Anne-Sophie Merritt, a researcher at the Institute of Environmental Medicine, has investigated how much air pollution people are exposed to depending on their mode of transport.
Text: Annika Lund, first published in Medicinsk Vetenskap nr 2 2025
How did you conduct the study?
"We hired three people who travelled by bus, bike, or on foot along four major streets in Stockholm: Vallhallavägen, Sveavägen, Odengatan and Solnavägen. We had measured two-kilometre stretches, and the participants moved back and forth simultaneously in two-hour sessions in the morning, at lunchtime, and in the afternoon. They wore monitors that recorded the levels of black carbon, one of the most common and harmful fine particles.
Who was exposed to the most air pollution?
"Black carbon levels were highest on the bus across all four streets. Cyclists were exposed to slightly more black carbon than pedestrians. However, bus journeys are shorter in duration. Cyclists also breathe more heavily, so the dose of black carbon they inhale is higher. Overall, the levels were higher in the morning than later in the day.
Why do you investigate this?
"Research on personal exposure to air pollution usually focuses on residential addresses. But people are not at home all the time, so this was a way to explore personal exposure more accurately. We also hope that our results can inform decision-makers and city planners.
What do you mean by that?
"In the study, we also had people cycle with monitors along two parallel streets where one is more heavily trafficked than the other, even though they are very close together. For example, two people cycled in parallel along Sveavägen and Västmannagatan. Odengatan was paired with Frejgatan and Valhallavägen with Östermalmsgatan.
What did you find?
"Those who cycled along the less busy streets were exposed to 30 per cent less air pollution, and they also had a much more pleasant and safer cycling experience. Cyclists on Valhallavägen, where the cycle lane runs through a tree-lined median, also seemed to be exposed to less pollution. This is worth considering when planning cycle lanes.
Anne-Sophie Merritt is Head of the Environmental Medicine Unit at the Centre for Occupational and Environmental Medicine in Region Stockholm.
