China has reportedly built the biggest air purification tower in the world, standing¹ at 100 metres (328 feet).

据报道，中国建造了世界上最大的空气净化站，高达100米。

This is particularly good news as China is the world's deadliest nation for outdoor air pollution, according to the World Health Organisation² (WHO).

世界卫生组织说，这对中国来说尤其合适，中国是最需要治理空气污染的国家。

Another report by WHO warns that air pollution is the biggest environmental risk to health, responsible for one in nine deaths annually³ worldwide and killing⁴ around 3 million each year. This is only getting worse.

世界卫生组织发出警告，空气污染对健康的危害最大，全球每年死亡率达九分之一，因为空气污染死亡的人数年均三百万。而且空气污染日益严重。

In the northern Chinese city of Xian, there is some hope. Here, the experimental tower is having a positive effect on air quality in the area, reports the South China Morning Post.

但是在西安，这种中国北方城市，希望犹存。《南华早报》说实验站确实改善了空气质量。

Cao Junji, who leads the research on the tower, told the paper:The tower has no peer in terms of size...The results are quite encouraging.

实验站的负责人曹军骥告诉《南华早报》：“我们的实验站是目前世界上规模最大的……带来的效果令人欣喜。”

He said initial results looked good, with the tower pumping out 10 million cubic metres (353 million cubic feet) of clean air per day since it was launched last year.

他说初步结果还不错，实验站去年启动，每天释放一千万立方米的洁净空气。

On days where pollution reached critical levels, which more frequently happens in winter when Xian relies heavily on coal, the purifying tower brought it down to a moderate level. PM2.5 - the fine particles in smog that are most harmful to health - fell 15 per cent during heavy pollution on average.

每年冬天，西安要用煤，污染常常在此时达到峰值，当时净化站使峰值回落到常态。雾霾中的细小颗粒PM2.5对健康影响最大，在重度污染的情况下，下降了15%。

But Junji pointed⁵ out that results aren't conclusive⁶ and testing is still ongoing⁷.

但是军骥说结果还不能最终确定，仍需测试。

The purifying system works by pulling the air inside greenhouses at the base of the tower and heating it via solar energy. The hot air then rises through the tower, passing through layers of cleaning filters.

净化系统的工作原理是先把空气吸入实验站底部的温室，通过太阳能加热，热空气上升至站顶，通过层层净化器后排出。