Shifting PM_2.5 Control from Mass to Toxicity for Health Equity Worldwide

Fine particulate matter (PM_2.5) remains the leading cause of premature deaths, despite declining mass concentrations of PM_2.5 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 PM_2.5 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 PM_2.5 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 PM_2.5 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.