2.5 - a small number, making a big impact in China. PM2.5 is a measurement of fine airborne particles hazardous to our health. Now it's also a brand name. Entrepreneur Zhao Danqing is cashing in on public outrage at air quality in China's smog-choked cities. High-tech fabrics are his thing. He started off selling quick-dry underwear for soldiers. Now he's selling the PM2.5 face mask. He claims it will protect wearers against the microscopic pollutants.