Abstract
Agricultural machinery (AM) represents a dominant yet underregulated non-road emission source worldwide, with the health risks and key toxic drivers of its real-world particulate matter (PM) emissions still poorly understood. Taking China as a typical example, this study combined field sampling with multi-scale chemical analysis to characterize the chemical composition and oxidative potential (OP) of exhaust PM from AM under real-world operating conditions, followed by a national-scale emission assessment. The results show that while the PM emission factor under China III standard shows a 50% reduction compared to China II-compliant AM, the emitted PM exhibits a 2.7 times higher OP, suggesting a potential increase in health risks per mass. This toxicity paradox arises from the increased abundance of redox-active components: Fe, Zn, Mn, and high-ring polycyclic aromatic hydrocarbons (PAHs). Single-particle analysis reveals that in China III PM, Fe-rich particles are particularly significant, acting as carriers of heavy metals (Zn, Mn, V, Cr, Co, Pb) and showing a strong correlation with carcinogenic PAHs such as BaP. Isolated Fe-rich particles exhibit significantly higher OP than total PM, confirming their significant role. National estimates show that from 2017 to 2023, implementation of the China III standard decreased PM emissions by 53% but OP risk by only 21%, aligning with limited reductions in PAH and Fe emissions. China III tractors with low and medium power, which contribute significantly to AM PM emissions (71%) and OP risk (62%), should be prioritized.