Resolving the argument in Washington over the need to reduce airborne-particle emissions in the United States will not clean up the air in India or China (see Nature 568, 433; 2019). Research on air pollution should move beyond statistical analysis of premature deaths to demonstrating measurable human-health benefits from cleaner air. We therefore need more data on victims’ exposures and the long-term mechanisms for specific causes of death.

Outdoor (but not indoor) air pollution is currently assessed by monitoring concentrations of regulated air pollutants — including particles — the adverse effects of which are gauged according to their size. To track their physiological impact after inhalation, we need a paradigm similar to that originally used for tobacco toxins: identify the hazardous constituents, determine the latent period before disease development, and assess the cumulative effects of long-term exposure.