Safecast, a trusted provider of radiation data in post-quake Japan, is now expanding with challenge funding to create a real-time map of air quality in U.S. cities. A team of volunteers, scientists and developers quickly formed Safecast in the wake of the 2011 Fukushima nuclear disaster, when demand for radiation monitoring devices and data far surpassed the supply. The project has collected more than 4 million records and become the leading provider of radiation data. With News Challenge funding, Safecast will measure air quality in Los Angeles and expand to other U.S. cities. Disclosure: Knight Foundation Trustee Joi Ito is an officer of the Momoko Ito Foundation, which is receiving the funds on behalf of Safecast.