Matt Myers attended our workshop in September, and he used it straight through December. On December 7th, he sent me a picture of the blackest HEPA (and pre-filter) I’ve ever seen. Yikes!
Time for a new filter! I’d be happy that black gunk is in the filter and not in my lungs.
Thomas is a new Assistant 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.