# Assessment of Carbon Emissions at the Logistics and Transportation Stage of Prefabricated Buildings
## 2 Research Boundary and Key Parameters
### Selection of Carbon Emission Factors  
The carbon emission factors involved in the entire life cycle of prefabricated buildings mainly include energy carbon emission factors, construction material carbon emission factors, transportation tool carbon emission factors, and machinery and equipment carbon emission factors. In contrast, the logistics and transportation stage mainly involves three carbon emission sources: energy, transportation tools, and machinery and equipment. Carbon emissions associated with energy in the logistics and transportation stage can be roughly divided into fossil energy carbon emissions and electricity carbon emissions. Electricity energy does not produce carbon emissions during use but emits CO\({}_{2}\) during production [16], hence the need to consider the impact of electricity on carbon emission levels in this study. The logistics transportation phase is mainly carried out by rail, road, and waterway; therefore, only the carbon emission factors generated by the means of transportation involved in these three transportation modes were considered in this study. Carbon emissions from mechanical equipment generated during the vertical transportation (loading and unloading) of prefabricated components also need to be considered--mainly the consumption of gasoline, diesel, and electricity (where energy is mainly consumed by the gantry crane in the component plant and the tower crane at the construction site) [17]. The differences in fuel types, extraction and processing technologies, and testing methods have led to different values of energy carbon emission factors measured by different organizations. To ensure the authenticity and reliability of the data, we gave priority to the data applicable to China's national conditions. In order to summarize and calculate the prefabricated assembled fossil fuel carbon emission factors for the building phase, the carbon content per unit calorific value and carbon oxidation rate, recommended by the 2006 IPCC National Greenhouse Gas Inventory and the Carbon Emission Calculation Standard for Buildings (GB/T 51366-2019), were utilized. The average low-level heat generation value was sourced from the 2020 China Energy Statistical Yearbook. To facilitate the calculation, fossil fuel carbon emission factors were expressed firstly, in different units of measurement, as shown in Table 2. The units were then converted to common domestic units using Equation (3) (kgCO\({}_{2}\)/kg). The discount standard coal coefficient is the average low calorific value of fuel divided by the low calorific value of standard coal, when using standard coal as a unit. Raw coal can be divided into three types based on the degree of carbonization: lignite, bituminous coal, and anthracite. The average low-level heat generation value was used to determine the heat generation value of raw coal. \[\text{DEF}=\text{DCC}\times\text{DOF}\times\frac{44}{12}; \tag{2}\]  
\[\text{CEF}=\text{DEF}\times\text{Avg.LHV}. \tag{3}\]  
DEF: Default emission factor. DCC: Default carbon content. DOF: Default oxidation factor. Avg. LHV: Average low-level heat generation value. CEF: Carbon emission factor. There are significant regional differences in the carbon emissions associated with power, with northeastern and northern China power grids dominated by thermal power generation, which has a large carbon emission factor. Central and southern China are dominated by hydro power generation; therefore, their carbon emission factor is smaller. Based on the data provided by the IPCC and the research results of references [18; 19], the carbon emission factors of power energy for different regions of China are summarized in Table 3.  
Considering the types, weights, volumes, stacked layers, and transportation costs of building materials and prefabricated components, vehicles with different loads and power types need to be selected for transportation. The Standard for Calculating Carbon Emissions of Construction (GB/T 51366-2019) factors for carbon emissions from transportation are listed in Table 4.