A single breath of wind contains small eddies and currents that vary in speed and direction with differentfrequencies.

一阵风包含着因频率不同而速度及方向有差的气流。

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But when a violent wind bends tall poplars and scatters the leaves in eddies, when it uproots trees and carries off the roofs of buildings, who can doubt the existence of air?

但是当暴风吹弯了高大的杨树，把树叶吹散成涡旋，当它连根拔起树，吹走建筑的屋顶，谁会怀疑空气的存在呢？

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"A researcher I was speaking to recently reckons green walls in urban canyon environments (areas where walls are higher than the width of the road separating them) are more effective than trees at collecting particles because the way the wind eddies around and then moves down the wall, " Laurence said.

CNN: Green walls create new urban jungles