Atmospheric Autoxidation of Polycyclic Aromatic Hydrocarbons Offset Air Quality and Health Gains from Solid Fuel Restriction.

Residential solid fuel combustion (RSFC) emits hazardous pollutants threatening air quality and human health, prompting China to reduce RSFC in key urban areas and implement controls on anthropogenic VOCs and NOx. However, uncoordinated emission reductions could pose new atmospheric challenges. The presence of polycyclic aromatic hydrocarbons (PAHs) in RSFC emissions warrants significant attention. Existing strategies predominantly target primary emissions, overlooking transformation products that could exert broader environmental impacts on the regional scales. Here, we identified an unexpected rearrangement-driven autoxidation pathway of naphthalene tricyclic-peroxy-radicals (TPRs). Quantum chemical calculations, lab experiments, and atmospheric modeling show that under low-NO conditions, TPRs rapidly generate highly oxygenated products, whereas high-NO environments promote epoxide formation, representing a new class of secondary organic aerosol precursors. This mechanism also extends to other PAHs such as methylnaphthalene, anthracene, and phenanthrene. Incorporating a time-dependent perspective, risk assessments reveal that transformation products exhibit reduced carcinogenicity yet enhanced mutagenicity and respiratory and skin toxicity, indicating that failing to consider atmospheric processing leads to substantial underestimation of RSFC impacts. These findings underscore that mitigation strategies must address both primary emissions and secondary PAH transformations, especially under low-NO conditions, while accelerating clean-energy transitions in rural areas, improving combustion efficiency, and accounting for the regional transport of pollutants.