Shifting PM2.5 Control from Mass to Toxicity for Health Equity Worldwide.

Fine particulate matter (PM2.5) remains the leading cause of premature deaths, despite declining mass concentrations of PM2.5 in the atmosphere. Age-standardized attributable death rates demonstrated divergent trends worldwide over the past decade, indicating that the uniform toxicity assumption underlying current regulations warrants re-examination. In this perspective, we synthesize recent advances in toxicological evaluation, epidemiological research, and modeling studies to advocate for a toxicity-based control as a future promising option. Incomplete combustion sources, especially residential solid fuels and wildfires, exhibit the highest toxicity per unit PM2.5 mass from primary emissions to secondary aging. Integrating source-specific toxicities, high-risk regions (South Asia, Southeast Asia, Sub-Saharan Africa, Andean Latin America, and China) show substantially elevated toxicity-adjusted PM2.5 exposure. Low-income populations, which account for around 8.2% of the global population, bear 24.0% of the global cumulative toxicity-adjusted exposure burden, mainly driven by reliance on cheap solid fuels and wildfire emissions. We suggest that prioritizing control of high-toxicity PM2.5 sources in low- and midlow-income regions could complement current mass-based reductions to further mitigate health inequalities. This toxicity-focused framework offers actionable pathways for policymakers and environmental justice scholars, aligning air quality management with climate, equity, and sustainable development goals.