In this episode, groups of citizen scientists use apps and maps to help researchers gather data about medical conditions. Sensors on asthma inhalers generate real-time maps of environmental dangers to help patients and physicians in Louisville, Kentucky. In West Oakland, California, citizens confront air pollution and rising asthma rates by collecting traffic data. Citizen scientists are fighting mosquito-borne diseases with apps and crowd-sourced data in Barcelona, Houston, and New Orleans. Part of "The Crowd and the Cloud" series.