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Purifying the air with plants

Which tree species are best at filtering out air pollution, thus improving the air quality in cities? Measurements in Botaniska’s Arboretum are going to provide the answer to that question in a research project with scientists from Botaniska and the Universities of Gothenburg and Lund.

Purifying the air with plants – trees' significance for air quality in cities

More and more people are moving into cities and there is great pressure to densify built-up areas. Densification often occurs at the cost of green belts, but parks and other greenery in cities contribute ecosystem services that are vital for city-dwellers' well-being. One such ecosystem service is that a city's trees can filter out air pollution and reduce the population's exposure to harmful substances in the air. However, knowledge is scanty about how great the significance is of trees to purify the air. It is also unclear which tree species are best att absorbing air pollution.

"In this research project, we want to answer questions like: How much does a city's greenery influence the level of air pollution in the city environment? Which trees purify the air most effectively? How should the city's greenery be designed to contribute most effectively to the filter effect? Knowledge like this can be used in city planning among other things, to create sustainable cities", explains Dr. Jenny Klingberg, researcher and environmental communicator at the Botanical Garden.

There is a proven connection between exposure to air pollution and increased risk for cardiovascular illnesses and respiratory problems. Particles in particular constitute health hazards but it has not yet been fully established which components in air pollution particles are most dangerous. Particle-bound PAHs (polycyclic aromatic hydrocarbons) are suspected of standing for most of the effects. Among PAHs, benzo(a)pyrene (BaP) is the most carcinogenic.

"We're going to focus on measuring PAHs in this project, but even measure the air pollutant nitrogen dioxide (NO2) that exceeds permitted levels in many cities. Traffic is an important source of emissions when it comes to both NO2 and PAHs in built-up areas", declares project leader Professor Håkan Pleijel from the Department of Biological and Environmental Sciences at the University of Gothenburg.

During the summer of 2018, leaves and needles were collected from 12 different species in Botaniska's Arboretum. An almost 20-metre-long pair of carbon fibre telescope-secateurs was ordered especially from the USA to be able to reach the leaves high up at the tops of the trees. The leaves and needles are now being analysed in laboratories to find out how much air pollution has stuck to them.
"The Arboretum offers a unique opportunity to test many different tree species from similar environmental conditions and exposure to air pollution. We're going to learn masses about which species are best at filtering out air pollution from the air", says Dr. Henrik Sjöman, the scientific curator at Botaniska and a researcher at the Swedish University of Agricultural Sciences (SLU) at Alnarp.

The research project "Purifying the air with plants – can urban vegetation reduce exposure to PAHs?" is financed by FORMAS. The project is ongoing during 2018-2020 and led by Prof. Håkan Pleijel. Other collaborating researchers are Ass. Prof. Bo Strandberg from the Division of Occupational and Environmental Medicine at the University of Lund, and Dr. Jenny Klingberg and Dr. Henrik Sjöman from the Gothenburg Botanical Garden.

Updated: 2020-02-14 08:30