Activity-level correction method for non-road construction machinery: Improving carbon and pollutant emission inventory accuracy and synergistic reduction assessment in Beijing, China

Abstract

Non-road mobile machinery (NRMM) is a major contributor to air pollution and carbon emissions in megacities such as Beijing. Traditional emission inventories primarily rely on static registration data and lack mechanisms to reflect real-world activity, which often leads to systematic overestimation. This study develops an activity-level correction method for construction machinery based on extensive on-site and telephone surveys covering 2584 units. The method adjusts utilization rates and operating hours by machinery type and year of manufacture, producing a refined 2024 emission inventory for Beijing. After correction, the number of active machines decreased by 34.8%, revealing a substantial amount of inactive equipment in the registry. Excavators and forklifts showed the highest usage intensity (1210 h yr⁻¹ and 1187 h yr⁻¹) and dominated emissions, together contributing over 57% of total CO₂ and pollutant emissions. The updated inventory estimated annual emissions of 7791.7 t CO, 1533.0 t VOCs, 5413.9 t NOx, 421.6 t PM_2.5, and 1732.3 kt CO₂, which were significantly lower and more realistic than values based on uncorrected data. A synergistic reduction assessment of four major mitigation measures showed that phasing out old machinery and promoting electrification achieved the strongest combined reductions in both CO₂ and air pollutants, whereas emission-standard upgrades mainly reduced air pollutants with limited carbon-reduction benefits. This study provides a scientific basis for dynamic and data-driven management of non-road machinery and offers policy guidance for integrated pollutant and carbon control in urban environments.