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Do Ultrafine Particles (UFPs) Lead To Increased Hospital Admissions?

Featured Publication, EPI,

Over the past decades, epidemiological studies have clearly demonstrated the effects of air pollution on health. There are now explicit recommendations from the World Health Organization regarding guidelines for particulate matter, especially PM2.5 (particulate matter with a diameter of less than 2.5 µm). However, it is still unclear to what extent smaller size fractions of airborne particles – ultrafine particles (UFPs; particles with a diameter of less than 0.1 µm (= 100 nm)) – contribute to health effects. Ultrafine particles contribute only negligibly to the particle mass but dominate particle number and surface area and are therefore considered relevant from a toxicological perspective. However, epidemiological studies are lacking to conclusively demonstrate the effects on human health.

Ultrafine particles are not measured at official monitoring stations, therefore long-term measurements at research stations are necessary to investigate their effects. Researchers at Helmholtz Munich, led by Prof. Annette Peters and Dr. Susanne Breitner-Busch from the Institute of Epidemiology, were able to identify a significantly increased risk of respiratory mortality five to seven days after exposure to ultrafine particles in a previous study. This association was particularly evident for the smallest particle sizes, measuring only 10-30 nm.

In their new study, the researchers examined the effects of ultrafine particles on hospital admissions for cardiovascular and respiratory diseases. Data from three German cities, Dresden, Leipzig, and Augsburg, were analyzed over eight consecutive years (2010-2017). A unique feature of this study is the use of multiple measurement stations per city, representing both urban background concentrations and exposures in high-traffic areas of the cities.

The study observed more hospital admissions for cardiovascular and respiratory diseases on days with particle exposure, although the effects for ultrafine particles were not statistically significant. When specific subfractions were examined, an increase of 1,630 particles/cm3 of particles 30-100 nm in diameter led to a 1.16% increase in the risk of respiratory hospitalization (95% confidence interval: 0.31%; 2.02%). However, the effects were more pronounced for particles that dominate the mass of particulate matter rather than the number of particles. The study observed a 1.55% increase in hospital admissions (95% confidence interval: 0.86%; 2.25%) for an increase of 829 particles/cm3 of particles with a diameter of 100-800 nm. These findings were consistent and could be validated with the results for PM2.5.

"The study underpins the impact of air pollution on health. It shows that air pollution is a complex mixture of air pollutants, consisting of particles and gases, and emphasizes that for future risk assessments, measurements of ultrafine particles are necessary in addition to the legally required monitoring of fine particulate matter and nitrogen dioxide and ozone," says Prof. Annette Peters. In this context, the World Health Organization has already called for lower limits for established air pollutants in 2021 and the inclusion of more high-quality data on ultrafine particles, as well as the integration of UFPs into existing routine measurements, which forms a crucial basis for investigating health effects.

This study was conducted by Helmholtz Munich in collaboration with the Saxon State Office for Environment, Agriculture, and Geology.


About the scientists

Prof. Dr. Annette Peters, Director of the Institute of Epidemiology at Helmholtz Munich

Dr. Susanne Breitner-Busch, Senior Scientist at the Research Group “Environmental Risks” at Helmholtz Munich

Maximilian Schwarz, Ph.D. Student at the Institute of Epidemiology at Helmholtz Munich

Original publication

Schwarz et al. (2023): Impact of ultrafine particles and total particle number concentration on five cause-specific hospital admission endpoints in three German cities. Environment International. DOI: 10.1016/j.envint.2023.108032

More information

For more information on the previous study of ultrafine particles in three German cities here.

The study displayed the basis for the new results. 


Funding information

Supported by grants from the Saxon State Office for Environment, Agriculture and Geology, Dresden, Germany.

Porträt Maximilian Schwarz

Maximilian Schwarz

PhD Student