Work

Persistent carcinogenic risk from PM2.5-bound metals despite substantial concentration reductions: Evidence from a Chinese megacity during the COVID-19 lockdown

Year: 2026

Type: article

Abstract: Health benefits from emission controls are often inferred from reductions in fine particulate matter (PM 2.5 ) mass, yet this metric can underrepresent toxicity from PM 2.5 -bound metals. Using the COVID-19 lockdown as an intervention-like natural experiment, this study quantified how PM 2.5 -bound metals, emission sources, and inhalation health risks changed in Guangzhou, China. Hourly measurements of 16 metals were coupled with positive matrix factorization and source-specific risk apportionment for pre-lockdown, lockdown, and post-lockdown periods. The lockdown controls reduced PM 2.5 mass by 28.8% and total metal concentrations by 36.3%, while total non-carcinogenic and carcinogenic risks decreased by 50.4% and 41.7%, respectively. However, carcinogenic risks during the lockdown remained approximately 9.6 times the safety criteria adopted in this study (1 × 10 -6 ) for children and 38 times for adults, driven mainly by Cr(VI) and As. Vehicle emissions remained the dominant carcinogenic-risk source, contributing more than 70% even under strict mobility restrictions, indicating a persistent role of non-exhaust brake and tire wear. Ship-related non-carcinogenic risks rebounded after the lockdown, consistent with port congestion and prolonged berthing during logistics recovery. Under the proportional-reduction assumption used in the scenario analysis, reaching the safety criteria would require further uniform reductions of 89.5–97.4% in source-attributed carcinogenic metal concentrations relative to the lockdown conditions, which is impractical as a single-step mass-reduction target. These findings support phased risk-oriented management that combines source-specific controls with feasible interim risk-reduction benchmarks and progressively tightens them toward the long-term health-protective criteria.

Source: Atmospheric Environment X

DOI: 10.1016/j.aeaoa.2026.100523