Airborne particle pollution does not decline outside rush hour in Copenhagen

Green Innovation 5. may 2022 1 min PhD student Marie Bergmann Written by Kristian Sjøgren

People cycling through Copenhagen inhale just as many ultrafine particles in and outside the rush hour. Nevertheless, air quality improves when cycling through parks away from the major highways. New insights into air quality in cities should be incorporated into urban planning so that cyclists are exposed to less pollution, says a researcher.

People cycling through Copenhagen during the rush hour are exposed to many ultrafine particles (aerodynamic diameter <0.1 µm) from internal combustion vehicles.

Ultrafine particles (UFP) are not regulated in the same way as larger particles or nitrogen oxides, but studies indicate that they could harm health even more.

A new study shows that cyclists in Copenhagen cannot avoid the potentially harmful health effects of inhaling many ultrafine particles by cycling outside rush hour because the concentration of ultrafine particles does not decline when traffic volumes decrease.

The results surprised a researcher behind the study.

“This was unexpected. We thought that the concentration of ultrafine particles would decline as traffic volumes decreased after the rush hour, but that did not happen. Our results provide new insight into the quantity of ultrafine particles to which cyclists are exposed in Copenhagen at different times of the day,” explains Marie Bergmann, PhD student, Section of Environmental Health, Department of Public Health, University of Copenhagen.

The research has been published in Environmental Pollution.

Cycled an 8.5-kilometre route in Copenhagen

Marie Bergmann cycled the same route through Copenhagen 61 times during September and October 2020.

She started from the University of Copenhagen and followed an 8.5-kilometre route covering mostly high-traffic streets in Copenhagen, including Nørrebrogade, Åboulevarden, Jagtvej and Kongens Nytorv.

Marie Bergmann carried a handheld nanoparticle counter called a DISCmini to measure the concentration of ultrafine particles at 1-second intervals. The DISCmini was fitted close to her collarbone to enable air sampling within the breathing zone, capturing the quantity of ultrafine particles a cyclist would normally inhale.

Marie Bergmann cycled the route about 20 times during each of the following time periods: morning and afternoon rush hour (starting at 7:45 and 15:45) and morning non-rush hour (starting at 9:45).

“The concentration of ultrafine particles varies greatly by season and by location and is highest on busy routes. We wanted to determine cyclists’ exposure at different times of the day in Copenhagen,” says Marie Bergmann.

Time of day did not affect pollution concentration

The study found no difference in exposure for cycling through Copenhagen during morning rush-hour traffic or waiting until later in the morning.

The mean concentration averaged 18,556 particles per cm3 during the morning rush hour and 17,560 particles per cm3 during the afternoon rush hour versus 18,882 particles per cm3 outside the rush hour in late morning.

In addition, the study found that major intersections or roundabouts with traffic lights and busy road segments with congestion had the highest concentrations of ultrafine particles: 38,000–42,000 particles per cm3. The concentration increased to 44,000–51,000 particles per cm3 at road works and construction sites.

The concentration was about 12,000 ultrafine particles per cm3 on less busy roads with more open spaces and 15,000 particles per cm3 in bus-only zones such as on Nørrebrogade.

By comparison, the concentration in a natural environment, such as a mountain landscape, is about 1,000 ultrafine particles per cm3.

The researchers also found that wind speed and temperature explained about 46% of the variation in the concentration.

“Our figures clearly show that cyclists stopped at traffic lights are exposed to high concentrations of ultrafine particles and also higher than the concentrations recorded by municipal air quality monitoring stations. This is important to consider in setting limit values for the concentration of ultrafine particles to which commuting cyclists are exposed,” explains Marie Bergmann.

Separating bicycles from cars

Marie Bergmann does not take a position on whether the ultrafine particle concentrations in Copenhagen are high or low. They are higher than in some European cities but lower than in others.

Nevertheless, this research shows what can be done at both the societal and individual levels to reduce exposure to these potentially harmful particles.

In societal terms, this new knowledge can be incorporated into urban planning policies for infrastructure, including moving cycling lanes away from busy roads and closing off road segments to private motor vehicles, since this would minimise cyclists’ exposure to air pollution and maximise public health benefits.

The individual cyclists commuting through cities may consider cycling on less busy roads or through parks, which have lower concentrations of ultrafine particles.

“Although studies have shown that urban cyclists are exposed to air pollution, remember that studies also show that urban cycling is still healthier than not cycling at all. The positive health benefits of cycling generally outweigh the negative effects of air pollution,” concludes Marie Bergmann.

Ultrafine particle exposure for bicycle commutes in rush and non-rush hour traffic: a repeated measures study in Copenhagen, Denmark” has been published in Environmental Pollution. The research was funded by the Health and Care Department of the City of Copenhagen and a 2018 Novo Nordisk Foundation Challenge Programme grant to Rudi Westendorp for the project Harnessing the Power of Big Data to Address the Societal Challenge of Ageing.

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