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Study finds long-term exposure to black carbon from traffic exhaust at residential address increases the risk of stroke

Long-term residential exposure to locally emitted black carbon (BC) from traffic exhaust increases the risk of stroke even in low-pollution environments, according to a study by researchers at Karolinska Institutet and other universities in Sweden. The open-access study, published in the journal Environmental Health Perspectives, suggests that it is mainly black carbon from traffic exhaust that increases the risk for stroke, and not particulate matter from other sources.

Researchers at Karolinska Institutet, University of Gothenburg, Umeå University, the Swedish Meteorological and Hydrological Institute and SLB analysis-Environmental unit in Stockholm found few consistent associations were observed between different particulate components and ischemic heart disease (IHD) or stroke. However, long-term residential exposure to locally emitted BC from traffic exhaust was associated with stroke incidence.

We see that these emissions have consequences even in low-pollution environments like Swedish cities.

—Petter Ljungman, first author

The researchers followed almost 115,000 middle-aged healthy individuals living in Gothenburg, Stockholm and Umeå over a period of 20 years. During this time, some 3,100 of the people suffered a stroke. With the help of dispersion models and Swedish emission inventories, the researchers were able to estimate how much different local emission sources, including from traffic exhaust, road wear and residential heating, contributed to particulate matter and black carbon at specific addresses in these cities.

The researchers found that for every 0.3 micrograms per cubic meter (μg/m3) of black carbon from traffic exhaust, the risk of stroke increased by 4%. Similar associations were not seen for black carbon emitted from residential heating or for particulate matter in general, neither from inhalable particles with a diameter of 10 micrometers or less (PM10) or from particles with a diameter of 2.5 micrometers or less (PM2.5).

In the studied cities, the annual averages of PM2.5 ranged from 5.8 to 9.2 μg/m3, considerably lower than current European Union standard of 25 μg/m3. There is currently no specific metric for black carbon in EU, which includes it as part of its broader regulation of particulate matter.

The study was funded by the Swedish Environmental Protection Agency as part of the Swedish Clean Air and Climate Research Program.


  • Petter L. S. Ljungman, Niklas Andersson, Leo Stockfelt, Eva M. Andersson, Johan Nilsson Sommar, Kristina Eneroth, Lars Gidhagen, Christer Johansson, Anton Lager, Karin Leander, Peter Molnar, Nancy L. Pedersen, Debora Rizzuto, Annika Rosengren, David Segersson, Patrik Wennberg, Lars Barregard, Bertil Forsberg, Gerd Sallsten, Tom Bellander, and Göran Pershagen (2019) “Long-Term Exposure to Particulate Air Pollution, Black Carbon, and Their Source Components in Relation to Ischemic Heart Disease and Stroke” Environmental Health Perspectives 127:10 doi: 10.1289/EHP4757


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