Fine particulate matter, especially particles with a diameter of less than 10 ?m (PM10), is a known health risk in our cities. While acute consequences such as respiratory and cardiovascular problems are well documented, the long-term effects of exposure have remained unclear. A new study entitled "Medium-Term Lag-Response Associations Between PM10 Exposure and All-Cause Mortality in Valencia and London: A Time-Stratified Case-Crossover Study," published in the prestigious Journal of Epidemiology and Global Health, has now systematically investigated this question – and arrived at surprising results.

The research analyzed, for the first time, the medium-term effects of PM10 on mortality rates in two European metropolises: London and Valencia. The team examined whether deaths increase up to 21 days after high levels of fine particulate matter. To do this, the researchers used an established method to control for the influence of confounding factors such as temperature and isolate the pure correlations.

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The result: The study confirms that particulate matter increases the risk of death in both cities in the short term. However, Valencia revealed another worrying development: In addition to the immediate effects, there was a clear and significant increase in deaths 14 days after PM10 exposure. This delayed peak did not occur in London in the same way. Furthermore, the researchers were able to show that a model that considers particulate matter exposure over several days best explains the health risks. This confirms the assumption that the consequences of particulate matter exposure can build up slowly over time.

"Our results show that particulate matter causes not only immediate but also delayed health problems," the study authors stated. "Especially for vulnerable groups such as the elderly or patients with pre-existing chronic conditions, precautionary measures should be taken not only during periods of high exposure but also for the two to three weeks following."

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These findings have direct practical implications:

Early warning systems should be supplemented with medium-term risk forecasts.

Hospitals can better plan their resources by anticipating an increase in emergency room visits in the weeks following particulate matter events.

Health authorities and physicians can issue targeted recommendations, such as the use of masks and air purifiers, or the avoidance of strenuous outdoor physical activity.

The study fills an important knowledge gap and underscores that the health consequences of particulate matter do not end on the day of exposure but can develop over weeks. This knowledge is essential for more effective public health protection. To learn more about our research, please read our publication in the Journal of Epidemiology and Global Health: https://doi.org/10.1007/s44197-025-00459-x.