Size-segregated emission characteristics and associated toxicity of polycyclic aromatic compounds from agricultural...

Non-road agricultural machinery (AM) emissions now exceed road vehicles as major atmospheric particulate contributors in China. Though recent changes to fuels and emission standards have been implemented, their effects on particle size-resolved chemical compositions and public health impacts remain poorly understood. This study systematically analyzed the particle size-resolved polycyclic aromatic compounds (PACs) chemical composition from 5 AM, evaluating the impacts of fuel type (diesel B0, biodiesel B5/B20), emission standards (stage II/III), and working status (idling, moving, working) on emission characteristics and health risks. Key findings include: (1) Average emission factors for PPAHs, OPAHs, and SPAHs were 1.1 ± 1.6, 0.7 ± 0.7, and 0.03 ± 0.04 mg/kg, respectively. Compared with diesel B0, B5 reduced PAC emissions while B20 increased emissions by 34.8 %. (2) PAC emissions primarily concentrated in PM_0.1-0.5 (>80 % mass fraction). Size distribution showed stronger dependence on emission standards and operating modes than fuel types. Stricter standards reduced total emissions by ∼80 % but boosted ultrafine particle emissions, particularly raising ultrafine oxygenated-PAHs 2.6-fold. (3) Carcinogenic risk assessment demonstrated 41.4 % toxicity reduction with B5 but increased risk with B20. While new standards reduced overall toxicity, the carcinogenic contribution from ultrafine particles quadrupled. These findings provide scientific basis for evaluating real-world AM emissions and formulating health-oriented control strategies under evolving regulatory frameworks.