The Smog Free Project is the cleanest park in Beijing where people can experience clean air for free. Daan Roosegaarde and his team of experts are using patented ion technology to make the world's largest smog vacuum cleaner. Copper coils buried in the ground create a positively charged electrostatic field. All particles of ten nanometres or more -- including smog -- become positively charged, and thus attracted to the grounded earth, where they are collected. "It's a loop of fresh air," says Roosegaarde. The collected smog is then turned into Smog Rings that are sold to visitors, who - by buying or sharing the smog ring - donate 1,000 cubic meters of clean air to the city of Beijing.