Does the DIY purifier work? Test results (1, 2) give a conclusive answer, but this series of pictures gives a visceral answer. I took a picture of the HEPA about every seven days for four weeks. Glad that black gunk’s not stuck in my lungs instead.
In static form, here’s Week 0 and Week 5:
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.