## 2 Background  
GPP serves as a strategic policy instrument that integrates environmental sustainability criteria into public procurement processes. By prioritizing products and services with internationally recognized eco-certification standards, GPP advances sustainable development goals through market-driven mechanisms [17]. This approach is based on two complementary theoretical frameworks. First, [PERSON] (1985) conceptualizes environmental issues as global public goods, and emphasizes the necessity of public participation and social innovation to achieve sustainability [19]. Building on this perspective, [PERSON] (1995) proposed the ecological modernization theory, positing GPP as a legitimized governance mechanism that integrates technological, market, and institutional coordination to enhance environmental policy effectiveness [20]. Together, these theories present two roles of GPP in that it embodies the collective value of environmental governance while exemplifying the advance of policy instruments in addressing sustainability challenges. The theoretical foundations have translated into concrete institutional reforms globally. Since the United Nations Sustainable Development Summit introduced the concept of sustainable public procurement in 2002, developed countries have progressively established operational frameworks for GPP implementation. For example, since the enactment of the Resource Conservation and Recovery Act in 1976, the United States has systematically enhanced its GPP system [21]. Japan institutionalized its approach in 2000 with the Green Procurement Law, which requires government agencies and public organizations to formulate green purchasing plans and report on the implementation progress [22]. Meanwhile, the European Union has integrated a life-cycle costing (LCC) mechanism into public procurement regulations through amendments to Directive 2014/24/EU, explicitly incorporating carbon emissions performance as an evaluation criterion [23]. In Australia, each state and territory's local councils have their own unique green procurement policies, which are crucial for advancing the circular economy through the purchase of waste-derived products and play a significant role in environmental sustainability management and green procurement [24; 25]. In South American countries such as Peru, public procurement accounts for 11.7% of GDP, and the two main categories of publicly procured products are offset paper and medium-density particleboard (MDP) furniture [26; 27]. Although South Africa currently has no specific legislation on green public procurement; however, existing regulations allow procuring entities to incorporate environmental considerations into their procurement practices [28]. These cross-national experiences demonstrate that GPP has evolved from basic green procurement toward an integrated framework embedding environmental economics, climate mitigation, and multilevel governance. Although institutional advancements in GPP are evident, its actual effectiveness depends on the balance between strict regulations and flexible implementation strategies. [PERSON] (2012) demonstrated this balance in the Italian context, where mandatory requirements were effectively combined with digital procurement platforms, financial incentives, and public-private research partnerships to advance low-carbon technologies [29]. However, persistent challenges have revealed gaps. [PERSON] et al. (2013) find that while regulatory pressure and stakeholder demands promote compliance, insufficient environmental expertise among officials often undermines policy outcomes [30]. Similarly, [PERSON] et al. (2014) further identify \"institutional suspension\" in municipal GPP programs, where implementation gaps emerge from misaligned policy structures and operational practices [31]. Collectively, these findings illustrate that the effectiveness of GPP hinges not only on well-designed regulatory frameworks but also on coherent institutional environments and adaptable implementation strategies.