In her work with the Bus Riders Union, Francisca Porchas has helped prevent 33 premature deaths, 805 asthma attacks, and 7,000 lost workdays — just by convincing Los Angeles to replace dirty diesel buses with ones that run on compressed natural gas. Answering reader questions, Porchas shares more impressive stats about her org’s successes, discusses her strategy for luring drivers out of their cars, and explains the meaning of “drive-by pollution.”