The vision of Italian architect Stefano Boeri is starting to take shape around the world, with his so-called vertical forest towers going up in Switzerland and Milan. Now the Chinese region of Liuzhou will also play home to some of his handiwork, with construction underway on a so-called Forest City that is hoped to soak up some of the country's infamous air pollution.
The Liuzhou Forest City will be constructed in the mountainous region of Liuzhou, in Southern China.
Commissioned by the Liuzhou Municipality Urban Planning department, the city will host some 30,000 residents and feature the hallmarks of a typical city, such as offices, houses, hotels, hospitals and schools. These buildings will draw on geothermal energy and rooftop solar panel for their power needs.
The city will be clad in trees and plants – not just in the parks, gardens and city streets, but over building facades too. This will total 40,000 trees and almost one million plants, drawn from more than 100 species. It will absorb an estimated 10,000 tons of C02 and 57 tons of pollutants each year, plus it will produce a claimed 900 tons of oxygen annually.
The city will be built to the north of the existing city of Liuzhou, which is home to around a million and a half inhabitants. The Forest City will be connected to this metropolis by way of a fast rail line occupied by electric cars. Construction is currently underway, with the Liuzhou Forest City expected to be completed by 2020.
Source: Stefano Boeri Architetti
1st; vegetation is not producing ozone: "potential of emissions from urban vegetation --combined-- with anthropogenic emissions to produce ozone and particulate matter has long been recognized." Note the critical word 'combination'.
2nd: The study is looking at one variable in isolation: "we investigate how heat waves affect emissions of volatile organic compounds from urban/suburban vegetation". Not the over-all benefit/loss of vegetation in urban environments.
One example why #2 is important: the "up to 60%" contribution due to a 5C rise in simulated temperature. However, "Trees and other plants help cool the environment, making vegetation a simple and effective way to reduce urban heat islands." "Evapotranspiration, alone or in combination with shading, can help reduce peak summer temperatures by 2–9°F (1–5°C)."
https://www.epa.gov/heat-islands/using-trees-and-vegetation-reduce-heat-islands
So more vegetation helps reduce high temperatures, which counters the release of VOCs due to high temperatures.