A Non-Negligible Source of Ultrafine Elemental Carbon: Agricultural Machinery─after Enhanced Fuel Quality and Emission Standards

Against China’s backdrop of substantial on-road vehicle emission reductions, nonroad sources─particularly agricultural machinery (AM)─have become significant contributors to elemental carbon (EC). The impact of rapidly updated fuels and emission standards on AM’s particle size-resolved EC and health effects remains unclear. This study measured EC size distributions from five AM units, further evaluating fuel types (petrodiesel B0 vs biodiesel B5/B20) and emission standards (Stage II vs Stage III) on emission characteristics and size distributions. The results show that (1) AM’s mean EC emission factor (EF) was 367.3 ± 476.5 mg/kg─exceeding typical on-road mobile sources─with char-EC and soot-EC comprising 7.3% and 92.7% of EF_EC respectively. (2) Fuel type and emission standards exerted significant influence on EC emissions, particularly within the ultrafine particle fraction. Newer standards increased ultrafine EC emissions by 3.6-fold and using B20 elevated total EC by 24.3% versus using B0. (3) By incorporating deposition and clearance efficiency across different particle sizes, modeled respiratory deposition of EC yielded 237.9 mg/kg (children) and 163.9 mg/kg (adults). The pulmonary region constituted the primary deposition target site, then head airways, with the tracheobronchial receiving the least. This work provides essential data for evaluating AM emissions under new frameworks.