Another report by WHO warns that air pollution is the biggest environmental risk to health, responsible for one in nine deaths annually worldwide and killing around 3 million each year. This is only getting worse.
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.
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.
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.
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.
Air quality measurements were taken over 10 square kilometres (3.86 square miles) around the site over the last few months.
But Junji pointed out that results aren't conclusive and testing is still ongoing.
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.