A quantile perspective on the effects of supply chain, digitalization, and government spending on air pollution in Vietnam

This study examines the asymmetric effects of supply chain (SC) activity, digitalization (DI), economic growth (GDP), energy consumption (EN), and government final consumption expenditure (GE) on air pollution (AP) in Vietnam over the period of 1996–2023. To capture distribution-dependent heterogeneity, the analysis employs Quantile-on-Quantile Regression (QQR), Quantile-on-Quantile Granger Causality (QQGC), and Kernel Regularized Least Squares (KRLS). The results reveal pronounced asymmetric effects across pollution regimes. In particular, EN and SC have positive effects on AP at higher quantiles (0.75–0.95), with QQR coefficients reaching significant magnitudes, indicating substantial pollution amplification under high-emission conditions. In contrast, DI and GE reduce AP at lower to middle quantiles (0.20–0.50), but their mitigating effects weaken or reverse at upper pollution quantiles. The QQGC results confirm significant distribution-dependent predictive relationships from macroeconomic factors to AP, while KRLS estimates corroborate the dominant nonlinear patterns identified by the quantile-based analysis. Overall, the findings highlight that the environmental impacts of economic and policy variables in Vietnam are regime-specific, underscoring the need for differentiated and quantile-informed policy interventions targeting energy use, SC intensity, and digital transformation.