Black carbon (BC) is the light absorbing component of particulate matter (PM) pollution emitted by biomass and fossil fuel combustion. Common sources include wood heaters, internal combustion engines, and wildfires. Prolonged exposure to these combustion emissions increases the incidence of respiratory diseases and other adverse health impacts. Black carbon is also a short-lived but powerful climate forcer in the atmosphere: Only carbon dioxide contributes more to global radiative forcing. Monitoring and mitigating black carbon pollution is critical to protecting human health and the environment.