An amazing story jumped out of the newspaper at me recently. A young man gave his fiancee a smog free engagement ring ( https://www.nytimes.com/2018/09/19/fashion/weddings/a-wedding-ring-with-a-dirty-little-secret.html ).
A what?
Four years ago, Daan Roosegaarde, a Dutch artist and technologist, was visiting Beijing, China, a city notorious for its air pollution. When he returned home, Roosegaarde decided to design “the world’s largest smog vacuum cleaner” — a smog free tower that sucks in 30,000 cubic meters of air every hour (shown at right). The air is cleaned, then returned to the environment. But what to do with all the junk the air surrendered?
An analysis under a microscope revealed about half of this pollution was carbon. Put carbon under enough pressure for enough time, and you get diamonds. 
Roosegaarde can’t make diamonds of course, but that revelation gave him the idea to make designer jewelry. The result is a “smog free ring” — basically a compressed black mass encased in a clear cube, the result of pulling hundreds of thousands of gallons of pollution from the air.
Will this idea catch on? Roosegaarde’s business, Studio Roosegaarde in Rotterdam, Netherlands, doesn’t publish sales figures, but said it has had “requests from several couples across the world.” It’s the perfect gift for an environmentalist or anyone concerned with the social and ethical implications of diamond mining. Proceeds from the sale of each ring, which costs 250 euros (about $290), go toward building more smog free towers. In addition to Beijing, towers are now in Rotterdam; Kraków, Poland; and Tianjin, China. Mexico City is scheduled to get one sometime this fall, and India and Colombia are in negotiations. And because the pollution is different in each city, clients can choose which city’s pollution they want in their ring.
After visiting Beijing myself this spring, I wish him well.
Engagement and tower photos are from the New York Times article; the ring photo is from Kickstarter.com by way of Google Images.