We all know that trees help clean the air in cities, but which ones are the most effective? Most effective.
For this study, a team from the University of Gothenburg, led by Professor Håkan Playgel, analyzed the leaves and needles of 11 species of trees growing in the same area of the Gothenburg Botanical Gardens. Deciduous trees consisted of poplar, cherry, rowan, beech, oak, walnut and birch, while conifers consisted of larch, spruce, fir and black pine.
Scientists have turned their attention to polycyclic aromatic hydrocarbons (PAHs), as much of the urban air pollution comes from cars. A total of 32 PAHs were analyzed, some of which were particle bound and others gaseous.
Among all trees, black pine and fir were found to absorb acicular gaseous PAHs the best. As an added bonus, unlike deciduous trees that lose their leaves in winter, most conifers keep their needles all year round and are able to trap his PAHs in both summer and winter.
conifer do Larch, a coniferous tree, has been shown to be the best absorber of particle-bound PAHs. All deciduous trees came next, though. This is likely due to the fact that broader leaves have a larger surface area to trap particles than the thin needles of spruce, fir, and pine trees.
The scientists noted that the pollutants did not appear to affect the photosynthetic capacity of the trees, but added that this may not be the case in more polluted cities. Concerns have been expressed about the potential for contaminants to accumulate in the soil when leaves and needles containing PAHs are dropped as those leaves and needles decompose over time.
Furthermore, the team suggests that simply lining the streets with trees is not always the best approach. Pollutants can become trapped near roads. In such situations, using slow-growing plants such as hedges may be more effective.
A paper on this study was recently published in the journal ecological indicator.
Source: University of Gothenburg
