Airborne particulate matter (PM) increases morbidity and mortality resulting from cardiopulmonary diseases including cancer. We hypothesized that PM is genotoxic to alveolar epithelial cells (AEC) by causing DNA damage and apoptosis. PM caused dose-dependent AEC DNA strand break formation, reductions in mitochondrial membrane potential (Δψ_m), caspase 9 activation, and apoptosis. An iron chelator and a free radical scavenger prevented these effects. Finally, overexpression of Bcl-xl, a mitochondrial anti-apoptotic protein, blocked PM-induced Δψ_m and DNA fragmentation. We conclude that PM causes AEC DNA damage and apoptosis by mechanisms that involve the mitochondria-regulated death pathway and the generation of iron-derived free radicals.