Environmental tobacco smoke poses a significant health risk after long-term exposure in enclosed spaces, though it still ranks low on gross causes of air pollution, a list topped by transportation, industrial and agricultural emissions, power generation and residential heating and cooking. Yet while smoking is not a leading human cause of air pollution, air pollution has now been deemed a leading environmental cause of cancer deaths. The International Agency for Research on Cancer, a branch of the World Health Organization, announced this October that air pollution causes lung cancer and increases the risk for bladder cancer.2 As air pollution, like tobacco smoke, is found to be carcinogenic, the line between human and environmental health blurs. Public health strategists, air quality experts, and policymakers alike have every incentive to make clean air a priority.