Over at Instructables, BB pal Eric Paulos and and his students Stacey Kuznetsov, George Davis, and Jian Cheung in Carnegie Mellon University's Living Environments Lab explain how to make illuminated balloons that change color based on the local air quality. Each balloon is outfitted with a tri-color LED, tiny air quality sesnsor, rechargeable battery, and a few other inexpensive components. I'd love to encounter these as I walk through the city at night! Air Quality Balloons