175 ADP-minerals & metals 3.74E-08 24.19% 5.57E08 35.98% 6.16E-08 39.83% 1.55E-07 ADP-fossil fuels 4.14E+0 0 21.93% 1.44E+0 1 76.06% 3.80E-01 2.01% 1.89E+0 1 WDP 1.95E-01 46.93% 1.59E01 38.22% 6.18E-02 14.85% 4.16E-01 PM 4.45E-07 23.59% 1.43E06 75.87% 1.02E-08 0.54% 1.89E-06 COMPARISON OF DAE AND LCA RESULTS A direct comparison between DAE and LCIA results is not feasible because DAE estimates emissions of CO2, NOx, TSP, and PM into the air from various operations. On the other hand, LCIA results are environmental impacts quantified by converting output elementary flows, such as CO2, CH4, NOx, PM, SOx, CFCs, etc., from the LCI phase into impact indicators such as GWP-fossil, AP, ODP, EP, and others. The impact indicators are quantified by classifying emissions according to their contribution to the relevant indicators. The extent of contribution of emissions to the different indicators is quantified by using characterization factors in LCA. Figure 8 shows an example of the classification and characterization of results from the LCI phase to impact indicators. To compare the results of the two methods, the emissions to air estimated in the LCI phase have been used. Table 6 presents the air emissions estimated from both methods for the cradle-to-gate system boundary. It can be noted that there are differences in the results; for example, the CO2 emissions estimated by LCA are higher than those from DAE. Conversely, the TSP and PM emissions estimated by DAE are higher than those from LCA. The reason for this difference is the scope of the two methods and the EFs used. Figure 9 shows a pictorial representation of the scope of the two methods. In the DAE estimation, the focus is solely on estimating on-site air emissions from different operations (Scope 1). While in LCA, the focus is on estimating emissions to air, water, and soil, as well as waste generation, both from the site under study and from the supply chain of resources consumed at the site (Scopes 1-3). This is one of the reasons for the higher CO2 emissions estimate in the LCA. Although LCA covers a broader scope, TSP and PM emissions estimated from LCA are lower in comparison to DAE (see Table 6). This is because in LCA, TSP and PM emissions are estimated only for the supply chain of resources, and on-site diffused dust (TSP and PM) emissions from material processing, material handling, and wind erosion are not considered in the LCI dataset used in LCA. This indicates that on-site TSP and PM emissions are higher at the quarry, highlighting their site-specific importance. The lack of inclusion of dust emissions in LCA has also been identified through a review conducted by Lee et al. (2024). Additionally, this difference is due to the differences in EFs used in the two methods.
RkJQdWJsaXNoZXIy MTM0Mzk2