consequences of this for human health in more detail. To do this, they conducted a multi-centre epidemiological study in the three German cities of Dresden, Leipzig and Augsburg from 2010 to 2017. In order to map different exposure situations, the researchers used measurement data from several measurement stations per city and used a novel statistical approach to analyze the data. This enabled them to achieve a high level of standardization and comparability between measurement stations - usually a major problem when measuring and analyzing ultrafine particles.
Harmful to health, but so far insufficiently recorded
The evaluation of the data showed that mortality due to respiratory diseases was higher in urban areas where there was a particularly large amount of ultrafine dust in the air. Specifically, the research team found that respiratory mortality increased by 4.46 percent with a concentration increase of 3223 particles per cubic centimeter. These results were independent of exposure to other particulate air pollutants such as coarser fine dust with a diameter of 2.5 microns and more. At the same time, the effect of the ultrafine dust on the respiratory mortality risk was significantly higher than that of the coarser particles.
"These results are another step towards a better understanding of the health effects of ultrafine particles and their possible inclusion in future routine monitoring," says Schwarz. As early as 2021, the World Health Organization recommended more data on ultrafine dust and the need for epidemiological studies. Until now, the normal monitoring of air quality has only recorded the total values for fine dust and for gaseous pollutants such as nitrogen oxides. However, the current study has shown that the concentrations of ultrafine dust do not develop proportionally to the fine dust measurement values of the larger particle classes PM2.5 and PM10. "Various sources, temporal-spatial patterns and the urban atmosphere result in almost no correlation between these size classes of particulate matter," explains the team. A separate monitoring of ultrafine dust is correspondingly important.
Source: Helmholtz Zentrum München German Research Center for Environmental Health (GmbH); Article: American Journal of Respiratory and Critical Care Medicine, doi: 10.1164/rccm.202209-1837OC