On days when Beijing's pollution is heavy, you can smell and taste the foul air-whether on the street or inside. Air pollution seeps into many buildings through window seals and open doors. On most days levels of dangerous pollutants are somewhat lower inside than outside, but not much lower.This unhappy fact has fueled a market for indoor air filters from such companies as Chicago's Blueair and Switzerland's IQAir. A basic model will set you back at least $800. And you should have one in each room of your home, school, restaurant, or office.A simple and less costly way may be at hand. During the Beijing "airpoca-lypse" of January 2013, when fine particles in the air reached highly unsafe levels, Thomas Talhelm began researching how air filters work. Talhelm, a Fulbright scholar spending a year in China studying the impact of farming on culture, realized that the essential components-a HEPA filter, a fan, and a Velcro strap to hold them together-could be purchased on Taobao, China's leading e-commerce site, for less than $35. So he rigged up his own filter and invested in a $260 particle monitor to see how well it worked.
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