奇速英语

绿化新方式—可移动的“城市树”

Air pollution is one of the world's invisible killers. It causes seven million deaths a year, making it the largest single environmental health risk. In urban areas, air pollution is particularly serious. More than 80% of people living in areas where pollution is monitored are exposed to air quality levels that exceed WHO limits. And given that by 2050 two thirds of the global population will be urban.
One well-established way to reduce air pollution is to plant trees, as their leaves catch and absorb harmful particulates. But planting new trees is not always a good choice for lack of enough space. That's why the "City Tree", a mobile installation which removes pollutants from the air, has been becoming popular in cities around the world, including Oslo, Paris, Brussels and Hong Kong.
Each City Tree is just under 4 meters tall, nearly 3 meters wide and 2.19 meters deep, available in two types: with a chair or a bench. A display is included for information or advertising. Berlin-based Green City Solutions claims its invention has the environmental benefit of up to 275 actual trees.
But the City Tree isn't, in fact, a tree at all— it's a moss culture. "Moss cultures have a much larger leaf surface area than any other plant. That means we can capture more pollutants," said Zhengliang Wu, co-founder of Green City Solutions.
The huge surfaces of moss in each tree can remove dust, nitrogen dioxide and ozone gases from the air. It requires very little maintenance: solar panels provide electricity, while rainwater is collected into a reservoir and then pumped into the soil.
To monitor the health of the moss, the City Tree has sensors which measure soil humidity, temperature and water quality. "We also have pollution sensors inside the installation, which help monitor the local air quality and tell us how efficient the tree is." Wu said. Its creators say that each City Tree is able to absorb around 250 grams of particulate matter a day and contributes to the capture of greenhouse gases by removing 240 metric tons of CO2 a year.