Comparative Analysis of National Emission Inventories and Field Measurements for Agricultural Tractors

Abstract Purpose This study compared the agricultural tractor emission inventory systems in Korea, the United States, and Europe to identify discrepancies between inventory reference values (CAPSS, EPA, EEA) and field measurements obtained using a Portable Emission Measurement System (PEMS) under real-world operating conditions. Methods Emission data derived from PEMS-based studies were compiled to summarize emission factors (EFs) and load factors (LFs) across various agricultural tasks. These values were systematically compared with the default parameters used in each national inventory. Additionally, four estimation scenarios were developed—inventory defaults, measured LF, measured EF, and combined measured EF and LF—to calculate and contrast emissions during idling, driving, plowing, and rotary tillage. Results Measured LFs ranged from 0.2 to 0.9, varying significantly by task, even among tractors with similar rated power. Relative to inventory defaults, Korea (CAPSS = 0.48) underestimated LF by approximately 25%, the United States (EPA = 0.59) overestimated by 27%, while Europe (EEA = 0.50) closely matched the measured average. For EF, Europe exhibited a progressive decline in CO and NO x emissions in line with tightening regulations, whereas several Tier 4 tractors in the United States showed higher CO and NO x levels than inventory assumptions. Across scenarios, the inventory-default case consistently underestimated total emissions. The measured LF scenario elevated emissions in high-load tasks (plowing and rotary tillage), while the measured EF scenario tended to overestimate emissions in low-load and underestimate in high-load operations. Conclusions Fixed EF and LF values fail to capture the variability of agricultural tractor emissions under actual working conditions. These findings underscore the need to revise inventory parameters using PEMS-derived field data to improve accuracy and representativeness.