Structural comparison of RTCs, RICs and PIOTs

Figure 5 provides a visualization of all PIOT flows in the two approaches, showing (Fig. 5a) the dominance of the flows between the economy and natural resources via raw materials and residuals in the process model approach, versus a dominant fertilizer production sector in the previous MFA-based approach (Fig. 5b). Since all flows represent N, this difference is due primarily to the fertilizer manufacturing sector. Residuals in Fig. 5a come primarily from the purge stream of air, since the yield of the Haber–Bosch process is low and recycle is needed. An interaction from the hog farming sector is also clearly visible in Fig. 5a, since N in manure is classified into residuals.