Construction-Phase Carbon Emission Accounting and Boundary Optimization for Power Transmission and Transformation Projects: A Case Study in Shanxi, China

Carbon emission accounting for power transmission and transformation projects is increasingly needed to support low-carbon grid infrastructure, but existing studies often pay limited attention to the construction phase and rely on generalized emission factors that may not reflect regional electricity and industrial conditions. This study develops a construction-phase carbon emission accounting framework for a representative 1000 kV power transmission and transformation project in Shanxi Province, China. The framework defines a construction-specific accounting boundary covering material production, material transportation, construction electricity use, machinery fuel use, and installation-related vehicle fuel use. It also incorporates province-specific electricity and material emission factors to improve the regional representativeness of the inventory. The results show that the total construction-phase carbon footprint of the project was 1.92 × 105 t CO2eq, with material-production emissions accounting for 87.23%. Off-site transmission line works and major production works were the dominant engineering divisions, contributing 39.40% and 33.79% of total emissions, respectively. Steel and cement-concrete products were the major material sources, jointly accounting for 89.78% of material-production emissions. Compared with national average factors, Shanxi-specific factors reduced estimated material emissions by 9.18%, while increasing the estimates for aluminum products and mixed electricity, indicating that regionalized factors can change both total results and source-level contributions. A contribution-based screening analysis further showed that 8.44% and 21.59% of the data streams accounted for 95% and 99% of cumulative construction-phase emissions, respectively. These findings highlight the importance of construction-phase boundary definition and regional emission-factor selection in project-level carbon accounting for power grid infrastructure.