Some years ago, working with Putney Society, we reviewed, as far as we were able, the effectiveness of the City Tree; this summarises what we found: In December 2020, Wandsworth Council installed a City Tree near outside the PretoRestaurant with the aim of filtering “particulate matter and fine dust out of the surrounding air, while simultaneously purifying and cooling the air.” But how effective is it in reducing such the highly-affected levels of pollution there? City Trees work by drawing air over panels of living moss, remove polluting fine particles and cool the air. It’s manufactured and marketed by Green City Solutions (GCS) of Bestensee, Germany. As far as we were able to determine, there are no peer research evaluations of the device, the nearest being research commissioned directly by GCS from an independent laboratory, the Leibniz Institute for Tropospheric Research (TROPOS). TROPOS carried out tests in January 2020 to measure the filter effect of the new CityTreemodel CT2020 at distances of 1, 3 and 5 metres; for ultrafine particles (and it’s not entirely clear what size this referred to) These reductions were not especially impressive, either in their size or, especially, in their extent. The Council made the ambitious claim that “residents and visitors to Putney High Streetare benefiting from cleaner air” from the installation of the City Tree. However, the only realistic conclusion to be drawn from the measurements provided by GCS, is that - except in a small area next to the Tree - it is virtually ineffective in reducing pollution overall.
Furthermore, to achieve any realistic lowering of particulate pollution in Putney High Street,many more Trees would need to be installed. It’s not clear what the current cost of each Tree was then, but in 2018 it was £17,600, excluding installation
In other words, the Tree is an expensive irrelevance. It does have a nice seat, though.
Richard Carter ● 16d