Outdoor air pollution accounts for an estimated 4.2 million deaths worldwide, the majority of which are caused by exposure to fine particulate matter (or PM2.5) air pollution. Most of these deaths occur in low- and middle-income countries (LMICs). Reducing PM2.5 air pollution is thus crucial for improving public-health outcomes in those countries. Measuring and reducing the health impacts of PM2.5 is especially challenging in many LMICs because ground-level...